In future investigation, if reduction of hippocampal tau is observed in another tauopathy animal model with hypersomnolence, detailed examinations, such as tau release into ISF, output of the glymphatic pathway, and abnormal phosphorylation and aggregation of tau proteins in the hippocampus should be investigated after chronic administration of an OX2R-selective agonist. Here, HCRTR2 is linked to tauopathy.