Measurement of pharmacological depression of exploratory activity in mice: a contribution to the problem of time-economy and sensitivity.

Abstract

Changes in exploratory behaviour in mice due to two variables, size of test enclosure and intensity of illumination, each at three levels were tested repeatedly over five exposures. The most suitable procedure for eliciting depressant effects of drugs on exploratory activity was to use a small enclosure (8×24 cm) with dim illumination (2 lx), and to partially habituate the animals to this environment before giving drugs. Under these conditions the amount of walking and rearing by untreated mice was about 70% of the maximal values obtained. It was also found that test sessions lasting for one minute provided sufficient information. In the selected “optimal” setting, the lowest effective depressant doses of chlorpromazine and barbitone were 0.3 mg/kg and 5.0 mg/kg, respectively, while under other conditions it was necessary to use higher doses of the drugs to obtain similar effects, and occasionally, increases in activity were also recorded. Since it took not more than 70 sec to test each mouse, up to 200 animals could be tested each day, which makes it possible to determine both dose- and time-response relationships quite rapidly. These results suggest ways in which experimental variables can be manipulated to “tune-up” exploratory behaviour and to make it more sensitive to specific types of psychotropic drugs.