Sexual Differences in Cell Loss during the Post-Hatch Development of Song Control Nuclei in the Bengalese Finch.

Birdsongs and the regions of their brain that control song exhibit obvious sexual differences. However, the mechanisms underlying these sexual dimorphisms remain unknown. To address this issue, we first examined apoptotic cells labeled with caspase-3 or TUNEL in Bengalese finch song control nuclei - the robust nucleus of the archopallium (RA), the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the high vocal center (HVC) and Area X from post-hatch day (P) 15 to 120. Next, we investigated the expression dynamics of pro-apoptotic (Bid, Bad and Bax) and anti-apoptotic (Bcl-2 and Bcl-xL) genes in the aforementioned nuclei. Our results revealed that the female RA at P45 exhibited marked cell apoptosis, confirmed by low densities of Bcl-xL and Bcl-2. Both the male and female LMAN exhibited apoptotic peaks at P35 and P45, respectively, and the observed cell loss was more extensive in males. A corresponding sharp decrease in the density of Bcl-2 after P35 was observed in both sexes, and a greater density of Bid was noted at P45 in males. In addition, we observed that RA volume and the total number of BDNF-expressing cells decreased significantly after unilateral lesion of the LMAN or HVC (two areas that innervate the RA) and that greater numbers of RA-projecting cells were immunoreactive for BDNF in the LMAN than in the HVC. We reasoned that a decrease in the amount of BDNF transported via HVC afferent fibers might result in an increase in cell apoptosis in the female RA. Our data indicate that cell apoptosis resulting from different pro- and anti-apoptotic agents is involved in generating the differences between male and female song control nuclei.

鸟鸣及其大脑中控制鸣叫的区域呈现出明显的性别差异。然而，这些性别二态性的潜在机制仍然未知。为了解决这一问题，我们首先在孟加拉雀鸣叫控制核——原纹状体粗核（RA）、前脑新纹状体外侧巨细胞核（LMAN）、高级发声中枢（HVC）以及从孵化后第15天到第120天的X区中，检测了用半胱天冬酶 - 3或TUNEL标记的凋亡细胞。接下来，我们研究了上述核中促凋亡（Bid、Bad和Bax）和抗凋亡（Bcl - 2和Bcl - xL）基因的表达动态。我们的研究结果显示，在第45天，雌性RA出现明显的细胞凋亡，这通过低密度的Bcl - xL和Bcl - 2得以证实。雄性和雌性LMAN分别在第35天和第45天出现凋亡峰值，并且观察到雄性的细胞损失更为广泛。在第35天后，两性中都观察到Bcl - 2密度相应地急剧下降，并且在第45天雄性中Bid的密度更大。此外，我们观察到在LMAN或HVC（两个支配RA的区域）单侧损伤后，RA体积以及表达脑源性神经营养因子（BDNF）的细胞总数显著减少，并且在LMAN中向RA投射的细胞对BDNF呈免疫反应的数量比在HVC中更多。我们推断，通过HVC传入纤维运输的BDNF量的减少可能导致雌性RA中细胞凋亡增加。我们的数据表明，由不同的促凋亡和抗凋亡因子导致的细胞凋亡参与了雄性和雌性鸣叫控制核之间差异的产生。