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

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.

Effect of nanostructures on anchoring stem cell-derived neural tissue to artificial surfaces.

OBJECTIVE: Chronic application of brain implants monitoring or modulating neuronal activity are hindered by the foreign body response of the tissue. Topographical modification of implant surfaces may reduce negative tissue response by imitating the structure of the extracellular matrix and therefore affecting the attachment and behavior of neural cells. APPROACH: In our in vitro study, the effect of nanostructuring was investigated on two commercially used neural implant materials: silicon and platinum. The adhesion, survival and arrangement of neural stem cells (NE4C) and microglial cells (BV2) were investigated and compared to nanostructured and flat Si and Pt surfaces using cell viability studies and fluorescent microscopy image analysis. MAIN RESULTS: Our data indicated that neural cells established strong adhesive couplings with each other, instead of binding to the artificial surfaces. SIGNIFICANCE: The phenomena resemble some features of in vivo separation of living tissue from the implanted artificial material, providing an in vitro model for studying immune response.