BDNF and depressive symptom measurement: More specifically, estrogen is known to regulate BDNF, neurotransmitter-synthesizing enzymes, neurotransmitter-metabolizing enzymes, and their receptors by acting on Estrogen Receptor α (ERα) and ERβ distributed in various parts of the brain, including depression-related hypothalamus, hippocampus, and serotonin neurons of dorsal raphe [81,82].