Opposite effects of naltrexone on ETOH intake by Syracuse high and low avoidance rats

Rats which were selectively bred for good (Syracuse High Avoidance: SHA) and poor (Syracuse Low Avoidance: SLA) shuttle-box avoidance learning were used to assess the effects of naltrexone on ethanol ingestion. Male rats from both strains were offered a free choice of water and ethanol (10%, v/v) for two 8-day periods between which was inserted a 4-day period of forced ethanol consumption. The net ethanol consumption and ethanol preference ratio were significantly greater in control SHA rats than in control SLA rats in the first choice period, but they did not differ in the forced and the second choice periods. Chronic naltrexone administration from an implanted 30-mg pellet showed bidirectional effects, i.e., suppression of ethanol consumption in SLA animals and enhancement in SHA rats.