Transcranial light affects the expression of brain encephalopsin and plasma monoamine concentration in the mouse

Abstract

Encephalopsin (OPN3) belongs to the light-sensitive transmembrane receptor family mainly expressed in the brain and retina. It is believed that light affects mammalian circadian rhythmicity only through the retinohypothalamic tract, which transmits light information to the suprachiasmatic nucleus in the hypothalamus. However, it has been shown that light penetrates the skull. Here, we present the effect of transcranial light treatment on OPN3 expression and monoamine concentrations in mouse brain and other tissues. Mice were randomly assigned to control group, morning-light group and evening-light group, and animals were illuminated transcranially five times a week for 8 min for a total of 4 weeks. The concentrations of OPN3 and monoamines were analysed using western blotting and HPLC, respectively. We report that transcranial light treatment affects OPN3 expression in different brain areas and plasma/adrenal gland monoamine concentrations. In addition, when light was administered at a different time of the day, the response varied in different tissues. These results provide new information on the effects of light on transmitters mediating mammalian rhythmicity.

Transcranial Light Alters Melanopsin and Monoamine Production in Mouse (Mus musculus) Brain

“…It should be remembered that mice are nocturnal animals and the ML group was illuminated in the beginning of their resting state, which might disturb the circadian rhythm and stress the animals. We have previously published results regarding the effects of transcranial light on monoamine concentrations in plasma and adrenal gland samples [20]. We showed that the levels of dopmanine and noradrenaline increased, and the levels of adrenaline decreased with transcranially illuminated mouse [20].…”

“…Since OPN4 is known to have an important role in light transmission through the eyes, and on the other hand, OPN4 is shown to be expressed in the hypothalamus [27], it may be capable of activating circadian signaling pathways directly by transcranially penetrated light, although we acknowledge that there might be some light transmitted through the transcranially illuminated ocular photoreceptors [49,50]. Even though the absorption maximum of our light source (450 nm) [20] was not optimal for the OPN4 expression maximum (476 -484 nm) [51,52], we were able to obtain significant results in this study.…”

“…The intensity of the light in the headphones of the light source (Valkee NPT 1000, Valkee Inc., Oulu, Finland) was 2.00 × 10 15 photons/cm 2 /s. We have presented the spectrum of the headphones in our previous article with an intensity peak at approximately 450 nm [20]. There is no significant heat effect caused by the device, since only a non-measurable small fraction of the mechanical heat produced by the light source (totally less than 14.7 mW) is conducted into the ear canal.…”

“…As shown, OPN4 is expressed in the vertebrate brain [25,27,39], and opsins can be stimulated transcranially [20]. Additionally, monoamines play a role in light signaling [40], and also e.g.…”

“…It has been also proved that light is capable of phosphorylating OPN4, which inhibits the G protein-coupled activation [18], although only some OPN4 gene variants have been shown to affect the responses to light stimulus [19]. Notwithstanding general criticism, we have recently shown that it is possible to stimulate brain opsins by illuminating the brain via ear canals [20].…”