Dloniak S M, Deviche P
Department of Zoology, Michigan State University, 203 Natural Sciences, East Lansing, Michigan, 48824-1115, USA.
Horm Behav. 2001 Mar;39(2):95-105. doi: 10.1006/hbeh.2000.1621.
In seasonally breeding male oscines, song learning and expression are controlled by brain regions (vocal control regions, VCRs) that exhibit seasonal neural plasticity in adulthood. Several VCRs contain androgen receptors, and gonadal androgens play important roles in the control of seasonal structural and functional changes of VCRs. Recent studies also found that adult VCRs are influenced by factors other than gonadal hormones, including photoperiod, but the relative importance of these factors and their mechanisms of action are poorly understood. To address this issue, we investigated the contributions of photoperiod and testicular androgens to the regulation of VCR volumes and to the control of song expression in adult dark-eyed juncos, Junco hyemalis. Exposing castrated (CX) photosensitive males to long days (LD) enhanced their high vocal center (HVc) volumes compared to those of males held on short days (SD). These volumes were not further increased by concurrent testosterone (T) treatment, revealing a marked and gonadal androgen-independent stimulatory influence of photoperiod on the size of this brain region. HVc sizes were smaller in LD-exposed photorefractory than photosensitive males irrespective of whether birds were intact or had been castrated before photoperiodic manipulations, but HVc sizes increased in response to T treatment in intact photorefractory males. Thus, LD exposure can increase HVc volumes in the absence of gonadal T, but large volume induction in photorefractory males requires elevated plasma T levels. Testosterone treatment of SD-exposed photosensitive males increased HVc, but not Area X, MAN, or RA volumes. Only T-treated males sang and this treatment given to castrates was equally effective behaviorally when administered to photosensitive, photostimulated, or photorefractory juncos. This result indicates that the stimulating influence of LD exposure on HVc volumes is insufficient to induce song in the absence of elevated plasma T levels.
在季节性繁殖的雄性鸣禽中，鸣叫学习和表达受大脑区域（发声控制区域，VCRs）控制，这些区域在成年期表现出季节性神经可塑性。几个VCRs含有雄激素受体，性腺雄激素在控制VCRs的季节性结构和功能变化中起重要作用。最近的研究还发现，成年VCRs受性腺激素以外的因素影响，包括光周期，但这些因素的相对重要性及其作用机制尚不清楚。为了解决这个问题，我们研究了光周期和睾丸雄激素对成年暗眼灯草鹀（Junco hyemalis）VCRs体积调节和鸣叫表达控制的作用。与短日照（SD）饲养的雄性相比，将阉割（CX）的光敏雄性暴露于长日照（LD）下可增加其高位发声中枢（HVc）的体积。同时给予睾酮（T）处理并没有进一步增加这些体积，这表明光周期对该脑区大小有显著的、与性腺雄激素无关的刺激作用。无论鸟类是否完整或在光周期处理前已被阉割，暴露于LD的光不应期雄性的HVc大小都比光敏雄性小，但完整的光不应期雄性对T处理的反应是HVc大小增加。因此，在没有性腺T的情况下，LD暴露可增加HVc体积，但光不应期雄性的大体积诱导需要升高的血浆T水平。对SD暴露的光敏雄性进行睾酮处理可增加HVc，但不增加X区、MAN或RA的体积。只有接受T处理的雄性鸣叫，当给予阉割雄性这种处理时，无论其处于光敏、光刺激或光不应期，在行为上都是同样有效的。这一结果表明，在没有升高的血浆T水平的情况下，LD暴露对HVc体积的刺激作用不足以诱导鸣叫。
