An improved multiple-site optical membrane potential-recording system to obtain high-quality single sweep signals in intact rat cerebral cortex.

We improved our optical recording system to record epifluorescence optical signals from the intact cerebral cortex. Using custom-made fiber optic illumination equipment and tandem lens optics excluding a dichroic mirror, we successfully obtained high-quality single sweep optical signals in vivo in rat sensorimotor cortex. After reduction of pulsation artifacts with software originally designed for prolonged continuous recording under spontaneous breathing, the signal-to-noise ratio of the optical signal was sufficient to analyse evoked responses quantitatively. We were able to make isochrones for the onset of responses based on single sweep optical recordings. We further examined the effect of baclofen using this isochrone map, and succeeded in quantitatively demonstrating the inhibitory effect on the spatial pattern of neural activity in the rat sensorimotor cortex by calculating the area of response region on the isochrone map. Thus, our improved system provides sustained single sweep records suitable for quantitative analysis using epifluorescence optics.