HTR6 and Alzheimer disease: The efficiency of 5-HT6R antagonists to alleviate cognitive impairments in a number of rodent models of neurodevelopmental, psychiatric, and neurodegenerative diseases [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31], in addition to its absence in peripheral organs, makes it a therapeutic target of choice for the treatment of cognitive symptoms of schizophrenia, autism spectrum disorders, and dementia associated with Alzheimer’s disease.