Alvarez-Buylla A, Ling C Y, Yu W S
Rockefeller University, New York, New York 10021.
J Comp Neurol. 1994 Sep 8;347(2):233-48. doi: 10.1002/cne.903470207.
Neurogenesis occurs in adult song birds, which suggests that neurons born after hatching may contribute to histogenesis and plasticity of the avian brain. However, little is known about the overall contribution to the mature brain of neurons born in juveniles and adults, and how this process affects different regions of the avian brain. In fact, studies of the histogenesis of the avian forebrain have made the classical assumption that neuronal birth ends before hatching. Here we determined the contribution of neurons born before and after hatching to different regions throughout the adult canary brain. Male canaries were injected with [3H]-thymidine at different times during embryonic, juvenile, and adult life. The position of labeled neurons was mapped in parasagittal brain sections. Because all birds were killed as adults, results indicate the time of birth of neurons that survived to adulthood in different structures of the avian brain. Injection at embryonic day (E) 5 or E9 resulted in labeled neurons in all regions of the neuroaxis. The vast majority of neurons outside of the telencephalon were born before E9. One exception was a discrete region in the dorsal thalamus, a part of the song-control circuit, where neurons continued to be born after E9. Most regions of the telencephalon had a high proportion of its neurons labeled by the embryonic injections. In particular, archistriatum, anterior neostriatum, and the hippocampus had most of their neurons labeled before hatching. This indicates that many of the telencephalic neurons born in the embryo are long lived and are not replaced by other neurons that continue to be added to the telencephalon after hatching. Neurons labeled by [3H]-thymidine injections after hatching were restricted to the telencephalon and contributed importantly to many regions. In particular, the avian striatum (lobus parolfactorius, LPO) received a large number of its neurons during the first 20 days of life, but continued to incorporate new neurons throughout juvenile and adult life. Neurons continued to be added to the telencephalon of adults (even in 4-year-old birds). The distribution of labeled neurons after [3H]-thymidine injections in adults was similar to that observed in latter stages of juvenile development. The contribution of neurons born at different ages from embryonic development to adulthood varied among different anatomical subdivisions of the canary brain. this could, in part, explain differences in the cytoarchitecture and plasticity between brain regions. Neurogenesis after hatching may allow the modification of selected brain circuits as the bird matures and ages.
神经发生在成年鸣禽中出现，这表明孵化后产生的神经元可能有助于鸟类大脑的组织发生和可塑性。然而，对于幼鸟和成年鸟出生的神经元对成熟大脑的总体贡献，以及这个过程如何影响鸟类大脑的不同区域，我们知之甚少。事实上，对鸟类前脑组织发生的研究做出了一个经典假设，即神经元的产生在孵化前就结束了。在这里，我们确定了孵化前后出生的神经元对成年金丝雀大脑不同区域的贡献。在胚胎期、幼年期和成年期的不同时间，给雄性金丝雀注射[3H] - 胸腺嘧啶核苷。在矢状脑切片中绘制标记神经元的位置。由于所有鸟类均在成年时被处死，结果表明了在鸟类大脑不同结构中存活至成年的神经元的出生时间。在胚胎第5天（E5）或E9注射导致神经轴的所有区域都有标记神经元。端脑以外的绝大多数神经元在E9之前出生。一个例外是背侧丘脑的一个离散区域，它是鸣叫控制回路的一部分，在E9之后仍有神经元持续产生。端脑的大多数区域有很大比例的神经元被胚胎期注射标记。特别是，古纹状体、前新纹状体和海马体的大多数神经元在孵化前就被标记。这表明许多胚胎期出生的端脑神经元寿命很长，并且不会被孵化后继续添加到端脑的其他神经元所取代。孵化后通过[3H] - 胸腺嘧啶核苷注射标记的神经元仅限于端脑，并且对许多区域有重要贡献。特别是，鸟类纹状体（嗅觉叶，LPO）在生命的前20天接收了大量神经元，但在整个幼年和成年期都持续纳入新的神经元。成年鸟（甚至4岁的鸟）的端脑仍持续添加神经元。成年鸟注射[3H] - 胸腺嘧啶核苷后标记神经元的分布与幼鸟发育后期观察到的相似。从胚胎发育到成年不同年龄出生的神经元对金丝雀大脑不同解剖亚区的贡献各不相同。这在一定程度上可以解释脑区之间细胞结构和可塑性的差异。孵化后的神经发生可能使鸟类在成熟和衰老过程中对特定脑回路进行修饰。
