EFFECTS OF APOMORPHINE AND AMPHETAMINE ON SCHEDULE-CONTROLLED BEHAVIOR - REVERSAL OF TETRABENAZINE SUPPRESSION AND DOPAMINERGIC CORRELATES

Injection of 1.5 mg/kg tetrabenazine (TBZ) abolished lever-pressing in rats maintained on a variable-interval schedule of food reinforcement. This effect was correlated with a decrease in central dopamine (DA), noradrenaline (NA), and 5-hydroxytryptamine (5-HT) levels. DA concentration in different brain regions were lowered by approximately 70-80%; NA and 5-HT were reduced by a lesser extent ranging from 20-50%. Apomorphine (0.2-0.8 mg/ kg), although decreasing behavioral response rate when injected alone, partially restored lever-pressing after TBZ but was less effective as a reversing agent than amphetamine at the same dose levels. Apomorphine (0.75 mg/kg) also reduced the rate of DA, but not of NA, disappearance in the brain after tyrosine hydroxylase inhibition, suggesting that apomorphine acts by stimulating DA receptors. The results are discussed in terms of the possible mechanisms of action of the drugs investigated and the relative importance of the roles of DA and NA in mediating conditioned behavioral processes is considered. © 1969.