ANALYSIS OF THE RESPONSES OF MYENTERIC NEURONS IN THE SMALL-INTESTINETO CHEMICAL-STIMULATION OF THE MUCOSA

Responses of myenteric AH and S neurons to local application of chemic als to the mucosa of the guinea pig small intestine were obtained usin g conventional intracellular recording techniques. Preparations were d issected to reveal the myenteric plexus over one-half of the circumfer ence of the gut with intact mucosa on the other half. Neurons were imp aled within the exposed one-half, whereas potential stimulants, in buf fered saline, were transiently applied to the mucosa, 1-1.5 mm circumf erential from the impalement. The stimulants elicited action potential s (AP) in AH neurons that did not arise from synaptic activity. AH neu rons also responded with slow excitatory postsynaptic potentials (EPSP ). S neurons were activated synaptically, via fast and slow EPSP, but not nonsynaptically. Mucosal application of solutions of a low pH (3-5 ) or a high pH (9-11) were both effective stimulants. Solutions of a n eutral pH, which was also a control for mild mechanical stimulation, w ere usually ineffective. Both a short-chain fatty acid, acetate (pH 7. 2), and Ei-hydroxytryptamine elicited responses in each neuronal type. We conclude that myenteric AH neurons of the guinea pig distal ileum are primary afferent neurons that respond to a variety of mucosally ap plied chemical stimuli with burst of AP. In addition, the physiologica lly evoked transmission of slow EPSP to AH neurons suggests that prima ry afferent neurons interconnect in a self-reinforcing network. S neur ons are second or higher order neurons in the reflex pathways.