Specific expression of the cell cycle regulation proteins, GADD34 and PCNA, in the peri-infarct zone after focal cerebral ischaemia in the rat

Cell cycle proteins play key roles in cell survival or death under pathological conditions. Expression of growth arrest and DNA damage-inducible protein, GADD34 and proliferating cell nuclear antigen (PCNA) have been investigated in the core and peri-infarct zone at 2 and 24 h after middle cerebral artery occlusion (MCAO). At these times after MCAO, numerous GADD34-positive cells were present, particularly in the peri-infarct zone (e.g. 24 +/- 4 and 52 +/- 6 immunopositive cells/0.25 mm2 at 2 and 24 h, respectively, in cortex). PCNA-immunopositive cells were barely detectable in the peri-infarct zone at 2 h; however, numerous PCNA-immunopositive cells were present in this zone by 24 h (0.7 +/- 0.3 and 10.6 +/- 1.5 immunopositive cells/0.25 mm2, respectively) as well as in the adjacent cortex and in the contralateral cingulate cortex. Most GADD34-immunopositive cells coexpressed the neuronal marker Neu-N with a smaller number coexpressing the microglial marker, Mrf-1. Evidence of morphologically 'abnormal' and 'normal' GADD34 immunopositive neurons was found within the peri-infarct zone. The majority of PCNA immunopositive cells were Mrf-1 positive with a smaller number Neu-N positive. Double-labelling revealed colocalization of GADD34 and PCNA in some cells within the peri-infarct zone and in the ependymal cells lining the ventricles. The presence of GADD34 and PCNA in a key anatomical location pertinent to the evolving ischaemic lesion indicates that GADD34, either alone or in combination with PCNA, has the potential to influence cell survival in ischaemically compromised tissue.

Sudden unexplained death in adults caused by intracranial pathology

Sudden unexplained deaths as a result of intracranial lesions in adults are an important component of medicolegal practice and are best examined as a combined effort by a forensic pathologist, or a histopathologist experienced in coroner's necropsies, and a neuropathologist. Analysis of case material on file in the University of Glasgow's departments of forensic medicine and science, and neuropathology showed that the principal causes were sudden unexplained death in epilepsy (SUDEP), intracranial haemorrhage, either natural or after trauma, purulent meningitis or an abscess, and tumours. The mechanisms of death are considered to be the rapid increase of intracranial pressure caused by bleeding into the various compartments of the brain, or an acute obstructive hydrocephalus, and in cases where death is very rapid, autonomic and/or neurochemical dysfunction.

In situ DNA fragmentation occurs in white matter up to 12 months after head injury in man

Using the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick-end labelling (TUNEL) histochemical technique, evidence for DNA fragmentation was sought in the hippocampus, cingulate gyrus and insula from 18 patients who survived for up to 12 months after head injury, and 15 matched controls. Both conventional (haematoxylin and eosin and Luxol-fast blue/cresyl violet) and immunohistochemical (glial fibrillary acidic protein, CD68) staining techniques were used to identify the cellular response and its time course in the regions of interest. Only the occasional TUNEL-positive (+) cell/unit area was seen in any area of the control brains. In contrast there were more TUNEL+ cells/unit area in the injured brains. TUNEL+ cells were present in white matter and their average numbers ranged from three to five per unit area for up to 3 months survival in the extreme capsule and the parasagittal white matter, with similar numbers in the hippocampus, and between two and three per unit area in the parasagittal white matter and hippocampus of the cases surviving up to 12 months post injury. Between one and two TUNEL+ cells/unit area were also seen in grey matter, of which most appeared as neurones. About 5% of the TUNEL+ cells in white matter had the morphological features of apoptosis: the corresponding figure in grey matter was less than 1%. In many instances the TUNEL+ cells were also CD68+ and appeared by light microscopy to be macrophages. It was concluded that, as reflected by TUNEL histochemistry, long-term DNA fragmentation is present in white matter after traumatic brain injury in man.

A review and rationale for the use of genetically engineered animals in the study of traumatic brain injury

The mechanisms underlying secondary cell death after traumatic brain injury (TBI) are poorly understood. Animal models of TBI recapitulate many clinical and pathologic aspects of human head injury, and the development of genetically engineered animals has offered the opportunity to investigate the specific molecular and cellular mechanisms associated with cell dysfunction and death after TBI, allowing for the evaluation of specific cause-effect relations and mechanistic hypotheses. This article represents a compendium of the current literature using genetically engineered mice in studies designed to better understand the posttraumatic inflammatory response, the mechanisms underlying DNA damage, repair, and cell death, and the link between TBI and neurodegenerative diseases.

The structural basis of moderate disability after traumatic brain damage

The objective was to discover the nature of brain damage in survivors of head injury who are left with moderate disability. Macroscopic and microscopic examination was carried out on the brains of 20 persons who had died long after a head injury that had been treated in a neurosurgical unit. All had become independent but had various disabilities (moderate disability on the Glasgow outcome scale) Most deaths had been sudden, which had led to their referral from forensic pathologists. Post-traumatic epilepsy was a feature in 75%. An intracranial haematoma had been evacuated in 75%, and in 11 of the 15 with epilepsy. Diffuse axonal injury was found in six patients, five of the mildest type (grade 1) and one of grade 2. No patient had diffuse thalamic damage but one had a small focal ischaemic lesion in the thalamus. No patient had severe ischaemic brain damage, but three had moderate lesions which were bilateral in only one. No patient had severe cortical contusions. In conclusion, the dominant lesion was focal damage from an evacuated intracranial haematoma. Severe diffuse damage was not found, with diffuse axonal injury only mild and thalamic damage in only one patient.

Ebselen protects both gray and white matter in a rodent model of focal cerebral ischemia

BACKGROUND AND PURPOSE

The neuroprotective efficacy of an intravenous formulation of the antioxidant ebselen has been comprehensively assessed with specific regard to conventional quantitative histopathology, subcortical axonal damage, neurological deficit, and principal mechanism of action.

METHODS

Transient focal ischemia (2 hours of intraluminal thread-induced ischemia with 22 hours of reperfusion) was induced in the rat. Ebselen (1 mg/kg bolus plus 1 mg/kg per hour IV) or vehicle was administered at the start of reperfusion and continued to 24 hours. Neurological deficit was assessed 24 hours after ischemia. Gray matter damage was evaluated by quantitative histopathology. Axonal damage was determined with amyloid precursor protein immunohistochemistry used as a marker of disrupted axonal flow and Tau-1 immunohistochemistry to identify oligodendrocyte pathology. Oxidative damage was determined by 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxynonenal (4-HNE) immunohistochemistry.

RESULTS

Ebselen significantly reduced the volume of gray matter damage in the cerebral hemisphere (by 53.6% compared with vehicle, P<0.02). Axonal damage was reduced by 46.8% (P<0.002) and the volume of oligodendrocyte pathology was reduced by 60.9% (P<0.005). The neurological deficit score was reduced by 40.7% (P<0.05) and the volume of tissue immunopositive for 8-OHdG and 4-HNE was reduced by 65% (P<0.002) and 66% (P<0.001), respectively, in ebselen-treated animals.

CONCLUSIONS

Delayed (2-hour) treatment with intravenous ebselen significantly reduced gray and white matter damage and neurological deficit associated with transient ischemia. The reduction in tissue displaying evidence of oxidative stress suggests that the major mechanism of action is attenuation of free radical damage.

Characterization of the microglial response to cerebral ischemia in the stroke-prone spontaneously hypertensive rat

Stroke-prone spontaneously hypertensive rats (SHRSP) sustain more ischemic damage after middle cerebral artery occlusion than do their reference strain, the Wistar-Kyoto rat (WKY). The cause of increased stroke sensitivity is still under investigation. In general, SHRSP display a greater response to inflammatory stimuli than do WKY. Because inflammatory cells may influence the extent of damage in experimental stroke, this study has investigated the acute inflammatory response to focal ischemia in SHRSP and WKY. Adult male SHRSP (n=5) and WKY (n=5) were anesthetized and underwent distal middle cerebral artery occlusion. After 24 hours of recovery, infarct volume, neutrophil counts, and activated microglia counts were performed. SHRSP displayed more ischemic damage than did WKY (135+/-4.7 versus 102+/-4.7 mm(3) [mean+/-SEM], P<0.005). Brain neutrophil counts were extremely low in both strains. SHRSP displayed significantly more activated microglia than did WKY in the ipsilateral hemisphere (respective SHRSP versus WKY values [mean+/-SEM] were 88+/-3.6 versus 51+/-3.4 per mm(2) for the cortical peri-infarct region [P<0.005] and 183+/-7.9 versus 156+/-3.7 per mm(2) for the infarct core [P<0.05]) and in the contralateral hemisphere (eg, respective SHRSP versus WKY values were 102+/-3.2 versus 50+/-3.1 per mm(2) for the sensorimotor cortex [P<0.0001]). No neutrophils and very few activated microglia were found within the brains of naive rats. However naive SHRSP possessed more microglia (resting and activated) than did naive WKY. This study demonstrates a more pronounced microglial response to focal ischemia in SHRSP compared with WKY and provides evidence of a potential role for inflammatory processes in response to ischemic damage.

TUNEL-positive staining in white and grey matter after fatal head injury in man

Paraffin sections from the hippocampus, the cingulate gyrus and the insula of 18 head-injured patients who survived between 5 hours and 10 days, and 18 age-matched controls, were stained by the terminal deoxynucleotidyl transferase mediated biotinylated deoxyuridine triphosphate nick end labelling (TUNEL) technique for evidence of in situ DNA fragmentation. Additional staining techniques (HE, combined LFB/CV and immunohistochemistry for GFAP and CD68) were used to characterize any lesions and their time course. Only the occasional TUNEL+ cell per area was seen in the control brains. TUNEL+ cells were identified in both grey and white matter of the head-injured material and their numbers peaked between 24 and 48 hours and were still present at 10 days. Within the hippocampus, fewer TUNEL+ cells were seen in grey (between 3-5 per area) than in the white matter, (up to 51+ per area) whereas in the cingulate gyrus and in the insula, the number of TUNEL+ cells was always greater in the cortex (between 11-20 per area) than in white matter (6-10 per area). In the grey matter, most TUNEL+ cells had the morphology of necrosis. However, the histological appearances of some of the neurons (2-3%), and of oligodendroglia and macrophages in white matter (about 5%) were those of apoptosis.

Pharmacologic inhibition of poly(ADP-ribose) polymerase is neuroprotective following traumatic brain injury in rats

The nuclear enzyme poly(ADP-ribose) polymerase (PARP), which has been shown to be activated following experimental traumatic brain injury (TBI), binds to DNA strand breaks and utilizes nicotinamide adenine dinucleotide (NAD) as a substrate. Since consumption of NAD may be deleterious to recovery in the setting of CNS injury, we examined the effect of a potent PARP inhibitor, GPI 6150, on histological outcome following TBI in the rat. Rats (n = 16) were anesthetized, received a preinjury dose of GPI 6150 (30 min; 15 mg/kg, i.p.), subjected to lateral fluid percussion (FP) brain injury of moderate severity (2.5-2.8 atm), and then received a second dose 3 h postinjury (15 mg/kg, i.p.). Lesion area was examined using Nissl staining, while DNA fragmentation and apoptosis-associated cell death was assessed with terminal deoxynucleotidyl-transferase-mediated biotin-dUTP nick end labeling (TUNEL) with stringent morphological evaluation. Twenty-four hours after brain injury, a significant cortical lesion and number of TUNEL-positive/nonapoptotic cells and TUNEL-positive/apoptotic cells in the injured cortex of vehicle-treated animals were observed as compared to uninjured rats. The size of the trauma-induced lesion area was significantly attenuated in the GPI 6150-treated animals versus vehicle-treated animals (p < 0.05). Treatment of GPI 6150 did not significantly affect the number of TUNEL-positive apoptotic cells in the injured cortex. The observed neuroprotective effects on lesion size, however, offer a promising option for further evaluation of PARP inhibition as a means to reduce cellular damage associated with TBI.

Neuropathology in vegetative and severely disabled patients after head injury

OBJECTIVE

To discover if the neuropathology differs in head-injured patients who were in a vegetative state (VS) or were severely disabled at time of death.

METHODS

Review of 35 VS cases and 30 severely disabled cases treated in this institute in the acute stage, surviving at least a month; all brains were fixed for 3 weeks before full neuropathologic examination.

RESULTS

The severely disabled cases were older, had a higher incidence of skull fracture and of evacuated intracranial hematoma, and they had more cortical contusions. Diffuse axonal injury (DAI) was less common in the severely disabled cases, particularly its most severe grade. Structural damage in the thalamus was much less common in severely disabled cases. Half of the severely disabled patients had neither grade 2 or 3 DAI nor thalamic damage and 10 of these 15 cases did not have ischemic brain damage either. These combinations did not occur in a single VS case. However, some severely disabled cases had similar lesions to VS cases, and this included some patients who were in a minimally conscious state as well as some who were out of bed and mobile.

CONCLUSIONS

Half the severely disabled cases had only focal brain damage, a feature not found in any VS cases. In the severely disabled patients with lesions similar to those of VS cases it is likely that a greater quantitative amount of damage occurred in the VS cases.

Axonal injury is accentuated in the caudal corpus callosum of head-injured patients

Amyloid precursor protein (APP) accumulation is a sensitive marker for the axonal damage that is commonly seen in the brain as the result of head injury. This form of damage is particularly associated with midline structures such as the corpus callosum, although it is not clear whether some areas are more susceptible than others. The aim of this study was to determine if there was a differential distribution of axonal injury throughout the corpus callosum after head injury in an unselected group of cases. Coronal tissue sections from eight cases were taken at different levels through the corpus callosum, including the genu, body, and splenium. The sections were immunostained with an antibody to APP, and the amount of axonal damage at the different levels was quantified using computer image analysis to build up a rostro-caudal profile for each case. The profiles revealed a significantly higher APP load in caudal parts of the corpus callosum. This supports previous nonquantitative reports in the literature and has important implications in terms of choosing where tissue should be sampled to maximize the chance of detecting axonal injury post mortem.

TUNEL-positive staining of surface contusions after fatal head injury in man

In frontal lobe contusions obtained post mortem from 18 patients who survived between 6 h and 10 days after head injury, DNA fragmentation associated with either apoptotic and/or necrotic cell death was identified by the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labelling (TUNEL) histochemical technique. Additional histological techniques were also used to identify regional and temporal patterns of tissue damage. TUNEL-positive cells were present in both the grey and white matter of the contusion, where they peaked in number between 25 and 48 h, and were still identifiable at 10 days post injury. Fewer TUNEL-positive cells were observed in grey than in white matter; and most TUNEL-positive neurons in the grey matter demonstrated the morphological features of necrosis. However, the morphology of some TUNEL-stained neurons, and of TUNEL-stained oligodendroglia and macrophages in white matter was suggestive of apoptosis. Apoptosis was not seen in age- and sex-matched controls, none of whom had died from intracranial pathology or had pre-existing neurological disease. These findings suggest that multiple cell types in frontal lobe contusions exhibit DNA fragmentation and that both necrosis and apoptosis are likely to contribute to post-traumatic pathology. These findings provide further evidence that the observations made in animal models of traumatic brain injury have fidelity with clinical head injury.

Global hypoxia per se is an unusual cause of axonal injury

Irreversible hypoxic brain damage and axonal injury are present in over 90% of fatal blunt head injuries. Given the frequency of each, difficulties arise as to whether or not they are due to different mechanisms and, as such, can be separately recognised and quantified. Recent literature has raised the possible role of hypoxia in the formation of axonal bulbs. The present study of 17 cases of cardio-respiratory arrest, 12 of status epilepticus, 3 of carbon monoxide poisoning and 12 controls was designed to test the relationship between hypoxia and axonal injury and to test the hypothesis whether or not the two entities can be separated into primary and secondary forms of traumatic brain injury. Axonal damage was seen in 9/17 and 7/12 of the cases with cardiac arrest and status epilepticus, respectively, in most of whom there was also evidence of raised intracranial pressure (ICP). All 3 cases of carbon monoxide poisoning had evidence of white matter damage in keeping with the classical pattern of selective vulnerability. It is concluded that the great majority of axonal damage identified in cases dying after cardiac arrest and status epilepticus can be attributed to raised ICP and the vascular complications of internal herniation. However, in some cases, axonal damage was seen in the absence of an elevated ICP, although its amount and distribution were different from diffuse axonal injury. In many cases there was an increase in expression of neuronal beta amyloid precursor protein.

Apoptosis after traumatic brain injury

Apoptosis of neurons and glia contribute to the overall pathology of traumatic brain injury (TBI) in both humans and animals. In both head-injured humans and following experimental brain injury, apoptotic cells have been observed alongside degenerating cells exhibiting classic necrotic morphology. Neurons undergoing apoptosis have been identified within contusions in the acute port-traumatic period, and in regions remote from the site of impact in the days and weeks after trauma. Apoptotic oligodendrocytes and astrocytes have been observed within injured white matter tracts. We review the regional and temporal patterns of apoptosis following TBI and the possible mechanisms underlying trauma-induced apoptosis. While excitatory amino acids, increases in intracellular calcium, and free radicals can all cause cells to undergo apoptosis, in vitro studies have determined that neural cells can undergo apoptosis via many other pathways. It is generally accepted that a shift in the balance between pro- and anti-apoptotic protein factors towards the expression of proteins that promote death may be one mechanism underlying apoptotic cell death. The effect of TBI on regional cellular patterns of expression of survival promoting-proteins such as Bcl-2, Bcl-xL, and extracellular signal regulated kinases, and death-inducing proteins such as Bax, c-Jun N-terminal kinase, tumor-suppressor gene, p53, and the caspase family of proteases are reviewed. Finally, in light of pharmacologic strategies that have been devised to reduce the extent of apoptotic cell death in animal models of TBI, our review also considers whether apoptosis may serve a protective role in the injured brain.

Hypoglycaemia is a cause of axonal injury

Axonal injury as demonstrated immunohistochemically is increasingly being recognized at post-mortem in patients who have been unconscious, and in some cases the cause of the coma may not be immediately apparent. Considerations include microscopical diffuse traumatic axonal injury and axonal injury associated with a range of metabolic encephalopathies. In this study, extensive neurohistological examination was undertaken in 13 patients in whom coma was attributed to hypoglycaemia and in whom neurohistological examination had revealed varying degrees of widely distributed neuronal necrosis: in five of these cases there was also evidence that the intracranial pressure had been high with internal hernation. It is concluded that a significant amount of axonal injury found in these 13 cases can be attributed to hypoglycaemia per se although the amount and distribution of the axonal damage is altered in the presence of raised intracranial pressure. However, in some cases axonal damage is seen in the absence of an elevated intracranial pressure and in one case its distribution closely mimicked that seen in microscopical diffuse traumatic axonal injury. This further demonstrates that not all axonal pathology is traumatic, and that adequate sampling and care in interpretation of Abeta-PP staining is required in forensic practice.

Recent advances in neurotrauma

The frequency of and outcome from acute traumatic brain injury (TBI) in humans are detailed together with a classification of the principal focal and diffuse pathologies, and their mechanisms in extract laboratory models are outlined. Particular emphasis is given to diffuse axonal injury, which is a major determinant of outcome. Cellular and molecular cascades triggered by injury are described with reference to the induction of axolemmal and cytoskeletal abnormalities, necrotic and apoptotic cell death, the role of Ca2+, cytokines and free radicals, and damage to DNA. It is concluded that TBI in humans is heterogeneous, reflecting various pathologies in differing proportions in patients whose genetic background (APOE gene polymorphisms) contributes to the outcome at 6 months. Although considerable progress has been made in the understanding of TBI, much remains to be determined. However, a deeper understanding of the pathophysiological events may lead to the possibility of improving outcome from rational targeted therapy.

The neuropathology of the vegetative state after an acute brain insult

The vegetative state is often described clinically as loss of function of the cortex while the function of the brainstem is preserved. In an attempt to define the structural basis of the vegetative state we have undertaken a detailed neuropathological study of the brains of 49 patients who remained vegetative until death, 1 month to 8 years after an acute brain insult. Of these, 35 had sustained a blunt head injury and 14 some type of acute non-traumatic brain damage. In the traumatic cases the commonest structural abnormalities identified were grades 2 and 3 diffuse axonal injury (25 cases, 71%). The thalamus was abnormal in 28 cases (80%), and in 96% of the cases who survived for more than 3 months. Other abnormalities included ischaemic damage in the neocortex (13 cases, 37%) and intracranial haematoma (nine cases, 26%). In the non-traumatic cases there was diffuse ischaemic damage in the neocortex in nine cases (64%) and focal damage in four (29%); the thalamus was abnormal in every case. There were cases in both groups where the cerebral cortex, the cerebellum and the brainstem were of structurally normal appearance. In every case, however, there was profound damage to the subcortical white matter or to the major relay nuclei of the thalamus, or both. These lesions render any structurally intact cortex unable to function because connections between different cortical areas via the thalamic nuclei are no longer functional, and there is also extensive damage to afferent and efferent cerebral connections.

NMDA receptor blockade fails to alter axonal injury in focal cerebral ischemia

The ability of the NMDA receptor antagonist, MK-801, to protect myelinated axons after focal cerebral ischemia has been examined. Amyloid precursor protein (APP) immunocytochemistry was used to assess the anatomic extent of axonal injury, and conventional histopathology was used to assess the volume of ischemic damage to neuronal perikarya. The middle cerebral artery was permanently occluded in 16 cats. The cats were treated with either vehicle or MK-801 as a 0.5-mg/kg bolus at 15 minutes before middle cerebral artery occlusion, followed by an infusion of 0.14 mg/kg per hour. After 6 hours, the animals were killed and the brains processed for histology and immunocytochemistry. The volume of neuronal necrosis was determined from 16 preselected coronal levels of the brain. The circumscribed zones of APP accumulation in axons were mapped onto images at the same 16 coronal levels, and quantitative analysis was performed using a transparent counting grid, randomly placed over each image. The histologic appearance and anatomic location of axons with increased APP immunoreactivity was similar in animals treated with vehicle and MK-801. MK-801 failed to reduce the hemispheric APP score significantly. In vehicle-treated animals, there was a significant association between the volume of neuronal necrosis and the amount of APP immunoreactivity. MK-801 significantly reduced the slope of the association between the volume of neuronal necrosis and the amount of APP immunoreactivity compared with that observed in vehicle-treated animals. As a result, the ratio of hemispheric APP score and volume of neuronal necrosis was significantly increased with MK-801 treatment. The inability of NMDA receptor antagonists to protect axons may limit their functional efficacy in improving functional outcome after stroke.