Viscerotopic representation of the upper alimentary tract in the rat: Sensory ganglia and nuclei of the solitary and spinal trigeminal tracts

TLDR

The study aimed to map the viscerotopic organization of the upper alimentary tract in the IXth and Xth cranial nerve ganglia and related medullary nuclei. In 172 rats, tracers (HRP, WGA‑HRP, CT‑HRP) were injected into the IXth and Xth cranial nerves and into the musculature and mucosa of the upper alimentary and respiratory tracts to trace afferent pathways. The tracers revealed a fused IX/X ganglion with overlapping topography, distinct NTS subnuclei innervated by different upper alimentary regions, and two main afferent groups: a viscerotopic NTS network for ingestive/respiratory reflexes and a PTI/spinal trigeminal pathway likely mediating visceral nociceptive/chemosensory reflexes.

Abstract

Abstract The aim of this study was to map the viscerotopic representation of the upper alimentary tract in the sensory ganglia of the IXth and Xth cranial nerves and in the subnuclei of the solitary and spinal trigeminal tracts. Therefore, in 172 rats 0.5–65 μl of horseradish peroxidase (HRP), wheat germ agglutinin‐HRP, or cholera toxin‐HRP were injected into the trunks and major branches of the IXth and Xth cranial nerves as well as into the musculature and mucosa of different levels of the upper alimentary and respiratory tracts. The results demonstrate that the sensory ganglia of the IXth and Xth nerves form a fused ganglionic mass with continuous bridges of cells connecting the proximal and distal portions of the ganglionic complex. Ganglionic perikarya were labeled in crude, overlapping topographical patterns after injections of tracers into nerves and different parts of the upper alimentary tract. After injections into the soft palate, pharynx, esophagus, and stomach, anterograde labeling was differentially distributed in distinct subnuclei in the nucleus of the tractus solitarius (NTS). Palatal and pharyngeal injections resulted primarily in labeling of the interstitial and intermediate subnuclei of the NTS and in the paratrigeminal islands (PTI) and spinal trigeminal complex. Esophageal and stomach wall injections resulted in labeling primarily of the subnucleus centralis and subnucleus gelatinosus, respectively. The distribution of upper alimentary tract vagal‐glossopharyngeal afferents in the medulla oblongata has two primary groups of components, i.e., a viscertopic distribution in the NTS involved in ingestive and respiratory reflexes and a distribution coextensive with fluoride‐resistant acid‐phosphatase‐positive regions of the PTI and spinal trigeminal nucleus presumably involved in visceral reflexes mediated by nociceptive or chemosensitive C fibers.