[Electroacupuncture ameliorates chronic restraint stress-induced depressive-like behavior by modulating paraventricular nucleus corticotropin-releasing hormone neuron activity in mice].

OBJECTIVES: To investigate the effect of electroacupuncture (EA) at "Hegu" (LI4) and "Taichong" (LR3) on depressive-like behaviors and corticotropin-releasing hormone (CRH) neuron-related activity in paraventricular nucleus (PVN) in mice exposed to chronic restraint stress (CRS), so as to explore its possible mechanism.

METHODS: Male C57BL/6J mice and CRH-Cre mice were used in the separate experimental cohorts of this study. A CRS-induced depressive-like behavior model was established and treated with bilateral EA at LI4 and LR3 (2 Hz, 0.5 mA, 30 min in duration of stimulation, once daily for 7 d). Behavioral changes were evaluated using forced swimming, tail suspension and open-field tests. Serum CRH, adrenocorticotropic hormone (ACTH) and corticosterone (CORT) levels were measured using ELISA. The PVN neuronal activation and the proportion of c-Fos-positive cells among mCherry-labeled PVN CRH neurons were evaluated using immunofluorescence staining and c-Fos/mCherry co-labeling. Event-related PVN CRH neuron calcium activity was recorded by using fiber photometry. Chemogenetic activation with clozapine-N-oxide (CNO) was further used to observe the behavioral changes under subthreshold stress and EA intervention effect.

RESULTS: Compared with the blank group, the model group showed a significant increase in the immobility time in the forced swimming and tail suspension tests (P<0.01, P<0.001), distance traveled in the peripheral zone in the open-field test (P<0.001), contents of serum CRH, ACTH and CORT (P<0.000 1, P<0.001), number of c-Fos positive cell in the PVN (P<0.05), and the percentage of c-Fos/mCherry double-positive cells among the mCherry-positive cells (P<0.05). Compared with the model group, EA shortened the immobility time in the forced swimming and tail suspension tests (P<0.05), decreased the distance traveled in the peripheral zone of the open-field test (P<0.001), reduced the contents of serum ACTH and CORT (P<0.05, P<0.000 1), and decreased the number of PVN c-Fos-positive cell and the percentage of c-Fos/mCherry double-positive cells among the mCherry-positive cells (P<0.05), while serum CRH presented a lowering trend without statistically significant difference. The ΔF/F area under the curve and peak ΔF/F within the 0-5 s time window were considerably lower during and after EA than EA pre-treatment (P<0.001, P<0.05, P<0.000 1). Under the subthreshold stress, chemogenetic activation of PVN CRH neurons prolonged the immobility time in the forced swimming and tail suspension tests (P<0.000 1, P<0.001) and reduced the distance traveled in the peripheral zone in the open-field test (P<0.05, P<0.001);after EA, these behavioral changes were reversed (P<0.001, P<0.000 1, P<0.05).

CONCLUSIONS: EA at LI4 and LR3 can ameliorate CRS-induced depressive-like behaviors by down-regulating hypothalamic-pituitary-adrenal axis-related hormone responses, reducing PVN neuronal activation, decreasing the proportion of c-Fos-positive cells among the mCherry-labeled PVN CRH neurons, and modulating event-related PVN CRH neuron calcium activity.