Objective: Nitric oxide (NO) is a gaseous messenger that mediates many physiological functions, including neuronal excitability, vascular tone and angiogenesis. Nitric oxide synthases are a family of enzymes that catalyzes the production of NO. While activation of endothelial NOS (eNOS) has been shown to be neuroprotective, activation of neuronal NOS (nNOS) and inducible NOS (iNOS) worsens ischemic damage. Although the role of NOS in acute stroke is well-established, their contribution in stroke recovery is less clear. Our lab recently demonstrated that optogenetic neuronal stimulation can enhance post-stroke recovery. As NOS mediates many physiological processes important for stroke recovery, we investigate whether NOS is involved in stimulation-enhanced recovery. We hypothesize that neuronal stimulations promote recovery by altering NOS expression.
Methods: Thy-1-ChR2-YFP line-18 transgenic male mice were used. Mice underwent experimental stroke induced by an intraluminal middle cerebral artery suture occlusion. Repeated optogenetic stimulations in the contralesional cerebellar dentate nucleus (cLCN) were administered from post-stroke day5-14. Functional recovery was evaluated by sensory-motor behavior tests. Mice were sacrificed at post-stroke day15, ipsilesional and contralesional motor and sensory cortices were dissected. qPCR was performed to examine expression of nNOS, iNOS and eNOS.
Results: Our data showed that stimulated stroke mice recovered quickly, with significantly faster rotating beam speed at day14 post-stroke (p<0.001). Quantitative PCR revealed that stimulations significantly reduced nNOS expression, while no change was detected for eNOS and iNOS. Interestingly, nNOS was significantly reduced in the contralesional primary motor cortex in cLCN-stimulated stroke mice (p<0.001), suggesting the involvement of nNOS in the contralesional cortex in stroke recovery.
Conclusion: Optogenetic stimulations promote post-stroke recovery and selectively reduced nNOS expression in the contralesional motor cortex. Current ongoing studies examine the nNOS signaling pathway after stimulation and the effect of manipulating nNOS expression in stroke recovery.