Evidence that enteric cholinergic neurones project orally in the intestinal nerve of the chicken

The intestinal nerve of the chicken, which runs almost the whole length of the small and large intestine, was studied in vitro, using suction electrodes for stimulation and recording. Lengths of nerve with side branches intact in the region of the ileum and rectum were used. The spike discharges that were evoked by supramaximal stimulation of a side branch were recorded at oral and aboral ends of the main nerve trunk. Exposure of the preparation to hexamethonium (550 microM) reversibly abolished or greatly reduced the amplitude of the largest component of the evoked oral response in eighteen experiments, but was without effect on the evoked aboral response in ten experiments. No evidence of a nicotinic cholinergic component to the evoked aboral response was obtained at distances up to 12.5 mm along the nerve. There was also no evidence for a projection of post-ganglionic neurones along the stimulated side branch. The mean conduction velocity of the preganglionic nerve fibres was 0.25 +/- 0.02 m. s-1 while that for the post-ganglionic nerve fibres was 0.66 +/- 0.11 m.s-1. These results suggest that both groups of nerve fibres are non-myelinated. 8-16 d after side branch transection, stimulation of the side branch evoked no oral response in five experiments and a hexamethonium-insensitive response in seven others. In a further four experiments a hexamethonium-sensitive component was seen, but it constituted only a small part of the evoked oral response. It is postulated that transection results in the degeneration of cholinergic nerves in the intestinal nerve. The results suggest that enteric cholinergic nerves form part of a pathway which projects orally along the ileal and rectal segments of the intestinal nerve.