Biochemical and functional properties of distinct nicotinic acetylcholine receptors in the superior cervical ganglion of mice with targeted deletions of nAChR subunit genes

Abstract

Nicotinic acetylcholine receptors (nAChR) mediate fast synaptic transmission in ganglia of the autonomic nervous system. Here, we have determined the subunit composition of hetero-pentameric nAChRs in the mouse superior cervical ganglion (SCG), the function of distinct receptors (obtained by deletions of nAChR subunit genes), and mechanisms at the level of nAChRs that might compensate for the loss of subunits. As shown by immunoprecipitation and Western blots, wild type (WT) mice expressed (%): α3β4 (55), α3β4α5 (24), and α3β4β2 (21) nAChRs. nAChRs in β4 knockout (KO) mice were reduced to less than 15 % of controls and no longer contained the α5 subunit. Compound action potentials, recorded from the postganglionic (internal carotid) nerve and induced by preganglionic nerve stimulation, did not differ between α5β4 KO and WT, suggesting that the reduced number of receptors in the KO did not impair transganglionic transmission. Deletions of α5 or β2 did not affect the overall number of receptors and we found no evidence that the two subunits substitute for each other. In addition, dual KOs allowed us to study the functional properties of distinct α3β4 and α3β2 receptors that have previously only been investigated in heterologous expression systems. The two receptors strikingly differed in the decay of macroscopic currents, the efficacy of cytisine, and their responses to the α-conotoxins AuIB and MII. Our data - based on biochemical and functional experiments and several mouse KO models - clarifies and significantly extends previous observations on the function of nAChRs in heterologous system and the SCG.

Lidocaine effects on acetylcholine-elicited currents from mouse superior cervical ganglion neurons

“…The similarity of the actions evoked by lidocaine in dissociated SCG neurons and in oocytes microtransplanted with muscle-type nAChR has two relevant implications: i) It indicates that lidocaine has similar modulating actions on different heteromeric nAChRs, including muscle-type and α3β4 nAChRs, which is the main subtype in sympathetic neurons; but also most likely over α3β4α5 and α3β4β2, which together constitute almost half the number of nAChRs in the mouse SCG neurons (David et al, 2010). This being of particular interest because many molecules acting on nAChRs have marked specificity on particular subtypes.…”

“…In the peripheral and central nervous system there are different subtypes of nAChRs, generically called neuronal nAChRs. In mammalian autonomic ganglia neurons, including the superior cervical ganglion (SCG), the predominant nAChR is the heteromeric α3β4 subtype, though there are a significant percentage of combinations with α5 and/or β2 subunits (Gotti et al, 2009;David et al, 2010). Moreover, homomeric α7 receptors are also present, but their currents are only evoked in the presence of PNU 120569 (David et al, 2010).…”

“…In mammalian autonomic ganglia neurons, including the superior cervical ganglion (SCG), the predominant nAChR is the heteromeric α3β4 subtype, though there are a significant percentage of combinations with α5 and/or β2 subunits (Gotti et al, 2009;David et al, 2010). Moreover, homomeric α7 receptors are also present, but their currents are only evoked in the presence of PNU 120569 (David et al, 2010). Finally, the two main nAChRs subtypes in the mammalian central nervous system are α4β2 and α7 (Flores et al, 1992;Barrera and Edwardson, 2008) though combinations of α (2-5) with β (2-4) subunits and receptors formed by α9 and/or α10 are also present (Dani and Bertrand, 2007).…”

Nicotinic Regulation of Energy Homeostasis

“…Immunochemical and functional studies in rodents have shown that ganglionic neurons express high levels of α3β4 receptors in the somatic/dendritic compartment along with two minor populations of α3α5β4 and α3β2β4 receptors with different physiological and pharmacological properties (David et al, 2010;Mao et al, 2006). Low levels of α4* nAChRs may be expressed during development (Scholze et al, 2011).…”

“…Low levels of α4* nAChRs may be expressed during development (Scholze et al, 2011). α7 receptors are also expressed, although they are perisynaptic (Berg & Conroy, 2002) and their contribution to ganglionic transmission in rodents may be modest (David et al, 2010). nAChRs are also expressed on presynaptic terminals of ganglionic neurons where they positively regulate noradrenaline or acetylcholine release (Fischer, Orr-Urtreger, Role, & Huck, 2005;Kristufek, Stocker, Boehm, & Huck, 1999).…”