Temporal modulation of sodium current kinetics in neuron cells by near-infrared laser

Effects of Photodynamic Therapy on Nav1.7 Expression in Spinal Dorsal Root Ganglion Neurons

OBJECTIVE

The aim of this study was to examine the effects of photodynamic therapy (PDT) on the expression of Nav1.7 in spinal dorsal root ganglion (DRG) neurons.

METHODS

The primary DRG neurons from newborn SD rats were cultured. The cells were identified by neuron-specific enolase immunofluorescence staining. DRG neurons were divided into four groups: control group, photosensitizer group, laser group, and PDT group. The cell viability was detected by a cell counting kit-8 (CCK8) assay. qRT-PCR and Western blotting were used to determine the mRNA and protein expression levels of Nav1.7 in DRG neurons.

RESULTS

The purity of the cultured primary DRG neurons was greater than 90%. Compared with the control group, no significant change was found in the cell viability of the photosensitizer group, while the viability in the laser group and the PDT group was significantly reduced. The mRNA and protein expression levels of Nav1.7 were significantly greater in the laser group and the PDT group than in the control group. At the same time, the mRNA and protein expression levels of Nav1.7 were greater in the laser group than in the PDT group.

CONCLUSION

Both laser and PDT could upregulate the expression of Nav1.7 in DRG neurons, and the promoting effect might be related to the pain induced by clinical treatment. This study provides a research basis for the use of laser and PDT to treat pain. A better understanding of the relationship between Nav1.7 and PDT can help clinicians better manage PDT-related pain.

Gold Nanoparticles for Modulating Neuronal Behavior

Understanding the detailed functioning and pathophysiology of the brain and the nervous system continues to challenge the scientific community, particularly in terms of scaling up techniques for monitoring and interfacing with complex 3D networks. Nanotechnology has the potential to support this scaling up, where the eventual goal would be to address individual nerve cells within functional units of both the central and peripheral nervous system. Gold nanoparticles provide a variety of physical and chemical properties that have attracted attention as a light-activated nanoscale neuronal interface. This review provides a critical overview of the photothermal and photomechanical properties of chemically functionalized gold nanoparticles that have been exploited to trigger a range of biological responses in neuronal tissues, including modulation of electrical activity and nerve regeneration. The prospects and challenges for further development are also discussed.

Optical Stimulation of Neurons

Our capacity to interface with the nervous system remains overwhelmingly reliant on electrical stimulation devices, such as electrode arrays and cuff electrodes that can stimulate both central and peripheral nervous systems. However, electrical stimulation has to deal with multiple challenges, including selectivity, spatial resolution, mechanical stability, implant-induced injury and the subsequent inflammatory response. Optical stimulation techniques may avoid some of these challenges by providing more selective stimulation, higher spatial resolution and reduced invasiveness of the device, while also avoiding the electrical artefacts that complicate recordings of electrically stimulated neuronal activity. This review explores the current status of optical stimulation techniques, including optogenetic methods, photoactive molecule approaches and infrared neural stimulation, together with emerging techniques such as hybrid optical-electrical stimulation, nanoparticle enhanced stimulation and optoelectric methods. Infrared neural stimulation is particularly emphasised, due to the potential for direct activation of neural tissue by infrared light, as opposed to techniques that rely on the introduction of exogenous light responsive materials. However, infrared neural stimulation remains imperfectly understood, and techniques for accurately delivering light are still under development. While the various techniques reviewed here confirm the overall feasibility of optical stimulation, a number of challenges remain to be overcome before they can deliver their full potential.

Optogenetic approaches to retinal prosthesis

The concept of visual restoration via retinal prosthesis arguably started in 1992 with the discovery that some of the retinal cells were still intact in those with the retinitis pigmentosa disease. Two decades later, the first commercially available devices have the capability to allow users to identify basic shapes. Such devices are still very far from returning vision beyond the legal blindness. Thus, there is considerable continued development of electrode materials, and structures and electronic control mechanisms to increase both resolution and contrast. In parallel, the field of optogenetics--the genetic photosensitization of neural tissue holds particular promise for new approaches. Given that the eye is transparent, photosensitizing remaining neural layers of the eye and illuminating from the outside could prove to be less invasive, cheaper, and more effective than present approaches. As we move toward human trials in the coming years, this review explores the core technological and biological challenges related to the gene therapy and the high radiance optical stimulation requirement.

980-nm infrared laser modulation of sodium channel kinetics in a neuron cell linearly mediated by photothermal effect

Photothermal effect (PE) plays a major role in the near-infrared laser interaction with biological tissue. But, quite few interactions can be quantitatively depicted. Here, a two-step model is proposed to describe a 980-nm infrared laser interaction with neuron cell in vitro. First, the laser-induced temperature rises in the cell surrounding area were measured by using an open pipette method and also calculated by solving the heat conduction equation. Second, we recorded the modifications on sodium (Na) channel current in neuron cells directly by using a patch clamp to synchronize the 980-nm laser irradiation and obtained how the electrophysiological function of neuron cells respond to the temperature rise. Then, the activation time constants, τ(m), were extracted by fitting the sodium currents with the Hodgkin-Huxley model. The infrared laser modulation effect on sodium currents kinetics was examined by taking a ratio between the time constants with and without the laser irradiations. The analysis revealed that the averaged ratio at a specific laser exposure could be well related to the temperature properties of the Na channel protein. These results proved that the modulation of sodium current kinetics of a neuron cell in vitro by 980-nm laser with different-irradiation levels was linearly mediated corresponding to the laser-induced PE.