Long-term UVA eye irradiation causes decreased learning ability in mice.

Abstract

Long-term eye radiation with ultraviolet A (UVA) denatures the cells of the cerebral hippocampus. However, the influence on memory and learning ability in mice is not known. HR-1 mice were used. We irradiated the eyes or dorsal skin of the mice with UVA at a dose of 110 kJ/m(2) using an FL20SBLB-A lamp for 6, 12, and 24 months. The mean escape latency in the water maze was significantly increased in the UVA-irradiated mice in comparison with that seen in the controls. In the mice in which UVA eye irradiation was performed for 24 months, the depression of memory and learning ability was remarkable. The acetylcholinesterase activity, choline acetyltransferase activity, and acetylcholine content in the brain in the UVA eye-irradiated mice were significantly less than those observed in the control mice. Furthermore, during UVA eye irradiation, the levels of β-amyloid (Aβ), γ-secretase, which produces Aβ peptide, and advanced glycation end products increased. Moreover, the effects of UVA eye irradiation increased with the duration of irradiation (or aging), and the introduction of glucose into the brain also decreased with UVA eye irradiation. These results indicate that UVA eye irradiation induces a decreased memory and learning ability in mice.