Rhythmic light flicker rescues hippocampal low gamma and protects ischemic neurons by enhancing presynaptic plasticity

The complex relationship between specific hippocampal oscillation frequency deficit and cognitive dysfunction in the ischemic brain is unclear. Here, using a mouse two-vessel occlusion (2VO) cerebral ischemia model, we show that visual stimulation with a 40 Hz light flicker drove hippocampal CA1 slow gamma and restored 2VO-induced reduction in CA1 slow gamma power and theta-low gamma phase-amplitude coupling, but not those of the high gamma. Low gamma frequency lights at 30 Hz, 40 Hz, and 50 Hz, but not 10 Hz, 80 Hz, and arrhythmic frequency light, were protective against degenerating CA1 neurons after 2VO, demonstrating the importance of slow gamma in cognitive functions after cerebral ischemia. Mechanistically, 40 Hz light flicker enhanced RGS12-regulated CA3-CA1 presynaptic N-type calcium channel-dependent short-term synaptic plasticity and associated postsynaptic long term potentiation (LTP) after 2VO. These results support a causal relationship between CA1 slow gamma and cognitive dysfunctions in the ischemic brain.


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October 2018
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The data supporting the findings of this study is available with the article and its Supplementary Information file, or is available from the corresponding author upon request. The source data underlying Fig.1b- The moue brain atlas iamges on the left of Supplementary Fig. 2a was derived from Allen Mouse Brain atlas (http://atlas.brain-map.org/atlas? atlas=1&plate=100960240). Supplementary Fig. 8a protein sequence alignment was performed using CLUSTALW multiple sequence alignment at https:// www.genome.jp/tools-bin/clustalw.
Sample sizes were selected based on the previous examples of similar work in the literature. Adult male C57Bl/6 mice (3 months old) and adult male Thy1-YFP-H mice (3 months old) mice were used in this study. A total of 112 mice with the same age (3-month-old) and sex (male) were first randomly assigned to two groups (56 each) to receive Sham or 2VO surgery, respectively. For stroke behavioral analyses, each group had at least 7 mice to allow for statistic analyses. For electrophysiological recordings, at least 3 mice with more than 10 brain slices were used. These sample size allowed for acceptable statistical analyses to be performed while minimize numbers of animals for experiments dictated by the magnitude of experiment-to experiment variation.
Efforts were made to minimize the number of mice used. The inclusion criterion was based on the identical age and sex of the mice. The exclusion criterion was when the mouse failed to survive 2VO surgery at the end of the 14 d periods of the experimentation. Data derived from all qualified animals were included in the analyses and presentation of the results.
To achieve meaningful statistical differences, minimal of 5 mice per group were used in the LFP in vivo recordings, behavioral studies, RGS12 gene expression modifications experiments as indicated in the figure legends. For tissue section staining and Western blotting experimentation, at least 3 mice per group were used except 2 mice in western blotting of 3day. Where representative images are shown, at least three repeats have been performed with similar results.
Mice used in the current study were randomly assigned into each group to maintain a total randomization. After the surgery, mice in each group were randomly assigned to receive LED light or occluded LED treatment.
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