Nucleus of the solitary tract in the C57BL/6J mouse: Subnuclear parcellation, chorda tympani nerve projections, and brainstem connections

Sensory inputs from the oropharynx terminate in both the trigeminal brainstem complex and the rostral part of the nucleus of the solitary tract (nTS). Taste information is conveyed via the facial and glossopharyngeal nerves while general mucosal innervation is carried by the trigeminal and glossopharyngeal nerves. In contrast, the caudal nTS receives general visceral information largely from the vagus nerve. Although the caudal nTS shows clear morphological and molecularly delimited subdivisions, the rostral part does not. Thus, linking taste-induced patterns of activity to morphological subdivisions in the nTS is challenging. To test whether molecularly-defined features of the rostral nTS correlate with patterns of taste-induced activity, we combined immunohistochemistry for markers of various visceral afferent and efferent systems with c-Fos-based activity maps generated by stimulation with a sour tastant, 30mM citric acid. We further dissociated taste-related activity from activity arising from acid-sensitive general mucosal innervation by comparing acid-evoked c-Fos in wildtype and “taste blind”, P2X2/P2X3 double knockout (P2X-dblKO) mice. In wildtype mice, citric acid stimulation evoked significant c-Fos activation in the central part of the rostral nTS – activity that was largely absent in the P2X-dblKO mice. P2X-dblKO mice, like wildtype mice, did exhibit acid-induced c-Fos activity in the dorsomedial trigeminal brainstem nucleus situated laterally adjacent to the rostral nTS. This dorsomedial nucleus also showed substantial innervation by trigeminal nerve fibers immunoreactive for CGRP, a marker for polymodal nociceptors suggesting that trigeminal general mucosal innervation carries information about acids in the oral cavity.

mentioning

confidence: 99%

Immunocytochemical organization and sour taste activation in the rostral nucleus of the solitary tract of mice

Stratford

Thompson

Finger

2016

“…Results from double‐labeling with a CHAT antibody revealed that rostral medial cholinergic cells intermingle with profuse varicosities arising from the cNST that appear to contact the somata and dendrites (Figure 5c 2 ,c 3 ), suggesting a robust influence of visceral signals on these parasympathetic neurons. Although frank gustatory responses are sparse in the medial subdivision, consistent with evidence for weak primary afferent input (Breza & Travers, ; Ganchrow et al, ; Whitehead, ), dendrites from PGPs at the rostral pole of NST extend laterally into the zone of primary afferent terminations (Kim, Chiego, & Bradley, ). Thus, these rostral PGPs are in a position to be modulated by both taste and visceral signals, consistent with observations that both types of signals can modulate salivation (Gjorstrup, ; Hockman, Hagstrom, & Hoff, ; Kawamura & Yamamoto, ; Matsuo et al, ; Ueda et al, ) and other functions, including gastric motility (Inui‐Yamamoto et al, ; Wicks et al, ).…”

Section: Discussionmentioning

confidence: 54%

“…We used an antibody to detect the P2X2 purinergic receptor (RRID: AB_2040054) which co‐localizes with the distribution of primary afferent gustatory terminals in the rNST (Bartel, ; Ganchrow et al, ). The antibody was raised against the intracellular C‐terminus of the receptor and data from the manufacturer show that this antibody stains a band at ~75 kDa, which is blocked by pre‐incubation with the control peptide.…”

Section: Methodsmentioning

confidence: 99%

“…We used the nomenclature of rNST subdivisions as initially described in rats by Whitehead (), and applied to mice by Ganchrow et al (). Although these subdivisions were originally defined by cytoarchitecture and myeloarchitecture using stains for somata or myelinated fibers, our recent work suggests that immunohistochemical staining for P2X2, which identifies the terminal field of primary gustatory afferent fibers (Bartel, ; Breza & Travers, ; Ganchrow et al, ; Vandenbeuch et al, ), is an excellent marker for the (rostral) central subdivision. Thus, we delineated the central subdivision with this staining and then defined the other subdivisions in relation to it; i.e., as medial, ventral, or lateral to P2X2 label.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, the central subdivision receives the most robust input from primary taste afferents and is the main source of ascending connections ultimately destined for the forebrain via the PBN. The lateral subdivision is more involved in somatosensory function, and the medial and ventral subdivisions are preferentially involved in parasympathetic and oromotor reflexes (Breza & Travers, ; Ganchrow et al, ; Halsell, Travers, & Travers, ; Stratford, Thompson, & Finger, ; Whitehead, ). The present study was designed to more carefully evaluate the identity of the rNST subdivisions that receive a projection from the cNST.…”

Section: Introductionmentioning

confidence: 99%

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Neurons with diverse phenotypes project from the caudal to the rostral nucleus of the solitary tract

Travers

Breza

Harley

et al. 2018

The nucleus of the solitary tract is a potential site for taste-visceral interactions. Connections from the caudal, visceral area of the nucleus (cNST) to the rostral, gustatory zone (rNST) have been described, but the phenotype of cells giving rise to the projection(s) and their distribution among rNST subdivisions are unknown. To determine these characteristics of the intrasolitary pathway, we injected pan-neuronal and floxed AAV viruses into the cNST of mice expressing cre in glutamatergic, GABAergic or catecholaminergic neurons. Particular attention was paid to the terminal field distribution in rNST subdivisions by simultaneously visualizing P2×2 localized to gustatory afferent terminals. All three phenotypically-identified pathways terminated in rNST, with the density greatest for glutamatergic and sparsest for catecholaminergic projections, observations supported by retrograde tracing. Interestingly, cNST neurons had more prominent projections to rNST regions medial and ventral to P2×2 staining, i.e., the medial and ventral subdivisions. In addition, GABAergic neurons projected robustly to the lateral subdivision and adjacent parts of the reticular formation and spinal trigeminal nucleus. Although cNST neurons also projected to the P2×2-rich central subdivision, such projections were sparser. These findings suggest that cNST visceral signals exert stronger excitatory and inhibitory influences on local autonomic and reflex pathways associated with the medial and ventral subdivisions compared to weaker modulation of ascending pathways arising from the central subdivision and ultimately destined for the forebrain.

5‐HT_3A‐driven green fluorescent protein delineates gustatory fibers innervating sour‐responsive taste cells: A labeled line for sour taste?

Stratford

Larson

Yang

et al. 2017

Taste buds contain multiple cell types with each type expressing receptors and transduction components for a subset of taste qualities. The sour sensing cells, Type III cells, release serotonin (5-HT) in response to the presence of sour (acidic) tastants and this released 5-HT activates 5-HT3 receptors on the gustatory nerves. We show here, using Htr3a-EGFP mice, that 5-HT3-expressing nerve fibers preferentially contact and synapse with Type III taste cells. Further, these 5-HT3-expressing nerve fibers terminate in a restricted central-lateral portion of the nucleus of the solitary tract (nTS) – the same area that shows increased c-Fos expression upon presentation of a sour tastant (30 mM citric acid). This acid stimulation also evokes c-Fos in the laterally adjacent mediodorsal spinal trigeminal nucleus (DMSp5), but this trigeminal activation is not associated with the presence of 5-HT3-expressing nerve fibers as it is in the nTS. Rather, the neuronal activation in the trigeminal complex likely is attributable to direct depolarization of acid-sensitive trigeminal nerve fibers, e.g. polymodal nociceptors, rather than through taste buds. Taken together, these findings suggest that transmission of sour taste information involves communication between Type III taste cells and 5-HT3-expressing afferent nerve fibers that project to a restricted portion of the nTS consistent with the mapping of taste quality information in the primary gustatory nucleus.