title: Sex steroid-induced neuroplasticity and behavioral activation in birds.
abstract: The brain of adult homeothermic vertebrates exhibits a higher degree of morphological neuroplasticity than previously thought, and this plasticity is especially prominent in birds. In particular, incorporation of new neurons is widespread throughout the adult avian forebrain, and the volumes of specific nuclei vary seasonally in a prominent manner. We review here work on steroid-dependent plasticity in birds, based on two cases: the medial preoptic nucleus (POM) of Japanese quail in relation to male sexual behavior, and nucleus HVC in canaries, which regulates song behavior. In male quail, POM volume changes seasonally, and in castrated subjects testosterone almost doubles POM volume within 2 weeks. Significant volume increases are, however, already observable after 1 day. Steroid receptor coactivator-1 is part of the mechanism mediating these effects. Increases in POM volume reflect changes in cell size or spacing and dendritic branching, but are not associated with an increase in neuron number. In contrast, seasonal changes in HVC volume reflect incorporation of newborn neurons in addition to changes in cell size and spacing. These are induced by treatments with exogenous testosterone or its metabolites. Expression of doublecortin, a microtubule-associated protein, is increased by testosterone in the HVC but not in the adjacent nidopallium, suggesting that neuron production in the subventricular zone, the birthplace of newborn neurons, is not affected. Together, these data illustrate the high degree of plasticity that extends into adulthood and is characteristic of avian brain structures. Many questions still remain concerning the regulation and specific function of this plasticity.
authors.affiliation: University of Liège, GIGA Neurosciences, Research Group in Behavioral Neuroendocrinology, Avenue de l'Hopital, 1 (BAT. B36), B-4000 Liège 1, Belgium. jbalthazart@ulg.ac.be
authors.forename: Jacques
authors.initials: J
authors.lastname: Balthazart
authors.forename: Thierry D
authors.initials: TD
authors.lastname: Charlier
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Barker
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamamura
authors.forename: Gregory F
authors.initials: GF
authors.lastname: Ball
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology; D002171:Canaries / Q000033:anatomy & histology / Q000502:physiology; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism; D002465:Cell Movement; D003370:Coturnix / Q000033:anatomy & histology / Q000502:physiology; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009473:Neuronal Plasticity / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D056920:Nuclear Receptor Coactivator 1 / Q000378:metabolism; D011301:Preoptic Area / Q000033:anatomy & histology / Q000378:metabolism; D000091042:Reelin Protein; D012621:Seasons; D012697:Serine Endopeptidases / Q000378:metabolism; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013739:Testosterone / Q000378:metabolism; D014828:Vocalization, Animal / Q000502:physiology
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D016326:Extracellular Matrix Proteins; D012739:Gonadal Steroid Hormones; D009419:Nerve Tissue Proteins; D000091042:Reelin Protein; D013739:Testosterone; D056920:Nuclear Receptor Coactivator 1; D012697:Serine Endopeptidases