レーザーによる神経機能調節とそのメカニズム

抄録

Low-reactive level laser therapy has been applied for pain relief and improvement of local circulation, and hasbeen popular in many clinical fields. The cellular mechanism, however, has not been fully clarified. Some basic researches indicated that laser suppresses neural activity by direct action on the nervous tissue, and affects membrane potential and the input membrane resistance of neurons. Using low-reactive level laser irradiation with a near-infrared diode laser (continuouswave; wavelength, 830 nm; power density, 1-5 W/cm²), we achieved inactivation of excitatory synaptic transmission in the central nervous system of rodents. In the study using cultured rat hippocampal neurons, the laser irradiation induced hyperpolarization of the membrane potential and reduction of input membrane resistance, suggesting that the laser suppressed synaptictransmission by opening potassium channels in the cells. The laser irradiation increased the content of adenosine triphosphate (ATP) in the tissue. Furthermore, laser-induced suppression of synaptic transmission was attenuated under application of anATP-sensitive potassium channel opener. These observations indicate that suppression of neural activity by low-reactive levellaser irradiation in a near-infrared wavelength is brought about by opening of ATP-sensitive potassium channels by the increasein intracellular ATP level. Recently, it was demonstrated that laser irradiation suppressed synaptic transmission morepotently in hippocampal slices at a low ATP content. This may contribute to the clinical phenomenon that more potent effectsof low-reactive level laser irradiation are often seen on tissue under pathological states than physiological states.