Synchronization of enteric neuronal firing during the murine colonic MMC

Abstract

DiI (1,1 didodecyl-3,3,3 ,3 -tetramethylindocarbecyanine perchlorate) retrograde labelling and intracellular electrophysiological techniques were used to investigate the mechanisms underlying the generation of spontaneously occurring colonic migrating myoelectric complexes (colonic MMCs) in mice. In isolated, intact, whole colonic preparations, simultaneous intracellular electrical recordings were made from pairs of circular muscle (CM) cells during colonic MMC activity in the presence of nifedipine (1-2 µM). During the intervals between colonic MMCs, spontaneous inhibitory junction potentials (IJPs) were always present. The amplitudes of spontaneous IJPs were highly variable (range 1-20 mV) and occurred asynchronously in the two CM cells, when separated by 1 mm in the longitudinal axis. Colonic MMCs occurred every 151 ± 7 s in the CM and consisted of a repetitive discharge of cholinergic rapid oscillations in membrane potential (range: 1-20 mV) that were superimposed on a slow membrane depolarization (mean amplitude: 9.6 ± 0.5 mV; half-duration: 25.9 ± 0.7 s). During the rising (depolarizing) phase of each colonic MMC, cholinergic rapid oscillations occurred simultaneously in both CM cells, even when the two electrodes were separated by up to 15 mm along the longitudinal axis of the colon. Smaller amplitude oscillations (< 5 mV) showed poor temporal correlation between two CM cells, even at short electrode separation distances (i.e. < 1 mm in the longitudinal axis). When the two electrodes were separated by 20 mm, all cholinergic rapid oscillations and IJPs in the CM (regardless of amplitude) were rarely, if ever, coordinated in time during the colonic MMC. Cholinergic rapid oscillations were blocked by atropine (1 µM) or tetrodotoxin (1 µM). Slow waves were never recorded from any CM cells. DiI labelling showed that the maximum projection length of CM motor neurones and interneurones along the bowel was 2.8 mm and 13 mm, respectively. When recordings were made adjacent to either oral or anal cut ends of the colon, the inhibitory or excitatory phases of the colonic MMC were absent, respectively. In summary, during the colonic MMC, cholinergic rapid oscillations of similar amplitudes occur simultaneously in two CM cells separated by large distances (up to 15 mm). As this distance was found to be far greater than the projection length of any single CM motor neurone, we suggest that the generation of each discrete cholinergic rapid oscillation represents a discreet cholinergic excitatory junction potential (EJP) that involves the synaptic activation of many cholinergic motor neurones simultaneously, by synchronous firing in many myenteric interneurones. Our data also suggest that ascending excitatory and descending inhibitory nerve pathways interact and reinforce each other.

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

“…In contrast to small intestine and in accordance with previous studies 27, 28 , we did not observe slow-wave-type electrical activity and rhythmic contractions of colonic circular smooth muscle cells (Fig. 3j-k and Supplementary Fig.…”

Neurogenic and myogenic motor activity in the colon of the guinea pig, mouse, rabbit, and rat

“…Motility patterns that propel fluid or solid boluses and that appear to require neuronal activity have been previously described in all four species [guinea pig (8,11,12,15), mouse (4,40,42), rabbit (14, 23-25, 28, 43), and rat (7,20,29)]. Physiological propulsion via purely myogenic motor activity has not been as widely reported, except in the stomach.…”

“…Propagating motor complexes occur spontaneously in the isolated colon and can also be triggered by local stimulation (distension or mucosal stroking) (8,22,27,31,35,38,39). These complexes are generated by synchronized firing of populations of ascending and descending myenteric interneurons (40) that activate excitatory motor neurons in a coordinated fashion (37). CMMCs consist of coordinated compound excitatory junction potentials at 1-2 Hz (40), coinciding with disinhibition of the circular muscle layer.…”

Potentiation of a functional autoantibody in narcolepsy by a cholinesterase inhibitor

“…21 Excitation of intrinsic cholinergic motor neurons has been shown to have an essential role in the generation of CMMCs. 27 In contrast, in the interval between CMMCs, inhibitory motor neurons maintain the circular smooth muscle under tonic inhibition. 23 We used the cholinesterase inhibitor, neostigmine, to further explore the mechanism of narcoleptic IgG-mediated disruption of enteric motor function.…”

“…21 As CMMCs are predominantly mediated by the release of acetylcholine from cholinergic motor neurons, 27 we used the cholinesterase inhibitor, neostigmine, to further define the mechanisms by which narcoleptic IgG mediates colonic dysfunction. In the isolated mouse colon, spontaneous, regular CMMCs were recorded as contractions mediated by excitatory motor activity migrating from the proximal to distal colon at intervals of 3-5 min, separated by periods of quiescence during which inhibitory motor activity regulates smooth muscle tone.…”