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------------------------------------------------------------------------ D2 Receptor Essential For Motivational Aspect Of Opiate Addiction ------------------------------------------------------------------------ WESTPORT, Aug 07 (Reuters) - The dopamine D2 receptor plays a crucial role in mediating the pleasurable effects of opiates, but does not appear to be involved in withdrawal symptoms, according to a report in the August 7 issue of Nature. Although the dopaminergic system is known to be involved in opioid addiction, little is known about the role each of the four types of dopamine receptor plays in mediating the rewarding effects of opiate use and the adverse effects of withdrawal. Dr. Rafael Maldonado of the Universite Rene Descartes in Paris and colleagues there and elsewhere in France engineered a strain of mice that lack the dopamine D2 receptor. The scientists administered morphine to the D2-knockout mice and found that the opioid's rewarding properties were completely suppressed in the mice, "[a]lthough the behavioural expression of morphine withdrawal was unchanged." The mice lacking the D2 receptor responded to food rewards in a similar manner to wild-type mice, suggesting the receptor's role in reward and motivation is specific to opioids. Dr. Maldonado and colleagues conclude that their findings "...have unambiguously demonstrated a dissociation between the mechanisms involved in the rewarding properties of opiates, which are related to their addictive capacities, and the somatic signs of the...withdrawal syndrome, which reveal the physical component of opiate dependence." Nature 1997;388:586-589. Copyright 1997 Reuters Limited. <http://www.reutershealth.com/news/docs/199708/19970807scd.html> ------------------------------------------------------------------------