Interaction between CO₂ and citrate ions in medullary reticular formation

¹ Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire

Ventilation was recorded in anesthetized rats during the injection of small quantities of Na citrate solution near the obex and during the application of electric pulses to the same region. Increases in Ve or ventilatory arrest were typical responses to these stimuli. Observations were made to determine whether either response could be altered by the inhalation of 10% CO₂ or 7% O₂ gas mixtures. Responses to 1.8 µl 2.8 mm Na citrate injections were diminished from controls while the animals were hyperventilating during CO₂ administration. In contrast, ventilatory responses to 1.4 mm Na citrate injections were potentiated during hyperventilation resulting from 7% O₂. Thus, hypercapnia depressed and hypoxia enhanced the excitability of those neurons of the medullary reticular formation which respond to citrate. The stabilizing action of calcium on the neurons is almost certainly removed by citrate. Several other carbohydrate intermediates besides citrate bind calcium ions as well. It is proposed that CO₂ under certain conditions might thereby regulate the repetitive discharge of certain groups of neurons in the medullary reticular formation.

Key Words: citrate effects on medulla • ventilatory responses by citrate and by electric pulses • ventilatory responses of anesthetized rats • citrate-CO₂ interaction • ventilatory responses from the reticular formation • alteration of ventilatory responses by CO₂

Submitted on October 4, 1963