40 Hz light flickering promotes sleep through cortical adenosine signaling

Abstract

Flickering light stimulation has emerged as a promising non-invasive neuromodulation strategy to alleviate neuropsychiatric disorders. However, the lack of a neurochemical underpinning has hampered its therapeutic development. Here, we demonstrate that light flickering triggered an immediate and sustained increase (up to 3 h after flickering) in extracellular adenosine levels in the primary visual cortex (V1) and other brain regions, as a function of light frequency and intensity, with maximal effects observed at 40 Hz frequency and 4000 lux. We uncovered cortical (glutamatergic and GABAergic) neurons, rather than astrocytes, as the cellular source, the intracellular adenosine generation from AMPK-associated energy metabolism pathways (but not SAM-transmethylation or salvage purine pathways), and adenosine efflux mediated by equilibrative nucleoside transporter-2 (ENT2) as the molecular pathway responsible for extracellular adenosine generation. Importantly, 40 Hz (but not 20 and 80 Hz) light flickering for 30 min enhanced non-rapid eye movement (non-REM) and REM sleep for 2–3 h in mice. This somnogenic effect was abolished by ablation of V1 (but not superior colliculus) neurons and by genetic deletion of the gene encoding ENT2 (but not ENT1), but recaptured by chemogenetic inhibition of V1 neurons and by focal infusion of adenosine into V1 in a dose-dependent manner. Lastly, 40 Hz light flickering for 30 min also promoted sleep in children with insomnia by decreasing sleep onset latency, increasing total sleep time, and reducing waking after sleep onset. Collectively, our findings establish the ENT2-mediated adenosine signaling in V1 as the neurochemical basis for 40 Hz flickering-induced sleep and unravel a novel and non-invasive treatment for insomnia, a condition that affects 20% of the world population.

Optochemical control of slow-wave sleep in the nucleus accumbens of male mice by a photoactivatable allosteric modulator of adenosine A2A receptors

“…We also reduced astrocyte calcium signaling by expressing the human plasma membrane calcium pump isoform type 2 (hPMCA2), which constitutively extrudes cytosolic calcium (Supplementary Fig. 4a ) 18 , 19 . Extracellular adenosine levels in the NAc were significantly reduced after the transition from SWS to wakefulness and increased during REM sleep (Supplementary Fig.…”

“…Previous reports showed that NAc A 2A Rs are involved in the impairment of discrimination learning, working memory, and psychomotor activity associated with schizophrenia 43 , 44 . Moreover, 40-Hz light flickering, recognized by the United States Food and Drug Administration as a prospective therapy for Alzheimer’s disease 45 , 46 , elevates extracellular adenosine levels in several brain regions that control important physiological processes, including the NAc 19 . Combining light flickering to induce ligand release with PAM optochemistry to enhance receptor activity may pave the way for innovative light-based therapeutic strategies to treat sleep and various brain disorders in the future.…”

Enhancement of spatial learning by 40 Hz visual stimulation requires parvalbumin interneuron-dependent hippocampal neurogenesis

“…The exact mechanism underlying how rhythmic 40 Hz light flicker alleviates neurological functional deficits is currently under intense discussion and investigation 6 . Existing evidence indicates that 40 Hz light flicker entrain with various brain areas, including the hippocampus, to stimulate responses in hippocampal neural circuits 4 , the circadian clock 37 , the glymphatic contraction 3 , microglial activation 1 , and secretion of selective neurochemical mediators such as adenosine 5,7 . However, these studies have primarily focused on acute and short-term exposure to 40 The long-term beneficial effect of 40 Hz light flicker was dependent on DG neurogenesis.…”

“…Recent studies of our own and others have demonstrated significant beneficial effects of rhythmic 40 Hz light flicker in alleviating cognitive deficits in animal models of AD [1][2][3] , stroke 4 , and ASD 5 . While the specific underlying mechanisms vary and are currently under rigorous investigation and debate 6 , several potential pathways have emerged, including the enhancement of mechanisms involved in the clearance of toxic materials [1][2][3] , improvement in synaptic connectivity and strength 4 , and increased neurochemical mediators 5,7 . Our human brain electroencephalogram studies have confirmed not only an increase in 40 Hz entrainment in various brain regions but also a substantial alteration in microstates associated with brain functions damaged in AD and stroke patients 8 .…”