A survey of oral cavity afferents to the rat nucleus tractus solitarii

Abstract

Visualization of myelinated fiber arrangements, cytoarchitecture, and projection fields of afferent fibers in tandem revealed input target selectivity in identified subdivisions of the nucleus tractus solitarii (NTS). The central fibers of the chorda tympani (CT), greater superficial petrosal (GSP), and glossopharyngeal (IX) nerves, three nerves that innervate taste buds in the oral cavity, prominently occupy the gustatorysensitive rostrocentral subdivision. In addition, CT and IX innervate and overlap in rostrolateral subdivision, which is primarily targeted by the lingual branch of the trigeminal nerve (LV). In rostrocentral subdivision, compared to the CT terminal field in rostrocentral subdivision, GSP appeared more rostral and medial, and IX was more dorsal and caudal. While IX and LV filled the rostrolateral subdivision diffusely, CT projected only to the dorsal and medial portions. The intermediate lateral subdivision received input from IX and LV but not CT or GSP. In the caudal NTS, the ventrolateral subdivision received notable innervation from CT, GSP, and LV, but not IX. No caudal subnuclei medial to solitary tract contained labeled afferent fibers. The data indicate selectivity of fiber populations within each nerve for functionally distinct subdivisions of the NTS, highlighting the possibility of equally distinct functions for CT in the rostrolateral NTS, and CT and GSP in the caudal NTS. Further, this provides a useful anatomical template to study the role of oral cavity afferents in the taste-responsive subdivision of the NTS as well as in subdivisions that regulate ingestion and other oromotor behaviors.

Topographical representations of taste response characteristics in the rostral nucleus of the solitary tract in the rat

“…The medial projections in GSP were clearly exhibited in the RC level (ϩ1.6 to ϩ2.0 mm in Fig. 20 of Corson et al 2012), which corresponded to r2, where large responses to sucrose were observed in the present study (Fig. 8C).…”

“…The region with large responses to sucrose was located more medially than the area responsive to NaCl. The spatial difference may be chiefly attributed to GSP afferents, which terminate more medially with the overlap of the CT afferents (Corson et al 2012). The medial projections in GSP were clearly exhibited in the RC level (ϩ1.6 to ϩ2.0 mm in Fig.…”

“…However, recent studies have reported overlapping terminal projections from these afferent nerves (Corson et al 2012;May and Hill 2006). In studies examining the oral receptive field properties of taste-sensitive neurons in the rNST, oral receptive field configurations in the horizontal plane were associated with afferent projections along the RC axis in the rNST (Halpern and Nelson 1965;Sweazey and Smith 1987;Travers and Norgren 1995).…”

Maintenance of Mouse Gustatory Terminal Field Organization Is Disrupted following Selective Removal of Peripheral Sodium Salt Taste Activity at Adulthood

“…Because the NST is angled ventrally from the caudal to rostral extents, these coronal sections best represent intermediate horizontal sections of the NST described earlier. Previous studies in rat and mice showed that all three afferent gustatory terminal fields terminate primarily in the rostral-central subdivision and, to a lesser extent, in the rostrallateral subdivision (Corson et al, 2012;Ganchrow et al, 2014). Consistent with what we found in the analysis of horizontal sections through the NST, there was qualitatively an overall increase in the amount of label associated with both GSP and CT but not IX (Fig.…”

“…6). Both the GSP and CT terminal fields extended more laterally in ␣ENaC KO animals than in controls, and almost all of the increase in label of these terminal fields was contained within the rostral-central subdivision of the NST and less so in the rostral-lateral subdivision (for a detailed description of the coronal subdivisions of the NST, see Corson et al, 2012;Ganchrow et al, 2014).…”