ELECTROPHYSIOLOGICAL PROPERTIES OF NEURONS IN THE INTERNAL AND EXTERNAL SUBMUCOUS PLEXUSES OF NEWBORN PIG SMALL-INTESTINE

1. Intracellular microelectrodes were used to identify three major ele ctrophysiological categories of neurone in both the internal and exter nal submucous plexuses of the porcine small intestine. 2. Two classes of neurone with a long-lasting after-hyperpolarization following their action potential were differentiated by the presence or absence of fa st excitatory synaptic inputs (EPSPs) and were termed AH neurones. S n eurones received ed fast EPSPs but did not display after-hyperpolariza tions. 3. The mean resting membrane potentials of the three groups of neurones showed a similar trend in both plexuses, with significantly h igher values for the two populations of AH neurone than for S neurones . No significant variation of input resistance with cell type was dete cted. Neuronal input resistance was significantly greater in the inter nal submucous plexus than in the external submucous plexus. 4. Over 80 % of AH neurones in the internal submucous plexus displayed fast EPSPs but a similar percentage of AH neurones in the external submucous ple xus did not show fast EPSPs. S neurones constituted 60% of cells studi ed in the internal submucous plexus but less than 30% of the cell popu lation in the external submucous plexus. 5. This study of porcine subm ucous neurones has revealed both similarities and differences to previ ous work in the guinea-pig small intestine. The most contrasting featu res are the relative abundance and subclassification of AH neurones in the pig in addition to the apparent paucity of slow synaptic potentia ls. The differences in the neuronal profiles of the internal and exter nal submucous plexuses may reflect a differentiation of function betwe en the two enteric nerve networks.