Breathing of awake goats during prolonged dysfunction of caudal M ventrolateral medullary neurons

H. V. Forster, L. G. Pan, T. F. Lowry, T. Feroah, W. M. Gershan, A. A. Whaley, M. M. Forster, B. Sprtel

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Abstract

Cooling the caudal M ventrolateral medullary (VLM) surface for 30 s results in a sustained apnea in anesthetized goats but only a 30% decrease in breathing in awake goats. The purpose of the present study was to determine, in the awake state, the effect of prolonged (minutes, hours) caudal M neuronal dysfunction on eupneic breathing and CO2 sensitivity. Dysfunction was created by ejecting excitatory amino acid receptor antagonists or a neurotoxin on the VLM surface through guide tubes chronically implanted bilaterally on a 10- to 12-mm2 portion of the caudal M VLM surface of 12 goats. Unilateral and bilateral ejections (1 μl) of selective antagonists for N-methyl-D-aspartic acid or non-N-methyl-D-aspartic acid receptors had no significant effect on eupneic breathing or CO2 sensitivity. Unilateral ejection of a nonselective excitatory amino acid receptor antagonist generally had no effect on eupneic breathing or CO2 sensitivity. However, bilateral ejection of this antagonist resulted in a significant 2-Torr hypoventilation during eupnea and a significant reduction in CO2 sensitivity to 60 ± 9% of control. Unilateral ejection of the neurotoxin kainic acid initially stimulated breathing; however, breathing then returned to near control with no incidence of apnea. After the kainic acid ejection, CO2 sensitivity was reduced significantly to 60 ± 7% of control. We conclude that in the awake state a prolonged dysfunction of caudal M VLM neurons results in compensation by other mechanisms (e.g., carotid chemoreceptors, wakefulness) to maintain near-normal eupneic breathing, but compensation is more limited for maintaining CO2 sensitivity.

Original languageEnglish (US)
Pages (from-to)129-140
Number of pages12
JournalJournal of applied physiology
Volume84
Issue number1
DOIs
StatePublished - Jan 1998

Keywords

  • Excitatory amino acid receptors
  • Regulation of breathing
  • Ventrolateral medulla

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    Forster, H. V., Pan, L. G., Lowry, T. F., Feroah, T., Gershan, W. M., Whaley, A. A., Forster, M. M., & Sprtel, B. (1998). Breathing of awake goats during prolonged dysfunction of caudal M ventrolateral medullary neurons. Journal of applied physiology, 84(1), 129-140. https://doi.org/10.1152/jappl.1998.84.1.129