CHARACTERIZATION OF RECEPTORS MEDIATING THE ACTIONS OF DOPAMINE ON AN IDENTIFIED INHIBITORY MOTONEURONE OF THE COCKROACH

soma of a prothoracic inhibitory motoneurone of the cockroach {Periplaneta americana) have been recorded under voltage-clamp conditions. 2. Dopamine generates inward currents that are extremely voltage-dependent: currents increase rapidly at membrane potentials more negative than about —120 to —150 mV and also show a peak at membrane potentials of approximately-20 mV. As a result of this voltage-dependence, dopamine induces a region of negative resistance in the current-voltage relationship of the neurone. 3. The dopaminergic agonists apomorphine, bromocryptine, ergometrine and A-6,7-DTN mimic the action of dopamine on this neurone, all having a similar voltage-dependence to that of dopamine. The selective D-l receptor agonist SK&F 82526 and the D-2 agonist LY171555, however, were both inactive on the preparation. 4. Responses to dopamine were suppressed by a number of D-l and D-2 receptor antagonists, indicating that the pharmacological profile of the dopamine-sensitive receptor in this insect preparation is different from that of vertebrate dopamine receptors