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Intracellular recordings were made from the internal and external submucosal ganglia of the porcine small intestine and neuronal properties were classified using two existing schemes for guinea-pig enteric neurones. In the first analysis, 77% of cells were designated as Type 4 since they were a heterogeneous population of neurones with the overlapping properties of S/Type 1 and AH/Type 2. The simplicity and usefulness of the second classification scheme was due to its emphasis on a single electrophysiological event, namely, the long-lasting after-hyperpolarization (AH) following the action potential. Eighty-eight percent of the cells studied were thus categorized as either AH (with an AH) or S (without an AH). All S neurones displayed fast synaptic potentials in response to stimulation of interganglionic fibre strands. AH neurones were subdivided into two groups dependent on whether they received fast synaptic inputs. Only by employing the second scheme of classification were differences in the neuronal characteristics and synaptic profiles between the two submucosal plexuses detected. It is concluded that the S and AH system of classification is the most appropriate method for the analysis of intracellular recordings from submucosal neurones in the porcine small intestine.

Intracellular recordings were made from neurones in the internal submucosal plexus (ISP) of porcine small intestine and synaptic inputs were investigated by focal stimulation of nerve fiber tracts. Nicotinic fast excitatory potentials (e.p.s.p.s) were recorded in all neurones, but slow e.p.s.p.s and slow inhibitory potentials (i.p.s.p.s) were rarely seen. Membrane potential changes similar to those occurring during the slow e.p.s.p. and slow i.p.s.p. could be evoked by exogenous application of neurotransmitters, even in neurones failing to display a nerve-mediated response. We suggest that the predominant source of the slow synaptic inputs to the ISP may be the neurones of the external submucosal plexus (ESP). The failure to record slow e.p.s.p.s and i.p.s.p.s could be a consequence of the anatomical arrangement of the submucosal plexuses whereby interconnecting strands between the ISP and ESP are inaccessible to the focal stimulation.