Electrical and synaptic behavior of enteric neurons

Regional complexity in enteric neuron wiring reflects diversity of motility patterns in the mouse large intestine

The enteric nervous system controls a variety of gastrointestinal functions including intestinal motility. The minimal neuronal circuit necessary to direct peristalsis is well-characterized but several intestinal regions display also other motility patterns for which the underlying circuits and connectivity schemes that coordinate the transition between those patterns are poorly understood. We investigated whether in regions with a richer palette of motility patterns, the underlying nerve circuits reflect this complexity. Using Ca²⁺ imaging, we determined the location and response fingerprint of large populations of enteric neurons upon focal network stimulation. Complemented by neuronal tracing and volumetric reconstructions of synaptic contacts, this shows that the multifunctional proximal colon requires specific additional circuit components as compared to the distal colon, where peristalsis is the predominant motility pattern. Our study reveals that motility control is hard-wired in the enteric neural networks and that circuit complexity matches the motor pattern portfolio of specific intestinal regions.

Patch clamp recording from enteric neurons in situ

The study of enteric neurons is key to understanding intestinal motility anGutn of therapeutic strategies for dealing with neurogenic disorders. However, enteric neurons have historically been inaccessible to patch-clamp recording. We report here the first technique that allows patch-clamp recording of neurons from the intact myenteric plexus of the mouse duodenum. The mucosa, submucosa and circular muscles are removed, exposing the myenteric plexus on the longitudinal muscle. Proteolytic treatment of exposed ganglia combined with gentle cell-surface cleaning allows gigaseal formation. Compared with previous studies using intracellular microelectrode recordings or cultured myenteric neurons, this technique provides an opportunity to explore properties of single or multiple ion channels in myenteric neurons in their native environment. The protocol-from the tissue preparation to patch-clamp recording-can be completed in ~4 h.

Neurochemical bases of visceral nociception: mathematical model

A mathematical model of visceral perception was constructed, comprising primary sensory, motor, intestinofugal and principal neurons, interstitial cells of Cajal and smooth muscle elements that are arranged in a functional circuit through chemical synapses. The mathematical description of constructive elements was based on detailed morphological, anatomical, electrophysiological and neuropharmacological characteristics of cells and chemical processes of electrochemical coupling. Emphasis was given to signal transduction mechanisms that involved multiple neurotransmitters and receptor polymodality. The role of co-transmission by acetylcholine (ACh), serotonin (5-HT), noradrenalin (NA), N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and their corresponding receptors-muscarinic and nicotinic type ACh receptors, beta-adrenoceptors, 5-HT(3/4) type serotonergic receptors, NMDA and AMPA receptors in pathogenesis of nociception was studied numerically. Results of computer simulations reproduced patterns of electrical activity of neurons and mechanical responses of the smooth muscle similar to those observed in in vivo and in vitro experiments when ACh, 5-HT, NA, NMDA and AMPA were acting either alone or co-jointly. The results provide neurochemical bases for explanation of pathophysiological mechanisms of visceral nociception, which cannot be elucidated by existing experimental methods. Care should be taken though when extrapolating the numerical results onto the actual system because of limiting assumptions of the model.