Hemodynamic response to optogenetic stimulation varied under different stimulus parameters.

The coupling between neuronal activity and cerebral blood flow(CBF), known as neurovascular coupling, serves as the basis of functional brain imaging. Optogenetics provides a precise and selective approach to manipulate the activity in cell-specific neurons. It has been used in neuroscience research for comprehensive understanding about the light-evoked neurovascular coupling in rodent neuronal circuits. However, the spatiotemporal CBF response characteristics under different stimulus parameters such as pulse width and frequency remains unclear due to the lack of efficient CBF imaging technology. In this work, we used laser speckle contrast imaging(LSCI) to study the spatiotemporal hemodynamic response to optogenetic stimulation with different pulse widths (5ms, 10ms, 20ms) and frequencies (5Hz, 10Hz, 20Hz) in Channelrhodopsin-2(ChR2) expressing rats. The results showed that the averaged CBF response generally increased along with higher pulse width or frequency. The CBF peak response was significantly higher at 20ms and it took significantly shorter time to reach response peak at 5Hz. Our work adds additional insights in understanding the cell-specific neurovascular coupling mechanism and provides informative reference when applying ChR2 optogenetics in neurological disease research.