Effects of phrenicotomy and exercise on hypoxia-induced changes in phrenic motor output.
To investigate models of plasticity in respiratory motor output, we determined the effects of chronic unilateral phrenicotomy and/or exercise on time-dependent responses to episodic hypoxia in the contralateral phrenic nerve. Anesthetized (urethane), ventilated, and vagotomized rats were presented with three, 5-min episodes of isocapnic hypoxia (11% O(2)), separated by 5 min of hyperoxia (50% O(2)). Integrated phrenic (and hypoglossal) nerve discharge were recorded before and during each hypoxic episode, for the first 5 min after the first hypoxic episode, and at 30 and 60 min after the final episode. Of 36 rats, one-half were sedentary while the other one-half had free access to a running wheel; each of these groups was split into three subgroups: 1) unoperated, 2) chronic left phrenicotomy (27-37 days), and 3) sham operated. Neither unilateral phrenicotomy nor running wheel activity influenced the short-term hypoxic phrenic response (during hypoxia) or long-term facilitation (posthypoxia). Posthypoxia frequency decline was exaggerated in phrenicotomized-sedentary rats relative to unoperated-sedentary rats (change in burst frequency = -23+/-4 vs. -11 +/-5 bursts/min, respectively; 5 min posthypoxia; P<0.05), an effect that was eliminated by spontaneous exercise. The results indicate that neither voluntary running nor unilateral phrenicotomy has major effects on time-dependent hypoxic phrenic responses, with the exception of an unexpected effect of phrenicotomy on posthypoxia frequency decline in sedentary rats.
Bach
K B
KB
Department of Comparative Biosciences and Center for Neuroscience, University of Wisconsin, Madison, Wisconsin 53706, USA.
Mitchell
G S
GS
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D003714:Denervation; D007002:Hypoglossal Nerve / Q000502:physiology; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D010791:Phrenic Nerve / Q000166:cytology / Q000502:physiology* / Q000601:surgery*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012132:Respiratory Muscles / Q000294:innervation / Q000502:physiology