Chemical coding of intrinsic and extrinsic nerves in the guinea pig gallbladder: Distributions of PACAP and orphanin FQ

The complexity of the neural regulation of the gallbladder is reflected by the variety of neuroactive compounds that are found in the intrinsic and ex trinsic nerves of the guinea pig gallbladder. The studies reported here use d antisera to test for the presence of gallbladder nerves that are immunore active for the neuroactive peptides, pituitary adenylyl activating polypept ide (PACAP), and/or orphanin FQ (OFQ, also known as nociceptin). PACAP immu noreactivity was observed in nerve fibers of the paravascular plexus that w ere also immunoreactive for calcitonin gene-related peptide. These nerve fi bers, which are also immunoreactive for substance P, could be followed into the ganglionated plexus. Within the ganglia, a small proportion of neurons was found to be immunoreactive for PACAP; these neurons were also immunore active for vasoactive intestinal peptide and nitric oxide synthase. Immunor eactivity for OFQ was observed in the perivascular plexus in nerve fibers t hat were also immunoreactive for tyrosine hydroxylase. These nerves were pr eviously shown to be immunoreactive for neuropeptide Y. In the ganglionated plexus, immunoreactivity was observed in all gallbladder neurons, as demon strated by double staining with antiserum directed against the neuron-speci fic RNA binding protein, Hu. OFQ immunoreactivity was also present in the s mall catecholaminergic neurons that are observed in a subset of the ganglia . These results further demonstrate the neurotransmitter diversity of the n erves of the gallbladder, and they provide an incentive for studies of the actions of these compounds in the gallbladder wall. Anat Rec 262:101-109, 2 001. (C) 2001 Wiley-Liss, Inc.