Sensitivity of compacta neurones in the rat substantia nigra slice to dopamine agonists.

Extracellular recordings were made from neurones in the zona compacta of the substantia nigra in a novel slice preparation in vitro. The pharmacological profile of some dopamine related drugs was assessed by their depressant action on neuronal firing after known concentrations were added to the perfusing media. The most potent drugs were the rigid stable dopamine analogues 2-amino-6,7-dihydroxy-1,2,3,4- tetrahydronapthalene (ADTN) and apomorphine. 2-Amino-5,6-dihydroxy-1,2,3,4- tetrahydronapthalene (5,6-ATN), was less potent than either. Octopamine, Norphenephrine , m- and p-tyramine were all less potent than dopamine. Although noradrenaline was equipotent to dopamine, alpha- and beta-adrenoreceptors were not involved since propranolol and phentolamine were not antagonists, while (-)-sulpiride, haloperidol and alpha-flupentixol were potent antagonists of the dopamine mediated responses.