The nerves innervating the tongue were stimulated electricany and multineuron responses were recorded i n the nucleus of the solitary tract. Stimulation of the chorda tympani and the IXth nerves evoked responses in the lateral and medial ipsilateral solitary nucleus in a rostral-caudal order. Responses to lingual nerve stimulation were found only i n the lateral, larger-celled portion of the ipsilateral solitary nucleus overlapping the chorda tympani and the IXth nerve areas. Stimulation of the above three nerves also evoked somewhat longer latency responses in the ambiguus nucleus. Responses to lingual nerve stimulation were found i n the XIIth nerve motor nucleus and the solitary nucleus at the level of the obex using high voltage levels of stimulation. The results were discussed in terms of the anatomical discreteness of the relays of the gustatory and the other tongue modalities in the solitary nucleus. These results were obtained in the white rats.Three nerves innervate the receptors of the tongue. The lingual, chorda tympani and IXth nerves supply fibers to the mechanical and thermal tongue receptors. The chorda tympani and IXth nerves also innervate gustatory receptors. In this experiment the nerves innervating the tongue receptors were stimulated electrically and multi-neuron responses recorded in the nucleus of the solitary tract. The results show the relationship among the terminal regions for the tongue afferents in the solitary nucleus. METHODSTwenty-three Sprague-Dawley rats weighing 250-300 gms were anesthetized with intraperitoneal injections of nembutal (40 mg/kg). The chorda tympani, the lingual or the IXth nerve was dissected free, cut, tied and stimulated electrically. The lingual nerve was stimulated in nine rats and the chorda tympani nerve was stimulated in six rats. Both nerves were stimulated at the point where they form a common bundle and stimulation was limited to one by section of the other central to the region in which they branch and become separate nerves. The IXth nerve was stimulated in eight rats at a point just central to the hyoid cartilage. The nerve was placed on a pair of silver electrodes and stimulated with a 0.5-1.0 volt, 1.0 msec square wave presented at J. COMP. NEUR., 124: 127-130.
Following determination of gustatory thresholds for QHC1 for 21 white rats using the 2-bottle preference method, lesions were placed in the tongue region of the nucleus of the solitary tract (STn) of the rats and postoperative threshold tests were determined. Evidence from 9 of the 21 rats showed that bilateral lesions in the tongue region of the STn resulted in an elevation of the mean threshold for QHC1 from a preoperative level of 32 X 10"°m olar to a level as high as 959 X 10"" molar postoperatively. Removal of the olfactory bulbs in 4 of the 9 rats indicated that gustatory deficits were not influenced by olfactory cues from the QHC1 solutions.
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