Mediodorsal thalamus projection to medial prefrontal cortical mediates social defeat stress-induced depression-like behaviors.

Clinical studies have shown that the mediodorsal thalamus (MD) may play an important role in the development of depression. However, the molecular and circuit mechanisms by which the mediodorsal thalamus (MD) participates in the pathological processes of depression remain unclear. Here, we show that in male chronic social defeat stress (CSDS) mice, the calcium signaling activity of glutamatergic neurons in MD is reduced. By combining conventional neurotracer and transneuronal virus tracing techniques, we identify a synaptic circuit connecting MD and medial prefrontal cortex (mPFC) in the mouse. Brain slice electrophysiology and fiber optic recordings reveal that the reduced activity of MD glutamatergic neurons leads to an excitatory-inhibitory imbalance of pyramidal neurons in mPFC. Furthermore, activation of MD glutamatergic neurons restores the electrophysiological properties abnormal in mPFC. Optogenetic activation of the MD-mPFC circuit ameliorates anxiety and depression-like behaviors in CSDS mice. Taken together, these data support the critical role of MD-mPFC circuit on CSDS-induced depression-like behavior and provide a potential mechanistic explanation for depression.