A Novel Î±-Conotoxin Mii-Sensitive Nicotinic Acetylcholine Receptor Modulates [ 3H]-Gaba Release In The Superficial Layers Of The Mouse Superior Colliculus
Mouse superficial superior colliculus (SuSC) contains dense GABAergic innervation and diverse nicotinic acetylcholine receptor subtypes. Pharmacological and genetic approaches were used to investigate the subunit compositions of nicotinic acetylcholine receptors (nAChR) expressed on mouse SuSC GABAergic terminals. [ 125I]-Epibatidine competition-binding studies revealed that the Î±3Î²2* and Î±6Î²2* nicotinic subtype-selective peptide Î±-conotoxin MII-blocked binding to 40 Â± 5% of SuSC nAChRs. Acetylcholine-evoked [ 3H]-GABA release from SuSC crude synaptosomal preparations is calcium dependent, blocked by the voltage-sensitive calcium channel blocker, cadmium, and the nAChR antagonist mecamylamine, but is unaffected by muscarinic, glutamatergic, P2X and 5-HT3 receptor antagonists. Approximately 50% of nAChR-mediated SuSC [ 3H]-GABA release is inhibited by Î±-conotoxin MII. However, the highly Î±6Î²2*-subtype-selective Î±-conotoxin PIA did not affect [ 3H]-GABA release. Nicotinic subunit-null mutant mouse experiments revealed that ACh-stimulated SuSC [ 3H]-GABA release is entirely Î²2 subunit-dependent. Î±4 subunit deletion decreased total function by >90%, and eliminated Î±-conotoxin MII-resistant release. ACh-stimulated SuSC [ 3H]-GABA release was unaffected by Î²3, Î±5 or Î±6 nicotinic subunit deletions. Together, these data suggest that a significant proportion of mouse SuSC nicotinic agonist-evoked GABA-release is mediated by a novel, Î±-conotoxin MII-sensitive Î±3Î±4Î²2 nAChR. The remaining Î±-conotoxin MII-resistant, nAChR agonist-evoked SuSC GABA release appears to be mediated via Î±4Î²2* subtype nAChRs. Novel Î±3Î±4Î²2 nicotinic subtype modulates superior colliculus GABA release.This study examined nicotinic acetylcholine receptor (nAChR) subtypes modulating GABA release in the superior colliculus, a region highly enriched in Î±-conotoxin MII-sensitive nAChRs. A novel functional Î±3Î±4Î²2 nAChR subtype was found to mediate superficial superior colliculus GABA release. This study confirms the expression of functional, non-Î±6Î²2-subtype, Î±-conotoxin MII-sensitive nAChRs in mammalian brain, and uncovers a new level of modulation of superior colliculus GABA release. Â© 2012 The Authors. Journal of Neurochemistry Â© 2012 International Society for Neurochemistry.
Journal of Neurochemistry
Digital Object Identifier (DOI)
McClure-Begley, Tristan D.; Wageman, Charles R.; Grady, Sharon R.; Marks, Michael J.; McIntosh, J. Michael; Collins, Allan C.; and Whiteaker, Paul, "A Novel Î±-Conotoxin Mii-Sensitive Nicotinic Acetylcholine Receptor Modulates [ 3H]-Gaba Release In The Superficial Layers Of The Mouse Superior Colliculus" (2012). Neurobiology. 379.