Immunohistochemical characterization of cardiac vagal preganglionic neurons in the rat

Cardiac vagal preganglionic neurons (CVN) control cardiac activity by negative chronotropic, dromotropic and inotropic effects. We attempted to characterize the distribution and neuronal properties of the CVN by using double labeling with the retrograde tracer cholera toxin B subunit (CTb) and immunohistochemistry for choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP) or nitric oxide synthase (NOS). Injection of CTb into the sinoatrial ganglia resulted in many retrogradely labeled of neurons in the dorsal motor nucleus of the vagus (DMV), the compact (AmC), semicompact (AmS), loose (AmL), external (AmE) formations of the nucleus ambiguus, and the intermediate zone (IZ) between DMV and the nucleus ambiguus. Almost all CTb-labeled neurons showed ChAT immunoreactivity in the DMV, AmC, AmS, AmL and IZ, but most of the CTb-labeled neurons showed no ChAT immunoreactivity in the AmE. Most of the CTb-labeled neurons were double-labeled with CGRP immunoreactivity in the AmC, AmS and AmL, but a few double-labeled neurons were found in the DMV, IZ and AmE. A few CTb-labeled neurons were double-labeled with NOS immunoreactivity only in the DMV. No TH-immunoreactive neurons were found among the CVN. These results indicate that there are four kinds of neurons among the CVN: non-cholinergic CVN in the AmE, cholinergic and CGRP-containing CVN in the AmC, AmS and AmL, and cholinergic or cholinergic and NOS-containing CVN in the DMV.