Transmitter substances contained in the petrosal ganglion cells determined by a double-labeling method in the rat

The presence of glutamate (Glu), aspartate (Asp) and substance P (SP) in the petrosal ganglion of rats anesthetized with pentobarbital sodium was studied using retrograde labeling of the carotid sinus nerve (CSN) with horseradish peroxidase (HRP) in combination with immunohistochemistry. (i) The incidence of HRP/Glu-labeled cells was the highest (32%, n = 3), followed in order by HRP/Asp-labeled cells (23%, n = 3) and HRP/SP-labeled cells (6%, n = 3). (ii) No significant difference was observed in the average diameter of HRP/Glu- and HRP/Asp-labeled cells, but the average diameter of HRP/SP-labeled cells was significantly larger than that of HRP/Glu- and HRP/Asp-labeled cells (P < 0.01). These results suggest that Glu may coexist with Asp, and SP-containing cells may form a different population from Glu- and Asp-containing cells in the petrosal ganglion. The physiological role of these transmitter substances is discussed.