Control of wheel running by near-ultraviolet light

Wheel running by mice was compared during incandescent and incandescent plus near-ultraviolet (UV) illumination in three experiments. During the daily 12-hour light period, running rates decreased with supplemental UV compared to previous incandescent only baselines. The decrements were systematically replicated in a second experiment using alternating UV exposure and recovery phases programmed across blocks of sessions. Again, running rates consistently decreased with supplemental UV irradiation of phases two and four compared to preceding baselines of phases one and three. In comparison, running rates were inconsistently affected during the 12-hour dark period in both experiments. A third experiment compared the relative decremental effects of UV, blue and red illumination. Baseline running rates monotonically decreased as an inverse function of wavelength for all subjects. The data suggest that the spectral composition of ambient illumination may affect behavior.