The Dorothy Russell Memorial Lecture. The molecular and cellular sequelae of experimental traumatic brain injury: pathogenetic mechanisms

The mechanisms underlying secondary or delayed cell death following traumatic brain injury (TBI) are poorly understood. Recent evidence from experimental models of TBI suggest that diffuse and widespread neuronal damage and loss is progressive and prolonged for months to years after the initial insult in selectively vulnerable regions of the cortex, hippocampus, thalamus, striatum, and subcortical nuclei. The development of new neuropathological and molecular techniques has generated new insights into the cellular and molecular sequelae of brain trauma. This paper will review the literature suggesting that alterations in intracellular calcium with resulting changes in gene expression, activation of reactive oxygen species (ROS), activation of intracellular proteases (calpains), expression of neurotrophic factors, and activation of cell death genes (apoptosis) may play a role in mediating delayed cell death after trauma. Recent data suggesting that TBI should be considered as both an inflammatory and/or a neurodegenerative disease is also presented. Further research concerning the complex molecular and neuropathological cascades following brain trauma should be conducted, as novel therapeutic strategies continue to be developed.

The neuronal cytoskeleton in acute brain injury

The microtubules, neurofilaments and microfilaments of the neuronal cytoskeleton are essential for the normal functioning of the neurone. Recent studies have shown that disruption of the cytoskeleton may represent a final pathway in many types of neuronal cell injury with both the somato-dendritic and axonal cytoskeleton being affected. This review discusses the current evidence on the role of the neuronal cytoskeleton in the pathogenesis of traumatic brain damage.

Protection by an adenosine analogue against kainate-induced extrahippocampal neuropathology

1. The glutamate analogue kainic acid produces neuronal damage in the central nervous system. We have reported that analogues of adenosine, such as R-N6-phenylisopropyladenosine (R-PIA) can, at doses as low as 10 microg/kg IP, prevent the hippocampal damage that follows the systemic administration of kainate. The present work was designed to examine purine protection against kainate in extrahippocampal regions by using histological methods. 2. The results show that R-PIA, at a dose of 25 microg/kg IP in rats, can protect against the neuronal damage caused by kainate in the basolateral amygdaloid nuclei, the pyriform cortex and around the rhinal fissure. This protection could be prevented by the simultaneous administration of the A1 adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine, confirming that the protection involved adenosine A1 receptors. No protection was observed in the posterior amygdaloid nuclei or the entorhinal cortex, suggesting the absence of relevant adenosine receptors or a different mechanism of excitotoxicity.

Topographical and quantitative assessment of white matter injury following a focal ischaemic lesion in the rat brain

Axonal injury following cerebral ischaemia has attracted less attention than damage in grey matter. However, it is becoming increasingly recognised that axons are highly vulnerable to focal ischaemia [D. Dewar, D.A. Dawson, Changes of cytoskeletal protein immunostaining in myelinated fibre tracts after focal cerebral ischaemia in the rat, Acta. Neuropathol., 93 (1997) 71-77] [2]; [L. Pantoni, J.H. Garcia, J.A. Gutierrez, Cerebral white matter is highly vulnerable to ischemia, Stroke, 27 (1996) 1641-1647] [10]; [P. S. Yam, T. Takasago, D. Dewar, D.I. Graham, J. McCulloch, Amyloid precursor protein accumulates in white matter at the margin of a focal ischaemic lesion, Brain Res., 760 (1997) 150-157] [15]. Since white matter does not contain neuronal cell bodies or synapses it is likely that the mechanisms of injury and strategies for its protection are different from those in grey matter. In order that the effect of therapeutic intervention on the protection of axons can be assessed, a method by which axonal injury can be mapped and quantified is required. For this purpose, we investigated immunocytochemical methods using amyloid precursor protein (APP) following permanent middle cerebral artery occlusion in the rat. APP is transported by fast anterograde axonal transport [E.H. Koo, S.S. Sisodia, D.R. Archer, L.J. Martin, A. Weidemann, K. Beyreuther, P. Fischer, C.L. Masters, D.L. Price, Precursor of amyloid protein in Alzheimer disease undergoes fast anterograde axonal transport, Proc. Natl. Acad. Sci. U.S.A. 87 (1990) 1561-1565] [7] and has been shown to accumulate following a variety of insults to axons, indicative of dysfunction of axonal transport [R.N. Kalaria, S.U. Bhatti, E.A. Palatinsky, D.H. Pennington, E.R. Shelton, H.W. Chan, G. Perry, W.D. Lust, Accumulation of the beta amyloid precursor protein at sites of ischemic injury in rat brain, Neuroreport, 4 (1993) 211-214] [4]; [T. Kawarabayashi, M. Shoji, Y. Harigaya, H. Yamaguchi, S. Hirai, Expression of APP in the early stage of brain damage, Brain Res., 563 (1991) 334-338] [5]; [N. Otsuka, M. Tomonaga, K. Ikeda, Rapid appearance of beta-amyloid precursor protein immunoreactivity in damaged axons and reactive glial cells in rat brain following needle stab injury, Brain Res., 568 (1991) 335-338] [9]; [K. Shigematsu, P. L. McGeer, Accumulation of amyloid precursor protein in neurons after intraventricular injection of colchicine, Am. J. Pathol., 140 (1992) 787-794] [12]. We have been able to map the topographical relationship between APP accumulation and region of infarction using immunocytochemistry and image analysis techniques. Additionally, using a semi-quantitative scoring system, we have demonstrated that there is a relationship between the amount of APP accumulation and the volume of infarction following middle cerebral artery occlusion. These methods will be useful in the future for the assessment of therapeutic interventions on the protection of axons following ischaemic injury.

Cortical cholinergic dysfunction after human head injury

Loss of cholinergic neurotransmission is implicated in memory impairment and cognitive dysfunction after head injury. The aim of the present study was to investigate presynaptic markers, particularly in relation to cholinergic neurotransmission in human postmortem brain from patients who died following a head injury and age-matched controls. Choline acetyltransferase activity and high-affinity nicotinic receptor binding sites were assayed in the inferior temporal gyrus, cingulate gyrus, and superior parietal cortex of 16 head-injured patients and 8 controls. Synaptophysin immunoreactivity was determined in the left cingulate gyrus from the same patient groups. In the head-injured group, choline acetyltransferase activity was consistently reduced in each cortical region compared to control subjects. The presence of a subdural haematoma and a prolonged survival period after head injury tended to be associated with lower choline acetyltransferase activity. In contrast to the marked reduction in choline acetyltransferase activity, nicotine receptor binding was unchanged in head-injured compared to control patients. Synaptophysin immunoreactivity in the cingulate gyrus was reduced by approximately 30% (p < 0.05) in the head-injured group compared to controls. Correlation of choline acetyltransferase activity with synaptophysin immunoreactivity indicated there is a deficit of cholinergic presynaptic terminals in postmortem human brain following head injury.

Selective astrocytic transgene expression in vitro and in vivo from the GFAP promoter in a HSV RL1 null mutant vector--potential glioblastoma targeting

Due to the lack of any effective therapy, novel approaches are currently being explored for the treatment of primary brain tumours. It has previously been demonstrated that variants of HSV-1 which are deleted in the RL1 gene and fail to produce the virulence factor ICP34.5 are potential candidates for tumour therapy. The RL1 variant 1716 replicates selectively within tumour cells and has the potential to deliver a therapeutic or tumour killing gene directly to the site of tumour growth. As many intracerebral tumours are glial and predominantly astrocytic in origin, we have evaluated the ability of 1716 to deliver a reporter gene specifically to astrocytes in vivo and in vitro using a 2.2 kb fragment which controls expression of the glial fibrillary acidic protein (GFAP), an astrocyte specific protein. Two 1716 variants, 1774 and 1775, were constructed which contain the GFAP-promoter element linked to the E. coli beta-galactosidase gene, inserted into the HSV-1 UL43 and US5 loci, respectively. In primary cultures, human primary tumour cell lines and established tumour cell lines in vitro, 1774 and 1775 gave high levels of expression of beta-galactosidase specifically in astrocytes. In vivo following intracerebral inoculation, both viruses demonstrated high levels of beta-galactosidase expression predominantly in astrocytes. These results indicate that the GFAP promoter element could be used for efficient and selective transgene delivery to human gliomas.

Glial-neuronal interactions in Alzheimer's disease: the potential role of a 'cytokine cycle' in disease progression

The role of glial inflammatory processes in Alzheimer's disease has been highlighted by recent epidemiological work establishing head trauma as an important risk factor, and the use of anti-inflammatory agents as an important ameliorating factor, in this disease. This review advances the hypothesis that chronic activation of glial inflammatory processes, arising from genetic or environmental insults to neurons and accompanied by chronic elaboration of neuroactive glia-derived cytokines and other proteins, sets in motion a cytokine cycle of cellular and molecular events with neurodegenerative consequences. In this cycle, interleukin-1 is a key initiating and coordinating agent. Interleukin-1 promotes neuronal synthesis and processing of the beta-amyloid precursor protein, thus favoring continuing deposition of beta-amyloid, and activates astrocytes and promotes astrocytic synthesis and release of a number of inflammatory and neuroactive molecules. One of these, S100beta, is a neurite growth-promoting cytokine that stresses neurons through its trophic actions and fosters neuronal cell dysfunction and death by raising intraneuronal free calcium concentrations. Neuronal injury arising from these cytokine-induced neuronal insults can activate microglia with further overexpression of interleukin-1, thus producing feedback amplification and self-propagation of this cytokine cycle. Additional feedback amplification is provided through other elements of the cycle. Chronic propagation of this cytokine cycle represents a possible mechanism for progression of neurodegenerative changes culminating in Alzheimer's disease.

Aging-associated changes in human brain

A wide variety of anatomic and histological alterations are common in brains of aged individuals. However, identification of intrinsic aging changes--as distinct from changes resulting from cumulative environmental insult--is problematic. Some degree of neuronal and volume loss would appear to be inevitable, but recent studies have suggested that the magnitudes of such changes are much less than previously thought, and studies of dendritic complexity in cognitively intact individuals suggest continuing neuronal plasticity into the eighth decade. A number of vascular changes become more frequent with age, many attributable to systemic conditions such as hypertension and atherosclerosis. Age-associated vascular changes not clearly linked to such conditions include hyaline arteriosclerotic changes with formation of arterial tortuosities in small intracranial vessels and the radiographic changes in deep cerebral white matter known as "leukoaraiosis." Aging is accompanied by increases in glial cell activation, in oxidative damage to proteins and lipids, in irreversible protein glycation, and in damage to DNA, and such changes may underlie in part the age-associated increasing incidence of "degenerative" conditions such as Alzheimer disease and Parkinson disease. A small number of histological changes appear to be universal in aged human brains. These include increasing numbers of corpora amylacea within astrocytic processes near blood-brain or cerebrospinal fluid-brain interfaces, accumulation of the "aging" pigment lipofuscin in all brain regions, and appearance of Alzheimer-type neurofibrillary tangles (but not necessarily amyloid plaques) in mesial temporal structures.

Neuroprotective efficacy of ebselen, an anti-oxidant with anti-inflammatory actions, in a rodent model of permanent middle cerebral artery occlusion

1. The aim of this study was to investigate whether delayed treatment with the anti-oxidant and anti-inflammatory agent ebselen reduces the volume of infarction in a rodent model of permanent focal cerebral ischaemia. 2. Ebselen (10 or 30 mg kg-1) or vehicle was administered by gavage 30 min and 12 h after the induction of cerebral ischaemia by permanent occlusion of the left middle cerebral artery (MCA). Animals were killed 24 h following MCA occlusion, and the volumes of ischaemic damage in the ebselen and control groups were evaluated by quantitative histopathology. 3. Ebselen was quickly absorbed following oral (gavage) administration and reached peak levels in the plasma by 1 h post-administration (plasma selenium level of 0.68 +/- 0.04 and 0.84 +/- 0.1 microgram ml-1 for 10 and 30 mg kg-1, respectively, compared to control level of 0.51 +/- 0.02 microgram kg-1). 4. Treatment with the lower dose of ebselen (10 mg kg-1) significantly (P < 0.01) reduced the volume of infarction in the cerebral hemisphere and cerebral cortex (by 31.8% and 36.7%, respectively compared with the placebo group). 5. The neuroprotective efficacy of the higher dose ebselen (30 mg kg-1) was less than that of the lower dose ebselen (10 mg kg-1). The volume of ischaemic damage in the cerebral hemisphere was reduced by 23.7% (P < 0.02), and cerebral cortex by 27.5% (P < 0.01). 6. Both doses of ebselen (10, 30 mg kg-1) had no therapeutic efficacy on the caudate nucleus, where ischaemia was most severe, in this model. 7. Free radical-mediated injury is normally associated with reperfusion of ischaemic tissue. The present results suggest that oxidative injury is also a significant contributor to brain damage in models of maintained (permanent) ischaemia and that ebselen is effective in attenuating this free radical-induced damage.

The attenuation of kainate-induced neurotoxicity by chlormethiazole and its enhancement by dizocilpine, muscimol, and adenosine receptor agonists

Systemically administered kainate (10 mg.kg-1) caused neuronal loss in both the hippocampus and the entorhinal regions of the rat brain. This resulted in a loss of 68.3 +/- 13.8 and 53.3 +/- 12.8% of pyramidal neurones in the hippocampal CA1 and CA3a regions, respectively. Chlormethiazole attenuated the loss of neurones in the hippocampal cell layers CA1 (cell loss 10 +/- 3.2%) and CA3a (cell loss 10 +/- 7.7%). The neuroprotective activity of chlormethiazole was apparent in the presence or absence of a low dose of clonazepam (200 micrograms.kg-1 i.p.). The kainate-induced damage could also be measured by the increase in binding of the peripheral benzodiazepine ligand ([3H]PK11195) in the hippocampus. In kainate-treated rats there was a 350-500% increase in binding indicative of reactive gliosis. Chlormethiazole prevented this elevation in a dose- and time-dependent manner, with an ED50 of 10.64 mg.kg-1 and an effective therapeutic window from 1 to 4 h posttreatment. Dizocilpine also attenuated damage significantly. The GABAA agonist muscimol was also able to attenuate the increase in [3H]PK11195 binding in a dose-dependent manner, with an ED50 of approximately 0.1 mg.kg-1. If muscimol, dizocilpine, or the adenosine A1 receptor agonist R-N6-phenylisopropyl-adenosine were administered together with chlormethiazole at their respective ED25 doses, a potentiation was apparent in the degree of neuroprotection. It is concluded that the combination of neuroprotective agents with different mechanisms of action can lead to a synergistic protection against excitotoxicity.

Progressive atrophy and neuron death for one year following brain trauma in the rat

Although atrophic changes have been well described following traumatic brain injury (TBI) in humans, little is known concerning the mechanisms or progression of brain tissue loss. In the present study, we evaluated the temporal profile of histopathological changes following parasagittal fluid-percussion (FP) brain injury in rats over 1 year postinjury. Anesthetized 3-4 month-old Sprague-Dawley Rats (n = 51) were subjected to FP brain injury of high severity (2.5-2.9 atm, n = 51) or sham treatment (n = 27). At 1 h, 2 h, 48 h, 1 week, 2 weeks, 1 month, 2 months, 6 months and 1 year after brain injury or sham treatment, these animals were humanely euthanized. Brain sections were analyzed with image-processing techniques to determine the extent of cortical tissue loss and shrinkage of the hippocampal pyramidal cell layer. In addition, cell counting was performed to determine the number of neurons in the dentate hilus of the hippocampus, and glial fibrillary acidic protein (GFAP) immunostaining was used to reveal reactive astrocytosis. Examination of the injured brains revealed substantial and progressive tissue loss with concomitant ventriculomegaly in the hemisphere ipsilateral to injury. The regions with the most notable progressive atrophy included the cortex, hippocampus, thalamus, and septum. Quantitative analysis demonstrated a significantly progressive loss of cortical tissue as well as shrinkage of the hippocampal pyramidal cell layer ipsilateral to injury over 1 year following injury. In addition, reactive astrocytosis in regions of atrophy and progressive bilateral death of neurons in the dentate hilus was observed for 1 year following injury. These results suggest that a chronically progressive degenerative process may be initiated by brain trauma. Thus, there is a temporally broad window within which to introduce novel therapeutic strategies designed to ameliorate the short and long-term consequences of brain trauma.

Loss of axonal microtubules and neurofilaments after stretch-injury to guinea pig optic nerve fibers

Axonal swellings, characterized by focal accumulations of membranous organelles at presumed sites of interrupted axonal transport, occur in diffuse axonal injury (DAI) in human, blunt head injury and in animal models of nondisruptive axonal injury. Membranous organelles are transported by fast axonal transport in association with microtubules. Although loss of microtubules has been documented at levels of injury severe enough to result in permeabilization of the axolemma to tracers such as horseradish peroxidase, there has been no detailed analysis of responses by microtubules in less severe or milder forms of nondisruptive axonal injury. To test the hypothesis that in less severe forms of axonal injury there is a rapid response by axonal microtubules that might provide an explanation for loss of fast axonal transport, we have carried out a morphometric analysis of microtubules in CNS axons after stretch-injury. There is loss of microtubules at nodes of Ranvier with nodal blebs within 15 min of injury, and in internodal axonal swellings between 2 and 4 h. There is a return to control values at nodes of Ranvier by 4 h, and at the internode by 24 h. There is no loss of microtubules at paranodes, although there is a reduction in their density in the first 2 h after injury. The greatest loss of microtubules occurs at sites of axolemma infolding. Hypothetical mechanisms that might lead to this loss resulting in focal disruption of fast axonal transport and the formation of axonal swellings are discussed.

Amyloid precursor protein accumulates in white matter at the margin of a focal ischaemic lesion

Amyloid precursor protein (APP) is transported by fast anterograde axonal transport. Since disruption of this transport results in APP accumulation, APP has been proposed as a sensitive marker of axonal injury. In the present study, axonal injury in subcortical white matter and myelinated fibre tracts permeating the striatum, 24 h after permanent middle cerebral artery occlusion in the rat, has been examined by assessing the location and extent of APP immunoreactivity. Increased APP immunoreactivity was present in both areas. This was localised to a circumscribed zone immediately adjacent to the boundary of the ischaemic lesion in grey matter. The amount of APP immunoreactivity was associated with the volume of the ischaemic lesion in individual animals. Increased APP immunoreactivity in subcortical white matter and myelinated fibre tracts at the margin of the ischaemic zone may prove to be a valuable marker for assessing strategies to protect axons after an ischaemic insult.

High frequency of apolipoprotein E epsilon 2 allele in hemorrhage due to cerebral amyloid angiopathy

From the somewhat conflicting published data on apolipoprotein E (apoE) genotype in hemorrhage due to cerebral amyloid angiopathy (CAA), it is unclear whether apoE genotype influences the risk of CAA-related hemorrhage independently of its association with concomitant Alzheimer's disease (AD). We determined the apoE genotypes of 36 patients presenting with cerebral hemorrhage associated with histologically confirmed CAA. The frequency of apoE epsilon 2 was 0.25 and the frequency of apoE epsilon 4 was 0.18. Patients with CAA-related hemorrhage and concomitant AD pathology (CERAD criteria, n = 17) had a high apoE epsilon 4 frequency, close to that in AD cases without hemorrhage. Patients in whom CAA-related hemorrhage occurred in the absence of significant AD pathology (n = 13) had an apoE epsilon 4 frequency somewhat lower than non-AD controls without hemorrhage. However, in CAA-related hemorrhage, the apoE epsilon 2 frequency was high regardless of whether significant AD pathology was present. We conclude that whereas possession of apoE epsilon 2 may be a risk factor for cerebral hemorrhage due to CAA, apoE epsilon 4 is a risk factor for concomitant AD but not an independent risk factor for CAA-related hemorrhage.

A beta 42 is the predominant form of amyloid beta-protein in the brains of short-term survivors of head injury

Fatal head injury results in the formation of diffuse parenchymal deposits of amyloid beta-protein (A beta) in the brains of approximately 30% of individuals. We used carboxyl terminal-specific antisera to examine the exact nature of these deposits in paraffin sections of neocortex from seven head-injured patients. Immunostaining for A beta 42 was observed in all parenchymal deposits whereas staining for A beta 40, the form of the protein which predominates in serum and cerebrospinal fluid, was seen in only a small proportion of deposits. The relative paucity of A beta 40 suggests that post-traumatic deposits do not arise as a result of passive leakage from damaged cerebral blood vessels but are similar to the early A beta 42 parenchymal deposits seen in Down's syndrome and Alzheimer's disease.

Axonal cytoskeletal changes after non-disruptive axonal injury

In animal models of human diffuse axonal injury, axonal swellings leading to secondary axotomy occur between 2 and 6 h after injury. But, analysis of cytoskeletal changes associated with secondary axotomy has not been undertaken. We have carried out a quantitative analysis of cytoskeletal changes in a model of diffuse axonal injury 4 h after stretch-injury to adult guinea-pig optic nerves. The major site of axonal damage was the middle portion of the nerve. There was a statistically significant increase in the proportion of small axons with a diameter of 0.5 micron and smaller in which there was compaction of neurofilaments. Axons with a diameter greater than 2.0 microns demonstrated an increased spacing between cytoskeletal elements throughout the length of the nerve. However, in the middle segment of the nerve these larger axons demonstrated two different types of response. Either, where periaxonal spaces occurred, there was a reduction in axonal calibre, compaction of neurofilaments but no change in their number, and a loss of microtubules. Or, where intramyelinic spaces occurred there was an increased spacing between neurofilaments and microtubules with a significant loss in the number of both. Longitudinal sections showed foci of compaction of neurofilaments interspersed between regions where axonal structure was apparently normal. Neurofilament compaction was correlated with disruption of the axolemma at these foci present some hours after injury. We suggest that the time course of these axonal cytoskeletal changes after stretch-injury to central axons is shorter than those changes documented to occur during Wallerian degeneration.

Kainate-evoked release of adenosine from the hippocampus of the anaesthetised rat: possible involvement of free radicals

Using microdialysis in the hippocampus of anaesthetised rats, the concentration of extracellular adenosine was estimated to be 0.8 microM. Kainic acid (0.1-25 mM) in the perfusate evoked a concentration-dependent release of adenosine with an EC50 of 940 microM. Two 5-min pulses of 1 mM kainic acid in the perfusate increased the dialysate levels with an S2/S1 ratio of 0.52 +/- 0.03. Kainate-evoked release of adenosine was reduced significantly by 10 microM tetrodotoxin and by a kappa-receptor agonist, U50, 488H (100 microM). The S2/S1 ratio was reduced by 4.5 microM 6-cyano-7-nitroquinoxaline-2,3-dione, a non-NMDA receptor antagonist, but not by the NMDA receptor blockers (+)-MK-801 (dizocilpine; 100 microM) or (+/-)-2-amino-5-phosphonopentanoic acid (1 mM), indicating a non-NMDA receptor-mediated process. The S2/S1 ratio was also reduced significantly by 10 mM ascorbic acid, 10 mM glutathione (a scavenger of hydroperoxides), and 1 mM oxypurinol (a xanthine oxidase inhibitor), indicating the possible involvement of free radicals. Neither the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (100 microM) nor the A1 adenosine receptor agonist R(-)-N6-(2-phenylisopropyl)adenosine (100 microM) affected release. Adenosine release evoked by kainic acid is therefore mediated by activation of non-NMDA receptors and may involve the propagation of action potentials and the production of free radicals.

Presenilin-1 polymorphism and amyloid beta-protein deposition in fatal head injury

Approximately 30% of patients with fatal head injuries have deposits of amyloid beta-protein (A beta); these are predominantly individuals carrying the epsilon 4 allele of apolipoprotein E (apoE). A beta deposition occurs in Alzheimer's disease (AD), for which approximately 50% of the genetic risk is attributed to apoE epsilon 4. The 1,1 genotype of a presenilin-1 (PS-1) polymorphism has been suggested to account for about half of the remaining genetic risk for AD. We related the PS-1 genotypes of 90 head-injured individuals to A beta deposition and apoE genotype. There was no difference in PS-1 genotype or allele frequencies between individuals with and without A beta deposits. Eighteen of 23 individuals with A beta deposits had apoE epsilon 4 as a risk factor. Three of five individuals without apoE epsilon 4 had the PS-1 1,1 genotype. If PS-1 genotype influences A beta deposition the effect is small and is overwhelmed by that of apoE genotype.

Is beta-APP a marker of axonal damage in short-surviving head injury?

beta-Amyloid precursor protein (beta-APP), a normal constituent of neurons which is conveyed by fast axonal transport, has been found to be a useful marker for axonal damage in cases of fatal head injury. Immunocytochemistry for beta-APP is a more sensitive technique for identifying axonal injury than conventional silver impregnation. This study was designed to determine how quickly evidence of axonal damage and bulb formation appears. Using this method a variety of brain areas were studied from 55 patients who died within 24 h of a head injury. Immunocytochemical evidence of axonal injury was first detected after 2 h survival, axonal bulbs were first identified after 3 h survival, and the amount of axonal damage and axonal bulb formation increased the longer the survival time.

A new experimental model of contusion in the rat. Histopathological analysis and temporal patterns of cerebral blood flow disturbances

The authors have devised a simple reproducible rodent model of focal cortical injury that uses a mechanical suction force applied through intact dura. The time course and pattern of changes in neurons, glia, and microvasculature were investigated using this model. Early traumatic disruption of the blood-brain barrier and hemorrhage do not occur in this model; however, many of the features of human contusion seen with light and electron microscopy are closely reproduced. At the site of injury, early swelling and lucency of neural dendritic processes have been shown to precede an astrocyte response. In the absence of perivascular hemorrhage, delayed perivascular protein leakage and polymorphonuclear infiltration of the damaged cortex occurs, which is suggestive of an acute inflammatory response. Cerebral blood flow (CBF) has been measured using 14C-iodoantipyrine autoradiography at 30 minutes, 4 hours, and 24 hours after induction of negative-pressure injury in rats anesthetized with halothane and in time-matched sham-operated controls. A significant reduction in blood flow in the sensorimotor cortex at the site of the injury was present at 30 minutes, 4 hours, and 24 hours after induction of the lesion, compared to the contralateral cortex (superficial lamina, ipsilateral 50 +/- 7 ml/100 g/minute, contralateral 112 +/- 26 ml/100 g/minute). The CBF was significantly reduced at the ipsilateral entorhinal cortex at 30 minutes postinjury but no significant reduction was demonstrated at later time points. Although marked alterations in CBF occurred in this cortical injury model, the magnitude and duration of the reduction in CBF are not consistent with those necessary for production of ischemic cell damage. These data indicate that this model of cortical injury can be used to examine biomechanical aspects of contusion without domination by ischemic pathophysiology.

The neuronal cytoskeleton: an insight for neurosurgeons

The cytoskeleton is important in the structure and function of the neuron. Disruption of the cytoskeletal proteins occurs in a variety of forms of acute brain injury including cerebral ischaemia and diffuse anonal injury. The final common pathway mediating neuronal cell death involves loss of the integrity of the cytoskeleton and these disturbances may have a key role in the progression of events following acute brain injury. This review aims to provide an insight into the neuronal cytoskeleton in the normal state and in disorders encountered in neurosurgical practice.

Alteration in brain presenilin 1 mRNA expression in early onset familial Alzheimer's disease

The expression of the presenilin 1 (PS-1) gene has been investigated by in situ hybridization in early onset familial Alzheimer's disease (FAD), late onset Alzheimer's disease (AD) and normal control brain. Mutations in this gene are responsible for chromosome 14-linked FAD. We have found that presenilin 1 mRNA is present throughout the human brain with a distribution consistent with both a glial and neuronal localization. The in situ hybridization pattern was similar for the controls, the early onset FAD cases and the late onset AD cases. However, one of the two forms of the mRNA for PS-1, the long form (which contains a sequence encoding a four amino acid (VRSQ) insert at its 5' end) was significantly reduced in early onset FAD brain compared with late onset AD. We suggest that this long transcript may alter the normal pathway for processing of amyloid precursor protein, the protein which appears to be central in the pathogenesis of AD.