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See detailSeasonal plasticity in the song control system - Multiple brain sites of steroid hormone action and the importance of variation in song behavior
Ball, Gregory F.; Auger, Catherine J.; Bernard, Daniel J. et al

in Annals of the New York Academy of Sciences (2004), 1016

Birdsong, in non-tropical species, is generally more common in spring and summer when males sing to attract mates and/or defend territories. Changes in the volumes of song control nuclei, such as HVC and ... [more ▼]

Birdsong, in non-tropical species, is generally more common in spring and summer when males sing to attract mates and/or defend territories. Changes in the volumes of song control nuclei, such as HVC and the robust nucleus of the arcopallium (RA), are observed seasonally. Long photoperiods in spring stimulate the recrudescence of the testes and the release of testosterone. Androgen receptors, and at times estrogen receptors, are present in HVC and RA as are co-factors that facilitate the transcriptional activity of these receptors. Thus testosterone can act directly to induce changes in nucleus volume. However, dissociations have been identified at times among long photoperiods, maximal concentrations of testosterone, large song control nuclei, and high rates of song. One explanation of these dissociations is that song behavior itself can influence neural plasticity in the song system. Testosterone can act via brain-derived neurotrophic factor (BDNF) that is also released in HVC as a result of song activity. Testosterone could enhance song nucleus volume indirectly by acting in the preoptic area, a region regulating sexual behaviors, including song, that connects to the song system through catecholaminergic cells. Seasonal neuroplasticity in the song system involves an interplay among seasonal state, testosterone action, and behavioral activity. [less ▲]

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See detailModulation of steroid activity by transcription coactivators in songbirds
Charlier, Thierry ULg; Auger, Catherine J; Balthazart, Jacques ULg et al

in Hormones & Behavior (2003), 44

Songbirds have developed a specialized, steroid-dependent telencephalic vocal control system for the production of learned vocalization. Recent progress in the study of the mechanisms by which steroid ... [more ▼]

Songbirds have developed a specialized, steroid-dependent telencephalic vocal control system for the production of learned vocalization. Recent progress in the study of the mechanisms by which steroid receptors act on the eukaryotic genome has highlighted the role of a newly discovered protein family, the Nuclear Receptor Coactivators. More specifically, the CREB-binding protein (CBP) and the Steroid Receptor Coactivator-1 (SRC-1) have been shown to be actively involved in mediating steroid hormone action in the developing rat brain. The distribution of the coactivator SRC-1 was analyzed in canaries by in situ hybridization. A very broad but heterogeneous distribution of the transcript was observed, mainly in steroid-sensitive areas of the hypothalamus, the song control system and several catecholaminergic areas. The presence of SRC-1 in these regions was also confirmed by immunocytochemistry. A similar very high concentration of the coactivator CBP protein was also found in steroid-sensitive areas of the hypothalamus and in the song system. Sex differences in SRC-1 mRNA concentration were detected in HVC and in area X. Moreover, preliminary data obtained independently in starlings (CBP) and in quail (SRC-1) suggest that the expression of coactivators is regulated by steroids as well as by photoperiod. The presence of these steroid receptor coactivators in the telencephalic song control nuclei and in catecholaminergic cell groups that innervate the song system and their possible regulation by photoperiod and/or steroids support the idea that SRC-1 and CBP could play an important role in the control of singing behavior by modulating estrogen and androgen receptor action. [less ▲]

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