McKenzie Andrew T, Nnadi Oge, Slagell Kat D, Thorn Emma L, Farrell Kurt, Crary John F
Apex Neuroscience, Salem, Oregon, USA.
Brain Preservation Foundation, Ashburn, Virginia, USA.
Free Neuropathol. 2024 Apr 23;5:10. doi: 10.17879/freeneuropathology-2024-5373. eCollection 2024 Jan.
Fluid preservation is nearly universally used in brain banking to store fixed tissue specimens for future research applications. However, the effects of long-term immersion on neural circuitry and biomolecules are not well characterized. As a result, there is a need to synthesize studies investigating fluid preservation of brain tissue. We searched PubMed and other databases to identify studies measuring the effects of fluid preservation in nervous system tissue. We categorized studies based on the fluid preservative used: formaldehyde solutions, buffer solutions, alcohol solutions, storage after tissue clearing, and cryoprotectant solutions. We identified 91 studies containing 197 independent observations of the effects of long-term storage on cellular morphology. Most studies did not report any significant alterations due to long-term storage. When present, the most frequent alteration was decreased antigenicity, commonly attributed to progressive crosslinking by aldehydes that renders biomolecules increasingly inaccessible over time. To build a mechanistic understanding, we discuss biochemical aspects of long-term fluid preservation. A subset of lipids appears to be chemical altered or extracted over time due to incomplete retention in the crosslinked gel. Alternative storage fluids mitigate the problem of antigen masking but have not been extensively characterized and may have other downsides. We also compare fluid preservation to cryopreservation, paraffin embedding, and resin embedding. Overall, existing evidence suggests that fluid preservation provides maintenance of neural architecture for decades, including precise structural details. However, to avoid the well-established problem of overfixation caused by storage in high concentration formaldehyde solutions, fluid preservation procedures can use an initial fixation step followed by an alternative long-term storage fluid. Further research is warranted on optimizing protocols and characterizing the generalizability of the storage artifacts that have been identified.
在脑组织库中，液体保存几乎被普遍用于存储固定组织标本以供未来研究应用。然而，长期浸泡对神经回路和生物分子的影响尚未得到充分表征。因此，有必要综合研究脑组织的液体保存情况。我们检索了PubMed和其他数据库，以识别测量液体保存对神经系统组织影响的研究。我们根据所使用的液体防腐剂对研究进行分类：甲醛溶液、缓冲溶液、酒精溶液、组织透明化后的储存以及冷冻保护剂溶液。我们确定了91项研究，其中包含197项关于长期储存对细胞形态影响的独立观察。大多数研究未报告因长期储存而产生的任何显著变化。当有变化时，最常见的变化是抗原性降低，这通常归因于醛类的渐进性交联，随着时间的推移，生物分子越来越难以接近。为了建立机制性理解，我们讨论了长期液体保存的生化方面。随着时间的推移，一部分脂质似乎会因在交联凝胶中保留不完全而发生化学改变或被提取。替代储存液可减轻抗原掩盖问题，但尚未得到广泛表征，可能还有其他缺点。我们还将液体保存与冷冻保存、石蜡包埋和树脂包埋进行了比较。总体而言，现有证据表明，液体保存可在数十年内维持神经结构，包括精确的结构细节。然而，为了避免因储存在高浓度甲醛溶液中而导致的过度固定这一公认问题，液体保存程序可采用初始固定步骤，然后使用替代的长期储存液。有必要进一步研究优化方案，并确定已识别的储存假象的普遍性。
