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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

View larger version (25K): [in a new window]   Fig. 1. Variables associated with fictive breathing recorded from the in vitro brainstem–spinal cord preparation at pH levels ranging from 7.4 to 8.2. (A) Fictive breath frequency; (B) episodes per minute; (C) breaths per episode; (D) integrated vagal activity; (E) fictive breath duration. The data are reported as the mean ± 1 s.e.m. *Significant difference from the value at pH 8.2; significant difference between the control and chronically hypercapnic groups. The solid bold line through the data in A is a first order regression line (control, r2=0.83; chronic hypercapnia, r2=0.96). The dotted lines are 95% confidence intervals.

View larger version (16K): [in a new window]   Fig. 2. The effects of midbrain transection on fictive (A) breathing frequency, (B) episodes per minute and (C) breaths per episode recorded in vitro from control (open symbols) and chronically hypercapnic (CHC; closed symbols) brainstem–spinal cord preparations. Circles and squares represent values recorded prior to and following midbrain transection, respectively. *Significant difference from the value at pH 8.0 within any given group; significant difference between the control and CHC groups; significant difference before and after transection in either group.

View larger version (12K): [in a new window]   Fig. 3. Variables associated with breathing during a 9 day exposure to CHC in vivo. (A) Breathing frequency; (B) episodes per minute; (C) breaths per episode. *Significant difference from the day 0 value. The letter `a' indicates a significant difference (on days 2–9) from the value on day 1.

View larger version (37K): [in a new window]   Fig. 4. The effects of CHC and midbrain transection on the acute hypercapnic ventilatory response recorded in vivo. Open symbols represent control (Cont) animals; closed symbols represent chronically hypercapnic (CHC) animals. Circles and squares represent values recorded prior to (intact) and following (transected) in vivo midbrain transection, respectively. (A) Breathing frequency; (B) breaths per episode; (C) episodes per minute; (D) breath amplitude; (E) total ventilation index; (F) breath duration. *Significant difference from the value at [CO2]=0% within any given group; significant difference between the control and CHC groups; significant difference before and after transection in either group.

View larger version (24K): [in a new window]   Fig. 5. The effects of chronic hypercapnia (CHC) (C,D) or control normocapnia (A,B) on the breathing frequency response to acute hypercapnia in vivo with the olfactory nerves intact (A,C) or denervated (B,D). The letters `a', `b' and `c' indicate that the three values in each panel are significantly different from one another. The asterisk in B indicates a significant difference from the first air value (white bar).