BASE-LEVEL OF MOTOR-ACTIVITY DETERMINES T HE DIRECTION OF THE MOTOR EFFECT OF APOMORPHINE

In male mice of BALB/c and SHR strains with the highest base level of locomotion and rearings apomorphine (5 mg/kg) decreased these forms of motor activity while in C57BL/6 mice with the lowest base level of mo tor activity apomorphine increased it. In mice of C57BR and C3H/A stra ins with intermediate base level there was a tendency for an increase in activity. Extinction of exploratory motor activity in BALB/c as a r esult of foul consecutive testings in the same experimental chamber wi th hourly intervals induced a decrease in activity of the animals by h alf. Being injected against this background the same dose of apomorphi ne (5 mg/kg) twice increased locomotion and rearings in these mice.