observed between AA and ANA rats (Kiianmaa et al., 1995). AA rats have lower mRNA levels for the NR1-4 splice variant of the N-methyly-D-aspartate (NMDA) receptor within the hippocampus than the ANA rat, whereas protein levels do not differ (Winkler et al., 1999). Additionally, the AA rat has lower NPY-Y2 receptor mRNA levels within the medial amygdala as well as lower NPY mRNA levels within the hippocampus than their ANA counterparts (Caberlotto et al., 2001). The AA rat has greater or lower mu-opiod receptor levels (depending on the brain region evaluated) in the limbic system, compared with the ANA rat (Soini et al., 1998, 1999). The HPA-system appears to regulate ethanol-intake in the AA, but not the ANA, rat (Fahlke and Eriksson, 2000). These authors reported that adrenalectomy, and cor-ticosterone replacement, altered ethanol intake in AA, but not ANA, rats. Overall, the findings suggest that differences in 5-HT, DA, NMDA, NPY and endogenous opioid systems may contribute to the disparate alcohol drinking behaviors of the AA and ANA rats.
