Objective To investigate the effects of electroacupuncture (EA) at Baihui (GV20) and Hegu (LI4) on postoperative cognitive dysfunction (POCD) in aged rats, and to clarify whether these effects are exerted through regulation of the NOD-like receptor pyrin domain-containing protein 3 (NLRP3)/cysteine-aspartic protease-1 (Caspase-1) signaling pathway.

Methods Forty 20-month-old SD rats, equivalent to approximately 60 years of age in humans, were divided by the random number table method into the control group (C group), electroacupuncture group (E group), surgery group (S group), and electroacupuncture plus surgery group (ES group), with 10 rats in each group. A POCD model in aged rats was established by splenectomy combined with exploratory laparotomy. Rats in the E and ES groups received electroacupuncture intervention at Baihui (GV20) and Hegu (LI4), using a 2 Hz/15 Hz disperse-dense wave, 1 mA current, 30 min per session, once daily for 5 consecutive days. Cognitive function was evaluated using the Morris water maze, Y-maze, and novel object recognition tests. Pathological changes in the hippocampus were observed by hematoxylin-eosin (HE) staining, Nissl staining, and dUTP nick-end labeling (TUNEL) staining. Immunofluorescence was used to detect the expression of NLRP3 in hippocampal tissue. Western blotting was used to detect changes in the expression of NLRP3 inflammasome-related proteins, including NLRP3, Caspase-1, and apoptosis-associated speck-like protein (ASC), the inflammatory factors IL-1β and IL-18, and the anti-apoptotic protein B-cell lymphoma/leukemia-2 (Bcl-2). Real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) was used to detect the mRNA expression levels of IL-1β and IL-18 in the hippocampus.

Results The interaction effect between surgery and electroacupuncture was significant. Further simple effect analysis showed that, in the absence of electroacupuncture, compared with the C group, rats in the S group had a prolonged escape latency (27.00±4.21) s vs. (47.68±9.00) s, reduced number of platform crossings (6.20±1.64) times vs. (0.80±0.84) times, reduced spontaneous alternation rate (66.10±9.94)% vs. (41.43±7.34)%, and reduced novel object recognition index (72.31±6.25)% vs. (46.36±8.68)%. Hippocampal neuronal structural damage was observed, the number of neurons in the hippocampal CA1 region decreased (61.67±17.39) cells/high-power field vs. (20.67±4.51) cells/high-power field, the apoptosis index increased (4.65±1.09 vs. 49.38±6.85), and the integrated fluorescence intensity of NLRP3 in hippocampal tissue increased (0.25±0.05 vs. 0.59±0.03). The expression levels of NLRP3 (0.80±0.05 vs. 1.12±0.04), Caspase-1 (0.59±0.03 vs. 1.23±0.03), ASC (0.67±0.02 vs. 1.24±0.02), IL-1β (0.68±0.04 vs. 1.12±0.08), and IL-18 (0.41±0.04 vs. 1.15±0.07) were all increased, while Bcl-2 expression decreased (0.88±0.10 vs. 0.27±0.03) (all P ＜ 0.05). Under surgical conditions, compared with the S group, rats in the ES group showed improved cognitive function, reduced hippocampal neuronal structural damage, increased number of neurons in the hippocampal CA1 region (20.67±4.51) cells/high-power field vs. (56.00±6.08) cells/high-power field, decreased apoptosis index (49.38±6.85 vs. 10.87±1.18), and reduced integrated fluorescence intensity of NLRP3 in hippocampal tissue (0.59±0.03 vs. 0.32±0.05). The expression levels of NLRP3 (1.12±0.04 vs. 0.84±0.03), Caspase-1 (1.23±0.03 vs. 0.69±0.02), ASC (1.24±0.02 vs. 1.04±0.04), IL-1β (1.12±0.08 vs. 0.81±0.02), and IL-18 (1.15±0.07 vs. 0.78±0.05) were all decreased, while Bcl-2 expression increased (0.27±0.03 vs. 0.84±0.03) (all P ＜ 0.05).

Conclusions Electroacupuncture at Baihui and Hegu can improve cognitive function in aged rats with POCD. Its effects are associated with inhibition of the NLRP3/Caspase-1 signaling pathway and attenuation of hippocampal neuroinflammatory responses and neuronal apoptosis.