Meeting Abstract
African clawed frogs (Xenopus laevis) produce mating calls driven by a central pattern generator (CPG). Calls are sexually differentiated, and male courtship vocalizations require circulating androgens. Previous work has shown that ovariectomized female Xenopus develop the male-typical fast trill call after approximately 8 weeks of testosterone (T) treatment. To assess the timing of testosterone-induced masculinization, we studied T-treated female calling at 2 week intervals over 10 weeks. Call rates masculinized gradually over the testing period. We also recorded “fictive vocalizations”, laryngeal nerve activity corresponding to vocalizations, from an isolated brain preparation in which the vocal CPG can be activated. Eight and ten weeks post treatment, females produced sustained calling rates of 42-55 Hz, slightly below the normal range of male calling, and fictive calling rates of 40-62 Hz, comparable to in vivo results. We found male-like vocal patterns in vivo (~37 Hz), and in vitro (~23 Hz) as early as 2 weeks post treatment, indicating a rapid masculinization process. In males, local field potential (LFP) recordings in the premotor nucleus during fictive vocalizations show a “wave” of activity coinciding with each call that persists when the premotor nucleus is surgically isolated from the rest of the CPG. These LFP waves were observed in T-treated female brains 2-4 weeks post treatment in intact and separated CPGs. While LFP waves were not observed in intact brains of control females, we recorded LFP waves in the isolated premotor nuclei of a control female. This result indicates that elements of the male vocal CPG are present in females, but may be functionally distinct due unique network properties of the female CPG. Our data collectively demonstrate that testosterone induced changes to adult female vocal circuits can occur within 2 weeks, potentially driven by altered synaptic properties.
