Background: Advancements in genome editing technology and the globalization of life science research have highlighted the need for refined techniques in individualizing fertilized mouse eggs. Traditional embryo transfer surgery, which demands precise and objective success assessment, presents challenges for technical mastery and animal welfare. To address these issues, we developed a novel culture medium incorporating a dye library that enhances the visibility of ultrafine capillaries. Results: We screened 32 compounds based on their color properties and excluded those with clear cytotoxicity through colony formation inhibition tests. Five compounds demonstrated developmental outcomes comparable to those of the control group during embryo culture. Gene expression analysis revealed high correlation with control embryos, indicating no adverse developmental impact. No maternal toxicity was observed during and after embryo transfer using the dyed medium, which also produced normal offspring. A randomized survey confirmed improved visibility compared to conventional methods. Conclusion This study successfully identified nontoxic dyes that enhance the visibility of embryo transfer culture media, potentially improving precision and animal welfare in embryological research. Based on our findings, adding Brilliant Blue FCF or Fast Green FCF to the medium is recommended.

In Mongolian gerbils, bilateral common carotid artery occlusion (BCCAO) for several minutes induces ischemia, due to an incomplete circle of Willis, resulting in delayed neuronal cell death in the Cornet d'Ammon 1 (CA1) region of the hippocampus. Neuronal cell death in the hippocampus and changes in behavior were examined after BCCAO was performed for 5 min in the gerbils. One day after BCCAO, the pyramidal neurons of the CA1 region of the hippocampus showed degenerative changes (clumped chromatin in nuclei). At 5 and 10 days after BCCAO, extensive neuronal cell death was observed in the hippocampal CA1 region. Cognitive performance was evaluated by using the radial maze and passive avoidance tests. In the radial maze test, which examines win-stay performance, the number of errors was significantly higher in ischemic gerbils than in sham-operated gerbils on days 1 and 2 post-operation. In the passive avoidance test, the latency and freezing times were significantly shorter in ischemic gerbils than in sham-operated gerbils on the days 1, 2, and 4–6 post-operation. These results indicate that transient forebrain ischemia impairs cognitive performance, even immediately after the ischemic insult when there are only subtle signs of neuronal cell death.
CA1 Region, Hippocampal ; Carotid Artery, Common ; Cell Death ; Chromatin ; Circle of Willis ; Freezing ; Gerbillinae ; Hippocampus ; Ischemia ; Neurons ; Prosencephalon ; Pyramidal Cells