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First published online August 17, 2007
Journal of Experimental Biology 210, 3015-3026 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005983

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Developmental changes in central O₂ chemoreflex in Rana catesbeiana: the role of noradrenergic modulation

Stéphanie Fournier, Mathieu Allard, Stéphanie Roussin and Richard Kinkead^*

Department of Pediatrics, Université Laval, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Québec City, QC, Canada

View larger version (19K): [in this window] [in a new window]   Fig. 1. The effects of exposing brainstem preparations to acute hypoxia on (A) lung burst frequency (N=7 in each group) and (B) buccal burst frequency. These experiments were performed on brainstems from pre-metamorphic tadpoles (grey) and adult bullfrogs (black). Representative trigeminal neurograms (V, trigeminal nerve) showing changes in fictive breathing during hypoxia are shown on the right. Note that the neurograms shown in B correspond to parts of those in A but on shorter time scale, to illustrate the two types of fictive breathing movements produced by this preparation. For these neurograms, the y-axis scales are the same in both panels. Values are means ± s.e.m. *Value statistically different from baseline at P<0.05.

View larger version (15K): [in this window] [in a new window]   Fig. 2. (A,B) The effects of the selective 1-adrenoceptor antagonist prazosine (Pr; 0.5 µmol l–1) and the selective 2-adrenoceptor antagonist RX821002 (RX; 25 µmol l–1) on the fictive lung ventilation frequency response to hypoxia measured in (A) the pre-metamorphic (control, N=7; Pr, N=5; RX, N=10) and (B) adult groups (control, N=7; Pr, N=6; RX, N=6). Note that in these figures, the control data (grey symbols; broken line) was transposed from Fig. 1 to facilitate comparisons. Trigeminal neurograms (V, trigeminal nerve) showing changes in respiratory-related motor output under baseline and hypoxic conditions in the presence of the antagonists prazosine or RX 821002 in both stage groups are shown on the right. Values are means ± s.e.m. *Value statistically different from baseline at P<0.05.

View larger version (23K): [in this window] [in a new window]   Fig. 3. (A) Stage-dependent changes in fictive lung burst frequency during noradrenaline (NA; 5 µmol l–1) application. The histograms (left) show the mean data and the trigeminal neurograms (V, trigeminal nerve; right) show representative recordings obtained under baseline conditions and following NA bath application. Data are reported for both stage groups (pre-metamorphic: grey bars, N=6; and adults: black bars, N=6). (B,C) The same experiment was performed in the presence of the GABAA/glycine antagonist mixture (bicuculline 1.25 µmol l–1/strychnine 1.5 µmol l–1) in both stage groups. For these experiments, representative trigeminal neurograms showing respiratory-related activity observed under each condition are shown below the histograms. Values are means ± s.e.m. *Values statistically different from baseline at P<0.05; value statistically different from corresponding mixture value at P<0.05.

View larger version (11K): [in this window] [in a new window]   Fig. 4. (A) Stage-dependent changes in fictive lung burst frequency during bath application of the 1-adrenoceptor agonist phenylephrine (Phe; 25 µmol l–1). (B,C) The effects of Phe application on lung burst frequency in the presence of the GABAA/glycine antagonist mixture (bicuculline 1.25 µmol l–1/strychnine 1.5 µmol l–1) in (B) the pre-metamorphic and (C) adult groups (N=6, each group). Values are means ± s.e.m. *Values statistically different from baseline at P<0.05.

View larger version (10K): [in this window] [in a new window]   Fig. 5. (A) Stage-dependent changes in fictive lung burst frequency during bath application of the 2-adrenoceptor agonist clonidine (Clo; 25 µmol l–1). (B,C) The effects of Clo application on lung burst frequency in the presence of the GABAA/glycine antagonist mixture (bicuculline 1.25 µmol l–1/strychnine 1.5 µmol l–1) in (B) the pre-metamorphic and (C) adult groups (N=6, each group). Values are means ± s.e.m. *Values statistically different from baseline at P<0.05; value statistically different from corresponding mixture value at P<0.05.

View larger version (10K): [in this window] [in a new window]   Fig. 6. Effects of GABAA/glycine antagonist mixture (bicuculline 1.25 µmol l–1/strychnine 1.5 µmol l–1) bath application on lung burst frequency under `baseline' and hypoxic conditions. The histograms show lung burst frequency measured at the end of the 10 min hypoxic period in the presence of the antagonist mixture. These experiments were performed on preparations from pre-metamorphic tadpoles (A; grey bars, N=6) and adult bullfrogs (B; black bars, N=6). (C) In adults, these experiments were also performed using low [HCO –3] aCSF (tadpole) (N=4) to determine whether the composition of the aCSF contributes to the effect observed in B. Values are means ± s.e.m. *Value statistically different from baseline at P<0.05; values statistically different from corresponding mixture values at P<0.05.

View larger version (10K): [in this window] [in a new window]   Fig. 7. Effects of bath application of the selective GABAB agonist baclofen (0.5 µmol l–1) on lung burst frequency response to application of the 1-adrenoceptor agonist phenylephrine (Phe; 25 µmol l–1) in (A) the pre-metamorphic (N=5) and (B) adult groups (N=4). To facilitate comparisons, control data from both stage groups (grey symbols, broken lines; N=6 in each group) were transposed from Fig. 4. Trigeminal neurograms (V, trigeminal nerve) presented below show representative respiratory-related activity recorded under each condition. Values are means ± s.e.m. *Values statistically different from baseline at P<0.05.

View larger version (10K): [in this window] [in a new window]   Fig. 8. Effects of the selective GABAB agonist baclofen (0.5 µmol l–1) on the lung burst frequency responses to hypoxia in (A) the pre-metamorphic group and (B) adult group. Responses were measured under control (drug-free) conditions (N=7, in each group) and in the presence of baclofen (N=6, in each group). Note that in these figures, the control data (grey symbols, broken lines) were transposed from Fig. 1 to facilitate comparisons. Trigeminal neurograms (V, trigeminal nerve) presented below show representative respiratory-related activity recorded under each condition. Values are means ± s.e.m. *Values statistically different from baseline at P<0.05.

View larger version (19K): [in this window] [in a new window]   Fig. 9. Buccal burst frequency data obtained during each series of experiments for brainstem preparations from pre-metamorphic tadpoles (grey bars) and adult bullfrogs (black bars). Data were obtained before and after application of (A) noradrenaline (NA; 5 µmol l–1), (B) GABAA/glycine antagonist mixture (bicuculline 1.25 µmol l–1/strychnine 1.5 µmol l–1), (C) the 1-adrenoceptor agonist phenylephrine (Phe; 25 µmol l–1), (D) the 2-adrenoceptor agonist clonidine (Clo; 25 µmol l–1), or (E) aCSF hypoxia. Note that application of the bicuculine/strychnine mixture abolished fictive buccal burst frequency in all preparations (only data from NA experiments are shown), and this could not be restored by any experimental treatment. Values are means ± s.e.m. *Values statistically different from baseline at P<0.05; **values statistically different from baseline at P<0.10.