BDNF and depressive symptom measurement: This downregulation of BDNF is closely associated with impaired synaptic plasticity, a hallmark of depression and mood dysregulation [47,48] Conversely, animals resilient to chronic stress exhibit an adaptive upregulation of BDNF, mediated by permissive histone modifications such as H3K4me3, which help maintain neural plasticity and mood stability [51].