Differentiation of the cardio vascular center of the medulla

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The aim of this project is to identify premotor neurons in the medulla for i)cuataneous vasoconstrictors, ii)cardiac sympathetic nerve, iii)vasoconstrictors of muscles and iv)vasoconstrictors of the visceral organs.Experiments were performed in anesthetized (Urethane 1g/kg iv)and immobilized rabbits. Worming of the thermoreguratory center of the hypothalamus (the preoptic area of the anterior hypothalamus, POAH) evokes vasodilation of the skin. Using this response, reticulospinal (antidromically activated from the spinal cord) neurons whose activity reduced by worming of the POAH were searched in the rostral medulla. Some reticulospinal neurons in the rostral ventormedial reticular formation showed inhibitory response to this worm stimulation and its temporal response patters were very similar to responses of the cutaneous sympathetic nerves. Therefore, these neurons were concluded as candidates of the premotor neurons for the cutaneous vasoconstrictors.Inhalation of the low oxygen gas (3%) inhibits activity of the cardiac sympathetic nerves and reduces heart rate in vagotomized rabbits. Using this response, premotor neurons were searched in the rostral ventrolateral medulla (RVLM). About 20% of barosensitive reticulospinal neurons in the RVLM were inhibited by inhalation of low oxygen gas. Therefore, these neurons were thought to be premotor neurons for cardiac sympathetic nerves.We succeeded to identify two kinds of premotor neurons in the medulla and these data will be published soon.