Neuroanatomical evidence for indirect connections between the medial preoptic nucleus and the song control system: possible neural substrates for sexually motivated song.

In European starlings ( Sturnus vulgaris) as in other seasonally breeding songbirds, a major function of song during the breeding season is mate attraction, and song in this context is highly sexually motivated. Song learning, perception, and production are regulated by nuclei of the song control system, but there is no evidence that these nuclei participate in the motivation to sing. Evidence suggests that the medial preoptic nucleus (POM), a diencephalic nucleus outside of the song control system, might regulate the motivation to sing, at least in a sexual context. If the POM is involved in the regulation of sexually motivated song, then this structure must interact with the song control system. To examine possible neuroanatomical connections between the POM and song control nuclei a tract-tracing study was performed in male starlings using the antero- and retrograde tract tracer, biotinylated dextran amine (BDA). No direct connections were identified between the POM and song control nuclei; however, labeled fibers were found to terminate in a region bordering dorsal-medial portions of the robust nucleus of the archistriatum (RA). Additionally, several indirect routes via which the POM might communicate with the song control system were identified. Specifically, POM projected to dorsomedial nucleus intercollicularis (DM), mesencephalic central gray (GCt), area ventralis of Tsai (AVT), and locus ceruleus (LoC), structures projecting directly to nuclei involved in song production (DM --> vocal-patterning and respiratory nuclei; GCt, AVT, LoC --> RA and HVC, and the context in which song is sung (AVT --> area X). These results are consistent with the possibility that the POM regulates sexually motivated song through interactions with brain regions involved in vocal production.