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First published online July 25, 2005
Journal of Experimental Biology 208, 2981-3001 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01732
Optical studies of nicotinic acetylcholine receptor subtypes in the guinea-pig enteric nervous system
1 Department of Neuroscience, University of Pennsylvania School of Medicine,
Philadelphia, PA 19104-6074, USA
2 Department of Physiology, University of Pennsylvania School of Medicine,
Philadelphia, PA 19104-6074, USA
* Author for correspondence (e-mail: bmsalzbe{at}mail.med.upenn.edu)
Accepted 2 June 2005
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 
3-, 4-,
3/5-, ß2-, ß4- and 7-subunits, combined with
radioimmunoassays and immunocytochemistry, we demonstrate that guinea-pig
enteric ganglia contain all of these nAChR-subunits with the exception of
4, 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 voltage-sensitive
dyes and a high-speed CCD camera, in conjunction with specific antagonists to
various nAChRs, to elucidate some of the distinct contributions of the
individual subtypes to the behaviour of enteric networks. In the guinea-pig,
the submucous plexus has the extraordinary advantage that it is virtually
two-dimensional, permitting optical recording, with single cell resolution, of
the electrical activity of all of its neurones. In this plexus, the
block of 3ß2-, 3ß4- and/or 7-nAChRs always
results in a decrease in the magnitude of the synaptic response. However, the
magnitude of the fast excitatory post-synaptic potentials (epsps) evoked by
electrical stimulation of a neighbouring ganglion varies from cell to cell,
reflecting the differential expression of subunits already observed using
mAbs, as well as the strengths of the activated synaptic inputs. At the same
time, we observe that submucous neurones have a substantial mecamylamine
(Mec)-insensitive (non-nicotinic) component to their fast epsps, which may
point to the presence of purinergic or serotonergic fast epsps in this system.
In the myenteric plexus, on the other hand, the antagonist-induced changes in
the evoked synaptic response vary depending upon the location of the
stimulating electrode with respect to the ganglion under study. The range of
activity patterns that follows sequential pharmacological elimination of
individual subtypes suggests that nAChRs may be capable of regulating the
activity of both excitatory and inhibitory pathways, in a manner similar to
that described in the central nervous system.
Key words: submucous plexus, myenteric plexus, high-speed optical recording, voltage-sensitive dye
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