Here, we describe a protocol for implementing mild anesthesia and acupuncture treatment on a chronic hypoxia mouse model and conducting behavioral tests to assess the cognitive alterations post-treatment.
The treatment of central nervous disorders has consistently posed significant challenges to the medical field. Acupuncture, a non-pharmacological practice rooted in traditional Chinese medicine, entails the insertion of fine needles into precise points on the body and is commonly employed for the management of diverse conditions. Recently, acupuncture has emerged as a promising therapeutic intervention for a range of neurological diseases, including anxiety and respiratory disorders. However, the potential of acupuncture in treating cognitive dysfunction induced by chronic hypoxia has not yet been explored. This paper presents a comprehensive protocol for establishing a mouse model of chronic hypoxia-induced cognitive impairment, administering mild anesthesia, performing acupuncture treatment, and assessing behavioral changes and memory abilities using open field tests and water mazes. The step-by-step protocol provides detailed instructions on accurately locating and positioning acupoints and needles for cognitive improvement. By employing this protocol, researchers can conduct systematic studies to thoroughly evaluate the therapeutic potential of acupuncture for cognitive dysfunction.
The global population is currently facing a critical aging problem, resulting in a rapid increase in the prevalence of cognitive disorders. The worldwide incidence of cognitive impairment is approximately 53.97 per 1000 person-years1. Chronic cerebral hypoxia caused by vascular dysfunction or circulatory/respiratory disorders remains one of the major risk factors for age-related dementia2. Previous studies have demonstrated that cerebral hypoxia can increase amyloid-β deposition by modifying BACE1 expression3. Additionally, hypoxia has been associated with glial-cell dysregulation and neuroinflammation4,5. Despite the growing magnitude of this issue, effective Western medicines for preventing chronic hypoxia-induced cognitive decline are currently lacking. Non-pharmacological traditional Chinese medicine, particularly acupuncture, has been used for thousands of years to treat cognitive disorders and has shown promising results in alleviating neurodegenerative diseases6,7. The Baihui, Shenting, and Zusanli acupoints are effective points for treating cognitive dysfunction8,9. Clinical studies have demonstrated that electro-acupuncture therapy significantly improves the Montreal Cognitive Assessment (MoCA) and Mini-Mental State Examination (MMSE) scores in patients with vascular cognitive impairment and effectively ameliorates cognitive dysfunction8. Although studies have suggested that acupuncture can significantly enhance the memory ability of rats with arterial ligation-an acute cerebral hypoxia models10, an acute cerebral hypoxia model, there is no report on the effects of acupuncture in any rodent model with chronic hypoxia-induced cognitive disorders. The lack of research into the mechanism has considerably impeded its clinical application.
Previous research has demonstrated that subjecting rats to a hypoxic environment for a period of 8 weeks can significantly elevate levels of oxidative stress and inflammation in the brain, resulting in a decline in memory function11. The present study aims to investigate the impact of acupuncture on rodent models in order to further our understanding. It is worth noting, however, that anesthesia is typically required during acupuncture treatment in rodents due to the potential for agitation during repeated stimulation. Prolonged anesthesia can significantly impact cognitive function in mice, as most anesthetic drugs can suppress neural activity and impede information processing, leading to behavioral deficits12. Several studies have shown that administering 2.5% sevoflurane for a duration of 6 h can notably impair spatial memory, learning ability, and attention in mice13. Furthermore, evidence suggests that high doses of anesthesia may result in neuronal death or nerve damage in mice14. Therefore, it is imperative to identify a suitable approach to minimize the overall amount of anesthesia used. In this study, we introduce an effective acupuncture method for treating mice with cognitive impairment, along with behavioral tests to assess their memory abilities. Importantly, we present a modified pre-treatment anesthesia technique that can effectively reduce the total dosage of anesthesia administered during the experiment.
The animal experiments were conducted with the approval of the Committee on Animal Research and Ethics of the Hebei Yiling Medical Research Institute (approval number: N2022148). Male C57BL/6J mice weighing 18-22 g (see Table of Materials) were housed in the new drug evaluation center of Hebei Yiling Medical Research Institute. They were provided with normal food and clean water and exposed to artificial light for 12 h daily. The rooms maintained a controlled temperature range of 20-26 °C and relative humidity of 40%-70%.
1. Establishment of a chronic hypoxia mouse model (Figure 1)
2. Anesthesia (Figure 2)
3. Electro-acupuncture treatment
4. Open field test (Figure 5)
NOTE: The open field test is a conventional method used to assess the autonomous behavior, exploratory behavior, cognitive abilities, and anxiety behavior of experimental animals in novel and unfamiliar environments22. It consists of an open-field reaction box and a recording device.
5. Water maze (Figure 5)
NOTE: The water maze test is frequently employed as a behavioral assessment tool in experiments involving mice to evaluate their spatial learning and memory capabilities23.
6. Hematoxylin and eosin (HE) staining (Figure 6)
NOTE: Histological examination of the hippocampal region assists in assessing the establishment of the hypoxia model and determining the efficacy of acupuncture treatment.
Characterizing mouse locomotion trajectories in the open field experiment
The trajectory map reveals that mice in the normal group exhibit a profound inclination for exploration in unfamiliar environments. Their activity trajectories are primarily concentrated in the corners while covering the entire open field (left panel). In contrast, the long-term hypoxia model group of mice displays a significantly diminished desire to explore novel surroundings. They predominantly linger in the corners without exhibiting any exploratory behavior toward the center of the open field (middle panel). Following acupuncture treatment, the exploratory activity of hypoxia-induced mice shows improvement, and their behavior of venturing toward the center of the open field is reinstated (right panel) (Figure 5A).
Characterization of spatial learning and memory in mice
In the normal group, mice spent a relatively longer amount of time in the target quadrant and crossed the platform more frequently, as shown in the trajectory map (left panel). The long-term hypoxic model group of mice demonstrated weakened spatial memory capabilities compared to the normal group, as indicated by their inability to locate the target quadrant within the specified time (middle panel). Following acupuncture treatment, the mice showed significant improvement in their hypoxia-induced spatial memory capabilities. They displayed more organized exploratory behavior and spent a noticeably longer time in the target quadrant (right panel) (Figure 5B).
Histological examination of mouse brain
In the control group, the arrangement of neurons in the hippocampal region of mice (upper left panel) demonstrated regularity, whereas it was disrupted in the long-term hypoxic model group (upper right panel). Conversely, the treatment group exhibited an improvement in the arrangement of neurons (lower panel). Furthermore, the model group displayed exacerbated shrinkage of mouse neuronal nuclei compared to the control group, but this effect was partially alleviated in the treatment group. (Figure 6).
Figure 1: Establishment of a mouse model for hypoxia-induced cognitive impairment. The mice were exposed to hypoxia from day 1 to day 90. Electric acupuncture therapy was administered daily from day 75, with each treatment cycle lasting 6 days and a total of 2 treatment cycles. There was a 1-day break between cycles. Behavioral testing was conducted on day 93. Histological examination and behavioral testing can be conducted on day 65 to confirm the establishment of the model in the hippocampal region. Abbreviations: Mon: month. Please click here to view a larger version of this figure.
Figure 2: Anesthesia pre-treatment prior to electro-acupuncture. Before undergoing electro-acupuncture treatment, the mice were anesthetized using an (A) anesthesia device. The mice were then placed into a (B) chamber box with (C) 2% Isoflurane in the chamber. (D) The duration of the modified anesthesia method was shorter compared to the classical anesthesia method. (E) Mice subjected to mild anesthesia retain their reaction to foot stimulation. Please click here to view a larger version of this figure.
Figure 3: Anatomical structure of acupuncture points on the mouse head. This figure depicts the anatomical positions of GV20 (Baihui), GV24 (Shenting), and ST36 (Zusanli) in mice. (A) An anatomical view of the mouse head showing the frontal and parietal bones. (B) An anatomical view of the mouse leg showing the tibia, fibula, and fibular head. (C) Locations of acupuncture points on the mouse head. (D) GV20 is located on the midline of the forehead, at the midpoint between the tips of the ears, and directly on top of the parietal bone. GV24 is located on the midline of the forehead, just anterior to the junction of the frontal and parietal bones. ST36 is located on the outer side of the hind leg, approximately 2mm below the fibular head. Please click here to view a larger version of this figure.
Figure 4: Electro-acupuncture treatment. The mice underwent needle stimulation at specific points on GV20 (Baihui), GV24 (Shenting), and bilateral ST36 (Zusanli) while under anesthesia. Please click here to view a larger version of this figure.
Figure 5: Representative results of the open field test and water maze test after electro-acupuncture treatment. (A) The open field test was conducted to evaluate the behavioral changes in mice subjected to chronic hypoxia (CH) and acupuncture (EA) treatment. Three representative trajectory plots were generated from the test. (B) The water maze test was conducted to evaluate the spatial memory of mice subjected to chronic hypoxia and acupuncture treatment. Three representative trajectory plots were generated from the test. Please click here to view a larger version of this figure.
Figure 6: Histological examination of mouse brain after electro-acupuncture treatment. Histological pictures of the mice in the control group (upper left panel), the hypoxia group (upper right panel), and the treatment group (lower panel). Scale bars: 100 µm. Please click here to view a larger version of this figure.
Acupuncture, a non-pharmacological medical practice originating in China over 2,000 years ago, involves the insertion of thin needles into specific points on the body known as acupuncture points. These points are believed to be connected by channels or meridians through which the body's vital energy, or "qi," flows24. By stimulating these points, acupuncture aims to restore balance and harmony to the body. It has been shown to effectively treat various conditions, including chronic pain, anxiety/depression, digestive problems, menstrual cramps, and respiratory disorders25,26,27,28,29. In recent years, acupuncture has emerged as an effective therapeutic intervention for neuronal diseases, including cognitive dysfunction. Multiple studies have demonstrated its ability to modulate neurotransmitters, increase cerebral blood flow, reduce oxidative stress, and enhance neuroplasticity20,30,31,32. Consequently, it is increasingly recognized as a safe and effective treatment option, particularly when used alongside conventional medical care33. However, despite its long history and widespread use, the mechanism of action of acupuncture remains incompletely understood. One theory proposes that acupuncture stimulates the release of endorphins, the body's natural painkillers, thereby alleviating pain and promoting a sense of well-being34. Another theory suggests that acupuncture may affect the autonomic nervous system, which regulates various involuntary bodily functions35,36. Although our understanding of acupuncture's mechanisms is still developing, there is growing recognition among scientists that a standardized laboratory methodology for acupuncture, especially using rodent models, is essential to guide research in this area.
The selection of an appropriate anesthesia protocol is the initial crucial step in conducting acupuncture in a mouse model. Traditional protocols often involve continuous high-dose anesthesia, which can have significant effects on the mouse's nervous system and may result in false-negative behavioral test results after acupuncture treatment. In this study, we propose an improved protocol that utilizes a sealed anesthesia box to gas-anesthetize the mice until they lose consciousness. Subsequently, a stable state is maintained using a low-dose anesthetic during the acupuncture treatment. This method helps to minimize functional and behavioral abnormalities caused by excessive anesthesia dosing and enhances the accuracy of the experiments. Additionally, researchers can opt for isoflurane instead of ketamine and xylazine as it offers faster recovery time and reduces the systemic toxicity risks associated with ketamine and xylazine37. However, it is important to note that false negative results caused by anesthesia may still occur. Even mild anesthesia continuing for 2 consecutive weeks can have a negative impact on cognition38. In order to more accurately evaluate the effectiveness of the treatment, researchers can incorporate an additional group of anesthetized mice that receive no treatment for comparison purposes. Another critical aspect of acupuncture treatment in mice is determining the combination of acupoints. Commonly used acupoints for central nervous system diseases in humans include Baihui (GV20), Yintang (EX-HN3), Shenting (GV24), and Zusanli (ST36)39,40,41. In this study, we focused on the inclusion of Baihui (GV20), Shenting (GV24), and Zusanli (ST36) for the treatment. Despite the challenges posed by the small size of mice in acupoint localization, joint positioning based on anatomical structures proves to be an effective method. Lastly, determining the appropriate stimulation frequency and intensity is another key step in performing acupuncture treatment in mice. In this study, we utilized low-frequency electro-acupuncture at 2 Hz and a moderate intensity of 2 mA. Although the therapeutic outcome of acupuncture is evident, further exploration is required to understand its underlying mechanism.
Despite the broad potential applications of acupuncture in the treatment of neurological disorders, this technique has certain limitations. One limitation is its high dependence on the operator's experience, which can result in suboptimal outcomes or harm to experimental subjects when performed by inexperienced operators. Another limitation is the need for improvement in clinical acupuncture treatment to enhance its effectiveness. Currently, researchers are studying the combination of acupuncture with other therapies, such as pharmacological interventions and cognitive training, in order to improve treatment outcomes42. Additionally, technological advancements have led to the development of new techniques, like transcranial magnetic stimulation (TMS), which can be used in conjunction with acupuncture to further enhance cognitive function43. Despite these limitations, acupuncture has shown significant benefits in the treatment of various neurological disorders and holds great potential for future applications, particularly when combined with other therapies. This article provides detailed methods for constructing a mouse model of chronic hypoxia-induced cognitive impairment, the process of acupuncture treatment, and behavioral testing methods. These methods can assist researchers in conducting thorough studies on the application and mechanism of acupuncture, thereby promoting the advancement of traditional Chinese medicine.
The authors have nothing to disclose.
This work was supported by S&T Program of Hebei (NO.E2020100001, and NO.22372502D), High-level S & T Innovation and Entrepreneurship Talent Project of Shijiazhuang (No. 07202203).
10% paraformaldehyde solution | Bioroyee (Beijing) Biotechnology Co., Ltd | RL3234 | |
ANY-maze | Science | SA201 | Video tracking system |
C75BL/6J mice | BEIJING HFK BIOSCIENCE CO.,LTD | No.110322220103041767 | Gender: Male, Weight: 18–22 g |
Electroacupuncture device | Great Wall | KWD-808 I | |
Hwato acupuncture needle | Suzhou Medical Appliance Factory | 2655519 | |
Isoflurane | RWD Life Science Co.,Ltd | R510-22 | |
NanoZoomer Digital Pathology | Hamamatsu Photonics K. K | C9600-01 | |
Small animal anesthesia machine | RWD | YL-LE-A106 |