NON-ADRENERGIC NON-CHOLINERGIC ASCENDING REFLEX MOTILITY OF COLONIC LONGITUDINAL AND CIRCULAR MUSCLES

Because of high medical and social impact of the diseases of intestinal system the contribution of neurotransmitter systems to the peristaltic activity of large intestine is a matter of experimental and clinical interest. Electrical field stimulation (0.8 ms, 40 V, 2, 5 or 10 Hz, 20 s), partitioned organ bath and drugs were used aiming to display non-adrenergic non-cholinergic motility in isolated colonic segment-preparations in rat experimental model. The application of electrical stimulation to the middle or to the distal part of the colonic segments elicited ascending motility of the proximal part of the preparations due to excitation of the ascending reflex pathways serving the longitudinal and circular muscles. Both muscle layers responded with frequency-dependent contractions as the contractions of the longitudinal muscle were significantly more expressed as compared to those of the circular muscle (12.8 +/- 1.3 mN vs. 6.3 +/- 0.5 mN, at 5-Hz stimulation). Tetrodotoxin (0.1 mu M) prevented the electrically-induced ascending motor responses of both muscles indicating their neurogenic nature. Cholinergic and adrenergic receptors-related drugs were used to indicate the effects of non-adrenergic non-cholinergic neurotransmissions on the ascending motility. In atropine-pretreated (0.3 mu M) preparations the contractions of longitudinal and circular muscle significantly decreased and an initial relaxation preceded the contractions of the circular muscle (1.1 +/- 0.1 mN and 4.1 +/- 0.3 mN, respectively). In the presence of additionally added propranolol (0.1 mu M) and prazosin (0.1 mu M) the ascending reflex responses of both muscles induced by electrical stimulation applied at a distance of 10 mm consisted of an initial relaxation followed by contraction as the responses of the longitudinal muscle were lower by amplitude. Relaxation without contraction characterized the electrically-evoked ascending responses of longitudinal and circular muscles recorded at a distance of 20 mm from the excited distal part of the segmentpreparations suggesting the presence of longer inhibitory and shorter stimulatory pathways of non-adrenergic non-cholinergic neurotransmissions involved in the colonic ascending neuromuscular connections.