Microglial Proliferation Patterns Following Damage To The Olfactory Bulb In Adult Zebrafish
The plasticity of the zebrafish olfactory system is a useful model for examining immune cell response after injury. Microglia are the resident immune cells that respond to damage in the CNS. We previously demonstrated the time course of the microglial response to olfactory bulb (OB) injury in adult zebrafish; however, it is unclear whether the response is from proliferating resident microglia or peripheral migration. We hypothesize that after damage, there will be an increase in resident microglia, followed by the influx of peripheral macrophages, rather than localized cellular proliferation.
A direct lesion to the OB in the whole fish was compared to a direct lesion to the isolated brain in culture removed of all afferent input. 4C4 antibody was used to label microglia, and PCNA antibody was used to label proliferating cells. There were some proliferating microglia in both OBs at most time points after injury, with a notable increase at 12h and 24h after injury in the whole fish. In the isolated brain, there were few to no proliferating microglial profiles in either OBs. Significant increases in activated microglial profiles following 1, 4, and 12h after injury to the isolated brain suggest that microglia can respond to signals without afferent input or peripheral influence, up to a certain time after injury. Our findings suggest that local proliferation may not be a major contributor to the microglial response to OB injury. Further work is required to explore microglial proliferation patterns and their potential role in recovery and regeneration after injury.