Schedules for neurite elongation experiment. The schedules for neurite elongation experiments including culture conditions and laser light irradiation are shown in upper part of the figure (see text for further details). The dotted arrows indicate the daily exposure to 20 sec laser pulse. Micrographs show PC12 cells cultured without (a, b) and with (c, d) NGF in the medium. Scale bar: a, c 100 μμ b, d 50 μμ. Pictures of living cells were taken every days, after laser irradiation. Abbreviations: DIV, days in vitro; NGF, nerve growth factor.