Impact of light irradiation on preservation and function of mammalian spermatozoa

Light irradiation has been demonstrated to exert positive effects on gametes, and particularly on sperm. In effect, a high number of studies conducted in several species, including humans, mice, pigs, cattle and sheep, and using different light sources (such as lasers and light-emitting diodes) have demonstrated that photo-stimulation increases sperm motility. In addition, other works have shown that sperm fertilizing ability both in vitro and in vivo can be increased following light irradiation; there are also some evidences pointing out to an extend of lifespan of preserved semen. Notwithstanding, no study has reported a detrimental effect of visible light on DNA integrity. The mechanisms through which light exerts its effects are not completely elucidated, but mounting evidence gives cell photosensitizers, especially those present in the mitochondria, a vital role. Stimulating these molecules turns into an increase in the production of ATP and Ca²⁺ influx, which contributes to explain the effects of light upon spermatozoa. Additionally, the presence of opsins in spermatozoa as well as the potential influence of light on the conformation of other proteins may also be involved in the sperm response to light. However, there are still a significant number of points that need to be addressed and their elucidation may contribute to increase the utilization of light irradiation for sperm preservation and ART.