Identification Of A Prefrontal-to-Amygdala Pathway For Chronic Stress-induced Anxiety

Anxiety is the major prevalent disorder of psychiatric disorders.In the brain,the medial prefrontal cortex(m PFC)and amygdala exert reciprocally structural and functional connected and work in concert to orchestrate the expression of emotions,such as anxiety and fear.Under physiological conditions,the m PFC inputs to the amygdala,where it provides powerful inhibitory top–down control of inappropriate emotion expression by suppressing amygdala hyperactivity and limiting its output.However,under adverse conditions such as exposure to chronic or inescapable stress that induces the development of psychiatric conditions including depression and anxiety disorders,the prefrontal control becomes defective,leading to aberrant amygdala activation and deficits in emotion and behavior.A large number of anatomical evidence has revealed that the amygdala-projecting m PFC neurons send most of their fibers to the basolateral amygdala(BLA)but less to the lateral or central subregion.The PNs in BLA project to other brain regions,including cortex,hippocampus and thalamus,which receive and integrate information.Unlike neurons in m PFC and hippocampus,although the PNs in BLA are spatially intermingled,previous studies have identified considerable between-PN heterogeneity based on connections with downstream brain regions,their gene expression,and have different or even opposite roles in amygdala-associated function.Although a wealth of clinical and preclinical data has shown that the pivotal role of defective m PFC-to-amygdala communication for the pathogenesis of stress-related neuropsychiatric disorders,many questions are needed to be investigated.For example,during exposure to chronic or inescapable stress,what specific changes occur in m PFC inputs to the diverse BLA PNs? How do the changes in these inputs contribute to the emotional and behavioral adversity induced by stress?To answer these issues,we stablished a rodent anxiety model induced by chronic restraint stress(CRS)exposure.We stereotaxically injected AAV-Ch R2 tagged with enhanced green fluorescent protein(e GFP)under the control of Ca MKIIa into bilateral m PFC.Using whole-cell patch recording and optogenetics,the responses of BLA PNs to m PFC inputs were explored between control and CRS mice.We found that CRS selectively enhanced the dorsal medial prefrontal cortex(dm PFC)but not ventral medial prefrontal cortex(vm PFC)or ventral hippocampus(v HPC)-driven glutamatergic transmission onto BLA PNs.However,CRS does not affect both dm PFC,vm PFC and v HPC-driven GABAergic transmission onto BLA PNs.As aresult,the dm PFC-driven excitatory-inhibitory balance shifted to excitation in BLA PNs induced by CRS.Subsequently,we tested the potential effects of CRS on the responses of BLA distinct PNs to dm PFC.Given that all neurons in the BLA are innervated by m PFC.We co-injected AAV-Ca MKII-Ch R2-e GFP and retro-beads into bilateral dm PFC.Thus the BLA PNs were divided into two populations in terms of their differential connection with dm PFC,with one being reciprocally connected with dm PFC(dm PFC?BLA PNs)and the other only receiving mono-directional dm PFC inputs(dm PFC?BLA PNs).We found that CRS selectively induced the dm PFC-driven excitatory–inhibitory(E–I)balance shifted to excitation in dm PFC?BLA but not in dm PFC?BLA PNs,caused by selective increase of presynaptic glutamate release onto the dm PFC?BLA PNs.Critically,the increased prefrontal glutamate release onto the dm PFC?BLA PNs were well correlated with the increased anxiety-like behavior in stressed mice.Using low-frequency optogenetic stimulation to normalize the stress-induced augmentation of prefrontal glutamate release sufficed to alleviate the increase of anxiety-like behavior induced by stress.Together,we identified target cell connectivity-based dysregulation of dm PFC-to-BLA pathway for stress-induced increase of anxiety.Thus targeting the altered communication in this pathway may be of translational value for treatment of stress-related psychiatric illness.