The Effects of Amphetamine and Ethanol on Habituation of Exploratory Responses of Rats in Novel and Familiar Environments

To study the relationship between level of arousal and rate of habituation in rats, the current research manipulated arousal level using sedatives (ethanol 200 and 600 mg/kg) and stimulants(d-amphetamine 0.6 and 2.4 mg/kg). Furthermore, in order to investigate the possible contributions of differences in familiarity of the subjects with the test environment in producing discrepant reports about arousal-habituation relationships, half of the rats were tested in a completely novel cage without saline- pre-injection, while the other half were repeatedly given salinepreinjections and exposures to the test cage. Habituation was measured mainly as rate of change of responding level; i.e. slope of response as a function of time. Familiarity was found to facilitate habituation of some qualitatively measured(observer-rated) exploratory and locomotor activity, but not that of quantitative(automatically detected and recorded) activity scores. It had no significant interaction effect with drug treatment on either type of measure. The high dose of amphetamine(2.4 mg/kg) was found to disrupt habituation of both measures of locomotor activity regardless of degree of familiarity with the test environment. When separate analyses of drug effects were made for the two familiarity conditions, the low dose of amphetamine was found to disrupt habituation of the quantitative measure only in the familiar condition . In addition, the low dose of ethanol facilitated and retarded habituation of quantitative measure in the familiar and the novel conditions, respectively. Finally, the high dose of ethanol facilitated habituation of the quantitative measure only in the familiar condition. Some of these effects were independent of baseline activity levels. The present findings have implications for drug research in which exploratory behavior is studied.