Taste systems of the petrosal ganglion of the rat glossopharyngeal nerve

Abstract

Single unit recordings were taken from sensory ganglion cells in the petrosal ganglion (PG) of the glossopharyngeal nerve of the rat. These taste units were examined with respect to spontaneous and evoked discharge patterns and responsiveness to a wide variety of chemical compounds, most of natural occurrence. Spontaneous activity patterns, with few exceptions, tended to be extremely irregular with both bursting (clusters of 2–3 spikes) and grouping (large groups of spikes as in evoked discharges). Most interspike interval histograms of spontaneous activity were multimodal, similar to rat geniculate ganglion (GG) units. Evoked discharges usually displayed grouping of spikes, and long latencies of onset and persistence of discharge after rinse were sometimes seen. Little response was shown to nucleotides or salts. Units responsive to amino acids tended to show large discharge to only one or two amino acids; and the most responsive amino acid usually varied from cell to cell. Units responsive to alkaloids only responded to a few alkaloids with atropine and quinine being the most stimulatory. Units responsive to acids only discharged to a few of the acids tested and often acids of low pH elicited no discharge. Saccharin activated units responsive to both sugar and alkaloids. A few units highly responsive to both sugar and alkaloids were seen. The units were placed into four clusters on the basis of chemicals activating them and certain neurophysiological characteristics: PG salt units, PG acid units and, tentatively, amino acid (sugar) units and X (alkaloid and alkaloid plus) units. The PG salt units did not show the exclusive sensitivity to sodium and lithium compounds as did the GG salt units. The PG acid units could also be differentiated from the GG acid units. The petrosal amino acid and X units, on the other hand, could not be differentiated from similar units in the rat GG.