Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
Horm Behav. 2010 Apr;57(4-5):381-9. doi: 10.1016/j.yhbeh.2010.01.008. Epub 2010 Jan 29.
In male song sparrows (Melospiza melodia), territorial challenges during the breeding season can rapidly increase circulating levels of testosterone (T). During the non-breeding season, male song sparrows are highly aggressive, but the gonads are regressed and plasma T levels are non-detectable and unaffected by territorial challenges. The pro-hormone dehydroepiandrosterone (DHEA) is elevated in song sparrow plasma and brain during the non-breeding season and may be locally converted to sex steroids in the brain to regulate aggression. The enzyme 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (3beta-HSD) converts DHEA to androstenedione (AE) using the cofactor NAD(+), and this is a critical rate-limiting step. We predicted that brain 3beta-HSD activity varies seasonally and is rapidly modulated by aggressive challenges. In the first study, brain 3beta-HSD activity was highest in the non-breeding season in specific regions. In the second study, a simulated territorial challenge rapidly increased aggressive behavior in non-breeding song sparrows. Brain 3beta-HSD activity, when measured without exogenous NAD(+), increased by approximately 250 to 500% in telencephalic regions of challenged subjects. When brain 3beta-HSD activity was measured with exogenous NAD(+), these effects of territorial challenges were not observed. These data suggest that territorial challenges rapidly increase endogenous NAD(+) levels or increase 3beta-HSD activity specifically within a NAD-rich subcellular compartment. Together, these two studies suggest a shift from systemic to local sex steroid signaling in the non-breeding season. Local steroid signaling produces high spatial and temporal specificity of steroid signals and avoids the costs of high systemic T levels during the non-breeding season.
在雄性麻雀（Melospiza melodia）中，繁殖季节的领地挑战会迅速增加循环中的睾丸酮（T）水平。在非繁殖季节，雄性麻雀具有很强的攻击性，但性腺退化，血浆 T 水平无法检测到，也不受领地挑战的影响。前激素脱氢表雄酮（DHEA）在非繁殖季节的麻雀血浆和脑中升高，并且可能在脑中局部转化为性激素以调节攻击性。酶 3β-羟甾类脱氢酶/Δ5-Δ4 异构酶（3β-HSD）使用辅酶 NAD（+）将 DHEA 转化为雄烯二酮（AE），这是一个关键的限速步骤。我们预测，大脑 3β-HSD 活性随季节变化，并且可以迅速被攻击性挑战所调节。在第一项研究中，大脑 3β-HSD 活性在非繁殖季节的特定区域最高。在第二项研究中，模拟的领地挑战会迅速增加非繁殖期麻雀的攻击性行为。当在没有外源性 NAD（+）的情况下测量脑 3β-HSD 活性时，受挑战的麻雀大脑中脑区的活性增加了约 250%至 500%。当用外源性 NAD（+）测量脑 3β-HSD 活性时，这些领地挑战的影响则没有观察到。这些数据表明，领地挑战会迅速增加内源性 NAD（+）水平，或者专门在 NAD 丰富的亚细胞隔室中增加 3β-HSD 活性。这两项研究共同表明，在非繁殖季节，从系统到局部的性激素信号发生了转变。局部类固醇信号产生了高时空特异性的类固醇信号，并避免了非繁殖季节高系统性 T 水平的成本。
