The influence of electronic acupuncture at a specific frequency in facilitating the passage of NGF through the blood-brain barrier and its effect on learning and memory in MCAO/R rats

Background: The blood-brain barrier (BBB) maintains the balance of the internal environment of the brain and strictly controls substance exchange between the brain and blood dynamically but stably. Transient increases in the permeability of the BBB plays an important role in helping macromolecular drugs enter the brain to exert their pharmacological effects. Previous research has revealed that electronic acupuncture (EA) stimulation connecting Baihui (GV20) and Shuigou (GV26) at a specific frequency can enhance the permeability of the BBB at 8 minutes after the intervention and induce the entry of 20 kDa fluorescein isothiocyanate-dextran (FITC-dextran) into the cerebral cortex, but whether it can also allow drugs to pass the BBB remains unknown. We hypothesized that EA at a specific frequency could open the BBB and induce the entry of nerve growth factor (NGF) into the brain to exert its therapeutic effect. Methods: First, the middle cerebral artery occlusion (MCAO) model is adopted and changes in the permeability and structure of the BBB are assessed by measuring both the intensity of Evans blue (EB) staining and the cerebral infarction volume, and by evaluating the ultrastructure of the BBB. Then, a laser spectrometer and immunofluorescence are used to observe entry of NGF into the brain. Finally, the learning and memory ability of rats are assessed and the DeadEnd (TM) M Fluorometric TUNEL System is applied to assess apoptosis in the hippocampus. Results: Our results showed that, in the first, the BBB was essentially repaired three weeks after MCAO operation. Secondly, Electronic Acupuncture (EA) stimulation at a specific frequency can enhance BBB permeability in the prefrontal cortex and induce NGF uptake by prefrontal neurons. Finally, in the presence of EA stimulation, entry of NGF into the brain promoted learning and memory in rats and inhibited the apoptosis of neurons in the hippocampus. Conclusions: In this study, the timing of BBB repair in the MCAO model was determined under pathological conditions and the EA stimulation can induce the entry of NGF into the brain to exert its therapeutic effect. EA could serve as a new strategy for delivering therapeutics to the central nervous system (CNS), given that EA stimulation at a specific frequency was shown to increase the permeability of the BBB. Further study of the mechanism underlying the opening of the BBB and its timing is needed.