INTRODUCTION: Microglia are the resident immune cells of the central nervous system (CNS) and play a key role in maintaining the normal function of the retina and brain. Recent studies suggest that of microglia may regulate synaptic structure and function by pruning functionally weak synapses. The retinal circuit is infiltrated by microglia by embryonic (E) day 11.5, where they reside in the emerging inner plexiform layer (IPL) and outer plexiform layer (OPL) during development and throughout adulthood. However, in what ways microglia regulate neuronal circuit formation during development and signal transmission in the retina remains unknown.

AIM(S): This study aimed to investigate whether continuous depletion of microglia during embryonic and early postnatal development affects the structural organization and morphology of the retina.

METHOD(S): Microglia were depleted using the CSF1R inhibitor PLX5622 from E17.5 hence during embryonic and early postnatal development. Retinal tissue was analyzed using immunohistochemistry and laser confocal microscopy. Quantitative image analysis by Imaris was performed to assess retinal layer organization, thickness, structure shape and distribution, and synaptic markers in microglia-depleted and control retinas.

RESULTS: Morphological analysis showed no significant differences between PLX-treated and control retinas in layer thickness or in the sphericity and volume of ribbon synapses. However, there seems to be a trend (p-value: 0.079) towards lower number of ribbon synapses in the OPL of PLX-treated retinas (788 ± 144) compared to controls (994 ± 49).

CONCLUSIONS: Although microglia are implicated in synaptic refinement, our preliminary findings suggest that their depletion does not overtly disrupt the gross morphological organization of the developing retina. Future studies should investigate potential subtle circuit-level or functional consequences and explore compensatory mechanisms that may preserve retinal structure in the absence of microglia.