BDNF and depressive symptom measurement: The presence of a 66Met-derived despair phenotype at baseline in our hBDNFVal66Met model is consistent with the broader literature on the role of BDNF in animal models of depression, where deficient BDNF expression results in social defeat and learned helplessness phenotypes,20, 21 and likely occurs via the disrupted activity-dependent release of BDNF induced by the 66Met substitution.