Comparison between transgenic and AAV-PHP.eB-mediated expression of GCaMP6s using in vivo wide-field functional imaging of brain activity.

We employ transcranial wide-field single-photon imaging to compare genetically encoded calcium sensors under transgenic or viral vector expression strategies. Awake, head-fixed animals and brief visual flash stimuli are used to assess function. The use of awake transcranial imaging may reduce confounds attributed to cranial window implantation or anesthesia states. We report differences in wide-field epifluorescence brightness and peak Δ F / F 0 response to visual stimulation between expression strategies. Other metrics for indicator performance include fluctuation analysis (standard deviation) and regional correlation maps made from spontaneous activity. We suggest that multiple measures, such as stimulus-evoked signal-to-noise ratio, brightness, and averaged visual Δ F / F 0 response, may be necessary to characterize indicator sensitivity and methods of expression. Furthermore, we show that strategies using blood brain barrier-permeable viruses, such as PHP.eB, yield comparable expression and function as those derived from transgenic mice. We suggest that testing of new genetically engineered activity sensors could employ a single-photon, wide-field imaging pipeline involving visual stimulation in awake mice that have been intravenously injected with PHP.eB.