At 20 mM, it has been shown that the firing rates of VTA neurons are altered. Using whole-cell patch clamp, 20 mM ethanol has been reported to increase the firing rate of dissociated VTA DA neurons by 6% [22]. More recently the cell-attached recording technique has been used to show that DA neurons in the medial VTA in mice are more sensitive to ethanol, and 20 mM ethanol was found to produce an increase in firing rate of 21% [23]. A history of alcohol exposure has been shown to be important in the medial VTA. In brain slices obtained from mice given intermittent access to alcohol during adolescence (PD30–60), 10 mM ethanol has been shown to increase the firing rate of DA neurons in the medial VTA 7.7%, whereas no effect was seen in brain slices from alcohol-naïve mice [24]. While 20 mM ethanol has been found to increase the firing rate of VTA DA neurons in the rat, the firing rates of VTA GABA neurons have been found to decrease by 41% at this concentration [25].
