Regulatory peptide and serotonin content and brush-border enzyme activity in the rat gastrointestinal tract following neonatal treatment with capsaicin; lack of effect on epithelial markers

The possible trophic influence of the capsaicin-sensitive extrinsic innervation of the gastrointestinal mucosa was investigated. Rats were treated neonatally with capsaicin. The gastrointestinal content of serotonin and glucagon-like immunoreactivity were used as a measure of the effect on the endocrine gut mucosa and gastrointestinal aminopeptidase and alkaline phosphatase activities were used as a measure of the effect on the gut brush-border. The gastrointestinal content of the neuropeptides substance P, VIP and CGRP were used to monitor effects on the innervation of the gut. The depletion of substance P-immunoreactivity(-IR) and calcitonin gene-related peptide(CGRP)-IR in extracts of urinary bladder and lung from the capsaicin-treated rats is evidence of the efficacy of capsaicin treatment in affecting a loss of C-fibre sensory nerves. The significant depletion of CGRP-IR measured in the stomach and duodenum of capsaicin-treated rats indicated the loss of the C-fibre sensory innervation to the gastrointestinal tract. The gastrointestinal content of VIP and substance P, which are predominantly within intrinsic gut neurones, were unaffected by capsaicin treatment. In all regions of the gastrointestinal tract of capsaicin-treated rats, the serotonin and glucagon-IR levels were not significantly different from those in controls. Similarly the levels of activity of the brush-border enzymes were not significantly effected by capsaicin treatment. This suggests the absence of any major trophic influence of capsaicin-sensitive sensory nerves on the gut endocrine mucosa and the brush border.