CYP19A1 and Alzheimer disease: The circumstance that aromatase is upregulated in some regions of AD brains (e.g., the CA4 region of the hippocampus (shown in this study), the prefrontal cortex [32], and the nucleus basalis of Meynert [31]), but downregulated in other regions (e.g., the supraoptic nucleus, the infundibular nucleus, and the medial mamillary nucleus [31]), suggests that the regulation of aromatase expression is very complex.