Chronic stress and its effects on behavior, RNA expression of the bed nucleus of the stria terminalis, and the M-current of NPY neurons
Mood disorders, like major depressive disorder, can be precipitated by chronic stress and are more likely to be diagnosed in cisgender women than in cisgender men. This suggests that stress signaling in the brain is sexually dimorphic. We used a chronic variable mild stress paradigm to stress female and male mice for 6 weeks, followed by an assessment of avoidance behavior: the open field test, the elevated plus maze, the light/dark box emergence test, and the novelty suppressed feeding test. Additional cohorts were used for bulk RNA-Sequencing of the anterodorsal bed nucleus of the stria terminalis (adBNST) and whole-cell patch clamp electrophysiology in NPY-expressing neurons of the adBNST to record stress-sensitive M-currents. Our results indicate that females are more affected by chronic stress as indicated by an increase in avoidance behaviors, but that this is also dependent on the estrous stage of the animals such that diestrus females show more avoidant behaviors regardless of stress treatment.  Results also indicate that NPY-expressing neurons of the adBNST are not major mediators of chronic stress as the M-current was not affected by treatment. RNA-Sequencing data suggests sex differences in estrogen signaling, serotonin signaling, and orexin signaling in the adBNST. Our results indicate that chronic stress influences behavior in a sex- and estrous stage-dependent manner but NPY-expressing neurons in the BNST are not the mediators of these effects. Overall design: To study differential expression of genes in the anterodorsal bed nucleus of the strai terminalis in mice after exposure to chronic variable mild stress or control conditions. Differential expression was analyzed with the following parameters: sex + condition + sex:condition.