We are investigating a firing prolongation of the rat striatal neuron after the repetitive optogenetic stimulation observed in an acute striatal slice. In this report, we tested whether the prolongation could be observed in vivo. Wistar Thy-1.2 promoter ChannelRhodopsin-2 Venus Rats were anesthetized and placed in a stereotaxic frame. A wire tetrode was coupled with a 500 μm plastic optic fiber and inserted into the striatum of the rat anesthetized by urethane. We were able to observe the firing prolongation after repetitive photostimulation using the tetrode with the optical fiber.