Nicotinic acetylcholine receptor expression in rat dorsal root ganglion neurons

Dorsal root ganglia (DRG) contain neurons whose axons convey somatosensory information, including pain, from the periphery to the central nervous system (CNS). These neurons are known to express a variety of nicotinic acetylcholine receptors (nAChR), including those that are being investigated as therapeutic targets for the treatment of chronic and neuropathic pain syndromes. Previous reports indicate that rat DRG neurons express nAChRs consistent with an α3β4*-, α4β2*-, and α7-like composition (*, denotes the possible presence of additional subunits). However, transcripts for other nAChR subunits including α6, α9, and α10 have also been reported. Therefore, additional nAChR subtypes with these subunits were hypothesized to also be expressed. In this dissertation, reverse-transcription polymerase chain-reaction (RT-PCR) was used to identify transcripts for the nAChR subunits present in dissociated lumbar DRG neurons from rat. Pharmacological characterization of acetylcholine-gated currents (IACh) was performed using whole-cell patch-clamp electrophysiology. Individual nAChR subtypes were identified using novel subtype-selective α-conotoxins (α-Ctxs). The results of these experiments demonstrate for the first time the presence of α6β4* nAChRs in neurons outside the CNS and, in particular, in DRG neurons. No evidence was found for IACh mediated by nAChRs containing the α9 subunit. Chapter 1 begins with an overview of nAChRs and a review of the current literature concerning the expression of nAChRs by DRG neurons. The experimental results of this investigation are reported in Chapter 2. iv Lastly, in Chapter 3, the implications of these findings are discussed in the context of treatment of pain syndromes by ligands that target nAChRs.