The nucleus of the solitary tract in the monkey: Projections to the thalamus and brain stem nuclei

Abstract

The projections of the nucleus of the solitary tract (NST) were studied by autoradiographic anterograde fiber-tracing and horseradish peroxidase (HRP) retrograde cell-labeling. Tritiated proline and leucine were deposited in electrophysiologically identified regions of NST. Injections of NST at levels caudal to where the vagus enters the nucleus, from which responses were evoked by stimulation of cranial nerves IX and X, revealed topographically organized bilateral projections to, most prominently, the ventrolateral medullary reticular formation which contains neurons of the ambiguus complex, and to the lateral and medial parabrachial nuclei, including a small portion of the medially adjacent central gray substance. Labeled fibers in the ventrolateral reticular formation were present from the nucleus retroambigualis rostralward to the retrofacial nucleus, with the densest concentration located over the nucleus ambiguus proper. The parabrachial projection was confirmed using HRP and shown to originate from cells in the medial subdivision of NST. Due to the problem of fibers en passant, it was not possible to interpret conclusively the cell-labeling seen around the solitary tract after HRP injections made in the region of the nucleus ambiguus. Labeled fibers were also traced from caudal NST to the dorsal motor nucleus of the vagus, but their origin could not be determined with certainty. Other labeled axons, traced to circumscribed parts of the inferior olivary complex and via the contralateral medial lemniscus to VPL of the thalamus, were shown in HRP experiments to originate from the dorsal column nuclei rather than NST. No labeled fibers were traced into the spinal cord, nor were any cells labeled in NST after large HRP deposits in upper cervical segments. Isotope deposits at levels of NST rostral to the entrance of the vagus, from which responses were evoked by rapid stimulation of the tongue, revealed an ipsilateral projection which ascends as a component of the central tegmental tract to the parvicellular part of the ventral posteromedial thalamic nucleus (VPMpc). After small HRP deposits in VPMpc, labeled cells in NST were restricted to the rostral part of the lateral subdivision. No labeled axons were traced from rostral NST to the ambiguus complex or parabrachial area. Injections of 3H-amino acids at intermediate levels of NST resulted in fiber-labeling in VPMpc, the parabrachial area, and the ambiguus complex.

Ascending Projections from the Area Postrema and the Nucleus of the Solitary Tract of Suncus Murinus

“…In the suncus, as in other mammals, the Pb is the major target for projections from the NTS, and has generally been regarded as a relay of visceral and gustatory afferents to higher levels (Norgren and Leonard, 1973;Sakai et al, 1977;Norgren, 1978;Ricardo and Koh, 1978;Beckstead et al, 1980;King, 1980;Herbert et al, 1990). Physiological studies have suggested that taste-responsive neurons are primarily located in the MPb and that viscerosensory-responsive neurons are located in the LPb (Norgren and Pfaffmann, 1975;Hermann and Rogers, 1985;Ward, 1989;Halsell and Frank, 1991).…”

“…Based on neurological studies showing that the NTS controls the gastrointestinal tract via the dorsal motor nucleus of the vagus (DMV) (Morest, 1967;Cottle and Calaresu, 1975;Norgren, 1978;Beckstead et aL, 1980;Rogers et aL, 1980;Arends et al , 1988), and controls the pharynx, larynx, and esophagus via the nucleus ambiguus (Amb) (Morest, 1967;Cottle and Calaresu, 1975 Cunningham et al, 1991), the NTS appears to play an important role as the afferent system of all visceromotor reflexes, including the emetic response. Nevertheless, to define the neural pathways involved in the vomiting reflex, further comparative studies are necessary, especially in species having vomiting peculiarities.…”

Beyond flavour to the gut and back

“…Then, gustatory information in the VPMpc is transferred to the granular IC [51,52] which projects to the lateral and basal nuclei of the amygdala [53] and the orbitofrontal cortex (OFC) where visual and olfactory modalities converge with taste and oral texture [51,52,[54][55][56]. In the rodent, the taste part of the NTS projects to the PBN [57] which projects to the VPMpc, the central nucleus of the amygdala (CEA), and to the hypothalamus [58,59] (Fig. 2), and the PBN has reciprocal connections from the CEA and hypothalamus [60,61].…”

“…3), the visceral region in the caudal part of the NTS projects to the PBN. The PBN projects to the rostral half of the VPMpc (the non-taste part), the CEA, the lateral hypothalamic nuclei, the VTA, and to the SN in macaques [52,57,62,63]. The visceral part of VPMpc projects to the agranular insula which is located just posterior to the OFC [64,65] and the insula projects to the ventral striatum (VS) [66].…”

“…The CEA receives visceral information directly from the PBN [52,57,62,63,125,126] and gustatory information from the posterior OFC [56,127] while the lateral nucleus of the amygdala (BLA) receives gustatory information from the IC [128,129]. There are some connections between the CEA and BLA [130].…”