Regeneration of nerve fibres across a colonic anastomosis in the guinea‐pig

Resection and re‐anastomosis of the bowel interrupts enteric neuronal pathways. The re‐establishment of neuronal connections across a colonic anastomosis was studied using immunohistochemical, retrograde tracing and physiological techniques. In control guinea‐pig proximal colon, retrograde labelling with 1,1′‐didodecyl‐3,3,3,3′‐tetramethylindocarbocyanine perchlorate (DiI) revealed that enteric neurons with anally‐directed projections are more numerous and have longer axons than orally‐projecting neurons. In resected bowel, up to 26 weeks after re‐anastomosis, descending neuronal pathways were substantially interrupted. Immunohistochemical labelling of nerve fibres revealed that some enteric nerve fibres did regenerate across narrow regions of the anastomosis, growing preferentially in the oral to anal direction. However, nerve fibres immunoreactive for neurofilament protein triplet were substantially depleted in myenteric ganglia anal to the anastomosis, even after the longest recovery periods, demonstrating that axonal regrowth was limited. This was confirmed in retrograde tracing studies, as no nerve cell bodies oral to an anastomosis were labelled when DiI was placed on myenteric ganglia just anal to the anastomosis. Physiological studies confirmed that regrowth of nerve fibres across the anastomosis occurred and that it was asymmetric, as electrical stimulation led to aboral conduction across the anastomosis more reliably than oral conduction, as measured by circular muscle contraction. After resection and re‐anastomosis of the colon, the disruption of neuronal pathways in the enteric nervous system was observed, with limited and preferential re‐establishment of aborally‐directed long connections.