Neuropeptides and catecholamines in efferent projections of the nuclei of the solitary tract in the rat

Abstract

This study focuses on the involvement of catecholamines and nine different peptides in efferents of the nucleus of the solitary tract to the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and different parabrachial and hypothalamic nuclei in the rat. A double-labeling technique was used that combines a protein-gold complex as the retrograde tracer with immunohistochemistry. Catecholaminergic projection neurons were the most numerous type observed and projected mainly ipsilaterally to all targets studied. Most projections arose from areas overlying the dorsal motor nucleus, mainly the medial nucleus. Neurons synthesizing somatostatin, met-enkephalin-Arg-Gly-Leu, dynorphin B, neuropeptide Y, and neurotensin projected to all structures examined. Somatostatin and enkephalin immunoreactive projection cells were the most numerous. They were located in close proximity to each other, including all subnuclei immediately surrounding the solitary tract, bilaterally. Most dynorphin and neuropeptide Y immunoreactive projection cells were found rostral to that of enkephalinergic and somatostatinergic projections, and mainly in the ipsilateral medial nucleus. Neurotensinergic projections were sparse and from dorsal and dorsolateral nuclei. Substance P and cholecystokinin contribute to parabrachial afferents. The location of substance P immunoreactive projection cells closely resembled that of enkephalinergic and somatostatinergic projections. Projecting cholecystokinin immunoreactive cells were observed in dorsolateral nucleus. Bombesin immunoreactive cells in dorsal nucleus projected to either the parabrachial or hypothalamic nuclei. No vasoactive intestinal polypeptide-containing cells were detected. Thus, most catecholaminergic and neuropeptidergic efferents originated from different populations of cells. It is proposed that catecholaminergic neurons constitute the bulk of solitary efferents and that they may contribute to autonomic neurotransmission. Peptidergic neurons mainly form other subgroups of projections and may play a role in modulating the physiological state of the target nuclei.

Divergent projections of catecholaminergic neurons in the nucleus of the solitary tract to limbic forebrain and medullary autonomic brain regions

“…The retrograde labeling is not likely due to significant uptake of tracer from the areas adjacent to the injection sites for the following reasons: 1) injections centered in the PGi and the CNA that were used in the analysis did not significantly encroach on neighboring nuclei ; 2) independent anterograde and retrograde tracing studies (Van Bockstaele et al, 1989;Riche et al, 1990;Roder and Ciriello, 1993;Jia et al, 1997) support projections from the PGi and CNA; and 3) the retrogradely labeled neurons within the dorsal medulla was comparable to the anatomical distribution previously described in other studies (Van Bockstaele et al, 1989;Jia et al, 1997).…”

“…As such, these afferent inputs have been implicated in the regulation of cardiovascular, respiratory and general visceral activities. NTS neurons are known to contain neurochemically distinct types of neurons expressing both neuropeptides and neurotransmitters (Herbert and Saper, 1990;Riche et al, 1990;Gray, 1990,1995) A major subset of neurons in the NTS contain catecholamines, including noradrenaline and adrenaline (Hokfelt et al, 1984;Kalia et al, 1985). Specifically, the catecholamine-containing neurons of the A2 noradrenergic group are primarily distributed within the medial division of the NTS.…”

“…Previous anatomical tracing studies using wheat germ agglutinin-conjugated horseradish peroxidase coupled to gold (WGA-Au-HRP) have provided evidence for efferent projections from the NTS to the central nucleus of the amygdala (CNA; Ricardo and Koh, 1978;Riche et al, 1990;Jia et al, 1997). Likewise, using the same retrograde tracer, a projection from the nucleus paragigantocellularis (PGi) to the NTS was established (Ross et al, 1985;Hancock, 1988;Van Bockstaele et al, 1989;Mtui et al, 1995;Aicher et al, 1996).…”

“…Retrograde tracing studies in combination with immunohistochemistry have shown that CNAprojecting neurons from the NTS express tyrosine hydroxylase (TH) immunoreactivity (Riche et al, 1990;Jia et al, 1997). Moreover, recent evidence showed that very few PGi-projecting neurons in the NTS are catecholaminergic.…”

Anxiolytic-Like Action of Neuropeptide Y: Mediation by Y1 Receptors in Amygdala, and Dissociation from Food Intake Effects

“…Since a similar colo caliza. tion seems to be present in the central amygdaloid nucleus (Zardetto-Smith and Gray 1990;Riche et al 1990), NPY could exert its anxiolytic-like effect on this structure in an analogous manner. However, NPYin the amygdala also coexists with somatostatin and gamma-aminobutyric acid in a population of intrinsic interneurons similar to those seen in the neocortex and striatum (McDonald 1989;McDonald and Pearson 1989).…”