PKMζ Controls The Persistence Of Fear Extinction

Objective:Fear is normally promote individuals to generate an adaptive response to danger. However, extreme fear and anxiety can become harmful and maladaptive, and lead to fear and anxiety disorders, such as posttraumatic stress disorder (PTSD). Exposure-based psychotherapy is widely used to treat fear disorders, but it cannot permanently erase maladaptive fear, and fear often returns under some conditions. However, currently the molecular mechanisms underlying the deficit in persistence of extinction memory are poorly known, and there is no selective methods to modulating the retention of extinction memory to prevent the return of fear. Thus, a deeper understanding the neurobiological mechanisms of extinction has significant clinic implications and may aid to develop more effective therapies.Methods:In animal studies, the mechanisms underlying fear and exposure therapy can be investigated using Pavlovian fear conditioning and extinction. Experiment1:Alteration of PKMζ levels in amygdala and mPFC after extinction training and spontaneous recovery of fear. Experiment2:effect of overexpression of PKM^in IL and PrL on spontaneous recovery of fear memory. Experiment3:effect of overexpression of PKMζ in IL and PrL on reinstatement and renewal of fear memory. Experiment4:effect of activation of noradrenergic, glutamatergic and dopaminergic systems on retention of extinction and PKMζ levels in mPFC. Experiment5:effect of knockdown PKMζ levels in infralimbic cortex on NMDA, D1receptor agonist, and NE-induced enhancement of retention of extinction memory.Results:The first part of the study①Post hoc revealed that compared with and groups of naive and fear conditioning, PKMζ protein was significantly increased in the group of extinction (P<0.05), and compared with the group of fear conditioning+extinction, PKMζ protein was significantly decreased in the group of extinction+14day (P<0.05). In PrL, BLA and CeA, there are no significant effect of treatment (P>0.05).②PKMζexpression in the IL was significantly increased one weeks after lentivirus infusion in the group infused with the LVPKMζ-GFP, compared to that infused with LVGFP. Post hoc revealed that compared with LVGFP group, freezing was significantly decreased in the LVPKMζ-GFP group during spontaneous recovery test (P<0.05).③Post hoc revealed that compared with LVGFP group, freezing was significantly decreased in the LVPKMζ-GFP group during spontaneous recovery test (P<0.05). Post hoc revealed that compared with LVGFP group, freezing was significantly decreased in the LVPKMζ-GFP group during reinstatement and renewal test (P<0.05, P<0.05). The second part of the study①Post hoc revealed that compared with and groups of vehicle, PKMζ protein was significantly increased in the group with infusions of NMDA, D1receptor agonist and NE (P<0.05).②Post hoc revealed that compared with LVGFP group, freezing was significantly decreased in the LVDN-PKMζ-GFP group during spontaneous recovery test (P<0.05).Conclusion:Through a series of experiments, the study has demontstrated that PKMζ controls the persistence of fear extinction. The main conclusions are as follows:(1) Here we demonstrate a key role of PKMzeta in the deficit of retention of extinction memory of fear. We found increased PKMzeta levels in infralimbic cortex (IL) but not prelimbic cortex (PrL) are associated with the extinction training, and decreased PKMzeta levels in IL was associated with spontaneous recovery of fear. Then we found overexpression of PKMzeta in IL but not PrL enhanced retention of extinction memory and prevent the spontaneous recovery of fear, even when the PKMzeta overexpression was applied out of time window of consolidation of extinction memory. PKMzeta overexpression in IL synthetize with fear extinction can also prevent reinstatement and renewal of fear memory.(2)We found activation of dopaminergic, glutamatergic and noradrenergic system enhanced retention of extinction memory, and the effects were dependent on PKMzeta activity in IL. PKMzeta maybe a new potential candidate for treatment of fear disorder. Therefore, this study makes further research about the biological mechanisms of fear conditioning and provide a theoretical basis for looking for the elimination of PTSD drug treatment targets.