A Semiquantitative Analysis of the Chorda Tympani Taste Pathway in the Rat Brain with the 2-deoxyglucose Method

Abstract

This thesis is based on a semiquantitative analysis of four nuclear relay centers [nucleus tractus solitarius (NTS), parabrachial nucleus (PBN), ventroposteromedial nucleus (VPM), gustatory neocortex (GNC)] in the chorda tympani nerve pathway. Metabolic changes were examined by the 2-deoxyglucose method in which one chorda tympani nerve was chemically stimulated and its contralateral side lesioned. Coronal sections of four taste centers were prepared for autoradiography and Nissl staining. Densities of the autoradiograms were determined by means of a video based image processor. Relative differences in the optical density ratios of the stimulated versus lesioned nuclear grey matter areas to white matter areas indicate an effect of the stimulation on the uptake of the radioactive glucose analog. Greater 2-deoxyglucose uptake on the intact side reflects increased cellular functional activity which was noted in the first (NTS) and possibly the second (PBN) levels of the chorda tympani pathway. The highest brain levels showed no significant changes in glucose metabolism. The 2-deoxyglucose method was verified in this study by several criteria and the neuroanatomy of the chorda tympani is discussed. Also, improvements for the study of the taste pathway using the 2-deoxyglucose method are suggested. Metabolic increases in some taste nuclei support the thesis that the chorda tympani projection pathway as reported in previous literature can be demonstrated and analyzed semiquantitatively using the 2-deoxyglucose method