Laser action spectrum of reduced excitability in nerve cells.

The change in excitability of unstained nerve cells from neonatal rat cerebellum was measured as a function of the energy flux and wavelength of incident laser light. The energy flux was in the range of 0 to 100 microJ/sq. microns. 6 wavelengths between 490 and 685 nm were used. Laser pulses above a threshold energy flux significantly reduced the cells' excitability as measured by extracellular stimulation. The sensitivity of the cells, defined as the inverse of the threshold energy density, increased by an order of magnitude toward the shorter wavelengths. These results are consistent with primary absorption of the light by mitochondrial enzymes, resulting in local heating followed by mitochondrial calcium release into the cytoplasm.