Neurochemically, higher levels of 5-HT (Ahtee and Eriksson, 1972, 1973; Korpi et al., 1988) as well as dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels, the latter reflecting DA metabolism (Honkanen et al., 1994), were found in certain CNS regions of AA rats compared with ANA rats, suggesting possible genetic subtypes among the selectively bred alcohol-preferring rats. In other work, Katner and Weiss (2001) compared rats from the AA, ANA, and Wistar lines for extracellular concentrations of DA in the nucleus accumbens (Acb) using a no-net-flux microdialysis procedure. Their results indicated that changes in Acb extracellular DA levels predicted high ethanol preference, with rats predisposed to high ethanol intake having a greater DA response to ethanol. These results paralleled other findings from Honkanen and colleagues’ study (1994), although differences in Acb extracellular DA levels following ethanol have not always been 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
