Fig. 1. Effects of 2 h hypoxia on respiratory-related neural activity from pre-metamorphic, post-metamorphic and adult brainstems. Raw (V) and integrated (V) activity recorded from the trigeminal cranial nerve (CN V) preparations from (A) stage XIV pre-metamorphic tadpole, (B) stage XXIV post-metamorphic tadpole and (C) adult brainstem during control conditions, 10 min and 120 min hypoxia, and recovery. Fictive gill and lung burst activity are present in the pre-metamorphic tadpole after 2 h, but neural activity ceased in the post-metamorphic and adult preparations. An example of a single non-respiratory burst is shown for the post-metamorphic brainstem during hypoxia.