title: Further functional in vitro comparison of pre- and postsynaptic dopamine receptors in the rabbit caudate nucleus.
abstract: Slices of the rabbit caudate nucleus were preincubated with 3H-dopamine or 3H-choline and then superfused and stimulated electrically. DiPr-5,6-ADTN reduced the stimulation-evoked overflow of tritium over the same concentration range, independently of whether slices had been preincubated with 3H-dopamine or 3H-choline, and the same was true for apomorphine, NPA and pergolide. Three other putative dopamine receptor agonists, namely 3-PPP, DPI and SKF 38393, failed to decrease the evoked overflow of tritium. Each of six antagonists--(-)-sulpiride, (+)-sulpiride, CGP 11109 A, cis-flupentixol, domperidone and corynanthine--increased the evoked overflow over the same concentration range in experiments with 3H-dopamine and in those with 3H-choline. For each of these antagonists except cis-flupentixol, and also for chlorpromazine, haloperidol and rauwolscine, the pA2 values against apomorphine obtained in 3H-dopamine and in 3H-choline experiments were closely similar. The antagonist effect of cis-flupentixol against apomorphine was not purely competitive. (-)-Sulpiride was a more potent antagonist than (+)-sulpiride, and cis-flupentixol was more potent than trans-flupentixol. This study supplements a previous one in which (+/-)-sulpiride, metoclopramide and molindone were used as antagonists. It is a functional in vitro approach to receptor characterization, as opposed to radioligand binding studies or in vivo investigations. The results show that a large number of dopamine receptor agonists and antagonists are unable to distinguish between the presynaptic, release-inhibiting dopamine autoreceptors and those postsynaptic dopamine receptors which, when activated, depress the release of acetylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001058:Apomorphine / Q000031:analogs & derivatives / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D002421:Caudate Nucleus / Q000378:metabolism*; D002794:Choline / Q000378:metabolism; D003000:Clonidine / Q000494:pharmacology; D005260:Female; D008297:Male; D010880:Piperidines / Q000378:metabolism; D011817:Rabbits; D011954:Receptors, Dopamine / Q000378:metabolism*
chemical_list: D001552:Benzazepines; D010880:Piperidines; D011954:Receptors, Dopamine; C009074:N-n-propylnorapomorphine; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; C026539:preclamol; D003000:Clonidine; D001058:Apomorphine; D002794:Choline; D000109:Acetylcholine