Structural differences in the enteric neural network in murine colon: impact on electrophysiology

Abstract

The enteric neural network in the proximal murine colon shows a regularly occurring hypoganglionic region, which is here characterized by using anatomical and electrophysiological techniques. Staining with NADPH diaphorase, methylene blue, and cuprolinic blue in standard whole mounts and three-dimensional gut preparations of the murine proximal colon consistently revealed two hypoganglionic areas surrounded by a dense clustering of enteric neurons. This irregularity in the ganglionic plexus was found to be present in mice of three different genetic backgrounds, as well as in rats. The lack of myenteric ganglia in these regions was associated with an absence of the longitudinal muscle layer, as shown in cross sections. Histochemical identification of interstitial cells of Cajal in Kit W-lacZ/ϩ transgenic mice showed Kit-positive cells oriented parallel to both muscle layers of the colon. Kit-positive cells oriented parallel to the longitudinal muscle layers were absent in the hypoganglionic area described. Electrical field stimulation elicited TTX-sensitive inhibitory junction potentials (IJPs), which showed region-specific characteristics. The initial partly apamin-sensitive hyperpolarization was present in all parts of the murine colon, whereas a second sustained N G -nitro-L-argininesensitive hyperpolarization was absent in the cecum and decreased from the proximal to the distal colon. Dissecting the hypoganglionic area from the surrounding tissue abolished the otherwise normal inhibitory neurotransmission to the circular muscle (1.6 Ϯ 1.4 and 2.6 Ϯ 1.7 mV for the fast and slow component of IJP amplitude in the hypoganglionic area vs. 16.5 Ϯ 1.9 and 23.7 Ϯ 2.7 mV for the fast and slow component of IJP amplitude in the neuron-rich area, respectively, P Ͻ 0.01, n ϭ 6), whereas dissection of an area of identical size with an intact myenteric network showed normal inhibitory neurotransmission, indicating that the hypoganglionic area receives essential functional neural input from the neuron-rich surrounding tissue. In summary, in the murine and rat proximal colon, a constant and distinct hypoganglionic region is described with important concomitant changes in local electrophysiology. mouse; enteric nervous system; smooth muscle; inhibitory junction potentials SINCE THE ORIGINAL DESCRIPTION of the enteric nervous system in the small bowel by Auerbach (1), it has been believed that the enteric ganglia form a regular network over the entire length of the gut wall. Distribution of subgroups of enteric neurons is known to vary along the longitudinal axis of the gut as demonstrated, for example, for nitric oxide (NO) synthase (NOS)-containing neurons (25, 26), but it is assumed that there is a homogeneous distribution of the neural network within a short gut segment. The shape of the small and large intestine in mammals resembles an elongated hollow organ. In contrast to simple tubes, however, the gut has to generate the force needed to ensure intraluminal transport (6,14). Accordingly, a sophisticated neural and muscul...

Interstitial cells of Cajal integrate excitatory and inhibitory neurotransmission with intestinal slow-wave activity

“…Tissue preparation for electrophysiological experiments and intracellular recordings of smooth muscle cells of the circular muscle layer of mouse proximal colon and ileum were performed exactly as described previously [51][52][53] . Nifedipine (1 mM) was present throughout all experiments.…”

Nociceptin effect on intestinal motility depends on opioid-receptor like-1 receptors and nitric oxide synthase co-localization

“…The present study shows am involvement of nociceptin and the ORL1 in ascending myenteric neuronal network circuits in the colon and increases our current understanding about ORL1 neurotransmission. EJP, which represents excitatory cholinergic neurotransmission was reduced by nociceptin [33] , in a [Nphe 1 ]NOC-reversible manner at all involved sites of stimulation, but also shortened the transmission distance. This observation leads us to postulate that not only motor neurons, but also interneurons are modulated by nociceptin.…”

“…Intracellular recordings of circular colonic smooth muscle cells were performed as detailed previously [32,33] . Neurons were stimulated with single electrical pulses (15 V; 0.3 ms duration) using single or multiple platinum electrodes as described previously [32,33] .…”

“…Neurons were stimulated with single electrical pulses (15 V; 0.3 ms duration) using single or multiple platinum electrodes as described previously [32,33] . Membrane potentials were recorded as described previously [25] .…”

“…The amplitudes of junction potentials were measured and compared to membrane potential prior to electrical stimulus application. The EJP represents excitatory cholinergic neurotransmission, the sIJP inhibitory nitrergic neurotransmission and the fIJP purinergic inhibitory neurotransmission as detailed earlier [33] . Increasing the nociceptin concentrations (1 nmol/L-1 µmol/L), led to a significant reduction in EJP in the mouse proximal colon and this effect was reversed by addition of [NPhe ]NOC (n = 6; Figure 5C).…”