INTRAVENOUS HEROIN AND ETHANOL SELF-ADMINISTRATION BY ALCOHOL-PREFERRING AA AND ALCOHOL-AVOIDING ANA RATS

The alcohol-preferring AA rats have previously been shown to drink mor e solution containing the opioid etonitazene than the alcohol-avoiding ANA rats. The present experiments were initiated to see whether the l ine difference in opioid and alcohol intake would persist if an intrav enous (IV) route of self-administration is used. Following establishme nt of stable heroin responding (0.03 mg/kg per infusion), AA and ANA r ats were first subjected to three within-session dose-response determi nations during which they were allowed to respond for ascending heroin doses (0.0075, 0.015, 0.03, and 0.06 mg/kg per infusion) and then to one progressive-ratio schedule session. AA rats obtained more heroin i nfusions than ANAs during the first acquisition sessions but there wer e no significant differences between the lines either in their baselin e heroin responding, across the ascending within-session doses, or on the progressive ratio probe. When, after additional heroin baseline se ssions, ethanol (1.0 mg/kg per infusion) was substituted for heroin, A A rats initially increased their responding and showed stable rates fu r responding across ascending ethanol doses (2.0 and 4.0 mg/kg), where as ANAs declined below their heroin baseline. These findings give evid ence for only an initial line difference in IV opiate self-administrat ion but for a sustained difference in IV ethanol self-administration, thus suggesting that the differential alcohol drinking of the AA and A NA rats is dependent at least partly on non-oral factors.