New insights in gill/buccal rhythm spiking activity and CO2 sensitivity in pre- and postmetamorphic tadpoles (Pelophylax ridibundus)

•Analysis of the buccal activity of facial nerve neurograms recorded in vitro in a European frog species, Pelophylax ridibundus.•Continues Wavelet Transform spectra, gill/buccal cycle segmentation and positioning using cross-correlation function.•Fast frequency buccal intraburst oscillations (20-30 Hz).•Lengthening of the buccal interburst period induced by hypercapnia in both pre- and postmetamorphic tadpoles.•Increase of the occurrence of episodic lung bursts in hypercapnia in Pelophylax ridibundus.

Central CO2 chemosensitivity is crucial for all air-breathing vertebrates and raises the question of its role in ventilatory rhythmogenesis. In this study, neurograms of ventilatory motor outputs recorded in facial nerve of premetamorphic and postmetamorphic tadpole isolated brainstems, under normo- and hypercapnia, are investigated using Continuous Wavelet Transform spectral analysis for buccal activity and computation of number and amplitude of spikes during buccal and lung activities. Buccal bursts exhibit fast oscillations (20-30 Hz) that are prominent in premetamorphic tadpoles: they result from the presence in periodic time windows of high amplitude spikes. Hypercapnia systematically decreases the frequency of buccal rhythm in both pre- and postmetamorphic tadpoles, by a lengthening of the interburst duration. In postmetamorphic tadpoles, hypercapnia reduces buccal burst amplitude and unmasks small fast oscillations. Our results suggest a common effect of the hypercapnia on the buccal part of the Central Pattern Generator in all tadpoles and a possible effect at the level of the motoneuron recruitment in postmetamorphic tadpoles.