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First published online January 8, 2007
Journal of Experimental Biology 210, 227-237 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02606

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Afferent input modulates the chronic hypercapnia-induced increase in respiratory-related central pH/CO₂ chemosensitivity in the cane toad (Bufo marinus)

Afshan Gheshmy, Ali Anari, Donela Besada and Stephen G. Reid^*

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

View larger version (24K): [in this window] [in a new window]   Fig. 1. Fictive breathing (vagal motor output) recorded from isolated brainstem-spinal cord preparations (at pH 7.5) taken from (A) control toads with the olfactory nerves intact, (B) control toads following olfactory denervation, (C) chronically hypercapnic toads with the olfactory nerves intact and (D) chronically hypercapnic toads following olfactory denervation. In all cases the upper trace represents the raw electroneurogram (eng X) and the lower trace ( eng X) represents the integrated electroneurogram.

View larger version (21K): [in this window] [in a new window]   Fig. 2. The effects of chronic hypercapnia (CHC) and olfactory denervation (OD) on (A,B) fictive breathing frequency (fictive breaths min-1), (C,D) the number of fictive episodes min-1 and (E,F) the number of fictive breaths per episode recorded from in vitro brainstem-spinal cord preparations taken from control (A,C,E) and CHC (B,D,F) toads. Open symbols represent preparations taken from animals with the olfactory nerves intact (OI). Filled symbols represent preparations taken from animals in which the olfactory nerves were cut (OD) prior to CHC. The data are plotted as the mean ± 1 s.e.m. Letters (a-c) represent significant differences between ventilatory parameters measured at different artificial cerebral spinal fluid (aCSF) pH levels within any group. A number sign (#) represents a difference between the OI and OD groups. A plus sign (+) represents a difference between the control and CHC groups (comparing panel A with B, C with D and E with F).

View larger version (22K): [in this window] [in a new window]   Fig. 3. The effects of chronic hypercapnia (CHC) and olfactory denervation (OD) on (A,B) integrated area of the fictive breaths (Vxs), (C,D) the total fictive ventilation index (Vxs min-1) and (E,F) fictive breath duration (s) recorded from in vitro brainstem-spinal cord preparations taken from control (A,C,E) and CHC (B,D,F) toads. The data are plotted as the mean ± 1 s.e.m. Symbols and abbreviations are the same as those in Fig. 2.

View larger version (28K): [in this window] [in a new window]   Fig. 4. The effects of chronic hypercapnia (CHC; open squares), chronic hyperoxia (CHO; filled circles) and chronic hyperoxic hypercapnia (CHH; filled triangles) on (A) fictive breathing frequency (fictive breaths min-1), (B) fictive episodes min-1, (C) fictive breaths per episode, (D) integrated fictive breath area (Vxs), (E) total fictive ventilation index (Vxs min-1) and (F) fictive breath duration (s) recorded from in vitro brainstem-spinal cord preparations. The data are plotted as the mean ± 1 s.e.m. Letters (a-c) represent significant differences at the different artificial cerebral spinal fluid (aCSF) pH levels within any group. A plus sign (+) represents a difference from the CHC value. A number sign (#) represents a difference from the CHH value.

View larger version (22K): [in this window] [in a new window]   Fig. 5. (A,B) Breathing frequency (breaths min-1), (C,D) integrated breath area (Vxs) and (E,F) total ventilation index (Vxs min-1) as a function of the inspired CO2 level recorded in vivo from control (A,C,E) and CHC (B,D,F) toads. Open circles (A,C,E) and open squares (B,D,F) represent animals with the olfactory nerves intact (OI). Filled circles (A,C,E) and filled squares (B,D,F) represent animals that underwent olfactory denervation (OD) prior to the 10-day period of CHC (or control conditions). The data are plotted as the mean ± 1 s.e.m. Letters (a-c) represent significant differences at the different inspired CO2 levels within any group. A number sign (#) represents a difference between the OI and OD groups. A plus sign (+) represents a difference between the control and CHC groups (comparing panel A with B, C with D and E with F).

View larger version (12K): [in this window] [in a new window]   Fig. 6. (A) Breathing frequency (breaths min-1), (B) integrated breath area (Vxs) and (C) total ventilation index (Vxs min-1) as a function of inspired CO2 levels recorded in vivo from toads exposed to CHC (circles) or CHH (triangles). The data are plotted as the mean ± 1 s.e.m. Letters (a-c) represent significant differences at the different inspired CO2 levels within any group. A number sign (#) represents a difference between the CHC and CHH groups.

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