Enteric neural modulation of slow-wave activity in cat colon

Role of the interstitial cells of Cajal in the control of gut motility

BACKGROUND

The interstitial cells of Cajal (ICCs) are a population of cells in the gastrointestinal tract which have a role in the control of gut motility.

METHOD

A comprehensive review of the scientific literature was undertaken to assess current understanding of the morphology, structure, identification, distribution, development and function of these cells.

RESULTS AND CONCLUSIONS

ICCs have an important role in the control of gut motility. Experimental evidence from animal studies suggests roles as pacemakers and coordinators of gut motor activity, and as intermediaries in the neural control of motility. With an increasing understanding of the distribution and behaviour of these cells in the healthy or diseased human gastrointestinal tract, there is the potential to develop novel therapeutic approaches to diseases that have gut dysmotility as a contributory factor.

New transmitters and new targets in the autonomic nervous system

Several recent findings have made research into the autonomic nervous system even more exciting, such as the revelation that nitric oxide is a major neurotransmitter, the delineation of the physiological roles for purines and vasoactive intestinal peptide, and the discovery that the interstitial cells of Cajal are major target cells for enteric innervation. Nitric oxide is probably the major neurotransmitter evoking inhibitory junction potentials in smooth muscle. ATP is a mediator of non-adrenergic non-cholinergic enteric innervation, as well as being a fast neurotransmitter in peripheral and autonomic neuro-neuronal synapses. The interactions between enteric nerves and both immune cells and interstitial cells of Cajal (as pacemaker cells of gut smooth muscle) are forcing a rethink of many aspects of gut physiology.

Role of M1 muscarinic receptors in the parasympathetic control of colonic motility in cats and rabbits

1. The effects of pirenzepine (a selective blocking agent of M1 muscarinic receptors) were studied on excitatory junction potentials (EJPs) and inhibitory junction potentials (IJPs) elicited on colonic smooth muscle by stimulation of efferent parasympathetic nerve fibres in anaesthetized cats and rabbits. 2. Pirenzepine (25 micrograms kg-1 to 0.2 mg kg-1, i.v.) decreased the amplitude of EJPs or abolished them. In pirenzepine, parasympathetic stimulation elicited IJPs in most cases. 3. In both species, pirenzepine initiated spontaneous IJPs, indicating an increase in the activity of the non-adrenergic, non-cholinergic (NANC) inhibitory neurones. 4. The results suggest that M1 muscarinic receptors are involved in synaptic transmission within intramural plexuses, at interneuronal synapses in the parasympathetic excitatory pathway to colonic smooth muscle, but are not involved in the pathway to the NANC inhibitory neurones. The facilitation of IJPs by pirenzepine suggests that, under normal physiological conditions, NANC neurones are tonically inhibited by an intramural nervous circuit involving M1 muscarinic receptors.