BLOOD-PRESSURE REGULATION BY AORTIC BARORECEPTORS IN BIRDS

This review summarizes current knowledge of avian baroreceptor locatio n, innervation pattern, and function. Birds have one set of arterial b aroreceptors associated with the root of the aortic arch and innervate d bilaterally by the aortic nerves, branches of the vagus originating from the nodose ganglia. There is a tonic level of baroreceptor input to the baroregulatory mechanisms in the brain stem, and this barorecep tor input is necessary for the maintenance of normotensive pressure in birds Arterial blood pressure rises acutely and remains chronically e levated after barodenervation. Few studies of baroreceptor or barorefl ex function have been made in birds. Baroreceptors discharge in systol e with properties similar to high-threshold, slowly, adapting mammalia n baroreceptors. Evaluating the results of studies of baroreflex funct ion in birds is problematic, since these studies were inconsistent in methodology. They were done in either awake or anesthetized animals, a nd several different methods for varying arterial pressure were used. It is recommended that baroreflex function be assessed by examining th e correlation between spontaneously occurring values of heart rate or cardiac output and arterial pressure measured simultaneously in awake, unrestrained animals. The contribution of baroreceptors to cardiovasc ular control during exercise and submersion, and possible roles of the baroreflex in homeostasis, are discussed. This review emphasizes the lack of data about the nature of baroreceptors and their participation in the integrated control of the circulation in birds.