Brain lactate uptake increases at the site of impact after traumatic brain injury

Although glucose is the main carbohydrate energy substrate for the normal brain, several studies published over the last 10 years now challenge this assumption. The activated brain increases its metabolism to meet increased energy demands by glycolysis after injury. In vitro studies now show that lactate alone can serve as an energy source to maintain synaptic function. In this study, we used 14C-lactate to test the hypothesis that blood lactate is acutely taken up by the injured brain, after fluid percussion injury (FPI) in the rat. 50 microCi radioactive lactate was injected i.v. immediately after FPI, in injured and sham rats. After 30 min, the brain was removed, frozen, and cut into 20 microm sections for autoradiography. Uptake of 14C-label was mainly concentrated at the injury site (2.5 times greater) although uninjured brain also took up the 14C-label. This increased concentration of radioactive lactate at the injury site suggests that the injured brain may use the lactate as an energy source.     

Brain temperature and outcome after severe traumatic brain injury

Introduction  In humans, raised body temperature is linked to poor outcome after brain injury. Because deviations between brain and body temperature have been reported after severe traumatic brain injury (TBI), the aim of this study was to explore the relationship between initial and mean brain temperature and survival at 3 months. Methods  Intraparenchymal temperature was measured 3–4 cm within white matter. Logistic regression was used to explore linear and quadratic relationships between initial and average brain temperature and survival at 3 months. Results  In 36 patients, initial brain temperatures ranged from 33.5 to 39.2°C (median 37.4°C). There was no evidence of an association between initial brain temperature and risk of death, either linear (odds ratio [OR] 95% confidence interval [CI]=1.3 [0.68 to 2.5], p=0.42) or quadratic (p=0.26). Assuming a linear relationship, patients with higher mean brain temperatures were less likely to die: OR (95% CI) for death per 1°C was 0.31 (0.09 to 1.1), p=0.06. However, by fitting the quadratic relationship, there was a suggestion that both high and low temperatures were associated with increased risk of death: p=0.06. Conclusion  Initial brain temperature measured shortly after adminission did not predict outcome. There is a suggestion that patients with “middle range” temperatures were less likely to die.     

Postinjury treatment with rolipram increases hemorrhage after traumatic brain injury

The pathology caused by traumatic brain injury (TBI) is exacerbated by the inflammatory response of the injured brain. Two proinflammatory cytokines that contribute to inflammation after TBI are tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). From previous studies using the parasagittal fluid-percussion brain injury model, we reported that the anti-inflammatory drug rolipram, a phosphodiesterase 4 inhibitor, reduced TNF-α and IL-1β levels and improved histopathological outcome when administered 30 min prior to injury. We now report that treatment with (±)-rolipram given 30 min after injury significantly reduced TNF-α levels in the cortex and hippocampus. However, postinjury administration of (±)-rolipram significantly increased cortical contusion volume and increased atrophy of the cortex compared with vehicle-treated animals at 10 days postinjury. Thus, despite the reduction in proinflammatory cytokine levels, histopathological outcome was worsened with post-TBI (±)-rolipram treatment. Further histological analysis of (±)-rolipram-treated TBI animals revealed significant hemorrhage in the contused brain. Given the well-known role of (±)-rolipram of increasing vasodilation, it is likely that (±)-rolipram worsened outcome after fluid-percussion brain injury by causing increased bleeding.     

Anoxic depolarization determines ischemic brain injury

Abstract

To clarify the role of anoxic depolarization (AD) in ischemic brain injury, we examined the correlation between AD and ischemia-induced neuronal injury. Twenty-eight rats underwent transient forebrain ischemia with lowering of blood pressure and bilateral carotid occlusion while direct current shiftslelectrocorticogram, and cortical blood flow (COBF) were epidurally recorded from the right parietal cortex. One week later the right parietal cortex was studied histopathologically. AD appeared 0.5-3.0 min after carotid occlusion in 21 of28 animals. Circulation was reinitiated 75 min afterAD onset in 77 rats (group A) and 10 min after onset in 70 rats (group B). AD did not develop during 20 min of ischemia in 7 rats (group C). All 72 rats (6 from group A and 6 from group B) in which CoBF decreased below 9.5% of control flow exhibited AD. Histopathologic examination disclosed massive neuronal necrosis in 5 of the 6 group A animals with marked flow reduction but in none from group B. CoBF fell between 9.5% and 20% in 74 rats, among these, AD appeared in 9 (5 from group A and 4 from group B) but not in 5 (group C). Massive neuronal necrosis was demonstrated in 3 of5 rats from group A. Ischemic neuronal changes were absent or minimal in only 7/5 ofgroup A animals, a much lower fraction than in group B (4/4, p<0.05) or in group.C (5/5/, p<0.05). When CoBF remained above 20% of control flow during ischemia (2 rats) no AD or irreversible injury occurred. The present study suggests that AD is a more reliable determinant of irreversible brain injury than degree of CBF reduction, and also demonstrates that 75 min is the critical duration of AD for irreversible brain injury at brain temperatures around 37° C. [Neural Res 1998; 20: 343-348]     

Coagulopathy in traumatic brain injury

Abnormalities in blood coagulation, although quite common after traumatic brain injury (TBI), are of unknown significance. The authors review the clinical and pathophysiological features of this phenomenon and emphasize its origin in disseminated intravascular coagulation. This connection provides a possible explanation for much of the cerebral ischema that accompanies TBI, namely intravascular microthrombosis. The authors’ own research findings support this contention and suggest possible therapeutic avenues. A number of compelling studies demonstrate that DIC is a common and important consequence of TBI. In particular, posttraumatic coagulapathy appears to be linked to secondary cerebral injury. Although the extent of this process has yet to be elucidated fully, coagulation abnormalities are evident soon after trauma. This allows early identification of patients likely to suffer secondary complications and provides an opportunity to evaluate promising agents that may mitigate posttraumatic DIC and related pathologies in these patients. This is an area deserving of more intensive research.     

Cerebral extracellular lactate increase is predominantly nonischemic in patients with severe traumatic brain injury

Growing evidence suggests that endogenous lactate is an important substrate for neurons. This study aimed to examine cerebral lactate metabolism and its relationship with brain perfusion in patients with severe traumatic brain injury (TBI). A prospective cohort of 24 patients with severe TBI monitored with cerebral microdialysis (CMD) and brain tissue oxygen tension (PbtO₂) was studied. Brain lactate metabolism was assessed by quantification of elevated CMD lactate samples (>4 mmol/L); these were matched to CMD pyruvate and PbtO₂ values and dichotomized as glycolytic (CMD pyruvate >119 μmol/L vs. low pyruvate) and hypoxic (PbtO₂ <20 mm Hg vs. nonhypoxic). Using perfusion computed tomography (CT), brain perfusion was categorized as oligemic, normal, or hyperemic, and was compared with CMD and PbtO₂ data. Samples with elevated CMD lactate were frequently observed (41±8%), and we found that brain lactate elevations were predominantly associated with glycolysis and normal PbtO₂ (73±8%) rather than brain hypoxia (14±6%). Furthermore, glycolytic lactate was always associated with normal or hyperemic brain perfusion, whereas all episodes with hypoxic lactate were associated with diffuse oligemia. Our findings suggest predominant nonischemic cerebral extracellular lactate release after TBI and support the concept that lactate may be used as an energy substrate by the injured human brain.     

Rescue of ischemic brain injury by adenoviral gene transfer of glial cell line-derived neurotrophic factor after transient global ischemia in gerbils

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor (TGF)-beta superfamily, is one of the most potent neurotrophic factors and promotes survival of many populations of cells. We examined neuroprotective effect of an adenoviral vector encoding glial cell line-derived neurotrophic factor (AxCAhGDNF) on the transient global ischemia. Gerbils received administration of AxCAhGDNF or an adenoviral vector encoding bacterial beta-galactosidase gene (AxCALacZ) through the lateral ventricle. Two days later, occluding bilateral common carotid arteries for 5 min using aneurysm clips produced the transient global forebrain ischemia. Animals showed intense immunolabeling for GDNF in ependymal cells on 2, 4 and 7 days after the operation. The exogenous gene transducted by adenovirus in the same cells was detected by in situ hybridization. The treatment with AxCAhGDNF significantly prevented the loss of hippocampal CA1 pyramidal neurons 2 to 7 days after the operation, as compared to AxCALacZ treatment. Also terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end labeling (TUNEL) staining was markedly reduced in the case with AxCAhGDNF treatment at 7 days after the operation. These results indicated that the adenovirus-mediated gene transfer of GDNF might prevent the delayed neuronal death of stroke and other disorders of the cerebral vasculature.     

Vascular endothelial growth factor increases neurogenesis after traumatic brain injury

Activation of endogenous stem cells has been proposed as a novel form of therapy in a variety of neurologic disorders including traumatic brain injury (TBI). Vascular endothelial growth factor (VEGF) is expressed in the brain after TBI and serves as a potent activator of angiogenesis and neurogenesis. In this study, we infused exogenous VEGF into the lateral ventricles of mice for 7 days after TBI using mini-osmotic pumps to evaluate the effects on recovery and functional outcome. The results of our study show that VEGF significantly increases the number of proliferating cells in the subventricular zone and in the perilesion cortex. Fate analysis showed that most newborn cells differentiated into astrocytes and oligodendroglia and only a few cells differentiated into neurons. Functional outcome was significantly better in mice treated with VEGF compared with vehicle-treated animals after TBI. Injury size was significantly smaller at 90 days after TBI in VEGF-treated animals, suggesting additional neuroprotective effects of VEGF. In conclusion, VEGF significantly augments neurogenesis and angiogenesis and reduces lesion volumes after TBI. These changes are associated with significant improvement in recovery rates and functional outcome.     

亚低温对大鼠脑缺血再灌注损伤的保护研究

目的观察亚低温对大鼠全脑缺血再灌注后海马CAI区神经元凋亡的影响,探讨亚低温对缺血再灌注脑损伤的保护作用。方法SD大鼠30只随机分为对照组（n=10）,常温缺血组（n=10）,亚低温组（n=10）,采用改良的Pulsinelli-Brierley4血管法建立全脑缺血再灌注动物模型,缺血30min后再灌注72h,尼氏体染色观察海马区存活锥体细胞数,TUNEL法检测缺血后海马CAI区神经元凋亡情况,电镜下观察神经细胞形态学改变。结果与对照组比较,常温缺血组的海马CAI区存活的锥体细胞数目减少（P〈0.01）;与常温缺血组比较,亚低温组海马CAI存活的锥体细胞数目明显增多（P〈0.01）。对照组、亚低温组的海马CAI区神经元凋亡数目和凋亡指数明显低于常温缺血组。在电镜下观察亚低温能明显减轻缺血后脑组织病理形态学的损害程度。结论亚低温可以抑制脑缺血再灌注后的神经细胞凋亡,对神经细胞有保护作用。     

Brain morphometry changes and depressive symptoms after traumatic brain injury

Traumatic brain injury (TBI) is associated with an increased risk of depressive symptoms. Recent imaging studies on spontaneous depression have implicated several brain structures; however, few studies have done the same for post-TBI depression. We report on a pilot observational study correlating atrophy of brain regions of interest in subjects after TBI with depressive symptoms measured by the Beck Depression Inventory-II. Regional brain volumes were calculated on both acute and 6-month MRI using an automated segmentation algorithm (FreeSurfer). Percent volume changes in brain regions were correlated with BDI-II scores using Spearman's rank order correlation coefficient. Correction for multiple comparisons was performed using the false discovery rate (FDR). Three regions of interest (left rostral anterior cingulate and bilateral orbitofrontal cortex) were found to be significantly correlated with depressive symptoms (FDR 0.05). With FDR 0.1, six regions were significantly correlated. The use of volumetric analysis of brain regions of interest to study post-TBI depression is worthy of further study. Regions associated with depressive symptoms in this pilot study were similar to those implicated in study of spontaneous depression.     

Neuroglobin expression in rats after traumatic brain injury

In this study,we used a rat model of severe closed traumatic brain injury to explore the relationship between neuroglobin,brain injury and neuronal apoptosis.Real-time PCR showed that neuroglobin mRNA expression rapidly increased in the rat cerebral cortex,and peaked at 30 minutes and 48 hours following traumatic brain injury.Immunohistochemical staining demonstrated that neu-roglobin expression increased and remained high 2 hours to 5 days following injury.The rate of in-crease in the apoptosis-related Bax/Bcl-2 ratio greatly decreased between 30 minutes and 1 hour as well as between 48 and 72 hours post injury.Expression of neuroglobin and the anti-apoptotic factor Bcl-2 greatly increased,while that of the proapoptotic factor decreased,in the cerebral cortex post severe closed traumatic brain injury.It suggests that neuroglobin might protect neurons from apoptosis after traumatic injury by regulating Bax/Bcl-2 pathway.     

RIP1/3对创伤性脑损伤后神经元的作用及其机制研究

目的 探讨RIP1/3对创伤性脑损伤(TBI)后神经元的影响及其作用机制。方法 将体外培养的皮层神经元分为4组:siRIP组、Nec-1预处理组、阴性质粒转染组和对照组。通过慢病毒转染法分别干涉RIP1、RIP3表达,建立离体TBI损伤模型,通过流式细胞学检测划伤后神经元存活情况。对体外培养的皮层神经元敲除RIP1/3,建立谷氨酸诱导神经元损伤模型,通过流式细胞学检测谷氨酸刺激后神经元存活情况。结果 siRIP组及Nec-1预处理组机械性损伤后神经元存活率高于阴性质粒转染组和对照组。Nec-1预处理组谷氨酸损伤后神经元存活率高于对照组,而siRIP组存活率与对照组和阴性转染组比较未见显著差异。结论 RIP1和RIP3可能对TBI诱导后神经元死亡有作用,而RIP1抑制剂Nec-1可能对TBI具有脑保护作用。RIP1/3与谷氨酸兴奋毒性诱导细胞死亡无关,而Nec-1对于谷氨酸损伤具有潜在保护作用,并可能存在特异性靶点。     

外伤后急性半球脑肿胀的手术治疗

目的 探讨外伤后急性大脑半球肿胀（ACHS）的治疗效果以及影响疗效的主要因素.方法 对38例外伤后急性半球脑肿胀病人的资料进行回顾性分析.所有患者均接受了去骨瓣减压手术.结果 大骨瓣减压术后,CT影像显示脑中线结构无明显移位、环池结构清晰.术后6个月按GOS评分标准评估：良好14例（占36.8%）、中残9例（占23.7%）、重残5例（占13.2%）、植物生存4例（占10.5%）、死亡6例（占15.8%）.结论 早期去骨瓣减压手术可改善患者预后,而脑肿胀合并急性硬膜下血肿、手术后出血性脑挫伤处血肿量明显增加以及出现创伤后大面积脑梗死的患者预后较差.     

Alterations in cerebral oxygen metabolism after traumatic brain injury in children

Traumatic brain injury (TBI) is the most common cause of acquired disability in children. Metabolic defects, and in particular mitochondrial dysfunction, are important contributors to brain injury after TBI. Studies of metabolic dysfunction are limited, but magnetic resonance methods suitable for use in children are overcoming this limitation. We performed noninvasive measurements of cerebral blood flow and oxygen metabolic index (OMI) to assess metabolic dysfunction in children with severe TBI. Cerebral blood flow is variable after TBI but hypoperfusion and low OMI are predominant, supporting metabolic dysfunction. This finding is consistent with preclinical and adult clinical studies of brain metabolism and mitochondrial dysfunction after TBI.     

钙离子在创伤性脑损伤中的致病机制研究

创伤性脑损伤（TBI）是一类常见且严重威胁公众健康的疾病,国内外对TBI发病机制和治疗方面的研究都有了巨大突破。通过对国内外文献研究发现,TBI后所致神经损害包括原发性和继发性损伤两大类机制,而钙离子（Ca²⁺）在TBI继发性损伤中扮演着极其重要的角色。本文围绕Ca²⁺在TBI后继发性损害的致病机制及其治疗展望综述如下。     

Inhaled nitric oxide reduces secondary brain damage after traumatic brain injury in mice

Ischemia, especially pericontusional ischemia, is one of the leading causes of secondary brain damage after traumatic brain injury (TBI). So far efforts to improve cerebral blood flow (CBF) after TBI were not successful because of various reasons. We previously showed that nitric oxide (NO) applied by inhalation after experimental ischemic stroke is transported to the brain and induces vasodilatation in hypoxic brain regions, thus improving regional ischemia, thereby improving brain damage and neurological outcome. As regional ischemia in the traumatic penumbra is a key mechanism determining secondary posttraumatic brain damage, the aim of the current study was to evaluate the effect of NO inhalation after experimental TBI. NO inhalation significantly improved CBF and reduced intracranial pressure after TBI in male C57 Bl/6 mice. Long-term application (24 hours NO inhalation) resulted in reduced lesion volume, reduced brain edema formation and less blood–brain barrier disruption, as well as improved neurological function. No adverse effects, e.g., on cerebral auto-regulation, systemic blood pressure, or oxidative damage were observed. NO inhalation might therefore be a safe and effective treatment option for TBI patients.     

钾通道Kv4.2、Kv1.4在硫化氢后处理对大鼠短暂全脑缺血神经保护中的作用研究

目的研究硫氢化钠(sodium hydrosulfide,Na HS)后处理对短暂全脑缺血大鼠海马中钾通道Kv4.2和Kv1.4 mRNA表达变化的影响及其脑保护作用,从而探讨Na HS对大鼠短暂全脑缺血神经保护作用的机制。方法用4VO方法建立大鼠短暂性全脑缺血(transient global cerebral ischemia,t GCI)模型,大鼠被随机分配到3组,分别为:假手术组(sham)、t GCI组、Na HS后处理组。Na HS后处理组为t GCI之后1 d,给予大鼠腹腔注射Na HS 24μmmol/kg或者180μmmol/kg。通过尼氏染色与Neu N免疫染色确定海马神经元的死亡,通过RT-PCR方法检测海马组织Kv4.2和Kv1.4mRNA水平的表达变化。结果 (1)与t GCI组比较,在t GCI之后1 d给予24μmol/kg Na HS后处理使海马CA1区存活细胞数目显著增加,而高剂量的Na HS(180μmol/kg)后处理对t GCI大鼠海马CA1区则无明显的保护作用。(2)在Re 26 h和Re 48 h,海马组织中Kv4.2、Kv1.4的mRNA表达水平均明显低于假手术组(P<0.05)。在Re 26 h+Na HS组,kv4.2(1.24±0.08)和kv1.4(1.11±0.07)的mRNA表达水平均分别高于Re 26 h组的kv4.2(0.75±0.04)和kv1.4(0.79±0.06),差异均有显著性(P<0.05)。结论外源性Na HS可能通过上调大鼠t GCI后海马区Kv4.2和Kv1.4 mRNA的表达,从而导致膜电位超极化,降低神经元兴奋性和氧耗,继而保护神经元免受脑缺血损伤。     

Striatal cells containing the Ca2+-binding protein calretinin (protein 10) in ischemia-induced neuronal injury

The present study concerns the vulnerability of striatal interneurons immunopositive for the Ca²⁺-binding protein calretinin to ischemic neuronal injury. An immunohistochemical study was carried out on the striata of rats which had undergone transient middle cerebral artery occlusion. Two weeks after the ischemia, there was a marked reduction in the number of calretinin-positive neurons in the ipsilateral ischemic lesion, although the striatal interneurons positive for parvalbumin, which are a neuronal population distinct from the calretinin-immunoreactive cells in the striatum, were spared in the insulted areas. The present data indicate that the striatal calretinin-positive neurons are less resistant to transient ischemia, suggesting that there may exist vulnerability differences among the striatal interneurons in ischemia-induced neuronal injury.     

Lactate shuttling and lactate use as fuel after traumatic brain injury: metabolic considerations

Lactate is proposed to be generated by astrocytes during glutamatergic neurotransmission and shuttled to neurons as ‘preferred'' oxidative fuel. However, a large body of evidence demonstrates that metabolic changes during activation of living brain disprove essential components of the astrocyte–neuron lactate shuttle model. For example, some glutamate is oxidized to generate ATP after its uptake into astrocytes and neuronal glucose phosphorylation rises during activation and provides pyruvate for oxidation. Extension of the notion that lactate is a preferential fuel into the traumatic brain injury (TBI) field has important clinical implications, and the concept must, therefore, be carefully evaluated before implementation into patient care. Microdialysis studies in TBI patients demonstrate that lactate and pyruvate levels and lactate/pyruvate ratios, along with other data, have important diagnostic value to distinguish between ischemia and mitochondrial dysfunction. Results show that lactate release from human brain to blood predominates over its uptake after TBI, and strong evidence for lactate metabolism is lacking; mitochondrial dysfunction may inhibit lactate oxidation. Claims that exogenous lactate infusion is energetically beneficial for TBI patients are not based on metabolic assays and data are incorrectly interpreted.     

大鼠脑损伤后谷氨酸引起乳酸含量变化的作用机制

目的探讨大鼠脑损伤后谷氨酸引起乳酸含量变化的作用机制。方法28只大鼠随机分为对照组、犬尿烯酸（KYN）灌注组、Ouabain灌注组及Ba^2＋灌注组,每组7只。在建立大鼠局部脑损伤模型前后,应用微透析技术将格林液、KYN、Ouabain和Ba2＋分别灌注到各组大鼠致伤脑区,在致伤前45min开始和致伤后90min内,观察3种药物对脑损伤后乳酸含量的影响。结果对照组伤前乳酸含量为（0.28±0.07）mmol/L,脑损伤后引起乳酸含量迅速升高,伤后15min达到峰值（0.75±0.18）mmol/L,乳酸含量持续升高60min后逐渐下降至接近伤前水平。Ouabain灌注组及KYN灌注组伤后乳酸含量升高幅度减弱,持续时间缩短。Ba^2＋灌注组乳酸含量升高幅度增加,持续时间延长。结论脑损伤后异常增加的谷氨酸作用于兴奋性氨基酸受体偶联离子通道,引起细胞外K^＋增加,使Na^＋-K^＋泵活性增强,继而导致糖酵解代谢水平增高,乳酸含量增加。