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Recently, infrared light has been shown to both stimulate and inhibit excitatory cells. However, studies of infrared light
for excitatory cell inhibition have been constrained by the use of invasive and cumbersome electrodes for cell excitation
and action potential recording. Here, we present an all optical experimental design for neuronal excitation, inhibition,
and action potential detection. Primary rat neurons were transfected with plasmids containing the light sensitive ion
channel CheRiff. CheRiff has a peak excitation around 450 nm, allowing excitation of transfected neurons with pulsed
blue light. Additionally, primary neurons were transfected with QuasAr2, a fast and sensitive fluorescent voltage
indicator. QuasAr2 is excited with yellow or red light and therefore does not spectrally overlap CheRiff, enabling
imaging and action potential activation, simultaneously. Using an optic fiber, neurons were exposed to blue light
sequentially to generate controlled action potentials. A second optic fiber delivered a single pulse of 1869nm light to the
neuron causing inhibition of the evoked action potentials (by the blue light). When used in concert, these optical
techniques enable electrode free neuron excitation, inhibition, and action potential recording, allowing research into
neuronal behaviors with high spatial fidelity.
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