Rate-depressant effects of ethanol on fixed-ratio responding in ALKO AA and ANA rats

The ALKO AA and ANA rats have been selectively bred for high versus low ethanol preference, respectively. AA rats have been shown to self-administer ethanol, whereas ANA rats do not. These animals also show a range of differences on tasks which measure sensitivity to ethanol, but the relationship between ethanol intake and sensitivity to this drug in these rats is not clear. This study examined sensitivity to ethanol in AA and ANA rats as determined by ethanol's rate depressant effects on schedule controlled (Fixed-Ratio (FR) 32) responding reinforced by water deliveries. Non-drug rates of responding were similar for both lines across baseline, sham injection and vehicle conditions. Ethanol produced dose-dependent decreases in responding in both the AA and ANA rats. Dose-response curves indicated that AA rats were slightly more sensitive to the acute effects of ethanol than were ANA rats, with ED50 values of 0.52 and 0.69 g/kg for AA and ANA rats, respectively. Overall, however, the effects of ethanol on rats of responding were similar across the two lines of rats. While it is possible that constraints on behavior imposed by FR schedules could be masking underlying differences in tissue sensitivity between these animals, the results indicate that ethanol intake under preference or reinforcement conditions does not appear to be highly controlled by initial sensitivity to ethanol as measured by effects on operant performance.