Synaptic connections of extrinsic nerve fibers in the myenteric plexus of the rat duodenum.

In the present study the degeneration of extrinsic nerve fibers was first investigated in the duodenal myenteric plexus after their transection, and subsequently synaptic connections of the extrinsic nerve fibers were observed with their degenerative changes to examine the relationship of the extrinsic nerve fibers with the neuronal circuits in the myenteric plexus. Adult rats were anesthetized with pentobarbital, and the extrinsic nerve fibers running with the coeliac and superior mesenteric arteries were cut at about 2 mm distance from the coeliac ganglia to duodenum. Their duodena were fixed at 6 and 12 hours, and 1, 2, 4, 7 and 11 days after the extrinsic denervation, and their myenteric plexuses were observed with the electron microscope. Then, montages on 22 fields of the myenteric plexuses of 7 days after the denervation were made, and the number of all synapses and degenerated synapses in them was counted in each montage. 1. The degenerated changes of the extrinsic nerve fibers Three types of the degenerated axons were found in stages ranging from 12 hours to 11 days after the extrinsic denervation as follows: 1) Type I appeared mainly at 1 and 2 days. The electron density in the axoplasm decreased, and the synaptic vesicles accumulated in the central area of the axoplasm. 2) Type II appeared, also, at 1 and 2 days. The electron dense material occupied the axoplasm or the myelin-like structure appeared in the slightly swollen axons. 3) Type III appeared in stages from 1 to 11 days. Electron dense bodies appeared in the axoplasm.(ABSTRACT TRUNCATED AT 250 WORDS)