Why might the NAc shell and core play distinct roles in ethanol self-administration? Although both the shell and the core express GABAAR α4 subunits, we observed that GABAAR α4 subunit reductions in the NAc core had no effect on instrumental responding for ethanol (present study) or on home cage ethanol intake (Rewal et al. 2009). Rather, the NAc shell appears to be the critical site for the decreases in ethanol self-administration after α4 reductions. The shell and core have distinct patterns of afferent inputs and efferent outputs, defining distinct circuits that likely underlie distinct behaviors (Brog et al. 1993; Robbins & Everitt 2002). The shell projects to the lateral hypothalamus and this connection may be especially important for consummatory behaviors; the shell and core also project to distinct areas of the ventral pallidum (Groenewegen et al. 1999). The core receives input from more dorsal areas of the medial prefrontal cortex, while the shell receives input from more ventral regions (Groenewegen et al. 1999). These anatomical differences may contribute to behavioral differences. Whereas the core is hypothesized to contribute to stimulus-appropriate
