Electrophysiological effects of dopamine autoreceptor antagonists, (+)-AJ 76 and (+)-UH 232.

The weak aminotetralin stimulants, (+)-AJ 76, cis-(+)-5-methoxy-1-methyl-2-(n-propylamino)tetralin and (+)-UH 232, cis-(+)-5-methoxy-1-methyl-2-(di-n-propylamino)tetralin, were tested for their effects on firing rates of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNPC). (+)-AJ 76 and (+)-UH 232 antagonized the depression of DA neuron firing rates following autoreceptor stimulation by apomorphine. Thus, just as they antagonize DA autoreceptors on presynaptic terminals, these aminotetralins also antagonize the somatodendritic DA autoreceptor. However, in contrast to terminal autoreceptors where (+)-AJ 76 is the most potent antagonist, (+)-UH 232 is the most potent on cell body autoreceptors. (+)-AJ 76 and (+)-UH 232 also reversed the depression of DA neurons arising from activation of negative feedback pathways by amphetamine-induced DA release in postynaptic areas. Based on potencies to reverse amphetamine and apomorphine, respectively, the postsynaptic/presynaptic potency ratios for (+)-AJ 76, (+)-UH 232, and haloperidol were all near unity. It is concluded that (+)-AJ 76 and (+)-UH 232 antagonize both postsynaptic and somatodendritic sites with equal potencies, and that their weak stimulant properties may be due to a preferential antagonism of nerve terminal autoreceptors.