BAROSENSITIVE AND CHEMOSENSITIVE NEURONS IN THE RAT MEDULLA - A DOUBLE-LABELING STUDY WITH C-FOS GLUTAMATE, GAD, PNMT AND CALBINDIN/

The purpose of this study was to survey distribution and density of th e barosensitive and chemosensitive neurons in the medulla of rats anes thetized with fentanyl/midazolam, using immunohistochemical methods. A fter stimulation of the arterial baroreceptor or the chemoreceptor, we identified c-Fos-labeled neurons with immunoreactions to antisera of glutamate, PNMT, GAD and calbindin in the nucleus tractus solitarii (N TS) and the ventrolateral medulla (VLM). The double-labeled neurons we re located in the medial part of the NTS, and in the lateral part of t he paragigantocellular reticular nucleus and the ventral division of t he ambiguus nucleus. Main findings were as follows: (1) No significant difference was found in distribution and density of glutamatergic, ad renergic and calbindin-containing neurons between the barosensitive an d chemosensitive types; (2) a few GABAergic neurons were distributed a lmost evenly in the NTS and VLM, and in these neurons the barosensitiv e type outnumbered the chemosensitive one; (3) glutamatergic and calbi ndin-containing neurons were dominant in the NTS; adrenergic neurons i n the VLM; (4) as for the adrenergic neurons in the NTS, the chemosens itive type significantly outnumbered the barosensitive one. This study showed that distribution and density of the barosensitive neurons, ei ther glutamatergic, adrenergic, or calbindin-containing neurons, overl apped with those of the chemosensitive corresponding neurons, suggesti ng presence of the neural matrix of the cardiopulmonary interaction. E xceptionally, the number of the barosensitive GABAergic neurons was si gnificantly larger than that of the chemosensitive GABAergic ones.