Chronic hypercapnia modulates respiratory-related central pH/CO2 chemoreception in an amphibian, Bufo marinus.
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.
Gheshmy
Afshan
A
The Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada.
Vukelich
Robert
R
Noronha
Angelo
A
Reid
Stephen G
SG
D000818:Animals; D001933:Brain Stem / Q000502:physiology; D002024:Bufo marinus / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism*; D002628:Chemoreceptor Cells / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia; D066298:In Vitro Techniques; D012143:Respiratory Physiological Phenomena; D013116:Spinal Cord / Q000502:physiology
D002245:Carbon Dioxide