Rat substantia nigra was injected with 1 μg of purified pertussis toxin, a substance which inactivates the inhibitory guanine nucleotide regulatory unit of adenylate cyclase. In comparison to saline-injected animals, the pertussis toxin-treated animals showed almost no inhibition of dopaminergic neurons in response to dopamine applied iontophoretically or the dopamine agonist (−)-apomorphine given intravenously. These results provide evidence that a guanine nucleotide regulatory protein is involved as a transducer in mediating the physiological actions of dopamine autoreceptors.
