Line differences in ethanol consumption and immobility in the forced swim test, but not in stress reactivity, in alcohol preferring (P) and nonpreferring (NP) rats

There is evidence to support a relationship between stress, depression, and alcoholism. Animal models have been developed to ascertain the impact of stress on depressive-like symptoms and ethanol intake. The swim test susceptible (SUS) line of rats selectively bred for enhanced susceptibility to stress-induced immobility in the forced swim test (FST) also show high voluntarily ethanol intake comparable to intake by P rats, suggesting that SUS rats may drink to alleviate a negative affective state. However, P rats spend less time immobile than NP rats in the FST, suggesting that depressive-like symptoms are not associated with ethanol preference, but P rats elevate drinking in response to stress. Thus, it is unclear whether high ethanol intake is related to stress, depressive-like symptoms, or both. To investigate this interaction, ethanol-naive male NP (n = 32) and P (n = 35) rats were divided into four stress groups: footshock, white noise, restraint, and no stress. Stressors were 30 minutes in duration and ended 10 minutes prior to the FST in which time spent immobile and struggling was observed for 10 minutes. Forty-eight hours following the FST, all rats (including additional groups of FST-naive rats, n = 9/line) were given continuous access to 10% ethanol and water. After 2 weeks to acclimate to the ethanol rats received their respective stress or no stress treatments at weekly intervals for 3 weeks. P rats drank more ethanol than NP rats, but both lines increased their intake over the 6-week access period. No main effects of stress were evident when compared on stress days. Analysis of the final week of ethanol drinking revealed that P rats exposed to footshock showed elevated drinking compared to unstressed and FST-naive rats, and restrained and unstressed NP rats tended to drink more than FST-naive rats. Consistent with prior research, NP rats spent more time immobile than P rats in the FST. A trend for an effect of stress on immobility appeared to be mediated by the ability of restraint stress to reduce immobility. While these data demonstrate stress-related increases in drinking, no stress-induced enhancement of immobility was evident in the P and NP lines. Further, while both ethanol intake and immobility differed between the P and NP lines, stress did not appear to mediate these behaviors in a line-dependent manner. Subsequent research using the SUS and swim test resistant (RES) lines in comparison to the P and NP line may reveal how selective breeding for different phenotypes converges on alcohol-related behaviors. Supported by AA07462 and AA015512 METHODS