Pharmacological characterization of nicotinic receptor-stimulated GABA release from mouse brain synaptosomes.
Several recent electrophysiological studies have demonstrated that nicotinic agonists stimulate the release of gamma-aminobutyric acid (GABA) from rodent brain tissue. Our studies used a neurochemical approach to characterize nicotinic receptor-stimulated [3H]-GABA release from mouse brain synaptosomes. Nicotine increased [3H]-GABA release from synaptosomes preloaded with [3H]-GABA in a concentration-dependent manner. This release appeared rapidly, was Ca++ dependent, and was partially (about 50%) blocked by 100 nM tetrodotoxin and totally blocked by mecamylamine and dihydro-beta-erythroidine. alpha-Bungarotoxin had no effect. Twelve nicotinic agonists were compared for their effects on [3H]-GABA release. The agonists differed in potency (EC50) and efficacy (Emax). The EC50 and Emax values were significantly correlated (r = 0.95, P <.001 for EC50; r = 0.93, P <.01 for Emax) to values obtained for these same agonists when 86Rb+ efflux was determined. A significant correlation (r = 0.84, P <.01) was found when the EC50 values for agonist-stimulated [3H]-GABA release and IC50 values for agonist inhibition of [3H]-L-nicotine binding were compared. Differences in [3H]-GABA release were detected in 12 brain regions and maximal release was significantly correlated with [3H]-nicotine binding. The pharmacological and regional comparisons suggest that the nAChR that stimulates [3H]-GABA release is the one that binds [3H]-nicotine with high affinity (alpha4beta2). Unequivocal evidence that the receptor that modulates nicotine-stimulated [3H]-GABA release contains a beta2 subunit was obtained in a study using wild-type, heterozygous and homozygous beta2 null mutant mice. [3H]-GABA release and [3H]-nicotine binding decreased along with the number of copies of the null mutant gene.
Lu
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Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado, USA.
Grady
S
S
Marks
M J
MJ
Picciotto
M
M
Changeux
J P
JP
Collins
A C
AC
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000502:physiology; D013574:Synaptosomes / Q000187:drug effects* / Q000502:physiology; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D014316:Tritium; D005680:gamma-Aminobutyric Acid; D009538:Nicotine