Amyloid beta-protein length and cerebral amyloid angiopathy-related haemorrhage

The relationship between amyloid beta-protein (A beta) length and the apolipoprotein E (APOE) epsilon 2 allele, which is over-represented in cerebral amyloid angiopathy-related haemorrhage (CAAH), has not previously been examined. Of 57 CAA patients studied, 37 had CAAH. All patients, particularly those with CAAH had more blood vessels immunoreactive for A beta 40 than A beta 42 in both the leptomeninges and cerebral cortex. CAAH patients had more A beta 40-immunoreactive blood vessels in the leptomeninges (p < 0.001) and cortex (p = 0.027) than had non-haemorrhage patients. Cortical blood vessels, the usual source of haemorrhage in CAAH, were more frequently A beta 42 immunoreactive in APOE epsilon 2 carriers than in non-epsilon 2 carriers (p = 0.022). The APOE epsilon 2 allele may predispose to CAAH by increasing the seeding of cortical blood vessels by A beta 42.

Traumatic axonal injury: practical issues for diagnosis in medicolegal cases

In the 25 years or so after the first clinicopathological descriptions of diffuse axonal injury (DAI), the criterion for diagnosing recent traumatic white matter damage was the identification of swollen axons ('bulbs') on routine or silver stains, in the appropriate clinical setting. In the last decade, however, experimental work has given us greater understanding of the cellular events initiated by trauma to axons, and this in turn has led to the adoption of immunocytochemical methods to detect markers of axonal damage in both routine and experimental work. These methods have shown that traumatic axonal injury (TAI) is much more common than previously realized, and that what was originally described as DAI occupies only the most severe end of a spectrum of diffuse trauma-induced brain injury. They have also revealed a whole field of previously unrecognized white matter pathology, in which axons are diffusely damaged by processes other than head injury; this in turn has led to some terminological confusion in the literature. Neuropathologists are often asked to assess head injuries in a forensic setting: the diagnostic challenge is to sort out whether the axonal damage detected in a brain is indeed traumatic, and if so, to decide what - if anything - can be inferred from it. The lack of correlation between well-documented histories and neuropathological findings means that in the interpretation of assault cases at least, a diagnosis of 'TAI' or 'DAI' is likely to be of limited use for medicolegal purposes.

beta-amyloid (Abeta)42(43), abeta42, abeta40 and apoE immunostaining of plaques in fatal head injury

beta-Amyloid (Abeta) deposits are found in the brains of approximately one-third of patients who die within days after a severe head injury; their presence correlating strongly with possession of an apolipoprotein E (apoE)-epsilon4 allele. The aim of the study was to investigate the relationship between Abeta42, Abeta40 and apoE immunostaining of Abeta plaques in the cerebral cortex and the relevance of apoE genotype in 23 fatally head-injured patients. These cases were known to have Abeta deposits from a previous study in which they were examined and semiquantified and related to apoE genotype. In the present study, the temporal cortex was probed using four different antibodies that recognize Abeta42(43), Abeta40 and an antibody to apoE. Abeta42(43)-positive plaques were observed in all of the 23 cases and Abeta40 immunoreactivity in only 11 of the 23 cases. In addition, semiquantitative analysis showed that relatively fewer plaques were detected with anti-Abeta40 than anti-Abeta42(43). ApoE-immunoreactive plaques were identified in 18 of the 23 cases. The number of plaques stained for apoE was relatively less than for Abeta42(43) but greater than for Abeta40. Furthermore, the density of Abeta plaques detected using either Abeta42(43), Abeta40 or apoE antibodies was associated with possession of apoE-epsilon4 in an allele dose-dependent manner. The results are consistent with Abeta42(43) as the initially deposited species in brain parenchyma and provide evidence that apoE is involved in the early stages of amyloid deposition. Further, the findings may be of relevance to the role of apoE genotype in influencing outcome after acute brain injury.

Association of interleukin-1 gene polymorphisms with Alzheimer's disease

Interleukin-1 (IL-1) is markedly overexpressed in Alzheimer's disease. We found the IL-1A 2,2 genotype in 12.9% of 232 neuropathologically confirmed Alzheimer's disease patients and 6.6% of 167 controls from four centers in the United Kingdom and United States (odds ratio, 3.0; controlled for age and for ApoE [apolipoprotein E] genotype). Homozygosity for both allele 2 of IL-1A and allele 2 of IL-1B conferred even greater risk (odds ratio, 10.8). IL-1 genotypes may confer risk for Alzheimer's disease through IL-1 overexpression and IL-1-driven neurodegenerative cascades.

Tissue tears in the white matter after lateral fluid percussion brain injury in the rat: relevance to human brain injury

A characteristic feature of severe diffuse axonal injury in man is radiological evidence of the "shearing injury triad" represented by lesions, sometimes haemorrhagic, in the corpus callosum, deep white matter and the rostral brain stem. With the exception of studies carried out on the non-human primate, such lesions have not been replicated to date in the multiple and diverse rodent laboratory models of traumatic brain injury. The present report describes tissue tears in the white matter, particularly in the fimbria of Sprague-Dawley rats killed 12, 24, and 48 h and 7 days after lateral fluid percussion brain injury of moderate severity (2.1-2.4 atm). The lesions were most easily seen at 24 h when they appeared as foci of tissue rarefaction in which there were a few polymorphonuclear leucocytes. At the margins of these lesions, large amounts of accumulated amyloid precursor protein (APP) were found in axonal swellings and bulbs. By 1 week post-injury, there was macrophage infiltration with marked astrocytosis and early scar formation. This lesion is considered to be due to severe deformation of white matter and this is the first time that it has been identified reproducibly in a rodent model of head injury under controlled conditions.

Absence of cystatin C mutation in sporadic cerebral amyloid angiopathy-related hemorrhage

In Icelandic pedigrees a cystatin C mutation, glutamine 68 (L68Q), causes autosomal dominant cerebral amyloid angiopathy-related hemorrhage (CAAH). We examined 33 patients with sporadic CAAH for this mutation. None carried L68Q and, including this report, only one of 52 published cases of sporadic CAAH has had the cystatin C mutation. Despite vascular colocalization of cystatin C with amyloid beta-protein, cystatin C L68Q is rare in sporadic CAAH.

Comparison of different methods of intracerebral administration of radioiododeoxyuridine for glioma therapy using a rat model

The Auger electron emitting agent 5-[125I]iodo-2'-deoxyuridine (i.e. [125I]IUdR) holds promise for the treatment of residual glioma after surgery because this thymidine analogue kills only proliferating cells. However, malignant cells which are not synthesizing DNA during exposure to the radiopharmaceutical will be spared. To determine whether tumour incorporation of [125I]IUdR could be enhanced by protracted administration, we used a C6 cell line, growing in the brains of Wistar rats, as a glioma model and compared three methods of intracerebral delivery of [125I]IUdR. Twenty-four hours after administration of drug, autoradiography of brain sections demonstrated nuclear uptake of the radiopharmaceutical in cells throughout tumour while normal brain cells remained free of radioactivity. The [125I]IUdR labelling indices (% +/- s.e.m.) achieved were 6.2 (0.4) by single injection, 22.5 (4.1) using a sustained release polymer implant (poly(lactide-co-glycolide)) and 34.3 (2.0) by mini-osmotic pump. These results emphasize the need for a sustained delivery system as a prerequisite for effective treatment. These findings are also encouraging for the development of a sustained release system for radiolabelled IUdR for use in the treatment of intracranial tumours, particularly in the immediate postoperative setting.

Impaired cerebral autoregulation 24 h after induction of transient unilateral focal ischaemia in the rat

Cerebral blood flow (CBF) and cerebral autoregulation have been investigated 24 h after transient focal ischaemia in the rat. Cerebral blood flow was measured autoradiographically before and during a moderate hypotensive challenge, to test autoregulatory responses, using two CBF tracers, (99m)Tc-d,l-hexamethylproyleneamine oxide and 14C-iodoantipyrine. Prior to induced hypotension, CBF was significantly reduced within areas of infarction; cortex (28 +/- 20 compared with 109 +/- 23 mL/100 g/min contralateral to ischaemic focus, P = 0.001) and caudate (57 +/- 31 compared with 141 +/- 32 mL/100 g/min contralaterally, P = 0.005). The hypotensive challenge (mean arterial pressure reduced to 60 mmHg by increasing halothane concentration) did not compromise grey matter autoregulation in the contralateral hemisphere; CBF data were not significantly different at normotension and during hypotension. However, in the ipsilateral hemisphere, a significant volume of cortex adjacent to the infarct, which exhibited normal flow at normotension, became oligaemic during the hypotensive challenge (e.g. frontal parietal cortex 109 +/- 15% to 65 +/- 15% of cerebellar flow, P < 0.01). This resulted in a 2.5-fold increase in the volume of cortex which fell below 50% cerebellar flow (39 +/- 34 to 97 +/- 46 mm3, P = 0.003). Moderate hypotension induced a significant reduction in CBF in both ipsilateral and contralateral subcortical white matter (P < 0.01). In peri-infarct caudate tissue, CBF was not significantly affected by hypotension. In conclusion, a significant volume of histologically normal cortex within the middle cerebral artery territory was found to have essentially normal levels of CBF but impaired autoregulatory function at 24 h post-ischaemia.

APOE epsilon4 allele and amyloid beta-protein deposition in long term survivors of head injury

Head injury and APOE epsilon4 are risk factors for Alzheimer's disease (AD). We previously found that deposits of amyloid beta-protein (Abeta) occur in fatal head injury, more frequently in patients with APOE epsilon4. We postulated that Abeta deposits triggered by injury could, in survivors, lead to AD-like pathology later in life. Here, we compared Abeta deposits in 21 long term survivors of head injury (up to 20 years) with age and APOE genotype matched controls. In both groups Abeta deposits were more common among patients with APOE epsilon4. However, Abeta deposits were not more common among survivors of head injury than controls. The findings support previous studies associating APOE epsilon4 with deposition of Abeta. However pathogenetic mechanisms other than Abeta deposition may explain the association of head injury with AD.

Axonal cytoskeletal responses to nondisruptive axonal injury and the short-term effects of posttraumatic hypothermia

In human diffuse axonal injury (DAI), axons are exposed to transient tensile strain. Over the ensuing several hours, injured axons enter a "pathological cascade" of events that lead to secondary axotomy. Use of animal models of traumatic axonal injury (TAI) has allowed description of a number of pathological changes before axotomy occurs, including structural and functional changes in the axolemma, disorientation, and/or loss of microtubules, either compaction and/or dispersion of neurofilaments together with focal compaction at sites where continuity of the axolemma is lost. Recent literature suggests that use of hypothermia may improve behavioral outcomes or reduce the number/density of injured axons in which axonal transport is altered after TAI. But there is presently no ultrastructural, pathological explanation as to how hypothermia may act at the level of the axon to reduce posttraumatic loss of axoplasmic transport. In this study, we tested the hypothesis that posttraumatic hypothermia may ameliorate (a) alteration of axonal transport and (b) early pathological changes in the axonal cytoskeleton prior to secondary axotomy. We have undertaken a pilot study within 4 h of stretch injury to adult guinea pig optic nerve axons as a model of TAI and applied stereological techniques to assess differences in pathology in animals either maintained at 37.5 degrees C or cooled to 32-32.5 degrees C for 2 or 4 h after injury. We provide quantitative evidence that posttraumatic hypothermia significantly reduces the number of axons labelled for beta-APP, a marker for disruption of fast axonal transport, and reduces the loss of microtubules and compaction of neurofilaments, which occurs in normothermic animals over the first 4 h after injury.

Apolipoprotein E and the response of the brain to injury

Apolipoprotein E (apoE) is an important part of the means by which lipids are transported in the nervous system. This transport system provides injured nerve cells, the cholesterol and phospholipids for the maintenance and repair of membranes, the growth of neurites, dendritic remodelling and synaptogenesis, and the effect of injury to the nervous system is now known in part to be modulated by the various isoforms of apoE. After the demonstration of an association between the apoE epsilon 4 and increased risk of subsequent development of both sporadic and late-onset form Alzheimer's disease, recent studies have provided additional evidence for the possibility that apoE may play an isoform-specific role in determining both the initial response and the subsequent consequences to acute brain injury. Further studies are required to better understand not only the response(s) of the nervous system to injury, but also the relationship between acute injury to the brain and the subsequent development of neurodegenerative disorders.

Calpain activation and cytoskeletal protein breakdown in the corpus callosum of head-injured patients

Calpain-mediated breakdown of the cytoskeleton has been proposed to contribute to brain damage resulting from head injury. We examined the corpus callosum from patients who died after a blunt head injury in order to determine if there was evidence of these pathophysiological events in a midline myelinated commissure that is susceptible to damage after human head injury. Western blotting revealed marked reductions in the levels of neurofilament triplet proteins 200 and 68kDa in the corpus callosum of head-injured patients compared with control subjects. Neurofilament 200kDa levels were significantly reduced as detected by either phosphorylation-dependent or -independent antibodies. In contrast, there were minimal changes in the levels of beta-tubulin or the microtubule-associated protein, tau, in the head-injured patients, although amyloid precursor protein immunostaining demonstrated axonal damage in 9 of the 10 patients. The inactive 800kDa and active 76kDa subunits of mu-calpain were present in control subjects and head-injured patients. However, there was a significant increase in the levels of calpain-mediated spectrin breakdown products in head-injured patients compared with the control subjects. The results demonstrate that following human blunt head injury, there is a significant degradation of neurofilament proteins and increased levels of calpain-mediated spectrin breakdown products within the corpus callosum. Therefore, our data support the hypothesis that calpain-mediated breakdown of the cytoskeleton may contribute to axonal damage after head injury.

The apolipoprotein E epsilon2 allele and the pathological features in cerebral amyloid angiopathy-related hemorrhage

Cerebral amyloid angiopathy (CAA) is associated with apolipoprotein E (APOE gene, apoE protein) polymorphism: current evidence suggests that the epsilon4 allele is a risk factor for the development of CAA and the epsilon2 allele predisposes to hemorrhage. We sought to determine the relationship between the APOE epsilon2 allele and both the immunoreactivity profiles and vascular complications of CAA. We performed immunohistochemistry for amyloid beta-protein (A beta), apoE, cystatin C, and activated microglia, and examined the morphology of cortical and leptomeningeal vessels in 37 CAA-related hemorrhage (CAAH), 26 Alzheimer disease (AD) patients, and 20 controls. The extent of immunostaining of vessels for A beta, apoE, cystatin C, and perivascular activated microglia increased from controls through AD to a maximum in CAAH patients. Among cases with CAA (37 CAAH, 19 AD, and 6 controls, n = 62) vascular apoE (p < 5 x 10(-4)), cystatin C (p < 10(-4)), activated microglia (p < 10(-4)), vessels with a high ratio of wall thickness to lumen diameter (p < 0.003) as well as dilated/microaneurysmal vessels (p < 0.01) were present more frequently in patients with hemorrhage than without; however, these features were not associated with the APOE epsilon2 allele. Fibrinoid necrosis alone was associated with the APOE epsilon2 allele (p < 0.04) and we suggest that over-representation of APOE epsilon2 in CAAH may result from its association with fibrinoid necrosis.

Mitochondrial DNA deletions in acute brain injury

We hypothesized that generation of free radicals following acute brain injury leads to increased accumulation of mitochondrial DNA deletions. We determined the prevalence of two deletions (mtDNAdelta4977bp and mtDNAdelta7436hP) in brain from 53 patients with a short survival interval (mean 5 days) following transient global cerebral ischaemia due to cardiorespiratory arrest, 14 patients with long survival (mean 8.75 years) following traumatic brain injury and 43 age-matched controls. A higher prevalence of mtDNA delta4977bp was found in aged controls. There was a strong correlation between the presence of the two mtDNA deletions in individual cases (p < 0.05). The deletion prevalence did not differ significantly between short-term survivors of global ischaemia (57% mtDNAdelta4977bP, 62% mtDNAdelta7436bp) and controls (54% mtDNAdelta4977bp, 56% mtDNAdelta7436bp). Unexpectedly, there was a lower prevalence of deleted mtDNA in long-term survivors of traumatic brain injury (14.3% mtDNAdelta7436bp, p < 0.05) raising the possibility that free radical-induced accumulation of mtDNA damage may selectively influence the survival of mitochondria or their host.

Freeze-fracture and cytochemical evidence for structural and functional alteration in the axolemma and myelin sheath of adult guinea pig optic nerve fibers after stretch injury

Recent work in animal models of human diffuse axonal injury has generated the hypothesis that, rather than there being physical disruption of the axolemma at the time of injury, a pertubation of the membrane occurs, which leads, over time, to a dysfunction of the physiology of the axolemmal. This dysfunction is posited to lead to a disruption of ionic homeostasis within the injured axon, leading to secondary axotomy some hours after the initial insult. We decided to test the hypothesis that membrane pump/ion channel activity or function is compromised and this would be reflected in structural changes within the axolemma and myelin sheath. We used freeze fracture and cytochemical techniques to provide evidence for change in membrane structure and the activity of membrane pumps after nondisruptive axonal injury in the adult guinea pig optic nerve. Within 10 min of injury, structural changes occurred in the distribution and number of intramembranous particles (IMPs) in the internodal axolemma. By 4 h, there was novel labeling for Ca-ATPase membrane pump activity at the same site. There was loss of IMPs from the nodal axolemma extending over several hours after injury. There was loss of both membrane pump Ca-ATPase and p-nitro-phenylphosphatase (p-NPPase) activity of the node. There was loss of ecto-Ca-ATPase activity but increased labeling for p-NPPase activity at sites of dissociation of compacted myelin. Quantitative freeze-fracture demonstrated statistically significant changes in membrane structure. We provide support for the hypothesis that structural and functional changes occur in the axolemma and myelin sheath at nondisruptive axonal injury.

Influence of apolipoprotein E genotype on neuronal damage and apoE immunoreactivity in human hippocampus following global ischemia

Apolipoprotein E (apoE) influences the response to and outcome from brain injury possibly through alterations in neuronal repair mechanisms. This study aimed to determine alterations in neuronal and glial apoE after brain injury in patients and sought to determine whether possession of an apoE-epsilon4 allele influences the degree of apoE immunoreactivity or the degree of neuronal damage following brain injury. ApoE immunoreactivity and neuronal damage were semiquantitatively assessed in the temporal lobe of a group of controls (n = 44) and in a group of patients who had an episode of global ischemia and subsequently died (n = 58, survival ranged from 1 hour to 3 months). There was a significant degree of neuronal damage in all hippocampal sectors and in the neocortex of the global ischemia group compared with controls (p < 0.0001). Glial apoE immunoreactivity was significantly increased in hippocampal sectors (CA1, CA2, CA3/CA4, dentate fascia) in the global ischemia group compared with controls (p < 0.01). Neuronal apoE immunoreactivity was significantly increased in all hippocampal sectors (CA1, CA2, CA3/CA4, dentate fascia) and in the neocortex of the global ischemia group compared with controls (p < 0.0001). There was a significant and positive association between the degree of neuronal apoE immunoreactivity and the degree of neuronal damage in the global ischemia cases (r2 = 0.691, p < 0.001) and there was not an association in the control group. Possession of an apoE-epsilon4 allele did not influence the degree of neuronal or glial apoE immunoreactivity or the degree of neuronal damage in the global ischemia cases or the controls. The data indicate apoE is markedly increased in neurons and glia following brain injury. In this study, apoE genotype did not appear to influence neuronal damage, glial apoE or intraneuronal apoE following injury

A comparison of manual and semi-automated methods in the assessment of axonal injury

Diffuse axonal injury (DAI) in the central nervous system is a common cause of post-traumatic coma and may result in varying degrees of disability up to and including the vegetative state. Experimental studies in man and animals have previously relied upon semi-quantitative grading systems for determining the relationship between the extent of DAI and the clinical features of patients. Using beta-amyloid precursor protein immunocytochemistry for the detection of DAI in sections of corpus callosum from 15 cases of fatal head injury, we have developed a quantitative image analysis technique for the assessment of axonal injury. This new method is objective and reproducible and should allow better correlation with biomechanical, radiological, and clinical parameters to increase our understanding of DAI.

Is there a genetic basis for the deposition of beta-amyloid after fatal head injury?

1. Alzheimer's disease is a heterogeneous disorder that may be caused by genetic or environmental factors or by a combination of both. Abnormalities in chromosomes 1, 14, and 21 have all been implicated in the pathogenesis of the early-onset form of the disease, while the epsilon 4 allele of the apolipoprotein E gene (on chromosome 19) is now recognized as a risk factor for early- and late-onset sporadic and familial Alzheimer's disease. 2. The best-established environmental trigger for the disease is a head injury, based on epidemiological and neuropathological evidence. Approximately 30% of patients who die after a single episode of severe head injury show intracerebral deposition of beta-amyloid protein (A beta), a protein that is thought to be central to the pathogenesis of Alzheimer's disease. 3. Recent studies have revealed an over-representation of the apoE epsilon 4 allele in those head-injured patients displaying A beta pathology, thus providing the first evidence for a link between a genetic susceptibility (apoE epsilon 4) and an environmental trigger (head injury) in the development of Alzheimer-type pathology.

Interindividual differences in the levels of the glutamate transporters GLAST and GLT, but no clear correlation with Alzheimer's disease

Alzheimer's disease is a common progressive neurodegenerative disease of unknown etiology. Several different pathological processes have been identified in the brains of Alzheimer patients. To determine if reduced glutamate uptake is a contributing factor, we have measured the levels of the glutamate transporter proteins GLAST (EAAT1) and GLT (EAAT2) in human autopsy samples. The postmortem proteolysis of these proteins turned out to be fairly rapid. Brains from 10 Alzheimer and 10 control patients were therefore obtained with a relatively short postmortem delay (5 hr on average). GLT (N-terminal and central parts), GLAST (C-terminal), glial fibrillary acidic protein (GFAP) and inositol (1,4,5)-triphosphate (IP3)-receptor immunoreactivities were determined in the cingulate and inferior temporal gyri by immunoblotting. The Na+-dependent "binding" of D-[3H]aspartate and the glutamate uptake after solubilization and reconstitution in liposomes were determined for comparison. An individual variation in GLAST and GLT levels was found, but no significant correlation with Alzheimer's disease, except for a 14% lower ratio of N-terminal to central GLT immunoreactivity (P < 0.04). The levels of GLAST and GLT showed negative correlation in agreement with the idea that these proteins are differentially regulated. In conclusion, Alzheimer's disease brains can have both normal and reduced levels of GLAST and GLT.

The neuronal cytoskeleton is at risk after mild and moderate brain injury

Recent studies have described alterations in cytoskeletal proteins such as microtubule-associated protein 2 (MAP-2) and neurofilament (NF) resulting from moderate and severe experimental brain injury; however, few have investigated the consequences of mild injury, which is associated clinically and experimentally with cognitive dysfunction and neuronal damage. To contrast cytoskeletal changes within 7 days following mild injury with those following moderate injury, we subjected anesthetized, adult rats to mild (1.1-1.3 atm) or moderate (2.3-2.5 atm) lateral fluid percussion brain injury or sham injury. Rats were sacrificed at 6 h (n=4 mild; n=4 moderate; n=2 sham), 24 h (n=4 mild; n=4 moderate; n=1 sham), or 7 days (n=5 mild; n=4 moderate; n=1 sham) following injury, and immunohistochemistry was performed for MAP-2 and NF. Both mild and moderate injury produced notable cytoskeletal changes in multiple brain regions; however, mild injury generally resulted in a lesser degree of MAP-2 and NF loss over a smaller spatial extent. When compared to moderately injured animals, animals subjected to mild injury showed substantially delayed MAP-2 and NF alterations within the cortex and hippocampal dentate gyrus and no evidence of MAP-2 loss in the hippocampal CA3 region. While mild and moderate injury resulted for the most part in similar patterns of axonal injury, tissue tears in the fimbria and loss of NF immunoreactivity in regions containing injured axons were only observed following moderate injury. Elucidating the effects of modulating injury severity may yield insight into the mechanisms involved in traumatic damage to the cytoskeleton and guide future treatment strategies.

Axonal cytoskeletal changes after nondisruptive axonal injury. II. Intermediate sized axons

Earlier studies of axonal cytoskeletal responses to stretch injury in the guinea pig optic nerve, a model of nondisruptive axonal injury such as occurs in human diffuse axonal injury, have demonstrated different cytoskeletal responses between the smallest and largest axons. But these form only approximately 3% of the total number of axons in the optic nerve. It was then posited that the pathology described in the latter axons may not be representative of the pathology in the majority of axons after stretch injury. In order to test this hypothesis, we carried out a quantitative, morphological analysis of structural changes in the cytoskeleton of intermediate (axonal diameter of 0.5-2.0 mM) sized axons at 4 h after stretch injury. Neurofilaments in axons up to 1.00 microm in diameter increased in number and in axons up to 1.50 microm diameter were compacted. This did not occur in larger axons (diameter of 1.51-2.00 microm) in the present study. However, there was focal compaction of neurofilaments in some of the larger fibers at sites where the integrity of the axolemma was lost. The response by microtubules to stretch injury differed from that of neurofilaments in that there was an increased spacing between microtubules and a loss of their number in axons of >1.51 microm diameter. We provide quantitative, morphological evidence (a) that the neurofilamentous cytoskeleton of different sized axons responds in different ways to stretch and (b) that the response by microtubules differs from that of neurofilaments.

Craniocerebral trauma: protection and retrieval of the neuronal population after injury

OBJECTIVE

To review the consequences of mechanical injury to the brain with an emphasis on factors that may explain the variability of outcomes and how this might be influenced.

METHODS

Information regarding the pathophysiology of traumatic brain damage contained in original scientific reports and in review articles published in recent years was reviewed from the perspective of a clinical neurosurgeon and a neuropathologist, each with major research interests in traumatic brain damage. The information was compiled on the basis of the knowledge of and personal selection of articles that were identified through selective literature searches and current awareness profiles. A systematic literature review was not conducted.

RESULTS

Mechanical input affects neuronal and vascular elements and is translated into biological effects on the brain through a complex series of interacting cellular and molecular events. Whether these lead to permanent structural damage or to resolution and recovery is determined by the balance between processes that, on the one hand, mediate the effects of initial injury and subsequent secondary insults and, on the other, are manifestations of the brain's protective, reparative response. Experimental and clinical research has identified opportunities for altering the balance in a way that might promote recovery, but data demonstrating that this can lead to substantial clinical benefit are lacking. Recent evidence of genetically determined, individual susceptibility to the effects of injury may explain some of the puzzling variability in outcome after apparently similar insults and may also provide new opportunities for treatment.

CONCLUSION

The understanding of traumatic brain damage that is being gained from recent research is widening and broadening perspectives from the traditional focus on mechanical, vascular, and metabolic effects to encompass wider, neurobiological issues, drawn from the fields of neurodevelopment, neuroplasticity, neurodegeneration, and neurogenetics. Neurotrauma is a fascinating area of neuroscience research, with promise for the translation of knowledge to improved clinical management and outcome.

Histopathological responses in the CNS following inoculation with a non-neurovirulent mutant (1716) of herpes simplex virus type 1 (HSV 1): relevance for gene and cancer therapy

The RL1 gene of herpes simplex virus (HSV) encodes a polypeptide, ICP34.5 which is a specific virulence determinant. RL1 null mutants fail to replicate in both the PNS and CNS and are incapable of causing encephalitis. Additionally, RL1 null mutants have the capacity to replicate in actively dividing cells but fail to replicate in growth arrested or terminally differentiated cells. This selective replication phenotype has highlighted their use as both tumour killing agents and gene delivery vehicles particularly to the nervous system. Before their full potential can be assessed, however, it is necessary to determine the pathological and immune responses induced following direct intracerebral inoculation. Fourteen mice were injected in the left cerebral hemisphere with a high dose of the HSV-1, RL1 null mutant 1716. At regular time intervals up to 28 days, the mice were killed and the distribution of virus antigen, histopathological changes and immune responses in the CNS determined by H & E staining and immunohistochemistry. Control mice were injected with either wild type HSV-1 or buffer. At early times post-inoculation with 1716, there is a low grade meningoencephalitis with a limited inflammatory response. This is accompanied by virus antigen expression confined to the site of inoculation. By 28 days the CNS is histopathologically normal; virus antigen and immune responses are no longer detectable. These findings demonstrate that infection of the CNS by RL1 null mutants of HSV results in a finite, self-limiting response and highlights their potential for therapeutic use.