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First published online March 2, 2006
Journal of Experimental Biology 209, 1135-1146 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02106

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Chronic hypercapnia modulates respiratory-related central pH/CO₂ chemoreception in an amphibian, Bufo marinus

Afshan Gheshmy, Robert Vukelich, Angelo Noronha and Stephen G. Reid^*

The Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada

^* Author for correspondence (e-mail: sgreid{at}utsc.utoronto.ca)

Accepted 24 January 2006

Anuran amphibians have multiple populations of pH/CO₂-sensitive respiratory-related chemoreceptors. This study examined in cane toads (Bufo marinus) whether chronic hypercapnia (CHC) altered the pH/CO₂ sensitivity of central respiratory-related chemoreceptors in vitro and whether CHC altered the acute hypercapnic ventilatory response (HCVR; 5% CO₂) in vivo. Toads were exposed to CHC (3.5% CO₂) for 9 days. In vitro brainstem–spinal cord preparations were used to examine central respiratory-related pH/CO₂ chemosensitivity. CHC augmented in vitro fictive breathing as the pH of the superfusate was lowered from 8.2 to 7.4. Midbrain transection in vitro (at a level known to reduce the clustering of breaths) did not alter this augmentation. In vivo, CHC did not alter the acute HCVR but midbrain transection changed the breathing pattern and increased the overall level of ventilation. CHC did not alter the effect of olfactory CO₂ chemoreceptor denervation on the acute HCVR in vivo but did alter the response when returned to normal air. The results indicate that CHC increases the response of central pH/CO₂ chemoreceptors to changes in cerebrospinal fluid pH in vitro yet this increase is not manifest as an increase in the HCVR in vivo.

Key words: brainstem–spinal cord, central pH/CO₂ chemoreceptors, chronic hypercapnia, hypercapnic ventilatory response, olfactory CO₂ chemoreceptor, cane toad, Bufo marinus

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				A. Gheshmy, A. Anari, D. Besada, and S. G. Reid Afferent input modulates the chronic hypercapnia-induced increase in respiratory-related central pH/CO2 chemosensitivity in the cane toad (Bufo marinus) J. Exp. Biol., January 15, 2007; 210(2): 227 - 237. [Abstract] [Full Text] [PDF]