Meningeal lymphatic vessels (MLVs) play an important role in the removal of toxins and metabolites from brain tissues1,2,3. Damage of MLVs in various brain diseases, including tumors, traumatic brain injuries, hemorrhages, and neurodegenerative processes, is accompanied by a decrease in the MLV functions leading to the progression of these pathologies1,2,3,4,5,6. Therefore, the development of methods for the stimulation of MLVs opens new horizons in the emergence of effective technologies for the treatment of brain diseases. Recently, non-invasive technology for effective transcranial photobiomodulation (tPBM) has been proposed to stimulate MLVs and remove toxins such as blood and Aβ from the brain5,7,8,9,10,11,12. It is interesting to note that deep sleep is a natural factor for the activation of lymphatic drainage processes in the brain13,14. Based on this fact, it is logical to assume that the tPBM of MLVs during sleep may have more effective therapeutic effects than during wakefulness9,11,12,15. However, there are currently no commercial technologies for tPBM during sleep16. In addition, animal experiments to study the therapeutic effects of tPBM are performed under anesthesia, which is required to accurately deliver light to the brain. However, anesthesia significantly affects the brain's drainage, which reduces the quality of research results17.
Aβ is a metabolic product of normal neural activity18. As it was established in cultured rat cortical neurons, Aβ is released from them at high rates into the extracellular space (2-4 molecules/neuron/s for Aβ)19. There is evidence that the dissolved form of Aβ, located in the extracellular and perivascular spaces, is most toxic to neurons and synapses20. The soluble Aβ is rapidly cleared from the human brain during 1-2.5 h21. MLVs are the tunnels for removal of the soluble Aβ from the brain1,7 that declines with age, leading to the accumulation of Aβ in the aged brain1,22. There is evidence that extracellular abnormalities of Aβ levels in the brain correlate with cognitive performance in aging and are associated with the development of Alzheimer's disease (AD)23,24. Therefore, aged and old rodents are considered alternatives to transgenic models for the study of amyloidosis, including AD25,26.
This study presents an original and portable tPBM technology under electroencephalographic (EEG) control of deep or non-rapid eye movement (NREM) sleep in non-anesthetized male C57BL/6 mice of different ages to stimulate lymphatic clearance of Aβ from the brain into the peripheral lymphatic system (the deep cervical lymph nodes, dcLNs).