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Received November 9, 2001
Accepted after revision January 25, 2002
1 Department of Medical Physiology, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1
2 Department of Medical Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada
3 Explorations Fonctionnelles Respiratoires, G.Hopital Pitié-Salpétriere, 47-83 boulevard de l'Hopital, 75651 Paris Cedex 13, France
* To whom correspondence should be addressed. E-mail: wilsonr{at}ucalgary.ca.
In Rana catesbeiana the upper airways are used for two distinct yet highly coordinated ventilatory behaviours: buccal ventilation and lung inflation cycles. How these behaviours are generated and coordinated is unknown. The purpose of this study was to identify putative rhythmogenic brainstem loci involved in these ventilatory behaviours. We surveyed the isolated postmetamorphic brainstem to determine sites where local depolarization, produced by microinjecting the non-NMDA glutamate receptor agonist, AMPA, augmented the ventilatory motor patterns. Two sites were identified: a caudal site, at the level of cranial nerve (CN) X, where AMPA injections caused increased buccal burst frequency but abolished lung bursts, and a rostral site, between the levels of CN VIII and IX, where injections increased the frequency of both types of ventilatory bursts. These two sites were further examined using GABA microinjections to locally inhibit cells. GABA injected into the caudal site suppressed the buccal rhythm but the lung rhythm continued, albeit at a different frequency. When GABA was injected into the rostral site the lung bursts were abolished but the buccal rhythm continued. When the two sites were physically separated by transection, both rostral and caudal brainstem sections were capable of rhythmogenesis. The results suggest the respiratory network within the amphibian brainstem is composed of at least two distinct but interacting oscillators, the buccal and lung oscillators. These putative oscillators may provide a promising experimental model for studying coupled oscillators in vertebrates.
(Resubmitted 9 November 2001; accepted after revision 25 January 2002)
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