DRD2 and Alzheimer disease: Reduced levels of serotonin 5-HT7 receptors wereobserved in the brain of aging rodents,28 and decreased expression of 5-HT7 receptors in the hippocampuswas linked to age-related memory impairment.29 The dopamine D2 receptor acquired considerable importanceas a potential target for BPSD after clinical studies revealed changesin the abundance of dopamine D2 receptors in AD patientsthat manifest behavioral abnormalities.30−32 Other studies suggestedthat dysfunction of dopaminergic signaling may result in the onsetof apathy and loss of enjoyment in AD patients.