HTR4 and Alzheimer disease: In addition, reduced DRN5-HT-CA1CaMKII serotonergic transmission promotes hyperactivity of CA1CaMKII neurons in 5×FAD mice, and activation of DRN5-HT neurons ameliorates cognitive deficits in AD via 5-HT1BR/5-HT4R -mediated modulation of CA1CaMKII neurons [68,211].