Distribution of enteric nerve cells that project from the small intestine to the coeliac ganglion in the guinea-pig.

The retrograde tracing agent, Fast blue, was injected into the coeliac ganglia of guinea-pigs and 4-7 days later, nerve cell bodies containing this dye were examined in the small intestine. The cell bodies were found in the ganglia of the myenteric plexus but not in submucous ganglia. The labeled cell bodies were large, on average 42 by 19 microns when viewed in whole mounts, with 4-9 fine processes. The cells increased in frequency anally along the small intestine; the number of neurons per unit length of gut in the distal ileum was more than double that near the duodeno-jejunal flexure. At all points along the intestine the nerve cells were more numerous near the mesenteric attachment than opposite this attachment. About half of the neurons showed immunoreactivity for VIP. It is deduced that the neurons that project from the intestine to the coeliac ganglion are likely to be second-order neurons in the afferent limbs of intestino-visceral reflex pathways.