PROGRESSIVE REORGANIZATION OF THE MYENTERIC PLEXUS DURING ONE-YEAR FOLLOWING REANASTOMOSIS OF THE ILEUM OF THE GUINEA-PIG

The enteric nervous system appears to play a pivotal role in the funct ional recovery of the gastrointestinal tract after partial resection a nd reanastomosis, but the structural changes following surgery are not fully understood. The present study was designed to clarify the proce sses of myenteric plexus regeneration up to one year after transection and reanastomosis of the ileum of the guinea pig. The following techn iques were used: nicotinamide adenine dinucleotide (NADH) diaphorase h istochemistry, immunostaining of neuron-specific enolase (NSE) in whol e-mount preparations, and transmission electron microscopy. Two months after transection and reanastomosis, myenteric ganglion cells with NA DH diaphorase reactions were scarce in the center of the lesion, and w ere less numerous in adjacent areas (3 mm in width) than in the contro l ileum. In the areas adjacent to the lesion, a few large extraganglio nic neurons that did not completely compensate for the loss of ganglio n neurons were observed. The remaining ileum showed no changes in NADH diaphorase staining pattern at this stage. Two to 12 months after tra nsection and reanastomosis, ectopic large neurons gradually increased in number not only in the areas adjacent to the lesion but also in par t of the remaining ileum, up to 10 cm from the lesion. Concomitantly, large ganglion neurons decreased in number in these areas. In other il eal regions (more than 10 cm distant from the site of transection), no obvious changes in NADH diaphorase staining were noted throughout the observation period. The outgrowth of NSE-containing nerve fibers from the severed stumps was seen two weeks after transection. Six weeks la ter, numerous bundles of fine nerve fibers with NSE were shown to inte rconnect the oral and anal cut ends of the myenteric plexus, but they exhibited no subsequent alterations. Transmission electron microscopy, revealed that regenerating nerve fiber bundles appeared initially amo ng irregularly arranged smooth muscle cells eight weeks after the oper ation, as expected from light-microscopic observations. These findings suggest that myenteric ganglion cell bodies, unlike myenteric nerve f ibers, require a longer term of reconstruction than previously believe d after transection and reanastomosis of the ileum of the guinea pig.