  Central CO2chemosensitivity is crucial for all air-breathing vertebrates and
raises the question of itsrole in ventilatory rhythmogenesis. In this study,
neurograms of ventilatory motor outputs recorded infacial nerve of
premetamorphic and postmetamorphic tadpole isolated brainstems, under normo-
andhypercapnia, are investigated using Continuous Wavelet Transform spectral
analysis for buccal activityand computation of number and amplitude of spikes
during buccal and lung activities. Buccal burstsexhibit fast oscillations
(20-30 Hz) that are prominent in premetamorphic tadpoles: they result from
thepresence in periodic time windows of high amplitude spikes. Hypercapnia
systematically decreases thefrequency of buccal rhythm in both pre- and
postmetamorphic tadpoles, by a lengthening of the interburstduration. In
postmetamorphic tadpoles, hypercapnia reduces buccal burst amplitude and
unmasks smallfast oscillations. Our results suggest a common effect of the
hypercapnia on the buccal part of the CentralPattern Generator in all tadpoles
and a possible effect at the level of the motoneuron recruitment
inpostmetamorphic tadpoles.
