Differential control over postganglionic neurons in rat cardiac ganglia by NA and DmnX neurons: anatomical evidence

Abstract

. Differential control over postganglionic neurons in rat cardiac ganglia by NA and DmnX neurons: anatomical evidence. Am J Physiol Regul Integr Comp Physiol 286: R625-R633, 2004. First published November 26, 2003 10.1152/ajpregu.00143. 2003.-In previous single-labeling experiments, we showed that neurons in the nucleus ambiguus (NA) and the dorsal motor nucleus of the vagus (DmnX) project to intrinsic cardiac ganglia. Neurons in these two motor nuclei differ significantly in the size of their projection fields, axon caliber, and endings in cardiac ganglia. These differences in NA and DmnX axon cardiac projections raise the question as to whether they target the same, distinct, or overlapping populations of cardiac principal neurons. To address this issue, we examined vagal terminals in cardiac ganglia and tracer injection sites in the brain stem using two different anterograde tracers {1,1Ј-dioleyl-3,3,3Ј,3Ј-tetramethylindocarbocyanine methanesulfonate and 4-[4-(dihexadecylamino)-styryl]-N-methylpyridinium iodide} and confocal microscopy in male Sprague-Dawley rats. We found that 1) NA and DmnX neurons innervate the same cardiac ganglia, but these axons target separate subpopulations of principal neurons and 2) axons arising from neurons in the NA and DmnX in the contralateral sides of the brain stem enter the cardiac ganglionic plexus through separate bundles and preferentially innervate principal neurons near their entry regions, providing topographic mapping of vagal motor neurons in left and right brain stem vagal nuclei. Because the NA and DmnX project to distinct populations of cardiac principal neurons, we propose that they may play different roles in controlling cardiac function. brain stem; parasympathetic; anterograde tracing; heart; baroreflex VAGAL EFFERENT NERVE ACTIVATION induces negative chronotropic, dromotropic, and inotropic changes in the heart (13, 16). Our knowledge, however, of how the brain stem circuitry is organized to control the heart via the vagus is limited because of the complexity of brain-heart connections and limitations of previous anatomic techniques (8).Vagal efferent preganglionic axons arise mainly from neurons in two brain stem nuclei [the nucleus ambiguus (NA) and the dorsal motor nucleus of the vagus (DmnX)], whereas a small number of vagal efferent axons arise from neurons in the intermediate zone between DmnX and NA. The functional roles of cardiac neurons in these nuclei are not well understood (6,8,11,13,16,25). Furthermore, neurons in different cardiac ganglia control heart rate, arteriovenous (A-V) conduction, and myocardial contractility (17,18,(20)(21)(22). In contrast to the conventional concept that cardiac ganglia are simple relay stations for central nervous system input, these structures are more likely operating as complex integration centers (19, 23). They consist of sensory neurons, motor neurons, and interneurons that employ complex chemical coding (12,26) and are involved in local, as well as central, cardiac reflexes (1,19,23,27). Thus a major questi...

Separate neurochemical classes of sympathetic postganglionic neurons project to the left ventricle of the rat heart

“…The parasympathetic innervation of the rat heart is derived from preganglionic neurons in the medulla oblongata projecting axons in the vagus nerve to postganglionic neurons in the intracardiac ganglia (Cheng and Powley 2000;Cheng et al 1999Cheng et al , 2004. Previous studies have demonstrated that parasympathetic intracardiac neurons in rats and guinea-pigs can be classified into different subpopulations on the basis of their neurochemistry (Richardson et al 2003;Steele et al 1994), suggesting that intrinsic cardiac neurons may be chemically coded, as has been described for other neurons in the autonomic nervous system (Benarroch 1994;Furness et al 1992Furness et al , 1989Anderson 1995, 1997;Hökfelt 1991;Lundberg et al 1982).…”

Methods of assessing vagus nerve activity and reflexes

“…In contrast, DMNX neurons have nonmyelinated axons, show little or no respiratory- and cardiac-modulation, have smaller effects on HR, and possibly stronger dromotropic (decreases in A-V nodal conduction) and inotropic (decreases in contractility) effects [99, 100, 109]. NA and DMNX neurons have been reported to innervate distinct populations of neurons within cardiac ganglia, consistent with different functional roles [110]. …”

Alterations of calcium channels and cell excitability in intracardiac ganglion neurons from type 2 diabetic rats

“…The structural and functional alterations in every site of the arterial baroreflex arc are responsible for the T2DM-induced impairment of the arterial baroreflex sensitivity. Some previous studies have shown that parasympathetic cardiac neurons in the nucleus ambiguus in the brainstem extensively project to the ICG (1,9,10). More importantly, the arterial baroreflex control of the heart rate is almost totally abrogated when domoic acid lesion of the nucleus ambiguus stops the above projection to the ICG (11).…”