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First published online June 11, 2007
Journal of Experimental Biology 210, 2046-2056 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003202
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Effects of medullary Raphé stimulation on fictive lung ventilation during development in Rana catesbeiana

Olivier Belzile1, Roumiana Gulemetova2 and Richard Kinkead2,*

1 Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA
2 Department of Pediatrics, Laval University, Centre de Recherche Hôpital St-François d'Assise, Québec City, Québec, G1L 3L5, Canada

* Author for correspondence (e-mail: richard.kinkead{at}crsfa.ulaval.ca)

Accepted 13 March 2007

To better understand serotonergic modulation of air breathing during bullfrog development, we measured changes in fictive lung ventilation frequency associated with focal stimulation of the rostral region of the medullary Raphé neurons. Electrical (3 to 33 Hz) and chemical (glutamate microinjections; 0.5 mol l–1, 0.3–10 nl) activation of Raphé neurons was performed in brainstem preparations from three developmental stages (pre- and metamorphic tadpoles and adult frogs). Fictive lung ventilation was recorded extracelluarly from the Vth and Xth cranial nerves. Electrical stimulation of Raphé neurons caused a frequency-dependent increase in lung burst frequency in pre-metamorphic tadpoles only. In metamorphic tadpoles, an increase in fictive lung ventilation was observed at 20 Hz only. Electrical stimulation had no effect in preparations from adult frogs. Glutamate microinjections elicited similar responses as a lung burst frequency increase was observed in the pre-metamorphic group only. Regardless of the stimulation technique used, the increase in fictive lung ventilation was attenuated by the selective 5-HT3 antagonist tropisetron (5–20 µmol l–1). Results from immunohistochemical analysis of the Raphé region stimulated do not correlate with functional data as the number of 5-HT immunoreactive neurons within this region increases during development. We conclude that, in this preparation, stimulation of lung ventilation by the medullary Raphé is restricted to early (pre-metamorphic) stages.

Key words: brainstem, bullfrog, control of breathing, development


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© The Company of Biologists Ltd 2007