IL-1β In Brain Tissues Research Articles

Inhibition of IL-6 methylation by Saikosaponin C regulates neuroinflammation to alleviate depression.

Saikosaponin C (SSc) increases the expression of synaptic proteins and has a unexplored role in the prevention of AD and other neurodegeneration in humans. Therefore, we hypothesized that SSc has the potential to relief of depressive symptoms. Here, our study assessed the role of SSc on depression-like behaviors caused by a chronic social defeat stress (CSDS) in mice and explored the underlying mechanisms. Behavioral tests were conducted to verify the efficacy of SSC in treating depression-like behavior in mice. The levels of IL-6, TNF-α and IL-1β in brain tissue and BV2 cells were determined by ELISA. The effect of SSc on dendritic spine density was determined by Golgi staining. The percentage of monocytes in peripheral blood was measured using flow cytometry. The levels of STAT3 and DNMT1 under the influence of SSc were assessed by immunofluorescence. Protein expression of DNMT1, DNMT3a, DNMT3b, p-STAT3 and STAT3 in brain and BV2 cells was studied by Western blot. OE-DNMT1 was induced in the experiment to verify the inhibitory effect of DNMT1 on IL-6 methylation in SSC. Luciferase was used to detect SSC specific fragments affecting IL-6 methylation. SSC treatment significantly alleviated depressive-like behavior, inhibited the levels of inflammatory cytokines including IL-6, IL-1β and TNF-α, increased dendritic spine density and promoted synaptic plasticity in mice. SSC downregulated IL-6, STAT3 and DNMT1 expression in vivo and in vitro. SSC also decreased the percentage of monocytes in peripheral blood and suppressed neuroinflammation in mice. Overexpression of DNMT1 by shRNA abolished the inhibitory effect of SSc on IL-6 methylation. This study showed that SSc reduced IL6 methylation by inhibiting DNMT1 protein, induced a decrease in IL6 expression, promoted synaptic plasticity, and attenuated CSDS-induced depression-like behavior.

Safety Assessments of Electroacupuncture-Mediated Blood–Brain Barrier Opening: An Animal Study

The presence of the Blood–Brain barrier (BBB) makes it difficult for therapeutic agents to reach the brain to treat brain diseases. As an emerging treatment, electroacupuncture (EA)-mediated BBB opening can temporarily increase the permeability of the brain blood vessels to increase the concentration of the therapeutic agent in the brain parenchyma, which offers great clinical benefits. Recent studies have suggested that BBB opening with excessive exposure levels may cause tissue/cell damage and short-term behavioral changes. Here, we investigated whether the EA-mediated BBB opening cause serious adverse events in the normal rat brain tissue and motor behavior, such as brain tissue damage, histopathologic alteration, or aggravated behavioral changes. EA was performed on the accupoint GV26 and GV20. Evans Blue Assay (EBA) and fluorescein isothiocyanate (FITC)–dextran Assay were performed to assess the BBB permeability. Immunofluorescence of GFAP-positive cells was marked and Hematoxylin-eosin (HE) Staining was carried out for assessing brain cortex damage. Tunel Assay was conducted to assess cell apoptosis. ELISA was used to measure the contents of TNF-α and IL-1β in brain tissue to explore the inflammatory response. The open field test, balance beam test and Y-Maze test were carried out to assess and neural behaviour. EA can induce an increase in BBB permeability on rats, allowing the macromolecular tracer Evans blue (EB) and Fluorescein Isothiocyanate (FITC)–Dextran to enter the brain. Histological analysis indicated that there was no obvious red blood cell leakage and a cellular apoptotic response in the brain tissue of rats with EA treatment. In addition, EA stimulation at specific parameters did not impair the rats’ motor ability, balance and coordination, and short-term spatial learning and memory. Our results suggest that EA can safely and effectively open the BBB in rats without causing brain damage and behavioral memory impairment.

Zunyimycin C enhances immunity and improves cognitive impairment and its mechanism.

This study aimed to explore the efficacy of zunyimycin C in the immunological enhancement of hypoimmune mice and improvement of cognitive impairment in a mice model of Alzheimer's disease (AD). Zunyimycin C was administered intranasally to interfere with AD mouse models or gavage to hypoimmune animals. Results of the Morris water maze (MWM) showed that zunyimycin may improve the learning and memory abilities of the AD mice model. The results of differential expression analysis of mRNA levels of inflammatory factors and pathways in brain tissues of the AD mouse model suggested that differential expression was more obvious under Zun-Int L. Western blot revealed that the relative expression of glial fibrillary acidic protein in the brain tissue of the AD mouse model in the Zun-Pre group was significantly higher than that in the other groups, and the difference was statistically significant. The relative expression of interleukin (IL)-6 protein in the brain tissue of mice in the low-dose intervention group was significantly lower than that in the other groups, and the difference was statistically significant. As for hypoimmune animals, short chain fatty acids (SCFAs) assay and intestinal flora assay results showed that zunyimycin C may change intestinal flora diversity and SCFA biosynthesis. The prophylactic administration of zunyimycin C could not inhibit acute neuroinflammation in AD mice. Zunyimycin C may participate in the immune response by activating the Ras-Raf-MEK-ERK signaling pathway to stimulate microglia to produce more inflammatory factors. Zunyimycin C may inhibit autophagy by activating the PI3K-AKT-mTOR signaling pathway, promote cell survival, mediate neuroprotective effects of reactive microglia and reactive astrocytes, and reduce IL-1β in brain tissue and IL-6 secretion, thereby attenuating neuroinflammation in AD mice and achieving the effect of improving learning and memory impairment. Zunyimycin C may play a role in immunological enhancement by changing intestinal flora diversity and SCFAs.

A novel nano material for anti-cerebral ischaemia: preparation and application of borneol angelica polysaccharide liposomes

Objective: To investigate the preparation of novel nanoliposomes (Borneol Angelica Polysaccharide Liposomes, BAPL) for anti-cerebral ischaemia and verify its curative effects and mechanism. Methods: By applying a uniform experiment design to investigate the fitting combination of BAPL. Encapsulation Efficiency Evaluation of BAPL Preparation; Particle Size and Surface Potential Evaluation of BAPL Biological activity; Cerebral ischaemia models of rats Evaluation of BAPL curative effects and mechanism. Results: (1) The fitting combination of lecithin, Cholesterol, AP mass and the borneol mass was 60 mg, 60 mg, 45 mg and 5 mg. the highest encapsulation efficiency was 80.4%, the particle size was 179.1 nm, and the surface zeta potential was −17.2 mV. It conforms to the nano-material standards. (2) The results of animal experiments show that: In the BAPL group, the infarct volume of TTC staining was significantly decreased, and the expression levels of NF-κBp65, TLR-4, IL-8, IL-6, IL-1β in brain tissue were significantly decreased, while the expression levels of ZO-1, ZO-2, IL-10 were significantly increased after cerebral ischaemia-reperfusion. Conclusion: BAPL is a novel nano and effective material for anti-cerebral ischaemia.

Qishen Yiqi Dropping Pill facilitates post-stroke recovery of motion and memory loss by modulating ICAM-1-mediated neuroinflammation

BackgroundPromotion of functional recovery in patients is the primary goal of stroke management. However, its achievement is low due to the lack of full understanding of the complex pathological process of stroke and therefore limited therapeutic strategies. Qishen Yiqi Dropping Pill (QSYQ) is a component-based Chinese medicine that has been widely used in clinical treatment of ischemic cardiovascular diseases. Our previous studies indicated that QSYQ were protective for acute ischemic stroke in animal models and this study aimed to investigate the effect of QSYQ on brain function during stroke recovery. MethodsThe therapeutic effects of QSYQ were evaluated by neurological deficit score, dark avoidance test, gait analysis, Morris water maze and brain tissue atrophy volume in a rat model of middle cerebral artery occlusion (MCAO) with ischemia for 60 min. The underlying mechanisms of QSYQ accelerating the functional recovery of MCAO rats was then revealed using proteomic sequencing and validated by immunohistochemistry, qRT-PCR and ELISA assays. The active components in QSYQ were elucidated by molecular docking and verified biochemically in vitro. ResultsQSYQ treatment for 28 days significantly improved the neurological function, gait, spontaneous activity, spatial memory, and reduced brain atrophy in MCAO rats. Proteomic analysis of ischemic brain region and the following bioinformatics studies showed that QSYQ intervention markedly modulated neuroinflammatory responses post stroke, in which ICAM-1 played a dominant role. In particular, QSYQ reversed high cerebral expression of ICAM-1 in MCAO rats and decreased the content of TNF-α, IL-6 and IL1β in brain tissue and serum. In vitro, it was found that the active component rosmarinic acid in QSYQ evidently inhibit the expression of ICAM-1 caused by oxygen glucose deprivation/reoxygenation injury via using immunofluorescence staining. ConclusionQSYQ effectively accelerates the recovery of motor impairment and memory loss in rats after stroke via downregulation of ICAM-1-mediated neuroinflammation, and rosmarinic acid is one of its main active components.

Effects of Xiao-Cheng-Qi decoction on brain edema and inflammatory factors in rats with severe traumatic brain injury

To observe the effects of the Chinese medicine prescription Xiao-Cheng-Qi decoction (XCQD) on acute brain edema and inflammatory factors in rats with severe traumatic brain injury (sTBI). A total of 108 male Sprague-Dawley (SD) rats were divided into control group, sham operation group, sTBI model group, and XCQD low, medium, high dose groups by random number table method, with 18 rats in each group. sTBI rat model was prepared according to the modified Freeney method. At 6 hours after injury, the XCQD low, medium, and high dose groups were given XCQD 1.80, 2.78, and 4.59 g/kg by gavage, respectively, and the other three groups were given the same amount of normal saline, once a day for 3 days. After 3 days of injury, rats in each group were sacrificed after the modified neurologic severity score (mNSS) assessed. Pathological changes of brain tissue were observed under light microscope after hematoxylin eosin (HE) staining, water content of brain tissue was measured by dry-wet specific gravity method, and the expressions of aquaporin 4 (AQP4), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in brain tissue were detected by Western blotting. Serum TNF-α and IL-1β levels were detected by enzyme linked immunosorbent assay (ELISA). Compared with the normal group, the mNSS score of rats increased significantly, the structure of brain tissue was disordered, and pathological changes appeared such as inflammation, edema, pyknosis of nerve nuclei, water content, the protein expressions of AQP4, TNF-α and IL-1β in brain tissue, and the contents of TNF-α, IL-1β in serum were significantly increased. After XCQD intervention, the above indexes were significantly improved. Compared with sTBI model group, the mNSS score of XCQD medium and high dose groups significantly decreased (6.94±1.16, 6.88±1.02 vs. 8.61±1.09, both P < 0.05), and the pathological changes such as brain edema and inflammation were alleviated. Brain tissue water content, AQP4 protein expression and contents of serum TNF-α, IL-1β in XCQD low, medium, and high dose groups significantly decreased compared with sTBI model group [brain tissue water content: (78.25±0.71)%, (77.62±0.44)%, (76.70±0.74)% vs. (80.08±0.66)%; the expression of brain AQP4 protein (AQP4/β-actin): 0.86±0.13, 0.84±0.22, 0.65±0.13 vs. 1.08±0.14; serum TNF-α (ng/L): 106.34±15.07, 95.75±17.26, 89.00±17.36 vs. 141.96±29.47; serum IL-1β (ng/L): 90.41±12.88, 72.82±13.51, 71.32±16.79 vs. 128.57±22.56, respectively, all P < 0.05]. The protein expressions of TNF-α,IL-1β in brain tissue of XCQD medium and high dose groups also significantly decreased compared with sTBI model group [TNF-α (TNF-α/β-actin): 0.90±0.24, 0.79±0.35 vs. 1.17±0.15; IL-1β (IL-1β/β-actin): 0.91±0.21, 0.68±0.28 vs. 1.23±0.08, respectively, all P < 0.05]. Brain tissue water content, the expression of brain AQP4 protein, the levels of brain tissue and serum IL-1β in XCQD high dose group improved more significant than those of XCQD low dose group. XCQD can alleviate the acute brain edema in sTBI rats, and it is dose-dependent. The mechanism may be relevant to reduce the secondary inflammatory response of sTBI by inhibiting the expression of inflammatory factors TNF-α and IL-1β.

Antiapoptotic and Anti-Inflammatory Effects of CPCGI in Rats with Traumatic Brain Injury.

BackgroundCompound porcine cerebroside and ganglioside injection (CPCGI) has been used for the treatment of certain brain disorders. Apoptosis and inflammation were reported to be involved in the pathogenesis of traumatic brain injury (TBI). Therefore, this study primarily investigated the effects of CPCGI on mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling in a rat model of controlled cortical impact (CCI).Materials and MethodsCPCGI (0.6 mL/kg) was administered intraperitoneally 30 min after the induction of CCI. Mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling were evaluated 24 h after CCI, and apoptotic cell death, neutrophil infiltration, and astrocyte and microglial activation were determined by TUNEL and immunofluorescent staining 3 days after CCI.Results1) CPCGI markedly enhanced cytosolic and mitochondrial Bcl-xL levels, the mitochondrial Bcl-xL/Bax ratio, and mitochondrial cytochrome (cyt) c levels and reduced cytosolic cyt c levels, caspase-3 activity, and nuclear AIF levels in brain tissues after traumatic injury; however, CPCGI had no significant effects on cytosolic or mitochondrial Bax levels, the cytosolic Bcl-xL/Bax ratio, or mitochondrial AIF levels. Moreover, CPCGI markedly reduced the TUNEL staining score in the contusion region. 2) CPCGI markedly reduced cytosolic and nuclear PARP levels and nuclear NF-κB p65 levels in brain tissues after traumatic injury but had no significant effect on cytosolic NF-κB p65 levels. In addition, CPCGI markedly reduced caspase-1 activity and the levels of caspase-1, ICAM-1, TNF-α, and IL-1β in brain tissues after traumatic injury and decreased the immunoreactivities of neutrophils, GFAP and Iba-1 in the region of CCI-induced contusion.ConclusionThese data suggest that CPCGI can reduce brain injury due to trauma by suppressing both mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling.

The study on the effect of depression on breast cancer incidence through IDO/kynurenine pathway.

e13569 Background: Psychosocial factors have been considered as the most common causes for women with breast cancer. However, it remains unclear whether mental stress can influence cancer incidence and progression. This study aims to investigate the relationship between them and the potential molecular mechanism. Methods: Depression model was established by restricting MMTV-PyMT mice in a 50ml-fixator for 4 h per day for 21 consecutive days. Behavioral tests including light-dark box test, open-field test and force swimming test were performed. Then blood, brain and mammary samples were collected at the indicated time points. ELISA was used to detect the concentration of neurotransmitters serotonin, epinephrine and norepinephrine and inflammatory factors IL-6, TNF-a and IL-1β in brain tissue and serum. Real-time quantitative qPCR and western blot were used to detect indoleamine 2, 3-dioxygenase (IDO) expression. The level of tryptophan was measured by high performance liquid chromatography(HPLC). Flow cytometry was used to evaluate the exhaustion of CD8+ T cells. Besides, the correlation between IDO expression detected by immunohistochemistry and the severity of mammary tumors was analyzed in the tumor specimens. Results: We observed that chronic stress caused depression-like behaviors, abnormal secretion of neurotransmitters serotonin, epinephrine and norepinephrine and promoted the development of breast cancer in MMTV-PyMT mice. Depression elevated the secretion of inflammatory factors IL-6, TNF-a and IL-1β in brain tissue and serum, which upregulated the expression of IDO and decreased the level of tryptophan in mice. Furthermore, T cells are sensitive to low tryptophan concentration, so elevated IDO expression suppressed and exhausted CD8+ T cells, ultimately promoting cancer incidence. Administration of xiaoyao pill (a well-known Chinese herbal formula for treating depression) or IDO inhibitor reversed the depression-like behaviors in mice and slowed the development of breast cancer. At the same time, the analysis of clinical samples showed that depression identified by Hamilton Depression Scale(HAMD) and IDO expression in mammary tumor tissues were positively correlated with the severity of mammary tumors. Conclusions: Altogether, our results suggest that depression can promote tumor immune privilege and cancer occurrence through inducing upregulated IDO expression.

Effects of dexmedetomidine combined with targeted temperature management on the expression of hippocampal P2X7 receptor and antisense hypoxia inducible factor-1α in rats with traumatic brain injury

Objective To investigate the effects of dexmedetomidine (Dex) combined with targeted temperature management (TTM) on the expression of hippocampal P2X7 receptor and antisense hypoxia inducible factor (aHIF)-1α in rats with traumatic brain injury (TBI). Methods A model of TBI was established through controlled cortical impact using rats after 1 week of adaptive feeding. Then, 15 rats were randomly selected as a control group, while the others were set as a model group. The successfully modeled rats were divided into five groups (n=15), according to the random number table method: a sham operation group, a TBI group, a TBI+Dex group, a TBI+TTM group and a TBI+Dex+TTM group. After corresponding treatment, their behaviors were tested, and the expression of tumor necrosis factor (TNF)-α/interleukin (IL)-1β in brain tissue and the expression of hippocampal P2X7 receptor and aHIF- 1α were analyzed. Results Rats in each group did not die. Compared with the TBI, TBI+Dex and TBI+TTM groups, the TBI+Dex+TTM group presented remarkably reduced escape latency on Days 3-5 and shortened exploration duration on Day 6 (P<0.05), as well as decreased expression of TNF-α and IL-1β in brain tissues (P<0.05), reduced expression of hippocampal P2X7 receptor and increased amounts of aHIF- 1α (P< 0.05). Conclusions Dex combined with TTM can effectively decline the concentration of P2X7 receptor, down-regulate the levels of TNF-α and IL-1β, and increase the level of aHIF- 1α, which can be served as a promising therapy for TBI rats. Key words: Brain injuries, traumatic; Dexmedetomidine; Targeted temperature management; P2X7 receptor; Antisense hypoxia inducible factor- 1α

Mechanism of action of Zhuyu Annao pill in mice with cerebral intrahemorrhage based on TLR4.

To explore the protective effect and possible mechanism of action of Zhuyu Annao pill in mice with intracerebral hemorrhage (ICH). Sixty mice were divided into the control group, hemorrhage group, drug-treated group (after hemorrhage), TLR4-knockout hemorrhage group and TLR4-knockout hemorrhage+drug-treated group (after hemorrhage) with 12 in each group. Model of autologous ICH was established in all groups. After drilling and 12h of fasting, models in the control group hemorrhage group and TLR4-knockout hemorrhage group were all drenched with 10mL/kg distilled water by intragastric administration. Models in the drug-treated group and TLR4-knockout hemorrhage+drug-treated group were drenched with 6.25g/kg of Zhuyu Annao pill. All groups were treated for 7d. Longa scoring method was used to measure the neurological defect scores and determine the brain water contents of all groups; ELISA was employed to detect the inflammatory factor interleukin (IL)-6, tumor necrosis factor-α (TNF-α) and IL-1β in brain tissues; and Western blot was applied to test the expression quantities of apoptotic protein Bax and anti-apoptotic protein Bcl-2 in brain tissues. At day 3 and 7, compared with the hemorrhage group, the neurological defect scores of the drug-treated group, TLR4-knockout hemorrhage group and TLR4-knockout hemorrhage+drug-treated group decreased significantly (P<0.05). Compared with the hemorrhage group, the brain water contents of the drug-treated group, TLR4-knockout hemorrhage group and TLR4-knockout hemorrhage+drug-treated group reduced significantly (P<0.05). Compared with the hemorrhage group, the inflammatory factor IL-6, TNF-α and IL-1β of the drug-treated group, TLR4-knockout hemorrhage group and TLR4-knockout hemorrhage+drug-treated group decreased significantly (P<0.05). Compared with the hemorrhage group, the expression of apoptotic protein Bax of the drug-treated group, TLR4-knockout hemorrhage group and TLR4-knockout hemorrhage+drug-treated group decreased significantly and the expression of anti-apoptotic protein Bcl-2 increased significantly (P<0.05). Zhuyu Annao pill can alleviate encephaledema for mice with ICH and reduce inflammatory responses and nerve cell apoptosis. TLR4 can mediate inflammatory injury induced by ICH. Thus, Zhuyu Annao pill can play a protective role for brains by decreasing the expression of TLR4.

Progesterone inhibits the expression of cycloxygenase-2 and interleukin-1β in neonatal rats with hypoxic ischemic brain damage

Recent studies found that progesterone (PROG) has a noticeable preventive effect on brain injuries. However, the underlying mechanisms of these effects, particularly on hypoxic ischemic brain damage (HIBD), remain unclear. This study observed the influence of PROG on the expression of cycloxygenase-2 (COX-2) and interleukin-1β (IL-1β) in HIBD neonatal rats, and explored the corresponding molecular mechanisms underlying the neuroprotective effect of PROG. Sixty 7-day-old neonatal Wistar rats were divided into sham operation (control), hypoxic ischemia (HI), and drug prophylaxis (PROG) groups, and HIBD animal models were routinely established. The PROG group was intraperitoneally injected with 0.5 g/L PROG at a dosage of 8 mg/kg 30 min before establishment of the model. All the animals were sacrificed 24 h after modeling. Changes in the COX-2 and IL-1β contents in the brain tissues were determined using enzyme-linked immunosorbent assay. Protein expression was observed using immunohistochemistry, and mRNA expression was determined using reverse transcription polymerase chain reaction. The expression and contents of COX-2 and IL-1β in the HI group were significantly higher than those in the control group (P < 0.01). Compared with the HI group, the PROG group showed noticeably lower expression and contents of COX-2 and IL-1β (P < 0.05). In conclusion, PROG can inhibit the expression of COX-2 and IL-1β in brain tissue, further reducing the level of COX-2 and IL-1β, which may be one of the mechanisms for protection from HIBD.

Effect of dexamethasone on cerebral white matter development of premature rats and its mechanism

Objective By making models of premature animal,explores the effects of dexamethasone on the brain development of premature rats and its mechanisms.Methods Eighteen SD rats were randomly divided into high-dexamethasone(H-Dex) group,low-dexamethasone (L-Dex) group and normal saline(NS) control group,with 6 rats in each group.The pregnant rats in L-Dex group were injected with dexamethasone [0.1 mg/(kg·d)] from 16 to 18 days of pregnancy,while the pregnant rats in H-Dex group were injected with dexamethasone [0.5 mg/(kg· d)] ; the pregnant rats in NS control group were injected with 0.9％ NaCl of the same volume.All of the fetal rats were received after administrating caesarean operation on the day 19 of pregnancy.Rats were sacrificed at the directed time and brain tissue was prepared.Histological feature and the water content of the brains were observed.Level of apoptosis was measured by flow cytometry.The expressions of myelin basic protein (MBP) and interleukin(IL)-1β in brain tissue homogenate were detected by ELISA.Results (1) The brain water contents of rats in H-Dex group,L-Dex group and NS control group were (85.94 ± 0.54) ％,(86.08 ± 1.01) ％,(86.94 ± 0.82) ％.Compared with NS control group,the water contents of Dex group were lower (P ＜ 0.05).(2) Glial cells of brain cortex in L-Dex group and H-Dex group were more mature than in NS control group,and the changes in H-Dex group was more significant.(3) The expressions of MBP in brain tissue of H-Dex group,L-Dex group and NS control group were (5.73 ± 1.06) μg/mg,(5.46 ±0.77) μg/mg and (2.42 ±0.52) μg/mg.Compared with NS control group,Dex group was higher(P ＜0.05).While the expressions of IL-1β in brain tissue of H-Dex group,L-Dex group and NS control group were (249.05 ± 11.29) pg/g,(257.47 ± 9.33) and (292.66 ± 21.51) pg/g.Compared with NS control group,Dex group was lower(P ＜ 0.05).There was no significant difference between H-Dex group and L-Dex group(P ＞ 0.05).(4) The level of apoptosis in H-Dex group,L-Dex group and NS control group were (18.07 ± 1.63) ％,(6.88 ± 0.47) ％ and (2.00 ± 0.32) ％.Compared with NS control group,the level of apoptosis in Dex group was higher(P ＜0.05),and H-Dex group was higher than that in L-Dex group.Conclusion (1) Using dexamethasone prophylactic could promote the development of glial cells,reduce the water content,increase the expressions of MBP,and decrease the expressions of IL-1β in brain tissues.It indicates that dexamethasone may play a major role in maturation of fetal brain.(2) Using dexamethasone prophylactic could increase the amounts of the apoptosis cells,and this effect is dose-dependent.It indicates that dexamethasone may have a negative effect on the fetal brain and suggestes that using dexamethasone in premature infant should be cautious,and if it has to,using a lower dose. Key words: Brain development; Dexamethasone; Cell apoptosis; Myelin basic protein; Interleukin-1β; Premature rat