BDNF and depressive symptom measurement: Additionally, experiments in female Sprague–Dawley rats with a post-ovariectomy timeframe of 8 weeks showed that ovariectomy triggered high levels of depression-like behaviors in the tail suspension test associated with a decrease in BDNF levels in the hippocampus but not in the prefrontal cortex; these alterations were ameliorated by 8 weeks of exercise on a treadmill or E2 administration (136).