Nicotinic acetylcholine receptor-mediated [3H]dopamine release from hippocampus

The mechanism of nicotinic acetylcholine receptor (nAChR)-induced hippocampal dopamine (DA) release was investigated using rat hippocampal slices. nAChRs involved in hippocampal DA and norepinephrine (NE) release were investigated using prototypical agonists and antagonists and several relatively novel compounds: ABT-594 (R)-5-(2-azetidinylmethoxy)-2-chloropyridine], (+/-)-UB-165 (2-chloro-5-pyridyl)-9-azabicyclo 4.2.1]non2-ene], and MG 624 N,N,N-triethyl-2-4-(2 phenylethenyl)phenoxy]-ethanaminium iodine]. (+/-)-Epibatidine, (+/-)-UB-165, anatoxin-a, ABT-594, (-)-nicotine, 1,1-dimethyl-4-phenyl-piperazinium iodide, and (-)-cytisine (in decreasing order of potency) evoked (3)H]DA release in a mecamylamine-sensitive manner. Aside from (+/-)-UB-165, all the agonists displayed full efficacy relative to 100 microM (-)-nicotine in (3)H]DA release. In contrast, (+/-)-UB-165 was a partial agonist, evoking 58% of 100 microM (-)-nicotine response. Mecamylamine, MG 624, hexamethonium, d-tubocurare, and dihydro-beta-erythroidine (in decreasing order of potency), but not alpha-conotoxin-MII, methyllycaconitine, alpha-conotoxin-ImI, or alpha-bungarotoxin, attenuated 100 microM (-)-nicotine-evoked (3)H]DA release in a concentration-dependent manner. (+/-)-UB-165, ABT-594, and MG 624 exhibited different pharmacologic profiles in the (3)H]NE release assay when compared with their effect on (3)H]DA release. ABT-594 was 4.5-fold more potent, and (+/-)-UB-165 was a full agonist in contrast to its partial agonism in (3)H]DA release. MG 624 potently and completely blocked NE release evoked by 100 microM (-)-nicotine and 10 microM (+/-)-UB-165, whereas it only partially inhibited (-)-nicotine-evoked (3)H]DA release. In conclusion, we provide evidence that (3)H]DA can be evoked from the hippocampus and that the pharmacologic profile for nAChR-evoked hippocampal (3)H]DA release suggests the involvement of alpha3beta4(*) and at least one other nAChR subtype, thus distinguishing it from that of nAChR-evoked hippocampal (3)H]NE release.