title: Rapid seasonal-like regression of the adult avian song control system.
abstract: We analyzed how rapidly avian song control nuclei regress after testosterone (T) withdrawal. Regression of neuronal attributes resulting from T withdrawal has been observed in several animal models. The time course over which regression occurs is not known, however. To address this issue, we castrated adult male white-crowned sparrows and rapidly shifted them to short-day photoperiods after being held under breeding conditions (long-day photoperiod and systemic T exposure) for 3 weeks. We found that the volume of one song nucleus, HVC, regressed 22% within 12 h after T withdrawal. Changes in HVC neuron density after T withdrawal were dynamic; density increased at 12 h and then decreased by 4 days. HVC neuron number was reduced by 26% by 4 days. The volumes of Area X and the robust nucleus of the arcopallium (RA) were significantly regressed by 7 and 20 days, respectively. RA somatic area and neuronal spacing were significantly reduced by 2 days. The rapidity of HVC regression is unprecedented among vertebrate models of hormone-sensitive neural circuits. These results reveal that the rapid regression of the song control system provides a model for the important role sex steroid hormones play in mediating adult neural plasticity and in neuroprotection.
authors: Graduate Program in Neurobiology and Behavior, University of Washington, Box 351525, Seattle, WA 98195-1525, USA. ckthomps@u.washington.edu
authors: Christopher K
authors: CK
authors: Thompson
authors: George E
authors: GE
authors: Bentley
authors: Eliot A
authors: EA
authors: Brenowitz
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D006728:Hormones / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D008959:Models, Neurological; D009474:Neurons / Q000378:metabolism; D010477:Perfusion; D012044:Regression Analysis; D012621:Seasons; D020308:Songbirds; D013997:Time Factors; D014828:Vocalization, Animal
chemical_list: D006728:Hormones