Central pattern generators (CPG) in the brainstem are considered to underlie vocalizations in many vertebrate species, but the detailed mechanisms underlying how motor rhythms are generated, coordinated, and initiated remain unclear. We addressed these issues using isolated brain preparations of Xenopus laevis from which fictive vocalizations can be elicited. Advertisement calls of male X. laevis that consist of fast and slow trills are generated by vocal CPGs contained in the brainstem. Brainstem central vocal pathways consist of a premotor nucleus (DTAM) and a laryngeal motor nucleus (n.IX-X) with extensive reciprocal connections between the nuclei. In addition, DTAM receives descending inputs from the extended amygdala. We found that unilateral transection of the projections between DTAM and n.IX-X eliminated premotor fictive fast trill patterns but did not affect fictive slow trills, suggesting that the fast and slow trill CPGs are distinct; the slow trill CPG is contained in n.IX-X and the fast trill CPG spans DTAM and n.IX-X. Midline transections that eliminated the anterior, the posterior, or both commissures caused no change in the temporal structure of fictive calls, but bilateral synchrony was lost, indicating that the vocal CPGs are contained in the lateral halves of the brainstem and that the commissures synchronize the two oscillators. Furthermore, eliminating the inputs from extended amygdala to DTAM in addition to the anterior commissure resulted in autonomous initiation of fictive fast, but not slow trills by each hemibrainstem, indicating that the extended amygdala provides a bilateral signal to initiate fast trills.
- central pattern generator
- parabrachial nucleus
- Copyright © 2016, Journal of Neurophysiology