THE EFFECTS OF 6-HYDROXYDOPAMINE LESIONS OF THE NUCLEUS-ACCUMBENS ANDTHE MESOLIMBIC DOPAMINE SYSTEM ON ORAL SELF-ADMINISTRATION OF ETHANOLIN THE RAT

Rats readily learn to self-administer ethanol using a procedure where ethanol is introduced in the presence of a sweetener. After gradual re moval of the sweetener, sufficient quantities of ethanol are self-admi nistered in non fluid-, non food-deprived rats to produce reliable blo od ethanol concentrations. Previous studies using this self-administra tion model have shown that dopamine receptor antagonists injected syst emically or directly into the terminal regions of the mesolimbic dopam ine system decrease lever pressing for ethanol, suggesting an importan t role for dopamine in ethanol reinforcement. The purpose of the prese nt study was to test the hypothesis that the mesolimbic dopamine syste m is a critical substrate for ethanol reinforcement. Results of this s tudy show that 6-hydroxydopamine (6-OHDA)-induced lesions of the mesol imbic dopamine system, sufficient to produce a 93% depletion of dopami ne in the nucleus accumbens, an 85% depletion in the olfactory tubercl e, an 82% depletion in the frontal cortex and a 78% depletion in the a mygdala, failed to alter ethanol self-administration as measured by th e total lever presses. However, the 6-OHDA lesion Tats showed an alter ed pattern of responding for ethanol: an increase in the slope of the regression line of cumulative responses vs. time and an increase in th e frequency of responding at inter-response intervals of 4-6 and 6-8 s post 6-OHDA lesion; suggesting that this lesion produced a subtle cha nge in motor or attentional function. The results of this study indica te that while the mesolimbic dopamine system may contribute to the rei nforcing actions of ethanol, it is not critical for maintaining ethano l reinforcement.