Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, HMRB 162, Health Sciences Centre, 3330 Hospital Drive NW, AB, T2N 4N1, Calgary, Canada.
Mol Brain. 2022 May 2;15(1):38. doi: 10.1186/s13041-022-00926-7.
Adult neurogenesis, the proliferation and integration of newly generated neurons, has been observed in the adult mammalian hippocampus of many species. Numerous studies have also found adult neurogenesis in the human hippocampus, but several recent high-profile studies have suggested that this process is considerably reduced in humans, occurring in children but not in adults. In comparison, rodent studies also show age-related decline but a greater degree of proliferation of new neurons in adult animals. These differences may represent biological species differences or could alternatively be explained by methodological differences in tissue handling and fixation. Here, we examine whether differences in the post-mortem interval between death and tissue fixation might impact subsequent detection of adult neurogenesis due to increased tissue degradation. Because there are fewer new neurons present in older subjects to begin with we hypothesized that, subject age might interact significantly with post-mortem interval in the detection of adult neurogenesis. We analyzed neurogenesis in the hippocampus of rats that were either perfusion-fixed or the brains extracted and immersion-fixed at various post-mortem intervals. We observed an interaction between animal age and the time delay between death and tissue fixation. While similar levels of neurogenesis were observed in young rats regardless of fixation, older rats had significantly fewer labeled neurons when fixation was not immediate. Furthermore, the morphological detail of the labeled neurons was significantly reduced in the delayed fixation conditions at all ages. This study highlights critical concerns that must be considered when using post-mortem tissue to quantify adult neurogenesis.
成人神经发生，即新神经元的增殖和整合，已在许多物种的成年哺乳动物海马体中观察到。大量研究还在人类海马体中发现了成人神经发生，但最近几项备受瞩目的研究表明，这一过程在人类中大大减少，仅发生在儿童期，而不在成年期。相比之下，啮齿动物研究也显示出与年龄相关的衰退，但成年动物中新神经元的增殖程度更高。这些差异可能代表了生物学物种差异，或者可以通过组织处理和固定方面的方法学差异来解释。在这里，我们研究了死后到组织固定之间的死后间隔时间的差异是否会由于组织降解增加而影响成年神经发生的后续检测。由于年龄较大的受试者一开始就存在较少的新神经元，我们假设，受试者的年龄可能会与成年神经发生的检测中死后间隔时间发生显著交互作用。我们分析了在不同死后间隔时间下进行灌注固定或提取脑组织并进行浸泡固定的大鼠海马体中的神经发生。我们观察到动物年龄与死亡和组织固定之间的时间延迟之间存在相互作用。虽然年轻大鼠无论固定方式如何，神经发生水平相似，但在固定不及时的情况下，老年大鼠的标记神经元数量明显减少。此外，在所有年龄组中，在延迟固定条件下，标记神经元的形态细节明显减少。这项研究强调了在使用死后组织来定量成年神经发生时必须考虑的关键问题。
