A vocal CPG underlies divergent vocalizations in X. laevis and X. petersii
(A) Schematic representation of the known hindbrain vocal central pattern generator nuclei. The vocal motor nucleus (n.) IX-X contains vocal motor neurons. These neurons send their axons via the vocal (laryngeal) nerve to the larynx, the vocal effector organ. Fictive calling can be recorded from the vocal nerve using a suction electrode. Premotor neurons in the Xenopus parabrachial area (PBX) project monosynaptically to the vocal motor nucleus. In PBX, whole cell electrodes can record activity associated with fictive calling.
(B) Representative example of X. laevis fictive calling, consisting of a series of long, fast rate CAP trills (~60 Hz; blue box, Nerve) and a simultaneously recorded premotor vocal neuron (Neuron). Temporally expanded recording (dashed box) of a single X. laevis call with introductory trill (grey box) and fast trill (blue box) and corresponding premotor neuron activity (right).