Histological and electrophysiological evidence on the safe operation of a sharp-tip multimodal optrode during infrared neuromodulation of the rat cortex

Abstract

Infrared neuromodulation is an emerging technology in neuroscience that exploits the inherent thermal sensitivity of neurons to excite or inhibit cellular activity. Since there is limited information on the physiological response of intracortical cell population in vivo including evidence on cell damage, we aimed to create and to validate the safe operation of a microscale sharp-tip implantable optrode that can be used to suppress the activity of neuronal population with low optical power continuous wave irradiation. Effective thermal cross-section and electric properties of the multimodal microdevice was characterized in bench-top tests. The evoked multi-unit activity was monitored in the rat somatosensory cortex, and using NeuN immunocytochemistry method, quantitative analysis of neuronal density changes due to the stimulation trials was evaluated. The sharp tip implant was effectively used to suppress the firing rate of neuronal populations. Histological staining showed that neither the probe insertion nor the heating protocols alone lead to significant changes in cell density in the close vicinity of the implant with respect to the intact control region. Our study shows that intracortical stimulation with continuous-wave infrared light at 1550 nm using a sharp tip implantable optical microdevice is a safe approach to modulate the firing rate of neurons.

Thermal neuromodulation using pulsed and continuous infrared illumination in a penicillin-induced acute epilepsy model

“…After that, room temperature physiological saline solution was dripped on the sponge to prevent dehydration of the cortical tissue as well as to provide mechanical stabilization for the ECoG array. A silicon-based optical probe (optrode; 16 , 21 , 24 ) designed for infrared stimulation (see “ Infrared stimulation protocol ” section for detailed information) was inserted through the aperture (Fig. 1 B) into the brain tissue to a depth of 1.2 mm with a slow speed (2 m/s; to decrease the insertion-related mechanical tissue damage 25 ).…”

“…In this study, cortical heating is carried out using an optrode probe, which is a multimodal photonic device that uses pulsed and continuous NIR light illumination to conduct a controlled cortical heating 16 . Horváth et al have proved that this optrode device can be efficiently, repeatedly and safely used to perform deep tissue INM in anesthetized rats 16 , 21 . Here, infrared-based neuromodulation was performed in nine anesthetized rats.…”

Modulatory Effects on Laminar Neural Activity Induced by Near-Infrared Light Stimulation with a Continuous Waveform to the Mouse Inferior Colliculus In Vivo

“…To investigate the INS-induced modulation of the neural activity, we delivered 1,940 nm CW stimulation to the IC of mice. Few studies have used CW near-INS for neural modulation ( Xia and Nyberg, 2019 ; Horvath et al, 2020 , 2022 ), with repetitive short and pulsed patterns applied in many studies ( Wells et al, 2005 ; Izzo et al, 2008 ; Cayce et al, 2011 ). Pulsed wave INS lasers can repeatedly deliver heat to the brain surface over a very short period ( Wells et al, 2005 ; Izzo et al, 2008 ; Schultz et al, 2012 ), which prevents heat from rapidly diffusing to the surrounding area.…”

Infrared Neuroglial Modulation of spinal locomotor networks

“…Compared to electrical stimulation, INS presents advantages in terms of spatial precision and eliminates the need for genetic modifications or the use of exogenous chromophores. Despite the absence of standardized equipment for INS, ongoing developments are rapidly emerging, opening up new possibilities [72][73][74][75] , including the recent validation of INS for chronic deep brain stimulation (DBS) 76 . However, the path to clinical applications will require advancements both in fundamental understanding of INS mechanisms and in technological innovations to fully exploit the potential of this neurostimulation method.…”