Morphological comparison of the microglial cell population between organotypic retinal cultures and axotomised retinas in vivo

Purpose: Retinal organotypic cultures (ROCs) have been used since the early 1930s as in vivo surrogates to study retinal ganglion cell (RGC) loss and neuroprotection. In this work we purposed to analyse and compare the morphological changes of microglial cells (MCs) along time in ROCs and axotomised retinas. Methods: C57/Bl6 mice were used. For the in vitro model, retinas were dissected and cultured in supplemented medium. In the in vivo model, the left optic nerve (ONC) was crushed. In both models, retinas were analysed at 24‐h intervals for up to 7 days. MCs were then immunodetected with anti‐Iba1 antibody and then photographed in the ganglion cell layer (GCL) of the retina using a confocal microscope. Finally, their morphology was quantitatively analysed using the free Image J Fiji software. Results: After ONC, the number of MC processes decreased significantly from day 1 to 7 compared to intact retinas. Similarly, we observed a significant decrease in the number of processes of in vitro MCs, which was significantly greater than after axotomy in vivo The total length of the processes decreased in both models up to 7 days. When studying the size of the MCs, it was observed that from 1 to 7 days MCs were bigger in vitro than in vitro and in both models than in intact retinas. Conclusions: The morphology of MCs differs in vivo and in vitro , suggesting a differential activation.