Nanosecond laser pulse stimulation of spiral ganglion neurons and model cells

Abstract

Optical stimulation of the inner ear has recently attracted attention, suggesting a higher frequency resolution compared to electrical cochlear implants due to its high spatial stimulation selectivity. Although the feasibility of the effect is shown in multiple in vivo experiments, the stimulation mechanism remains open to discussion. Here we investigate in single-cell measurements the reaction of spiral ganglion neurons and model cells to irradiation with a nanosecond-pulsed laser beam over a broad wavelength range from 420 nm up to 1950 nm using the patch clamp technique. Cell reactions were wavelength-and pulse-energy-dependent but too small to elicit action potentials in the investigated spiral ganglion neurons. As the applied radiant exposure was much higher than the reported threshold for in vivo experiments in the same laser regime, we conclude that in a stimulation paradigm with nanosecond-pulses, direct neuronal stimulation is not the main cause of optical cochlea stimulation.

Millisecond infrared laser pulses depolarize and elicit action potentials on in-vitro dorsal root ganglion neurons

“…What remains unclear is how this transient heating elicits membrane depolarization of neurons and action potentials. Several mechanisms of action have been suggested, including the generation of transient capacitive currents [14,17], the stimulation of temperature sensitive ion channels [15,16], the generation of small pores in the plasma membrane [20] or the generation of laser-generated pressure pulses [18]. Our results show that IR laser pulses depolarize DRG neurons without the involvement of thermo-sensitive TRPV channels since the use of ruthenium red, a general blocker of TRP channels did not modify the depolarization amplitude.…”

“…Infrared laser pulses have been shown to induce intracellular calcium transients implicating mitochondria in neonatal cardiomyocytes [10] and in neonatal spiral and vestibular ganglion neurons [11] and to depolarize membranes in HEK293 cells [12], dorsal root ganglion neurons [13], oocytes, HEK cells and artificial layers [14], retinal and vestibular primary neurons [15,16], hippocampal neurons [17], spiral ganglion neurons [18], brain slices [19] and in vestibular hair cells and afferent neurons [20]. What remains unclear is whether an universal photothermal mechanism exists and how the transient heating induced by the IR laser pulse elicits membrane depolarization of neurons and action potentials or modulates intracellular signalling.…”

“…What remains unclear is whether an universal photothermal mechanism exists and how the transient heating induced by the IR laser pulse elicits membrane depolarization of neurons and action potentials or modulates intracellular signalling. Several mechanisms of action have been suggested, including the generation of transient capacitive currents [14,17], the stimulation of temperature sensitive ion channels [15,16], the generation of small pores in the plasma membrane [21] or the generation of laser-generated pressure pulses [18].…”

Infrared neural stimulation fails to evoke neural activity in the deaf guinea pig cochlea

“…Laser sources used for INS have been shown to generate an acoustic click from rapid expansion of heated water, resulting in an optoacoustic mediated response (Teudt et al, 2011). Optoacoustic generation of sound has been shown to be applicable to many different wavelengths, including those used by INS, and appears to be driven by water or haemoglobin absorption (Schultz et al, 2012;Rettenmaier et al, 2014). Therefore, if the deafening process is not complete and functional hair cells remain, the generation of an acoustic click during INS may lead to a response mediated by activation of residual hair cells by this acoustic artefact.…”

Signal and response properties indicate an optoacoustic effect underlying the intra-cochlear laser-optical stimulation

“…The optical intra-cochlear stimulation is based on direct activation of the spiral ganglion neurons [7][8][9][10][11] or on the optoacoustic effect [12][13][14][15][16] . The optoacoustic mechanism deflects the basilarmembrane of the cochlea and activates the inner hair cells.…”