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The hot plate test is a test of the pain response in animals, similar to the tail flick test. It is used in basic pain research and in testing the effectiveness of analgesics by observing the reaction to pain caused by heat.

It was proposed by Eddy and Leimbach in 1953.[1] They used a behavioral model of nociception where behaviors such as jumping and hind paw-licking are elicited following a noxious thermal stimulus. Licking is a rapid response to painful thermal stimuli that is a direct indicator of nociceptive threshold. Jumping represents a more elaborated response, with a latency, and encompasses an emotional component of escaping.[2]

ProcedureEdit

  • A transparent glass cylinder is used to keep the animal on the heated surface of the plate.[3]
  • The temperature of the hot plate is set using a thermoregulated water-circulated pump.
  • The time of latency is defined as the time period between the zero point, when the animal is placed on the hot plate surface, and the time when the animal licks its paw or jumps off to avoid thermal pain.[4][5]

Research findingsEdit

Sex studies using antidepressantsEdit

Significant differences in pain sensitivity in male and female mice have been observed in laboratory studies.[citation needed] The SSRI antidepressant paroxetine did not display a gender difference in antinociceptive effects in mice.[6]

Gene knockout studiesEdit

A number of anatomically defined regulatory pathways in the central nervous system are involved in pain processes.[7] Knockouts of certain pain receptor genes have been used in experiments to determine the effect of analgesic drugs on nociception. Many different drug classes and their corresponding receptors have been examined. These studies give insights into the genetic mechanisms that underlie nociception.

Ion channelsEdit

Voltage-gated ion channels are implicated in pain sensation and transmission signaling mechanisms within both peripheral nociceptors and the spinal cord. Specific ion channel isoforms such as Nav1.7 and Nav1.8 sodium channels and Cav3.2 T-type calcium channels have distinct pro-nociceptive roles.[8]

Opioid receptorsEdit

Activation of the μ-opioid receptor (MOR) and norepinephrine reuptake inhibition (NRI) are mechanisms of acute and chronic pain. OPRM1 knockout mice were used to determine the relative contribution of MOR activation to tapentadol and morphine induced analgesia. Wild-type mice exhibited an antinociceptive effect ten times that of OPM1 knockouts. However, the OPRM1 knockouts still exhibited a slight analgesic effect to tapentadol but not to morphine. This indicated that the antinociceptive effect of tapentadol is based on a combined mechanism of action involving both MOR and NRI.[9]

Benzodiazepines and GABA receptorsEdit

Diazepam is a GABAA receptor benzodiazepine ligand that is an anxiety modulator. Studies using diazepam with the hot plate test showed that diazepam modified the behavioral structure of the pain response not from pain modulation but rather by reducing anxiety levels.[10]

EthicsEdit

Further information: Animal testing

The Ethical Committee of the International Association for the Study of Pain has developed guidelines for the ethical use of this procedure.[11] In the United States, such experiments must be approved by an Institutional Animal Care and Use Committee.[12]

ReferencesEdit

  1. (1953). Synthetic analgesics. II. Dithienylbutenyl- and dithienylbutylamines. J Pharmacol Exp Ther 107 (3): 385–393.
  2. ESPEJO, E (30 September 1993). Structure of the rat's behaviour in the hot plate test. Behavioural Brain Research 56 (2): 171–176.
  3. Hunskaar, Steinar, Berge, Odd-Geir; Hole, Kjell (1 August 1986). A modified hot-plate test sensitivie to mild analgesics. Behavioural Brain Research 21 (2): 101–108.
  4. Ripoll N, Hascoet M, Bourin M. The four-plates test: Anxiolytic or analgesic paradigm? Progress in Neuro-Psychopharmacology and Biological Psychiatry, July 2006 vol. 30 issue 5, 873-880.
  5. Tzschentke, T. M., Christoph, T.; Kogel, B.; Schiene, K.; Hennies, H.-H.; Englberger, W.; Haurand, M.; Jahnel, U.; Cremers, T. I. F. H.; Friderichs, E.; De Vry, J. (23 July 2007). ( )-(1R,2R)-3-(3-Dimethylamino-1-ethyl-2-methyl-propyl)-phenol Hydrochloride (Tapentadol HCl): a Novel  -Opioid Receptor Agonist/Norepinephrine Reuptake Inhibitor with Broad-Spectrum Analgesic Properties. Journal of Pharmacology and Experimental Therapeutics 323 (1): 265–276.
  6. Duman, E., Kesim, M., Kadioglu, M., Ulku, C., Kalyoncu, N., Yaris, E. 2006. Effect of gender on antinociceptive effect of paroxetine in hot plate test in mice. Progress in Neuro-Pharmacology and Biological Psychiatry. 30. 292–296.
  7. J. Lotsch, G. Geisslinger, I. Tegeder, Genetic modulation of the pharmacological treatment of pain, Pharmacol. Ther. 124 (2009) 168–184
  8. (2011). A novel slow-inactivation-specific ion channel modulator attenuates neuropathic pain. Pain 152: 833–843.
  9. (2011). The antinociceptive and antihyperalgesic effect of tapentadol is partially retained in OPRM1 (μ-opioid receptor) knockout mice. Neuroscience Letters 491: 104–107.
  10. (2012). The effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test: Anxiolysis vs. Pain modulation. Neuropharmacology 63: 310–321.
  11. (1983). Ethical guidelines for investigations of experimental pain in conscious animals. Pain 16: 109–10.
  12. Institutional Animal Care and Use Committee


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