Optical studies of nicotinic acetylcholine receptor subtypes in the guinea-pig enteric nervous system

Abstract

ErratumObaid, A. L., Nelson, M. E., Lindstrom, J. and Salzberg, B. M. (2005). Optical studies of nicotinic acetylcholine receptor subtypes in the guinea-pig enteric nervous system. J. Exp. Biol. 208, 2981-3001. In the original published on-line version of this paper, the acceptance date was incorrect. It should have read 2 June 2005. The error has been rectified and the current on-line version and print versions are correct.We apologise to authors and readers for any inconvenience this may have caused. 2981Decoding the structure and function of native nicotinic acetylcholine receptors (nAChRs) is complex. Although the expression of defined combinations of nAChR-subunits in Xenopus oocytes permits the comparison of pharmacological properties of individual nAChR-subtypes, single neurones often express more than one subtype, making the physiological roles of nAChRs in intact neuronal networks difficult to assess (Colquhoun and Patrick, 1997). The function of a given nAChR depends upon its pre-, post-or peri-synaptic location as well as the activity of neighbouring non-nicotinic receptors. In addition, the properties of any neuronal ensemble depend not only on the intrinsic conductances of its neurones and the specific attributes of its many synapses but also on the complex and nonlinear dynamic interactions that result from the multiple parallel connectivity of its component cells (Parsons et al., 1991). Therefore, to understand nicotinic responses at the network level, it is necessary to record at high spatial and temporal resolution to characterize the behaviour of individual neurones and at lower spatial resolution to capture a panoramic view of network activity and to assess the directionality of the nicotinic pathways along the circumferential as well as the longitudinal axes.The enteric nervous system (ENS) regulates most gastrointestinal functions. Its neurones are clustered in ganglia that interconnect to form distinct plexuses in the gut wall: the myenteric plexus lies between the longitudinal and circular muscle layers, and the submucous plexus between the circular muscle layer and the mucosa. The behaviour of the effector Nicotinic transmission in the enteric nervous system (ENS) is extensive, but the role of individual nicotinic acetylcholine receptor (nAChR) subtypes in the functional connectivity of its plexuses has been elusive. Using monoclonal antibodies (mAbs) against neuronal α3-, α4-, α3/α5-, β2-, β4-and α7-subunits, combined with radioimmunoassays and immunocytochemistry, we demonstrate that guinea-pig enteric ganglia contain all of these nAChR-subunits with the exception of α4, and so, differ from mammalian brain. This information alone, however, is insufficient to establish the functional role of the identified nAChR-subtypes within the enteric networks and, ultimately, their specific contributions to gastrointestinal physiology. We have used voltagesensitive dyes and a high-speed CCD camera, in conjunction with specific antagonists to various nAChRs, to elucidate some of the distinct cont...

Nicotinic Regulation of Energy Homeostasis

“…Electrophysiological evidence tallies well with expression studies, showing that 70% of AH neurons show typical α3β4-like responses, whereas the remaining AH neurons and S neurons have a different, and at present uncharacterized, nicotinic response (Galligan & North, 2004). Further electrophysiological studies with subtype-selective peptidic antagonists showed the presence of α3β2 and α3β2β4 responses (Obaid et al, 2005). Low levels of α7 mRNA are expressed in rat myenteric plexus (Garza et al, 2009) and both plexa of guinea pig (Obaid et al, 2005), although functional evidence for α7-like responses in enteric circuits is questioned (Galligan & North, 2004;Obaid et al, 2005).…”

“…mRNA expression studies in postnatal rats, which are thought to reflect adult expression patterns, showed an autonomic ganglia-like expression pattern of subunits with relatively high levels of α3, α5, and β4 mRNA and lower levels of β2 mRNA in the myenteric plexus of stomach and intestine and relatively low levels of α3, α5, and β4 mRNA in the submucosal plexus of the intestine (Garza, Huang, Son, & Winzer-Serhan, 2009). A similar pattern was observed in immunohistological experiments with subunit-selective monoclonal antibodies (Obaid, Nelson, Lindstrom, & Salzberg, 2005). Accordingly a large predominance of β4* over β2* nicotinic binding was observed in receptor autoradiography studies (Garza et al, 2009).…”

Synaptic Transmission at Functionally Identified Synapses in the Enteric Nervous System: Roles for Both Ionotropic and Metabotropic Receptors

“…By contrast, evidence for a role of the 3 and 4 subunits in synaptic transmission is strong (for review see [40]). Other evidence indicates that 2 subunits are expressed in enteric neurons [94] and the exact stoichiometry of enteric nAChR remains to be definitively identified.…”

Recent developments in VSD imaging of small neuronal networks

“…In that study, the authors found that nicotinic acetylcholine receptors (nAChRs) that reversibly desensitize following nicotine exposure may be responsible for the enhancement of neuronal activity observed following nicotine application (Obaid et al 1999). The same group then used VSD imaging to show that nAChRs may be capable of regulating the activity of both excitatory and inhibitory pathways (Obaid et al 2005). Similarly, another group used VSD imaging to examine the activity of neurons in the guinea-pig and mouse ENS (Neunlist et al 1999), and have gone on to use this technique to record the activity of cultured human myenteric neurons, recording spike discharge following nicotine application (Vignali et al 2010).…”