In 11 cordotomized (C2) rats with the vagi cut, monopolar electrical stimulation at a current intensity of 73+21 (S.E.) uA (n=6) to the intermediate region of the solitary nucleus elicited an increase (p<0.05) in regional blood flow (iodoantipyrine technique) of 71 % and 43 % in the frontal cortex and caudate nucleus, respectively. The findings suggest that some of the cardio-pulmonary and Cardio-vascular reflex mechanisms are involved in the regulation of the blood vessels of the brain. Key

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... ds: neurogenic control, vasopressin-induced pressor response. Purves and his colleagues (JAMES et al., 1969; PONTE and PURVES, 1974; JAMES and MACDONELL, 1975) first claimed that the cardio-vascular reflexes regulate the blood vessels of the brain. Activation of the baroreceptor and chemoreceptor could thus enhance autoregulatory vasoconstriction induced by increased arterial blood pressure and myogenic vasodilatation elicited by hypoxemia, respectively. Their results, however, have not been widely accepted by other investigators. The investigations reported to date were carried out more or less with physiological stimulation or inhibition of afferent apparatuses of the reflex, i.e., the baro-or chemoreceptor, or their afferent nerves. We thus attempted to demonstrate such regulation of the brain circulation by producing rather unspecific as well as forced activation of the reflex arcs. This activation was carried out by electrical stimulation of the medullary relay station of the reflex arcs, i.e., the intermediate region of the solitary nucleus (SOL). A preliminary account of the present work has been presented at the 60th Annual Meeting of the Physiological Society of Japan (NAKAI and OGINO, 1983) . Experiments were conducted on a total of 11 male Wistar rats weighing 306± 7 (S.E.) g. The animals were anesthetized (2% halothane), immobilized (d-tubocurarine, 0.5 mg/kg body weight, i.m.) and artificially ventilated. The cervical