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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 amphetamine‐regulated transcript peptide (CARTp) immunoreactivity in neurons and fibers within guinea pig atrial whole‐mount preparations containing the intrinsic cardiac ganglia. Many cardiac ganglia, but not all, in a given whole‐mount preparation, were innervated by CARTp‐immunoreactive (IR) fibers. Following explant culture of whole mounts for 72 hours, the CARTp‐IR fiber networks 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 present. The few intrinsic CARTp‐IR neurons also exhibited choline acetyltransferase (ChAT) immunoreactivity, indicating that they make up a small subpopulation of cholinergic postganglionic neurons. Some CARTp‐IR neurons also exhibited nitric oxide synthase (NOS) immunoreactivity, indicating that they were nitrergic as well. We compared the immunohistochemical staining patterns of CARTp‐IR fibers with the staining patterns of a number of other neurotransmitters or neurotransmitter synthetic enzymes that mark specific extrinsic inputs. The CARTp‐IR fibers were not immunoreactive for ChAT, tyrosine 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 cells 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. J. Comp. Neurol. 439:73–86, 2001. © 2001 Wiley‐Liss, Inc.