Act Locally and Think Globally: Intracerebral Testosterone Implants Induce Seasonal-like Growth of Adult Avian Song Control Circuits

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 99; no. 19; pp. 12421 - 12426
• Main Authors: Brenowitz, Eliot A., Lent, Karin
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 17.09.2002; National Acad Sciences
• Subjects: Adults; Androgens; Animal behavior; Animals; Aviculture; Biological Sciences; Bird songs; Birds; Blood plasma; Brain; Brain - drug effects; Brain - growth & development; Brain - physiology; Breeding seasons; Drug Implants; Efferent Pathways - drug effects; Efferent Pathways - growth & development; Efferent Pathways - physiology; Lent; Male; Neural conduction; Neurology; Neurons; Receptors, Androgen - drug effects; Receptors, Androgen - physiology; Seasons; Songbirds - anatomy & histology; Songbirds - growth & development; Songbirds - physiology; Telencephalon - drug effects; Telencephalon - physiology; Testosterone - administration & dosage; Vocalization, Animal - drug effects; Vocalization, Animal - physiology; Wild birds
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.192308799

There is pronounced seasonal plasticity in the morphology of the neural circuits that regulate song behavior in adult songbirds, primarily in response to changes in plasma testosterone (T) levels. Most song nuclei have androgen receptors. Afferent input from the telencephalic nucleus HVc (also known as the "high vocal center") is necessary for seasonal growth of the direct efferent target nuclei RA and area X. We asked here whether T-stimulated growth of HVc is sufficient to induce growth of its efferent nuclei. Intracerebral T implants were placed unilaterally near HVc or RA in photosensitive adult male white-crowned sparrows for one month. The T implant near HVc produced significant growth of the ipsilateral (but not contralateral) HVc, RA, and area X, and increased neuronal number in the ipsilateral HVc. The T implant near RA did not produce selective growth of ipsilateral RA, HVc, or area X. Intracerebral T implants did not elevate plasma T levels, nor did they stimulate growth of two peripheral androgen sensitive targets, the syrinx and the cloacal protuberance. These results suggest that seasonal growth of the adult song circuits results from T acting directly on HVc, which then stimulates the growth of RA and area X transynaptically.