ABSENCE OF OPIATE REWARDING EFFECTS IN MICE LACKING DOPAMINE D2 RECEPTORS

Dopamine receptors have been implicated in the behavioural response to drugs of abuse. These responses are mediated particularly by the meso limbic dopaminergic pathway arising in the ventral tegmental area and projecting to the limbic system, The rewarding properties of opiates(1 ) and the somatic expression of morphine abstinence(2) have been relat ed to changes in mesolimbic dopaminergic activity that could constitut e the neural substrate for opioid addiction(3), These adaptive respons es to repeated morphine administration have been investigated in mice with a genetic disruption of the dopaminergic D2 receptors(4). Althoug h the behavioural expression of morphine withdrawal was unchanged in t hese mice, a total suppression of morphine rewarding properties was ob served in a place-preference test. This effect is specific to the drug , as mice lacking D2 receptors behaved the same as wild-type mice when food is used as reward, We conclude that the D2 receptor plays a cruc ial role in the motivational component of drug addiction.