Injection of oxytocin into paraventricular nucleus reverses depressive-like behaviors in the postpartum depression rat model

Oxytocin (OXT) has been considered as a neuroregulator mediating social behaviors and stress-related disorders. Recent clinical studies suggest that OXT might also act as antidepressant in postpartum depression (PPD) patients, but the mechanism is still unknown. In the present study, we explored the effect of OXT in paraventricular nucleus (PVN) and possible signaling pathway involved in a PPD rat model induced by gestation restraint stress (GRS). PPD rats exhibited depressive-like behaviors with significantly longer immobility time, shorter climbing time, and lower sucrose consumption compared to the control rats. Plasma corticosterone (CORT) level was also higher in PPD rats. While PVN and supraoptic nucleus (SON) are main OXT synthesis regions in the brain, GRS-induced decrease of mRNA and peptide level of OXT was seen only in PVN. The expression of TrkB in PVN was increased in PPD rats. Local injection of OXT (20 ng) into PVN reversed GRS-induced depressive-like behaviors and high plasma CORT level in PPD rats. Moreover, injection of OXT also reversed GRS-induced increase of TrkB in PVN of PPD rats. All those data suggest that OXT plays an antidepressant role by, at least in part, modulating HPA axis via TrkB in PVN of PPD rats.