Distribution of cocaine- and amphetamine-regulated transcript peptide in the guinea pig intrinsic cardiac nervous system and colocalization with neuropeptides or transmitter synthetic enzymes

This study was conducted to establish the presence of cocaine- and amphetam ine-regulated transcript peptide (CARTp) immunoreactivity in neurons and fi bers within guinea pig atrial whole-mount preparations containing the intri nsic cardiac ganglia. Many cardiac ganglia, but not all, in a given whole-m ount preparation, were innervated by CARTp-immunoreactive (IR) fibers. Foll owing explant culture of whole mounts for 72 hours, the CARTp-IR fiber netw orks were absent, but the number of CARTp-IR neurons was increased markedly . These observations suggested that the majority of the CARTp-IR fibers in the intracardiac ganglia were derived from sources extrinsic to the heart. In control whole-mount preparations, very few CARTp-positive neurons were p resent. The few intrinsic CARTp-IR neurons also exhibited choline acetyltra nsferase (ChAT) immunoreactivity, indicating that they make up a small subp opulation of cholinergic postganglionic neurons. Some CARTp-IR neurons also exhibited nitric oxide synthase (NOS) immunoreactivity, indicating that th ey were nitrergic as well. We compared the immunohistochemical staining pat terns of CARTp-IR fibers with the staining patterns of a number of other ne urotransmitters or neurotransmitter synthetic enzymes that mark specific ex trinsic inputs. The CARTp-IR fibers were not immunoreactive for ChAT, tyros ine hydroxylase, calcitonin gene-related peptide, or substance P. However, virtually all CARTp-IR fibers exhibited immunoreactivity to neuronal NOS (a marker for nitric oxide-producing neurons). CARTp-IR cells and NOS-IR cell s were present in the nodose ganglia. In addition, CARTp-IR neurons in the nodose also were stained positively for NADPH-diaphorase. Thus, we propose that most CARTp-IR fibers within the guinea. pig intrinsic cardiac ganglia are vagal afferent fibers that also contain NOS. (C) 2001 Wiley-Liss, Inc.