The intramural pelvic nerves immunoreactive for calcitonin gene-related peptide in the rectum of normal and aganglionosis rat.

The distribution of calcitonin gene-related peptide-like immunoreactive (CGRP-LI) nerves was investigated immunohistochemically in the rectum of normal, capsaicin-treated and congenital aganglionosis rats. The rectum of the normal rat was densely supplied with both extrinsic and intrinsic nerves exhibiting CGRP-like immunoreactivity. Numerous CGRP-LI nerve fibres were seen in both the myenteric and submucous plexuses. Intrinsic CGRP-LI nerve cell bodies were sparsely found in both the ganglionated plexuses, while a large inflow of extrinsic CGRP-LI nerves was characteristically observed in the rat rectum. CGRP-like immunoreactive fibres were abundant in the intramural pelvic nerves which ascend proximally in the intermuscular zone and connect with the myenteric plexus of the rat distal bowel. As compared with CGRP-positive fibres, SP- or SK-positive fibres in the intramural pelvic nerves were far less frequent. The treatment with capsaicin in the neonatal period led to a marked depletion of CGRP-immunoreactivity in these extrinsic nerves as well as in the most terminal varicose fibres seen in the whole layers of the rectal wall. These findings suggest that the vast majority of CGRP-LI fibres in the intramural pelvic nerves are sensory in nature, and that the positive nerve fibres of extrinsic origin directly innervate each layer of the rat rectum. These CGRP-LI sensory fibres associated with the intramural pelvic nerves, may be of importance in the regulation of rectal and colonic function in normal rats. A dense innervation of CGRP-LI nerve fibres, some of which showed the varicose appearance, was also found in the rectum of congenital aganglionosis rats.(ABSTRACT TRUNCATED AT 250 WORDS)