Heterogeneity of Nicotinic Cholinergic Receptors in Rat Superior Cervical and Nodose Ganglia

Abstract

Nicotinic cholinergic receptors (nAChRs) are present in ganglia in the peripheral nervous system. In autonomic ganglia, they are responsible for fast synaptic transmission, whereas in the sensory ganglia and sensory neurons, they may be involved in modulation of neurotransmission. The present study measured nAChRs in several rat autonomic ganglia: the superior cervical ganglia (SCG), sensory nodose ganglia, stellate ganglia, and pelvic ganglia. The densities of the heteromeric nAChRs determined by receptor binding assay in those four ganglia are 481, 45, 9, and 11 fmol/mg protein, respectively. Immunoprecipitation studies with subunit-specific antibodies showed that a majority of the nAChRs in the SCG and nodose ganglia contain the ␣3 and ␤4 subunits, but a significant percentage of the nAChRs in these ganglia also contain ␣5 and ␤2 subunits. A small percentage of the nAChRs in nodose ganglia also contain ␣2 and ␣4 subunits. Sequential immunoprecipitation assays indicated that in the SCG, all ␣5 subunits are associated with ␣3 and ␤4 subunits, forming the mixed heteromeric ␣3␤4␣5 subtype. A receptor composed of ␣3, ␤2, and ␤4 subunits in the SCG was also detected. In rat SCG, we found the following distribution of nAChRs subtypes: 55 to 60% simple ␣3␤4 subtype, 25 to 30% ␣3␤4␣5 subtype, and 10 to 15% ␣3␤4␤2 subtype. These findings indicate that the nAChRs in SCG and nodose ganglia are heterogeneous, which suggests that different receptor subtypes may play different roles in these ganglia or may be activated under different conditions. Neuronal nicotinic cholinergic receptors (nAChRs) are ligand-gated ion channels present throughout the central and peripheral nervous systems. In the autonomic nervous system, they mediate the fast synaptic transmission crucial to the functions of both sympathetic and parasympathetic ganglia. In addition, they are found in sensory ganglia and sensory neurons (Mandelzys et al., 1990(Mandelzys et al., , 1994Flores et al., 1996), in which they may modulate neurotransmission (Cooper, 2001). These receptors are pentameric structures composed of ␣ and ␤ subunits. Nine ␣ (␣2-␣10) and three ␤ (␤2-␤4) subunits have been identified in the vertebrate nervous system. The heteromeric nAChRs are composed of at least one type of ␣ subunit and one type of ␤ subunit. For example, the ␣3␤4* and ␣4␤2* are the predominant heteromeric subtypes in autonomic ganglia and the central nervous system, respectively. By convention, the asterisk denotes the possibility that one or more unidentified subunits are present in those receptors. For example, although expression of ␣3 and ␤4 subunits or ␣3 and ␤2 subunits results in functional nAChRs in heterologous expression systems (Covernton et al

Nicotinic Regulation of Energy Homeostasis

“…In the nodose ganglion, binding to nicotinic ligands amounts to about 10% of the binding in autonomic motor ganglia, being 85% of them β4* receptors and 15% β2* receptors. The subtype composition of these receptors is very similar to those expressed in autonomic motor ganglia, since α3β4 accounts for 50%, α3α5β4 for 35%, and α3β2β4 for 15% of receptors (Mao, Yasuda, Fan, Wolfe, & Kellar, 2006).…”

“…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).…”

α-Conotoxin PeIA[S9H,V10A,E14N] Potently and Selectively Blocks α6β2β3 versus α6β4 Nicotinic Acetylcholine Receptors

“…Finally, it is noteworthy that PeIA[S9H,V10A,E14N] is 1300-fold more potent at blocking ␣3␤2 than ␣3␤4 nAChRs. This exquisite selectivity for ␣3␤2 nAChRs may be useful for distinguishing between these two subtypes in neurons such as those found in intracardiac ganglia (Bibevski et al, 2000) and superior cervical ganglia (Mao et al, 2006; David et al, …”

Endogenously Expressed Muscarinic Receptors in HEK293 Cells Augment Up-regulation of Stably Expressed α4β2 Nicotinic Receptors

“…Nicotine administered in vivo increases predominantly the ␣4␤2 nAChR subtype in the brain (1, 4); moreover, it does not increase the nAChRs in autonomic ganglia or adrenal gland (59,60), which appear to express predominantly ␣3␤4* nAChR subtypes and a smaller number of ␣3␤2* subtypes (61)(62)(63)(64). However, in mammalian cells transfected to heterologously express pairs of nAChR subunits that form potential receptor subtypes, exposure to nicotine for 3 days or longer increases […”

“…3 H]EB binding to several different subunit combinations, including ␣2␤2, ␣3␤2, ␣4␤2, ␣2␤4, ␣3␤4, and ␣4␤4 (27,37,64,65). Similarly, in the current studies, even a 24-h exposure of cells to either nicotine or carbachol increased almost all of the subtypes to some extent, with the ␣3␤4 subtype being the least affected (Table 1).…”