Psychology Wiki
Don't have an account?
Register
Register
in: Limbic system, Cerebrum, Diencephalon,
and 3 more

Changes: Hypothalamus

Back to page
Sign in to edit
(Ref)
(controls body temperature and pooping system)
 
(5 intermediate revisions by 3 users not shown)
Line 8: Line 8:
 
Image = LocationOfHypothalamus.jpg |
  
Image = LocationOfHypothalamus.jpg |
 
Caption = Location of the human hypothalamus |
  
Caption = Location of the human hypothalamus |
−
Image2 = Gray654.png |
 +
Image2 = Illu diencephalon .jpg|
  +
Caption2 = Dienchephalon |
−
Caption2 = Median sagittal section of brain of human embryo of three months. (Hypothalamus visible at center.) |
  
−
IsPartOf = |
 +
IsPartOf = |
 
Components = |
  
Components = |
 
Artery = |
  
Artery = |
Line 19: Line 19:
 
MeshNumber = A08.186.211.730.385.357 |
  
MeshNumber = A08.186.211.730.385.357 |
 
}}
  
}}
  +
The '''hypothalamus''' links the [[nervous system]] to the [[endocrine system]] via the [[pituitary gland]] (hypophysis). The hypothalamus, (from Greek ὑποθαλαμος = under the thalamus) is located below the [[thalamus]], just above the [[brain stem]]. This gland occupies the major portion of the ventral region of the [[diencephalon]]. It is found in all [[mammal]]ian [[brain]]s. In humans, it is roughly the size of an almond.
−
The '''hypothalamus''' (from Greek ὑποθαλαμος = under the thalamus) is a region of the mammalian [[brain]] located below the [[thalamus]], forming the major portion of the ventral region of the [[diencephalon]] and functioning to regulate certain [[metabolic]] processes and other [[autonomic]] activities. The hypothalamus links the [[nervous system]] to the [[endocrine system]] via the [[pituitary gland]], also known as the "master gland," by synthesizing and secreting [[hormone|neurohormones]], often called ''releasing hormones,'' as needed that control the secretion of [[hormones]] from the [[anterior pituitary gland]] — among them, [[gonadotropin-releasing hormone]] (GnRH). The [[neurons]] that secrete GnRH are linked to the [[limbic system]], which is primarily involved in the control of [[emotion]]s and [[sex]]ual activity. The hypothalamus also controls [[body temperature]], [[hunger]], [[thirst]], and [[Circadian rhythm|circadian cycles]].
 
   
  +
The hypothalamus regulates certain [[metabolic]] processes and other activities of the [[Autonomic Nervous System]]. It synthesizes and secretes [[hormones|neurohormones]], often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary [[hormones]].
−
==Hormones of the hypothalamus==
  
−
* [[Corticotropin-releasing hormone]] (CRH)
  
−
* [[Dopamine]]
  
−
* [[Gonadotropin-releasing hormone]] (GnRH)
  
−
* [[Growth hormone releasing hormone]] (GHRH)
  
−
* [[Somatostatin]]
  
−
* [[Thyrotropin-releasing hormone]] (TRH)
  
−
* [[Hypocretin]]
  
   
  +
The hypothalamus controls [[body temperature]], [[hunger]], [[thirst]], <ref>http://www.cancer.gov/Templates/db_alpha.aspx?CdrID=46359</ref> fatigue, anger, and [[Circadian rhythm|circadian cycles]].
−
==Boundaries==
  
  +
−
The anatomical boundaries of the hypothalamus are:
 
  +
==Inputs==
−
* ''rostral'', the [[lamina terminalis]].
 
  +
−
* ''caudal'', the posterior margin of the [[mamillary bodies]].
 
  +
The hypothalamus is a very complex region in the brain of humans, and even small nuclei within the hypothalamus are involved in many different functions. The [[paraventricular nucleus]] for instance contains [[oxytocin]] and [[vasopressin]] (also called antidiuretic hormone) neurons which project to the [[posterior pituitary]], but also contains neurons that regulate [[ACTH]] and [[Thyroid-stimulating hormone|TSH]] secretion (which project to the [[anterior pituitary]]), [[gastric reflexes]], [[maternal behavior]], [[blood pressure]], [[feeding]], [[immune responses]], and [[temperature]].
−
* ''dorsal'', the [[hypothalamic sulcus]].
 
  +
−
* ''medial'', the [[third ventricle]].
 
  +
The hypothalamus co-ordinates many hormonal and behavioural circadian rhythms, complexity patterns of neuroendocrine outputs, complex homeostatic mechanisms,<ref>http://www.sci.uidaho.edu/med532/hypothal.htm</ref> and many important behaviours. The hypothalamus must therefore respond to many different signals, some of which are generated externally and some internally. It is thus richly connected with many parts of the CNS, including the brainstem [[reticular formation]] and autonomic zones, the limbic forebrain (particularly the [[amygdala]], [[septum]], [[diagonal band of Broca]], and the [[olfactory bulb]]s, and the [[cerebral cortex]]).
−
* ''lateral'', the [[subthalamus]] and [[internal capsule]].
  
  +
−
* ''ventral'', the [[optic chiasm]], [[tuber cinereum]], [[mammillary bodies]], and [[posterior pituitary]].
  
  +
The hypothalamus is responsive to:
  +
  +
*Light: daylength and [[photoperiod]] for regulating [[circadian]] and seasonal rhythms
  +
*Olfactory stimuli, including pheromones
  +
*Steroids, including gonadal steroids and corticosteroids
  +
*Neurally transmitted information arising in particular from the heart, the stomach, and the reproductive tract
  +
*[[Autonomic Nervous System|Autonomic]] inputs
  +
*Blood-borne stimuli, including [[leptin]], [[ghrelin]], [[angiotensin]], [[insulin]], pituitary hormones, [[cytokines]], plasma concentrations of glucose and osmolarity etc
  +
*[[Stress (medicine)|Stress]]
  +
*Invading microorganisms by increasing body temperature, resetting the body's thermostat upward.
  +
  +
===Olfactory stimuli===
  +
  +
Olfactory stimuli are important for reproduction and neuroendocrine function in many species. For instance if a pregnant mouse is exposed to the urine of a 'strange' male during a critical period after coitus then the pregnancy fails (the [[Bruce effect]]). Thus during coitus, a female mouse forms a precise 'olfactory memory' of her partner which persists for several days.
  +
Pheromonal cues aid synchronisation of [[oestrus]] in many species; in women, synchronised [[menstruation]] may also arise from pheromonal cues, although the role of pheromones in humans is doubted by some.
  +
  +
===Blood-borne stimuli===
  +
  +
[[Peptide]] hormones have important influences upon the hypothalamus, and to do so they must evade the [[blood-brain barrier]]. The hypothalamus is bounded in part by specialized brain regions that lack an effective blood-brain barrier; the [[capillary endothelium]] at these sites is fenestrated to allow free passage of even large proteins and other molecules. Some of these sites are the sites of neurosecretion - the [[neurohypophysis]] and the [[median eminence]]. However others are sites at which the brain samples the composition of the blood. Two of these sites, the [[subfornical organ]] and the OVLT ([[organum vasculosum of the lamina terminalis]]) are so-called [[circumventricular organs]], where neurons are in intimate contact with both blood and [[Cerebrospinal fluid|CSF]]. These structures are densely vascularized, and contain osmoreceptive and sodium-receptive neurons which control [[drinking]], [[vasopressin]] release, sodium excretion, and sodium appetite. They also contain neurons with receptors for [[angiotensin]], [[atrial natriuretic factor]], [[endothelin]] and [[relaxin]], each of which is important in the regulation of fluid and electrolyte balance. Neurons in the OVLT and SFO project to the [[supraoptic nucleus]] and [[paraventricular nucleus]], and also to preoptic hypothalamic areas. The circumventricular organs may also be the site of action of [[interleukins]] to elicit both fever and ACTH secretion, via effects on paraventricular neurons.
  +
  +
It is not clear how all peptides that influence hypothalamic activity gain the necessary access. In the case of [[prolactin]] and [[leptin]], there is evidence of active uptake at the [[choroid plexus]] from blood into CSF. Some pituitary hormones have a negative feedback influence upon hypothalamic secretion; for example, [[growth hormone]] feeds back on the hypothalamus, but how it enters the brain is not clear. There is also evidence for central actions of [[prolactin]] and [[Thyroid-stimulating hormone|TSH]].
  +
  +
===Steroids===
  +
  +
The hypothalamus contains neurons that are sensitive to gonadal steroids and [[glucocorticoids]] – (the steroid hormones of the [[adrenal gland]], released in response to [[ACTH]]). It also contains specialised glucose-sensitive neurons (in the [[arcuate nucleus]] and [[ventromedial hypothalamus]]), which are important for [[appetite]]. The preoptic area contains thermosensitive neurons; these are important for [[TRH]] secretion.
  +
  +
===Neural inputs===
  +
  +
The hypothalamus receives many inputs from the [[brainstem]]; notably from the [[nucleus of the solitary tract]], the [[locus coeruleus]], and the [[ventrolateral medulla]]. [[Oxytocin]] secretion in response to suckling or vagino-cervical stimulation is mediated by some of these pathways; [[vasopressin]] secretion in response to cardiovascular stimuli arising from chemoreceptors in the [[carotid sinus]] and [[aortic arch]], and from low-pressure [[atrial volume receptors]], is mediated by others. In the rat, stimulation of the [[vagina]] also causes [[prolactin]] secretion, and this results in [[pseudo-pregnancy]] following an infertile mating. In the rabbit, coitus elicits reflex [[ovulation]]. In the sheep, cervical stimulation in the presence of high levels of estrogen can induce [[maternal behavior]] in a virgin ewe. These effects are all mediated by the hypothalamus, and the information is carried mainly by spinal pathways that relay in the brainstem. Stimulation of the nipples stimulates release of oxytocin and prolactin and suppresses the release of [[Luteinizing hormone|LH]] and [[Follicle-stimulating hormone|FSH]].
  +
  +
Cardiovascular stimuli are carried by the [[vagus nerve]], but the vagus also conveys a variety of visceral information, including for instance signals arising from gastric distension to suppress feeding. Again this information reaches the hypothalamus via relays in the brainstem.
  +
  +
==Nuclei==
  +
  +
The hypothalamic nuclei include the following:<ref>[http://www.psycheducation.org/emotion/pics/big%20hypothalamus.htm Diagram of Nuclei (psycheducation.org)]</ref><ref>[http://universe-review.ca/I10-80-nuclei.jpg Diagram of Nuclei (universe-review.ca)]</ref><ref>[http://www.utdallas.edu/~tres/integ/hom3/display13_04.html Diagram of Nuclei (utdallas.edu)]</ref>
   
−
==Hypothalamic nuclei==
  
 
[[Image:HypothalamicNuclei.PNG|thumb|350px|Hypothalamic nuclei]]
  
[[Image:HypothalamicNuclei.PNG|thumb|350px|Hypothalamic nuclei]]
−
{| class="wikitable"
+
{| class="wikitable"
 
|-
  
|-
 
|'''Region'''
  
|'''Region'''
−
|'''Medial Area'''
 +
|'''Area'''
−
|'''Lateral Area'''
 +
|'''Nucleus'''
  +
|'''Function'''
  +
<ref> Unless else specified in table, then ref is: Guyton Eight Edition </ref>
 
|-
  
|-
−
|Anterior
 +
|rowspan=8|Anterior
  +
|rowspan=5|Medial
−
|
  
−
[[Medial preoptic nucleus]]<br>
 +
| [[Medial preoptic nucleus]] ||
  +
*[[urinary bladder]] contraction
−
[[Supraoptic nucleus]]<br>
  
  +
*Decreased [[heart rate]]
−
[[Paraventricular nucleus]]<br>
  
  +
*Decreased [[blood pressure]]
−
[[Anterior nucleus]]<br>
  
−
[[Suprachiasmatic nucleus]]
  
−
|
  
−
[[Lateral preoptic nucleus]]<br>
  
−
[[Lateral nucleus]]<br>
  
−
Part of supraoptic nucleus
  
 
|-
  
|-
  +
| [[Supraoptic nucleus]] (SO) ||
−
|Tuberal
  
  +
*[[vasopressin]] release
−
|
  
−
[[Dorsomedial nucleus]]<br>
  
−
[[Ventromedial nucleus]]<br>
  
−
[[Arcuate nucleus]]
  
−
|
  
−
[[Lateral nucleus]]<br>
  
−
[[Lateral tuberal nuclei]]
  
 
|-
  
|-
  +
| [[Paraventricular nucleus]] (PV) ||
−
|Posterior
  
  +
*[[oxytocin]] release
−
|
  
  +
*[[vasopressin]] release<ref name=boron840> {{cite book |author=Walter F., PhD. Boron |title=Medical Physiology: A Cellular And Molecular Approaoch |publisher=Elsevier/Saunders |location= |year= |pages= |isbn=1-4160-2328-3 |oclc= |doi=}} Page 840 </ref>
−
Mammillary nuclei (part of [[mammillary body|mammillary bodies]])<br>
  
  +
|-
−
[[Posterior nucleus (hypothalamus)|Posterior nucleus]]
  
−
|[[Lateral nucleus]]
 +
| [[Anterior hypothalamic nucleus]] (AH) ||
  +
*[[thermoregulation]]
  +
*[[panting]]
  +
*[[sweating]]
  +
*[[thyrotropin]] inhibition
  +
|-
  +
| [[Suprachiasmatic nucleus]] (SC) ||
  +
*[[vasopressin]] release
  +
*[[Circadian rhythms]]
  +
|-
  +
|rowspan=3|Lateral || [[Lateral preoptic nucleus]] ||
  +
|-
  +
| [[Lateral hypothalamic nucleus|Lateral nucleus]] (LT) ||
  +
*[[thirst]] and [[hunger]]
  +
|-
  +
| Part of supraoptic nucleus (SO) ||
  +
*[[vasopressin]] release
  +
|-
  +
|rowspan=5|Tuberal
  +
|rowspan=3|Medial
  +
| [[Dorsomedial hypothalamic nucleus]] (DM) ||
  +
*[[gastrointestinal tract|GI]] stimulation
  +
|-
  +
| [[Ventromedial nucleus]] (VM) ||
  +
*[[satiety]]
  +
*[[neurendocrine]] control
  +
|-
  +
| [[Arcuate nucleus]] (AR)
  +
*[[neurendocrine]] control
  +
|-
  +
|rowspan=2| Lateral || [[Lateral hypothalamic nucleus|Lateral nucleus]] (LT) ||
  +
*[[thirst]] and [[hunger]]
  +
|-
  +
| [[Lateral tuberal nuclei]] ||
  +
|-
  +
|rowspan=3|Posterior
  +
|rowspan=2|Medial
  +
|Mammillary nuclei (part of [[mammillary body|mammillary bodies]]) (MB) ||
  +
*[[feeding reflexes]]
  +
|-
  +
| [[Posterior nucleus (hypothalamus)|Posterior nucleus]] (PN) ||
  +
*Increase [[blood pressure]]
  +
*[[Pupil|pupillary]] dilation
  +
*[[shivering]]
  +
|-
  +
| Lateral ||[[Lateral hypothalamic nucleus|Lateral nucleus]] (LT)
 
|}
  
|}
 
:''See also:'' [[ventrolateral preoptic nucleus]]
  
:''See also:'' [[ventrolateral preoptic nucleus]]
   
  +
==Outputs==
−
==Inputs to the hypothalamus==
  
−
[[Image:Illu diencephalon .jpg|thumb|300px|Dienchephalon]]
  
−
The hypothalamus is a very complex region, and even small nuclei within the hypothalamus are involved in many different functions. The [[paraventricular nucleus]] for instance contains [[oxytocin]] and [[vasopressin]] neurons which project to the [[posterior pituitary]], but also contains neurons that regulate [[ACTH]] and [[TSH]] secretion (which project to the [[anterior pituitary]]), [[gastric reflexes]], [[maternal behavior]], [[blood pressure]], [[feeding]], [[immune responses]], and [[temperature]].
  
   
  +
The outputs of the hypothalamus can be divided into two categories: neural projections, and endocrine hormones.<ref>http://thalamus.wustl.edu/course/hypoANS.html</ref>
−
The hypothalamus co-ordinates many seasonal and circadian rhythms, complex patterns of neuroendocrine outputs, complex homeostatic mechanisms, and many important stereotyped behaviours. The hypothalamus must therefore respond to many different signals, some of which are generated externally and some internally. The hypothalamus is thus richly connected with many parts of the CNS, including the brainstem [[reticular formation]] and autonomic zones, the limbic forebrain (particularly the [[amygdala]], [[septum]], [[diagonal band of Broca]], and the [[olfactory bulb]]s, and the [[cerebral cortex]]).
 
   
  +
===Neural projections===
−
The hypothalamus is responsive to:
  
   
  +
Most fiber systems of the hypothalamus run in two ways (bidirectional).
−
*Light: daylength and [[photoperiod]] for generating [[circadian]] and seasonal rhythms
  
  +
*Projections to areas [[Anatomical terms of location|caudal]] to the hypothalamus go through the [[medial forebrain bundle]], the [[mammillotegmental tract]] and the [[dorsal longitudinal fasciculus]].
  +
*Projections to areas rostral to the hypothalamus are carried by the [[mammillothalamic tract]], the [[Fornix of brain|fornix]] and [[terminal stria]].
   
  +
===Endocrine hormones===
−
*Olfactory stimuli, including pheromones
  
   
  +
The Hypothalamus affects the endocrine system and governs emotional behavior, such as, anger and sexual activity. Most of the hypothalamic hormones generated are distributed to the pituitary via the [[hypophyseal portal system]].<ref>http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/overview.html</ref> The hypothalamus maintains homeostasis this includes a regulation of blood pressure, heart rate, and temperature.
−
*Steroids, including gonadal steroids and corticosteroids
  
   
  +
The primary hypothalamic hormones are:
−
*Neurally transmitted information arising in particular from the heart, the stomach, and the reproductive tract
  
   
  +
{| class="wikitable"
−
*[[Autonomic]] inputs
  
  +
! Name !! Other Names !! Abbreviations !! Location !! Function
  +
|-
  +
| [[Corticotropin-releasing hormone]] || Corticotropin-releasing factor, Corticoliberin || CRH, CRF || [[Parvocellular part|parvocellular]] neuroendocrine neurons in the [[paraventricular nucleus]] || with [[vasopressin]], stimulates [[anterior pituitary]] to secrete [[Adrenocorticotropic hormone|ACTH]]
  +
|-
  +
| [[Dopamine]] || Prolactin-inhibiting hormone || DA, PIH || neuroendocrine neurons of the [[arcuate nucleus]] || inhibits secretion of [[prolactin]] from the [[anterior pituitary]]
  +
|-
  +
| [[Gonadotropin-releasing hormone]] || Luteinising-hormone releasing hormone || GnRH, LHRH || neuroendocrine neurons in the [[medial preoptic nucleus|medial preoptic]] and [[arcuate nucleus|arcuate nuclei]] || stimulates [[anterior pituitary]] to secrete [[Luteinizing hormone|LH]] and [[Follicle-stimulating hormone|FSH]]
  +
|-
  +
| [[Growth hormone-releasing hormone]] || Growth-hormone-releasing factor, somatocrinin || GHRH, GHRF, GRF || [[arcuate nucleus]] [[neuroendocrine]] neurons || stimulates [[anterior pituitary]] to secrete [[growth hormone]]
  +
|-
  +
| [[Melatonin]] || || || [[suprachiasmatic nucleus]] ||
  +
|-
  +
| [[Somatostatin]] || Growth hormone-inhibiting hormone, Somatotropin release-inhibiting factor || SS, GHIH, SRIF || neuroendocrine neurons of the [[periventricular nucleus]] || inhibits secretion of [[growth hormone]] from the [[anterior pituitary]]
  +
|-
  +
| [[Thyrotropin-releasing hormone]] || Thyrotropin-releasing factor, Thyroliberin, Protirelin || TRH, TRF || [[Parvocellular part|parvocellular]] neuroendocrine neurons in the [[paraventricular nucleus|paraventricular]] and [[anterior hypothalamic nucleus|anterior hypothalamic nuclei]] || stimulates [[anterior pituitary]] to secrete [[Thyroid-stimulating hormone|TSH]]
  +
|}
   
  +
See also: [[Hypocretin]]
−
*Blood-borne stimuli, including [[leptin]], [[ghrelin]], [[angiotensin]], [[insulin]], pituitary hormones, [[cytokines]], plasma concentrations of glucose and osmolarity etc
  
   
  +
==Control of food intake==
−
*[[Stress (medicine)|Stress]]
  
   
  +
The extreme [[Anatomical terms of location|lateral]] part of the [[ventromedial nucleus]] of the hypothalamus is responsible for the control of food intake. Stimulation of this area causes increased food intake. Bilateral [[lesion]] of this area causes complete cessation of food intake. Medial parts of the nucleus have a controlling effect on the lateral part. Bilateral lesion of the medial part of the ventromedial nucleus causes [[hyperphagia]] and obesity of the animal. Further lesion of the lateral part of the ventromedial nucleus in the same animal produces complete cessation of food intake.
−
*Invading microorganisms by increasing body temperature, resetting the bodys thermostat upward.
  
   
  +
There are different hypotheses related to this regulation:<ref>{{cite journal |author=Theologides A |title=Anorexia-producing intermediary metabolites |journal=Am J Clin Nutr |volume=29 |issue=5 |pages=552-8 |year=1976 |pmid=178168}}</ref>
−
===Olfactory stimuli===
  
−
Olfactory stimuli are important for reproduction and neuroendocrine function in many species. For instance, if a pregnant mouse is exposed to the urine of a 'strange' male during a critical period after coitus then the pregnancy fails (the [[Bruce effect]]). Thus during coitus, a female mouse forms a precise 'olfactory memory' of her partner which persists for several days.
  
−
Pheromonal cues aid synchronisation of [[oestrus]] in many species; in women, synchronised [[menstruation]] may also arise from pheromonal cues.
  
   
  +
#Lipostatic hypothesis - this hypothesis holds that [[adipose]] [[biological tissue|tissue]] produces a [[Humoral immunity|humoral]] signal that is proportionate to the amount of fat and acts on the hypothalamus to decrease food intake and increase energy output. It has been evident that a [[hormone]] [[leptin]] acts on the hypothalamus to decrease food intake and increase energy output.
−
===Blood-borne stimuli===
  
  +
#Gutpeptide hypothesis - [[Gastrointestinal tract|gastrointestinal]] hormones like Grp, [[glucagon]]s, [[Cholecystokinin|CCK]] and others claimed to inhibit food intake. The food entering the gastrointestinal tract triggers the release of these hormones which acts on the brain to produce satiety. The brain contains both CCK-A and CCK-B receptors.
−
[[Peptide]] hormones have important influences upon the hypothalamus, and to do so they must evade the [[blood-brain barrier]]. The hypothalamus is bounded in part by specialized brain regions that lack an effective blood-brain barrier; the [[capillary endothelium]] at these sites is fenestrated to allow free passage of even large proteins and other molecules. Some of these sites are the sites of neurosecretion - the [[neurohypophysis]] and the [[median eminence]]. However others are sites at which the brain samples the composition of the blood. Two of these sites, the [[subfornical organ]] and the OVLT ([[organum vasculosum of the lamina terminalis]]) are so-called [[circumventricular organs]], where neurons are in intimate contact with both blood and CSF. These structures are densely vascularized, and contain osmoreceptive and sodium-receptive neurons which control [[drinking]], [[vasopressin]] release, sodium excretion, and sodium appetite. They also contain neurons with receptors for [[angiotensin]], [[atrial natriuretic factor]], [[endothelin]] and [[relaxin]], each of which is important in the regulation of fluid and electrolyte balance. Neurons in the OVLT and SFO project to the [[supraoptic nucleus]] and [[paraventricular nucleus]], and also to preoptic hypothalamic areas. The circumventricular organs may also be the site of action of [[interleukins]] to elicit both fever and ACTH secretion, via effects on paraventricular neurons.
 
  +
#Glucostatic hypothesis - the activity of the satiety center in the ventromedial nuclei is probably governed by the [[glucose]] utilization in the neurons. It has been postulated that when their glucose utilization is low and consequently when the arteriovenous blood glucose difference across them is low, the activity across the neurons decrease. Under these conditions, the activity of the feeding center is unchecked and the individual feels hungry. Food intake is rapidly increased by intraventricular administration of [[2-Deoxy-D-glucose|2-deoxyglucose]] therefore decreasing glucose utilization in cells.
  +
#Thermostatic hypothesis - according to this hypothesis, a decrease in body temperature below a given set point stimulates appetite, while an increase above the set point inhibits appetite.
   
  +
==Sexual dimorphism==
−
It is not clear how all peptides that influence hypothalamic activity gain the necessary access. In the case of [[prolactin]] and [[leptin]], there is evidence of active uptake at the [[choroid plexus]] from blood into [[CSF]]. Some pituitary hormones have a negative feedback influence upon hypothalamic secretion; for example, [[growth hormone]] feeds back on the hypothalamus, but how it enters the brain is not clear. There is also evidence for central actions of [[prolactin]] and [[TSH]].
  
   
  +
Several hypothalamic nuclei are [[sexually dimorphic]], i.e. there are clear differences in both structure and function between males and females.
−
===Steroids===
  
−
The hypothalamus contains neurons that are sensitive to gonadal steroids and [[glucocorticoids]] – (the steroid hormones of the [[adrenal gland]], released in response to [[ACTH]]). It also contains specialised glucose-sensitive neurons (in the [[arcuate nucleus]] and [[ventromedial hypothalamus]]), which are important for [[appetite]]. The preoptic area contains thermosensitive neurons; these are important for [[TRH]] secretion.
  
   
  +
Some differences are apparent even in gross neuroanatomy: most notable is the [[sexually dimorphic nucleus]] within the [[preoptic area]], which is present only in males. However most of the differences are subtle changes in the connectivity and chemical sensitivity of particular sets of neurons.
−
===Neural inputs===
  
−
The hypothalamus receives many inputs from the [[brainstem]]; notably from the [[nucleus of the solitary tract]], the [[locus coeruleus]], and the [[ventrolateral medulla]]. [[Oxytocin]] secretion in response to suckling or vagino-cervical stimulation is mediated by some of these pathways; [[vasopressin]] secretion in response to cardiovascular stimuli arising from chemoreceptors in the [[carotid sinus]] and [[aortic arch]], and from low-pressure atrial volume receptors, is mediated by others. In the rat, stimulation of the [[vagina]] also causes [[prolactin]] secretion, and this results in [[pseudo-pregnancy]] following an infertile mating. In the rabbit, coitus elicits reflex [[ovulation]]. In the sheep, cervical stimulation in the presence of high levels of estrogen can induce [[maternal behaviour]] in a virgin ewe. These effects are all mediated by the hypothalamus, and the information is carried mainly by spinal pathways that relay in the brainstem. Stimulation of the nipples stimulates release of oxytocin and prolactin and suppresses the release of [[LH]] and [[FSH]].
  
−
Cardiovascular stimuli are carried by the [[vagus nerve]], but the vagus also conveys a variety of visceral information, including for instance signals arising from gastric distension to suppress feeding. Again this information reaches the hypothalamus via relays in the brainstem.
  
   
  +
The importance of these changes can be recognised by functional differences between males and females. For instance, the pattern of secretion of [[growth hormone]] is sexually dimorphic, and this is one reason why in many species, adult males are much larger than females.
−
==Projections==
  
   
  +
===Responses to ovarian steroids===
−
Most fiber systems of the hypothalamus run in two ways (bidirectional). Projections to areas [[Anatomical terms of location|caudal]] to the hypothalamus go through the medial forebrain bundle, the mammillotegmental tract and the dorsal longitudinal fasciculus. Projections to areas rostral to the hypothalamus are carried by the mammillothalamic tract, the fornix and stria terminalis.
 
−
==Sexual dimorphism==
  
   
−
The hypothalamus is [[sexually dimorphic]], i.e. there are clear differences in both structure and function between males and females. Some differences are apparent even in gross neuroanatomy: most notable is the [[sexually dimorphic nucleus]] within the [[preoptic area]], which is present only in males. However most of the differences are subtle changes in the connectivity and chemical sensitivity of particular sets of neurons. The importance of these changes can be recognised by functional differences between males and females. For instance, the pattern of secretion of [[growth hormone]] is sexually dimorphic, and this is one reason why in many species, adult males are much larger than females. Other striking functional dimorphisms are in the behavioral responses to [[ovarian steroids]] of the adult. Males and females respond differently to ovarian steroids, partly because the expression of estrogen-sensitive neurons in the hypothalamus is sexually dimorphic, i.e. estrogen receptors are expressed in different sets of neurons.
 +
Other striking functional dimorphisms are in the behavioral responses to [[ovarian steroids]] of the adult. Males and females respond differently to ovarian steroids, partly because the expression of estrogen-sensitive neurons in the hypothalamus is sexually dimorphic, i.e. estrogen receptors are expressed in different sets of neurons.
   
  +
[[Estrogen]] and [[progesterone]] can influence gene expression in particular neurons or induce changes in [[cell membrane]] potential and [[kinase]] activation, leading to diverse non-genomic cellular functions. Estrogen and progesterone bind to their cognate [[nuclear hormone receptor]]s, which translocate to the cell nucleus and interact with regions of DNA known as [[Hormone response element]]s (HREs) or get tethered to another [[transcription factor]]'s binding site. [[Estrogen receptor]] (ER) has been shown to transactivate other transcription factors in this manner, despite the absence of an [[estrogen response element]] (ERE) in the proximal promoter region of the gene. ERs and [[Progesterone receptor]]s (PRs) are generally gene activators, with increased mRNA and subsequent protein synthesis following hormone exposure.
−
[[Estrogen]] and [[progesterone]] act by influencing gene expression in particular neurons. To influence gene expression, estrogen binds to an intracellular receptor, and this complex is translocated to the cell nucleus where it interacts with regions of the DNA known as estrogen regulatory elements (EREs). Increased protein synthesis may follow as soon as 30 min later.
 
−
Thus, for estrogen to influence the expression of a particular gene in a particular cell, the following must occur:
  
−
* the cell must be exposed to estrogen
  
−
* the cell must express estrogen receptors
 
−
* the gene must be one that is regulated by an ERE.
  
   
 
Male and female brains differ in the distribution of estrogen receptors, and this difference is an irreversible consequence of neonatal steroid exposure. Estrogen receptors (and progesterone receptors) are found mainly in neurons in the anterior and mediobasal hypothalamus, notably:
  
Male and female brains differ in the distribution of estrogen receptors, and this difference is an irreversible consequence of neonatal steroid exposure. Estrogen receptors (and progesterone receptors) are found mainly in neurons in the anterior and mediobasal hypothalamus, notably:
−
* the preoptic area (where [[LHRH]] neurons are located)
 +
*the preoptic area (where [[LHRH]] neurons are located)
−
* the periventricular nucleus (where [[somatostatin]] neurons are located)
 +
*the periventricular nucleus (where [[somatostatin]] neurons are located)
−
* the [[ventromedial hypothalamus]] (which is important for sexual behavior).
+
*the [[ventromedial hypothalamus]] (which is important for sexual behavior).
   
  +
===Gonadal steroids in neonatal life of rats===
−
In neonatal life, gonadal steroids influence the development of the neuroendocrine hypothalamus. For instance, they determine the ability of females to exhibit a normal reproductive cycle, and of males and females to display appropriate reproductive behaviors in adult life. Thus, if a female rat is injected once with testosterone in the first few days of postnatal life (during the "critical period" of sex-steroid influence), the hypothalamus is irreversibly masculinized; the adult rat will be incapable of generating an LH surge in response to estrogen (a characteristic of females), but will be capable of exhibiting ''male'' sexual behaviors (mounting a sexually-receptive female). By contrast, a male rat castrated just after birth will be ''feminized'', and the adult will show ''female'' sexual behavior in response to estrogen (sexual receptivity, [[lordosis]]}.
 
   
  +
In neonatal life, gonadal steroids influence the development of the neuroendocrine hypothalamus. For instance, they determine the ability of females to exhibit a normal reproductive cycle, and of males and females to display appropriate reproductive behaviors in adult life.
−
In primates, the developmental influence of [[androgens]] is less clear, and the consequences are less complete. 'Tomboyism' in girls might reflect the effects of androgens on the fetal brain, but the sex of rearing during the first 2-3 years is believed by many to be the most important determinant of gender identity.
  
  +
  +
*If a ''female rat'' is injected once with testosterone in the first few days of postnatal life (during the "critical period" of sex-steroid influence), the hypothalamus is irreversibly masculinized; the adult rat will be incapable of generating an LH surge in response to estrogen (a characteristic of females), but will be capable of exhibiting ''male'' sexual behaviors (mounting a sexually receptive female).
  +
*By contrast, a ''male rat'' castrated just after birth will be ''feminized'', and the adult will show ''female'' sexual behavior in response to estrogen (sexual receptivity, [[lordosis]]}.
  +
  +
===Androgens in primates===
  +
  +
In primates, the developmental influence of [[androgens]] is less clear, and the consequences are less complete. 'Tomboyism' in girls might reflect the effects of androgens on the fetal brain, but the sex of rearing during the first 2-3 years is believed by many to be the most important determinant of gender identity, because during this phase either estrogen or testosterone will have permanent effects on either a female or male brain, influencing both heterosexuality and homosexuality.<ref>[[John Money]], 'The concept of gender identity disorder in childhood and adolescence after 39 years', Journal of Sex and Marital Therapy 20 (1994): 163-77.</ref>
   
 
The paradox is that the masculinizing effects of [[testosterone]] are mediated by estrogen. Within the brain, testosterone is aromatized to ([[estradiol]]), which is the principal active hormone for developmental influences. The human [[testis]] secretes high levels of testosterone from about week 8 of fetal life until 5-6 months after birth (a similar perinatal surge in testosterone is observed in many species), a process that appears to underlie the male phenotype. Estrogen from the maternal circulation is relatively ineffective, partly because of the high circulating levels of steroid-binding proteins in pregnancy.
  
The paradox is that the masculinizing effects of [[testosterone]] are mediated by estrogen. Within the brain, testosterone is aromatized to ([[estradiol]]), which is the principal active hormone for developmental influences. The human [[testis]] secretes high levels of testosterone from about week 8 of fetal life until 5-6 months after birth (a similar perinatal surge in testosterone is observed in many species), a process that appears to underlie the male phenotype. Estrogen from the maternal circulation is relatively ineffective, partly because of the high circulating levels of steroid-binding proteins in pregnancy.
   
  +
===Other influences upon hypothalamic development===
−
Sex steroids are not the only important influences upon hypothalamic development; stress in early life determines the capacity of the adult hypothalamus to respond to an acute stressor. Unlike gonadal steroid receptors, [[glucocorticoid]] receptors are very widespread throughout the brain; in the [[paraventricular nucleus]], they mediate negative feedback control of [[CRF]] synthesis and secretion, but elsewhere their role is not well understood.
  
  +
  +
Sex steroids are not the only important influences upon hypothalamic development; in particular, [[Puberty|pre-pubertal]] stress in early life determines the capacity of the adult hypothalamus to respond to an acute stressor.<ref>{{cite journal | last = Romeo | first = Russell D | coauthors = Rudy Bellani, Ilia N. Karatsoreos, Nara Chhua, Mary Vernov, Cheryl D. Conrad and Bruce S. McEwen | title = Stress History and Pubertal Development Interact to Shape Hypothalamic-Pituitary-Adrenal Axis Plasticity | journal = Endocrinology | volume = 147 | issue = 4 | pages = 1664-1674 | publisher = The Endocrine Society | date = 2005 | url = http://endo.endojournals.org/cgi/content/short/147/4/1664 | doi = 10.1210/en.2005-1432 | accessdate = 2007-10-16 }}</ref> Unlike gonadal steroid receptors, [[glucocorticoid]] receptors are very widespread throughout the brain; in the [[paraventricular nucleus]], they mediate negative feedback control of [[Corticotropin-releasing hormone|CRF]] synthesis and secretion, but elsewhere their role is not well understood.
  +
  +
==Effects of aging on the hypothalamus==
  +
  +
Studies in female mice have shown that both [[Supraoptic nucleus]] (SON) and [[Paraventricular nucleus]] (PVN) lose approximately one-third of IGF-1R immunoreactive cells with normal aging. Also, Old caloricly restricted (CR) mice lost higher numbers of IGF-1R non-immunoreactive cells while maintaining similar counts of IGF-1R immunoreactive cells in comparison to Old-Al mice. Consequently, Old-CR mice show a higher percentage of IGF-1R immunoreactive cells reflecting increased hypothalamic sensitivity to IGF-1 in comparison to normally aging mice. <ref>{{cite journal |author=Saeed O,Yaghmaie F,Garan SA,Gouw AM,Voelker MA,Sternberg H, Timiras PS. |title=Insulin-like growth factor-1 receptor immunoreactive cells are selectively maintained in the paraventricular hypothalamus of calorically restricted mice|journal=Int J Dev Neurosci |volume=25 |issue=1 |pages=23-8 |year=2007 |pmid=17194562}}</ref> <ref>{{cite journal |author=Yaghmaie F, Saeed O, Garan SA, Voelker MA, Gouw AM, Freitag W, Sternberg H, Timiras PS|title=Age-dependent loss of insulin-like growth factor-1 receptor immunoreactive cells in the supraoptic hypothalamus is reduced in calorically restricted mice |journal=Int J Dev Neurosci |volume=24 |issue=7 |pages=431-6 |year=2006 |pmid=17034982}}</ref>
  +
<ref>{{cite journal |author=F. Yaghmaie, O. Saeed, S.A. Garan, A.M. Gouw, P. Jafar, J. Kaur, S. Nijjar, P.S. Timiras, H. Sternberg, M.A. Voelker |title=Tracking changes in hypothalamic IGF-1 sensitivity with aging and caloric restriction |journal=Experimental Gerontology |volume=42 |issue=1-2 |pages=148-149 |year=2007 }}
  +
[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T6J-4KGG1P4-10&_user=10&_handle=C-WA-A-VD-VD-MsSAYWB-UUW-U-U-VD-U-U-AADUEEDBAV-AAZYCDYAAV-WUBCCYBZA-VD-U&_fmt=full&_coverDate=02%2F28%2F2007&_rdoc=45&_orig=browse&_srch=%23toc%235032%232007%23999579998%23639966!&_cdi=5032&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d5741475a812c1d5a283114bba5379a8]</ref>
   
 
==See also==
  
==See also==
 
*[[HPA axis]]
  
*[[HPA axis]]
  +
*[[Hypothalamo hypophyseal system]]
  +
*[[Hypothalamo pituitary adrenal system]]
  +
*[[Hypothalamus lesions]]
  +
*[[Medial forebrain bundle]]
 
*[[Neuroendocrinology]]
  
*[[Neuroendocrinology]]
  +
*[[Preoptic area]]
   
  +
==Additional images==
−
==References & Bibliography==
 
  +
<gallery>Image:Gray654.png|Median sagittal section of brain of human embryo of three months.</gallery>
−
==Key texts==
 
  +
  +
==References==
  +
{{reflist}}
  +
  +
  +
==References & Bibliography==
  +
==Key texts==
 
===Books===
  
===Books===
   
Line 153: Line 251:
 
*Arees, E.A. and Mayer, B, (1967) Anatomical connections between medial and lateral regions of the hypothalamus concerned with food intake, [[Science]] 157: 1574-5
  
*Arees, E.A. and Mayer, B, (1967) Anatomical connections between medial and lateral regions of the hypothalamus concerned with food intake, [[Science]] 157: 1574-5
 
*Grossman, S.P. (1960) Eating or drinking elicited by direct adrenergic or cholinergic stimulation of the hypothalamus, [[Science]] 132: 301-2.
  
*Grossman, S.P. (1960) Eating or drinking elicited by direct adrenergic or cholinergic stimulation of the hypothalamus, [[Science]] 132: 301-2.
−
*Hetherington, A.W. and Ranson, S.W. (1942) The relation of various hypothalamic lesions to adiposity in the rat, 76: 475-99.
+
*Hetherington, A.W. and Ranson, S.W. (1942) The relation of various hypothalamic lesions to adiposity in the rat, 76: 475-99.
 
==Additional material==
  
==Additional material==
 
===Books===
  
===Books===
Line 164: Line 262:
   
 
==External links==
  
==External links==
  +
*{{BrainMaps|Hypothalamus}}
 
* [http://endocrine-system.know-heart-diseases.com Endocrine system and hypothalamus]
  
* [http://endocrine-system.know-heart-diseases.com Endocrine system and hypothalamus]
 
* [http://brainmaps.org High-Resolution Cytoarchitectural Primate Brain Atlases]
  
* [http://brainmaps.org High-Resolution Cytoarchitectural Primate Brain Atlases]
Line 171: Line 270:
 
* [http://www.utdallas.edu/~tres/integ/hom3/display13_04.html Diagram of Nuclei (utdallas.edu)]
  
* [http://www.utdallas.edu/~tres/integ/hom3/display13_04.html Diagram of Nuclei (utdallas.edu)]
   
  +
−
{{endocrine_system}}
  
  +
−
{{limbic system}}
  
   
 
{{Diencephalon}}
  
{{Diencephalon}}
  +
{{Endocrine system}}
  +
{{Limbic system}}
   
−
[[Category:Endocrine system]]
  
−
[[Category:Limbic system]]
  
−
[[Category:Cerebrum]]
  
−
[[Category:Neuroanatomy]]
  
−
[[Category:Neuroendocrinology]]
  
   
  +
<!--
 
[[ca:Hipotàlem]]
  
[[ca:Hipotàlem]]
 
[[cs:Hypothalamus]]
  
[[cs:Hypothalamus]]
Line 188: Line 285:
 
[[es:Hipotálamo]]
  
[[es:Hipotálamo]]
 
[[fr:Hypothalamus]]
  
[[fr:Hypothalamus]]
  +
[[hr:Hipotalamus]]
  +
[[it:Ipotalamo]]
 
[[he:היפותלמוס]]
  
[[he:היפותלמוס]]
−
[[ja:視床下部]]
 +
[[la:Hypothalamus]]
  +
[[hu:Hipotalamusz]]
 
[[nl:Hypothalamus]]
  
[[nl:Hypothalamus]]
  +
[[ja:視床下部]]
 
[[no:Hypothalamus]]
  
[[no:Hypothalamus]]
 
[[pl:Podwzgórze]]
  
[[pl:Podwzgórze]]
Line 196: Line 297:
 
[[ru:Гипоталамус]]
  
[[ru:Гипоталамус]]
 
[[sk:Podlôžko]]
  
[[sk:Podlôžko]]
  +
[[fi:Hypotalamus]]
  +
[[sv:Hypotalamus]]
 
[[tr:Hipotalamus]]
  
[[tr:Hipotalamus]]
 
{{enWP| Hypothalmus}}
  
{{enWP| Hypothalmus}}
  +
-->
  +
[[Category:Cerebrum]]
  +
[[Category:Diencephalon]]
  +
[[Category:Endocrine system]]
  +
[[Category:Limbic system]]
  +
[[Category:Neuroanatomy]]
  +
[[Category:Neuroendocrinology]]

Latest revision as of 00:05, 11 September 2013

Assessment | Biopsychology | Comparative | Cognitive | Developmental | Language | Individual differences | Personality | Philosophy | Social |
Methods | Statistics | Clinical | Educational | Industrial | Professional items | World psychology |

Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Neuroscience · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology (Index, Outline)

Brain: Hypothalamus
LocationOfHypothalamus
Location of the human hypothalamus
Illu diencephalon
Dienchephalon
Latin hypothalamus
Gray's subject #189 812
Part of
Components
Artery
Vein
BrainInfo/UW hier-358
MeSH A08.186.211.730.385.357

The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus, (from Greek ὑποθαλαμος = under the thalamus) is located below the thalamus, just above the brain stem. This gland occupies the major portion of the ventral region of the diencephalon. It is found in all mammalian brains. In humans, it is roughly the size of an almond.

The hypothalamus regulates certain metabolic processes and other activities of the Autonomic Nervous System. It synthesizes and secretes neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones.

The hypothalamus controls body temperature, hunger, thirst, [1] fatigue, anger, and circadian cycles.

Inputs

The hypothalamus is a very complex region in the brain of humans, and even small nuclei within the hypothalamus are involved in many different functions. The paraventricular nucleus for instance contains oxytocin and vasopressin (also called antidiuretic hormone) neurons which project to the posterior pituitary, but also contains neurons that regulate ACTH and TSH secretion (which project to the anterior pituitary), gastric reflexes, maternal behavior, blood pressure, feeding, immune responses, and temperature.

The hypothalamus co-ordinates many hormonal and behavioural circadian rhythms, complexity patterns of neuroendocrine outputs, complex homeostatic mechanisms,[2] and many important behaviours. The hypothalamus must therefore respond to many different signals, some of which are generated externally and some internally. It is thus richly connected with many parts of the CNS, including the brainstem reticular formation and autonomic zones, the limbic forebrain (particularly the amygdala, septum, diagonal band of Broca, and the olfactory bulbs, and the cerebral cortex).

The hypothalamus is responsive to:

  • Light: daylength and photoperiod for regulating circadian and seasonal rhythms
  • Olfactory stimuli, including pheromones
  • Steroids, including gonadal steroids and corticosteroids
  • Neurally transmitted information arising in particular from the heart, the stomach, and the reproductive tract
  • Autonomic inputs
  • Blood-borne stimuli, including leptin, ghrelin, angiotensin, insulin, pituitary hormones, cytokines, plasma concentrations of glucose and osmolarity etc
  • Stress
  • Invading microorganisms by increasing body temperature, resetting the body's thermostat upward.

Olfactory stimuli

Olfactory stimuli are important for reproduction and neuroendocrine function in many species. For instance if a pregnant mouse is exposed to the urine of a 'strange' male during a critical period after coitus then the pregnancy fails (the Bruce effect). Thus during coitus, a female mouse forms a precise 'olfactory memory' of her partner which persists for several days. Pheromonal cues aid synchronisation of oestrus in many species; in women, synchronised menstruation may also arise from pheromonal cues, although the role of pheromones in humans is doubted by some.

Blood-borne stimuli

Peptide hormones have important influences upon the hypothalamus, and to do so they must evade the blood-brain barrier. The hypothalamus is bounded in part by specialized brain regions that lack an effective blood-brain barrier; the capillary endothelium at these sites is fenestrated to allow free passage of even large proteins and other molecules. Some of these sites are the sites of neurosecretion - the neurohypophysis and the median eminence. However others are sites at which the brain samples the composition of the blood. Two of these sites, the subfornical organ and the OVLT (organum vasculosum of the lamina terminalis) are so-called circumventricular organs, where neurons are in intimate contact with both blood and CSF. These structures are densely vascularized, and contain osmoreceptive and sodium-receptive neurons which control drinking, vasopressin release, sodium excretion, and sodium appetite. They also contain neurons with receptors for angiotensin, atrial natriuretic factor, endothelin and relaxin, each of which is important in the regulation of fluid and electrolyte balance. Neurons in the OVLT and SFO project to the supraoptic nucleus and paraventricular nucleus, and also to preoptic hypothalamic areas. The circumventricular organs may also be the site of action of interleukins to elicit both fever and ACTH secretion, via effects on paraventricular neurons.

It is not clear how all peptides that influence hypothalamic activity gain the necessary access. In the case of prolactin and leptin, there is evidence of active uptake at the choroid plexus from blood into CSF. Some pituitary hormones have a negative feedback influence upon hypothalamic secretion; for example, growth hormone feeds back on the hypothalamus, but how it enters the brain is not clear. There is also evidence for central actions of prolactin and TSH.

Steroids

The hypothalamus contains neurons that are sensitive to gonadal steroids and glucocorticoids – (the steroid hormones of the adrenal gland, released in response to ACTH). It also contains specialised glucose-sensitive neurons (in the arcuate nucleus and ventromedial hypothalamus), which are important for appetite. The preoptic area contains thermosensitive neurons; these are important for TRH secretion.

Neural inputs

The hypothalamus receives many inputs from the brainstem; notably from the nucleus of the solitary tract, the locus coeruleus, and the ventrolateral medulla. Oxytocin secretion in response to suckling or vagino-cervical stimulation is mediated by some of these pathways; vasopressin secretion in response to cardiovascular stimuli arising from chemoreceptors in the carotid sinus and aortic arch, and from low-pressure atrial volume receptors, is mediated by others. In the rat, stimulation of the vagina also causes prolactin secretion, and this results in pseudo-pregnancy following an infertile mating. In the rabbit, coitus elicits reflex ovulation. In the sheep, cervical stimulation in the presence of high levels of estrogen can induce maternal behavior in a virgin ewe. These effects are all mediated by the hypothalamus, and the information is carried mainly by spinal pathways that relay in the brainstem. Stimulation of the nipples stimulates release of oxytocin and prolactin and suppresses the release of LH and FSH.

Cardiovascular stimuli are carried by the vagus nerve, but the vagus also conveys a variety of visceral information, including for instance signals arising from gastric distension to suppress feeding. Again this information reaches the hypothalamus via relays in the brainstem.

Nuclei

The hypothalamic nuclei include the following:[3][4][5]

HypothalamicNuclei

Hypothalamic nuclei

Region Area Nucleus Function

[6]

Anterior Medial Medial preoptic nucleus
Supraoptic nucleus (SO)
Paraventricular nucleus (PV)
Anterior hypothalamic nucleus (AH)
Suprachiasmatic nucleus (SC)
Lateral Lateral preoptic nucleus
Lateral nucleus (LT)
Part of supraoptic nucleus (SO)
Tuberal Medial Dorsomedial hypothalamic nucleus (DM)
  • GI stimulation
Ventromedial nucleus (VM)
Arcuate nucleus (AR)
  • neurendocrine control
Lateral Lateral nucleus (LT)
Lateral tuberal nuclei
Posterior Medial Mammillary nuclei (part of mammillary bodies) (MB)
  • feeding reflexes
Posterior nucleus (PN)
Lateral Lateral nucleus (LT)
See also: ventrolateral preoptic nucleus

Outputs

The outputs of the hypothalamus can be divided into two categories: neural projections, and endocrine hormones.[8]

Neural projections

Most fiber systems of the hypothalamus run in two ways (bidirectional).

Endocrine hormones

The Hypothalamus affects the endocrine system and governs emotional behavior, such as, anger and sexual activity. Most of the hypothalamic hormones generated are distributed to the pituitary via the hypophyseal portal system.[9] The hypothalamus maintains homeostasis this includes a regulation of blood pressure, heart rate, and temperature.

The primary hypothalamic hormones are:

Name Other Names Abbreviations Location Function
Corticotropin-releasing hormone Corticotropin-releasing factor, Corticoliberin CRH, CRF parvocellular neuroendocrine neurons in the paraventricular nucleus with vasopressin, stimulates anterior pituitary to secrete ACTH
Dopamine Prolactin-inhibiting hormone DA, PIH neuroendocrine neurons of the arcuate nucleus inhibits secretion of prolactin from the anterior pituitary
Gonadotropin-releasing hormone Luteinising-hormone releasing hormone GnRH, LHRH neuroendocrine neurons in the medial preoptic and arcuate nuclei stimulates anterior pituitary to secrete LH and FSH
Growth hormone-releasing hormone Growth-hormone-releasing factor, somatocrinin GHRH, GHRF, GRF arcuate nucleus neuroendocrine neurons stimulates anterior pituitary to secrete growth hormone
Melatonin suprachiasmatic nucleus
Somatostatin Growth hormone-inhibiting hormone, Somatotropin release-inhibiting factor SS, GHIH, SRIF neuroendocrine neurons of the periventricular nucleus inhibits secretion of growth hormone from the anterior pituitary
Thyrotropin-releasing hormone Thyrotropin-releasing factor, Thyroliberin, Protirelin TRH, TRF parvocellular neuroendocrine neurons in the paraventricular and anterior hypothalamic nuclei stimulates anterior pituitary to secrete TSH

See also: Hypocretin

Control of food intake

The extreme lateral part of the ventromedial nucleus of the hypothalamus is responsible for the control of food intake. Stimulation of this area causes increased food intake. Bilateral lesion of this area causes complete cessation of food intake. Medial parts of the nucleus have a controlling effect on the lateral part. Bilateral lesion of the medial part of the ventromedial nucleus causes hyperphagia and obesity of the animal. Further lesion of the lateral part of the ventromedial nucleus in the same animal produces complete cessation of food intake.

There are different hypotheses related to this regulation:[10]

  1. Lipostatic hypothesis - this hypothesis holds that adipose tissue produces a humoral signal that is proportionate to the amount of fat and acts on the hypothalamus to decrease food intake and increase energy output. It has been evident that a hormone leptin acts on the hypothalamus to decrease food intake and increase energy output.
  2. Gutpeptide hypothesis - gastrointestinal hormones like Grp, glucagons, CCK and others claimed to inhibit food intake. The food entering the gastrointestinal tract triggers the release of these hormones which acts on the brain to produce satiety. The brain contains both CCK-A and CCK-B receptors.
  3. Glucostatic hypothesis - the activity of the satiety center in the ventromedial nuclei is probably governed by the glucose utilization in the neurons. It has been postulated that when their glucose utilization is low and consequently when the arteriovenous blood glucose difference across them is low, the activity across the neurons decrease. Under these conditions, the activity of the feeding center is unchecked and the individual feels hungry. Food intake is rapidly increased by intraventricular administration of 2-deoxyglucose therefore decreasing glucose utilization in cells.
  4. Thermostatic hypothesis - according to this hypothesis, a decrease in body temperature below a given set point stimulates appetite, while an increase above the set point inhibits appetite.

Sexual dimorphism

Several hypothalamic nuclei are sexually dimorphic, i.e. there are clear differences in both structure and function between males and females.

Some differences are apparent even in gross neuroanatomy: most notable is the sexually dimorphic nucleus within the preoptic area, which is present only in males. However most of the differences are subtle changes in the connectivity and chemical sensitivity of particular sets of neurons.

The importance of these changes can be recognised by functional differences between males and females. For instance, the pattern of secretion of growth hormone is sexually dimorphic, and this is one reason why in many species, adult males are much larger than females.

Responses to ovarian steroids

Other striking functional dimorphisms are in the behavioral responses to ovarian steroids of the adult. Males and females respond differently to ovarian steroids, partly because the expression of estrogen-sensitive neurons in the hypothalamus is sexually dimorphic, i.e. estrogen receptors are expressed in different sets of neurons.

Estrogen and progesterone can influence gene expression in particular neurons or induce changes in cell membrane potential and kinase activation, leading to diverse non-genomic cellular functions. Estrogen and progesterone bind to their cognate nuclear hormone receptors, which translocate to the cell nucleus and interact with regions of DNA known as Hormone response elements (HREs) or get tethered to another transcription factor's binding site. Estrogen receptor (ER) has been shown to transactivate other transcription factors in this manner, despite the absence of an estrogen response element (ERE) in the proximal promoter region of the gene. ERs and Progesterone receptors (PRs) are generally gene activators, with increased mRNA and subsequent protein synthesis following hormone exposure.

Male and female brains differ in the distribution of estrogen receptors, and this difference is an irreversible consequence of neonatal steroid exposure. Estrogen receptors (and progesterone receptors) are found mainly in neurons in the anterior and mediobasal hypothalamus, notably:

Gonadal steroids in neonatal life of rats

In neonatal life, gonadal steroids influence the development of the neuroendocrine hypothalamus. For instance, they determine the ability of females to exhibit a normal reproductive cycle, and of males and females to display appropriate reproductive behaviors in adult life.

  • If a female rat is injected once with testosterone in the first few days of postnatal life (during the "critical period" of sex-steroid influence), the hypothalamus is irreversibly masculinized; the adult rat will be incapable of generating an LH surge in response to estrogen (a characteristic of females), but will be capable of exhibiting male sexual behaviors (mounting a sexually receptive female).
  • By contrast, a male rat castrated just after birth will be feminized, and the adult will show female sexual behavior in response to estrogen (sexual receptivity, lordosis}.

Androgens in primates

In primates, the developmental influence of androgens is less clear, and the consequences are less complete. 'Tomboyism' in girls might reflect the effects of androgens on the fetal brain, but the sex of rearing during the first 2-3 years is believed by many to be the most important determinant of gender identity, because during this phase either estrogen or testosterone will have permanent effects on either a female or male brain, influencing both heterosexuality and homosexuality.[11]

The paradox is that the masculinizing effects of testosterone are mediated by estrogen. Within the brain, testosterone is aromatized to (estradiol), which is the principal active hormone for developmental influences. The human testis secretes high levels of testosterone from about week 8 of fetal life until 5-6 months after birth (a similar perinatal surge in testosterone is observed in many species), a process that appears to underlie the male phenotype. Estrogen from the maternal circulation is relatively ineffective, partly because of the high circulating levels of steroid-binding proteins in pregnancy.

Other influences upon hypothalamic development

Sex steroids are not the only important influences upon hypothalamic development; in particular, pre-pubertal stress in early life determines the capacity of the adult hypothalamus to respond to an acute stressor.[12] Unlike gonadal steroid receptors, glucocorticoid receptors are very widespread throughout the brain; in the paraventricular nucleus, they mediate negative feedback control of CRF synthesis and secretion, but elsewhere their role is not well understood.

Effects of aging on the hypothalamus

Studies in female mice have shown that both Supraoptic nucleus (SON) and Paraventricular nucleus (PVN) lose approximately one-third of IGF-1R immunoreactive cells with normal aging. Also, Old caloricly restricted (CR) mice lost higher numbers of IGF-1R non-immunoreactive cells while maintaining similar counts of IGF-1R immunoreactive cells in comparison to Old-Al mice. Consequently, Old-CR mice show a higher percentage of IGF-1R immunoreactive cells reflecting increased hypothalamic sensitivity to IGF-1 in comparison to normally aging mice. [13] [14] [15]

See also

Additional images

References

  1. ↑ http://www.cancer.gov/Templates/db_alpha.aspx?CdrID=46359
  2. ↑ http://www.sci.uidaho.edu/med532/hypothal.htm
  3. ↑ Diagram of Nuclei (psycheducation.org)
  4. ↑ Diagram of Nuclei (universe-review.ca)
  5. ↑ Diagram of Nuclei (utdallas.edu)
  6. ↑ Unless else specified in table, then ref is: Guyton Eight Edition
  7. ↑ Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch, Elsevier/Saunders. Page 840
  8. ↑ http://thalamus.wustl.edu/course/hypoANS.html
  9. ↑ http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/overview.html
  10. ↑ Theologides A (1976). Anorexia-producing intermediary metabolites. Am J Clin Nutr 29 (5): 552-8.
  11. ↑ John Money, 'The concept of gender identity disorder in childhood and adolescence after 39 years', Journal of Sex and Marital Therapy 20 (1994): 163-77.
  12. ↑ Romeo, Russell D, Rudy Bellani, Ilia N. Karatsoreos, Nara Chhua, Mary Vernov, Cheryl D. Conrad and Bruce S. McEwen (2005). Stress History and Pubertal Development Interact to Shape Hypothalamic-Pituitary-Adrenal Axis Plasticity. Endocrinology 147 (4): 1664-1674.
  13. ↑ Saeed O,Yaghmaie F,Garan SA,Gouw AM,Voelker MA,Sternberg H, Timiras PS. (2007). Insulin-like growth factor-1 receptor immunoreactive cells are selectively maintained in the paraventricular hypothalamus of calorically restricted mice. Int J Dev Neurosci 25 (1): 23-8.
  14. ↑ Yaghmaie F, Saeed O, Garan SA, Voelker MA, Gouw AM, Freitag W, Sternberg H, Timiras PS (2006). Age-dependent loss of insulin-like growth factor-1 receptor immunoreactive cells in the supraoptic hypothalamus is reduced in calorically restricted mice. Int J Dev Neurosci 24 (7): 431-6.
  15. ↑ F. Yaghmaie, O. Saeed, S.A. Garan, A.M. Gouw, P. Jafar, J. Kaur, S. Nijjar, P.S. Timiras, H. Sternberg, M.A. Voelker (2007). Tracking changes in hypothalamic IGF-1 sensitivity with aging and caloric restriction. Experimental Gerontology 42 (1-2): 148-149. [1]


References & Bibliography

Key texts

Books

Papers

  • Arees, E.A. and Mayer, B, (1967) Anatomical connections between medial and lateral regions of the hypothalamus concerned with food intake, Science 157: 1574-5
  • Grossman, S.P. (1960) Eating or drinking elicited by direct adrenergic or cholinergic stimulation of the hypothalamus, Science 132: 301-2.
  • Hetherington, A.W. and Ranson, S.W. (1942) The relation of various hypothalamic lesions to adiposity in the rat, 76: 475-99.

Additional material

Books

Papers



External links



v·d·e
Human brain: diencephalon (TA A14.1.08, GA 9.807)
Epithalamus

Surface

Pineal body · Habenula · Habenular trigone · Habenular commissure

Pretectal area · Habenular nuclei · Subcommissural organ


Thalamus

Surface

Stria medullaris of thalamus · Thalamic reticular nucleus · Taenia thalami

paired: AN · Ventral (VA/VL, VP/VPM/VPL) · Lateral (LD, LP, Pulvinar) · Metathalamus (MG, LG)

midline: MD · Intralaminar (Centromedian) · Midline nuclear group · Interthalamic adhesion

Mammillothalamic fasciculus · Pallidothalamic tracts (Ansa lenticularis, Lenticular fasciculus, Thalamic fasciculus) · PCML (Medial lemniscus, Trigeminal lemniscus) · Spinothalamic tract · Lateral lemniscus · Dentatothalamic tract · Acoustic radiation · Optic radiation · Subthalamic fasciculus · Anterior trigeminothalamic tract

Medullary laminae


Hypothalamus

Surface

Median eminence/Tuber cinereum · Mammillary body · Infundibulum


Autonomic zones

Anterior (parasympathetic/heat loss) · Posterior (sympathetic/heat conservation)

posterior pituitary: magnocellular/Paraventricular/Supraoptic (oxytocin/vasopressin)

other: parvocellular/Arcuate (dopamine/GHRH) · Preoptic (GnRH) · Suprachiasmatic (melatonin)

Lateral (hunger) · Ventromedial (satiety) · Dorsomedial (rage)


afferent (SN → Medial forebrain bundle) · efferent (Mammillothalamic fasciculus → AN, Stria terminalis → Amygdala, Dorsal longitudinal fasciculus → SC)

Posterior is diencephalon, but anterior is glandular


Subthalamus

Subthalamic nucleus · Zona incerta

Ventricular system:
Third ventricle

recesses: (Optic recess, Infundibular recess, Suprapineal recess, Pineal recess)

Hypothalamic sulcus · Tela chorioidea of third ventricle

Subfornical organ

Apertures: Interventricular/Monro

Posterior commissure

v·d·e
Human anatomy, endocrine system: endocrine glands
Hypothalamic/
pituitary axes



Thyroid gland (Parafollicular cell, Thyroid epithelial cell, Thyroid isthmus, Lobes of thyroid gland, Pyramid of thyroid)
Parathyroid gland (Oxyphil cell, Chief cell)



Chromaffin cells

Zona glomerulosa · Zona fasciculata · Zona reticularis

Paraganglia

Organ of Zuckerkandl · Aortic body · Carotid body


Testes · Ovaries · Corpus luteum



Pars nervosa · Median eminence · Infundibular stalk · Pituicyte · Herring bodies

Pars intermedia · Pars tuberalis · Pars distalis · Acidophils (Somatotropes, Lactotropes) · Basophils (Corticotropes, Gonadotropes, Thyrotropes)


Pineal gland

Pinealocyte · Corpora arenacea

Islets of pancreas

Alpha cell · Beta cell · Delta cell · PP cell · Epsilon cell


Human brain: Limbic system
Amygdala - Cingulate gyrus - Fornicate gyrus - Hippocampus - Hypothalamus - Mammillary body - Nucleus accumbens - Orbitofrontal cortex - Parahippocampal gyrus
Community content is available under CC-BY-SA unless otherwise noted.