Electrophysiology, shape, and chemistry of neurons that project from guinea pig colon to inferior mesenteric ganglia.

BACKGROUND & AIMS: Prevertebral sympathetic ganglia receive inputs from intestinofugal neurons, with cell bodies located in the wall of the bowel. Intestinofugal neurons are part of the afferent limbs of intestino-intestinal reflexes. The aim of this study was to define the properties of intestinofugal neurons using intracellular recordings.

METHODS

Intestinofugal neurons of the distal colon were retrogradely labeled from the inferior mesenteric ganglia. In whole mounts of the myenteric plexus/longitudinal muscle of the distal colon, labeled neurons were identified by their fluorescence and recordings were made using biocytin-filled electrodes. Labeled nerves were characterized immunohistochemically and morphologically.

RESULTS

Intestinofugal neurons were uniaxonal neurons with multiple dendrites that had lamellar expansions. They were immunoreactive for choline acetyltransferase. Stimulation of nerve fiber tracts elicited large-amplitude excitatory postsynaptic potentials in all labeled neurons. Some received spontaneous fast excitatory postsynaptic potentials. Those cells that fired action potentials fired only one or two at the start of a depolarizing current pulse. No intestinofugal neurons had Dogiel type II morphology or a late afterhyperpolarizing potential.

CONCLUSIONS

Intestinofugal neurons are likely to be activated by other neurons in the gut wall. They are not AH or Dogiel type II neurons. Thus they seem to be second order neurons in afferent pathways of intestino-intestinal reflexes.