Estrogen receptors colocalize to some neuronal populations that express BDNF and TrkB to regulate BDNF/TrkB expression and distribution, and this relationship has been shown to play a role in neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease (Sohrabji and Lewis, 2006). This evidence concerns the gene NTRK2 and early-onset autosomal dominant Alzheimer disease.