Blocking effects of ethanol on stress-induced activation of rat mesoprefrontal dopamine neurons.

We investigated the effects of ethanol on stress-induced activation of the brain dopamine (DA) systems in rats. Ethanol (0.5 and 1.0 g/kg) was injected IP 25 min before sacrifice (5 min before 20-min immobilization stress). Ethanol treatment by itself did not affect the levels of either DA or its major metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in the mesoprefrontal cortex, cingulate cortex, olfactory tubercle, or caudate putamen. Immobilization stress for 20 min caused increases in DOPAC levels in the prefrontal cortex (160% of control) and cingulate cortex (135% of control), but not in the olfactory tubercle or caudate putamen. The stress had no effects on DA levels in any of the four brain regions studied. Pretreatment with ethanol blocked, in a dose-dependent manner, the stress-induced increases in DOPAC levels in the mesoprefrontal cortex. The present data suggest that ethanol exhibits a blocking effect on stress-induced activation of the mesoprefrontal DA neurons. This blocking effect may be related to the anxiolytic action of ethanol.