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Reward system

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In neuroscience, the reward system is a collection of brain structures which regulate and control behavior by inducing pleasurable effects.

Anatomy

The major neurochemical pathway of the reward system in the brain involves the mesolimbic and mesocortical pathway. Of these pathways, the mesolimbic pathway probably plays the major role, and goes from the ventral tegmental area via the medial forebrain bundle to nucleus accumbens, where mainly dopamine is released. This acts on D2 receptors to inhibit the production of cAMP.

Modulation by drugs

Main article: Drug addiction#Psychological

Almost all drugs causing drug addiction increases the dopamine release in the mesolimbic pathway[1], e.g. opioids, nicotine, amphetamine, ethanol and cocaine. After prolonged use, psychological drug tolerance and sensitization arises.

Psychological drug tolerance

The reward system is partly responsible for the psychological part of drug tolerance. One explanation of this is a sustained activation of the CREB protein, causing a larger dose to be taken to reach the same effect. In addition, it leaves the user feeling generally depressed and dissatisfied, often leading to a return to the drug for an additional "fix".

Sensitization

Sensitization is an increase the user's sensitivity to the effects of the substance, counter to the effects of CREB. A transcription factor, known as delta FosB, is thought to be involved by activating genes that causes sensitization. The hypersensitivity that it causes is thought to be responsible for the intense cravings associated with drug addiction, and is often extended to even the peripheral cues of drug use, such as related behaviors or the sight of drug paraphernalia.



see also

External links

ja:報酬系
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