Immunohistochemical distribution of cocaine- and amphetamine-regulated transcript peptide - like immunoreactive (CART-LI) nerve fibers and various degree of co-localization with other neuronal factors in the circular muscle layer of human descending colon.

Cocaine- and amphetamine-regulated transcript peptide (CART) is a neuromediator and/or neuromodulator in nerve structures within the gastrointestinal tract, but knowledge about its distribution, functions and co-localisation with other neuronal factors, especially in humans, is very scarce. During the present investigation the distribution and immunohistochemical reaction (IR) of CART - like immunoreactive (CART-LI) nerve fibers in the circular muscle layer of human descending colon were studied. Fragments of human colon were processed for double labelling immunofluorescence using a mixture of anti-CART antibodies with antibodies against vesicular acetylocholine transporter (VAChT), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase - activating peptide (PACAP), substance P (SP), galanin (GAL) and nitric oxide synthase (NOS). Thick CART-LI nerve fibers formed a very dense meshwork within the colonic circular muscle layer in all patients studied. The highest number of CART - positive nerves also contained VAChT and/or VIP. A slightly lower level of co-localisation was observed in the case of CART and PACAP or CART and NOS. Only single nerve fibers were concurrently immunoreactive to CART and SP or CART and GAL. The present study reports for the first time a detailed description of the IR of CART-LI nerve fibers in the circular muscle layer within adult human descending colon.