Ileal and colonic propulsive behavior: contribution of enteric neural circuits

Experiments were conducted in vitro to determine the extent to which the intrinsic propulsive behavior of cat terminal ileum and colon is controlled by the enteric nervous system (ENS) and the myogenic control system. Oral and aboral ends of terminal ileal and colonic segments, 17 cm in length, were connected to a propulsion evaluation system that imposed input-output conditions of constant capacitance and negligible resistance. To determine the effect of inhibiting one or more components within the ENS on spontaneously occurring patterns of propulsive behavior, segments were arterially perfused with tetrodotoxin (3.1 X 10(-7) M), atropine sulfate (10(-6) M), tubocurarine chloride (1.5 X 10(-6) M), hexamethonium chloride (2.8 X 10(-5) M), or methysergide (2.8 X 10(-5) M). Results indicated that when cat ileal and colonic segments are evaluated under conditions requiring significant amounts of hydrostatic work to effect fluid ejection 1) the unmodulated myogenic control system is unable to induce significant amounts of fluid expulsion, 2) cholinergic excitatory motor neurons of the ENS are required for the generation of the intrinsic patterns of propulsive behavior normally observed to expel fluid, and 3) the spontaneous occurrence of intrinsic propulsive patterns requires the operation of ENS integrative mechanisms utilizing nicotinic cholinergic and serotonergic synapses.