Abstract
This work focuses on the optical stimulation of dorsal root ganglion (DRG) neurons through infrared laser light stimulation. We show that a few millisecond laser pulse at 1875 nm induces a membrane depolarization, which was observed by the patch-clamp technique. This stimulation led to action potentials firing on a minority of neurons beyond an energy threshold. A depolarization without action potential was observed for the majority of DRG neurons, even beyond the action potential energy threshold. The use of ruthenium red, a thermal channel blocker, stops the action potential generation, but has no effects on membrane depolarization. Local temperature measurements reveal that the depolarization amplitude is sensitive to the amplitude of the temperature rise as well as to the time rate of change of temperature, but in a way which may not fully follow a photothermal capacitive mechanism, suggesting that more complex mechanisms are involved.
Highlights
Infrared laser light has been shown to stimulate neurons and nerves [1]
3.1 IR laser pulses induce transient membrane potential variations in dorsal root ganglion (DRG) neurons All the tested DRG neurons were depolarized during the irradiation time by a single laser pulse with energy ranging from 5.6 to 25.2 J/cm2 (i.e. 0.44 to 2 mJ) by varying the exposure time from 2 to 9 ms at a constant optical power of 220 mW
Our results show that IR laser stimulations induce transient membrane potential changes on DRG neurons
Summary
Infrared laser light has been shown to stimulate neurons and nerves [1]. Using such a light has real advantages for controlling neuron activities: contactless, good spatial and temporal resolution. Infrared (IR) neural stimulation has been demonstrated to activate numerous nerves such as sciatic nerves [2,3], cavernous nerves [4], auditory nerves [5]. Clinical developments of such approaches have been restrained by the lack of information regarding the underlying mechanisms. Among the possible biophysical mechanisms underlying the laser-tissue interaction, such as photochemical, photothermal, photomechanical, photoablation [8], the photothermal effect appears to be the most likely [9]
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