- Research article
- Open access
- Published:
Electric vagal nerve stimulation inhibits inflammation and improves early postoperation cognitive dysfunction in aged rats
BMC Anesthesiology volumeĀ 19, ArticleĀ number:Ā 217 (2019)
Abstract
Background
This study aimed to evaluate effects of electric vagal nerve stimulation on early postoperation cognitive dysfunction in aged rats.
Methods
A total of 33 male Sprague Dawley rats were selected and assigned randomly to three groups, control group (C, nā=ā10), splenectomy group (S, nā=ā10) and splenectomy+vagal nerve stimulation group (SV, nā=ā13). Behavior and memory of rats were evaluated by Open Field Test and Morris Water Maze. Levels of TNF-Ī±, IL-6 and IL-10 in serum were measured by ELISA. The level of TNF-Ī± protein in hippocampus was assessed by Western blotting. rt-PCR was used to detect mRNA expression of NF-ĪŗB in hippocampus.
Results
During anesthesia/operation, vital life signs of rats were stable. In SV group, vagal nerve stimulation decreased heart rate lower than 10% of basic level and kept it at a stable range by regulating stimulation intensity. After stimulation stop, heart rate returned to the basic level again. This indicated that the model of vagal nerve stimulation was successful. Serum levels of TNF-Ī± and IL-6 increased by the operation/anesthesia, but they decreased with vagal nerve stimulation (all Pā<ā0.05). TNF-Ī± protein and mRNA expression of NF-ĪŗB in hippocampus were also eliminated by vagal nerve stimulation compared to S group (Pā<ā0.05). Results of Morris Water Maze showed escape latency of postoperation in S group was significantly longer than C group (Pā<ā0.05), and times of crossing platform in S group was lower than that of C group (Pā<ā0.05). Although escape latency of postopration in SV group was shorter than that of S group, there was no significant difference between two groups. Meanwhile there were no significant differences of behavior test in Open Field test between three groups, although vagal nerve stimulation improved partly active explore behavior compared to S group.
Conclusion
The inflammation caused by operation and general anesthesia was an important reason of early postoperation cognitive dysfunction, and electric vagal nerve stimulation could inhibit the inflammation. Meanwhile, vagal nerve stimulation could ameliorate early postoperation cognitive dysfunction partly, but its protective effects were not enough and should be studied and improved in future.
Background
Postoperation cognitive dysfunction (POCD) is a severe complication of surgery and general anesthesia. Fourteen percent of patients have been found cognitive decline and confusion after surgery with anesthesia [1, 2]. POCD is frequent in patients older than 60-year undergoing major non-cardiac surgery, which increases both morbidity and mortality [3]. These cognitive impairments are related to language comprehension, attention, social integration and short term memory. Also, POCD may extent recovery process and hospital stay, and diminish quality of patientsā life [4]. There are many risks developing postoperative cognitive decline in elderly patients, such as increased age, longer time in surgery, longer stay in an intensive care unit and mechanical ventilation time [2]. Although POCD is not rare, its underlying pathogenic mechanisms have not been known completely.
The systemic inflammation has been identified as an important process for occurrence and development of POCD [4, 5]. Not only surgical trauma, but also inhaled anesthetics could produce systemic inflammatory response, which leads to blood-brain barrier disruption, neuro-inflammation and cognitive dysfunction [6, 7]. So inhibiting this systemic inflammation might be a potential strategy preventing and/or treating cognitive dysfunction.
Vagal nerve has been identified to link to inflammatory response, its activity could suppress TNF-Ī± and other pro-inflammatory cytokines. This anti-inflammation arc has been well-known as cholinergic anti-inflammation pathway [8]. Vagal nerve regulates inflammatory response through hypothalamic-pituitary-adrenal axis, release of cortisol and vagovagal reflex [9]. Anti-inflammatory effects of vagal nerve stimulation (VNS) were firstly researched by Borovikova and colleague [10]. They found not only acetylcholine, as vagal neurotransmitter, inhibited release of inflammatory cytokines in lipopolysaccharide stimulated human macrophage cultures, but also direct VNS could reduce systemic inflammatory response and prevent progress of infectious shock by attenuating inflammatory cytokines synthesis. Following their works, the anti-inflammation mechanisms of VNS have been researched systemically. Although the whole mechanisms and the signaling pathway have been unknown completely, wider range of inflammatory disorders might be ameliorated by VNS [11].
The aim of this study, firstly, was to demonstrate whether surgery and general anesthesia could induce systemic- and neuro-inflammatory response and impair cognitive function in elder rats. Secondly, it was to evaluate effects of VNS improving cognitive dysfunction by inhibiting the inflammatory response.
Methods
Experimental animals
A total of 33 male Sprague Dawley (SD) rats were obtained from Beijing Vital River Laboratory Animal Technology Co. Ltd. (Beijing, 100,012, China. \ (Jing)2012ā0001.) and maintained in suitable rooms with controlled conditions of temperature at 22āĀ±ā1āĀ°C, 40āĀ±ā10% relative humidity and light-dark cycles (12āh- 12āh, light onset at 7:00). Five rats were housed in one cage. During this experiment, standard food and drink water were available to the animals ad libitum. This study was approved by the institution ethical committee for animal care and use, Sanbo Brain Hospital, Capital Medical University. All efforts were made to minimize the number of animals used and their suffering. Experiments were performed during day, always at the same time, to avoid circadian variations. After finishing behavior tests, all animals were humanely euthanized using intraperitoneal injection of 3% sodium pentobarbital (50āmg/kg) and rapid decapitation. The process was as soon as possible to avoid interference on the results of experiment.
Experiment protocol
A random number generator was used to allocate the rats into different groups: control group (nā=ā10, C group, 577.00āĀ±ā47.53āg) that received no surgery and anesthesia, splenectomy group (nā=ā10, S group, 577.60āĀ±ā33.73āg) that was isolated cervical vagal nerve without stimulation, and splenectomy+VNS group (nā=ā13, SV group, 571.15āĀ±ā50.63āg). Then all rats were conducted with Morris Water Maze (MWM) train (day 1ā4) and test on day 7, Open Field Test (OFT) train on day 3 and test on day 7, splenectomy was carried on the day 4. Finishing behavior tests, all animals were decapitated for tissue preparation on day 7 (Fig.Ā 1).
Electric vagal nerve stimulation
Rats were fixed in a cage and anesthetized with 1% propofol (Fresenius Kabi AB. Rapsgatan 7, 751 74 Uppsala. Sweden. Serial number: 10MC2871.) 80āmg/Kg intraperitoneally, after losing righting reflex, their tail vein was cathetered with 24-gauge catheter infusion set (Tuoren Medical Device Co., Ltd. Henan, 453,401, China.) for continuous propofol infusion [12]. During the experiment, rats were allowed to breathe pure oxygen through a tube filled with oxygen continuously, which fixed in front of their nose in order to prevent hypoxia. After 10āmin stabilization, heart rate was recorded as basic line. Thus, neck hair shaving and skin cleaning, aseptic technique was used to make a ventral midline incision in neck skin. Then skin and muscles were retracted. Because right vagal nerve primarily innervates atria and sinoatrial node, and these stimulation may induce significant change in cardiac rhythm. At the same time, right VNS produce smaller cardiorespiratory response, so right vagal nerve was applied [13, 14]. Isolating right cervical vagal nerve and common carotid artery bundle, a 1.5āmm diameter silver bipolar cuff electrode was gently wrapped around the nerve bundle and fixed to the sternocleidomastoid muscle. Then the electrode was connected to stimulator (BL-820 Biological signal acquisition and processing system. Chengdu Techman Software Co. Ltd. Sichuan, Chengdu, 610,100, China). The basic stimulation parameters were adapted to the threshold of individual animal and included 2āV, 10āHz and 1āms, but these parameters were regulated constantly to preserve heart rate lower than 10% of basic line [14,15,16,17].
Splenectomy
After 30āmin of VNS, splenectomy began with a small lateral peritoneal incision. Using 3.0 silk thread to dissociate and ligate spleen artery and vein at hilum of spleen, spleen was removed at the root of far end of spleen pedicle. The completely removed spleen was examined to ensure that no residual spleen was left. Then the incision was closed, covering it with sterile activated-iodine gauze, and securing it with adhesive tape. The operation time was within 60āmin.
Behavioral tests
Open field test
OFT was applied in an apparatus, which was made of brown plywood, surface area was 50āĆā50ācm, surrounded by 50ācm high walls. The floor was divided by black line into 25 rectangles. Rats were allowed to freely move in this apparatus for 5āmin. The movement of individual animal in the arena was automatically tracked by AVTAS ver5.0 animal video analysis system (AniLab Software & Istruments Co., Ltd. Ningbo, China.) The number of crossing and rearing activities by each rat during 5āmin was used to assess ratsā active explore behavior. After every test, the apparatus was cleaned with 5% ethanol.
Morris water maze
MWM was used to evaluate spatial reference learning and memory. A circle pool (150ācm in diameter and 80ācm deep) was filled with water and divided into four quadrants. An escape platform, which 40ācm in height and 15ācm in diameter, was submerged by 2ācm under water surface and conserved to the center of northwest (NW) quadrant of this pool. Water was maintained at temperature of 23āĀ±ā2āĀ°C. The evaluation consisted of four training days of five consecutive trails per day, the last trail of each day was accepted. Rats were randomly introduced in this tank from different quadrants facing wall to find the escape platform in 60ās. If the rats did not find the platform within 60s in the first trial, they were gently guided to the platform to remain for 30s. Then the rats were removed from the tank. This procedure ensured animals to retain visual-spatial information during trail. The movement of individual rat was automatically tracked by AVTAS ver5.0 animal video analysis system (AniLab Software & Istruments Co., Ltd. Ningbo, China.) On the last day of the test after operation, rats were assessed in this tank without the platform. The time to find the platform, the times of passing through the platform location, and the duration of time in the quarter of platform were counted.
Assessment of TNF-Ī±, IL-6, IL-10 in serum
Levels of serum TNF-Ī±, IL-6, IL-10 were measured by Enzyme-Linked Immunosorbent Assay (ELISA). Aliquots containing 100ul of serum were placed into wells of ELISA plates and the plate was incubated at 37āĀ°C for 2āh. Primary antibodies were rabbit monoclonal antibodies to TNF-Ī± (Huamei, Wuhan. Number CSB-E11987r, 1:100 dilution), IL-6 (Huamei, Wuhan. Number CSB-E04640r, 1:100 dilution), IL-10 (Huamei, Wuhan. Number CSB-E04595r, 1:100 dilution). The primary antibodies were added to each wells and incubated at 37āĀ°C for 1āh. After three washes with PBS-Tween 20 (0.1%), a horseradish-peroxidase-conjugated goat anti-rabbit IgG was added into the wells and incubated for 1āh at 37āĀ°C. The antibody-antigen complex was revealed by addition of 100ul of 2,2ā²-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) containing 0.3% H2O2 into each well. After 15āmin, optical density (OD) was determined using Bio Tek Epoch (Bio Tek Instruments, Inc. China. Beijing, 100,025, China.) at 450ānm. All samples were processed under the same experimental conditions and time.
TNF-Ī± protein in hippocampus
The proteins were extracted from hippocampus and their concentration was determined by Bicinchoninic Acid Kit (Catalog BCA02, Dingguo Changsheng Biology Technology LTD, Beijing, China). 30Ī¼g protein samples were separated by SDS-PAGE, followed by semi-dry transfer onto a PVDF membrane. The membrane was blocked in 5% non-fat dry milk. Further, membranes were incubated with rat monoclonal primary antibody, anti-TNF-Ī± and anti-tubulin, for overnight at 4āĀ°C. This was followed by triple washing with 0.1% TBST and incubation with HRP labeled secondary antibodies for 2āh at RT. Immunoreactive bands were detected by ECL and Western blot detection system using Quantity one (Bio-Rad Laboratories. Inc. Hercules, CA, USA). These steps were repeated triply in order to calculate mean value. Expressions of each interest protein were calculated after normalizing the interest protein with endogenous control tubulin in the same sample.
NF-ĪŗB in hippocampus expression
Total RNA was isolated from 100āmg of hippocampal cortex using 1āml of TRIzol (Invitrogen Corporation; Carlsbad, CA, USA) and then RNA was treated with RNase-free DNase I and quantified using Q5000 Spectrophotometer (Quawell Technology, Inc. San Jose, CA, USA). cDNA was obtained from 5Ī¼g of total RNA using 2ul of ReverTra Ace reverse transcriptase kit (Catalog TRT-101, TOYOBO STC (Shanghai) CO., LTD, Shanghai, China), 2ul of Oligo dT 50um, 2ul of dNTP mix 10āmM, and water grade molecular biology to 20ul. Retrotranscription conditions were 30āĀ°C for 10āmin, followed 42āĀ°C for 60āmin and 99āĀ°C for 5āmin, then 4āĀ°C for 5āmin. Finally, the cDNA was stored at āā20āĀ°C.
cDNA was used to amplify each gene using Sybr Green I (Catalog GG1301ā50, Gen-View Scientific Inc. Florida, USA). The amplification reactions contained 1 ul of respective SybrGreen I, 12.5ul of Mix (Catalog PER012ā1, Dingguo Changsheng Biology Technology LTD, Beijing, China), and 1ul of cDNA in a final volume of 25ul. The conditions were for qPCR were 3āmin for pre-denaturation at 95āĀ°C, followed by 35ācycles of amplification of 30s denaturation at 94āĀ°C, 30s annealing at 60āĀ°C and 30s extending at 72āĀ°C. The last extending step was 10āmin at 72āĀ°C. Rat GAPDH was used as internal control gene for normalization. The amplification assays were made using ABI PRISM 7700 Sequence Detection System (ThermoFisher Scientific (China) LTD, Shanghai, China). Primer pairs for quantitative real-time PCR were as follows: NF-ĪŗB, 5ā²-AACCTGGGAATACTTCATGTGACTAA-3ā²(sense) and 5ā²-GCACCAGAAGTCCAGGATTATAGC-3ā² (anti-sense), GADPH, 5ā²- GCTGAGTATGTCGTGGACTC-3ā² (sense) and 5ā²- TTGGTGGTGCAGGATGCATT-3ā² (anti-sense). The steps were repeated triply in order to calculate mean value. The 2-ĪĪCt analyses were applied to calculate the relative transcript levels expressed as fold change for gene expression [18].
Statistical analysis
SPSS 16.0 for Windows software package (SPSS, Inc., Chicago, IL, USA.) was used to perform statistical analysis. Quantitative data were expressed as meanāĀ±āstandard deviation (āxāĀ±ās). Normal distribution of data was check by Kolmogorov-Smirnov analysis. One-way ANOVA Post Hoc Multiple-Comparisons was used for multi-group comparisons of means. When homogeneity of variances occurred, L-S-D was used to compare between groups. When variances were heterogeneous, Dunnett T3 was used to compare between groups. Two-way repeated-measured ANOVA was use to analysis the data of escape latency. The mean difference was significant at 0.05 level.
Results
There were no significant different between three groups on body weight (Fā=ā0.073, Pā=ā0.930) and basic heart rate (Fā=ā1.163, Pā=ā0.326) (TableĀ 1). Three minutes after beginning of VNS, heart rates of SV group (312.85āĀ±ā27.52) was reduced significantly, compared to C group (373.90āĀ±ā21.40) and S group (375.30āĀ±ā16.26) (Fā=ā28.928, Pā<ā0.01). Three minutes after stopping VNS, heart rates of SV group (394.85āĀ±ā32.19) rose up, compared to C group (369.60āĀ±ā21.46) (Pā=ā0.021). Till to ten minute after stopping VNS, heart rates were not significantly different between three groups (Fā=ā0.230, Pā=ā0.796), and recovered to the basic level (Fig.Ā 2).
The level of inflammatory cytokines in serum
TNF-Ī± level was increased by surgery and general anesthesia in S group (61.028āĀ±ā8.642āpg/ml, Pā<ā0.001, Dunnett T3) and SV group (41.609āĀ±ā8.249āpg/ml, Pā<ā0.001, Dunnett T3), compared to C group (27.180āĀ±ā2.038āpg/ml). And it could be reduced by VNS, because TNF-Ī± in SV group was significant lower than that in S group (Pā<ā0.001, Dunnett T3). IL-6 level was similar to TNF-Ī±. Compared to C group (1.278āĀ±ā0.258āpg/ml), IL-6 in S group (6.789āĀ±ā1.827āpg/ml) and SV group (3.623āĀ±ā0.685āpg/ml) were increased significantly (Pā<ā0.001, Dunnett T3). But VNS decreased IL-6 in SV group compared to that of S group (Pā<ā0.001, Dunnett T3). Anti-inflammatory cytokine IL-10 was higher in S group (95.351āĀ±ā6.236āpg/ml) and SV group (99.387āĀ±ā5.236āpg/ml) caused by splenectomy and general anesthesia, compared to C group (38.587āĀ±ā0.645āpg/ml, Pā<ā0.001, Dunnett T3). However, there was no significant difference between IL-10 of S and SV group (Pā=ā0.302, Dunnett T3) (Fig.Ā 3).
The TNF-Ī± level in the hippocampus
As internal reference protein, tubulin level in three groups was no significant difference (Fā=ā0.036, Pā=ā0.965). Normalization with tubulin, TNF-Ī± of three groups was significant difference (Fā=ā10.018, Pā=ā0.002).TNF-Ī± in S group (8.00āĀ±ā1.99) was significantly higher than that in C group (4.78āĀ±ā0.63, Dunnett T3, Pā=ā0.025) and SV group (5.13āĀ±ā1.11, Dunnett T3, Pā=ā0.043). But TNF-Ī± protein of C and SV groups was similar (Dunnett T3, Pā=ā0.872) (Fig.Ā 4).
The NF-ĪŗB gene expression in the hippocampus
After normalization with endogenous control GAPDH, NF-ĪŗB expression in three groups was significantly different (Fā=ā12.648, Pā=ā0.001, ANOVA). NF-ĪŗB gene of S group (1.839āĀ±ā0.652) was increased significantly than that of C group (0.685āĀ±ā0.253, Pā<ā0.001, LSD) and SV group (0.849āĀ±ā0.258, Pā=ā0.001, LSD). And there was no significant difference of NF-ĪŗB gene expression between C and SV group (Pā=ā0.518, LSD) (Fig.Ā 5).
Locomotor and exploratory activities
OPT was used to evaluate rat crossing and rearing activities, before and after splenecotmy respectively. Before the surgery, there were no significant different on the number of crossing (Fā=ā0, Pā=ā0.995) and rearing between three groups (Fā=ā0.003, Pā=ā0.966). After the operation, the number of crossing (Fā=ā0.302, Pā=ā0.587) and the number of rearing (Fā=ā2.040, Pā=ā0.148) were also similar in three groups, but the number of crossing (11.85āĀ±ā15.44) and rearing (2.62āĀ±ā3.30) in SV group were higher than the number of crossing (10.00āĀ±ā13.19) and rearing (1.80āĀ±ā2.82) in S group (Fig.Ā 6).
Effects of VNS on the MWM test
As shown in (Fig.Ā 7), two-way repeated-measures ANOVA revealed that escape latency of three groups reduced over the 4ādays training period before the operation (Fā=ā103.062, Pā<ā0.01), and there was no interaction between days, splenecotmy and VNS (Fā=ā0.498, Pā=ā0.807). Also escape latency of each day was no significant difference between three groups during 4ādaysā training (Fā=ā1.715, Pā=ā0.208).
After the operation, S group had a longer escape latency (42.45āĀ±ā13.23) than C group (25.07āĀ±ā15.66, Pā=ā0.045, Dunnett T3). And escape latency of C and SV group (34.37āĀ±ā22.57, Pā=ā0.578) was not significantly different. So escape latency was reduced by VNS compared to S group, but the difference was not significant. Results of times of crossing platform after the operation were similar to the results of escape latency. The rats of S group (1.6āĀ±ā0.8) crossed few times than those of C group (2.9āĀ±ā1.9, Pā=ā0.046, LSD). And there was no significant difference between the times of crossing of C and SV groups (2.5āĀ±ā1.3, Pā=ā0.543, LSD). The times of crossing platform of SV group were more than that of S group, but the difference was not significant. After the operation, the duration of time spent in target quadrant was no significant difference between three groups (Fā=ā1.751, Pā=ā0.191). However, the time spending on the platform in S group (11.49āĀ±ā2.58) was shorter than that of C group (15.54āĀ±ā6.72) and SV group (15.73āĀ±ā6.88).
Discussion
Our results showed that surgery and general anesthesia could produce damage to memory and study capability, and aggravate POCD in elderly rats early after surgery and general anesthesia, because they induced systemic- and neuro-inflammation [19]. Although improvement of cognitive function was not significantly, electrical VNS did reduce POCD in some degree. The underlying mechanism might be related to inhibition of the inflammatory response caused by surgery and general anesthesia.
The inflammation caused by surgery and general anesthesia is one of most important reasons of POCD. There is strong evidence to suggest that acute inflammation affects and exacerbates cognitive function or cause delirium, one kind of clinical important postoperative complication. And ongoing inflammation might constantly impair cognitive function after surgery and anesthesia. Thus, inhibition or resolution of the inflammation is an important prerequisite for improvement of cognition [20]. In the present study, surgery and general anesthesia increased pro-inflammatory cytokines, TNF-Ī± and IL-6. Meanwhile, IL-10, a kind of anti-inflammatory cytokine, was also upgraded. These changes demonstrated that acute systemic inflammation was induced via activation of innate immune system.
As an initiating medium of systemic inflammation, TNF-Ī± activates and amplifies inflammation cascade. In addition, TNF-Ī± can do damage directly to blood brain barrier and induce inflammatory cells infiltration in hippocampus [21]. Besides, NF-ĪŗB is an essential transcription factor to regulate inflammation and innate immunity genes expression. Its activation eventually increases level of pro-inflammatory cytokines in brain, such as TNF-Ī± and IL-6, which subsequently cause cognitive impairment [22]. So NF-ĪŗB has been known as a potential therapeutic target, inhibition of NF-ĪŗB might improve cognitive dysfunction caused by sevoflurane anesthesia [23]. In our study, increase of pro-inflammation cytokines in serum and higher expression of TNF-Ī± and NF-ĪŗB in hippocampus provided directly evidences that surgery and general anesthesia might induce acute inflammation, which took place systemically and locally, and lead to cognitive damage early after surgery and general anesthesia.
As to why right vagal nerve was stimulated in our study, this was because heart rate changed obviously when it was stimulated [13]. In other words, the change of heart rate is not only the evidence that VNS is successful, but also is the baseline for regulating stimulation parameters, such as stimulation intensity and frequency. In the present study, 3āmin after onset of stimulation, heart rate reduced to about 85% of basic heart rate, and 10āmin after stop of stimulation, heart rate increased to basic level. During the operation, continuous VNS kept heart rate at this level, till the operation was finished. In addition, right VNS might produce relatively slighter interruption to circulation and respiration than left VNS [14].
The more important is that vagal nerve plays key role in inflammation regulation, which is known as cholinergic anti-inflammation pathway. The vagal nerve efferent fibers release acetylcholine, which binding with special receptor on macrophages and inhibit production and release of TNF-Ī± [24]. In our study, this effects of VNS were certified that VNS could decrease not only levels of pro-inflammatory cytokines in serum, such as TNF-Ī± and IL-6, also TNF-Ī± protein and transcription factor NF-ĪŗB in hippocampus were downgraded by VNS. As to the level of IL-10, although VNS could increase it slightly, there was no significant difference between S and SV groups. We inferred that anti-inflammation effects of vagal nerve focus on inhibition of pro-inflammatory cytokines, not upgrade of anti-inflammatory cytokines. So there was no significant change of IL-10.
Recently, Huffman and colleague reported that VNS could ameliorate cognitive response and decrease systemic and brain inflammation induced by lipopolysaccharide endotoxemia. In their study TNF-Ī± was significantly inhibited by VNS [25], which was similar to results of our research. Besides effects of inhibiting inflammatory response, cholinergic system might regulate hippocampus function and memory, so it is not impossible to prevent or ameliorate POCD by VNS [26].
OFT is used to evaluate spontaneous activity and anxiety-like behaviors. In this study, results of OFT demonstrated that spontaneous movement in three groups were similar after the operation. Although VNS could ameliorate crossing and rearing movement, a kind of actively explore behaviors [27], there were no significant difference between three group. VNS was reported to increase score of OFT in depression model of rat and antagonized depressive status [28]. The results in the present study were not contradictory with the previous study, however these effects of VNS in our study was not significant statistically.
After the operation and general anesthesia, learning and memory function of rats were damaged, as indicated by increase of escape latency, and decrease of times of crossing platform and time spending on target region. VNS, as a kind of treatment, in our study, it did decrease escape latency, lengthen time spending on target quarter, and increase times of crossing platform, when compared to S group. These results were consistent with previous study which reported VNS ameliorated cognitive function [29]. However, in this study, these effects of VNS were not enough to produce protection against POCD completely.
Above results of OFT and MWM tests provided evidences that POCD could occur early after surgery, and inflammation caused by surgery and general anesthesia played more important role to induce POCD. These results were similar to recent studies [30, 31]. However, the detail mechanisms of POCD have not completely elucidated. For example, systemic inflammation, neuroinflammatin, cerebral microemboli and hypotension, all of these may cause POCD. In other words, any pathogenies could cause POCD as long as they interrupt central nerve system metabolic status and its homeostasis [32]. As well known, inflammation is one relatively important pathogeny for POCD, but it is not the only. Thus, we could explain the results of our study. Because VNS could inhibit the inflammation induced by surgery and general anesthesia, which demonstrated by lower level of pro-inflammation cytokines in serum and pro-inflammation protein and transcription factor NF-ĪŗB in hippocampus. However, there might be other pathogenies to promote the development of POCD. So VNS could ameliorate learning, memory function and actively explore movement in some degree, but its protection was not sufficient.
Our study indicated that surgery and general anesthesia could induce systemic and local inflammation. At the same time, cognitive function of rats was damaged. VNS might inhibit the inflammation to produce protective effect against POCD in some degree. However, this protection of VNS was insufficient. Maybe combination of VNS with other therapies might provide better clinical effects, this need to be researched in future.
The limitation of this study
There were some limitations in our study. NF-ĪŗB is a key transcription factor to modulate inflammatory responses via regulating expression of pro-inflammation mediators. It is regulated by its inhibitor, IĪŗB. NF-ĪŗB will be released by degradation of IĪŗB. Then it enters nucleus and activates transcription of multiple inflammatory response genes by interacting with ĪŗB elements in promoter region. Thus, increased NF-ĪŗB activation is considered as an important pathogenic factor in many inflammatory disorders. In our study, we only tested total NF-ĪŗB expression. If the expression of IĪŗB in hippocampus was tested, the more information relative with central nerve systemic inflammatory response would be demonstrated.
Availability of data and materials
The data of this article is available from the corresponding author. The email address of the corresponding author is B2008194@126.com.
Abbreviations
- ELISA:
-
Enzyme-linked immunosorbent assay
- MWM:
-
Morris water maze
- OFT:
-
Open field test
- POCD:
-
Postoperation cognitive dysfunction
- VNS:
-
Vagal nerve stimulation
References
Xiong B, Shi Q, Fang H. Dexmedetomidine alleviates postoperative cognitive dysfunction by inhibiting neuron excitation in aged rats. Am J Transl Res. 2016;8(1):70ā80 PMID: 27069541.
NorkienÄ I, SamalaviÄius R, MisiÅ«rienÄ I, PaulauskienÄ K, Budrys V, IvaÅ”keviÄius J. Incidence and risk factors for early postoperative cognitive decline after coronary artery bypass grafting. Medicina (Kaunas). 2010;46(7):460ā4 PMID: 20966618.
Besch G, Vettoretti L, Claveau M, Boichut N, Mahr N, Bouhake Y, Liu N, Chazot T, Samain E, Pili-Floury S. Early post-operative cognitive dysfunction after closed-loop versus manual target controlled-infusion of propofol and remifentanil in patients undergoing elective major non-cardiac surgery: Protocol of the randomized controlled single-blind POCD-ELA trial. Medicine (Baltimore). 2018;97(40):e12558. https://doi.org/10.1097/MD.0000000000012558.
Zhu H, Liu W, Fang H. Inflammation caused by peripheral immune cells across into injured mouse blood brain barrier can worsen postoperative cognitive dysfunction induced by isoflurane. BMC Cell Biol. 2018;19(1):23. https://doi.org/10.1186/s12860-018-0172-1.
Zhang M, Zhang YH, Fu HQ, Zhang QM, Wang TL. Ulinastatin May Significantly Improve Postoperative Cognitive Function of Elderly Patients Undergoing Spinal Surgery by Reducing the Translocation of Lipopolysaccharide and Systemic Inflammation. Front Pharmacol. 2018;9:1007. https://doi.org/10.3389/fphar.2018.01007.
Cao Y, Li Z, Ma L, Ni C, Li L, Yang N, Shi C, Guo X. Isofluraneāinduced postoperative cognitive dysfunction is mediated by hypoxiaāinducible factorā1Ī±ādependent neuroinflammation in aged rats. Mol Med Rep. 2018;17(6):7730ā6. https://doi.org/10.3892/mmr.2018.8850.
Danielson M, Reinsfelt B, Westerlind A, Zetterberg H, Blennow K, Ricksten SE. Effects of methylprednisolone on blood-brain barrier and cerebral inflammation in cardiac surgery-a randomized trial. J Neuroinflammation. 2018;15(1):283. https://doi.org/10.1186/s12974-018-1318-y.
Zila I, Mokra D, Kopincova J, Kolomaznik M, Javorka M, Calkovska A. Vagal-immune interactions involved in cholinergic anti-inflammatory pathway. Physiol Res. 2017;66(Supplementum 2):S139ā45 PMID: 28937230.
Bonaz B, Sinniger V, Pellissier S. Vagus Nerve Stimulation at the Interface of Brain-Gut Interactions. Cold Spring Harb Perspect Med. 2018. https://doi.org/10.1101/cshperspect.a034199.
Borovikova LV, Ivanova S, Zhang M, Yang H, Botchkina GI, Watkins LR, Wang H, Abumrad N, Eaton JW, Tracey KJ. Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin. Nature. 2000;405(6785):458ā62. https://doi.org/10.1038/35013070.
Johnson RL, Wilson CG. A review of vagus nerve stimulaton as a therapeutic intervention. J Inflamm Res. 2018;11:203ā2123. https://doi.org/10.2147/JIR.S163248.
Li Z, Liu X, Zhang Y, Shi J, Zhang Y, Xie P, Yu T. Connection changes in somatosensory cortex induced by different doses of propofol. PLoS One. 2014;9(2):e87829. https://doi.org/10.1371/journal.pone.0087829.
Lee SW, Kulkarni K, Annoni EM, Libbus I, KenKnight BH, Tolkacheva EG. Stochastic vagus nerve stimulation affects acute heart rate dynamics in rats. PLoS One. 2018;13(3):e0194910. https://doi.org/10.1371/journal.pone.0194910.
Stauss HM. Differential hemodynamic and respiratory responses to right and left cervical vagal nerve stimulation in rats. Physiol Rep. 2017;5(7):e13244. https://doi.org/10.14814/phy2.13244.
Broncel A, Bocian R, KÅos-Wojtczak P, Konopacki J. Medial septal cholinergic mediation of hippocampal theta rhythm induced by vagal nerve stimulation. PLoS One. 2018;13(11):e0206532. https://doi.org/10.1371/journal.pone.0206532.
Stauss HM, Stangl H, Clark KC, Kwitek AE, Lira VA. Cervical vagal nerve stimulation impairs glucose tolerance and suppresses insulin release in conscious rats. Physiol Rep. 2018;6(24):e13953. https://doi.org/10.14814/phy2.13953.
Cao J, Lu KH, Powley TL, Liu Z. Vagal nerve stimulation triggers widespread responses and alters large-scale functional connectivity in the rat brain. PLoS One. 2017;12(12):e0189518. https://doi.org/10.1371/journal.pone.0189518.
Livak KJ, Schmittgen TD. Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method. Methods. 2001;25(4):402ā8. https://doi.org/10.1006/meth.2001.1262.
Xin X, Xin F, Chen X, Zhang Q, Li Y, Huo S, Chang C, Wang Q. Hypertonic saline for prevention of delirium in geriatric patients who underwent hip surgery. J Neuroinflammation. 2017;14(1):221. https://doi.org/10.1186/s12974-017-0999-y.
Nadelson MR, Sanders RD, Avidan MS. Perioperative cognitive trajectory in adults. Br J Anaesth. 2014;112(3):440ā51. https://doi.org/10.1093/bja/aet420.
Kalliolias GD, Ivashkiv LB. TNF biology, pathogenic mechanisms and emerging therapeutic strategies. Nat Rev Rheumatol. 2016;12(1):49ā62. https://doi.org/10.1038/nrrheum.2015.169.
Hua FZ, Ying J, Zhang J, Wang XF, Hu YH, Liang YP, Liu Q, Xu GH. Naringenin pre-treatment inhibits neuroapoptosis and ameliorates cognitive impairment in rats exposed to isoflurane anesthesia by regulating the PI3/Akt/PTEN signalling pathway and suppressing NF-ĪŗB-mediated inflammation. Int J Mol Med. 2016;38(4):1271ā80. https://doi.org/10.3892/ijmm.2016.2715.
Zheng JW, Meng B, Li XY, Lu B, Wu GR, Chen JP. NF-ĪŗB/P65 signaling pathway: a potential therapeutic target in postoperative cognitive dysfunction after sevoflurane anesthesia. Eur Rev Med Pharmacol Sci. 2017;21(2):394ā407 PMID: 28165545.
Bonaz B, Sinniger V, Pellissier S. Anti-inflammatory properties of the vagus nerve: potential therapeutic implications of vagus nerve stimulation. J Physiol. 2016;594(20):5781ā90. https://doi.org/10.1113/JP271539.
Huffman WJ, Subramaniyan S, Rodriguiz RM, Wetsel WC, Grill WM, Terrando N. Modulation of neuroinflammation and memory dysfunction using percutaneous vagus nerve stimulation in mice. Brain Stimul. 2019;12(1):19ā29. https://doi.org/10.1016/j.brs.2018.10.005.
Maurer SV, Williams CL. The Cholinergic System Modulates Memory and Hippocampal Plasticity via Its Interactions with Non-Neuronal Cells. Front Immunol. 2017;8:1489. https://doi.org/10.3389/fimmu.2017.01489.
Zhou JP, Wang F, Li RL, Yuan BL, Guo YL. Effects of febrile seizure on motor, behavior, spatial learning and memory in rats. Zhonghua Er Ke Za Zhi. 2004;42(1):49ā53 PMID: 14990108. Chinese.
Liu RP, Fang JL, Rong PJ, Zhao Y, Meng H, Ben H, Li L, Huang ZX, Li X, Ma YG, Zhu B. Effects of electroacupuncture at auricular concha region on the depressive status of unpredictable chronic mild stress rat models. Evid Based Complement Alternat Med. 2013;2013:789674. https://doi.org/10.1155/2013/789674.
Liu AF, Zhao FB, Wang J, Lu YF, Tian J, Zhao Y, Gao Y, Hu XJ, Liu XY, Tan J, Tian YL, Shi J. Effects of vagus nerve stimulation on cognitive functioning in rats with cerebral ischemia reperfusion. J Transl Med. 2016;14:101. https://doi.org/10.1186/s12967-016-0858-0.
Zhu YZ, Yao R, Zhang Z, Xu H, Wang LW. Parecoxib prevents early postoperative cognitive dysfunction in elderly patients undergoing total knee arthroplasty: A double-blind, randomized clinical consort study. Medicine (Baltimore). 2016;95(28):e4082. https://doi.org/10.1097/MD.0000000000004082.
Chen K, Wei P, Zheng Q, Zhou J, Li J. Neuroprotective effects of intravenous lidocaine on early postoperative cognitive dysfunction in elderly patients following spine surgery. Med Sci Monit. 2015;21:1402ā7. https://doi.org/10.12659/MSM.894384.
Pappa M, Theodosiadis N, Tsounis A, Sarafis P. Pathogenesis and treatment of post-operative cognitive dysfunction. Electron Physician. 2017;9(2):3768ā75. https://doi.org/10.19082/3768.
Acknowledgements
Not applicable.
Funding
Not applicable.
Author information
Authors and Affiliations
Contributions
JX is the first author who was responsible for the experiment. HJW is responsible for data analysis. JX and HJW made the equal contribution to the article. YB and YLG took part in revising this article, they gave constructive advices to this study and English writing. YXS is the corresponding author. All authors have read and approved the manuscript, and ensure that this is the case.
Corresponding author
Ethics declarations
Ethics approval and consent to participate
We informed the ethics committee of Sanbo Brain Hospital for animal care and use, Capital Medical University, and got their approval.
Consent for publication
There is no personal information in this article, so it is not applicable.
Competing interests
The authors declare that they have no competing interests.
Additional information
Publisherās Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
About this article
Cite this article
Xiong, J., Wang, H., Bao, Y. et al. Electric vagal nerve stimulation inhibits inflammation and improves early postoperation cognitive dysfunction in aged rats. BMC Anesthesiol 19, 217 (2019). https://doi.org/10.1186/s12871-019-0885-5
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/s12871-019-0885-5