A novel α-conotoxin MII-sensitive nicotinic acetylcholine receptor modulates [3H]-GABA release in the superficial layers of the mouse superior colliculus

• Published in: Journal of neurochemistry 2012-07, Vol.122 (1), p.48-57
• Main Authors: McClure-Begley, Tristan D., Wageman, Charles R., Grady, Sharon R., Marks, Michael J., McIntosh, J. Michael, Collins, Allan C., Whiteaker, Paul
• Format: Article
• Language: English
• Subjects: 6-Cyano-7-nitroquinoxaline-2,3-dione - pharmacology; Acetylcholine - pharmacology; Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - pharmacology; Animals; Biological and medical sciences; Bridged Bicyclo Compounds, Heterocyclic - pharmacokinetics; Bungarotoxins - pharmacology; Cell receptors; Cell structures and functions; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; Conotoxins - pharmacology; Dizocilpine Maleate - pharmacology; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists - pharmacology; Female; Fundamental and applied biological sciences. Psychology; GABA; gamma-Aminobutyric Acid - metabolism; In Vitro Techniques; Iodine Isotopes - pharmacokinetics; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); nicotinic acetylcholine receptors; Nicotinic Agonists - pharmacokinetics; Nicotinic Antagonists - pharmacology; Protein Binding - drug effects; Protein Subunits - genetics; Protein Subunits - physiology; Pyridines - pharmacokinetics; Receptors, Nicotinic - deficiency; Receptors, Nicotinic - physiology; Serotonin Antagonists - pharmacology; subunit-null mutant; Superior Colliculi - cytology; Superior Colliculi - drug effects; Superior Colliculi - metabolism; superior colliculus; synaptosome; Synaptosomes - drug effects; Synaptosomes - metabolism; Tritium - metabolism; Tropanes - pharmacology; Vertebrates: nervous system and sense organs; α-conotoxin MII
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2012.07759.x

J. Neurochem. (2012) 122, 48–57. 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 α3β2* and α6β2* nicotinic subtype‐selective peptide α‐conotoxin MII‐blocked binding to 40 ± 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 α‐conotoxin MII. However, the highly α6β2*‐subtype‐selective α‐conotoxin PIA did not affect [3H]‐GABA release. Nicotinic subunit‐null mutant mouse experiments revealed that ACh‐stimulated SuSC [3H]‐GABA release is entirely β2 subunit‐dependent. α4 subunit deletion decreased total function by >90%, and eliminated α‐conotoxin MII‐resistant release. ACh‐stimulated SuSC [3H]‐GABA release was unaffected by β3, α5 or α6 nicotinic subunit deletions. Together, these data suggest that a significant proportion of mouse SuSC nicotinic agonist‐evoked GABA‐release is mediated by a novel, α‐conotoxin MII‐sensitive α3α4β2 nAChR. The remaining α‐conotoxin MII‐resistant, nAChR agonist‐evoked SuSC GABA release appears to be mediated via α4β2* subtype nAChRs. Novel α3α4β2 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 α‐conotoxin MII‐sensitive nAChRs. A novel functional α3α4β2 nAChR subtype was found to mediate superficial superior colliculus GABA release. This study confirms the expression of functional, non‐α6β2‐subtype, α‐conotoxin MII‐sensitive nAChRs in mammalian brain, and uncovers a new level of modulation of superior colliculus GABA release.