Primary cortical glial reaction versus secondary thalamic glial response in the excitotoxically injured young brain: astroglial response and metallothionein expression

Neuroinflammation as a Key Driver of Secondary Neurodegeneration Following Stroke?

Ischaemic stroke involves the rapid onset of focal neurological dysfunction, most commonly due to an arterial blockage in a specific region of the brain. Stroke is a leading cause of death and common cause of disability, with over 17 million people worldwide suffering from a stroke each year. It is now well-documented that neuroinflammation and immune mediators play a key role in acute and long-term neuronal tissue damage and healing, not only in the infarct core but also in distal regions. Importantly, in these distal regions, termed sites of secondary neurodegeneration (SND), spikes in neuroinflammation may be seen sometime after the initial stroke onset, but prior to the presence of the neuronal tissue damage within these regions. However, it is key to acknowledge that, despite the mounting information describing neuroinflammation following ischaemic stroke, the exact mechanisms whereby inflammatory cells and their mediators drive stroke-induced neuroinflammation are still not fully understood. As a result, current anti-inflammatory treatments have failed to show efficacy in clinical trials. In this review we discuss the complexities of post-stroke neuroinflammation, specifically how it affects neuronal tissue and post-stroke outcome acutely, chronically, and in sites of SND. We then discuss current and previously assessed anti-inflammatory therapies, with a particular focus on how failed anti-inflammatories may be repurposed to target SND-associated neuroinflammation.

Impaired glymphatic system in secondary degeneration areas after ischemic stroke in rats

BACKGROUND

Pathomechanism of secondary degeneration in remote regions after ischemic stroke has not been totally clarified. Contrast-enhanced MRI with injecting Gd-DTPA in cisterna magna (CM) is regarded as an efficient method to measure glymphatic system function in brain. Our research aimed at evaluating glymphatic system changes in secondary degeneration areas by contrast-enhanced MRI.

METHODS

Ischemic stroke was induced by left middle cerebral artery occlusion (MCAO) model. A total of 12 Sprague-Dawley rats were randomly divided into three groups: control group with sham operations (n=4), the group of acute phase (1 day after MCAO) (n=4), and the group of subacute phase (7 days after MCAO) (n=4). Contrast-enhanced MRI was performed in 1days or 7days after operations respectively. All rats received an intrathecal injection of Gd-DTPA (2μl/min, totally 20μl) and high-resolution 3D T1-weighted MRI for 6 h. The time course of the signal-to-noise ratio (SNR) in substantia Nigra (SN) and ventral thalamic nucleus (VTN) was evaluated between two hemispheres in all rats.

RESULTS

In control group without ischemia, time-to-peak of SNR in SN was earlier than that in VTN. There were no differences of SNR between two hemispheres after intrathecal Gd-DTPA administration. In the group of acute phase, MRI revealed similar time course and time-to-peak of SNR between ipsilateral and contralateral VTN, while a tendency of higher SNR in ipsilateral SN than contralateral SN at 4h, 5h, 6h after Gd-DTPA injection. And time-to-peak of SNR was similar in bilateral SN. In the group of subacute phase, time-to-peak of SNR was similar in bilateral VTN, while longer in ipsilateral SN compared with contralateral side. In addition, SNR in T1WI in ipsilateral was significantly higher than SNR in contralateral SN and VTN at 5h (VTN, P= 0.003; SN, P=0.004) and 6h (VTN, P=0.015; SN, P=0.006) after Gd-DTPA injection.

CONCLUSION

Glymphatic system was impaired in ipsilateral SN and VTN after ischemic stroke, which may contribute to neural degeneration.

Inflammatory Responses in the Secondary Thalamic Injury After Cortical Ischemic Stroke

Stroke is one of the major causes of chronic disability worldwide and increasing efforts have focused on studying brain repair and recovery after stroke. Following stroke, the primary injury site can disrupt functional connections in nearby and remotely connected brain regions, resulting in the development of secondary injuries that may impede long-term functional recovery. In particular, secondary degenerative injury occurs in the connected ipsilesional thalamus following a cortical stroke. Although secondary thalamic injury was first described decades ago, the underlying mechanisms still remain unclear. We performed a systematic literature review using the NCBI PubMed database for studies that focused on the secondary thalamic degeneration after cortical ischemic stroke. In this review, we discussed emerging studies that characterized the pathological changes in the secondary degenerative thalamus after stroke; these included excitotoxicity, apoptosis, amyloid beta protein accumulation, blood-brain-barrier breakdown, and inflammatory responses. In particular, we highlighted key findings of the dynamic inflammatory responses in the secondary thalamic injury and discussed the involvement of several cell types in this process. We also discussed studies that investigated the effects of blocking secondary thalamic injury on inflammatory responses and stroke outcome. Targeting secondary injuries after stroke may alleviate network-wide deficits, and ultimately promote stroke recovery.

Factors Involved in the Functional Motor Recovery of Rats with Cortical Ablation after GH and Rehabilitation Treatment: Cortical Cell Proliferation and Nestin and Actin Expression in the Striatum and Thalamus

Previously we demonstrated, in rats, that treatment with growth hormone (GH) and rehabilitation, carried out immediately after a motor cortical ablation, significantly improved the motor affectation produced by the lesion and induced the re-expression of nestin in the contralateral motor cortex. Here we analyze cortical proliferation after ablation of the frontal motor cortex and investigate the re-expression of nestin in the contralateral motor cortex and the role of the striatum and thalamus in motor recovery. The rats were subjected to ablation of the frontal motor cortex in the dominant hemisphere or sham-operated and immediately treated with GH or the vehicle (V), for five days. At 1 dpi (days post-injury), all rats received daily injections (for four days) of bromodeoxyuridine and five rats were sacrificed at 5 dpi. The other 15 rats (n = 5/group) underwent rehabilitation and were sacrificed at 25 dpi. GH induced the greatest number of proliferating cells in the perilesional cortex. GH and rehabilitation produced the functional recovery of the motor lesion and increased the expression of nestin in the striatum. In the thalamic ventral nucleus ipsilateral to the lesion, cells positive for nestin and actin were detected, but this was independent on GH. Our data suggest that GH-induced striatal nestin is involved in motor recovery.

Glutamate Transport and Preterm Brain Injury

Preterm birth complications are the leading cause of child death worldwide and a top global health priority. Among the survivors, the risk of life-long disabilities is high, including cerebral palsy and impairment of movement, cognition, and behavior. Understanding the molecular mechanisms of preterm brain injuries is at the core of future healthcare improvements. Glutamate excitotoxicity is a key mechanism in preterm brain injury, whereby the accumulation of extracellular glutamate damages the delicate immature oligodendrocytes and neurons, leading to the typical patterns of injury seen in the periventricular white matter. Glutamate excitotoxicity is thought to be induced by an interaction between environmental triggers of injury in the perinatal period, particularly cerebral hypoxia-ischemia and infection/inflammation, and developmental and genetic vulnerabilities. To avoid extracellular build-up of glutamate, the brain relies on rapid uptake by sodium-dependent glutamate transporters. Astrocytic excitatory amino acid transporter 2 (EAAT2) is responsible for up to 95% of glutamate clearance, and several lines of evidence suggest that it is essential for brain functioning. While in the adult EAAT2 is predominantly expressed by astrocytes, EAAT2 is transiently upregulated in the immature oligodendrocytes and selected neuronal populations during mid-late gestation, at the peak time for preterm brain injury. This developmental upregulation may interact with perinatal hypoxia-ischemia and infection/inflammation and contribute to the selective vulnerability of the immature oligodendrocytes and neurons in the preterm brain. Disruption of EAAT2 may involve not only altered expression but also impaired function with reversal of transport direction. Importantly, elevated EAAT2 levels have been found in the reactive astrocytes and macrophages of human infant post-mortem brains with severe white matter injury (cystic periventricular leukomalacia), potentially suggesting an adaptive mechanism against excitotoxicity. Interestingly, EAAT2 is suppressed in animal models of acute hypoxic-ischemic brain injury at term, pointing to an important and complex role in newborn brain injuries. Enhancement of EAAT2 expression and transport function is gathering attention as a potential therapeutic approach for a variety of adult disorders and awaits exploration in the context of the preterm brain injuries.

Influence of Transgenic Metallothionein-1 on Gliosis, CA1 Neuronal Loss, and Brain Metal Levels of the Tg2576 Mouse Model of Alzheimer's Disease

The mouse model of Alzheimer’s disease (AD), Tg2576 mice (APP), has provided valuable information, such as the role of the metallothionein (MT) family in their behavioral and amyloidosis phenotypes. In this study, we further characterize the role of MT-1 by crossing Mt1-overexpressing mice with Tg2576 mice (APPTgMT). In 14-month-old mice, MT-1(/2) protein levels were dramatically increased by Mt1 overexpression throughout the cortex (Cx), which showed a prominent caudal-rostral gradient, and the hippocampus (HC). There was a trend for MT-1(/2) immunostaining to be increased in the areas surrounding the amyloid plaques in control male mice but not in Mt1-overexpressing mice. Gliosis was elicited by the amyloid plaques, but the effects of Mt1 overexpression were modest. However, in hippocampal western blots the microglial marker Iba-1 was increased in old male APPTgMT mice compared to APP-wild type (APPWT) mice, and the opposite was observed in young mice. Hippocampal CA1 neuronal loss was observed in Tg2576 mice, but was unaffected by Mt1 overexpression. Aging increased Zn and Cu levels differently depending on brain area, sex, and genotype. Thus, the effects of Mt1 overexpression on the phenotype of Tg2576 mice here studied are modest.

Melatonin Counteracts at a Transcriptional Level the Inflammatory and Apoptotic Response Secondary to Ischemic Brain Injury Induced by Middle Cerebral Artery Blockade in Aging Rats

Aging increases oxidative stress and inflammation. Melatonin counteracts inflammation and apoptosis. This study investigated the possible protective effect of melatonin on the inflammatory and apoptotic response secondary to ischemia induced by blockade of the right middle cerebral artery (MCA) in aging male Wistar rats. Animals were subjected to MCA obstruction. After 24 h or 7 days of procedure, 14-month-old nontreated and treated rats with a daily dose of 10 mg/kg melatonin were sacrificed and right and left hippocampus and cortex were collected. Rats aged 2 and 6 months, respectively, were subjected to the same brain injury protocol, but they were not treated with melatonin. mRNA expression of interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), Bcl-2-associated death promoter (BAD), Bcl-2-associated X protein (BAX), glial fibrillary acidic protein (GFAP), B-cell lymphoma 2 (Bcl-2), and sirtuin 1 was measured by reverse transcription–polymerase chain reaction. In nontreated animals, a significant time-dependent increase in IL-1β, TNF-α, BAD, and BAX was observed in the ischemic area of both hippocampus and cortex, and to a lesser extent in the contralateral hemisphere. Hippocampal GFAP was also significantly elevated, while Bcl-2 and sirtuin 1 decreased significantly in response to ischemia. Aging aggravated these changes. Melatonin administration was able to reverse significantly these alterations. In conclusion, melatonin may ameliorate the age-dependent inflammatory and apoptotic response secondary to ischemic cerebral injury.

Reduced zinc cytotoxicity following differentiation of neural stem/progenitor cells into neurons and glial cells is associated with upregulation of metallothioneins

We investigated zinc cytotoxicity in mouse neural stem/progenitor cells (NSPCs) and their differentiated progeny (neuronal/glial cells) in correlation with expression of metallothionein (MT) gene. Differentiated cells were less sensitive than NSPCs to ZnCl2 (IC50: 128μM vs. 76μM). Differentiation of immature NSPCs to the differentiated cells led to an increase in expression of MT family genes (Mt1, Mt2, Mt3, and Mt4). Zinc exposure induced a dose-dependent increase in expression level of Mt1 and that of Mt2 in both NSPCs and the differentiated cells. Our results showed that the reduced cytotoxicity of zinc associated with differentiation from NSPCs into their progeny was related to the upregulation of MTs.

Absence of metallothionein-3 produces changes on MT-1/2 regulation in basal conditions and alters hypothalamic-pituitary-adrenal (HPA) axis

Metallothioneins (MTs) are multipurpose proteins with clear antioxidant, anti-inflammatory and metal homeostasis properties. The roles of brain MT-1 and MT-2 are similar to those described in the periphery, and are inducible by metals, inflammatory and stress stimuli. MT-3, originally named growth inhibitory factor, exists mainly in the central nervous system, is hardly ever inducible and its functional role and regulation are poorly understood and controversial. In the present study we examined how absence of MT-3 affects phenotypic characteristics and its effects on MT1/2 expression in basal situation and after induction. Hyperactive behavior was found only in young male Mt-3 KO mice and disappeared in the older ones. Absence of MT-3 was associated with a significant increase of MT-1/2 protein levels in several brain areas but decreased MT-1 mRNA levels, which might be related to lower corticosterone levels. The response to stress or inflammation on corticosterone plasma levels was similar in wild type and Mt-3 KO mice, suggesting that the relevant MT-3 role as MT-1/2 regulator in basal conditions is lost when other important regulatory factors such as glucocorticoids or cytokines appear.

Overexpression of the nuclear factor kappaB inhibitor A20 is neurotoxic after an excitotoxic injury to the immature rat brain

BACKGROUND

The zinc finger protein A20 is an ubiquitinating/deubiquitinating enzyme essential for the termination of inflammatory reactions through the inhibition of nuclear factor kappaB (NF-kappaB) signaling. Moreover, it also shows anti-apoptotic activities in some cell types and proapoptotic/pronecrotic effects in others. Although it is known that the regulation of inflammatory and cell death processes are critical in proper brain functioning and that A20 mRNA is expressed in the CNS, its role in the brain under physiological and pathological conditions is still unknown.

METHODS

In the present study, we have evaluated the effects of A20 overexpression in mixed cortical cultures in basal conditions: the in vivo pattern of endogenous A20 expression in the control and N-methyl-d-aspartate (NMDA) excitotoxically damaged postnatal day 9 immature rat brain, and the post-injury effects of A20 overexpression in the same lesion model.

RESULTS

Our results show that overexpression of A20 in mixed cortical cultures induced significant neuronal death by decreasing neuronal cell counts by 45 ± 9%. in vivo analysis of endogenous A20 expression showed widespread expression in gray matter, mainly in neuronal cells. However, after NMDA-induced excitotoxicity, neuronal A20 was downregulated in the neurodegenerating cortex and striatum at 10-24 hours post-lesion, and it was re-expressed at longer survival times in reactive astrocytes located mainly in the lesion border. When A20 was overexpressed in vivo 2 hours after the excitotoxic damage, the lesion volume at 3 days post-lesion showed a significant increase (20.8 ± 7.0%). No A20-induced changes were observed in the astroglial response to injury.

CONCLUSIONS

A20 is found in neuronal cells in normal conditions and is also expressed in astrocytes after brain damage, and its overexpression is neurotoxic for cortical neurons in basal mixed neuron-glia culture conditions and exacerbates postnatal brain excitotoxic damage.

Metallothioneins and brain injury: What transgenic mice tell us

In rodents, the metallothionein (MT) family is composed of four members, MT-1 to MT-4. MT-1&2 are expressed in virtually all tissues including those of the Central Nervous System (CNS), while MT-3 (also called Growth Inhibitory Factor) and MT-4 are expressed prominently in the brain and in keratinizing epithelia, respectively. For the understanding of the physiological functions of these proteins in the brain, the use of transgenic mice has provided essential information. Results obtained inMT-1&2-null mice and in MT-1-overexpressing mice strongly suggeset that these MT isoforms are important antioxidant, anti-inflammatory and antiapoptotic proteins in the brain. Results inMT-3-null mice show a very different pattern, with no support for MT-1&2-like functions. Rather, MT-3 could be involved in neuronal sprouting and survival. Results obtained in a model of peripheral nervous system injury also suggest that MT-3 could be involved in the control of nerve growth.

Protective effects of quercetine on the neuronal injury in frontal cortex after chronic toluene exposure

The aim of this study was designed to evaluate the possible protective effects of quercetine (QE) on the neuronal injury in the frontal cortex after chronic toluene exposure in rats. The rats were randomly allotted into one of the three experimental groups, namely, groups A (control), B (toluene treated) and C (toluene-treated with QE), where each group contains 10 animals. Control group received 1 ml of normal saline solution, and toluene treatment was performed by the inhalation of 3000 ppm toluene in an 8-h/day and 6-day/week order for 12 weeks. The rats in QE-treated group was given QE (15 mg/kg body weight) once a day intraperitoneally for 12 weeks, starting just after toluene exposure. Tissue samples were obtained for histopathological investigation. To date, no histopathological changes of neurodegeneration in the frontal cortex after chronic toluene exposure in rats by QE treatment have been reported. In this study, the morphology of neurons in the QE treatment group was well protected. Chronic toluene exposure caused severe degenerative changes, shrunken cytoplasm and extensively dark picnotic nuclei in neurons of the frontal cortex. We conclude that QE therapy causes morphologic improvement in neurodegeneration of frontal cortex after chronic toluene exposure in rats. We believe that further preclinical research into the utility of QE may indicate its usefulness as a potential treatment on neurodegeneration after chronic toluene exposure in rats.

Interleukin-10 overexpression does not synergize with the neuroprotective action of RGD-containing vectors after postnatal brain excitotoxicity but modulates the main inflammatory cell responses

Antiinflammatory cytokines such as interleukin-10 (IL-10) have been used to modulate and terminate inflammation and provide neuroprotection. Recently, we reported that the modular recombinant transfection vector NLSCt is an efficient tool for transgene overexpression in vivo, which induces neuroprotection as a result of its RGD-mediated integrin-interacting capacity. We here sought to evaluate the putative synergic neuroprotective action exerted by IL-10 overexpression using NLSCt as a transfection vector after an excitotoxic injury to the postnatal rat brain. For this purpose, lesion volume, neurodegeneration, astroglial and microglial responses, neutrophil infiltration, and proinflammatory cytokine production were analyzed at several survival times after intracortical NMDA injection in postnatal day 9 rats, followed by injection of NLSCt combined with the IL-10 gene, a control transgene, or saline vehicle solution. Our results show no combined neuroprotective effect between RGD-interacting vectors and IL-10 gene therapy; instead, IL-10 overexpression using NLSCt as transfection vector increased lesion volume and neuronal degeneration at 12 hr and 3 days postlesion. In parallel, NLSCt/IL-10 treated animals displayed increased density of neutrophils and microglia/macrophages, and a reduced astroglial content of GFAP and vimentin. Moreover, NLSCt/IL-10 treated animals did not show any variation in interleukin-1β or tumor necrosis factor-α expression but a slight increase in interleukin-6 content at 7 days postlesion. In conclusion, overexpression of IL-10 by using NLSCt transfection vector did not synergistically neuroprotect the excitotoxically damaged postnatal rat brain but induced changes in the astroglial and microglial and inflammatory cell response.

Metallothionein and brain inflammation

Since the seminal discoveries of Bert Vallee regarding zinc and metallothioneins (MTs) more than 50 years ago, thousands of studies have been published concerning this fascinating story. One of the most active areas of research is the involvement of these proteins in the inflammatory response in general, and in neuroinflammation in particular. We describe the general aspects of the inflammatory response, highlighting the essential role of the major cytokine interleukin-6, and review briefly the expression and function of MTs in the central nervous system in the context of neuroinflammation. Particular attention is paid to the Tg2576 Alzheimer disease mouse model and the preliminary results obtained in mice into which human Zn(7)MT-2A was injected, which suggest a reversal of the behavioral deficits while enhancing amyloid plaque load and gliosis.

The comparison of mouse full metallothionein-1 versus alpha and beta domains and metallothionein-1-to-3 mutation following traumatic brain injury reveals different biological motifs

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, but current therapies are limited. Previously it has been shown that the antioxidant proteins metallothioneins (MTs) are potent neuroprotective factors in animal models of brain injury. The exogenous administration of MTs causes effects consistent with the roles proposed from studies in knock-out mice. We herewith report the results comparing full mouse MT-1 with the independent alpha and beta domains, alone or together, in a cryoinjury model. The lesion of the cortex caused the mice to perform worse in the horizontal ladder beam and the rota-rod tests; all the proteins showed a modest effect in the former test, while only full MT-1 improved the performance of animals in the rota-rod, and the alpha domain showed a rather detrimental effect. Gene expression analysis by RNA protection assay demonstrated that all proteins may alter the expression of host-response genes such as GFAP, Mac1 and ICAM, in some cases being the beta domain more effective than the alpha domain or even the full MT-1. A MT-1-to-MT-3 mutation blunted some but not all the effects caused by the normal MT-1, and in some cases increased its potency. Thus, splitting the two MT-1 domains do not seem to eliminate all MT functions but certainly modifies them, and different motifs seem to be present in the protein underlying such functions.

Zinc: the brain's dark horse

Zinc is a life-sustaining trace element, serving structural, catalytic, and regulatory roles in cellular biology. It is required for normal mammalian brain development and physiology, such that deficiency or excess of zinc has been shown to contribute to alterations in behavior, abnormal central nervous system development, and neurological disease. In this light, it is not surprising that zinc ions have now been shown to play a role in the neuromodulation of synaptic transmission as well as in cortical plasticity. Zinc is stored in specific synaptic vesicles by a class of glutamatergic or "gluzinergic" neurons and is released in an activity-dependent manner. Because gluzinergic neurons are found almost exclusively in the cerebral cortex and limbic structures, zinc may be critical for normal cognitive and emotional functioning. Conversely, direct evidence shows that zinc might be a relatively potent neurotoxin. Neuronal injury secondary to in vivo zinc mobilization and release occurs in several neurological disorders such as Alzheimer's disease and amyotrophic lateral sclerosis, in addition to epilepsy and ischemia. Thus, zinc homeostasis is integral to normal central nervous system functioning, and in fact its role may be underappreciated. This article provides an overview of zinc neurobiology and reviews the experimental evidence that implicates zinc signals in the pathophysiology of neuropsychiatric diseases. A greater understanding of zinc's role in the central nervous system may therefore allow for the development of therapeutic approaches where aberrant metal homeostasis is implicated in disease pathogenesis.

Molecular mechanisms involved in injury to the preterm brain

Injury to the premature brain is a major contributor to infant mortality and morbidity, often leading to mental retardation and sensory-motor impairment. The disease process is believed to be caused, sustained, and aggravated by multiple perinatal factors that team up in a multi-hit fashion. Clinical, epidemiological, and experimental studies have revealed that key factors such as inflammation, excitotoxicity, and oxidative stress contribute considerably to white- and gray-matter injury in premature infants, whose brains are particularly susceptible to damage. Depending on the timing, lesions of the immature brain may influence developmental events in their natural sequence and redirect subsequent development. We review current concepts on molecular mechanisms underlying injury to the premature brain.

Role of zinc in ALS

The causes of amyotrophic lateral sclerosis (ALS) are poorly understood. A small proportion, about 2%, is associated with a mutation in the superoxide dismutase (SOD1) gene, and mice expressing this mutant gene exhibit a progressive, ALS-like neurodegenerative disease. Studies of these animals, as well as of human post mortem tissue, reveal the presence of multiple pathological processes, including oxidative stress, glutamate excitotoxicity, neuroinflammation, mitochondrial degeneration, alterations in neurofilaments and neurotubules, mitochondrial damage, aggregation of proteins, abnormalities in growth factors, and apoptosis. We propose that alterations in the disposition of zinc ions may be important in the initiation and development of ALS. SOD1 binds zinc, and many of the mutant forms of this enzyme associated with ALS show altered zinc binding. Alterations in the expression of metallothioneins (MTs), which regulate cellular levels of zinc, have been reported in mutant SOD1 mice, and deletion of MTs in these animals accelerates disease progression. Zinc plays a key role in all the pathological processes associated with ALS. Our zinc hypothesis also may help explain evidence for environmental factors in some cases of ALS, such as in the Chamorro tribe in Guam and in the Gulf War.

Substantial migration of SVZ cells to the cortex results in the generation of new neurons in the excitotoxically damaged immature rat brain

Mammalian SVZ progenitors continuously generate new neurons in the olfactory bulb. After injury, changes in SVZ cell number suggest injury-induced migration. Studies that trace the migration of SVZ precursors into neurodegenerating areas are lacking. Previously, we showed a decrease in BrdU+SVZ cells following excitotoxic damage to the immature rat cortex. Here, we demonstrate that NMDA-induced injury forces endogenous Cell Tracker Green (CTG) labeled VZ/SVZ precursors out of the SVZ into the neurodegenerating cortex. CTG+/Nestin+/Filamin A+ precursors are closely associated with vimentin+/GFAP+/GLAST+ filaments and express both chemokine receptor CXCR4 and Robo1. In the cortex, SVZ-derived progenitors show a progressive expression of developing, migrating and mature neurons and glial markers. CTG+/GFAP+ astrocytes greatly outnumber CTG+/MAP2+/NeuN+ neurons. SVZ-derived progenitors differentiate into both tbr1+ cortical glutamatergic neurons and calretinin+ interneurons. But, there is little integration of these neurons into the existing circuitry, as seen by Fluorogold retrograde tracing from the internal capsule.

Distinct spatial and temporal activation of caspase pathways in neurons and glial cells after excitotoxic damage to the immature rat brain

Although cleaved caspase-3 is known to be involved in apoptotic cell death mechanisms in neurons, it can also be involved in a nonapoptotic role in astrocytes after postnatal excitotoxic injury. Here we evaluate participation of upstream pathways activating caspase-3 in neurons and glial cells, by studying the intrinsic pathway via caspase-9, the extrinsic pathway via caspase-8, and activation of the p53-dependent pathway. N-methyl-D-aspartate (NMDA) was injected intracortically in 9-day-old postnatal rats, which were sacrificed at several survival times between 4 hr postlesion (pl) and 7 days pl. We analyzed temporal and spatial expression of caspase-8, caspase-9, and p53 and correlation with neuronal and glial markers and caspase-3 activation. Caspase-9 was significantly activated at 10 hpl, strongly correlating with caspase-3. It was present mainly in damaged cortical and hippocampal neurons but was also seen in astrocytes and oligodendrocytes in layer VI and corpus callosum (cc). Caspase-8 showed a diminished correlation with caspase-3. It was present in cortical neurons at 10-72 hpl, showing layer specificity, and also in astroglial and microglial nuclei, mainly in layer VI and cc. p53 Expression increased at 10-72 hpl but did not correlate with caspase-3. p53 Was seen in neurons of the degenerating cortex and in some astrocytes and microglial cells of layer VI and cc. In conclusion, after neonatal excitotoxicity, mainly the mitochondrial intrinsic pathway mediates neuronal caspase-3 and cell death. In astrocytes, caspase-3 is not widely correlated with caspase-8, caspase-9, or p53, except in layer VI-cc astrocytes, where activation of upstream cascades occurs.

Survivin and heat shock protein 25/27 colocalize with cleaved caspase-3 in surviving reactive astrocytes following excitotoxicity to the immature brain

Following immature excitotoxic brain damage, distinct patterns of caspase activation have been described in neurons and glial cells. Neuronal cells show activation of the mitochondrial apoptosis pathway, caspase-3 cleavage and apoptotic cell death, while reactive astrocytes show caspase-3 cleavage that is not always correlated with enzymatic protease activity and does not generally terminate in cell death. Accordingly, the aim of the present study was to evaluate the astrocytic colocalization of cleaved caspase-3 and several anti-apoptotic proteins of the inhibitor of apoptosis proteins family (IAPs), such as survivin and cellular inhibitor of apoptosis-2 (cIAP-2), and the heat shock proteins (HSPs) family, Hsp25/27 and Hsc70/Hsp70, which can all prevent caspases from cleaving their substrates. At several survival times ranging from 4 h to 14 days after cortical excitotoxic damage induced by N-methyl-d-aspartate (NMDA) injection at postnatal day 9 in rat pups, single and double immunohistochemical techniques were performed in free floating cryostat sections and sections were analyzed by confocal microscopy. Our results show that survivin and Hsp25/27 are primarily expressed in reactive astrocytes of the damaged cortex and the adjacent white matter. In addition, both molecules strongly colocalize with cleaved caspase-3. Survivin is primarily located in the nucleus, like cleaved caspase-3; while Hsp25/27 is cytoplasmic but very frequently found in cells showing nuclear caspase-3. cIAP-2 was mostly found in damaged neurons but also in some glial scar reactive astrocytes and showed fewer correlation with caspase-3. Hsc70/Hsp70 was only expressed in injured neurons and did not correlate with caspase-3. Thus, we conclude that primarily survivin and Hsp25/27 may participate in the inhibition of cleaved caspase-3 in reactive astrocytes and may be involved in protecting astrocytes after injury.

Metallothionein in the central nervous system: Roles in protection, regeneration and cognition

Metallothionein (MT) is an enigmatic protein, and its physiological role remains a matter of intense study and debate 50 years after its discovery. This is particularly true of its function in the central nervous system (CNS), where the challenge remains to link its known biochemical properties of metal binding and free radical scavenging to the intricate workings of brain. In this compilation of four reports, first delivered at the 11th International Neurotoxicology Association (INA-11) Meeting, June 2007, the authors present the work of their laboratories, each of which gives an important insight into the actions of MT in the brain. What emerges is that MT has the potential to contribute to a variety of processes, including neuroprotection, regeneration, and even cognitive functions. In this article, the properties and CNS expression of MT are briefly reviewed before Dr Hidalgo describes his pioneering work using transgenic models of MT expression to demonstrate how this protein plays a major role in the defence of the CNS against neurodegenerative disorders and other CNS injuries. His group's work leads to two further questions, what are the mechanisms at the cellular level by which MT acts, and does this protein influence higher order issues of architecture and cognition? These topics are addressed in the second and third sections of this review by Dr West, and Dr Levin and Dr Eddins, respectively. Finally, Dr Aschner examines the ability of MT to protect against a specific toxicant, methylmercury, in the CNS.

Caspase-3 activation in astrocytes following postnatal excitotoxic damage correlates with cytoskeletal remodeling but not with cell death or proliferation

Caspase-3 has classically been defined as the main executioner of programmed cell death. However, recent data supports the participation of this protease in non-apoptotic cellular events including cell proliferation, cell cycle regulation, and cellular differentiation. In this study, astroglial cleavage of caspase-3 was analyzed following excitotoxic damage in postnatal rats to determine if its presence is associated with apoptotic cell death, cell proliferation, or cytoskeletal remodeling. A well-characterized in vivo model of excitotoxicity was studied, where damage was induced by intracortical injection of N-methyl-D-asparate (NMDA) in postnatal day 9 rats. Our results demonstrate that cleaved caspase-3 was mainly observed in the nucleus of activated astrocytes in the lesioned hemisphere as early as 4 h postlesion and persisted until the glial scar was formed at 7-14 days, and it was not associated with TUNEL labeling. Caspase-3 enzymatic activity was detected at 10 h and 1 day postlesion in astrocytes, and co-localized with caspase-cleaved fragments of glial fibrillary acidic protein (CCP-GFAP). However, at longer survival times, when astroglial hypertrophy was observed, astroglial caspase-3 did not generally correlate with GFAP cleavage, but instead was associated with de novo expression of vimentin. Moreover, astroglial caspase-3 cleavage was not associated with BrdU incorporation. These results provide further evidence for a nontraditional role of caspases in cellular function that is independent of cell death and suggest that caspase activation is important for astroglial cytoskeleton remodeling following cellular injury.

Delayed neurodegeneration and early astrogliosis after excitotoxicity to the aged brain

Excitotoxicity is well recognised as a mechanism underlying neuronal cell death in several brain injuries. To investigate age-dependent differences in neurodegeneration, edema formation and astrogliosis, intrastriatal N-methyl-d-aspartate injections were performed in young (3 months) and aged (22-24 months) male Wistar rats. Animals were sacrificed at different times between 12h and 14 days post-lesion (DPL) and cryostat sections were processed for Toluidine blue, Fluoro-Jade B staining, NeuN and GFAP immunohistochemistry. Our results show that both size of tissue injury and edema were reduced in the old subjects only up to 1DPL, correlating with a slower progression of neurodegeneration with peak numbers of degenerating neurons at 3DPL in the aged, contrasting with maximum neurodegeneration at 1DPL in the young. However, old animals showed an earlier onset of astroglial response, seen at 1DPL, and a larger area of astrogliosis at all time-points studied, including a greater glial scar. In conclusion, after excitotoxic striatal damage, progression of neurodegeneration is delayed in the aged but the astroglial response is earlier and exacerbated. Our results emphasize the importance of using aged animals and several survival times for the study of acute age-related brain insults.

Novel roles for metallothionein-I + II (MT-I + II) in defense responses, neurogenesis, and tissue restoration after traumatic brain injury: Insights from global gene expression profiling in wild-type and MT-I + II knockout mice

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, especially among young people. Inflammatory processes and oxidative stress likely underlie much of the damage elicited by injury, but the full repertoire of responses involved is not well known. A genomic approach, such as the use of microarrays, provides much insight in this regard, especially if combined with the use of gene-targeted animals. We report here the results of one of these studies comparing wild-type and metallothionein-I + II knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8, and 16 days postlesion (dpl) using Affymetrix genechips/oligonucleotide arrays interrogating approximately 10,000 different murine genes (MG_U74Av2). Hierarchical clustering analysis of these genes readily shows an orderly pattern of gene responses at specific times consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma, as well as a prominent effect of MT-I + II deficiency. The results thoroughly confirmed the importance of the antioxidant proteins MT-I + II in the response of the brain to injury and opened new avenues that were confirmed by immunohistochemistry. Data in KO, MT-I-overexpressing, and MT-II-injected mice strongly suggest a role of these proteins in postlesional activation of neural stem cells.

Endocannabinoids potently protect the newborn brain against AMPA-kainate receptor-mediated excitotoxic damage

Brain lesions induced in newborn mice or rats by the glutamatergic agonists ibotenate (acting on NMDA and metabotropic receptors) or S-bromowillardiine (acting on AMPA-kainate receptors) mimic some aspects of white matter cysts and transcortical necrosis observed in human perinatal brain damage associated with cerebral palsy. Exogenous and endogenous cannabinoids have received increasing attention as potential neuroprotective agents in a number of neurodegenerative disorders of the adult. One recent study showed neuroprotection by the cannabinoid agonist WIN-55212 in a newborn rat model of acute severe asphyxia. The present study was designed to assess the neuroprotective effects of the endogenous cannabinoid anandamide using a well-defined rodent model of neonatal excitotoxic brain lesions. In this model, anandamide provided dose-dependent and long-lasting protection of developing white matter and cortical plate reducing the size of lesions induced by S-bromowillardiine. Anandamide had only marginal neuroprotective effect against ibotenate-induced cortical grey matter lesions. Anandamide-induced neuroprotection against AMPA-kainate receptor-mediated brain lesions were blocked by a CB1 antagonist but not by a CB2 antagonist. Furthermore, anandamide effects were mimicked by a CB1 agonist but not by a CB2 agonist. Real-time PCR confirmed the expression of CB1 receptors, but not CB2 receptors, in the untreated newborn neocortex. Finally, neuroprotective effects of anandamide in white matter involved increased survival of preoligodendrocytes and better preservation of myelination. The present study provides experimental support for the role of endocannabinoids as a candidate therapy for excitotoxic perinatal brain lesions.

Lentiviral-mediated gene transfer of brain-derived neurotrophic factor is neuroprotective in a mouse model of neonatal excitotoxic challenge

Excitotoxicity may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected into the murine neopallium at postnatal day 5, the glutamatergic analog N-methyl-D-aspartate (NMDA) produces transcortical neuronal death and periventricular white matter cysts, which mimic brain damage observed in human term and preterm neonates at risk for developing cerebral palsy. We previously showed that intracerebral injection of brain-derived neurotrophic factor (BDNF) was neuroprotective in this model. Because BDNF does not easily cross the blood-brain barrier, alternative strategies to avoid repeated intracerebral injections of BDNF should be tested, particularly when the goal of such translational research is ultimately to achieve clinical application. The goal of the present study was to assess the protective role of lentiviral-mediated gene transfer of BDNF against excitotoxic lesions induced by NMDA in newborn mice. We first assessed the biological activity of BDNF gene transfer in vitro and determined the efficiency of gene transfer in our in vivo model. We next administered the BDNF-expressing vector by intracerebral injection in neonatal mice, 3 days before inducing NMDA lesions. When compared with a control green fluorescent protein-expressing lentiviral vector, administration of BDNF-expressing vector induced a significant protection of the periventricular white matter and cortical plate against the NMDA-mediated insult. Intraventricular delivery of the BDNF-expressing lentiviral vector was more efficient in terms of neuroprotection than the intraparenchymal route. Altogether, the present study shows that viral-mediated gene transfer of BDNF to newborn mouse brain is feasible and affords significant neuroprotection against an excitotoxic insult.

Patterns of excitotoxin-induced brain lesions in the newborn rabbit: a neuropathological and MRI correlation

There is pressing need to employ new advances in structural MR brain imaging to better diagnose brain damage in newborn infants. Timely application of such technology will enable improved therapeutic interventions. Diffusion-weighted sequences are a sensitive marker of very early neuronal injury, the spatial pattern of which provides critical information regarding the underlying pathophysiology. We have modified our murine model of excitotoxic neonatal brain injury to the rabbit, an animal whose brain is larger and where the neuroanatomic organization of the subcortical white matter more closely resembles that of the human. Utilizing this rabbit model, we undertook an MRI/histopathologic correlation. We found that as with the mouse, there is a spatiotemporal selectivity to the pattern of brain injury, and that the period from postnatal day (P) 7 to P9 in rabbits corresponds to the time of maximum vulnerability of the brain to excitotoxic white matter damage, which neuropathologically simulates periventricular leukomalacia (PVL). We additionally noted that diffusion-weighted imaging provided the most sensitive means of detecting such lesions and that this method was sensitive to structural maturational changes accompanying the normal cortical ontogeny. Taken together, our findings suggest that this rabbit model of perinatal excitotoxic brain injury will be a valuable addition to experimental approaches to further our understanding of perinatal brain damage, that diffusion-weighted imaging will be an invaluable adjunct to the diagnosis of such injury, and that therapeutic strategies aimed at interrupting the evolution of PVL should include targeting the pathophysiologic cascade induced by excitotoxic neonatal brain injury.

Inflammation in areas of remote changes following focal brain lesion

Focal brain lesions can lead to metabolic and structural changes in areas distant from but connected to the lesion site. After focal ischemic or excitotoxic lesions of the cortex and/or striatum, secondary changes have been observed in the thalamus, substantia nigra pars reticulata, hippocampus and spinal cord. In all these regions, inflammatory changes characterized by activation of microglia and astrocytes appear. In the thalamus, substantia nigra pars reticulata and hippocampus, an expression of proinflammatory cytokine like tumor necrosis factor-alpha and interleukin-1beta is induced. However, time course of expression and cellular localisation differ between these regions. Neuronal damage has consistently been observed in the thalamus, substantia nigra and spinal cord. It can be present in the hippocampus depending on the procedure of induction of focal cerebral ischemia. This secondary neuronal damage has been linked to antero- and retrograde degeneration. Anterograde degeneration is associated with somewhat later expression of cytokines, which is localised in neurons. In case of retrograde degeneration, the expression of cytokines is earlier and is localised in astrocytes. Pharmacological intervention aiming at reducing expression of tumor necrosis factor-alpha leads to reduction of secondary neuronal damage. These first results suggest that the inflammatory changes in remote areas might be involved in the pathogenesis of secondary neuronal damage.

Protective effects of melatonin against ethanol-induced reactive gliosis in hippocampus and cortex of young and aged rats

Evidence has been accumulated indicating that chronic ethanol consumption leads to direct or indirect changes in the viability of central nervous system cells. The effects of aging and chronic ethanol consumption on glial markers [glial fibrillary acidic protein (GFAP) and S100B] and oxidant and antioxidant status of rats were studied. Furthermore, protective effects of melatonin against aging and alcohol consumption were also assayed. Chronic ethanol administration to young and aged rats produced an increase in lipid peroxidation, and a decline in glutathione (GSH) levels, which was significantly reversed by the co-administration of melatonin. Lipid peroxidation status was markedly affected in aged rats treated with alcohol compared to the young rats. An age-related increase in GFAP and S100B levels were found in the cortex and hippocampus. Long-term alcohol exposure resulted in distinct elevation in GFAP content in young rats (P < 0.01) while there was less increase in the cortex of aged rats (P < 0.05). In old rats, hippocampal GFAP levels were not significantly changed by alcohol treatment (P > 0.05). Co-administration of melatonin with alcohol significantly reduced GFAP contents both in the hippocampus (P < 0.01) and cortex (P < 0.001) of aged rats. No significant effects of alcohol treatment were found on the levels of neuron-specific enolase (NSE) in aged rats. This finding suggests that melatonin exerts its protective effect on injured nervous tissues by scavenging free radicals and stabilizing glial activity against the damaging effects of ethanol and aging. Furthermore, this work suggests that the signal to initiate gliosis is mediated, at least indirectly, by free radical formation.

Topiramate prevents excitotoxic damage in the newborn rodent brain

Brain lesions induced in newborn mice by the glutamatergic agonists ibotenate (acting on NMDA and metabotropic receptors) and S-bromowillardiine (acting on AMPA-kainate receptors) mimic some aspects of white matter cysts and transcortical necrosis observed in human perinatal brain damage. Topiramate (TPM), already used in children to manage newly diagnosed and refractory epilepsy, has potential neuroprotective effects that may be useful in human perinatal brain lesions. In the excitotoxic newborn mouse model, TPM provided dose-dependent and long-lasting protection of developing white matter and cortical plate against S-bromowillardiine. TPM had no significant effect on ibotenate-induced brain lesions. TPM-induced neuroprotection potentially involved increased survival of pre-oligodendrocytes, decreased neuronal apoptosis, inhibition of microglial activation and astrogliosis, and decreased seizure activity. Diazepam, phenytoin, and carbamazepine had no neuroprotective effect in this model. The present study provides experimental support for the consideration of TPM as a candidate therapy for excitotoxic perinatal brain lesions.

Neuronal TGF-beta1 mediates IL-9/mast cell interaction and exacerbates excitotoxicity in newborn mice

Intraneocortical injection of ibotenate, a glutamate analog, in newborn mice produces damage mimicking lesions observed in human infants with cerebral palsy. Previous research using this model has demonstrated that pretreatment with IL-9, a Th2 cytokine, significantly exacerbated excitotoxic brain lesions. The goal of this study is to identify the underlying pathophysiological mechanism of lesion formation. Pretreatment with TGF-beta1 produced the same effects as IL-9 on ibotenate-induced lesions. IL-9 effects were abolished when a specific TGF-beta1 neutralizing antibody is administered at the same time. Real-time PCR, Western blot, and immunohistochemistry showed that pretreatment with IL-9 increased TGF-beta1 neocortical expression. In vitro studies using real-time PCR and immunocytochemistry demonstrated that neurons were a major contributor in IL-9-induced increase of TGF-beta1. In c-Kit mast cell-deficient mice, TGF-beta1 failed to exacerbate excitotoxic brain lesions, suggesting a key role of mast cells in TGF-beta1 effects. A specific inhibitor of mast cell degranulation and histamine receptor blockers abrogated TGF-beta1 effects on excitotoxic lesions, providing further evidence of mast cell involvement and the role of mast cell-derived histamine. Finally, in vitro studies using a mast cell line showed that TGF-beta1 increased histamine in the supernatant. In aggregate, these data support the notion that neuronal TGF-beta1 plays a key role in the IL-9/mast cell interaction, which leads to an exacerbation of neonatal excitotoxic damage through an increased extracellular histamine concentration. The identification of this pathway, if confirmed in human neonates, might have important implications for understanding and preventing cerebral palsy.

Astroglial nitration after postnatal excitotoxic damage: correlation with nitric oxide sources, cytoskeletal, apoptotic and antioxidant proteins

Oxygen free radicals and nitric oxide (NO) participate in the pathogenesis of acute central nervous system (CNS) injury by forming peroxynitrite, which promotes oxidative damage and tyrosine nitration. Neuronal nitration is associated with cell death, but little is known of the characteristics and cell fate of nitrated astrocytes. In this study, we have used a postnatal excitotoxic lesion model (intracortical NMDA injection) and our aims were (i) to evaluate the temporal and spatial pattern of astroglial nitration in correlation with the neuropathological process and the sources of NO; and (ii) to establish, if any, the correlation among astrocyte nitration and other events such as expression of cytoskeletal proteins, antioxidant enzymes, and cell death markers to cope with nitration and/or undergo cell death. Our results show that after postnatal excitotoxic damage two distinct waves of nitration were observed in relation to astrocytes. At 24 h post-lesion, early-nitrated astrocytes were found within the neurodegenerating area, coinciding with the time of maximal cell death. These early-nitrated astrocytes are highly ramified protoplasmic cells, showing diffuse glial fibrillary acidic protein (GFAP) content and expressing inducible NOS. At later time-points, when astrogliosis is morphologically evident, nitrated hypertrophied reactive astrocytes are observed in the penumbra and the neurodegenerated area, displaying increased expression of GFAP and vimentin cytoskeletal proteins and of metallothionein I-II and Cu/Zn superoxide dismutase antioxidant proteins. Moreover, despite revealing activated caspase-3, they do not show TUNEL labeling. In summary, we show that nitrated astrocytes in vivo constitute a subpopulation of highly reactive astrocytes which display high resistance towards oxidative stress induced cell death.

Proliferation dynamics of germinative zone cells in the intact and excitotoxically lesioned postnatal rat brain

BACKGROUND

The forebrain subventricular zone (SVZ)-olfactory bulb pathway and hippocampal subgranular zone (SGZ) generate neurons into adulthood in the mammalian brain. Neurogenesis increases after injury to the adult brain, but few studies examine the effect of injury on neural and glial precursors in the postnatal brain. To characterize the spatio-temporal dynamics of cell proliferation in the germinative zones, this study utilized a model of postnatal damage induced by NMDA injection in the right sensorimotor cortex at postnatal day 9. Dividing cell populations were labeled with 5-Bromodeoxyuridine (BrdU) in the intact and damaged postnatal brain. Identity of proliferating cells was determined by double immunolabeling with nestin, GFAP, NeuN and tomato lectin (TL).

RESULTS

In the control brain, grouped BrdU+ cells were observed in the Rostral Migratory Stream (RMS), SVZ and SGZ. Maximal proliferation was seen at P12, persisted until P23 and diminished by P49. After injury, a striking reduction in the number of BrdU+ cells was observed in the ipsilateral SVZ from 10 hours (58% decrease) until 14 days post-lesion (88% decrease). In contrast, an increase in grouped BrdU+ cells was seen in the striatum adjacent to the depleted SVZ. Significantly reduced numbers of BrdU+ cells were also seen in the RMS until 3 days post-lesion. No changes were noted in the SGZ. Both in controls and lesioned hemispheres, BrdU+ cells located in the germinal zones were mostly nestin positive and negative for GFAP, NeuN, and TL. In the SVZ area lining the ventricle, BrdU+/nestin+ cells were mainly located between TL+ ependyma and parenchymal GFAP+ astrocytes. After excitotoxicity, a decrease in the number and orientation of GFAP/nestin+ prolongations leaving the SVZ to the cortex, corpus callosum and striatum was noted until 5 days post-lesion.

CONCLUSION

Postnatal excitotoxic injury differentially affects proliferating cells in the germinative zones: no change is observed in the dentate gyrus whereas excitotoxicity causes a significant decrease in proliferating cells in the SVZ and RMS. Depletion of BrdU+ cells in the postnatal SVZ and RMS differs from previous studies after adult brain injury and may affect the SVZ-RMS migration and is suggestive of progenitor recruitment to injured areas.

Longitudinal thalamic diffusion changes after middle cerebral artery infarcts

BACKGROUND

Cerebral infarcts are responsible for functional alterations and microscopic tissue damage at distance from the ischaemic area. Such remote effects have been involved in stroke recovery. Thalamic hypometabolism is related to motor recovery in middle cerebral artery (MCA) infarcts but little is known concerning the tissue changes underlying these metabolic changes. Diffusion tensor imaging (DTI) is highly sensitive to microstructural tissue alterations and can be used to quantify in vivo the longitudinal microscopic tissue changes occurring in the thalamus after MCA infarcts in humans.

METHODS

Nine patients underwent DTI after an isolated MCA infarct. Mean diffusivity (MD), fractional anisotropy (FA), and thalamic region volume were measured from the first week to the sixth month after stroke onset in these patients and in 10 age matched controls.

RESULTS

MD significantly increased in the ipsilateral thalamus between the first and the sixth month (0.766 x 10(-3) mm(2)/s first month; 0.792 x 10(-3) mm(2)/s third month; 0.806 x 10(-3) mm(2)/s sixth month). No significant modification of FA was detected. In six patients, the ipsilateral/contralateral index of MD was higher than the upper limit of the 95% CI calculated in 10 age matched controls. An early decrease of MD preceded the increase of ipsilateral thalamic diffusion in one patient at the first week and in two other patients at the first month.

CONCLUSION

After MCA infarcts, an increase in diffusion is observed with DTI in the ipsilateral thalamus later than 1 month after the stroke onset. This is presumably because of the progressive loss of neurons and/or glial cells. In some patients, this increase is preceded by a transient decrease in diffusion possibly related to an early swelling of these cells or to microglial activation. Further studies in larger series are needed to assess the clinical correlates of these findings.

Metallothionein I and II mitigate age-dependent secondary brain injury

Both the immediate insult and delayed apoptosis contribute to functional deficits after brain injury. Secondary, delayed apoptotic death is more rapid in immature than in adult CNS neurons, suggesting the presence of age-dependent protective factors. To understand the molecular pathobiology of secondary injury in the context of brain development, we identified changes in expression of oxidative stress response genes during postnatal development and target deprivation-induced neurodegeneration. The antioxidants metallothionein I and II (MT I/II) were increased markedly in the thalamus of adult C57BL/6 mice compared to mice <15 days old. Target deprivation generates reactive oxygen species that mediate neuronal apoptosis in the central nervous system; thus the more rapid apoptosis observed in the immature brain might be due to lower levels of MT I/II. We tested this hypothesis by documenting neuronal loss after target-deprivation injury. MT I/II-deficient adult mice experienced greater thalamic neuron loss at 96 hr after cortical injury compared to that in controls (80 +/- 2% vs. 57 +/- 4%, P < 0.01), but not greater overall neuronal loss (84 +/- 4% vs. 79 +/- 3%, MT I/II-deficient vs. controls). Ten-day-old MT I/II-deficient mice, however, experienced both faster onset of secondary neuronal death (30 vs. 48 hr) and greater overall neuronal loss (88 +/- 2% vs. 69 +/- 4%, P = 0.02). MT I/II are thus inhibitors of age-dependent secondary brain injury, and the low levels of MT I/II in immature brains explains, in part, the enhanced susceptibility of the young brain to neuronal loss after injury. These findings have implications for the development of age-specific therapeutic strategies to enhance recovery after brain injury.

Role of metallothionein-III following central nervous system damage

We evaluated the physiological relevance of metallothionein-III (MT-III) in the central nervous system following damage caused by a focal cryolesion onto the cortex by studying Mt3-null mice. In normal mice, dramatic astrogliosis and microgliosis and T-cell infiltration were observed in the area surrounding the lesioned tissue, along with signs of increased oxidative stress and apoptosis. There was also significant upregulation of cytokines/growth factors such as tumor necrosis factor-alpha, interleukin (IL)-1 alpha/beta, and IL-6 as measured by ribonuclease protection assay. Mt3-null mice did not differ from control mice in these responses, in sharp contrast to results obtained in Mt1- Mt2-null mice. In contrast, Mt3-null mice showed increased expression of several neurotrophins as well as of the neuronal sprouting factor GAP-43. Thus, unlike MT-I and MT-II, MT-III does not affect the inflammatory response elicited in the central nervous system by a cryoinjury, nor does it serve an important antioxidant role, but it may influence neuronal regeneration during the recovery process.

Melatonin protects the central nervous system of rats against toluene-containing thinner intoxication by reducing reactive gliosis

Neuroprotective effects of melatonin against free radical damage have been studied extensively. Thinner containing 60-70% toluene is a neurotoxic mixture which is widely used as an aromatic industrial solvent. This product has been shown to cause functional and structural changes in the central nervous system. Toluene generates reactive oxygen species (ROS) and the toxic effects relating to these reactants. In the present study we investigated glial reactivity in hippocampus, cortex and cerebellum and the expression of glial fibrillary acidic protein (GFAP) after exposure of rats to toluene vapor (3000 ppm) for 45 days. We also examined the protective effects of melatonin against gliosis. Western blots demonstrated a marked elevation in total GFAP, a specific marker for astrocytes, by thinner fume inhalation in the hippocampus (P<0.001), cortex (P<0.01) and cerebellum (P<0.05) of rats. Melatonin administration prevented the increase of total GFAP induced by thinner fume inhalation. Thinner exposure caused a significant increase of lipid peroxidation products (malondialdehyde and 4-hydroxyalkenals) in all brain regions (P<0.01 for each region), and this elevation was also was inhibited by melatonin. Furthermore, melatonin augmented glutathione levels in all brain regions (P<0.05 for each region) investigated. In conclusion, melatonin treatment may provide neuroprotection against toluene neurotoxicity by increasing the survival of glial cells possibly by directly scavenging ROS and by indirectly augmenting their antioxidant capacity.

Upregulation of gp130 and STAT3 activation in the rat hippocampus following transient forebrain ischemia

To determine whether the pathophysiological processes after transient forebrain ischemia are mediated via a signal pathway involving gp130 (a signal transducer for the interleukin-6 family), we analyzed changes in the expression of gp130 and its downstream transcription factor, signal transducer and activator of transcription factor 3 (STAT3), in the rat hippocampus of a four-vessel occlusive ischemia model. Expression of gp130 mRNA was restricted to neurons of the pyramidal cell and granule cell layers in control animals. Four hours after ischemic injury, astrocytes expressed gp130 mRNA. Expression of gp130 increased preferentially in the CA1 and dentate hilar regions, and was maintained for at least 2 weeks. Increase in gp130 expression was accompanied by the activation of STAT3 following ischemic injury. Four hours after injury, STAT3 and phosphorylated STAT3 (pSTAT3) were observed in the nuclei of the dentate hilar region, and sequentially in the CA1 region at day 1. By day 3, STAT3 immunoreactivity markedly increased in these areas, where small cells with the morphology of astrocytes showed nuclear and cytoplasmic STAT3 and nuclear pSTAT3 immunoreactivities. These patterns were especially maintained in the CA1 area until 14 days of reperfusion. Double-labeling experiments revealed that the cells expressing STAT3 and pSTAT3 were glial fibrillary acidic protein-expressing reactive astrocytes. These results show a coordinated and long-lasting upregulation of gp130 mRNA and STAT3 activation in reactive astrocytes of the postischemic hippocampus, indicating that they may be involved in the astrocytic response to an ischemic insult.

Decrease of proinflammatory molecules correlates with neuroprotective effect of the fluorinated salicylate triflusal after postnatal excitotoxic damage

BACKGROUND AND PURPOSE

The fluorinated salicylate triflusal has been shown to have a neuroprotective effect after an excitotoxic lesion to the postnatal brain. In this regard, the aim of this study was to elucidate whether neuroprotection was associated with changes in the expression of proinflammatory molecules such as interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), inducible nitric oxide synthase (iNOS), or cyclooxygenase-2 (COX-2), well-known mediators of oxidative stress and inflammation, mechanisms underlying secondary damage occurring after excitotoxic/ischemic brain injury.

METHODS

Postnatal day 9 rats received an intracortical injection of N-methyl-D-aspartate followed by oral administration of triflusal (30 mg/kg) 8 hours later. Ten or 24 hours after lesion, animals were killed, and brain sections processed for the immunohistochemical demonstration of IL-1beta, TNF-alpha, iNOS, and COX-2.

RESULTS

Besides a reduction in the neurodegenerative area, triflusal strongly decreased iNOS immunolabeling at both survival times analyzed, attenuating iNOS immunoreactivity in astroglial cells and infiltrated neutrophils. Additionally, a moderate reduction in COX-2, IL-1beta, and TNF-alpha was observed. Triflusal decreased neuronal and microglial COX-2 expression at 10 and 24 hours after lesion and microglial and astroglial expression of IL-1beta and TNF-alpha at 24 hours after lesion. TNF-alpha expression in neuronal cells at 10 hours after lesion was, however, maintained.

CONCLUSIONS

This study suggests that triflusal neuroprotection is associated with a decrease of iNOS and other inflammatory mediators and therefore may constitute a good therapeutic agent in pathological situations in which regulation of inflammatory genes constitutes a relevant step in the outcome of the neurodegenerative event.

Altered glial fibrillary acidic protein content and its degradation in the hippocampus, cortex and cerebellum of rats exposed to constant light: reversal by melatonin

Reactive astrocytosis is a well-known phenomenon that occurs rapidly after physical or metabolic injury to the brain. One of the important events during astrocyte differentiation is the increased expression of glial fibrillary acidic protein (GFAP), a member of the family of intermediate filament structural proteins. Free radicals are neurotoxic and free radical scavengers have been shown to protect the brain against neurotoxic damage. In the present study, we examined the effect of melatonin on astrocytic reactivity by determining the expression of the glial marker, GFAP, in different brain regions. Rats were exposed to constant light to reduce endogenous melatonin production; half of the animals were injected with melatonin during the exposure to constant light for 7 days. Western blots showed increases in total and degraded GFAP content in the brain of rats exposed to constant light. Melatonin administration caused a reduction of degraded GFAP content. In addition, melatonin significantly reduced neural tissue lipid peroxidation while constant light significantly enhanced the breakdown of lipids in the brain. Brain glutathione levels decreased significantly as a result of constant light exposure; this reduction was reversed by melatonin administration. These results suggest that melatonin potentially protects both neurons and glial cells from free radicals; melatonin's protective actions are probably related to the antioxidant properties of the indole.