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

Abstract

The nucleus of the solitary tract (NTS) is a critical structure involved in coordinating autonomic and visceral activities. Previous independent studies have demonstrated efferent projections from the NTS to the nucleus paragigantocellularis (PGi) and the central nucleus of the amygdala (CNA) in rat brain. To further characterize the neural circuitry originating from the NTS with postsynaptic targets in the amygdala and medullary autonomic targets, distinct green or red fluorescent latex microspheres were injected into the PGi and the CNA, respectively, of the same rat. Thirty-micron thick tissue sections through the lower brainstem and forebrain were collected. Every fourth section through the NTS region was processed for immunocytochemical detection of tyrosine hydroxylase (TH), a marker of catecholaminergic neurons. Retrogradely labeled neurons from the PGi or CNA were distributed throughout the rostro-caudal segments of the NTS. However, the majority of neurons containing both retrograde tracers were distributed within the caudal third of the NTS. Cell counts revealed that approximately 27% of neurons projecting to the CNA in the NTS sent collateralized projections to the PGi while approximately 16% of neurons projecting to the PGi sent collateralized projections to the CNA. Interestingly, more than half of the PGi and CNA projecting neurons in the NTS expressed TH immunoreactivity. These data indicate that catecholaminergic neurons in the NTS are poised to simultaneously coordinate activities in limbic and medullary autonomic brain regions.

Fos expression in pontomedullary catecholaminergic cells following rapid eye movement sleep-like episodes elicited by pontine carbachol in urethane-anesthetized rats

“…Data also suggest that some neurons located in the medullary nucleus of the solitary tract have sleep promoting effects (Puizillout, 1986). Our finding that some A2/C2 neurons have reduced Fos expression following REMS-like episodes combined with anatomical evidence that some A2/C2 neurons project to the forebrain regions involved in the regulation of sleep (Blessing et al, 1982;Sakai et al, 1990;Reyes and Van Bockstaele, 2006) lends further support to this suggestion. Similarly, some LC, A5, A7 and SubC neurons project to both wake-promoting regions of the posterior hypothalamus and sleep-promoting regions of the anterior hypothalamus (Olson and Fuxe, 1972;Aston-Jones et al, 1986;Chou et al, 2002).…”

Central Autonomic System

“…The catecholaminergic A2 and C2 neurons in the NTS (also called NA2 and Ad2; Paxinos and Watson, 2014) project to many of the same targets mentioned above including the PAG, parabrachial nucleus, paraventricular nucleus, rostral ventrolateral medulla, amygdala and bed nucleus of the stria terminalis and median preoptic nucleus of the hypothalamus (Tucker et al, 1987;Riche et al, 1990;Reyes and Van Bockstaele, 2006;Campbell and Herbison, 2007;Gaykema et al, 2007;Itoi and Sugimoto, 2010) but not to the caudal ventrolateral medulla (Hermes et al, 2006). The A2/C2 neurons probably comprise a number of different functional pathways, e.g., hypoxia responsive A2/C2 neurons project to the paraventricular hypothalamic nucleus (King et al, 2012), while some A2/C2 neurons contain glucose transporters and may participate in glucose regulation (Balfour et al, 2006;Briski et al, 2009).…”

The learning of fear extinction

“…These probably act on vagal afferents (Izquierdo et al, 1959) that activate a pathway initiated by the nucleus of the solitary tract (NTS) through locally released norepinephrine (Clayton and Williams, 2000a;Clayton and Williams, 2000b;Clayton and Williams, 2000a-c;Williams et al, 1998;Chen and Williams, 2012;Mello-Carpes and Izquierdo, 2013), which projects to the nucleus paragigantocellularis, which innervates the locus coeruleus (LC) (Ennis and Aston-Jones, 1988;Reyes and Van Bockstaele, 2006), which sends noradrenergic fibers to many regions of the brain, including hippocampus and BLA (Gold and Zornetzer, 1983;Mello-Carpes and Izquierdo, 2013). The LC, hippocampus and BLA pathway plays, as is known, a key role in the regulation of memory processes (Gold and Zornetzer, 1983;McGaugh, 2000;Sara, 2009;Mello-Carpes and Izquierdo, 2013;Fiorenza et al, 2012).…”