Neural damage in the rat thalamus after cortical infarcts

CR8, a selective and potent CDK inhibitor, provides neuroprotection in experimental traumatic brain injury

Traumatic brain injury (TBI) induces secondary injury mechanisms, including cell cycle activation (CCA), that leads to neuronal death and neurological dysfunction. We recently reported that delayed administration of roscovitine, a relatively selective cyclin-dependent kinase (CDK) inhibitor, inhibits CCA and attenuates neurodegeneration and functional deficits following controlled cortical impact (CCI) injury in mice. Here we evaluated the neuroprotective potential of CR8, a more potent second-generation roscovitine analog, using the mouse CCI model. Key CCA markers (cyclin A and B1) were significantly up-regulated in the injured cortex following TBI, and phosphorylation of CDK substrates was increased. Central administration of CR8 after TBI, at a dose 20 times less than previously required for roscovitine, attenuated CCA pathways and reduced post-traumatic apoptotic cell death at 24 h post-TBI. Central administration of CR8, at 3 h after TBI, significantly attenuated sensorimotor and cognitive deficits, decreased lesion volume, and improved neuronal survival in the cortex and dentate gyrus. Moreover, unlike roscovitine treatment in the same model, CR8 also attenuated post-traumatic neurodegeneration in the CA3 region of the hippocampus and thalamus at 21 days. Furthermore, delayed systemic administration of CR8, at a dose 10 times less than previously required for roscovitine, significantly improved cognitive performance after CCI. These findings further demonstrate the neuroprotective potential of cell cycle inhibitors following experimental TBI. Given the increased potency and efficacy of CR8 as compared to earlier purine analog types of CDK inhibitors, this drug should be considered as a candidate for future clinical trials of TBI.

Cyclin D1 gene ablation confers neuroprotection in traumatic brain injury

Cell cycle activation (CCA) is one of the principal secondary injury mechanisms following brain trauma, and it leads to neuronal cell death, microglial activation, and neurological dysfunction. Cyclin D1 (CD1) is a key modulator of CCA and is upregulated in neurons and microglia following traumatic brain injury (TBI). In this study we subjected CD1-wild-type (CD1(+/+)) and knockout (CD1(-/-)) mice to controlled cortical impact (CCI) injury to evaluate the role of CD1 in post-traumatic neurodegeneration and neuroinflammation. As early as 24 h post-injury, CD1(+/+) mice showed markers of CCA in the injured hemisphere, including increased CD1, E2F1, and proliferating cell nuclear antigen (PCNA), as well as increased Fluoro-Jade B staining, indicating neuronal degeneration. Progressive neuronal loss in the hippocampus was observed through 21 days post-injury in these mice, which correlated with a decline in cognitive function. Microglial activation in the injured hemisphere peaked at 7 days post-injury, with sustained increases at 21 days. In contrast, CD1(-/-) mice showed reduced CCA and neurodegeneration at 24 h, as well as improved cognitive function, attenuated hippocampal neuronal cell loss, decreased lesion volume, and cortical microglial activation at 21 days post-injury. These findings indicate that CD1-dependent CCA plays a significant role in the neuroinflammation, progressive neurodegeneration, and related neurological dysfunction resulting from TBI. Our results further substantiate the proposed role of CCA in post-traumatic secondary injury, and suggest that inhibition of CD1 may be a key therapeutic target for TBI.

Early in vivo MR spectroscopy findings in organophosphate-induced brain damage-potential biomarkers for short-term survival

Organophosphates are highly toxic substances, which cause severe brain damage. The hallmark of the brain injury is major convulsions. The goal of this study was to assess the spatial and temporal MR changes in the brain of paraoxon intoxicated rats. T2-weighted MRI and ¹H-MR-spectroscopy were conducted before intoxication, 3 h, 24 h, and 8 days postintoxication. T2 prolongation mainly in the thalami and cortex was evident as early as 3 h after intoxication (4-6% increase in T2 values, P < 0.05). On spectroscopy, N-acetyl aspartate (NAA)/creatine and NAA/choline levels significantly decreased 3 h postintoxication (>20% decrease, P < 0.005), and 3 h lactate peak was evident in all intoxicated animals. On the 8th day, although very little T2 changes were evident, NAA/creatine and choline/creatine were significantly decreased (>15%, P < 0.05). Animals who succumbed had extensive cortical edema, significant higher lactate levels and a significant decrease in NAA/creatine and NAA/choline levels compared to animals which survived the experiment. Organophosphates-induced brain damage is obvious on MR data already 3 h postintoxication. In vivo spectroscopic changes are more sensitive for assessing long-term injury than T2-weighted MR imaging. Early spectroscopic findings might be used as biomarkers for the severity of the intoxication and might predict early survival.

Selective CDK inhibitor limits neuroinflammation and progressive neurodegeneration after brain trauma

Traumatic brain injury (TBI) induces secondary injury mechanisms, including cell-cycle activation (CCA), which lead to neuronal cell death, microglial activation, and neurologic dysfunction. Here, we show progressive neurodegeneration associated with microglial activation after TBI induced by controlled cortical impact (CCI), and also show that delayed treatment with the selective cyclin-dependent kinase inhibitor roscovitine attenuates posttraumatic neurodegeneration and neuroinflammation. CCI resulted in increased cyclin A and D1 expressions and fodrin cleavage in the injured cortex at 6 hours after injury and significant neurodegeneration by 24 hours after injury. Progressive neuronal loss occurred in the injured hippocampus through 21 days after injury and correlated with a decline in cognitive function. Microglial activation associated with a reactive microglial phenotype peaked at 7 days after injury with sustained increases at 21 days. Central administration of roscovitine at 3 hours after CCI reduced subsequent cyclin A and D1 expressions and fodrin cleavage, improved functional recovery, decreased lesion volume, and attenuated hippocampal and cortical neuronal cell loss and cortical microglial activation. Furthermore, delayed systemic administration of roscovitine improved motor recovery and attenuated microglial activation after CCI. These findings suggest that CCA contributes to progressive neurodegeneration and related neurologic dysfunction after TBI, likely in part related to its induction of microglial activation.

Early detection of secondary damage in ipsilateral thalamus after acute infarction at unilateral corona radiata by diffusion tensor imaging and magnetic resonance spectroscopy

Background

Traditional magnetic resonance (MR) imaging can identify abnormal changes in ipsilateral thalamus in patients with unilateral middle cerebral artery (MCA) infarcts. However, it is difficult to demonstrate these early changes quantitatively. Diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy (MRS) are potentially sensitive and quantitative methods of detection in examining changes of tissue microstructure and metabolism. In this study, We used both DTI and MRS to examine possible secondary damage of thalamus in patients with corona radiata infarction.

Methods

Twelve patients with unilateral corona radiata infarction underwent MR imaging including DTI and MRS at one week (W1), four weeks (W4), and twelve weeks (W12) after onset of stroke. Twelve age-matched controls were imaged. Mean diffusivity (MD), fractional anisotropy (FA), N-acetylaspartate (NAA), choline(Cho), and creatine(Cr) were measured in thalami.

Results

T1-weighted fluid attenuation inversion recovery (FLAIR), T2-weighted, and T2-FLAIR imaging showed an infarct at unilateral corona radiate but no other lesion in each patient brain. In patients, MD was significantly increased at W12, compared to W1 and W4 (all P< 0.05). NAA was significantly decreased at W4 compared to W1, and at W12 compared to W4 (all P< 0.05) in the ipsilateral thalamus. There was no significant change in FA, Cho, or Cr in the ipsilateral thalamus from W1 to W12. Spearman's rank correlation analysis revealed a significant negative correlation between MD and the peak area of NAA, Cho, and Cr at W1, W4, and W12 and a significant positive correlation of FA with NAA at W1.

Conclusions

These findings indicate that DTI and MRS can detect the early changes indicating secondary damage in the ipsilateral thalamus after unilateral corona radiata infarction. MRS may reveal the progressive course of damage in the ipsilateral thalamus over time.

Reduction of β-amyloid deposits by γ-secretase inhibitor is associated with the attenuation of secondary damage in the ipsilateral thalamus and sensory functional improvement after focal cortical infarction in hypertensive rats

Abnormal β-amyloid (Aβ) deposits in the thalamus have been reported after cerebral cortical infarction. In this study, we investigated the association of Aβ deposits, with the secondary thalamic damage after focal cortical infarction in rats. Thirty-six stroke-prone renovascular hypertensive rats were subjected to distal middle cerebral artery occlusion (MCAO) and then randomly divided into MCAO, vehicle, and N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) groups and 12 sham-operated rats as control. The DAPT was administered orally at 72 hours after MCAO. Seven days after MCAO, sensory function, neuron loss, and glial activation and proliferation were evaluated using adhesive removal test, Nissl staining, and immunostaining, respectively. Thalamic Aβ accumulation was evaluated using immunostaining and enzyme-linked immunosorbent assay (ELISA). Compared with vehicle group, the ipsilateral thalamic Aβ, neuronal loss, glial activation and proliferation, and the mean time to remove the stimulus from right forepaw significantly decreased in DAPT group. The mean time to remove the stimulus from the right forepaw and thalamic Aβ burden were both negatively correlated with the number of thalamic neurons. These findings suggest that Aβ deposits are associated with the secondary thalamic damage. Reduction of thalamic Aβ by γ-secretase inhibitor may attenuate the secondary damage and improve sensory function after cerebral cortical infarction.

Differential effects of injury severity on cognition and cellular pathology after contusive brain trauma in the immature rat

Although diffuse brain damage has been suggested to be the predominant predictor of neurological morbidity following closed head injury in infants and children, the presence of contusions also predicts long-term neurobehavioral dysfunction. Contusive brain trauma in the 17-day-old rat resulted in neurodegeneration and caspase activation in the cortex at 1 day, and in the thalamus at 3 days post-injury, and to a greater extent following a deeper impact. Cortical tissue loss in the 4-mm impact group was significantly greater than that in the 3-mm impact group (p < 0.05), and exhibited a time-dependent increase over the first 3 weeks post-injury. Traumatic axonal injury was observed in the white matter tracts below the site of impact at 1 day, and in the corpus callosum at 3 days, to a greater extent following 4-mm impact. In contrast, cellular caspase-3 activation in these white matter tracts was only observed at 24 h post-injury and was not affected by impact depth. Similarly, neurodegeneration and caspase activation in the hippocampus was restricted to the dentate gyrus and occurred to a similar extent in both injured groups. Only the 4-mm impact group exhibited learning deficits in the first week (p < 0.0001) that was sustained until the third week post-injury (p < 0.0001), while deficits in the 3-mm impact group were seen only at 3 weeks post-injury (p < 0.02). These observations demonstrate that increasing severity of injury in immature animals does not uniformly increase the extent of cellular damage, and that the progression of tissue damage and behavioral deficits varies as a function of injury severity.

Relevance of structural brain connectivity to learning and recovery from stroke

The physical structure of white matter fiber bundles constrains their function. Any behavior that relies on transmission of signals along a particular pathway will therefore be influenced by the structural condition of that pathway. Diffusion-weighted magnetic resonance imaging provides localized measures that are sensitive to white matter microstructure. In this review, we discuss imaging evidence on the relevance of white matter microstructure to behavior. We focus in particular on motor behavior and learning in healthy individuals and in individuals who have suffered a stroke. We provide examples of ways in which imaging measures of structural brain connectivity can inform our study of motor behavior and effects of motor training in three different domains: (1) to assess network degeneration or damage with healthy aging and following stroke, (2) to identify a structural basis for individual differences in behavioral responses, and (3) to test for dynamic changes in structural connectivity with learning or recovery.

Focal cortical infarcts alter intrinsic excitability and synaptic excitation in the reticular thalamic nucleus

Focal cortical injuries result in death of cortical neurons and their efferents and ultimately in death or damage of thalamocortical relay (TCR) neurons that project to the affected cortical area. Neurons of the inhibitory reticular thalamic nucleus (nRT) receive excitatory inputs from corticothalamic and thalamocortical axons and are thus denervated by such injuries, yet nRT cells generally survive these insults to a greater degree than TCR cells. nRT cells inhibit TCR cells, regulate thalamocortical transmission, and generate cerebral rhythms including those involved in thalamocortical epilepsies. The survival and reorganization of nRT after cortical injury would determine recovery of thalamocortical circuits after injury. However, the physiological properties and connectivity of the survivors remain unknown. To study possible alterations in nRT neurons, we used the rat photothrombosis model of cortical stroke. Using in vitro patch-clamp recordings at various times after the photothrombotic injury, we show that localized strokes in the somatosensory cortex induce long-term reductions in intrinsic excitability and evoked synaptic excitation of nRT cells by the end of the first week after the injury. We find that nRT neurons in injured rats show (1) decreased membrane input resistance, (2) reduced low-threshold calcium burst responses, and (3) weaker evoked excitatory synaptic responses. Such alterations in nRT cellular excitability could lead to loss of nRT-mediated inhibition in relay nuclei, increased output of surviving TCR cells, and enhanced thalamocortical excitation, which may facilitate recovery of thalamic and cortical sensory circuits. In addition, such changes could be maladaptive, leading to injury-induced epilepsy.

Iba1(+)/NG2(+) macrophage-like cells expressing a variety of neuroprotective factors ameliorate ischemic damage of the brain

In a transient 90-min middle cerebral artery occlusion (MCAO) model of rats, a large ischemic lesion is formed where macrophage-like cells massively accumulate, many of which express a macrophage marker, Iba1, and an oligodendrocyte progenitor cell marker, NG2 chondroitin sulfate proteoglycan (NG2); therefore, the cells were termed BINCs (Brain Iba1(+)/NG2(+) Cells). A bone marrow transplantation experiment using green-fluorescent protein-transgenic rats showed that BINCs were derived from bone marrow. 5-Fluorouracil (5FU) injection at 2 days post reperfusion (2 dpr) markedly reduced the number of BINCs at 7 dpr, causing enlargement of necrotic volumes and frequent death of the rats. When isolated BINCs were transplanted into 5FU-aggravated ischemic lesion, the volume of the lesion was much reduced. Quantitative real-time RT-PCR showed that BINCs expressed mRNAs encoding bFGF, BMP2, BMP4, BMP7, GDNF, HGF, IGF-1, PDGF-A, and VEGF. In particular, BINCs expressed IGF-1 mRNA at a very high level. Immunohistochemical staining showed that IGF-1-expressing BINCs were found not only in rat but also human ischemic brain lesions. These results suggest that bone marrow-derived BINCs play a beneficial role in ischemic brain lesions, at least in part, through secretion of neuroprotective factors.

Ginsenoside Rb(1) prevents image navigation disability, cortical infarction, and thalamic degeneration in rats with focal cerebral ischemia

Oral administration of red ginseng powder before but not after transient forebrain ischemia prevents delayed neuronal death in gerbils. One neuroprotective molecule within red ginseng powder is ginsenoside Rb(1). The mechanism of action(s) of ginsenoside Rb(1) remains to be determined. We performed intracerebroventricular infusion of 0.6 microg/d ginsenoside Rb(1) before or after permanent occlusion of the left middle cerebral artery in stroke-prone spontaneous hypertensive rats. Ginsenoside Rb(1) significantly decreased escape latency on repeated trials of the Morris water maze test, throughout the first to fourth trial days at 2 and 4 weeks after MCA occlusion (P<.05, P<.01 or P<.001). The ratio of the infarcted area to the left hemispheric area in the groups treated with 0.6 microg/d of ginsenoside Rb(1) was significantly smaller than that in the saline-treated ischemic group (P<.05 or P<.001). The continuous infusion of ginsenoside Rb(1) (0.06 microg/d) was less effective and the other doses examined were ineffective in ameliorating ischemia-induced image navigation disability and reducing cortical infarct size. There were significant differences in neuron numbers in the ventroposterior thalamic nucleus and in the left-to-right ratio of the thalamic area between the saline-infused ischemic group and the ginsenoside Rb(1)-treated ischemic group (P<.05 or P<.01). Moreover, ginsenoside Rb(1) at concentrations of 0.1 to 100 fg/mL (0.09 to 90 fM), facilitated neurite extension and rescued cortical neurons from lethal damage caused by the free radical-promoting agent FeSO(4), in vitro (P<.05 or P<.01). These findings suggest that ginsenoside Rb(1) protects the cerebral cortex against lethal ischemic damage possibly by acting as a neurotrophic factor-like agent and by scavenging free radicals, which are overproduced in situ during and after brain ischemia. The final link between the in vivo neuroprotective action and the in vitro neurotrophic and antioxidant activities of ginsenoside Rb(1) remains to be determined.

Neurogenesis and angiogenesis within the ipsilateral thalamus with secondary damage after focal cortical infarction in hypertensive rats

Neurogenesis and angiogenesis in the subventricular zone and peri-infarct region have been confirmed. However, newly formed neuronal cells and blood vessels that appear in the nonischemic ipsilateral ventroposterior nucleus (VPN) of the thalamus with secondary damage after stroke has not been previously studied. Twenty-four stroke-prone renovascular hypertensive rats were subjected to distal right middle cerebral artery occlusion (MCAO) or sham operation. 5'-Bromo-2'-deoxyuridine (BrdU) was used to label cell proliferation. Rats were killed at 7 or 14 days after the operation. Neuronal nuclei (NeuN), OX-42, BrdU, nestin, laminin(+), BrdU(+)/nestin(+), BrdU(+)/NeuN(+), nestin(+)/GFAP(+)(glial fibrillary acidic protein), and BrdU(+)/laminin(+) immunoreactive cells were detected within the ipsilateral VPN. The primary infarction was confined to the right somatosensory cortex. Within the ipsilateral VPN of the ischemic rats, the number of NeuN(+) neurons decreased, the OX-42(+) microglia cells were activated, and BrdU(+) and nestin(+) cells were detected at day 7 after MCAO and increased in number at day 14. Moreover, BrdU(+)/nestin(+) cells and BrdU(+)/NeuN(+) cells were detected at day 14 after MCAO. In addition, the ischemic rats showed a significant increase in vascular density in the ipsilateral VPN compared with the sham-operated rats. These results suggest that secondary damage with neurogenesis and angiogenesis of the ipsilateral VPN of the thalamus occurs after focal cortical infarction.

Focal cerebral ischemia in rats alters APP processing and expression of Abeta peptide degrading enzymes in the thalamus

We have previously demonstrated aggregation of amyloid precursor protein (APP) and beta-amyloid (Abeta) to dense plaque-like deposits in the thalamus of rats subjected to transient middle cerebral artery occlusion (MCAO). Here, we investigated the underlying molecular effects of MCAO on APP processing and expression profiles of Abeta degrading enzymes in the cortex adjacent to the infarct (penumbra) and ipsilateral thalamus 2, 7 and 30 days after ischemic insult. Enhanced beta-amyloidogenic processing of APP and altered insulin degrading enzyme and neprilysin expression were observed in the thalamus, but not the penumbral cortex, 7 and 30 days after MCAO coinciding with increased calcium levels and beta-secretase (BACE) activity. Consecutively, increased BACE activity associated with depletion of BACE trafficking protein GGA3, suggesting a post-translational stabilization of BACE. These results demonstrate that focal cerebral ischemia leads to complex pathogenic events in the thalamus long after the initial insult.

Combination treatment with normobaric hyperoxia and cilostazol protects mice against focal cerebral ischemia-induced neuronal damage better than each treatment alone

Normobaric hyperoxia (NBO) and cilostazol (6-[4-(1-cyclohexy-1H-tetrazol-5-yl)butoxyl]-3,4-dihydro-2-(1H)-quinolinone) (a selective inhibitor of phosphodiesterase 3) have each been reported to exert neuroprotective effects against acute brain injury after cerebral ischemia in rodents. Here, we evaluated the potential neuroprotective effects of combination treatment with NBO and cilostazol against acute and subacute brain injuries after simulated stroke. Mice subjected to 2-h filamental middle cerebral artery (MCA) occlusion were treated with NBO (95% O(2), during the ischemia) alone, with cilostazol (3 mg/kg i.p. after the ischemia) alone, with both of these treatments (combination), or with vehicle. The histological and neurobehavioral outcomes were assessed at acute (1 day) or subacute (7 days) stages after reperfusion. We measured regional cerebral blood flow (rCBF) during and after ischemia by laser-Doppler flowmetry and recovery (versus vehicle) in the combination therapy group just after reperfusion. Mean acute and subacute lesion volumes were significantly reduced in the combination group but not in the two monotherapy groups. The combination therapy increased endothelial nitric-oxide synthase (eNOS) activity in the lesion area after ischemia versus vehicle. Combination therapy with NBO plus cilostazol protected mice subjected to focal cerebral ischemia by improvement of rCBF after reperfusion, in part in association with eNOS activity.

Midline brain injury in the immature rat induces sustained cognitive deficits, bihemispheric axonal injury and neurodegeneration

Infants and children less than 4 years old suffer chronic cognitive deficits following mild, moderate or severe diffuse traumatic brain injury (TBI). It has been suggested that the underlying neuropathologic basis for behavioral deficits following severe TBI is acute brain swelling, subarachnoid hemorrhage and axonal injury. To better understand mechanisms of cognitive dysfunction in mild-moderate TBI, a closed head injury model of midline TBI in the immature rat was developed. Following an impact over the midline suture of the intact skull, 17-day-old rats exhibited short apnea times (3-15 s), did not require ventilatory support and suffered no mortality, suggestive of mild TBI. Compared to un-injured rats, brain-injured rats exhibited significant learning deficits over the first week post-injury (p<0.0005), and, significant learning (p<0.005) and memory deficits (p<0.05) in the third post-injury week. Between 6 and 72 h, blood-brain barrier breakdown, extensive traumatic axonal injury in the subcortical white matter and thalamus, and focal areas of neurodegeneration in the cortex and hippocampus were observed in both hemispheres of the injured brain. At 8 to 18 days post-injury, reactive astrocytosis in the cortex, axonal degeneration in the subcortical white matter tracts, and degeneration of neuronal cell bodies and processes in the thalamus of both hemispheres were observed; however, cortical volumes were not different between un-injured and injured rat brains. These data suggest that diffuse TBI in the immature rat can lead to ongoing degeneration of both cell soma and axonal compartments of neurons, which may contribute, in part, to the observed sustained cognitive deficits.

Long-term alterations in mu, delta and kappa opioidergic receptors following middle cerebral artery occlusion in mice

Alterations in the opioidergic system may play a role in the molecular mechanisms underlying neurochemical responses to cerebral ischaemia. The present study aimed to determine the delayed expression of mu, delta and kappa opioid receptors, following 1, 2, 7, and 30 days of middle cerebral artery occlusion (MCAO) in mice. Using quantitative autoradiography, we highlighted significant decreases in mu, delta and kappa opioid receptor expression in ipsilateral cortices from day 1 post-MCAO. Moreover, in contralateral nucleus lateralis thalami pars posterior, ipsi- and contralateral nucleus medialis dorsalis thalami, and ipsilateral substantia nigra, pars reticulata (SNr), kappa receptors were increased; mu receptor densities were decreased in nucleus ventralis thalami, pars posterior (VThP), and SNr. delta-Binding sites were increased in the striatum on day 30 post-MCAO. The alterations in opioid receptors in cortical infarcts were correlated with strong histological damage. Further reductions in opioid receptor densities in cortical infarcts were observed at later time points. In subcortical brain regions, opioid receptor densities were also altered but no histological damage was seen, except in the VThP, in which cell density was increased on day 30. Delayed reductions in opioid receptor densities in the infarct appeared as the continuation of the early processes previously demonstrated. However, changes in subcortical opioid receptor expression may correlate with neuronal alterations in remote brain regions. Changes in opioidergic receptor expression in these regions may be involved in the long-term consequences of stroke and could be used as biomarker of neuronal alteration through the use of imaging techniques in the clinic.

Acute and delayed neuroinflammatory response following experimental penetrating ballistic brain injury in the rat

Background

Neuroinflammation following acute brain trauma is considered to play a prominent role in both the pathological and reconstructive response of the brain to injury. Here we characterize and contrast both an acute and delayed phase of inflammation following experimental penetrating ballistic brain injury (PBBI) in rats out to 7 days post-injury.

Methods

Quantitative real time PCR (QRT-PCR) was used to evaluate changes in inflammatory gene expression from the brain tissue of rats exposed to a unilateral frontal PBBI. Brain histopathology was assessed using hematoxylin and eosin (H&E), silver staining, and immunoreactivity for astrocytes (GFAP), microglia (OX-18) and the inflammatory proteins IL-1β and ICAM-1.

Results

Time course analysis of gene expression levels using QRT-PCR indicated a peak increase during the acute phase of the injury between 3–6 h for the cytokines TNF-α (8–11 fold), IL-1β (11–13 fold), and IL-6 (40–74 fold) as well as the cellular adhesion molecules VCAM (2–3 fold), ICAM-1 (7–15 fold), and E-selectin (11–13 fold). Consistent with the upregulation of pro-inflammatory genes, peripheral blood cell infiltration was a prominent post-injury event with peak levels of infiltrating neutrophils (24 h) and macrophages (72 h) observed throughout the core lesion. In regions of the forebrain immediately surrounding the lesion, strong immunoreactivity for activated astrocytes (GFAP) was observed as early as 6 h post-injury followed by prominent microglial reactivity (OX-18) at 72 h and resolution of both cell types in cortical brain regions by day 7. Delayed thalamic inflammation (remote from the primary lesion) was also observed as indicated by both microglial and astrocyte reactivity (72 h to 7 days) concomitant with the presence of fiber degeneration (silver staining).

Conclusion

In summary, PBBI induces both an acute and delayed neuroinflammatory response occurring in distinct brain regions, which may provide useful diagnostic information for the treatment of this type of brain injury.

Structural and functional recovery elicited by combined putrescine and aminoguanidine treatment after aspirative lesion of the fimbria-fornix and overlying cortex in the adult rat

Damage to the adult CNS often causes permanent deficits. Based on a lesion model of septohippocampal pathway aspiration in the rat, we attempted to promote neuronal cell survival and post-traumatic recovery by using a pharmacological treatment combining aminoguanidine and putrescine (AGP). The functional recovery was followed over 15 weeks before morphological analysis. AGP treatment produced a persistent attenuation (approximately 50%) of the lesion-induced hyperactivity, a reduction (approximately 60%) in the sensorimotor impairments and an improved performance in the water-maze task which did not, however, rely upon improved memory capabilities. AGP weakened the lesion-induced decrease in ChAT-positive neurons in the medial septum and the extent of thalamic retrograde necrosis (by approximately 30% in each case) and resulted in a partial cholinergic reinnervation of the dentate gyrus. These promising results support the idea that coadministration of putrescine and aminoguanidine might become a potent way to foster structural and functional recovery (or compensation) in the adult mammalian CNS after injury.

Penetrating ballistic-like brain injury in the rat: differential time courses of hemorrhage, cell death, inflammation, and remote degeneration

Acute and delayed cerebral injury was assessed in a recently developed rat model of a penetrating ballistic-like brain injury (PBBI). A unilateral right frontal PBBI trajectory was used to induce survivable injuries to the frontal cortex and striatum. Three distinct phases of injury progression were observed. Phase I (primary injury, 0-6 h) began with immediate (<5 min) intracerebral hemorrhage (ICH) that reached maximal volumetric size at 6 h (27.0 +/- 2.9 mm(3)). During Phase II (secondary injury, 6-72 h), a core lesion of degenerate neurons surrounding the injury track expanded into peri-lesional areas to reach a maximal volume of 69.9 +/- 6.1 mm(3) at 24 h. The core lesion consisted of predominately necrotic cell death and included marked infiltration of both neutrophils (24 h) and macrophages (72 h). Phase III (delayed degeneration, 3-7 days) involved the degeneration of neurons and fiber tracts remote from the core lesion including the thalamus, internal capsule, external capsule, and cerebral peduncle. Overall, different time courses of hemorrhage, lesion evolution, and inflammation were consistent with complementary roles in injury development and repair, providing key information about these mediators of primary, secondary, and delayed brain injury development. The similarities/differences of PBBI to other focal brain injury models are discussed.

Changes in neuronal connectivity after stroke in rats as studied by serial manganese-enhanced MRI

Loss of function and subsequent spontaneous recovery after stroke have been associated with physiological and anatomical alterations in neuronal networks in the brain. However, the spatiotemporal pattern of such changes has been incompletely characterized. Manganese-enhanced MRI (MEMRI) provides a unique tool for in vivo investigation of neuronal connectivity. In this study, we measured manganese-induced changes in longitudinal relaxation rate, R(1), to assess the spatiotemporal pattern of manganese distribution after focal injection into the intact sensorimotor cortex in control rats (n=10), and in rats at 2 weeks after 90-min unilateral occlusion of the middle cerebral artery (n=10). MEMRI data were compared with results from conventional tract tracing with wheat-germ agglutinin horseradish peroxidase (WGA-HRP). Distinct areas of the sensorimotor pathway were clearly visualized with MEMRI. At 2 weeks after stroke, manganese-induced changes in R(1) were significantly delayed and diminished in the ipsilateral caudate putamen, thalamus and substantia nigra. Loss of connectivity between areas of the sensorimotor network was also identified from reduced WGA-HRP staining in these areas on post-mortem brain sections. This study demonstrates that MEMRI enables in vivo assessment of spatiotemporal alterations in neuronal connectivity after stroke, which may lead to improved insights in mechanisms underlying functional loss and recovery after stroke.

Sensorimotor and cognitive deficits after transient middle cerebral artery occlusion in the mouse

Whereas behavioral impairments after stroke are increasingly studied in the rat, little is known about the long-term functional consequences of focal ischemia in the mouse. To address this issue, Swiss mice underwent transient (60 min) intraluminal occlusion of the middle cerebral artery (MCAo) or sham surgery. Sensorimotor (chimney, accelerating rotarod, pole, corner, adhesive removal and staircase tests) and cognitive (passive avoidance and Morris water maze) performances were regularly assessed during 1 month, after which the final histological lesion was measured. Motor coordination and balance, assessed by the chimney and rotarod tests, were transiently altered by MCAo. Moreover, bradykinesia was evidenced by the pole test. The most striking and long-lasting (1 month) sensorimotor deficits were postural asymmetries on the corner test, bilateral skilled forepaw reaching deficits on the staircase test and a contralateral sensorimotor impairment on the adhesive removal test. MCAo animals showed normal spatial learning abilities on the Morris water maze test, but they displayed learning deficits measured by the passive avoidance test. This latter deficit was significantly correlated with both cortical and striatal damage. Our findings demonstrate the usefulness of three tests that had never been reported in the mouse after ischemia: the adhesive removal, staircase and pole tests, which showed deficits 1 month after ischemia and should therefore constitute meaningful tools in mice for assessing both neuroprotective and regenerative therapies in stroke preclinical studies.

Injury severity determines Purkinje cell loss and microglial activation in the cerebellum after cortical contusion injury

Clinical evidence suggests that the cerebellum is damaged after traumatic brain injury (TBI) and experimental studies have validated these observations. We have previously shown cerebellar vulnerability, as demonstrated by Purkinje cell loss and microglial activation, after fluid percussion brain injury. In this study, we examine the effect of graded controlled cortical impact (CCI) injury on the cerebellum in the context of physiologic and anatomical parameters that have been shown by others to be sensitive to injury severity. Adult male rats received mild, moderate, or severe CCI and were euthanized 7 days later. We first validated the severity of the initial injury using physiologic criteria, including apnea and blood pressure, during the immediate postinjury period. Increasing injury severity was associated with an increased incidence of apnea and higher mortality. Severe injury also induced transient hypertension followed by hypotension, while lower grade injuries produced an immediate and sustained hypotension. We next evaluated the pattern of subcortical neuronal loss in response to graded injuries. There was significant neuronal loss in the ipsilateral cortex, hippocampal CA2/CA3, and laterodorsal thalamus that was injury severity-dependent and that paralleled microglial activation. Similarly, there was a distinctive pattern of Purkinje cell loss and microglial activation in the cerebellar vermis that varied with injury severity. Together, these findings emphasize the vulnerability of the cerebellum to TBI. That a selective pattern of Purkinje cell loss occurs regardless of the type of injury suggests a generalized response that is a likely determinant of recovery and a target for therapeutic intervention.

Delayed administration of deferoxamine reduces brain damage and promotes functional recovery after transient focal cerebral ischemia in the rat

The mechanisms underlying functional recovery after stroke are poorly understood. Brain-adaptive responses to the hypoxic stress elicited by ischemia could contribute to these mechanisms. Indeed, hypoxia-inducible factor-1 (HIF-1), one of the main transcriptional factors regulated by oxygen level, increases the expression of several beneficial genes such as erythropoietin, glucose transporter-1 and vascular endothelial growth factor. In order to strengthen the expression of these hypoxia-inducible factors, we administered deferoxamine, an iron chelator known to stabilize HIF-1alpha protein expression, and examined its effects on the functional deficits induced by ischemia. Anesthetized Sprague-Dawley rats were subjected to 60 min of intraluminal occlusion of the middle cerebral artery. Chronic deferoxamine treatment (300 mg/kg, s.c.), or its vehicle, started 24 h after ischemia and was continued bi-weekly until the animals were killed. Sensorimotor deficits were periodically assessed over 2 months, and at this end point, the lesion volume was determined by histology. Treatment with deferoxamine significantly decreased the size of brain damage (-28%) after ischemia and improved behavioral recovery. Indeed, neurological score and sensorimotor performances in the adhesive removal test recovered earlier in the deferoxamine-treated animals. Moreover, the long-lasting skilled forepaw reaching deficits were attenuated by deferoxamine. Although an antioxidant effect of deferoxamine cannot be excluded, the hypothesis that its beneficial effects could be mediated by an increase in HIF-1 target genes merits further investigations. Our data suggest that delayed administration of deferoxamine could represent an interesting therapeutical approach to treat focal cerebral ischemia.

Necrosis, apoptosis and hybrid death in the cortex and thalamus after barrel cortex ischemia in rats

Focal ischemia in the cerebral cortex results in acute and delayed cell death in the ischemic cortex and non-ischemic thalamus. We examined the hypothesis that neurons in ischemic and non-ischemic regions died from different mechanisms; specifically, we tested whether a mixed form of cell death containing both necrotic and apoptotic changes could be identified in individual cells. Focal barrel cortex ischemia in rats was induced by occlusion of small branches of the middle cerebral artery (MCA) corresponding to the barrel cortex, local blood flow was measured by quantitative autoradiography. Cell death was visualized by 2,3,5-triphenyltetrazolium chloride (TTC) staining, hematoxylin-eosin (H&E) staining, the terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and caspase-3 staining 1 to 10 days after the ischemia. Electron microscopy was used for ultrastructural examination. Cell death occurred in the ipsilateral cortex 24 h after ischemia, followed by selective neuronal death in the ventrobasal (VB) thalamus 3 days later. TUNEL positive neurons were found in these two regions, but with striking morphological differences, designated as type I and type II TUNEL positive cells. The type I TUNEL positive cells in the ischemic cortex underwent necrotic changes. The type II TUNEL positive cells in the thalamus and the cortex penumbra region represented a hybrid death, featured by concurrent apoptotic and necrotic alterations in individual cells, including marked caspase-3 activation, nuclear condensation/fragmentation, but with swollen cytoplasm, damaged organelles and deteriorated membranes. Cell death in the thalamus and the cortex penumbra were attenuated by delayed administration of the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone (Z-VAD-FMK). Our data suggest that TUNEL staining should be evaluated with morphological changes, the hybrid death but not typical apoptosis occurs in the penumbra region and non-ischemic thalamus after cerebral ischemia.

Epileptogenesis after experimental focal cerebral ischemia

Cerebrovascular diseases are one of the most common causes of epilepsy in adults, and the incidence of stroke-induced epileptogenesis is increasing as the population ages. The mechanisms that lead to stroke-induced epileptogenesis in a subpopulation of patients, however, are still poorly understood. Recent advances in inducing epileptogenesis in rodent focal ischemia models have provided tools that can be used to identify the risk factors and neurobiologic changes leading to development of epilepsy after stroke. Here we summarize data from models in which epileptogenesis has been studied after focal ischemia; photothrombosis, middle cerebral artery (MCA) occlusion with filament, and endothelin-1-induced MCA occlusion. Analysis of the data indicates that neurobiologic changes occurring during stroke-induced epileptogenesis share some similarities to those induced by status epilepticus or traumatic 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.

Functional recovery of neuronal activity in rat whisker-barrel cortex sensory pathway from freezing injury after transplantation of adult bone marrow stromal cells

The effect of transplantation of adult bone marrow stromal cells (MSCs) into the freeze-lesioned left barrel field cortex in the rat was investigated by measurement of local cerebral glucose utilization (lCMR(glc)) in the anatomic structures of the whisker-to-barrel cortex sensory pathway. Bone marrow stromal cells or phosphate-buffered saline (PBS) were injected intracerebrally into the boundary zone 1 h after induction of the freezing cortical lesion. Three weeks after surgery, the 2-[(14)C]deoxyglucose method was used to measure lCMR(glc) during right whisker stimulation. The volume of the primary necrotic freezing lesion was significantly reduced (P<0.05), and secondary retrograde degeneration in the left ventral posteromedial (VPM) thalamic nucleus was diminished in the MSC-treated group. Local cerebral glucose utilization measurements showed that the freezing cortical lesion did not alter the metabolic responses to stimulation in the brain stem trigeminal nuclei, but eliminated the responses in the left VPM nucleus and periphery of the barrel cortex in the PBS-treated group. The left/right (stimulated/unstimulated) lCMR(glc) ratios were significantly improved in both the VPM nucleus and periphery of the barrel cortex in the MSC-treated group compared with the PBS-treated group (P<0.05). These results indicate that MSC transplantation in adults may stimulate metabolic and functional recovery in injured neuronal pathways.

Growth arrest and DNA damage-inducible gene 153 increases transiently in the thalamus following focal cerebral infarction

The thalamus degenerates following cerebral infarction in the territory supplied by the middle cerebral artery (MCA), and apoptosis is suspected to be the mechanism of this phenomenon. The author studied the role of the growth arrest and DNA damage-inducible gene (GADD) 153 in this thalamic degeneration. The MCA was occluded in stroke-prone spontaneously hypertensive rats. The expression of GADD 153 and Bcl-2, and the release of cytochrome c from the mitochondria to cytosol, were examined in the thalamus until 7 days after ischemia using in situ hybridization, immunoblot, immunohistochemistry and RT-PCR analyses. Gadd153 mRNA expression and GADD153 protein increased transiently at 2, 3, 5 and 7 days, and at 3 and 5 days after ischemia. Bcl-2 mRNA expression and Bcl-2 protein decreased at 3 and 5 days. The release of cytochrome c from the mitochondria was detected at 5 days. These results suggest that increased GADD 153 suppresses Bcl-2 expression, which causes the release of cytochrome c from the mitochondria and leads to thalamic degeneration.

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.

Biphasic expression of activating transcription factor-3 in neurons after cerebral infarction

It has been demonstrated that some of immediate early genes such as c-Jun are induced immediately and transiently following focal cerebral ischemia. Here we newly characterize the activating transcription factor (ATF)-3 as a focal ischemia associated immediate early gene. Using in situ hybridization and immunohistochemistry, we compared the expression profile of ATF-3 with those of ATF-2 and c-Jun after middle cerebral artery (MCA) occlusion. Focal cerebral ischemia induced two temporal and spatial patterns of ATF-3 expression. Early and transient induction of ATF-3 mRNA was observed in the core and margins of the cortex immediately after MCA occlusion. Late-onset and prolonged expression of ATF-3 mRNA and its protein were specifically identified in the peri-infarct cortex and thalamus where neurons survive at least 1 month. The expression profiles of ATF-3 and c-Jun were virtually similar, but c-Jun expression was also observed in other regions of the brain in control rats. Expression of ATF-2 was ubiquitously seen in neuronal cells throughout the brain in normal rats, but was suppressed in ischemic regions. Double immunohistochemical labeling revealed concurrent expression of ATF-3 and phospho-c-Jun in neurons. We conclude that the transcription factor ATF-3 is a suitable marker of neurons subjected to ischemic insult directly and indirectly, and that cooperative works of ATF-3 and c-Jun may be crucial triggers of various transcriptional responses to the ischemic insult.

MR imaging of postischemic neuronal death in the substantia nigra and thalamus following middle cerebral artery occlusion in rats

The goal of this study was to investigate apparent diffusion coefficient (ADC) and T(2) relaxation time (T(2)) in the substantia nigra and thalamus after middle cerebral artery occlusion in rats. In the substantia nigra ipsilateral to infarct, ADC was significantly lower and T(2) was significantly higher on the third and fourth days, but they did not change significantly on the first, second, eighth and 15th days. In the ipsilateral thalamus, ADC and T(2) did not change significantly between the first and fourth days, but were significantly lower on the eighth and 15th days. This combination of MR findings suggested that secondary degeneration in the thalamus was different from that in the substantia nigra.

Behavioral deficits and recovery following transient focal cerebral ischemia in rats: glutamatergic and GABAergic receptor densities

The neurobiologic mechanisms underlying the recovery process following stroke are poorly understood. The present study investigated glutamatergic and gamma-amino butyric acid (GABA)-ergic receptor densities following experimental stroke in rats exposed to different environmental housing or pharmacologic interventions. About 2 days after transient (120 min) middle cerebral artery (MCA) occlusion, the rats were singly housed in standard cages or were moved to an enriched environment and treated for 10 days with either 0.9% NaCl or with the alpha(2)-adrenoceptor antagonist, atipamezole (1.0 mg/kg, s.c.). The limb-placing, foot-slip, and water-maze tests were used to assess behavioral deficits and recovery following ischemia. The rats were decapitated on day 25 after the operation and their brains were processed for [3H]MK-801, [3H]D,L,-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), [3H]kainate, and [3H]muscimol autoradiography. Receptor binding site densities were different between sham-operated rats and ischemic rats only in the lesion core and lateral ventroposterior thalamic nucleus. Ischemic rats housed in an enriched environment and treated with atipamezole had better performance in the limb-placing test. The deficit in the water-maze test was most pronounced in ischemic rats housed in standard cages. There were a number of correlations between the behavioral data and receptor binding densities in ischemic rats. For example, recovery in the limb-placing test correlated with [3H]AMPA receptor binding sites in the contralateral frontal cortex (r=0.616, P<0.05), hindlimb cortex (r=0.649, P<0.05), and parietal cortex (r=0.674, P<0.05) in ischemic rats housed in an enriched environment. There were similar correlations between limb-placing recovery and [3H]kainate binding sites in the contralateral cortices in ischemic rats housed in standard cages. In addition, there were particularly strong clustered correlations between swimming speed in the water-maze test and [3H]AMPA receptor binding sites in the hippocampal subregions in the ischemic rats housed in an enriched environment. The present results suggest that transient focal cerebral ischemia does not induce significant long-term changes in glutamatergic and GABAergic receptors in areas remote from the infarct area. The correlational data, however, suggest an important role for the contralateral cortex in the behavioral outcome and maintenance of the recovered state of ischemic rats, depending on housing conditions. In addition, attenuation of spatial learning deficits observed in ischemic rats housed in an enriched environment might be due to an increase in the swimming speed through hippocampal AMPA receptor-mediated mechanisms.

Thalamic neuron apoptosis emerges rapidly after cortical damage in immature mice

In adults and children, head trauma can have long-term neuropathological and functional consequences. The thalamus is a major site of remote neurodegeneration after cortical damage in adult humans and experimental animals, but less is known about thalamic responses to cortical injury in the immature brain. This study introduces an in vivo model of axotomy/target deprivation-induced neuronal apoptosis in the dorsal lateral geniculate nucleus of the thalamus produced by unilateral ablation of the occipital cortex in the immature mouse. We specifically examined whether occipital cortex ablation in the immature brain causes apoptotic death of projection neurons in the dorsal lateral geniculate nucleus. After unilateral occipital cortex aspiration, 10-day-old C57BL/6 mice were recovered for up to 28 days. Fluorogold-prelabeled thalamocortical projection neurons were apoptotic at 36-48 h after ablation. The structural progression of apoptosis in the immature lateral geniculate nucleus reveals typical chromatolytic morphology by 18-24 h, followed by cytoplasmic shrinkage and chromatin condensation characteristic of end-stage apoptosis after 36-48 h. Electron microscopy confirmed the presence of apoptosis. This study shows internucleosomal DNA fragmentation and expression of cleaved caspase-3 occurs rapidly, being noted first at 18 h, well before the peak of apoptotic cell death occurring at 36 h after cortical damage in the immature brain. From these data we suggest that axotomy/target deprivation-induced cell death in the immature brain may: (1) differ from that previously reported in adult mice with respect to the time required for progression to cell death; (2) be mediated by caspase-3 activation.

Thalamic retrograde degeneration in the congenitally hydrocephalic rat is attributable to apoptotic cell death

Congenitally hydrocephalic HTX rats develop ventricular dilatation with extensive damage of the cerebral white matter. Recently, we have reported that neuronal cell death also occurs in the thalamus of HTX rats. To investigate the mechanism underlying this thalamic degeneration in these animals, we carried out a histopathological study of the brain at different phases of postnatal development. Eosinophilic neurons with condensed chromatin or fragmented nuclei were observed in the thalamus from postnatal day 17 onward. The incidence of cell death in the thalamus increased with the progression of hydrocephalus. Ultrastructurally, thalamic neurons occasionally had apoptotic features including nuclear chromatin condensation and marginalization. Immunohistochemically, single-stranded DNA-positive neuronal nuclei were found in the thalamus. They were also positively stained with the TUNEL method. Marked loss of myelin and axons with many TUNEL-positive oligodendrocytes were found in the cerebral white matter. These findings suggest that the neuronal cell death observed in the thalamus in hydrocephalic HTX rats is retrograde degeneration due to extensive damage of axons in the cerebral white matter and that the thalamic retrograde degeneration is attributable to apoptotic cell death.

Non-invasive induction of focal cerebral ischemia in mice by photothrombosis of cortical microvessels: characterization of inflammatory responses

In this study, we adapted the original rat photothrombosis model of Watson et al. (Ann Neurol 17 (1985) 497) for use in mice by refining the application route of the dye, illumination and stereotactic parameters. After intraperitoneal injection of the photosensitive dye Rose bengal, subsequent focal illumination of the brain with a cold light source through the intact skull led to focal cortical infarcts of reproducible size, location and geometry. Cresyl violet histology displayed well-demarcated infarcts that matured with time in a predictable manner. Microglial responses, as assessed by immunocytochemistry, against F4/80 and CD11b antigens were rapid and complete at the infarct site, but delayed and incomplete in degenerating fiber tracts and ipsilateral thalamic nuclei. In contrast to the rat, where the expression of CD4 and CD8 antigens discriminate distinct subpopulations of lesion-associated phagocytes, the expression of both markers was low to absent in the mouse model. In both rats and mice, cerebral photothrombosis shares essential inflammatory responses with focal ischemia induced by middle cerebral artery occlusion. It may provide a useful model to study functional aspects of lesion-associated and remote molecular responses in transgenic mice.

Stroke induces widespread changes of gene expression for glial cell line-derived neurotrophic factor family receptors in the adult rat brain

Gene expression for glial cell line-derived neurotrophic factor (GDNF) family ligands and receptors was analyzed with in situ hybridization after two focal ischemic insults of different severities. Focal ischemia was induced in rats by either 30 min or 2 h of middle cerebral artery occlusion (MCAO), causing damage to the striatum only, or involving also the parietal cortex, respectively. We found modest, transient elevation of GDNF mRNA in the dentate granule cell layer. In addition, the number of GDNF mRNA-expressing cells increased in the cortex and striatum after 2 h or 30 min of MCAO, respectively. No changes of neurturin or persephin mRNA expression were detected. Both c-Ret and GFRalpha1 mRNA levels were markedly increased in the ipsilateral cortex outside the ischemic lesion at 6-24 h after the 2-h insult, whereas GFRalpha2 expression was decreased in cortical areas both within and outside the lesion. Similar increases of c-Ret and GFRalpha1 mRNA levels were detected in the striatum, and to a lesser extent, in the cortex following 30 min of MCAO. The 2-h insult also gave rise to transient increases of c-Ret and GFRalpha1 mRNA in hippocampal subregions. Thirty minutes and 2 h of MCAO lead to elevated c-Ret, and GFRalpha1 or GFRalpha2 mRNA expression, respectively, in the ipsilateral ventroposterolateral thalamic nucleus. Both insults induced increased levels of GFRalpha1 mRNA in the subventricular zone of the lateral ventricle. Our data indicate major changes of GDNF family signaling in the forebrain, regulated mainly through altered receptor levels, in the post-ischemic phase. These changes could enhance neuroprotective and neuroregenerative responses both to endogenous and exogenous GDNF ligands.

Differentially altered cerebral metabolism in ischemic rats by alpha2-adrenoceptor blockade and its relation to improved limb-placing reactions

The selective alpha2-adrenoreceptor antagonist, atipamezole, improves behavioural performance of rats subjected to focal cerebral ischemia. The aim of the present study was to investigate whether the facilitatory effect of atipamezole on behaviour is related to altered neuronal activity in specific brain areas. The right middle cerebral artery of rats was occluded for 120 min using the intraluminal filament method. Starting on day 2 after induction of ischemia, atipamezole (1mg/kg, s.c.) or 0.9% NaCl was administered to ischemic or sham-operated rats once a day 30 min before the limb-placing test. [14C]Deoxyglucose ([14C]DG) uptake was used to measure neuronal activity 30 min after atipamezole or 0.9% NaCl administration on day 6 after ischemia. Ischemia induced a significant decrease in [14C]DG uptake in several cortical areas ipsilateral and contralateral to the lesion, in the ipsilateral thalamus, and bilaterally in the cerebellum and spinal cord. Administration of atipamezole normalised [14C]DG uptake particularly in the cerebellum and spinal cord both in sham-operated and ischemic rats and to a lesser extent in the thalamus in sham-operated rats. The pattern of altered cerebral [14C]DG uptake following alpha2-adrenoceptor blockade suggests that plasticity in the cerebellum and spinal cord contributes to the improved performance of ischemic rats in tests assessing tactile/proprioceptive limb-placing reactions.

Neuronal injury and loss after traumatic brain injury: time course and regional variability

We have examined regional neuronal injury after traumatic brain injury using Fluoro-Jade, an acidic dye that exhibits a marked affinity for both the degenerating neuronal cell body and its processes and have determined the extent to which early injury corresponds to regional patterns of neuronal loss. Rats (n=45) were subjected to lateral fluid percussion brain injury and euthanized at 3 h to 28 days post injury. Complementary Fluoro-Jade, silver impregnation methods and TUNEL were used to assess neuronal injury. Neuronal loss was evaluated in sections immunostained for NeuN, a neuronal specific nuclear protein. Overt neuronal cell loss was evident by 7 days post injury in the cortex, hippocampus and thalamus. Injured neurons were apparent in the ipsilateral cortex bordering the impact site, hippocampus (CA1 and dentate), thalamus, and vermis of the cerebellum as early as 3 h post injury. Degenerating neurons were maximal by 1 and 3 days in the cortex and hippocampus, by 3 and 7 days in the cerebellum, and by 7 days in the thalamus. The regional distribution of Fluoro-Jade-labeled neurons corresponded to a similar pattern of silver and TUNEL staining. Together, these findings demonstrate a regionally specific temporal pattern of neuronal injury that results in overt neuronal cell loss within both cortical and subcortical regions.

57Co SPECT, 99mTc-ECD SPECT, MRI and neuropsychological testing in senile dementia of the Alzheimer type

Inflammatory mechanisms contribute to the pathophysiology of senile dementia of the Alzheimer type (sDAT). Previous studies have shown that 57Co single photon emission computed tomography (SPECT) is able to visualize inflammatory lesions, probably by means of the final common pathway of Ca2+ homeostasis disturbance in both neuronal degeneration and inflammation. The aims of this study were: (1) to detect 57Co SPECT changes in sDAT patients; (2) to correlate these findings with those of conventional neuroimaging techniques and neuropsychological testing (NPT); and (3) to compare 57Co SPECT findings in sDAT patients with those in other types of dementia. Six patients suffering from probable sDAT were included and compared with four patients suffering from other types of dementia. All patients had a magnetic resonance imaging (MRI) scan, NPT, 57Co and 99mTc-ethyl cysteinate dimer (ECD) SPECT scan. Perfusion SPECT images were semiquantitatively evaluated by comparison with an age-matched normal database, while 57Co SPECT scans were assessed qualitatively. MRI and 99mTc-ECD SPECT scans yielded conclusive results with regard to the exclusion of other pathologies and the confirmation of the diagnosis. Using visual analysis, 57Co SPECT scans were unable to show any regional raised uptake, irrespective of the disorder, depth or extent of the perfusion defects, presence of atrophy on MRI or the results of NPT.

Cell death is prevented in thalamic fields but not in injured neocortical areas after permanent focal ischaemia in mice overexpressing the anti-apoptotic protein Bcl-2

Previous studies have suggested that various apoptotic-related proteins could be involved in the death process induced by cerebral ischaemia. In order to further clarify their role and examine how the anti-apoptotic protein Bcl-2 could influence this process, the time-course of mRNA expression of various cell death genes was studied from 1 to 14 days following permanent occlusion of the middle cerebral artery in wild-type (WT) and Bcl-2 transgenic mice, within and outside the area of infarction. No differences of the infarct sizes were observed between the two groups of mice, showing that the extent of neuronal injury could not have been lowered by the Bcl-2 transgene. Seven days after the ischaemic insult, the mRNA expression of the cell death gene effector cpp32 was dramatically upregulated in the penumbra of WT and Bcl-2 transgenic mice. Interestingly, the cpp32 transcript was markedly induced from 3 days in the ipsilateral thalamus of the two groups of mice. However, apoptotic bodies were observed in the thalamic field of WT but not transgenic mice. This suggests that cpp32 mRNA may be induced in an attempt to kill the injured cells and, in contrast to the penumbra, cell death in the thalamus may be prevented in Bcl-2 transgenic mice. Based on these results, the pathophysiological mechanisms that underly neuronal damage following ischaemia need consideration in order to evaluate the extent of neuroprotection that may be afforded by the Bcl-2 anti-apoptotic protein. Although the present study does not confirm previous data showing a protective role of Bcl-2 in neocortical infarcted areas, it suggests that anti-apoptotic therapies may constitute a possible treatment for areas of the brain remote from those directly affected by ischaemia.

Overexpression of Bcl-2 is neuroprotective after experimental brain injury in transgenic mice

The cell death regulatory protein, Bcl-2, has been suggested to participate in the pathophysiology of various neurological disorders, including traumatic brain injury (TBI). The cognitive function and histopathologic sequelae after controlled cortical impact brain injury were evaluated in transgenic (TG) mice that overexpress human Bcl-2 protein (n = 13) and their wild type (WT) controls (n = 9). Although brain-injured Bcl-2 TG mice exhibited similar posttraumatic deficits in a Morris water maze (MWM) test of spatial memory as their WT counterparts at 1 week postinjury, the preinjury learning ability of Bcl-2 TG mice was impaired significantly compared with their WT littermates (P < 0.05). In contrast, histopathologic analysis revealed significantly attenuated tissue loss in the ipsilateral hemisphere (p < 0.01) and decreased tissue loss in ipsilateral hippocampal area CA3 (P < 0.001) and the dentate gyrus (P < 0.01) in brain-injured Bcl-2 TG mice compared with brain-injured WT mice. Immunohistochemical evaluation of glial fibrillary acidic protein also revealed a significant decrease in reactive astrocytosis in the ipsilateral dorsal thalamus (P < 0.05) and the ventral thalamus (P < 0.01) in brain-injured Bcl-2 TG mice. These results suggest that overexpression of Bcl-2 protein may play a protective role in neuropathologic sequelae after TBI.

Heterogeneity of the microglial response in photochemically induced focal ischemia of the rat cerebral cortex

This study examined microglial responses after photochemically induced focal ischemia of the rat cortex. Microglial activation exceeded by far the area of the ischemic lesion. Based on morphological criteria and expression of immunomolecules three distinct patterns could be distinguished. (1) In the infarct core and the border zone microglia transformed into phagocytes and removed debris with the aid of hematogeneous macrophages. Exclusively in this area a subpopulation of CD8+ microglia/mnacrophages was present. (2) In secondarily degenerating fibre tracts and nuclei with retrograde neuronal loss, microglia were activated with a delay of days and showed increased expression of complement receptor 3, major histocompatibility complex class II and CD4 molecules, but only low phagocytic activity. (3) In remote ipsilateral cortex devoid of neuronal damage, microglia transiently responded by increased complement receptor 3, but not by major histocompatibility complex class II and CD4 expression. Furthermore, the total number of microglia had increased. This remote response could partly be blocked by dizocilpine maleate, a non-competitive N-methyl-D-aspartate receptor antagonist, implicating a functional role of spreading depression. Taken together, our findings point to a tight and differential regulation of microglial responses in the infarct core, degenerating fibre tracts and remote brain regions without neuronal loss.

Spatial cognitive performance after chronic focal cerebral ischemia in rats

The authors investigated the impairment of spatial cognitive performance in rats with chronic focal cerebral ischemia using the Morris maze, and examined the correlation between this deficit and other behavioral changes, such as step-through latency in passive avoidance task and neurologic score, or pathologic changes. The authors focused on the relationship between the damaged brain region and the affected spatial learning behavior. In the Morris maze task at 8 weeks after the middle cerebral artery (MCA) occlusion, escape latency, swimming path length, and percent time spent in goal quadrant of MCA-occluded rats were impaired, which correlated with shrinkage of the cortex involving parietal cortex, but not caudate-putamen (CP). Middle cerebral artery-occluded rats were also impaired in the percent time spent in the outermost annulus and in turning ratio, which significantly correlated with shrinkage of CP, but not cortex. Middle cerebral artery-occluded rats showed two typical search patterns; one was almost the same as that of sham-operated and intact rats, and the other was round shaped and had less turning behavior. Both subgroups of MCA-occluded rats divided by turning ratio had significantly impaired spatial cognitive performance, which indicates that the changes of search pattern did not affect cognitive performance in the Morris maze. The neurologic deficits recovered gradually after MCA occlusion, which correlated with shrinkage of cortex and CP. The step-through latency in passive avoidance task of the MCA-occluded rats was impaired, but did not correlate with shrinkage of cortex or CP. These results suggest that the long-term spatial cognitive deficit of MCA-occluded rats is in part associated with damage to the cortex involving parietal cortex, and that the change of search strategies is associated with damage to CP. These findings support the idea that different brain regions contribute differently to cognitive performance, search strategies, avoidance task, and neurologic performance, and may be useful for estimating the related region of functional disorder in the clinical situation.