An electrophysiological study of the projections of putative sensory neurons within the myenteric plexus of the guinea pig ileum.

Conduction of action potentials in the processes of AH (afterhyperpolarizing) neurons has been examined in the myenteric plexus of the guinea-pig small intestine. AH neurons are a morphologically distinct class of myenteric neurons in which the action potentials are followed by long lasting afterhyperpolarizations and which usually lack fast synaptic inputs. These neurons have large smooth cell bodies and several long processes. We have used electrophysiological methods, combined with intracellular injection of the fluorescent dye 5(6)-carboxyfluorescein, to examine the directions of projection and lengths of axons of AH neurons. AH neurons of the myenteric plexus projected circumferentially in both directions from the cell soma for electrophysiologically determined average distances of 0.74 +/- 0.05 mm. Thus, the neurons span about 1.5 mm of the circumference of the intestine. About one quarter of the AH neurons had one, or rarely two, processes that ran anally after initially projecting circumferentially. All processes conducted action potentials, with average conduction velocities of 0.23 +/- 0.02 ms-1.