ETHANOL WITHDRAWAL DOES NOT INDUCE A REDUCTION IN THE NUMBER OF SPONTANEOUSLY ACTIVE DOPAMINERGIC-NEURONS IN THE MESOLIMBIC SYSTEM

The effect of ethanol withdrawal, after chronic administration, on the electrophysiological properties of antidromically identified mesoaccu mbens dopaminergic neurons was studied in two groups of rats with rela tive controls (withdrawal from chronic saline). The first group was an esthetized with chloral hydrate whereas the second was immobilized wit h D-tubocurarine. In chloral hydrate anesthetized rats, a significant reduction in the number of spontaneously active dopamine neurons was o bserved as compared with chronic saline withdrawn controls. In contras t, in ethanol-withdrawn D-tubocurarine treated rats, the number of spo ntaneously active dopamine neurons, as measured by the cells/track ind ex, was found not different than chronic saline withdrawn controls. Fu rther, intravenous administration of apomorphine, did not reverse the reduced cells/track index in chloral-hydrate anesthetized rats but con sistently inhibited dopaminergic firing. Apomorphine-induced inhibitio n of firing was significantly more pronounced in ethanol withdrawn chl oral-hydrate anesthetized rats. Firing rate and firing pattern were fo und decreased during ethanol withdrawal irrespective of experimental c onditions. The results do not support the possibility that dopaminergi c neurons of the mesoaccumbens pathway might be affected by depolariza tion inactivation during ethanol withdrawal. Rather, they confirm a re duction of neuronal activity already reported by previous studies. The reduced cells/track index observed in chloral hydrate anesthetized ra ts during ethanol withdrawal awaits an alternative explanation to the depolarization inactivation mechanism.