Bright light exposure induces dynamic changes of spatial memory in nocturnal rodents

Bright light has been reported to improve spatial memory of diurnal rodents, yet how it will influence the spatial memory of nocturnal rodents is unknown. Here, we found that dynamic changes in spatial memory and anxiety were induced at different time point after bright light treatment. Mice maintained in brighter light exhibited impaired memory in Y maze at one day after bright light exposure, but showed significantly improved spatial memory in the Y maze and Morris water maze at four weeks after bright light exposure. We also found increased anxiety one day after bright light exposure, which could be the reason of impaired memory. However, no change of anxiety was detected after four weeks. Thus, we further explore the underlying mechanism of the beneficial effects of long term bright light on spatial memory. Golgi staining indicated that the structure of dendritic spines changed, accompanied by increased expression of synaptophysin and postsynaptic density 95 in the hippocampus. Further research has found that bright light treatment leads to elevated CaMKII/CREB phosphorylation levels in the hippocampus, which are associated with synaptic function. Moreover, higher expression of brain-derived neurotrophic factor (BDNF) was followed by increased phosphorylated TrkB levels in the hippocampus, indicating that BDNF/TrkB signaling is also activated during this process. Taken together, these findings revealed that bright light exposure with different duration exert different effects on spatial memory in nocturnal rodents, and the potential molecular mechanism by which long term bright light regulates spatial memory was also demonstrated.