OXYGEN-SENSING NEURONS IN THE CAUDAL HYPOTHALAMUS AND THEIR ROLE IN CARDIORESPIRATORY CONTROL

Work from this laboratory has shown that the caudal hypothalamus modul ates the cardiorespiratory responses to hypoxia. The purpose of this r eview is to describe the modulation of respiratory output by the cauda l hypothalamus during hypoxia and how neurons in this area respond to hypoxia. The diaphragmatic activity response to hypoxia was significan tly attenuated following microinjection of either cobalt chloride or k ynurenic acid into the caudal hypothalamus of rats. In addition, cauda l hypothalamic neurons in anesthetized rats and cats responded to hypo xia with an increased firing frequency. This response was maintained i n the absence of input from the vagus and carotid sinus nerves in the cat. When recorded extracellularly or by whole-cell patch clamp in vit ro, these neurons responded to hypoxia with an increase in firing freq uency, membrane potential and inward current. These results suggest th at the caudal hypothalamus exerts excitatory influence on respiration during hypoxia, that may originate from the ability of these neurons t o sense changes in oxygen levels. (C) 1997 Elsevier Science B.V.