Neurite growth of trigeminal ganglion neurons in vitro with near-infrared light irradiation.

Trigeminal ganglion (TG) neurons play an essential role in the sensory nerves of the face. Damaged TG neurons resulting from the accidental and non-intentional nerve lesions, commonly identified as neuropathic pain, which is known to cause intense pain and sensory abnormalities. For the treatment, surgical methods are conducted when the pharmacological treatment fails to provide satisfactory recovery. However, the process of surgery or drug intake can burden the patient or cause side effects. One of the logical choices of study becomes photobiomodulation (PBM) referred to as therapeutic approaches based on the interactions of visible or near-infrared (NIR) photons with biomolecules inside cells or tissues. In this study, we constructed a PBM illumination setup to stimulate the cultured primary TG neurons and compared the growth morphology between the non-irradiated control group and irradiation group with NIR laser of 808 nm wavelength. In addition, we applied various radiant exposures of 1, 2, and 10 J/cm with different pulse frequencies of 1, 10, and 100 Hz. We found that PBM could promote neurite growth of TG neurons, and it works at relatively low energy densities at 1 and 2 J/cm. The irradiation group in the pulsed wave mode with the frequency of 10 Hz was found to be the most effective when compared to other frequencies. Thus, PBM on TG neurons facilitated neuronal growth in vitro in a dose and frequency-dependent fashion. PBM may provide a potential therapeutic approach to treat damaged peripheral nerves.