OBJECTIVE To investigate the apoptosis-inducing effect of esculetin （Esc） on acute myeloid leukemia （AML） HL-60 cells by regulating the protein kinase B （AKT）/S-phase kinase-associated protein 2 （SKP2）/MutT homolog 1 （MTH1） pathway. METHODS AML HL-60 cells were randomly divided into control group （routine culture）， Esc low-concentration group （L-Esc group， 25 μmol/L Esc）， Esc medium-concentration group （M-Esc group， 50 μmol/L Esc）， Esc high-concentration group （H-Esc group， 100 μmol/L Esc）， and high-concentration of Esc+ SC79 （AKT agonist） group （100 μmol/L Esc+5 μmol/L SC79）. Cell proliferation in each group was detected by MTT assay and colony formation assay. The level of reactive oxygen species （ROS） in cells was measured by using the CM-H2DCFDA fluorescent probe. Cell apoptosis was analyzed by flow cytometry. Western blot assay was performed to detect the expression levels of apoptosis-related proteins [B-cell lymphoma 2 （Bcl-2）， Bcl-2-associated X protein （Bax）， cleaved caspase-3]， AKT/SKP2/MTH1 pathway-related proteins （p-AKT， AKT， SKP2， MTH1）， along with the upstream and downstream proteins of AKT phosphatidylinositol 3-kinase （PI3K）， cyclin-dependent kinase inhibitor 1 （P21） and cyclin-dependent kinase inhibitor 1B （P27）. RESULTS Compared with control group， the cell viability， colony number， and the phosphorylation levels of AKT and PI3K proteins as well as protein expressions of SKP2， MTH1 and Bcl-2 were significantly decreased （P＜0.05）， while ROS level， apoptosis rate， and the expression levels of Bax， cleaved caspase-3， P21 and P27 proteins were significantly increased （P＜0.05）. Moreover， the effects of Esc exhibited concentration-dependence （P＜0.05）. Compared with H-Esc group， above indexes of high-concentration of Esc+ SC79 group were reversed significantly （P＜0.05）. CONCLUSIONS Esc may promote massive ROS production and induce activation of apoptosis in HL-60 cells by inhibiting the AKT/SKP2/MTH1 pathway， thus inhibiting the proliferation of HL-60 cells.

Objective: To determine the association between exposure to entertainment screen content on mobile phones and symptoms of anxiety-depression co-morbidity among college students,so as to provide evidence for mental health interventions. Methods: A baseline survey was conducted from April to May 2019. A total of 1 135 college students were selected from one university each in Shangrao City, Jiangxi Province and Hefei City, Anhui Province using cluster random sampling method. A follow up study was conducted in November 2019, resulting in 1 110 matched valid responses. Self rating questionnaires were used to assess the exposure of entertainment screen content. The Depression Anxiety Stress Scale-21(DASS-21) and the Patient Health Questionnaire-9 (PHQ-9) were used to evaluate the anxiety symptoms, depressive symptoms, and symptoms of anxiety-depression co-morbidity among college students. A multivariate binary Logistic regression model was constructed following initial intergroup comparisons with Chi-square test to determine the association between baseline exposure to mobile entertainment screen content and the risk of symptoms of anxiety depression co-morbidity at baseline and the 6 month follow up. Results: The prevalence rates of symptoms of anxiety-depression co-morbidity among college students were 25.4% and 20.6% at baseline and follow up, respectively.After adjusting for confounding factors such as gender, self rated family economic status and self rated health status, the results of multivariate binary Logistic regression analysis showed that compared with the appropriate exposure level group, the exposure of entertainment screen content on mobile phones at baseline, including frequent exposure to reading( OR =1.65,95% CI =1.14-2.39), occasional exposure to other entertainment screen content ( OR =1.46,95% CI =1.01-2.10)and frequent exposure to other entertainment screen content( OR =1.76,95% CI =1.20-2.60), increased the co-occurrence risk of symptoms of anxiety-depression co-morbidity among college students during the follow up period (all P <0.05). Conclusion Occasional or frequert exposure to mobile entertainment screen content can increase the risk of symptoms of anxiety depression co-morbidity among college students.

ObjectiveTo investigate the mechanism by which the Zishen Huoxue prescription （ZSHXP） ameliorates cognitive dysfunction in rats with vascular dementia （VD） induced by the bilateral common carotid artery ligation （2-VO model rats） through regulating the glucose-regulated protein 78 （GRP78）/protein kinase R-like endoplasmic reticulum kinase （PERK）/activating transcription factor 4 （ATF4） signaling pathway. MethodsA VD rat model was established via the 2-VO method. A total of 72 male Sprague-Dawley （SD） rats were randomly divided into six groups： Sham group， Model group， donepezil hydrochloride group （0.45 mg·kg^-1）， and ZSHXP groups at low （8.90 g·kg^-1）， medium （17.80 g·kg^-1）， and high （35.60 g·kg^-1） doses，with 12 rats in each group. The Morris Water Maze test was utilized to assess spatial learning and memory abilities of rats， and the Novel Object Recognition test was used to evaluate cognitive performance. Hematoxylin-eosin （HE） and Nissl staining were applied to observe the histological and morphological changes in hippocampal tissues. Transmission electron microscopy （TEM） was used to observe the morphological changes of endoplasmic reticulum in rat hippocampal neurons. Immunofluorescence staining was adopted to detect the colocalization of neuronal nuclei antigen （NeuN） with GRP78 and βⅢ Tubulin with gasdermin D （GSDMD） in hippocampal neurons. Western blot was used to detect the expression levels of endoplasmic reticulum stress （ERS）-related proteins including GRP78， PERK， ATF4， phosphorylated protein kinase R-like endoplasmic reticulum kinase （p-PERK）， C/EBP homologous protein （CHOP）， NOD-like receptor protein 3 （NLRP3）， Caspase-1 and GSDMD. ResultsCompared with the sham operation group， the model group showed a significantly prolonged escape latency （P<0.01）， a significant decrease in the number of platform crossings and the residence time in the target quadrant （P<0.01）， and a markedly reduced recognition index （P<0.01）. Histological observations revealed that the hippocampal neurons in the model group were disorderly arranged with reduced quantity， deformed and shrunken cell bodies， and pyknotic and hyperchromatic nuclei. The number of Nissl bodies decreased significantly. The number of endoplasmic reticula reduced obviously， accompanied by abnormal dilation and swelling， and the loss of normal folding structure. The fluorescence colocalization of NeuN with GRP78 and βⅢ Tubulin with GSDMD in the hippocampus was significantly increased in the model group. The protein expression levels of GRP78， p-PERK/PERK， ATF4， CHOP， NLRP3， GSDMD and Caspase-1 in the model group were significantly elevated （P<0.01）. Compared with the model group， the donepezil hydrochloride group and the ZSHXP medium- and high-dose groups had a significantly shortened escape latency （P<0.01） and an increased number of platform crossings （P<0.05， P<0.01）. The residence time in the target quadrant was increased in the donepezil hydrochloride group and all ZSHXP groups （P<0.05， P<0.01）， with a significantly improved recognition index （P<0.01）. In the donepezil hydrochloride group and all ZSHXP groups， the number of hippocampal neurons increased with a more compact arrangement and reduced nuclear hyperchromasia. The number of Nissl bodies increased with morphological structures tending to be normal. In the ZSHXP high-dose group， the number of endoplasmic reticula increased and the folding structure was restored. The fluorescence colocalization of NeuN with GRP78 and βⅢ Tubulin with GSDMD in the hippocampus was significantly weakened in the treatment groups. In the donepezil hydrochloride group， the protein expressions of GRP78， ATF4 and CHOP were increased （P<0.01）， while the expression of p-PERK/PERK was decreased （P<0.05）. In the ZSHXP low-dose group， the expressions of GRP78， p-PERK/PERK and CHOP were elevated （P<0.05， P<0.01）. The ZSHXP medium- and high-dose groups showed a significant decrease in the protein expressions of p-PERK/PERK， ATF4 and CHOP （P<0.01）， and the high-dose group had a markedly reduced GRP78 protein expression （P<0.01）. In the donepezil hydrochloride group， the Caspase-1 protein expression was increased （P<0.01） and the NLRP3 protein expression was decreased （P<0.01）. In the ZSHXP low-dose group， the GSDMD expression was elevated （P<0.01） while the NLRP3 protein expression was reduced （P<0.01）. After treatment with medium and high doses of ZSHXP， the protein expression levels of NLRP3， GSDMD and Caspase-1 were significantly decreased （P<0.01）. ConclusionThe ameliorative effect of ZSHXP on cognitive function in 2-VO model rats may be associated with its regulation of the GRP78/PERK/ATF4 signaling pathway， which ameliorates ERS and inhibits neuronal pyroptosis.

ObjectiveTo investigate the mechanism by which the Zishen Huoxue prescription （ZSHXP） ameliorates cognitive dysfunction in rats with vascular dementia （VD） induced by the bilateral common carotid artery ligation （2-VO model rats） through regulating the glucose-regulated protein 78 （GRP78）/protein kinase R-like endoplasmic reticulum kinase （PERK）/activating transcription factor 4 （ATF4） signaling pathway. MethodsA VD rat model was established via the 2-VO method. A total of 72 male Sprague-Dawley （SD） rats were randomly divided into six groups： Sham group， Model group， donepezil hydrochloride group （0.45 mg·kg^-1）， and ZSHXP groups at low （8.90 g·kg^-1）， medium （17.80 g·kg^-1）， and high （35.60 g·kg^-1） doses，with 12 rats in each group. The Morris Water Maze test was utilized to assess spatial learning and memory abilities of rats， and the Novel Object Recognition test was used to evaluate cognitive performance. Hematoxylin-eosin （HE） and Nissl staining were applied to observe the histological and morphological changes in hippocampal tissues. Transmission electron microscopy （TEM） was used to observe the morphological changes of endoplasmic reticulum in rat hippocampal neurons. Immunofluorescence staining was adopted to detect the colocalization of neuronal nuclei antigen （NeuN） with GRP78 and βⅢ Tubulin with gasdermin D （GSDMD） in hippocampal neurons. Western blot was used to detect the expression levels of endoplasmic reticulum stress （ERS）-related proteins including GRP78， PERK， ATF4， phosphorylated protein kinase R-like endoplasmic reticulum kinase （p-PERK）， C/EBP homologous protein （CHOP）， NOD-like receptor protein 3 （NLRP3）， Caspase-1 and GSDMD. ResultsCompared with the sham operation group， the model group showed a significantly prolonged escape latency （P<0.01）， a significant decrease in the number of platform crossings and the residence time in the target quadrant （P<0.01）， and a markedly reduced recognition index （P<0.01）. Histological observations revealed that the hippocampal neurons in the model group were disorderly arranged with reduced quantity， deformed and shrunken cell bodies， and pyknotic and hyperchromatic nuclei. The number of Nissl bodies decreased significantly. The number of endoplasmic reticula reduced obviously， accompanied by abnormal dilation and swelling， and the loss of normal folding structure. The fluorescence colocalization of NeuN with GRP78 and βⅢ Tubulin with GSDMD in the hippocampus was significantly increased in the model group. The protein expression levels of GRP78， p-PERK/PERK， ATF4， CHOP， NLRP3， GSDMD and Caspase-1 in the model group were significantly elevated （P<0.01）. Compared with the model group， the donepezil hydrochloride group and the ZSHXP medium- and high-dose groups had a significantly shortened escape latency （P<0.01） and an increased number of platform crossings （P<0.05， P<0.01）. The residence time in the target quadrant was increased in the donepezil hydrochloride group and all ZSHXP groups （P<0.05， P<0.01）， with a significantly improved recognition index （P<0.01）. In the donepezil hydrochloride group and all ZSHXP groups， the number of hippocampal neurons increased with a more compact arrangement and reduced nuclear hyperchromasia. The number of Nissl bodies increased with morphological structures tending to be normal. In the ZSHXP high-dose group， the number of endoplasmic reticula increased and the folding structure was restored. The fluorescence colocalization of NeuN with GRP78 and βⅢ Tubulin with GSDMD in the hippocampus was significantly weakened in the treatment groups. In the donepezil hydrochloride group， the protein expressions of GRP78， ATF4 and CHOP were increased （P<0.01）， while the expression of p-PERK/PERK was decreased （P<0.05）. In the ZSHXP low-dose group， the expressions of GRP78， p-PERK/PERK and CHOP were elevated （P<0.05， P<0.01）. The ZSHXP medium- and high-dose groups showed a significant decrease in the protein expressions of p-PERK/PERK， ATF4 and CHOP （P<0.01）， and the high-dose group had a markedly reduced GRP78 protein expression （P<0.01）. In the donepezil hydrochloride group， the Caspase-1 protein expression was increased （P<0.01） and the NLRP3 protein expression was decreased （P<0.01）. In the ZSHXP low-dose group， the GSDMD expression was elevated （P<0.01） while the NLRP3 protein expression was reduced （P<0.01）. After treatment with medium and high doses of ZSHXP， the protein expression levels of NLRP3， GSDMD and Caspase-1 were significantly decreased （P<0.01）. ConclusionThe ameliorative effect of ZSHXP on cognitive function in 2-VO model rats may be associated with its regulation of the GRP78/PERK/ATF4 signaling pathway， which ameliorates ERS and inhibits neuronal pyroptosis.

Alzheimer’s disease (AD) is a central neurodegenerative disease characterized by progressive cognitive decline and memory impairment in clinical. Currently, there are no effective treatments for AD. In recent years, a variety of therapeutic approaches from different perspectives have been explored to treat AD. Although the drug therapies targeted at the clearance of amyloid β-protein (Aβ) had made a breakthrough in clinical trials, there were associated with adverse events. Neuroinflammation plays a crucial role in the onset and progression of AD. Continuous neuroinflammatory was considered to be the third major pathological feature of AD, which could promote the formation of extracellular amyloid plaques and intracellular neurofibrillary tangles. At the same time, these toxic substances could accelerate the development of neuroinflammation, form a vicious cycle, and exacerbate disease progression. Reducing neuroinflammation could break the feedback loop pattern between neuroinflammation, Aβ plaque deposition and Tau tangles, which might be an effective therapeutic strategy for treating AD. Traditional Chinese herbs such as Polygonum multiflorum and Curcuma were utilized in the treatment of AD due to their ability to mitigate neuroinflammation. Non-steroidal anti-inflammatory drugs such as ibuprofen and indomethacin had been shown to reduce the level of inflammasomes in the body, and taking these drugs was associated with a low incidence of AD. Biosynthetic nanomaterials loaded with oxytocin were demonstrated to have the capability to anti-inflammatory and penetrate the blood-brain barrier effectively, and they played an anti-inflammatory role via sustained-releasing oxytocin in the brain. Transplantation of mesenchymal stem cells could reduce neuroinflammation and inhibit the activation of microglia. The secretion of mesenchymal stem cells could not only improve neuroinflammation, but also exert a multi-target comprehensive therapeutic effect, making it potentially more suitable for the treatment of AD. Enhancing the level of TREM2 in microglial cells using gene editing technologies, or application of TREM2 antibodies such as Ab-T1, hT2AB could improve microglial cell function and reduce the level of neuroinflammation, which might be a potential treatment for AD. Probiotic therapy, fecal flora transplantation, antibiotic therapy, and dietary intervention could reshape the composition of the gut microbiota and alleviate neuroinflammation through the gut-brain axis. However, the drugs of sodium oligomannose remain controversial. Both exercise intervention and electromagnetic intervention had the potential to attenuate neuroinflammation, thereby delaying AD process. This article focuses on the role of drug therapy, gene therapy, stem cell therapy, gut microbiota therapy, exercise intervention, and brain stimulation in improving neuroinflammation in recent years, aiming to provide a novel insight for the treatment of AD by intervening neuroinflammation in the future.

Objective : To investigate the protective effect of dimethyl fumarate(DMF) on maternal intrahepatic cholestasis(ICP) during pregnancy induced by di(2-ethylhexyl) phthalate(DEHP) exposure and its mechanism. Methods : Thirty-two 8-week-old female institute of cancer research(ICR) mice were randomly divided into 4 groups: Ctrl group, DEHP group, DMF group and DEHP+DMF group. DEHP and DEHP+DMF groups were treated with DEHP(200 mg/kg) by gavage every morning at 9:00 a.m. DMF and DEHP+DMF groups were treated with DMF(150 mg/kg) from day 13 to day 16 of gestation by gavage. After completion of gavage on day 16 of pregnancy, maternal blood, maternal liver, placenta, and amniotic fluid were collected from pregnant mice after a six-hour abrosia. The body weight of the mother rats and the body weight of the fetus rats were sorted and analyzed; the levels of total bile acid(TBA), alkaline phosphatase(ALP), aspartate aminotransferase/alanine aminotransferase(AST/ALT) in serum and TBA in liver, amniotic fluid and placenta were detected by biochemical analyzer; HE staining was used to observe the pathological changes of liver tissue; Quantitative reverse transcription PCR(RT-qPCR) was used to detect the expression levels of tumor necrosis factor-α(TNF-α), interleukin(IL)-6, IL-1, IL-18 and NOD-like receptor thermal protein domain associated protein 3(NLRP3) in the liver; Western blot was used to detect the expression of the nuclear factor KappaB(NF-κB) and NLRP3. Results : Compared with the control group, the body weight of the DEHP-treated dams and pups decreased(P<0.05); the levels of TBA, ALP, AST/ALT in the serum of dams and the levels of TBA in the liver, amniotic fluid, and placenta of dams increased(P<0.05); the histopathological results showed that liver tissue was damaged, bile ducts were deformed, and there was inflammatory cell infiltration around them; the levels of inflammation-related factors TNF-α, IL-6, IL-1, IL-18 and NLRP3 transcription in maternal liver increased(P<0.05); the expression of NF-κB and NLRP3 protein in maternal liver significantly increased( P<0. 05). Compared with the DEHP group,the body weight of both dams and fetuses significantly increased in DEHP + DMF group( P<0. 05); the levels of TBA,ALP,AST/ALT in the serum of dams and amniotic fluid of fetuses decreased( P<0. 05); the degree of liver lesions was improved; the transcription levels of inflammation-related factors TNF-α,IL-6,IL-1,IL-18 and NLRP3 in maternal liver decreased( P<0. 05); the expression of NF-κB and NLRP3 protein in maternal liver significantly decreased( P<0. 05). Conclusion DMF can effectively protect the DEHP exposure to lead to female ICP,and its mechanism may be through inhibiting the NF-κB/NLRP3 pathway and reducing liver inflammation.

BACKGROUND:The self-renewal and multi-directional differentiation of pluripotent stem cells possess the potential to revolutionize people's understanding of biology,medicine,development,and disease.Stem cells play an important role in the early stage of embryonic development,and the study of them could be beneficial to understanding of the basic principles of biological development and tissue or organ formation,exploring the potential mechanisms of various diseases,studying the repair and regeneration of damaged tissues or organs,and promoting drug discovery and personalized treatment. OBJECTIVE:To review the research progress of pluripotent stem cells,summarize and categorize the fundamental types of pluripotent stem cells,and elucidate the lineage situations of various types of pluripotent stem cells in common mammals. METHODS:PubMed,Web of Science,CNKI,and WanFang databases were searched systematically,with the keywords"pluripotent stem cells;embryonic stem cells;induced pluripotent stem cells;expanded potential stem cells;livestock pluripotent stem cells"in English and Chinese.The 99 articles related to mammalian pluripotent stem cells were systematically screened according to inclusion and exclusion criteria,and then reviewed. RESULTS AND CONCLUSION:(1)According to classical theory in mouse embryonic stem cell research,the pluripotent state of stem cells is divided into two forms:na?ve and primed.Na?ve state corresponds to the inner cell mass of pre-implantation embryos before attachment to the uterine wall,while primed state corresponds to the epiblast after implantation.These two states exhibit significant differences in epigenetic features,transcriptional activity,external signal dependency,and metabolic phenotype.It is later discovered that there is an intermediate state between na?ve and primed called formative pluripotency.Therefore,the pluripotency of pluripotent stem cells is a continuous developmental process rather than a unique cell state.(2)In addition to obtaining pluripotent stem cells from the inner cell mass,there are various methods and lineages for acquiring pluripotent stem cells,including embryonic germ cells established using primitive germ cells from mouse embryos,induced pluripotent stem cells created by the dedifferentiation of adult mouse and human fibroblasts with four factors—Oct3/4,Sox2,c-Myc,and Klf4;embryonic stem cell-like cell lines cultured from somatic cell nuclear transfer,parthenogenesis,neonatal or adult testicular or ovarian tissue,very small embryonic-like stem cells derived from various adult tissues and expanded pluripotent stem cells derived from pre-implantation stages.These pluripotent stem cells all share the common characteristics of continuous self-renewal,expressing core pluripotency factors and possessing the ability to differentiate into the three primary germ layers.(3)Currently,pluripotent stem cells are being used for disease modeling to study the mechanisms of various diseases and develop new drugs.Simultaneously,scientists are attempting to use pluripotent stem cells to cultivate various tissues and organs,offering new possibilities for regenerative medicine and transplantation.However,the clinical application of pluripotent stem cells faces safety challenges,including issues of cell mutations and immune rejection.Continual improvement in the methods of generating pluripotent stem cells will make them safer and more efficient for clinical applications.(4)Based on the methods of obtaining and lineage establishment of pluripotent stem cells in mice and humans,various types of pluripotent stem cells have been established in livestock,including embryonic stem cells,induced pluripotent stem cells,germ lineages of pluripotent stem cells,and expanded potential stem cells.Research on livestock pluripotent stem cells opens up new avenues for animal reproduction,breeding,genetic engineering,disease modeling,drug screening,and the conservation of endangered wildlife.

BACKGROUND:Flap transplantation technique is a commonly used surgical procedure for the treatment of severe tissue defects,but postoperative flap necrosis is easily triggered by ischemia-reperfusion injury.Therefore,it is still an important research topic to improve the survival rate of transplanted flaps. OBJECTIVE:To review the pathogenesis and latest treatment progress of flap ischemia-reperfusion injury. METHODS:CNKI,WanFang Database and PubMed database were searched for relevant literature published from 2014 to 2024.The search terms used were"flap,ischemia-reperfusion injury,inflammatory response,oxidative stress,Ca2+overload,apoptosis,mesenchymal stem cells,platelet-rich plasma,signaling pathways,shock wave,pretreatment"in Chinese and English.After elimination of irrelevant literature,poor quality and obsolete literature,77 documents were finally included for review. RESULTS AND CONCLUSION:Flap ischemia/reperfusion injury may be related to pathological factors such as inflammatory response,oxidative stress response,Ca2+overload,and apoptosis,which can cause apoptosis of vascular endothelial cells,vascular damage and microcirculation disorders in the flap,and eventually lead to flap necrosis.Studies have found that mesenchymal stem cell transplantation,platelet-rich plasma,signaling pathway modulators,shock waves,and pretreatment can alleviate flap ischemia/reperfusion injuries from different aspects and to varying degrees,and reduce the necrosis rate and necrosis area of the grafted flap.Although there are many therapeutic methods for skin flap ischemia/reperfusion injury,a unified and effective therapeutic method has not yet been developed in the clinic,and the advantages and disadvantages of various therapeutic methods have not yet been compared.Most of the studies remain in the stage of animal experiments,rarely involving clinical observations.Therefore,a lot of research is required in the future to gradually move from animal experiments to the clinic in order to better serve the clinic.

ObjectiveTo understand the epidemiological distribution and gene evolutionary variation of influenza A (H3N2) viruses in Fengxian District, Shanghai, in the surveillance year of 2023, and to provide a reference basis for influenza prevention and control. MethodsThe prevalence of influenza virus in Fengxian District in the 2023 influenza surveillance year (April 2023‒March 2024) was analyzed. The hemagglutinin (HA) gene, neuraminidase (NA) gene, and amino acid sequences of 75 strains of H3N2 influenza viruses were compared with the vaccine reference strain for similarity matching and phylogenetic evolutionary analysis, in addition to an analysis of gene characterization and variation. ResultsIn Fengxian District, there was a mixed epidemic of H3N2 and H1N1 in the spring of 2023, with H3N2 being the predominant subtype in the second half of the year, and Victoria B becoming the predominant subtype in the spring of 2024. A total of 75 influenza strains of H3N2 with HA and NA genes were distributed in the 3C.2a1b.2a.2a.2a.3a.1 and B.4 branches, with overall similarity to the reference strain of the 2024 vaccine higher than that of the reference strain of the 2022 and 2023 vaccine. Compared with the 2023 vaccine reference strain, three antigenic sites and one receptor binding site were changed in HA, with three glycosylation sites reduced and two glycosylation sites added; where as in NA seven antigenic sites and the 222nd resistance site changed with two glycosylation sites reduced. ConclusionThe risk of antigenic variation and drug resistance of H3N2 in this region is high, and it is necessary to strengthen the publicity and education on the 2024 influenza vaccine and long-term monitoring of influenza virus prevalence and variation levels.