Excitation of medullary neurons by chemical agents

Abstract

Ventilatory responses and certain postural and autonomic responses were studied following injection of isotonic solutions of HCO₃-, HPO₄-, or citrate into the medullary reticular formation of decerebrated or anesthetized cats. In most respects the responses resulting from any of the three compounds are comparable to the effects of an electric stimulus applied in the same region. Attention was directed primarily to production of a state of ventilatory arrest (apneusis) and/or an alteration in minute volume of ventilation (Ve) by the compounds. Positive responses measured in this way were obtained in roughly 75% of trials. Apneusis in inspiration or expiration was usually followed by either an increase or decrease in Ve. Variations in the pH of the solutions from 6.5 to 8.2 by the addition of CO₂ or by HCl failed to alter significantly the ventilatory responses. Also, 1.5% citrate was a less effective stimulus to produce apneusis than 3% citrate, 3.6% phosphate, or 1.3% bicarbonate. After the period of apneusis, ventilation was increased in 55% of trials when 1.5% citrate was used; however, with 3% citrate a decrease in ventilation was more frequently observed. It is proposed that this action of all three compounds is related to their property to reversibly bind calcium ions.