ZAPIT: OPEN SOURCE RANDOM-ACCESS PHOTOSTIMULATION FOR NEUROSCIENCE

Aims: Optogenetic tools are invaluable for causally manipulating neural activity to dissect the circuits underlying behaviour. Galvanometric scanning systems for transcranial stimulation is an ideal, affordable solution for flexible and non-invasive optogenetic manipulations in mouse dorsal cortex. However, this method is technically challenging to implement, and no open-source solution currently exists. Here, we present ‘Zapit’, an open-source platform for spatio-temporally precise random-access scanning optogenetic experiments in head-fixed mice.
Methods: Zapit integrates commercially available hardware with intuitive software enabling users to build and control a laser-scanning optogenetic system. Zapit incorporates a laser, galvanometric scanners, dichroic and emission filters, and a camera for real-time visualisation. The open-source software includes a graphical interface for stimulation design and semi-automated calibration routines for precise light targeting. During experiments, users can effectively target multiple sites simultaneously, and can deliver stimuli with sub-millisecond latency.
Results: We present results from multiple laboratories actively using Zapit. The results demonstrate robust photoinhibition-mediated behavioural changes in awake behaving VGAT-ChR2-EYFP transgenic mice. Contingent on perturbation location and stimulus strength, photoinhibition produced reliable perceptual and/or choice impairments in behaviour. We also confirm efficacy with electrophysiological recordings. Zapit is compatible with several modifications, including a custom-built sound-attenuating enclosure, various lasers that differ in cost and wavelength (suited to opsins including Channelrhodopsin and Jaws), and customised optical components for dual-laser experiments.
Conclusions: Zapit provides an affordable, accessible and flexible solution for spatio-temporal, non-invasive optogenetic perturbation in head-fixed mice. The open-source system, code and assembly instructions are available on GitHub (https://github.com/Zapit-Optostim).