Heterogeneity of nicotinic cholinergic receptors in rat superior cervical and nodose ganglia

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 alpha 3 and beta 4 subunits, but a significant percentage of the nAChRs in these ganglia also contain alpha 5 and beta 2 subunits. A small percentage of the nAChRs in nodose ganglia also contain beta 2 and beta 4 subunits. Sequential immunoprecipitation assays indicated that in the SCG, all alpha 5 subunits are associated with alpha 3 and beta 4 subunits, forming the mixed heteromeric alpha 3 beta 4 alpha 5 subtype. A receptor composed of alpha 3, beta 2, and beta 4 subunits in the SCG was also detected. In rat SCG, we found the following distribution of nAChRs subtypes: 55 to 60% simple alpha 3 beta 4 subtype, 25 to 30% alpha 3 beta 4 alpha 5 subtype, and 10 to 15% alpha 3 beta 4 alpha 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.