Alterations in respiratory neuronal activities in the medullary 'pre-Bötzinger' region in hypocapnia.
'Pre-inspiratory' neuronal activities in a rostral ventrolateral medullary 'pre-Bötzinger' complex have been hypothesized to generate eupnea. Respiratory-modulated neuronal activities were recorded in this region in decerebrate, vagotomized, paralyzed, and ventilated cats, having bilateral carotid sinus nerve sections. As end-tidal partial pressures of carbon dioxide were reduced to hypocapnic levels, all neuronal activities which were tonic or expiratory inspiratory ('pre-inspiratory') either ceased or lost respiratory-modulation. Similarly, most expiratory and inspiratory expiratory activities did not maintain a phasic discharge. Half of the inspiratory neuronal activities did continue a phasic discharge, which commenced after phrenic activity or became independent of the phrenic rhythm. Results do not support a fundamental role of the 'pre-Bötzinger' complex in the neurogenesis of eupnea. Some neuronal activities can establish a phasic discharge in hypocapnia which is independent of the central respiratory rhythm. At normocapnia, this independent discharge is superseded and incorporated into the ponto-medullary respiratory neuronal circuit which generates eupnea.
St-John
W M
WM
Department of Physiology, Dartmouth-Hitchcock, Medical Center, Dartmouth Medical School, Lebanon, NH 03756-0001, USA. walter.stjohn@dartmouth.edu
D000818:Animals; D002415:Cats; D004594:Electrophysiology; D005260:Female; D016857:Hypocapnia / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D008526:Medulla Oblongata / Q000473:pathology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D010791:Phrenic Nerve / Q000503:physiopathology; D012137:Respiratory System / Q000294:innervation*