Roles of periaqueductal gray and nucleus tractus solitarius in cardiorespiratory function in the rat brainstem

Periaqueductal gray (PAG) and nucleus tractus solitarius (NTS) are importan t centres for regulation of cardiorespiratory function in cats. We aimed to study the effects of specific PAG stimulation on cardiorespiratory paramet ers in the rat. Microinjection of D,L-homocysteic acid (DLH) into dorsolate ral PAG of anaesthetised rats, led to: marked increases in respiratory freq uency (RF) and amplitude of diaphragmatic electromyogram, decreases in insp iratory and expiratory durations, and increased blood pressure and heart ra te. Following injection of propranolol (150 pmol, 30 nl), a beta-adrenergic antagonist, into the commissural subnucleus of NTS, the DLH-induced increa se in RI: was markedly attenuated. Inspiratory neurones (late I cells) in N TS were excited upon stimulation of PAG and their increased activity was ac companied by increased RF. The changes in activity of the late I cells in r esponse to stimulation of dorsolateral PAG provide physiological evidence o f a link, possibly noradrenergic, between the two nuclei and involvement of the NTS in control of respiratory functions orchestrated by the PAG. (C) 2 000 Elsevier Science B.V. All rights reserved.