Hypoperfusion and vasoreactivity in the thalamus and cerebellum after stroke

Increased Accumulation of 18F-FDG Incidentally Observed in Hyperacute Cerebral Infarction

ABSTRACT

A 75-year-old man with lung cancer undertook an 18F-FDG PET/CT for staging. He presented neurological symptoms immediately after the 30-minute scan. An emergent MRI study revealed hyperacute cerebral infarction with occlusion of a left MCA branch. At PET/CT, an increased 18F-FDG uptake was observed in the corresponding areas of infarction. In literature, acceleration of compensatory anaerobic glycolysis has been proposed as 1 of the causes of increased uptake in the penumbra of acute cerebral infarction, and a similar process was hypothesized in this case. In addition, a decreased 18F-FDG uptake in the ipsilateral thalamus was noted on the PET/CT images.

Diaschisis revisited: quantitative evaluation of thalamic hypoperfusion in anterior circulation stroke

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CT perfusion reveals thalamic hypoperfusion in acute anterior circulation stroke.

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This indirect phenomenon is referred to as ipsilateral thalamic diaschisis (ITD).

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Quantitative analysis indicates that ITD is a non-binary phenomenon.

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ITD is associated with lesion extent and involvement of the lentiform nucleus.

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Stroke outcome was not associated with ITD parameters.

Purpose

Ipsilateral thalamic diaschisis (ITD) refers to the phenomenon of thalamic hypoperfusion or hypometabolism due to a distant cerebral injury. To further investigate the characteristics and spectrum of ITD, we analyzed quantitative measurements of thalamic hypoperfusion in acute anterior circulation stroke.

Methods

We selected consecutive patients with large-vessel occlusion (LVO) anterior circulation stroke and available CT perfusion (CTP) examination on admission who underwent endovascular thrombectomy. Thalamic perfusion parameters on CTP were tested between ipsi- and contralesional thalamus and ischemic territory. Values were compared with thresholds from CTP analysis software. Associations of thalamic perfusion parameters with acute imaging and clinical data were determined in uni- and multivariate logistic regression analyses.

Results

Ninety-nine patients were included. All perfusion parameters indicated significant non-ischemic hypoperfusion of the thalamus, not reaching the levels of ischemia in the middle cerebral artery territory due to LVO (all p < 0.002). Multiple perfusion parameters exhibited significant association with ischemic lesion extent (relative cerebral blood flow [CBF]: β =  − 0.23, p = 0.022; Δtime to drain: β = 0.33, p < 0.001; ΔTmax: β =  − 0.36, p < 0.001) and involvement of the Lentiform Nucleus (Δmean transit time: β = 0.64, p = 0.04; Δtime to drain: β = 0.81, p = 0.01; ΔTmax: β =  − 0.82, p = 0.01). Symptom severity on admission exhibited minor significant association with reduction of thalamic CBF in uncorrected analysis (Odds ratio: 0.05, p = 0.049), but short- and long-term outcomes were unaffected by perfusion status. ITD reached guideline-based software-threshold levels in only one patient.

Conclusions

ITD in acute stroke is a non-binary phenomenon affected by lesion extent and involvement of the lentiform nucleus. We found uncorrected association of ITD with early clinical presentation, but no association with short- or long-term outcome was evident. Relevant misclassification of ITD by guideline-based CTP software was not indicated, which needs further dedicated testing.

Relationship Between Olfactory Disturbance After Acute Ischemic Stroke and Latent Thalamic Hypoperfusion

Odor detection, recognition, and identification were assessed in 19 acute ischemic stroke patients who had no magnetic resonance imaging-detectable thalamic lesions but in whom technetium-99m ethyl cysteinate dimer single photon emission tomography revealed thalamic hypoperfusion. Although these patients were unaware of reduced olfactory function, they exhibited significantly lower scores in tests for odor identification and recognition threshold as compared with 9 ischemic stroke controls that had normal thalamic hypoperfusion. However, absolute odor detection thresholds were similar in the 2 groups. These results demonstrate the usefulness of cerebral perfusion scintigraphy in assessing sensory loss after ischemic stroke and provide further evidence for the role of the thalamus in olfaction.

Characterizing ipsilateral thalamic diaschisis in symptomatic cerebrovascular steno-occlusive patients

The clinical significance of ipsilateral thalamic diaschisis (ITD) occurring after stroke is unknown. To characterize ITD, we investigate its hemodynamic, structural, and clinical implications. A single-institution prospective cross-sectional study was conducted using 28 symptomatic cerebrovascular steno-occlusive patients undergoing both BOLD-CVR and Diamox-challenged 15(O)-H2O-PET. Follow-up was at least three months. In addition, 15 age-matched healthy subjects were included. ITD was diagnosed based on a BOLD-CVR thalamic asymmetry index (TAI) > +2 standard deviations from healthy subjects. Cerebral blood flow differences were assessed using a PET-based TAI before and after Diamox challenge. Thalamic volume masks were determined using Freesurfer. Neurological status at symptom onset and after three months was determined with NIHSS and mRS scores. ITD was diagnosed in 15 of 28 (57%) patients. PET-TAI before and after Diamox challenge were increased in patients with ITD, indicating an ipsilateral thalamic blood flow decrease. Patients with ITD exhibited a marked ipsilateral thalamic volume decrease as compared to patients without ITD and healthy subjects. Furthermore, patients with ITD had worse NIHSS and mRS at symptom onset and after three months follow-up, even after adjustment for stroke volume. The presence of ITD is characterized by thalamic volume reduction, reduced thalamic blood flow, and worse neurological performance unrelated to stroke volume.

Thalamic diaschisis following perinatal stroke is associated with clinical disability

BACKGROUND

Perinatal stroke causes most hemiparetic cerebral palsy and leads to lifelong disability. Understanding developmental neuroplasticity following early stroke is increasingly translated into novel therapies. Diaschisis refers to alterations brain structures remote from, but connected to, stroke lesions. Ipsilesional thalamic diaschisis has been described following adult stroke but has not been investigated in perinatal stroke. We hypothesized that thalamic diaschisis occurs in perinatal stroke and its degree would be inversely correlated with clinical motor function.

METHODS

Population-based, controlled cohort study. Participants were children (<19 years) with unilateral perinatal stroke (arterial ischemic stroke [AIS] or periventricular venous infarction [PVI]), anatomical magnetic resonance imaging (MRI) >6 months of age, symptomatic hemiparetic cerebral palsy, and no additional neurologic disorders. Typically developing controls had comparable age and gender proportions. T1-weighted anatomical scans were parcellated into 99 regions of interest followed by generation of regional volumes. The primary outcome was thalamic volume expressed as ipsilesional (ILTV), contralesional (CLTV) and thalamic ratio (CLTV/ILTV). Standardized clinical motor assessments were correlated with thalamic volume metrics.

RESULTS

Fifty-nine participants (12.9 years old ±4.0 years, 46% female) included 20 AIS, 11 PVI, and 28 controls. ILTV was reduced in both AIS and PVI compared to controls (p < .001, p = .029, respectively). Ipsilesional thalamic diaschisis was not associated with clinical motor function. However, CLTV was significantly larger in AIS compared to both controls and PVI (p = .005, p < .001, respectively). CLTV was inversely correlated with all four clinical motor assessments (all p < .003).

CONCLUSION

Bilateral thalamic volume changes occur after perinatal stroke. Ipsilesional volume loss is not associated with clinical motor function. Contralesional volume is inversely correlated with clinical motor function, suggesting the thalamus is involved in the known developmental plasticity that occurs in the contralesional hemisphere after early unilateral injury.

Review : Progesterone and Recovery after Traumatic Brain Injury: An Overview

After traumatic brain injury (TBI), female animals often show better cognitive and behavioral recovery than male animals. In female animals, this advantage is conferred by higher levels of systemic progesterone at the time of injury. In rats, postmortem examination of brain tissue reveals that pseudo-pregnant female rats (high progesterone, low estrogen) have virtually no cerebral edema compared with male rats and low- progesterone-state normal cycling female rats after TBI. Progesterone injections can also eliminate cerebral edema in brain-injured male rats. Sex differences in the outcome of TBI highlight the importance of consid ering the timing of therapy and hormonal fluctuations in developing safe and effective treatments for CNS injury. NEUROSCIENTIST 4:435-442, 1998

Effects of high-fat diet on neuronal damage, gliosis, inflammatory process and oxidative stress in the hippocampus induced by transient cerebral ischemia

In this study, we investigated the effects of a normal diet (ND) and high-fat diet (HFD) on delayed neuronal death in the gerbil hippocampal CA1 region after transient cerebral ischemia. In the HFD-fed gerbils, ischemia-induced hyperactivity was significantly increased and neuronal damage was represented more severely compared to the ND-fed gerbils. Ischemia-induced glial activation was accelerated in the HFD-fed gerbils. Cytokines including interleukin-2 and -4 were more sensitive in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. Additionally, we found that decreased 4-HNE and SODs immunoreactivity and protein levels in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. These results indicate that HFD may lead to the exacerbated effects on ischemia-induced neuronal death in the hippocampal CA1 region after ischemia-reperfusion. These effects of HFD may be associated with more accelerated activations of glial cells and imbalance of pro- and anti-inflammatory cytokines and/or antioxidants after transient cerebral ischemia.

Mesenchymal stem cells improved the ultrastructural morphology of cerebral tissues after subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH) causes widespread disruption in the cerebral architecture.The process of SAH is complicated and many people lose their lives or become disabled after injury. Mesenchymal stem cells (MSCs) are considered as good candidate for repair of cerebral damage. The aim was to assess the ultrastructural changes in the rat cerebral tissue after intravenous transplantation of MSCs. Female Wistar rats (8 per group) weighing 275~300 g were assigned to control (SAH+PBS) and experimental groups (SAH+MSCs).The samples from middle cerebral arterial wall and parietal cerebral tissue were prepared for transmission electron microscopy (TEM) according to standard protocol. Fine architectures of the vessel wall, including the contraction of the inner layer, smooth muscle layer,as well as neural cells were observed after SAH. Cerebral arterial wall and cortex, including neuronal and glial cells were injured post SAH. But, administration of MSCs improved the structural integrity of cerebral tissues. Changes were much more balanced with their relative improvement in some areas. The role of MSCs for repairing the injured cerebral tissues post experimental SAH was approved by electron microscopy.

Type-1 interferons contribute to oxygen glucose deprivation induced neuro-inflammation in BE(2)M17 human neuroblastoma cells

BACKGROUND

Hypoxic-ischaemic injuries such as stroke and traumatic brain injury exhibit features of a distinct neuro-inflammatory response in the hours and days post-injury. Microglial activation, elevated pro-inflammatory cytokines and macrophage infiltration contribute to core tissue damage and contribute to secondary injury within a region termed the penumbra. Type-1 interferons (IFNs) are a super-family of pleiotropic cytokines that regulate pro-inflammatory gene transcription via the classical Jak/Stat pathway; however their role in hypoxia-ischaemia and central nervous system neuro-inflammation remains unknown. Using an in vitro approach, this study investigated the role of type-1 IFN signalling in an inflammatory setting induced by oxygen glucose deprivation (OGD).

METHODS

Human BE(2)M17 neuroblastoma cells or cells expressing a type-1 interferon-α receptor 1 (IFNAR1) shRNA or negative control shRNA knockdown construct were subjected to 4.5 h OGD and a time-course reperfusion period (0 to 24 h). Q-PCR was used to evaluate IFNα, IFNβ, IL-1β, IL-6 and TNF-α cytokine expression levels. Phosphorylation of signal transducers and activators of transcription (STAT)-1, STAT-3 and cleavage of caspase-3 was detected by western blot analysis. Post-OGD cellular viability was measured using a MTT assay.

RESULTS

Elevated IFNα and IFNβ expression was detected during reperfusion post-OGD in parental M17 cells. This correlated with enhanced phosphorylation of STAT-1, a downstream type-1 IFN signalling mediator. Significantly, ablation of type-1 IFN signalling, through IFNAR1 knockdown, reduced IFNα, IFNβ, IL-6 and TNF-α expression in response to OGD. In addition, MTT assay confirmed the IFNAR1 knockdown cells were protected against OGD compared to negative control cells with reduced pro-apoptotic cleaved caspase-3 levels.

CONCLUSIONS

This study confirms a role for type-1 IFN signalling in the neuro-inflammatory response following OGD in vitro and suggests its modulation through therapeutic blockade of IFNAR1 may be beneficial in reducing hypoxia-induced neuro-inflammation.

Apparent diffusion coefficient evaluation for secondary changes in the cerebellum of rats after middle cerebral artery occlusion

Supratentorial cerebral infarction can cause functional inhibition of remote regions such as the cerebellum, which may be relevant to diaschisis. This phenomenon is often analyzed using positron emission tomography and single photon emission CT. However, these methods are expensive and radioactive. Thus, the present study quantified the changes of infarction core and remote regions after unilateral middle cerebral artery occlusion using apparent diffusion coefficient values. Diffusion-weighted imaging showed that the area of infarction core gradually increased to involve the cerebral cortex with increasing infarction time. Diffusion weighted imaging signals were initially increased and then stabilized by 24 hours. With increasing infarction time, the apparent diffusion coefficient value in the infarction core and remote bilateral cerebellum both gradually decreased, and then slightly increased 3–24 hours after infarction. Apparent diffusion coefficient values at remote regions (cerebellum) varied along with the change of supratentorial infarction core, suggesting that the phenomenon of diaschisis existed at the remote regions. Thus, apparent diffusion coefficient values and diffusion weighted imaging can be used to detect early diaschisis.

Microglial activation milieu controls regulatory T cell responses

Although mechanisms leading to brain-specific inflammation and T cell activation have been widely investigated, regulatory mechanisms of local innate immune cells in the brain are only poorly understood. In this study, to our knowledge we show for the first time that MHC class II(+)CD40(dim)CD86(dim)IL-10(+) microglia are potent inducers of Ag-specific CD4(+)Foxp3(+) regulatory T cells (Tregs) in vitro. Microglia differentially regulated MHC class II expression, costimulatory molecules, and IL-10 depending on the amount of IFN-γ challenge and Ag dose, promoting either effector T cell or Treg induction. Microglia-induced Tregs were functionally active in vitro by inhibiting Ag-specific proliferation of effector T cells, and in vivo by attenuating experimental autoimmune encephalomyelitis disease course after adoptive transfer. These results indicate that MHC class II(+)CD40(dim)CD86(dim)IL-10(+) microglia have regulatory properties potentially influencing local immune responses in the CNS.

Altered functional connectivity of cognitive-related cerebellar subregions in well-recovered stroke patients

The cerebellum contains several cognitive-related subregions that are involved in different functional networks. The cerebellar crus II is correlated with the frontoparietal network (FPN), whereas the cerebellar IX is associated with the default-mode network (DMN). These two networks are anticorrelated and cooperatively implicated in cognitive control, which may facilitate the motor recovery in stroke patients. In the present study, we aimed to investigate the resting-state functional connectivity (rsFC) changes in 25 subcortical ischemic stroke patients with well-recovered global motor function. Consistent with previous studies, the crus II was correlated with the FPN, including the dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex, and the cerebellar IX was correlated with the DMN, including the posterior cingulate cortex/precuneus (PCC/Pcu), medial prefrontal cortex (MPFC), DLPFC, lateral parietal cortices, and anterior temporal cortices. No significantly increased rsFCs of these cerebellar subregions were found in stroke patients, suggesting that the rsFCs of the cognitive-related cerebellar subregions are not the critical factors contributing to the recovery of motor function in stroke patients. The finding of the disconnection in the cerebellar-related cognitive control networks may possibly explain the deficits in cognitive control function even in stroke patients with well-recovered global motor function.

Neuronal damage using fluoro-jade B histofluorescence and gliosis in the striatum after various durations of transient cerebral ischemia in gerbils

Ischemic damage occurs well in vulnerable regions of the brain, including the hippocampus and striatum. In the present study, we examined neuronal damage/death and glial changes in the striatum 4 days after 5, 10, 15 and 20 min of transient cerebral ischemia using the gerbil. Spontaneous motor activity was increased with the duration time of ischemia-reperfusion (I-R). To examine neuronal damage, we used Fluoro-Jade B (F-J B, a marker for neuronal degeneration) histofluorescence staining. F-J B positive cells were detected only in the 20 min ischemia-group, not in the other groups. In addition, we examined gliosis of astrocytes and microglia using anti-glial fibrillary acidic protein (GFAP) and anti- ionized calcium-binding adapter molecule 1 (Iba-1), respectively. In the 5 min ischemia-group, GFAP-immunoreactive astrocytes were distinctively increased in number, and the immunoreactivity was stronger than that in the sham-group. In the 10, 15 and 20 min ischemia-groups, GFAP-immunoreactivity was more increased with the duration of I-R. On the other hand, the immunoreactivity and the number of Iba-1-immunoreactive microglia were distinctively increased in the 5 and 10 min ischemia-groups. In the 15 min ischemia-group, cell bodies of microglia were largest, and the immunoreactivity was highest; however, in the 20 min ischemia-group, the immunoreactivity was low compared to the 15 min ischemia-group. The results of western blotting for GFAP and Iba-1 were similar to the immunohistochemical data. In brief, these findings showed that neuronal death could be detected only in the 20 min ischemia-group 4 days after I-R, and the change pattern of astrocytes and microglia were apparently different according to the duration time of I-R.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.

Vasoreactivity and peri-infarct hyperintensities in stroke

OBJECTIVE

It is unknown if impaired cerebral vasoreactivity recovers after ischemic stroke, and whether it compromises perfusion in regions surrounding infarct and other vascular territories. We investigated the regional differences in CO2 vasoreactivity (CO2 VR) and their relationships to peri-infarct T2 hyperintensities (PIHs), chronic infarct volumes, and clinical outcomes.

METHODS

We studied 39 subjects with chronic large middle cerebral artery territory infarcts and 48 matched controls. Anatomic and three-dimensional continuous arterial spin labeling imaging at 3-Tesla MRI were used to measure regional cerebral blood flow (CBF) and CO2 VR during normocapnia, hypercapnia, and hypocapnia in main arteries distributions.

RESULTS

Stroke patients showed a significantly lower augmentation of blood flow at increased CO2 but greater reduction of blood flow with decreased CO2 than the control group. This altered vasoregulatory response was observed both ipsilateral and contralateral to the stroke. Lower CO2 VR on the stroke side was associated with PIHs, greater infarct volume, and worse outcomes. The cases with PIHs (n = 27) had lower CBF during all conditions bilaterally (p < 0.0001) compared to cases with infarct only.

CONCLUSIONS

Perfusion augmentation is inadequate in multiple vascular territories in patients with large artery ischemic infarcts, but vasoconstriction is preserved. Peri-infarct T2 hyperintensities are associated with lower blood flow. Strategies aimed to preserve vasoreactivity after an ischemic stroke should be tested for their effect on long-term outcomes.

Task-evoked BOLD responses are normal in areas of diaschisis after stroke

OBJECTIVE

Cerebral infarction can cause diaschisis, a reduction of blood flow and metabolism in areas of the cortex distant from the site of the lesion. Although the functional magnetic resonance imaging (fMRI) blood oxygen level dependent (BOLD) signal is increasingly used to examine the neural correlates of recovery in stroke, its reliability in areas of diaschisis is uncertain.

DESIGN

The effect of chronic diaschisis as measured by resting positron emission tomography on task-evoked BOLD responses during word-stem completion in a block design fMRI study was examined in 3 patients, 6 months after a single left hemisphere stroke involving the inferior frontal gyrus and operculum.

RESULTS

The BOLD responses were minimally affected in areas of chronic diaschisis.

CONCLUSIONS

Within the confines of this study, the mechanism underlying the BOLD signal, which includes a mismatch between neuronally driven increases in blood flow and a corresponding increase in oxygen use, appears to be intact in areas of chronic diaschisis.

Intravenous administration of melatonin reduces the intracerebral cellular inflammatory response following transient focal cerebral ischemia in rats

We have previously shown that exogenous melatonin improves the preservation of the blood-brain barrier (BBB) and neurovascular unit following cerebral ischemia-reperfusion. Recent evidence indicates that postischemic microglial activation exaggerates the damage to the BBB. Herein, we explored whether melatonin mitigates the cellular inflammatory response after transient focal cerebral ischemia for 90 min in rats. Melatonin (5 mg/kg) or vehicle was given intravenously at reperfusion onset. Immunohistochemistry and flow cytometric analysis were used to evaluate the cellular inflammatory response at 48 hr after reperfusion. Relative to controls, melatonin-treated animals did not have significantly changed systemic cellular inflammatory responses in the bloodstream (P > 0.05). Melatonin, however, significantly decreased the cellular inflammatory response by 41% (P < 0.001) in the ischemic hemisphere. Specifically, melatonin effectively decreased the extent of neutrophil emigration (Ly6G-positive/CD45-positive) and macrophage/activated microglial infiltration (CD11b-positive/CD45-positive) by 51% (P < 0.01) and 66% (P < 0.01), respectively, but did not significantly alter the population composition of T lymphocyte (CD3-positive/CD45-positive; P > 0.05). This melatonin-mediated decrease in the cellular inflammatory response was accompanied by both reduced brain infarction and improved neurobehavioral outcome by 43% (P < 0.001) and 50% (P < 0.001), respectively. Thus, intravenous administration of melatonin upon reperfusion effectively decreased the emigration of circulatory neutrophils and macrophages/monocytes into the injured brain and inhibited focal microglial activation following cerebral ischemia-reperfusion. The finding demonstrates melatonin's inhibitory ability against the cellular inflammatory response after cerebral ischemia-reperfusion, and further supports its pleuripotent neuroprotective actions suited either as a monotherapy or an add-on to the thrombolytic therapy for ischemic stroke patients.

Minocycline modulates chemokine receptors but not interleukin-10 mRNA expression in hypoxic-ischemic neonatal rat brain

Hypoxic-ischemic (HI) brain injury in the perinatal period causes significant morbidity. Minocycline (MN) is a tetracycline derivative that has reduced brain injury in various animal models of neurodegeneration, including perinatal ischemia. To determine whether MN can modulate the expression of chemokine receptors and interleukin-10 (IL10) in a model of neonatal brain injury, we produced an HI insult to the right cerebral hemisphere (ipsilateral) of the 7-day-old rat (PD7) by right common carotid artery ligation and 2.25 hr of hypoxia in 8% oxygen. MN (45 mg/kg, i.p.) or vehicle (PBS) was injected twice: 2 days and immediately before the HI insult. At 0, 1, 3, and 24 hr and 14 days after HI, total RNA from the ipsilateral and contralateral (exposed to hypoxia only) hemispheres was extracted, reverse transcribed, and amplified with gene-specific primers using a semiquantitative RT-PCR for macrophage inflammatory protein-1alpha), interferon-inducible protein (IP-10), C-C chemokine receptor 5 (CCR5; MIP-1alpha receptor), C-X-C chemokine receptor 3 (CXCR3; IP-10 receptor), and IL10. We found that, in the ipsilateral hemisphere, a significant (P < 0.05) increase in MIP-1alpha, IP-10, CCR5, and CXCR3 mRNA levels was observed. MN treatment decreased mRNA levels for CCR5 and CXCR3. In contrast, the levels of antiinflammatory cytokine IL10 were markedly decreased as a result of HI insult. Treatment with MN, however, had no effect on IL10. We conclude that MN decreased proinflammatory chemokine receptor expression but had little or no influence on the expression of antiinflammatory cytokine IL10. These effects confirm the antiinflammatory effect of MN in neonatal HI brain injury.

Reduced regional cerebral blood flow in SPG4-linked hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) linked to the spastic gait gene 4 (SPG4) is controversial, as the "pure" form traditionally has been considered confined to the long axons of the spinal cord. However, recent immunolabeling experiments have demonstrated extensive Spastin expression in the cortex and striatum. This could indicate a more widespread neuropathology from mutations in the SPG4 gene than previously assumed. The aim of this study was therefore to ascertain the extent of cerebral involvement in SPG4 linked HSP by neuropsychological examination and measurement of the regional cerebral blood flow (rCBF) as an indirect marker of regional neuronal activity. Eighteen SPG4 patients and 18 matched control subjects were studied. Resting state rCBF was measured using Positron Emission Tomography (PET) and the (15)O-labelled water bolus technique and relative group differences were explored using Statistical Parametric Mapping (SPM 99). Neuropsychological assessment was performed using established and nationally validated tests (RH Basic Battery). Compared to healthy controls, the patient group had significantly decreased rCBF in the left fronto-temporal cortex (P<0.05), and more extensive changes were observed in a separate analysis of the most disabled individuals. The neuropsychological assessment revealed only significantly impaired recognition memory for faces. In summary, the findings support cerebral pathology in SPG4-linked HSP, although the decreased rCBF in fronto-temporal cortex was not associated with severe cognitive impairment.

Effects of MK-801 on nitrite and cGMP levels during focal cerebral ischemia in rats

Glutamate is a major excitatory neurotransmitter in the mammalian central nervous system and initiates the events leading to ischemic brain damage. Glutamate receptor antagonists are being used to reduce neuronal damage observed after hypoxia and ischemia. The glutamate receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo-(a,d)-cyclohepten-5,10-imine maleate (MK-801) crosses the blood-brain barrier readily and produces a non-competitive use-dependent blockade of the N-methyl-D-aspartate subtype of glutamate receptor. The aim of this study was to investigate effects of MK-801 administered before and just after the onset of ischemia in rats on nitrite and cyclic guanosine monophosphate (cGMP) levels. Focal cerebral ischemia in rats was produced by permanent occlusion of right middle cerebral artery (MCAO). Nitrite and cGMP levels were measured in both cortex and cerebellum at 0, 10, and 60 min following MCAO. The same parameters were measured in rats treated with MK-801 (0.5 mg/kg, i.p.) 30 min before or just after MCAO. Ipsilateral cortical nitrite levels were increased relative to contralateral cortex after MCAO. No significant changes were observed in cerebellum. The cGMP concentrations in both sides of the cortex and cerebellum were increased at 10 and 60 min compared with 0 min values. cGMP level in the ipsilateral cortex was higher than contralateral cortex, whereas the opposite was found for the cerebellum. MK-801 treatment before or just after MCAO decreased significantly nitrite and cGMP production. Our data indicate that MK-801 treatment before or just after focal ischemia prevents the increase in NO and cGMP production.

Tumor necrosis factor-alpha inhibits seizures in mice via p75 receptors

Brain inflammatory reactions have been described in various neurological disorders, including epilepsy. Although there is clear evidence that cytokines affect neuroglial functions and blood-brain barrier permeability, scarce information is available on the functional consequences of brain inflammation on seizures. We studied the role of tumor necrosis factor-alpha (TNF)-alpha and its p55 and p75 receptors in seizure modulation. We found that intrahippocampal injection of murine recombinant TNF-alpha potently inhibits seizure in mice while human recombinant TNF-alpha, which shows strong specificity for mouse p55 receptors, was ineffective. p75 receptors were detected in mouse hippocampal neurons, whereas p55 receptors were absent. Transgenic mice with a perturbed TNF-alpha system showed profound alterations in seizure susceptibility: astrocytic overexpression of TNF-alpha was associated with reduced seizures, whereas mice lacking TNF-alpha p75 or both p55 and p75, receptors showed prolonged seizures. Mice deficient in p55 receptor only showed reduced seizures; and both p75 and TNF receptor-associated factor 2 protein levels were upregulated in their hippocampi. Our findings show that increased brain levels of TNF-alpha result in significant inhibition of seizures in mice, and this action is mediated by neuronal p75 receptors. This evidence highlights a novel function of TNF-alpha in brain and indicates a new system for anticonvulsive intervention.

Calpain inhibitor inhibits p35-p25-Cdk5 activation, decreases tau hyperphosphorylation, and improves neurological function after spinal cord hemisection in rats

Aberrant calpain activation is a key mediator of neuron death. We examined the cell-permeable calpain inhibitor MDL28170 in the pathophysiological processes after spinal cord injury (SCI) including p35-p25- cyclin-dependent kinase-5 (Cdk5) activation, tau hyperphosphorylation, neuron cell death, calpain I activation, astrogliosis, and microglia activation. Our study showed that intrathecal administration of MDL28170 improved neurologic dysfunction, prevented neuron loss, decreased the number of apoptotic cells, and abated astrogliosis and microglia activation 7 days after spinal cord hemisection in rats. Reverse transcription polymerase chain reaction demonstrated calpain inhibition significantly attenuated the ratio of proapoptotic Bax/anti-apoptotic Bcl-2 mRNA in the lesion and penumbra after SCI. Calpain, the calcium-activated proteolytic enzyme, was found to digest p35 to its truncated product, p25. Moreover, abnormal Cdk5 activation by p25 and subsequent tau hyperphosphorylation triggers pathologic events leading to neurodegeneration and neurofibrillary tangles. We found p35-p25-Cdk5 activation and tau hyperphosphorylation in SCI, and then we showed that intrathecal MDL28170 treatment could diminish p35 truncation, and abrogate aberrant tau phosphorylation. Double labeling of calpain I and phosphorylated tau (AT8) in the same cells of spinal cord lesion further implicated pathogenesis of SCI. In conclusion, MDL28170 abated calpain I activation, inhibited apoptosis and neuron loss, quenched microglia and astrocyte activation, and significantly improved neurologic deficit one week after spinal cord hemisection. The neuroprotective mechanisms of calpain inhibitor in SCI could be attenuating upregulation of Bax/Bcl-2 ratio, preventing p35 truncation in the lesion and penumbra, and abrogating tau hyperphosphorylation.

Accelerated cerebral ischemic injury by activated macrophages/microglia after lipopolysaccharide microinjection into rat corpus callosum

In cerebral ischemic insults, activated inflammatory cells such as microglia and macrophages may be implicated in the pattern and degree of ischemic injury by producing various bioactive mediators. In the present study, we provide the evidence that activated microglia/macrophages accelerate cerebral ischemic injury by overexpression of inducible nitric oxide synthase (iNOS). To activate microglia/macrophages, a potent inflammation inducer lipopolysaccharide (LPS, 5 microg/5 microl) was microinjected into rat corpus callosum. Isolectin B4-positive microglia/macrophages were abundantly observed in ipsilateral hemisphere at 1 day after LPS injection. RT-PCR showed that LPS injection induced iNOS mRNA expression mostly in microglia/macrophages, peaking in intensity at 15 h after LPS injection. While ischemic injury was little evoked in control rats by 2-h middle cerebral artery occlusion (MCAO) followed by 3-h reperfusion, it was markedly increased in rats pre-injected with LPS 1 day before MCAO. However, no significant difference between control and LPS-pretreated groups was observed after 24-h reperfusion. The increased ischemic injury in LPS-treated rats was well correlated with iNOS level expressed over 3 orders of magnitude than in LPS-untreated rats. Immunohistochemical studies showed that iNOS- and nitrotyrosine (a peroxynitrite marker)-positive cells were prominent throughout the infarct area. NOS inhibitors aminoguanidine or N(G)-nitro-L-arginine, simultaneously injected with LPS, reduced the iNOS immunoreactivity and infarct volume, especially in penumbra regions. Total glutathione levels in ischemic regions were decreased more in LPS pre-injected rats than in control ones. Further defining the role of NO in cerebral ischemic insults would provide the rationale for new therapeutic strategies based on modulation of microglial and macrophageal NO production in the brain.

Transneuronal degeneration in patients with temporal lobe epilepsy: evaluation by MR imaging

The aim of this study was to assess the MR imaging findings of transneuronal degeneration of limbic system in the patients with temporal lobe epilepsy, and to detect the influence of surgery on the anatomy of the limbic system. Axial and coronal T1- and T2-weighted MR images were retrospectively analyzed in 34 patients with temporal lobe epilepsy, focusing on transneuronal degeneration. In 17 of the 34 patients, MR images were also analyzed after selective amygdalo-hippocampectomy. Atrophy of the fornix, mamillary body, mamillothalamic tract (MTT), and thalamus ipsilateral to the epileptic focus was demonstrated on MR images in 14.7, 17.6, 8.8, and 11.8% of the 34 patients, respectively. Focal hyperintensity of the thalamus was found on T2-weighted images in 8.8% of the 34 patients. In 17 patients who were evaluated before and after surgery, transneuronal degeneration was seen more frequently after surgery: fornix (11.8 vs 29.4%), mamillary body (11.8 vs 52.9%), MTT (5.9 vs 11.8%), and thalamus (11.8 vs 11.8%). Transneuronal degeneration of the limbic system is clearly demonstrated by MR imaging in patients with temporal lobe epilepsy, and surgical intervention induces transneuronal degeneration more frequently.

Time course of proliferation and elimination of microglia/macrophages in different neurodegenerative conditions

Ablation of the hindlimb area of the sensorimotor cortex produces degeneration in the cortex (invasive traumatic injury) and leads to retrograde and/or anterograde degeneration in the thalamus (non-invasive injury, distal reaction). This provides an useful model to study the proliferation and elimination of microglia/macrophages in different neurodegenerative conditions. Changes in the morphology, distribution and numbers of microglia in the affected cortex and thalamus were analyzed at various time points (12 h to 30 days) after injury. In parallel, proliferation was determined by immunocytochemistry for the proliferating cell nuclear antigen and cell death by the TUNEL method. Proliferation was an early event in the microglia/macrophage response (from 12 h in the cortex and from 2 days post-lesion in the thalamus) and persisted up to 30 days. The different microglia/macrophage phenotypes proliferated in a specific temporospatial pattern. In the lesioned cortex, early activation and proliferation of intrinsic microglia was accompanied, from the second post-lesion day, by monocyte entrance and proliferation of monocyte-derived cells. In contrast, accumulation of cells in the thalamus resulted from proliferation of intrinsic microglia, without apparent/significant monocytic recruitment. During the subsequent microglia/macrophages removal the majority of the cells in the cortex transformed into ameboid cells devoid of cell processes that progressively accumulated as fully-developed macrophages tissue within the lesion (3-14 days) ultimately migrating out to the meningeal connective tissue (14-30 days). Only some process-bearing cells, remaining in the cortical tissue bordering the lesion, underwent degeneration by 14-21 days post-lesion. In contrast, in the distal affected thalamic nuclei, microglial cell death occurred by 14-30 days post-lesion. Altogether, this study shows that both the origin and fate of microglia/macrophages depend on the nature of the lesion.

IGF-I and microglia/macrophage proliferation in the ischemic mouse brain

We have used a model of hypoxic-ischemic brain injury in adult male C57BL/6 mice to study insulin-like growth factor-I (IGF-I) and IGF-binding protein (IGFBP) expression in response to cerebral hypoxia-ischemia (H/I) in the adult mouse. A period of 20 min of H/I that resulted in histopathology in cortex, striatum, and thalamus was correlated with induction of mRNA for IGF-I, IGFBP-2, IGFBP-3, IGFBP-5, and glial fibrillary acidic protein (GFAP) by 4 days of recovery. Increased IGF-I mRNA was located within damaged regions and was surrounded by IGFBP-2 mRNA expression. The results of combined immunostaining/in situ hybridzation showed that the cells expressing IGFBP-2 mRNA were also GFAP-positive and comprised a subset of activated astrocytes immediately surrounding areas of damage. In contrast, staining within damaged regions showed high numbers of cells immunopositive for F4/80 and lectin B(4) indicative of microglia and macrophages but no cells immunopositive for the astrocytic proteins GFAP or S-100beta. Microglia/macrophages within the damaged areas expressed IGF-I mRNA and were also immunopositive for the proliferating cell nuclear antigen. To determine whether expression of IGF-I could contribute to proliferation of microglia, we treated purified cultures of adult brain microglia with IGF-I in the presence of (3)H-thymidine. IGF-I stimulated a twofold increase in DNA synthesis in cultures of adult brain microglia. Taken together with previous data demonstrating that IGF-I promotes proliferation of peripheral macrophages, these data support the hypothesis that IGF-I is an autocrine/paracrine mitogen for microglia/macrophages after H/I.

The effects of NMDA receptor antagonist MK-801 on lipid peroxidation during focal cerebral ischemia in rats

The effect of MK-801 on ischemic neuronal damage was studied in a rat model of permanent focal cerebral ischemia in terms of ipsilateral and contralateral cortical and cerebellar tissue lipid peroxides. Forty-five male Swiss Albino rats were assigned into one of four groups: sham operated as controls, subjected to right middle cerebral artery occlusion (MCAO) or injection of MK-801 (0.5 mg/kg i.p.) either 30 min before or just after right MCAO. Changes in lipid peroxides were expressed as nmol malondialdehyde (MDA) and conjugated diene (CD)/mg protein. MDA values after 60 min of ischemia relative to contralateral cortex and CD levels in 0, 10 and 60 min after ischemia were found to be higher in ipsilateral cortex than those in contralateral cortex. On the other hand, contralateral cerebellar MDA levels in 0 and 60 min of ischemia and CD levels in 0, 10 and 60 min after ischemia were found to be higher than those in ipsilateral cerebellum. Pharmacological inhibition of glutamate receptor by MK-801 before or just after permanent MCAO decreased significantly the MDA and CD levels in both cortex and cerebellum. Although no significant differences found in MDA values between rats pre- and posttreated with MK-801, CD levels in posttreated group seemed significantly lower than those in pretreated group. On the whole, these results suggest that MDA and CD represent early biochemical marker of lipid peroxidation in ischemic tissues, reflecting the radical-mediated tissue damage.

Lipid peroxidation in rat brain during focal cerebral ischemia: prevention of malondialdehyde and lipid conjugated diene production by a novel antiepileptic, lamotrigine

The effects of Lamotrigine (LTG) which blocks ischemia induced glutamate (Glu) release, on lipid peroxidation have been evaluated in cortical and cerebellar tissues of rat brain during focal cerebral ischemia. A total of 45 rats were randomly assigned into one of four groups; sham operated animals as controls, animals subjected to middle cerebral artery occlusion (MCAO) and treatment groups with LTG (20 mg/kg i.p.) either 30 min before or just after MCAO. Changes in lipid peroxides were expressed as nanomoles of malondialdehyde (MDA) and conjugated diene (CD) per milligram of protein. MDA values following 60 min of ischemia relative to contralateral cortex and CD levels in 0, 10 and 60 min of ischemia were found to be higher in the ipsilateral cortex than those in the contralateral cortex. On the other hand, contralateral cerebellar MDA levels after 0 and 60 min of ischemia and CD levels after 0, 10 and 60 min of ischemia were higher than those in the ipsilateral cerebellum. Pharmacological inhibition of Glu release significantly decreased the MDA and CD production in both cortex and cerebellum. Pre- or post-ischemic administration of LTG did not significantly change CD levels, but MDA levels in contralateral cortex were found to be significantly decreased than those in ischemic cortex in both pre- and post-treated group.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.

Microglial reaction induced by noncytotoxic methylmercury treatment leads to neuroprotection via interactions with astrocytes and IL-6 release

Microglial cells react early to a neurotoxic insult. However, the bioactive factors and the cell-cell interactions leading to microglial activation and finally to a neuroprotective or neurodegenerative outcome remain to be elucidated. Therefore, we analyzed the microglial reaction induced by methylmercury (MeHgCl) using cell cultures of different complexity. Isolated microglia were found to be directly activated by MeHgCl (10(-10) to 10(-6) M), as indicated by process retraction, enhanced lectin staining, and cluster formation. An association of MeHgCl-induced microglial clusters with astrocytes and neurons was observed in three-dimensional cultures. Close proximity was found between the clusters of lectin-stained microglia and astrocytes immunostained for glial fibrillary acidic protein (GFAP), which may facilitate interactions between astrocytes and reactive microglia. In contrast, immunoreactivity for microtubule-associated protein (MAP-2), a neuronal marker, was absent in the vicinity of the microglial clusters. Interactions between astrocytes and microglia were studied in cocultures treated for 10 days with MeHgCl. Interleukin-6 release was increased at 10(-7) M of MeHgCl, whereas it was decreased when each of these two cell types was cultured separately. Moreover, addition of IL-6 to three-dimensional brain cell cultures treated with 3 x 10(-7) M of MeHgCl prevented the decrease in immunostaining of the neuronal markers MAP-2 and neurofilament-M. IL-6 administered to three-dimensional cultures in the absence of MeHgCl caused astrogliosis, as indicated by increased GFAP immunoreactivity. Altogether, these results show that microglial cells are directly activated by MeHgCl and that the interaction between activated microglia and astrocytes can increase local IL-6 release, which may cause astrocyte reactivity and neuroprotection.

Biochemical evidence of crossed cerebellar diaschisis in terms of nitric oxide indicators and lipid peroxidation products in rats during focal cerebral ischemia

OBJECTIVES

Cerebral hypoperfusion in the contralateral cerebellar hemisphere after stroke is interpreted as a functional and metabolic depression, possibly caused by a loss of excitatory afferent inputs on the corticopontocerebellar pathway terminating in the cerebellar gray matter. This phenomenon is defined as crossed cerebellar diaschisis and can be diagnosed clinically by positron emission tomography, single-photon emission computed tomography, brain magnetic resonance imaging and electroencephalography in terms of regional cerebral blood flow or metabolic rate of oxygen measurements.

MATERIALS AND METHODS

In the present study, nitric oxide indicators (nitrite and cyclic guanosine monophosphate) and lipid peroxidation products (malondialdehyde and conjugated dienes) were measured in rat cerebral cortices and cerebella after permanent right middle cerebral artery occlusion in order to assess the crossed cerebellar diaschisis.

RESULTS

Nitrite values in ipsilateral cortex were significantly higher than those in contralateral cortex at 10 (P < 0.001) and 60 (P < 0.05) min of ischemia but no significant changes were observed in both cerebellum compared to the 0 min values. In both cerebral cortex and cerebellum cGMP levels at 10 and 60 min were significantly increased (P < 0.001). This increase was marked in ipsilateral cortex and contralateral cerebellum when compared with opposite cortex and cerebellum (P < 0.001). MDA values in ipsilateral cortex were significantly higher than those in contralateral cortex at 60 min of ischemia (P < 0.05). Contralateral cerebellar MDA values were found significantly higher than those in ipsilateral cerebellum at 0 (P<0.001) and 60 (P < 0.05) min of ischemia. In ipsilateral cortex, conjugated diene values at 0, 10, 60 min of ischemia were higher than those in contralateral cortex. On the other hand 0, 10, 60 min conjugated diene levels in contralateral cerebellum were significantly higher than those in ipsilateral cerebellum (P < 0.001).

CONCLUSION

These findings support the interruption of the corticopontocerebellar tract as the mechanism of the crossed cerebellar diaschisis.

Glial responses, clusterin, and complement in permanent focal cerebral ischemia in the mouse

There is considerable evidence that complement activation occurs within the CNS in inflammatory and degenerative disorders, but little is known about its involvement in the pathophysiology of cerebral ischemia. Our study sought to characterize the glial response and the expression of complement factors after permanent focal cerebral ischemia in the mouse, using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemistry. mRNA expression of glial fibrillary acidic protein (GFAP) increased at day 1 and peaked 3 days after middle cerebral artery (MCA) occlusion in the perifocal area. Immunohistochemical staining for GFAP indicated that astroglia were activated the day after MCA occlusion. Microglial activation, as assessed by lectin-binding experiments, increased by 1 day after MCA occlusion in the perifocal area and peaked at 3 days postocclusion. RT-PCR experiments demonstrated an increased expression of clusterin, C1qB, and C4 mRNA in the ischemic cortex, with a peak level at 3 days after MCA occlusion. Clusterin, C1qB, and C4 mRNA were located in the perifocal area, as assessed by in situ hybridization. Reactive astrocytes within the cortex medial to the ischemic lesion were found to be strongly immunoreactive for clusterin. In addition, we observed C1q-positive macrophage-like cells within the infarcted core at 3 days postocclusion. At 7 days after the onset of ischemia, increased C4 immunostaining was restricted to perifocal neurons. We conclude that local expression of complement components may contribute to the inflammation observed in this model, thereby representing an important process in secondary injury mechanisms after focal cerebral ischemia.

Crossed cerebellar diaschisis: assessment with dynamic susceptibility contrast MR imaging

The authors investigated the feasibility of using T2-weighted, half-Fourier rapid acquisition with relaxation enhancement, or RARE, dynamic susceptibility contrast magnetic resonance (MR) imaging to depict crossed cerebellar diaschisis. In 10 patients after unilateral supratentorial stroke, crossed cerebellar diaschisis was demonstrated in the relative regional cerebellar blood volume maps obtained with MR imaging. Cerebellar blood volume values for the nonaffected cerebellar hemisphere were significantly larger than those for the affected side (P = .0003).

Cerebral and cerebellar activation in correlation to the action-induced dystonia in writer's cramp

The pattern of brain perfusion of four patients with writer's cramp and four control subjects were examined using positron emission tomography scans after [(15)O] butanol injections. Each subject was scanned 12 times to cover three repetitions of four different motor tasks with the right hand. Drawing of horizontal lines and variable durations of the writing of a prelearned text were performed in a pseudorandom order, the latter task commencing either simultaneously with or 30 sec or 120 sec before the tracer injection. The perceived difficulty and signs of dystonia progressed in correlation to the duration of writing. Statistical parametric maps were calculated to test hypotheses of regional specific effects dependent on the performed motor tasks. The patients with writer's cramp had progressively increased activity in the left primary sensorimotor and premotor cortices, the left thalamus, and the cerebellum with a right-side predominance in correlation to the duration of writing. The regions with activity increases thus corresponded to a cerebrocerebellar motor circuit. The duration of writing correlated to a progressive reduction of activity in the patients' left supramarginal and angular gyri (Brodmann areas 40 and 39) and an inferior part of the left temporal lobe (area 20). The control subjects had neither a significant increase or decrease of activity in correlation to the duration of writing. Group-specific differences were confirmed statistically in split-plot interaction analyses.

Oligodendrocytes and microglia are selectively vulnerable to combined hypoxia and hypoglycemia injury in vitro

The major classes of glial cells, namely astrocytes, oligodendrocytes, and microglial cells were compared in parallel for their susceptibility to damage after combined hypoxia and hypoglycemia or hypoxia alone. The three glial cell types were isolated from neonatal rat brains, separated, and incubated in N2/CO2-gassed buffer-containing glucose or glucose substitutes, 2-deoxyglucose or mannitol (both nonmetabolizable sugars). The damage to the cells after 6 hours' exposure was determined at 0, 1, 3, 7 days based on release of lactate dehydrogenase and counting of ethidium bromide-stained dead cells, double-stained with cell-type specific markers. When 2-deoxyglucose replaced glucose during 6 hours of hypoxia, both oligodendrocytes and microglia rarely survived (18% and 12%, respectively). Astroglia initially increased the release of lactate dehydrogenase but maintained 98% to 99% viability. When mannitol, a radical scavenger and osmolarity stabilizer, replaced glucose during 6 hours of hypoxia, oligodendrocytes rarely survived (10%), astroglia survival remained at 99%, but microglia survival increased to 50%. After exposure to 6 and 42 hours, respectively, of hypoxic conditions alone, oligodendrocytes exhibited 10% survival whereas microglia and astroglia were only temporarily stressed and subsequently survived. In conclusion, oligodendrocytes, then microglia, are the most vulnerable glial cell types in response to hypoxia or hypoglycemia conditions, whereas astrocytes from the same preparations recover.

Diaschisis and neurobehavior

We review forms of diaschisis and their relationship with neurobehavioral and neuropsychological findings. The following forms of diaschisis are discussed: (1) cortico-cerebellar diaschisis; (2) cerebello-cortical diaschisis; (3) transhemispheric diaschisis; (4) cortico-thalamic diaschisis; (5) thalamo-cortical diaschisis; and (6) basal ganglia-cortical diaschisis. For each form, the neurobehavioral and neuropsychological findings are discussed. Diaschisis can be classified from the behavioral point of view as follows: (1) forms in which the metabolic effect at distance is not followed by neurobehavioral impairment; (2) forms in which the remote metabolic impairment could induce neurobehavioral and neuropsychological disorders; and (3) forms in which the role of the lesion itself and its remote metabolic effects on the production of neurobehavioral and neuropsychological abnormalities cannot be disentangled.

Changes in cerebral blood flow and vasoreactivity in response to acetazolamide in patients with transient global amnesia

OBJECTIVE

Previous reports about changes in cerebral blood flow (CBF) in transient global amnesia disclosed decreased flow in some parts of the brain. However, CBF analyses in most reports were qualitative but not quantitative. The purpose of this study was to determine changes in CBF in transient global amnesia.

METHODS

The CBF was measured and the vasoreactive response to acetazolamide was evaluated in six patients with transient global amnesia using technetium-99m hexamethylpropylene amine oxime single-photon emission computed tomography (SPECT). The CBF was measured during an attack in two patients and soon after an attack in the other four. About one month later, CBF was re-evaluated in each patient.

RESULTS

Two patients examined during an attack and one patient examined five hours after an attack had increased blood flow in the occipital cortex and cerebellum. Three patients examined at six to 10 hours after an attack had decreased blood flow in the thalamus, cerebellum, or putamen. These abnormalities of blood flow almost disappeared in all patients one month after onset. The vasodilatory response to acetazolamide, which was evaluated initially using SPECT, was poor in areas of increased blood flow. By the second evaluation of CBF with acetazolamide, the vasodilatory response had returned to normal.

CONCLUSIONS

In a patient with transient global amnesia, CBF increased in the vertebrobasilar territory during the attack and decreased afterwards. The vasodilatory response to acetazolamide may be impaired in the parts of the brain with increased blood flow. It is suggested that transient global amnesia is distinct from migraine but may share the same underlying mechanism.

Effects of Lamotrigine on brain nitrite and cGMP levels during focal cerebral ischemia in rats

Glutamate receptor antagonists are protective in animal models of focal cerebral ischemia. Lamotrigine (3,5-diamino-6-[2,3-dichlorophenyl]-1,2, 4-triazine) is an anticonvulsant drug that blocks voltage-gated sodium channels and inhibits the ischemia-induced release of glutamate. Experiments in primary neuronal cultures implicate nitric oxide (NO) as a mediator of glutamatergic neurotoxicity acting via N-Methyl-D-Aspartate (NMDA) receptors. The effect of glutamate release inhibitor, Lamotrigine upon NO and cGMP production has been examined in focal cerebral ischemia in rats. Focal cerebral ischemia was produced by the permanent occlusion of right middle cerebral artery (MCA) in urethane anesthetized rats. A number of indicators of brain NO production (nitrite, cGMP) were determined in ipsilateral and contralateral cerebral cortex and cerebellum after 0, 10, 60 min of focal cerebral ischemia. The same parameters were measured in rats treated with Lamotrigine (20 mg/kg, i.p.) 30 min before or just after the occlusion of the right MCA.

The effects of nitric oxide synthase inhibitor, L-NAME on NO production during focal cerebral ischemia in rats: could L-NAME be the future treatment of sudden deafness?

Recent evidence in primary neuronal cell culture implicates NO as a mediator of glutamatergic neurotoxicity acting via N-methyl-D-aspartate (NMDA) receptors. In this study, we investigated the effects of inhibition of NOsynthase activity in focal cerebral ischemia in rats. Focal cerebral ischemia was produced by permanent occlusion of right MCA in urethane anesthetized rats. A number of indicators of brain NO production, nitrite and cGMP were determined in ipsilateral and contralateral cerebral cortex and cerebellum after 0, 10 and 60 minutes of focal cerebral ischemia. The same parameters were measured in rats pre- and posttreated with the potent Nitric oxide synthase (NOS) inhibitor, NW-nitro-L-arginine methyl ester (L-NAME).

Primary demyelination and regeneration of ascending axons in the dorsal funiculus of the rat spinal cord following photochemically induced injury

The extent of primary demyelination and regeneration of ascending axons in the dorsal funiculus of the rat spinal cord was investigated following photochemically-induced ischaemic injury. Groups of rats were killed at intervals from 48h to 1 month after injury and a combination of light and electron microscopy and counting of axons in specific sites was used to study the axonal changes. Unmyelinated axons were noted in the dorsal rim of the lesion at its centre and at the centre of the gracile fasciculus at the caudal end of the lesion 7 days after injury. By 1 month, axons in these sites were thinly myelinated by Schwann cells or oligodendrocytes. In order to differentiate between remyelination of demyelinated axons and myelination of regenerated axons, axon counts were performed. The number of sub-pial axons present at the lesion centre did not change significantly from 48h to 1 month after injury, whereas the number of axons at the caudal end of the lesion increased significantly from 4 to 10 days after injury. We therefore conclude that sub-pial axons at the lesion centre are demyelinated between 4 and 7 days after injury and subsequently remyelinated by Schwann cells. At the caudal end of the lesion, a specific population of small diameter axons located at the centre of the gracile fasciculus regenerates for a distance of approximately 1 mm between 4 and 10 days after injury; these axons are then myelinated by oligodendrocytes or Schwann cells. In contrast, larger diameter axons of the gracile fasciculus do not show a regenerative response, demonstrating the variability of axonal responses to injury.

Cerebellar vascular response to acetazolamide in crossed cerebellar diaschisis: a comparison of 99mTc-HMPAO single-photon emission tomography with 15O-H2O positron emission tomography

Various observations on the cerebellar vasoreactivity in crossed cerebellar diaschisis (CCD) have previously been reported. The purpose of this study is to clarify the difference between oxygen-15 H2O positron emission tomographic (PET) and technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomograph (SPET) findings in CCD and to evaluate the effect of the absolute values of the cerebellar blood flow as measured by 15O-H2O PET on the 99mTc-HMPAO SPET findings. The subjects comprised 15 patients with a supratentorial infarct and CCD. The cerebellar blood flow increased by about 40% at 5 and 20 min after acetazolamide i.v. on both the CCD and the non-CCD side, as measured by 15O-H2O PET. The percentage differences in cerebellar blood flow between the CCD and the non-CCD side were -22.3%+/-5.7% in the resting state, -19. 6%+/-6.4% at 5 min after acetazolamide i.v. and 21.5%+/-6.7% at 20 min after acetazolamide i.v., as measured by 15O-H2O PET, while they were -10.6%+/-5.5% in the resting state and -5.6%+/-5.1% at 5 min after acetazolamide i.v., as measured by 99mTc-HMPAO SPET. After Lassen's linearization correction, the latter two measurements were -16.2%+/-7.7% and -9.6%+/-8.9%, respectively. The effect of acetazolamide did not differ between the CCD and the non-CCD side in 15O-H2O PET, while a greater response on the CCD side was observed in 99mTc-HMPAO SPET, even after Lassen's linearization correction. It is concluded that acetazolamide HMPAO SPET may overestimate the cerebellar vascular response on the CCD side (or underestimate it on the non-CCD side).

Development of brain damage after neonatal hypoxia-ischemia: excitatory amino acids and cysteine

The aim of this study was to investigate the possible role of excitatory amino acids (EAAs) and cysteine in the development of brain damage after hypoxia-ischemia (HI) in neonates. In a rat model of neonatal HI, changes in extracellular (ec) amino acids in cerebral cortex were measured with microdialysis and correlated with the extent of brain damage at the site of probe placement. Extracellular concentrations of glutamate, aspartate and cysteine increased during HI and remained elevated during reperfusion. During HI the pattern of EAA changes was the same in the infarcted, undamaged and border zone regions. During reperfusion, however, the ec concentrations of glutamate, aspartate and cysteine were higher in infarcted and border zone areas compared to undamaged tissue. HI also produced a slight increase of tissue concentration of cysteine and decrease of tissue concentration of glutamate in parietal cortex of the HI hemisphere. The effect of cysteine on brain damage induced by HI and glutamate was also investigated. A subtoxic dose of cysteine potentiated glutamate toxicity in the arcuate nucleus and enhanced brain infarction after HI in neonatal rats. The results show that in neonatal HI the extracellular levels of EAAs during HI are not directly related to brain injury but the EAA levels during reflow predict the extent of infarction. Cysteine increases HI-induced brain injury and potentiates glutamate toxicity in neonatal rats. Speculatively, elevated level of cysteine during reperfusion may participate in the excitotoxic cascade leading to brain injury.

Stable xenon CT in patients with chronic cerebrovascular disease

Xenon-enhanced CT (XeCT) is a method of measuring regional cerebral blood flow (rCBF). Although it is used for acute and perioperative assessment the ability of XeCT to show hypoperfused areas in vivo, as compared with morphological imaging modalities other than noncontrast CT, is not defined. Correlation with MRI helps to define the smallest detectable hypoperfused area. We examined 17 patients 6 weeks after acute cerebral infarcts with CT, XeCT and MRI and the findings were compared. All examinations were performed with the same slice angulation and thickness and the sizes of the abnormal areas were measured. XeCT showed a high correlation with MRI, but less so with conventional CT. Lesions appeared significantly smaller on CT than on XeCT or MRI. No significant difference between MRI and XeCT changes was found. The minimal lesion on MRI correlating with a hypoperfused area on XeCT was 0.8 cm2, whereas lesions measuring less than 0.5 cm2 on MRI could not be detected on XeCT. The good correlation between XeCT and MRI underlines the reliability of rCBF examinations with XeCT. A significant difference between CT and XeCT findings shows the difficulty of interpreting hypoperfused regions only by correlation with CT. Combined XeCT and MRI gives a better estimate of the vascular state of the brain.