Source of ventilatory complexity in the postmetamorphic tadpole brainstem, Pelophylax ridibundus: A pharmacological study

The neural respiratory output of isolated brainstems of post-metamorphic tadpoles displays two motor patterns, the buccal and the lung rhythms. Their global dynamics are complex and chaos-like. This study aimed at determining the source of this complexity. The neural respiratory output was recorded during exposure to increasing concentration of DAMGO or to reduced chloride concentration. Complexity was quantified with the noise limit (NL) and the largest Lyapunov exponent (LLE) values. DAMGO decreased lung frequency (p < 0.0001), NL (p < 0.0001) and LLE (p = 0.0001) without changing buccal frequency (p = 0.2392). Reduced concentration of chloride decreased buccal frequency (p = 0.011) without changing lung frequency (p = 0.2393) whereas NL (p = 0.011) and LLE (p = 0.027) increased significantly. When taking all the recordings into account, NL and LLE were correlated to lung frequency (r = 0.661, p < 0.0001 and r = 0.3948, p = 0.0012, respectively) but not to buccal frequency (r = 0.1191, p = 0.3487 and r = 0.2083, p = 0.0985, respectively). Therefore, the lung neural oscillator is both necessary and sufficient to the ventilatory complexity in the isolated brainstem of the post-metamorphic tadpole.