[Vascular reactivity of the brain in the pigeon Columba livia]

In experiments on awake relatively unrestrained pigeons, studies have been made on the reactions of the cerebrovascular bed to fixed functional loads of physical (orthostasis) and chemical (inhalation of hypoxic and hypercapnic gas mixtures) nature. Using hydrogen clearance method, the increase in the intensity of local cerebral blood flow in different structures of the telencephalon during inhalation of the mentioned gas mixtures was demonstrated. Bilateral vagotomy resulted in inversed reactions. Influence of functional loads was accompanied by changes in rheoencephalographic parameters. The data obtained suggest the existence of an evident reactivity of cerebral vessels in birds which is controlled by neurogenic mechanism of regulation of vascular tone.