The neurite outgrowth and gene expression of PC12 cells on collagen-coated glass plates under light-emitting diode (LED) irradiation and mixed light irradiation were investigated at several wavelengths (470, 525, 600, and 630 nm). We found that visible light regulated the neurite outgrowth of PC12 cells. Therefore, we investigated the expression level of p75NTR and TrkA in PC12 cells in order to evaluate whether gene expression in PC12 cells changed according to the wavelength of light used to irradiate these cells. When the PC12 cells were irradiated with mixed light or LED light for 10 min or 30 h in the presence of nerve growth factor (NGF), p75NTR expression was downregulated compared to that in PC12 cells cultured in the dark with NGF in the culture medium. Light irradiation influenced the expression of TrkA in the PC12 cells cultured with or without NGF. Light irradiation of PC12 cells regulated the expression of specific genes as well as neurite outgrowth.
