Respiratory and Cardiovascular Responses to Electrical Stimulation of the Avian Brain with Emphasis on Inhibitory Mechanisms

Abstract

Respiratory and circulatory responses to electrical brain stimulation were studied in 30 anesthetized chicken from about 850 histologically verified loci in an attempt 1) to delineate the limits and characterize the response patterns of a thalaniic cardioinhibitory area (Putkonen 1967) and 2) to extend exploration of respiratory and circulatory functions of the avian brain to telecephalic and mesencephalic levels. Apnea or partial respiratory inhibition were obtained from; 1) an anterolateral thalamic field in front and around the nurotundus, 2) the entire course of the quinto-frontal tract, which was the only forebrain site yielding apnea and from 3) a medial and a lateral mesencephalic area. The apnea from the antero-lateral thalamus was associated with progressive bradycardia and fall in blood pressure which both could be almost abolished during tracheal infusion of oxygen. Apneic bradycardia from the mesencephalic quinto-frontal tract was associated with hypertension thus mimicking the “diving reflex”. Varying patterns of respiratory and circulatory activation, often with vocalizations, were obtained from; 1) septal and preoptic areas, 2) medial archistriatal regions, 3) the occipito-mesencephalic tract and from 4) a large field in the mesencephalic lateral reticular formation. The results are discussed in relation to pertinent literature from birds and mammals with an emphasis on inhibitory mechanisms.