Evidence of ?-aminobutyric acidergic control over the catecholaminergic projection from the medulla oblongata to the central nucleus of the amygdala

Abstract

It is known that the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) project to the central nucleus of the amygdala (Ce), conveying visceral information. Conversely, the Ce sends projections to the NTS and the VLM. To understand better the role of catecholamine and gamma-aminobutyric acid (GABA) in these reciprocal connections, experiments were performed by combining lectin-conjugated horseradish peroxidase (WGA-HRP) anterograde and retrograde transport with preembedding immunocytochemistry to detect tyrosine hydroxylase (TH), and postembedding immunocytochemistry to detect GABA. The light microscopic study suggested that the majority of neurons in the NTS and the VLM projecting to the Ce were TH immunoreactive (TH-IR). Most of them were located at the level of the obex. Under the electron microscope, the GABAergic and non-GABAergic terminals were found to form synaptic contacts with the TH-(IR) or Ce-projecting or TH-IR/Ce-projecting double-labelled neurons of the NTS and VLM. The GABAergic terminals mostly formed symmetrical synaptic contacts with the postsynaptic structure in which perikarya (14-19%), dendrites (79-84%), and spines (2%) were observed. Approximately 94% of the axon terminals in the NTS and 90% of those in the VLM arising from the Ce were GABAergic and appeared not to form synaptic contacts with the TH-IR or Ce-projecting neurons in these regions. The present results demonstrated that the catecholaminergic neurons of the NTS and VLM projecting to the Ce receive an extensive GABAergic innervation and that the amygdala projection to the medulla is mostly GABAergic.

Medial Prefrontal Cortex

“…1E, F; see also Van Giersbergen et al, 1992;Dampney, 1994). The characteristic somatodendritic and axonal morphologies as well as distributions of THϩ neurons in the NTS have been reported in detail elsewhere (Halliday and McLachlan, 1991;Jia et al, 1997). In brief, THϩ immunoreactivity was present in neuronal cell bodies, smooth and spiny dendrites, as well as fine fragmented varicose fibers that were morphologically distinct from brown DAB labeled afferent IL fibers ( Fig.…”

“…A large proportion (78%) of THϩ neurons in the medial, intermediate, and commissural subnuclei of the NTS projects to the vlPAG, a structure involved in cardiovascular adjustments associated with fear and anxiety related behaviors (Chen et al, 1995). Moreover, Jia et al (1997) estimate that about 80% of THϩ NTS neurons and 90% of THϩ VLM neurons project directly to CEA, which is reciprocally connected to BLA (Fig. 5A) and participates in the autonomic regulation of visceral functions involving cardiovascular, respiratory and gastrointestinal activities.…”

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).…”

“…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.…”