RU486 pretreatment prevented the increased ethanol self-administration induced by nicotine pretreatment (Figure 5D). The mean ethanol intake for the group pretreated with RU486 and nicotine (0.74 ± 0.06 g/kg/session, n = 12) was significantly lower than the nicotine pretreatment alone (0.97 g/kg; n = 17) (p < INCB018424 solubility dmso 0.01) and nearly identical to the saline pretreatment control (Figure 5D, dashed line). Thus, nicotine required the activation

of stress hormone receptors to enhance subsequent ethanol self-administration. Because local infusions of RU486 into the VTA prevented the inhibition of ethanol-induced DA release, we hypothesized that stress hormone action altered ethanol-induced GABA transmission onto DA neurons. Therefore, we pretreated rats with RU486 prior to nicotine pretreatment and measured ethanol-induced sIPSCs 15 hr later. The nicotine-pretreatment potentiation of the sIPSC frequency by ethanol was prevented by RU486 pretreatment

(Figures 6A and 6B) (p < 0.05). The average sIPSC frequency BMN 673 nmr induced by ethanol (relative to basal) was 187% ± 12% after nicotine pretreatment (Figure 6B, red bar) and 118% ± 8% after RU486 and nicotine pretreatment (Figure 6B, blue bar). In addition, the enhanced paired-pulse depression after the nicotine pretreatment (78.6% ± 3.4%; see Figure 4D) was also prevented by RU486 (92.1% ± 3.0%; n = 15; data not shown) (p < 0.05). These results and others indicate that stress hormone receptor activation in response to nicotine pretreatment altered ethanol-induced GABA network activity in the VTA. Acute pretreatment with nicotine

induced a long-lasting attenuation of ethanol-induced DA signals within the mesoaccumbens pathway. The decreased ethanol-induced DA signals were due to an increase in GABAergic inhibition of DA neurons and a consequent decrease in VTA DA neuron firing. These nicotine-induced neuroadaptations PDK4 required a stress hormone signal that acted significantly within the VTA. Concomitant with these physiological changes, we also show that increases in ethanol self-administration induced by nicotine were prevented by RU486, a glucocorticoid/progesterone receptor antagonist (Cadepond et al., 1997). In addition to other interactions with ethanol (Al-Rejaie and Dar, 2006, Collins et al., 1996, Gulick and Gould, 2008 and López-Moreno et al., 2008), nicotine exposure influences subsequent ethanol consumption and abuse (Barrett et al., 2006, Grant, 1998, Lê et al., 2003, Morgen et al., 2008 and Smith et al., 1999). Although the development of drug abuse involves the mesolimbic DA system, there are little mechanistic data indicating how nicotine influences DA responses to ethanol. Our results suggest that nicotine acts through stress hormone signaling pathways in the VTA to enhance subsequent ethanol-induced GABAergic drive onto DA neurons, thereby decreasing ethanol-induced DA signals.