Abstract
Taste is one of the most important senses that allows for human survival. Recent electrophysiological investigations have revealed some information about the somatotopy of the rat nucleus tractus solitarius (NTS). The aim of this study was to assess rat NTS somatotopy using morphological techniques. Each animal was anesthetized and a retrograde axonal tracer, horseradish peroxidase, was injected intra- and submucosally into the anterior portion or the middle and posterior portions of the left half of rat tongue. After 24-48 hr, each rat was anesthetized again and perfusion-fixed. The brainstem was removed and cut in 50 μm-thick sections using a vibrotome. The sections were subjected to a tetramethylbenzidine-peroxidase reaction, and were then assessed under light-microscopy. The horseradish peroxidase that was deposited in the anterior third of the tongue labeled neuron cell bodies in the rostrofrontolateral region of the ipsilateral NTS, while that deposited in the middle and posterior thirds of the tongue labeled neuron cell bodies in the caudoposteromedial region of the ipsilateral NTS. There was no cross-projection. The morphological findings were in accord with the electrophysiological results in the literature. Retrograde labeling revealed a distinct pattern of neural projection that corresponded to the anterior portion, and the middle and posterior portions of the tongue.
