Other studies suggest differences in neurotransmission in the PFC between different rat strains. The Lewis rat strain self-administers alcohol at greater levels than the Fisher rat. The Lewis rats demonstrated lower basal levels of glutamate in the PFC than did the Fisher strain (Selim and Bradberry, 1996). In addition, alcohol-naive P rats have a lower extracellular concentration of DA in medial PFC than do non-EtOH preferring Wistar rats (Engleman et al., 2006). In the same study, however, acute EtOH administration did not alter DA levels in the PFC of either group. By contrast, the Sardinian alcohol-preferring rat (sP) showed greater basal levels of DA in the mPFC than did the Sardinian alcohol-nonpreferring (sNP) strain (Leggio et al., 2003). Although this does not rule out a role for PFC DA basal levels in alcohol seeking or the development of alcohol dependence, it is clear that factors other than basal DA levels are involved. For example, alcohol-preferring AA rats showed higher levels of mu-opioid binding in PFC under drug-naive conditions than did alcohol-avoiding ANA rats, as well as higher levels of proenkephalin
