Novel neurotransmitters of the human intrinsic cardiac nervous system

Abstract

This study was done to anatomically identify novel neurotransmitters localized to human intrinsic cardiac ganglia (ICG). Samples were collected from 8 patients during cardiothoracic surgery and processed for immunofluorescent detection of specific neuronal markers. Colocalization of markers was evaluated by confocal microscopy. All intrinsic cardiac neuronal somata showed immunoreactivity for the cholinergic marker choline acetyltransferase (ChAT). These somata were bordered by cholinergic varicosities, evident as punctate immunostaining for high affinity choline transporter. Moderate to intense staining for neuronal nitric oxide synthase (nNOS) was likewise associated with all ganglion neurons as well as some proximal axons and nerve fiber bundles connected to ICG. Many calcitonin gene‐related peptide (CGRP)‐immunoreactive nerve fibers were identified in ICG, often surrounding cholinergic/nitrergic neuronal somata. Fewer nerve fibers displayed substance P (SP)‐immunoreactivity, but all SP was colocalized with CGRP. These findings suggest that NO may play a prominent role in cholinergic transmission within the human heart, CGRP being another key neuromodulator in the human intrinsic cardiac nervous system. Identification of such novel mediators may lead to new paradigms for cardiac neuromodulation. Supported by the AHA SE Affiliate and the Canadian Institutes for Health Research.