David I. Graham

Focal Cerebral Ischaemia in the Rat: 1. Description of Technique and Early Neuropathological Consequences Following Middle Cerebral Artery Occlusion

A procedure for occluding the stem of the proximal middle cerebral artery of the rat is described. The operation is performed under anaesthesia through a small subtemporal craniectomy. After occlusion, 3 animals were perfused with carbon black and 8 with a FAM fixative (40% formaldehyde, glacial acetic acid, and methanol). The findings were compared with sham-operated animals. Carbon black studies demonstrated an area of impaired perfusion corresponding to the territory of the occluded artery in each animal. Neuropathological studies invariably showed that there was ischaemic brain damage in the cortex and basal ganglia. The frontal cortex was involved in every animal, as was the lateral part of the neostriatum; the sensorimotor and auditory cortex were involved in most animals, whereas the occipital cortex and medial striatum were involved only infrequently. The damage produced by ischaemia could be readily distinguished from the small local lesion seen at the surgical site in sham-operated animals. The ability to produce a consistent focal ischaemic lesion in the rodent brain provides a technical approach that is sufficiently reproducible to enable investigation of the pathophysiology of ischaemia using recently developed autoradiographic and neurochemical methods.

Glial‐Neuronal Interactions in Alzheimer's Disease: The Potential Role of a ‘Cytokine Cycle’ in Disease Progression

The role of glial inflammatory processes in Alzheimers 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 β‐amyloid precursor protein, thus favoring continuing deposition of β‐amyloid, and activates astrocytes and promotes astrocytic synthesis and release of a number of inflammatory and neuroactive molecules. One of these, S100β, 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 Alzheimers disease.

βA4 amyloid protein deposition in brain after head trauma

Abstract Previous reports have suggested that both repetitive head trauma and a single injury can be associated with the presence of diffuse βA4 amyloid protein plaques in long-term survivors. We have studied sixteen patients (aged 10-63 years) who sustained head injury and survived for only 6-18 days. Immunostaining with an antibody to βA4 amyloid showed extensive deposits of the protein in the cortex in six of the sixteen patients (38%). Thus, severe head injury can trigger βA4 deposition in the brain within days.

ISCHAEMIC BRAIN DAMAGE IN FATAL NON-MISSILE HEAD INJURIES

The incidence and distribution of ischaemic brain damage in a consecutive series of 151 patients who died as a result of a non-missile head injury in the Institute of Neurological Sciences was determined on the basis of a comprehensive neuropathological and neurohistological examination. Ischaemic damage was identified in 138 cases (91%) even after excluding cases who only had necrosis and infarction related to contusions or fat embolism, and infarction in the brain stem of the type conventionally associated with raised intracranial pressure. The ischaemic damage was assessed as severe in 37 (27%), moderately severe in 59 (43%) and mild in 42 (30%), and in the 138 cases with ischaemic brain damage it was found more frequently in the hippocampus (122 cases; 81%), and in the basal ganglia (119 cases; 79%) than in the cerebral cortex (70 cases; 46%) and in the cerebellum (67 cases; 44%). There were statistically significant correlations between ischaemic brain damage and either an episode of hypoxia or of raised intracranial pressure. From the nature of the brain damage it seems likely that much of it was due to a reduction in the cerebral perfusion pressure. This study has shown that ischaemic brain damage is common after head injury, that at least a proportion of it is probably avoidable, and that it is more important as a cause of mortality and morbidity after head injury than has been hitherto realised.

Protective Effect of the Glutamate Antagonist, MK-801 in Focal Cerebral Ischemia in the Cat

The effects of the glutamate N-methyl-D aspartate (NMDA) receptor antagonist, MK-801, upon ischemic brain damage has been examined in anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of one middle cerebral artery and the animals were killed 6 h later. The amount of early ischemic damage was assessed in coronal sections at 16 predetermined stereotactic planes. Pretreatment with MK-801 (5 mg/kg, i.v.), 30 min before occlusion of the middle cerebral artery significantly reduced the volume of ischemic damage (from 32.7 ± 4.0% of the cerebral hemisphere in vehicle-treated cats to 16.2 ± 4.5% in MK-801-treated cats). NMDA receptor antagonists that penetrate the blood-brain barrier, such as MK-801, merit further study as protective agents against ischemic brain damage.

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

Interleukin‐1 (IL‐1) is markedly overexpressed in Alzheimers disease. We found the IL‐1A 2,2 genotype in 12.9% of 232 neuropathologically confirmed Alzheimers 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 Alzheimers disease through IL‐1 overexpression and IL‐1–driven neurodegenerative cascades. Ann Neurol 2000;47:365–368

Focal Cerebral Ischaemia in the Rat: 2. Regional Cerebral Blood Flow Determined by [14C]Iodoantipyrine Autoradiography following Middle Cerebral Artery Occlusion

Local cerebral blood flow has been measured by quantitative autoradiography, employing [14C]iodoantipyrine as tracer, in rats killed half an hour after occlusion of the middle cerebral artery. The results were compared with pattern of local cerebral blood flow (CBF) in sham-operated rats and with neuropathological findings. In every animal there was a profound reduction (to 13% of control levels) in blood flow in the neocortex previously supplied by the occluded artery. The level of blood flow in the areas in which ischaemic brain damage occurred was 0.24 ±0.03 ml g−1 min−1 (mean ± SEM). This level of CBF is considerably greater than that reported following a similar surgical procedure in cats and primates. Moderate reductions in blood flow were also seen outside the territory of the occluded artery and in parts of the opposite hemisphere. Absolute increases in blood flow (hyperaemia) were seen only in the substantia nigra and globus pallidus ipsilateral to the occlusion. It is suggested that this finding and the reductions in blood flow outside the territory of the middle cerebral artery are reflections of alterations in neuronal function and metabolic activity secondary to the ischaemic lesion.

Experimental models of traumatic brain injury: Do we really need to build a better mousetrap?

Approximately 4000 human beings experience a traumatic brain injury each day in the United States ranging in severity from mild to fatal. Improvements in initial management, surgical treatment, and neurointensive care have resulted in a better prognosis for traumatic brain injury patients but, to date, there is no available pharmaceutical treatment with proven efficacy, and prevention is the major protective strategy. Many patients are left with disabling changes in cognition, motor function, and personality. Over the past two decades, a number of experimental laboratories have attempted to develop novel and innovative ways to replicate, in animal models, the different aspects of this heterogenous clinical paradigm to better understand and treat patients after traumatic brain injury. Although several clinically-relevant but different experimental models have been developed to reproduce specific characteristics of human traumatic brain injury, its heterogeneity does not allow one single model to reproduce the entire spectrum of events that may occur. The use of these models has resulted in an increased understanding of the pathophysiology of traumatic brain injury, including changes in molecular and cellular pathways and neurobehavioral outcomes. This review provides an up-to-date and critical analysis of the existing models of traumatic brain injury with a view toward guiding and improving future research endeavors.

Characterization of [3H]paroxetine binding to rat cortical membranes

Paroxetine is a selective and potent inhibitor of 5-hydroxytryptamine uptake into serotonergic neurons. The specific binding of [3H]paroxetine to rat cortical membranes at 22 degrees C was examined in this study. Our results indicate the presence of a single saturable high affinity binding component for [3H]paroxetine. Scatchard analysis revealed a Kd of 0.15 +/- 0.01 nM, and a Bmax of 549 +/- 36 fmol/mg protein. The kinetically derived dissociation constant was 0.034 +/- 0.008 nM. [3H]Paroxetine binding was inhibited selectively by 5-HT uptake blockers, and a good correlation was demonstrated between the potency of various drugs to inhibit [3H]paroxetine binding and [3H]5-hydroxytryptamine uptake. Also, lesions performed with the neurotoxin, 5,7-dihydroxytryptamine resulted in a 94% decrease in endogenous 5-hydroxytryptamine levels and concomitantly, a 90% reduction in [3H]paroxetine binding when compared to sham controls. These results indicate that the binding site labelled by [3H]paroxetine is associated with the neuronal 5-hydroxytryptamine transporter complex.

Focal Cerebral Ischaemia in the Cat: Treatment with the Glutamate Antagonist MK-801 After Induction of Ischaemia

The effects of the glutamate N-methyl-D-aspartate receptor antagonist MK-801 in reducing ischaemic brain damage have been examined in anaesthetised cats, with drug treatment being initiated 2 h after the induction of cerebral ischaemia. Focal cerebral ischaemia was produced by permanent occlusion of one middle cerebral artery, and the animals were killed 6 h later. The amount of early irreversible ischaemic damage was assessed at 16 predetermined stereotactic planes. Treatment with MK-801 (5 mg/kg, i.v.) 2 h after middle cerebral artery occlusion reduced significantly the volume of ischaemic damage (from 1,625 ± 384 mm3 of the cerebral hemisphere in vehicle-treated cats to 792 ± 385 mm3 in MK-801-treated cats). The demonstration of reduced ischaemic brain damage with MK-801, when the agent is administered after the induction of ischaemia, extends the therapeutic potential of such agents in the treatment of focal cerebral ischaemia in humans.