[Effects and mechanisms of electroacupuncture on fear extinction and sleep phase in single prolonged stress mice].

Objective: To observe the effects of electroacupuncture (EA) on fear extinction and sleep phase in single prolonged stress (SPS) mice, and explore its mechanism in view of the expression of relevant synaptic proteins.

Methods: Thirty-two C57BL/6J male mice were randomly divided into a control group, a model group, an EA group and a paroxetine (PRX) group, with 8 mice in each one. Modified SPS method was used to establish PTSD model in the model group, the EA group and the PRX group. Seven days after modeling completion, in the EA group, the intervention was delivered at "Baihui" (GV 20) and bilateral "Zusanli" (ST 36), with disperse-dense wave, 3 Hz/15 Hz in frequency and 1 mA in current intensity, for 30 min. In the PRX group, paroxetine solution (2.5 g/L) was administered intragastrically (10 mg/kg). The intervention was given once daily and for consecutive 10 days in the above two groups. The fear conditioning task and the elevated plus-maze test were adopted to evaluate the fear extinction and anxiety of the mice in each group. Using Medusa electroencephalogram (EEG) and electromyography (EMG) recording system from rats and mice, the sleep phase was determined in the mice. With Western blot method adopted, the protein expression of the postsynaptic density protein 95 (PSD95), activity-regulated cytoskeleton-associated protein (ARC), brain-derived neurotrophic factor (BDNF), N-methyl-D-aspartic acid receptor 2A (GluN2A), N-methyl-D-aspartic acid receptor 2B (GluN2B) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor 1 (GluA1) in the hippocampus was detected in the mice.

Results: Compared with the control group, the freezing time for the fear re-exposure in 3 min to 15 min and the fear extinction in 0 min to 3 min were prolonged (<0.05), the fear extinction index decreased (<0.05), and the open arm time (OT) of the elevated plus-maze was shortened (<0.05) in the model group. When compared with the model group, in the EA group and the PRX group, the freezing time for the fear re-exposure in 3 min to 6 min and 12 min to 15 min, as well as the fear extinction in 0 min to 3 min was shortened (<0.05), the fear extinction index increased (<0.05); the OT in elevated plus-maze was longer in the mice of the EA group (<0.05). The period of wake (Wake) was prolonged (<0.05), the non-rapid eye movement period (NREM) and the total sleep time (Sleep) were reduced in the model group (<0.05) in comparison with the control group. Compared with the model group, the Wake was declined (<0.05), and the NREM and Sleep increased in the EA group and the PRX group (<0.05). When compared with the control group, the protein expression of PSD95, ARC, BDNF, GluN2A and GluA1 in the hippocampus decreased (<0.05), and that of GluN2B increased (<0.05) in the model group. In the EA group and the PRX group, the protein expression of PSD95, ARC, BDNF, GluN2A and GluA1 in the hippocampus was elevated (<0.05), and that of GluN2B reduced (<0.05) when compared with the model group.

Conclusion: Electroacupuncture at "Baihui" (GV 29) and "Zusanli" (ST 36) can ameliorate anxiety-like behavior, fear extinction disorder and abnormal sleep phase in SPS mice, which may be related to the regulation of synaptic transmission and synaptic plasticity expression in the hippocampus.