Canoine Virginie, Fusani Leonida, Schlinger Barney, Hau Michaela
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA.
Dev Neurobiol. 2007 Jan;67(1):57-67. doi: 10.1002/dneu.20296.
Male aggressive behavior is generally regulated by testosterone (T). In most temperate breeding males, aggressive behavior is only expressed during the reproductive period. At this time circulating T concentrations, brain steroid receptors, and steroid metabolic enzymes are elevated in many species relative to the nonreproductive period. Many tropical birds, however, display aggressive behavior both during the breeding and the nonbreeding season, but plasma levels of T can remain low throughout the year and show little seasonal fluctuation. Studies on the year-round territorial spotted antbird (Hylophylax n. naevioides) suggest that T nevertheless regulates aggressive behavior in both the breeding and nonbreeding season. We hypothesize that to regulate aggressive behaviors during the nonbreeding season, when T is at its minimum, male spotted antbirds increase brain sensitivity to steroids. This can be achieved by locally up-regulating androgen receptors (ARs), estrogen receptors (ERs), or the enzyme aromatase (AROM) that converts T into estradiol. We therefore compared mRNA expression of AR, ERalpha, and AROM in free- living male spotted antbirds across reproductive and nonreproductive seasons in two brain regions known to regulate both reproductive and aggressive behaviors. mRNA expression of ERalpha in the preoptic area and AR in the nucleus taeniae were elevated in male spotted antbirds during the nonbreeding season when circulating T concentrations were low. This unusual seasonal receptor regulation may represent a means for the year-round regulation of vertebrate aggressive behavior via steroids by increasing the brain's sensitivity to sex steroids during the nonbreeding season.
雄性攻击行为通常受睾酮（T）调节。在大多数温带繁殖雄性动物中，攻击行为仅在繁殖期表现出来。此时，相对于非繁殖期，许多物种的循环T浓度、脑甾体受体和甾体代谢酶都会升高。然而，许多热带鸟类在繁殖季和非繁殖季都会表现出攻击行为，但T的血浆水平全年可能都保持较低，且几乎没有季节性波动。对全年具有领地意识的斑点蚁鸟（Hylophylax n. naevioides）的研究表明，T仍然在繁殖季和非繁殖季调节攻击行为。我们推测，在非繁殖季T处于最低水平时，为了调节攻击行为，雄性斑点蚁鸟会提高大脑对甾体的敏感性。这可以通过局部上调雄激素受体（ARs）、雌激素受体（ERs）或能将T转化为雌二醇的芳香化酶（AROM）来实现。因此，我们比较了自由生活的雄性斑点蚁鸟在繁殖季和非繁殖季两个已知能调节繁殖和攻击行为的脑区中AR、ERα和AROM的mRNA表达。在非繁殖季，当循环T浓度较低时，雄性斑点蚁鸟视前区的ERα和带状核中的AR的mRNA表达会升高。这种不寻常的季节性受体调节可能代表了一种通过在非繁殖季增加大脑对性甾体的敏感性，从而对脊椎动物攻击行为进行全年甾体调节的方式。
