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12 months p < 0.01). However, these did not reach the amplitudes found at 2 months. There was a 15% difference between 2 months and both aged groups, which was significant at 7 months (p < 0.05) but not at 12 months, implying a greater improvement in 12-month treated mice. Statistical differences between the groups for the ERGs at progressive stimulus light intensity are given in the figure legend. Significant improvements were also found in the b-wave of approximately 30% in the 7-month animals and 20% in the 12-month mice (both significant: 7 months and 12 months p < 0.001). But in both cases, improvements remained significantly different from 2 months responses by approximately 30% at higher intensities (7 months and 12 months p < 0.001). There were no timing differences. A significant improvement in the photopic b-wave was only found in 12-month mice of 20% (p < 0.05). No significant differences were found between these treated mice and 2-month-old animals, similar to the scotopic a-wave in treated 12 months mice. Again there were no timing differences. Retinae stained for COX (Fig. 2) showed that in each of the aged groups, COX levels were significantly greater in mice exposed to 670 nm than in their age-matched unexposed controls at both 7 months (p < 0.01) and 12 months (p < 0.05) groups. This confirmed an association between improved mitochondrial and retinal function. 4. Discussion Our results show that brief, daily 670 nm exposure over a month significantly improves both the photoreceptor-generated a-wave and the postreceptoral b-wave ERG, but that they do not completely mitigate the impact of aging. This mirrors findings where 670 nm light has been used to protect against light induced photoreceptor degeneration, significant protection was afforded, but this did not provide complete protection (Albarracin et al., 2011). However, ERGs are relatively crude, and are thought to be about 2 log units less sensitive than psychophysical responses (Ruseckaite et al., 2011). Hence, the magnitude of 670 nm on the aging retina may be greater than that revealed here. We did find significant im- provements in photopic responses at 12 months but not at 7 months. Hence, our data are consistent with a notion that 670 nm has a greater effect when animals are older. The reason for improvements in amplitude are unclear but may relate to increased ATP availability to Naþ/Kþ ATP pumps, as these pumps decline with age (de Lores Arnaiz and Ordieres, 2014). Alternatively, a general improvement in photoreceptor physiology may be due to reduced inflammation (Begum et al., 2013). Although near infrared light is of therapeutic value in induced pathology (Fitzgerald et al., 2013), it has not been extensively used in aging. However, we know that it reduces age-related inflam- mation and retinal stress (Begum et al., 2013, 2015; Calaza et al., 2015; Kokkinopoulos et al., 2013). The mechanism of action may relate to its absorption by cytochrome c oxidase in the electron transport chain. Subsequent changes in the redox state of this may increase ATP, which declines significantly by 4 months of age (Calaza et al., 2015; Gkotsi et al., 2014). However, there may not be a single mechanism behind improvements when exposure is over a long period (Karu, 1999). The cellular environment is different when tissue has suffered from induced pathology, where 670 nm has been used extensively (Fitzgerald et al., 2013) compared with that in aging. Aging is a chronic condition where mitochondria decline gradually. However, in both situations, the light appears to offer significant benefit without adverse effects. As such it may provide significant value in problems of general aging. Furthermore, as declining mitochon- drial function is implicated in age-related macular degeneration (Terluk et al., 2015), use of 670 nm light, particularly in early stages of the disease, could provide a therapeutic route to reducing its impact in a situation where little or no alternative exist. Disclosure statement The authors have no conflict of interest. Animals were used with University College London ethical committee approval under a Home Office animal project license. All animal procedures con- formed to the United Kingdom Animals Scientific Procedures Act 1986. Acknowledgements This research was supported by the Biotechnological and Bio- logical Sciences Research Council of the UK. Grant no BB/N000250/1. References Albarracin, R., Natoli, R., Rutar, M., Valter, K., Provis, J., 2011. 670 nm light mitigates oxygen-induced degeneration in C57BL/6J mouse retina. BMC Neurosci. 14, 125. Begum, R., Calaza, K., Kam, J.H., Salt, T.E., Hogg, C., Jeffery, G., 2015. Near-infrared light increases ATP, extends lifespan and improves mobility in aged Drosophila melanogaster. Biol. Lett. 11, 20150073. Begum, R., Powner, M.B., Hudson, N., Hogg, C., Jeffery, G., 2013. Treatment with 670 nm light up regulates cytochrome C oxidase expression and reduces inflam- mation in an age-related macular degeneration model. PLoS One 8, e57828. Birch, D.G., Anderson, J.L., 1992. Standardized full-field electroretinography. Normal values and their variation with age. Arch. Ophthalmol. 110, 1571e1576. Calaza, K.C., Kam, J.H., Hogg, C., Jeffery, G., 2015. Mitochondrial decline precedes phenotype development in the complement factor H mouse model of retinal degeneration but can be corrected by near infrared light. Neurobiol. Aging 36, 2869e2876. Catchpole, I., Germaschewski, V., Hoh Kam, J., Lundh von Leithner, P., Ford, S., Gough, G., Adamson, P., Overend, P., Hilpert, J., Lopez, F.J., Ng, Y.S., Coffey, P., Jeffery, G., 2013. 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