Aggression is a crucial behavior that impacts access to limited resources in different environmental contexts. Androgens synthesized by the gonads promote aggression during the breeding season. However, aggression can be expressed during the non-breeding season, despite low androgen synthesis by the gonads. The brain can also synthesize steroids ("neurosteroids"), including androgens, which might promote aggression during the non-breeding season. Male song sparrows, Melospiza melodia, are territorial year-round and allow the study of seasonal changes in the steroid modulation of aggression. Here, we quantified steroids following a simulated territorial intrusion (STI) for 10 min in wild adult male song sparrows during the breeding and non-breeding seasons. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we examined 11 steroids: pregnenolone, progesterone, corticosterone, dehydroepiandrosterone, androstenedione, testosterone, 5α-dihydrotestosterone, 17β-estradiol, 17α-estradiol, estriol, and estrone. Steroids were measured in blood and 10 microdissected brain regions that regulate social behavior. In both seasons, STI increased corticosterone in the blood and brain. In the breeding season, STI had no rapid effects on androgens or estrogens. Intriguingly, in the non-breeding season, STI increased testosterone and androstenedione in several behaviorally relevant regions, but not in the blood, where androgens remained non-detectable. Also in the non-breeding season, STI increased progesterone in the blood and specific brain regions. Overall, rapid socially modulated changes in brain steroid levels are more prominent during the non-breeding season. Brain steroid levels vary with season and social context in a region-specific manner and suggest a role for neuroandrogens in aggression during the non-breeding season.

攻击性是影响不同环境背景下有限资源获取的重要行为。性腺合成的雄激素会在繁殖季节促进攻击性。然而，尽管性腺合成的雄激素较低，但在非繁殖季节仍可能表现出攻击性。大脑还可以合成类固醇（“神经类固醇”），包括雄激素，这可能会在非繁殖季节促进攻击性。雄性歌麻雀（Melospiza melodia）全年都有领地，可以研究类固醇调节攻击性的季节变化。在这里，我们对野生成年雄性歌麻雀在繁殖季节和非繁殖季节模拟领地入侵 (STI) 10 分钟后的类固醇进行了定量。使用液相色谱-串联质谱 (LC-MS/MS)，我们检测了 11 种类固醇：孕烯醇酮、黄体酮、皮质酮、脱氢表雄酮、雄烯二酮、睾酮、5α-二氢睾酮、17β-雌二醇、17α-雌二醇、雌三醇和雌酮。在血液和 10 个调节社会行为的显微解剖大脑区域中测量了类固醇。在这两个季节，性传播感染都会增加血液和大脑中的皮质酮。在繁殖季节，性传播感染对雄激素或雌激素没有快速影响。有趣的是，在非繁殖季节，性传播感染会增加几个行为相关区域的睾酮和雄烯二酮，但不会增加血液中的雄激素，而血液中的雄激素仍然检测不到。同样在非繁殖季节，性传播感染会增加血液和特定大脑区域中的黄体酮。总体而言，在非繁殖季节，大脑类固醇水平的快速社会调节变化更为突出。 脑类固醇水平随季节和社会背景以特定区域的方式变化，表明神经雄激素在非繁殖季节的攻击行为中发挥作用。