STRUCTURE AND CHEMICAL CODING OF HUMAN, CANINE AND OPOSSUM GALLBLADDER GANGLIA

Immunohistochemistry and cholinesterase histochemistry were used to ev aluate the structure and neurotransmitter content of the ganglionated plexuses of the human, canine, and opossum (Monodelphis domestica) gal lbladders. In each species, the ganglionated plexus consisted of small (mean approximate to 4 neurons/ganglion), irregularly dispersed gangl ia that were interconnected by bundles of nerve fibers. The density of ganglia was about ten-fold higher in the opossum than in the human or the dog. Immunostaining for choline acetyltransferase (ChAT) was acco mplished in the human, dog, opossum, and the guinea pig where all neur ons were found to express ChAT-immunoreactivity. In the human, immunor eactivities for vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) were the most abundant followed by substance P (SP). In the dog , immunoreactivity for galanin (GAL) was the strongest, followed close ly by VIP and then by SP NPY-immunoreactive neurons were not observed in the dog, but immunoreactive nerve fibers were seen in the perivascu lar plexus. In the opossum, immunoreactivity for GAL was the most inte nse and abundant followed by SP, which was followed by VIP. NPY-immuno reactivity in the opossum was limited to scarce perivascular nerve fib ers. Immunoreactivity for calcitonin-gene-related peptide (CGRP) was n ot observed in neuronal somata, but CGRP/SP-immunoreactive nerve fiber s were a feature of each species studied. These findings, along with p reviously published work on the guinea pig, indicate that it is likely that all gallbladder neurons are cholinergic, and that VIP, SP, and N PY and/or GAL are commonly expressed in gallbladder neurons.