Effects of periadolescent ethanol exposure on alcohol preference in two BALB substrains.

Ethanol exposure during adolescence is a rite of passage in many societies, but only a subset of individuals exposed to ethanol becomes dependent on alcohol. To explore individual differences in response to ethanol exposure, we compared the effects of periadolescent ethanol exposure on alcohol drinking in an animal model. Male and female mice of two BALB substrains were exposed to ethanol in one of three forms--choice [water vs. 10% (volume/volume) ethanol], forced (10% ethanol in a single bottle), or gradual (single bottle exposure, starting with 0.5% ethanol and increasing at 2-day intervals to 10% ethanol)--from the 6th through the 12th week of age and administered two-bottle alcohol preference tests (10% ethanol vs. water) for 15 days immediately thereafter. All three forms of ethanol exposure increased alcohol preference in male and female BALB/cByJ mice, relative to findings for ethanol-naive control animals. Only gradual ethanol exposure produced an increase in alcohol preference in BALB/cJ mice. During extended alcohol preference testing (for a total of 39 days) of mice in the gradual ethanol exposure group, the higher alcohol preference of the gradual ethanol-exposed BALB/cByJ male mice persisted, but alcohol preference of control group female mice in this strain--formerly ethanol naive, but at this point having received 10% ethanol in the two-bottle paradigm for 15 days--rose to the level of alcohol preference of female mice in the gradual ethanol exposure group. This finding demonstrated that both adolescent and adult ethanol exposure stimulated alcohol preference in female mice of this strain. Across days of testing in adulthood, alcohol preference of the gradual ethanol-exposed BALB/cJ mice decreased, resulting in a lack of effect of gradual exposure to ethanol on alcohol preference in both male and female mice of this strain during the period of extended testing. These strain differences support a genetic basis for the effects of ethanol exposure on alcohol preference and fit within a body of literature, showing substantial individual differences in the effects of ethanol exposure among genetically undefined rats and differences in response to ethanol exposure among inbred rat strains. Exploration of the mechanisms underlying this gene by environment interaction in a mouse model may help elucidate individual differences in the effects of ethanol exposure in human beings and contribute to the understanding of the causes of alcoholism.