3H-SCH 23390 binding sites in the rat substantia nigra: evidence for a presynaptic localization and innervation by dopamine.
Chronic treatment with SCH 23390, a selective D-1 dopamine receptor antagonist, elicited a 32% increase in the density of 3H-SCH 23390 binding sites in nigral membrane preparations but failed to change the apparent KD of the ligand for its binding sites. Haloperidol, a D-2 dopamine receptor antagonist which blocks the dopamine-sensitive adenylate cyclase and (-) sulpiride, a selective D-2 dopamine receptor blocker, which does not block the dopamine-sensitive adenylate cyclase, failed to change both the Bmax and KD of 3H-SCH 23390 binding. Finally, the intrastriatal injection of kainic acid produced a marked decrease of both GAD activity and GABA content and 3H-SCH 23390 binding sites (65%) in the homolateral substantia nigra. The results show that in the rat substantia nigra most of the 3H-SCH 23390 binding sites have a presynaptic localization on the striato-nigral GABAergic afferent terminals and suggest that dopamine released from nigral dendrites exerts a tonic influence on these presynaptic D-1 dopamine receptors.
D000818:Animals; D001552:Benzazepines / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D005968:Glutamate Decarboxylase / Q000378:metabolism; D006220:Haloperidol / Q000494:pharmacology; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D008566:Membranes / Q000378:metabolism; D051381:Rats; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D013378:Substantia Nigra / Q000187:drug effects / Q000378:metabolism*; D013469:Sulpiride / Q000494:pharmacology; D013569:Synapses / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D001552:Benzazepines; D011954:Receptors, Dopamine; D005680:gamma-Aminobutyric Acid; D013469:Sulpiride; D005968:Glutamate Decarboxylase; D006220:Haloperidol; D007608:Kainic Acid; D004298:Dopamine