XenopusVocalizations Are Controlled by a Sexually Differentiated Hindbrain Central Pattern Generator

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Abstract
Male and female African clawed frogs (Xenopus laevis) produce rhythmic, sexually distinct vocalizations as part of courtship and mating. We found thatXenopusvocal behavior is governed by a sexually dimorphic central pattern generator (CPG) and that fictive vocalizations can be elicited from anin vitrobrain preparation by application of serotonin or by electrical stimulation of a premotor nucleus. Male brains produced fictive vocal patterns representing two calls commonly produced by malesin vivo(advertisement and amplectant call), as well as one call pattern (release call) that is common for juvenile males and femalesin vivobut rare for adult males. Female brains also produced fictive release call. The production of male calls is androgen dependent inXenopus; to test the effects of androgens on the CPG, we examined fictive calling in the brains of testosterone-treated females. Both fictive male advertisement call and release call were produced. This suggests that allXenopuspossess a sexually undifferentiated pattern generator for release call. Androgen exposure leads to a gain-of-function, allowing the production of male-specific call types without prohibiting the production of the undifferentiated call pattern. We also demonstrate that the CPG is located in the brainstem and seems to rely on the same nuclei in both males and females. Finally, we identified endogenous serotonergic inputs to both the premotor and motor nuclei in the brainstem that may regulate vocal activityin vivo.