Effects of apomorphine on escape performance and activity in developing rat pups treated with 6-hydroxydopamine...

The effects of apomorphine and excape learning were examined in normal developing rat pups and littermates preferentially depleted of brain dopamine by the intracisternal administration of 6-hydroxydopamine (6-OHDA) at 5 days of age, a treatment which resulted in a rapid and permanent reduction in brain dopamine to concentrations 12-29% of littermate controls while norepinephrine was not significantly altered. At 19 days of age both 0.1 and 1.0 mg/kg doses of apomorphine increased general motor activity in normal but not 6-OHDA treated pups (though these pups were significantly hyperactive prior to apomorphine). At 26 days only the 1.0 mg/kg dose increased motor activity in both normal and 6-OHDA pups. Exploratory activity at 30 days in both normal and 6-OHDA pups was first reduced then abolished by progressive doses of apomorphine. Stereotyped activity was increased by 0.1 and 1.0 mg/kg apomorphine at 19 days in both normal and 6-OHDA pups. By 26 days, apomorphine no longer produced intense sterotypies in normal pups, but did effect such responses in 6-OHDA treated animals. Administration of apomorphine resulted in a disruption of escape performance in a T-maze and shuttle box in normal pups only at 1.0 mg/kg but disrupted performance in 6-OHDA treated animals at both 0.1 and 1.0 mg/kg dosages. These results indicate a peak effect of apomorphine on general motor activity at three weeks of age in normal pups. Our results also suggest that apomorphine will disrupt escape learning, effects that appear to be correlated with the apomorphine induced increase in motor activity.