MAPT and Cognitive impairment: Consistent with AD patients, mice overexpressing human P301L Tau in the DRN recapitulate the degeneration of serotonergic system in AD patients, including profound 5-HT neuron loss, 5-HT neuron hyperexcitability, inflammation, axonal degeneration, as well as cognitive impairment and behavioral symptoms, including depressive- and anxiety-like behaviors, hyperlocomotion, and social deficits [172,176,177].