The density and distribution of ischemic brain injury in the rat following 2-10 min of forebrain ischemia

The density and distribution of brain damage after 2-10 min of cerebral ischemia was studied in the rat. Ischemia was produced by a combination of carotid clamping and hypotension, followed by 1 week recovery. The brains were perfusion-fixed with formaldehyde, embedded in paraffin, subserially sectioned, and stained with acid fuchsin/cresyl violet. The number of necrotic neurons in the cerebral cortex, hippocampus, and caudate nucleus was assessed by direct visual counting. Somewhat unexpectedly, mild brain damage was observed in some animals already after 2 min, and more consistently after 4 min of ischemia. This damage affected CA4 and CA1 pyramids in the hippocampus, and neurons in the subiculum. Necrosis of neocortical cells began to appear after 4 min and CA3 hippocampal damage after 6 min of ischemia, while neurons in the caudoputamen were affected first after 8-10 min. Selective neuronal necrosis of the cerebral cortex worsened into infarction after higher doses of insult. Damage was worst over the superolateral convexity of the hemisphere, in the middle laminae of the cerebral cortex. The caudate nucleus showed geographically demarcated zones of selective neuronal necrosis, damage to neurons in the dorsolateral portion showing an all-or-none pattern. Other structures involved included the amygdaloid, the thalamic reticular nucleus, the septal nuclei, the pars reticularis of the substantia nigra, and the cerebellar vermis.

Interaction of the p53-regulated protein Gadd45 with proliferating cell nuclear antigen

GADD45 is a ubiquitously expressed mammalian gene that is induced by DNA damage and certain other stresses. Like another p53-regulated gene, p21WAF1/CIP1, whose product binds to cyclin-dependent kinases (Cdk's) and proliferating cell nuclear antigen (PCNA), GADD45 has been associated with growth suppression. Gadd45 was found to bind to PCNA, a normal component of Cdk complexes and a protein involved in DNA replication and repair. Gadd45 stimulated DNA excision repair in vitro and inhibited entry of cells into S phase. These results establish GADD45 as a link between the p53-dependent cell cycle checkpoint and DNA repair.

Models for studying long-term recovery following forebrain ischemia in the rat. 2. A 2-vessel occlusion model

A model is described in which transient ischemia is induced in rats anaesthetized with N2O:O2 (70:30) by bilateral carotid artery clamping combined with a lowering of mean arterial blood pressure to 50 mm Hg, the latter being achieved by bleeding, or by bleeding supplemented with administration of trimetaphan or phentolamine. By the use of intubation, muscle paralysis with suxamethonium chloride, and insertion of tail arterial and venous catheters, it was possible to induce reversible ischemia for long-term recovery studies. Autoradiographic measurements of local CBF showed that the procedure reduced CBF in neocortical areas, hippocampus, and caudoputamen to near-zero values, flow rates in a number of subcortical areas being variable. Administration of trimethaphane or phentolamine did not affect ischemic and postischemic flow rates, nor did they alter recovery of EEG and sensory-evoked responses, but trimetaphan blunted the changes in plasma concentrations of adrenaline and noradrenaline. Recovery experiments showed that 10 min of ischemia gave rise to clear signs of permanent brain damage, with a small number of animals developing postischemic seizures that led to the death of the animals in status epilepticus. After 15 min of ischemia, such alterations were more pronounced, and the majority of animals died. It is concluded that the short revival times noted are explained by the fact that the model induces near-complete ischemia, and that recovery following forebrain ischemia is critically dependent on residual flow rates during the period of ischemia.

2016 Comprehensive Update of the Banff Working Group on Liver Allograft Pathology: Introduction of Antibody-Mediated Rejection

The Banff Working Group on Liver Allograft Pathology reviewed and discussed literature evidence regarding antibody-mediated liver allograft rejection at the 11th (Paris, France, June 5-10, 2011), 12th (Comandatuba, Brazil, August 19-23, 2013), and 13th (Vancouver, British Columbia, Canada, October 5-10, 2015) meetings of the Banff Conference on Allograft Pathology. Discussion continued online. The primary goal was to introduce guidelines and consensus criteria for the diagnosis of liver allograft antibody-mediated rejection and provide a comprehensive update of all Banff Schema recommendations. Included are new recommendations for complement component 4d tissue staining and interpretation, staging liver allograft fibrosis, and findings related to immunosuppression minimization. In an effort to create a single reference document, previous unchanged criteria are also included.

Differential regulation of mRNAs for nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3 in the adult rat brain following cerebral ischemia and hypoglycemic coma

In situ hybridization was used to study expression of mRNAs for members of the nerve growth factor (NGF) family in the rat brain after 2 and 10 min of forebrain ischemia and 1 and 30 min of insulin-induced hypoglycemic coma. Two hours after the ischemic insults, the level of brain-derived neurotrophic factor (BDNF) mRNA was markedly increased in the granule cells of the dentate gyrus, and at 24 h it was still significantly elevated. NGF mRNA showed a pronounced increase 4 h after 2 min of ischemia but had returned to a control level at 24 h. Both 2 and 10 min of ischemia caused a clear reduction of the level of mRNA for neurotrophin 3 (NT-3) in the dentate granule cells and in regions CA2 and medial CA1 of the hippocampus 2 and 4 h after the insults. The increase of BDNF mRNA could be partially blocked by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist NBQX but was not influenced by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. Both NBQX and MK-801 attenuated the decrease of NT-3 mRNA after ischemia. One and 30 min of hypoglycemic coma also induced marked increases in BDNF and NGF mRNA in dentate granule cells with maximal levels at 2 h. If the changes of mRNA expression lead to alterations in the relative availability of neurotrophic factors, this could influence functional outcome and neuronal necrosis following ischemic and hypoglycemic insults.

Association with Cdc2 and inhibition of Cdc2/Cyclin B1 kinase activity by the p53-regulated protein Gadd45

Recently Gadd45, a p53-regulated stress protein, has been implicated in the activation of a G2/M checkpoint after damage by UV radiation and alkylating agents. While inhibitory phosphorylation of Cdc2 and suppression of cyclin B1 levels are known to be involved in G2 delays after genotoxic stress, Gadd45 has now been found to directly inhibit the activity of Cdc2/Cyclin B1 complex, while it had no appreciable effect on Cdk2/ Cyclin E activity even at very high levels of Gadd45. In contrast, p21CiP1/Waf1 is an universal cdk/cyclin inhibitor and inhibited both of the cyclin complexes tested here. Gadd45 was also able to physically interact with Cdc2, but not Cyclin B1. Addition of Gadd45 to immunoprecipitated Cdc2/Cyclin B1 in vitro led to a dissociation of this complex, and thus may represent a new checkpoint mechanism whereby Cdc2/Cyclin B1 can be inhibited. With the use of an antisense approach, reduced Gadd45 expression attenuated the suppression of Cdc2/Cyclin B1 activity in UV-irradiated human cells. Taken together, these results implicate Gadd45 in the control of G2/M cell cycle progression after certain stresses.

Penumbral tissues salvaged by reperfusion following middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

The rat is now extensively used for studies on focal cerebral ischemia, and several novel pharmacological principles have been worked out in rat models of middle cerebral artery occlusion. The objective of the present study was to assess how ischemic tissue can be salvaged by reperfusion in a model of transient focal ischemia that gives infarction of both the caudoputamen and the neocortex.

METHODS

The middle cerebral artery of anesthetized rats was occluded for 15, 30, 60, 90, 120, or 180 minutes by an intraluminal filament, and recirculation was instituted for 7 days to allow assessment of the density and localization of ischemic brain damage using histopathologic techniques. Local cerebral blood flow was measured in separate animals to verify that removal of the filament was followed by adequate recirculation.

RESULTS

Following 15 minutes of middle cerebral artery occlusion seven of eight rats showed selective neuronal necrosis in the caudoputamen, while the neocortex was normal. After 30 minutes of occlusion, seven of eight animals had infarcts localized to the lateral caudoputamen, and four of eight had selective neuronal necrosis in the neocortex. Prolongation of the ischemia to 60 minutes induced cortical infarction in all eight rats. The infarct size increased progressively with increasing occlusion time, up to 120-180 minutes, when the infarcts were as extensive as those observed following 24 hours of permanent middle cerebral artery occlusion.

CONCLUSIONS

The results demonstrate a time window for salvage of penumbral tissues by reperfusion that is shorter than that suggested on the basis of previous data in other species. The results probably reflect a lower collateral blood flow in the rat than in other species. This should be taken into account when the effect of pharmacological agents is studied in rats.

Aggressive surgical management of craniopharyngiomas in children

The cases of 50 patients with craniopharyngioma operated on at The Hospital for Sick Children in Toronto between January, 1975, and December, 1989, are reviewed. All patients were under 18 years of age (mean 9.39 years). Headaches, endocrine deficiencies, and visual deficits were the most common symptoms on admission. Forty-five patients underwent what was considered by the surgeon to be total excision of their tumor, and five had subtotal excision. Tumors recurred in 17 patients (mean time of recurrence 32.6 months after surgery). One patient died in the postoperative period and three have been lost to follow-up study. Of the remaining 46 patients, 28 are leading a normal or nearly normal life, although all are receiving endocrine replacement and some have required help to overcome mild deficits in memory or visual acuity. Twelve patients are able to function reasonably well and attend school despite being hampered by intellectual or visual deficits or problems with weight control; four have a significant handicap, and two have died.

The effect of mild hyperthermia and hypothermia on brain damage following 5, 10, and 15 minutes of forebrain ischemia

The present study examines the effects of mild hypothermia and hyperthermia on the density and distribution of ischemic brain damage, and compares these effects to those induced by variations in the duration of ischemia. Body temperatures were maintained at 35 degrees C, 37 degrees C, and 39 degrees C, before, during, and after ischemia, and brain temperatures were held at similar values with a technique that in preliminary experiments proved to avoid intracerebral temperature gradients or overheating of surface structures. In all animals, brain damage was assessed by histopathological analysis of perfusion-fixed brains after six to seven days of recovery. Our results confirm previous findings showing that a decrease in temperature of only 2 degrees C significantly reduces damage to several selectively vulnerable neuronal populations. The results also showed that an increase in temperature of 2 degrees C significantly enhances brain damage. In general, a rise in temperature had effects similar to an increased duration of the ischemia. In some areas, such as the CA1-subiculum sectors of the hippocampus, temperature and ischemic duration altered damage in a gradual manner, but in others, such as the caudoputamen, there was a steplike change from virtually no to virtually complete damage. In some areas, the effects of hypothermia and hyperthermia appeared symmetrical around the normal temperature of 37 degrees C. Hyperthermia had some seemingly "specific" effects, however, notably the tendency to induce pannecrosis ("infarction") in the neocortex and caudoputamen, and to cause damage to the substantia nigra pars reticulata. The results underscore the potentially devastating effects of fever in patients with cerebrovascular disease.

p53-mediated DNA repair responses to UV radiation: studies of mouse cells lacking p53, p21, and/or gadd45 genes

Human cells lacking functional p53 exhibit a partial deficiency in nucleotide excision repair (NER), the pathway for repair of UV-induced DNA damage. The global genomic repair (GGR) subpathway of NER, but not transcription-coupled repair (TCR), is mainly affected by p53 loss or inactivation. We have utilized mouse embryo fibroblasts (MEFs) lacking p53 genes or downstream effector genes of the p53 pathway, gadd45 (Gadd45a) or p21 (Cdkn1a), as well as MEFs lacking both gadd45 and p21 genes to address the potential contribution of these downstream effectors to p53-associated DNA repair. Loss of p53 or gadd45 had a pronounced effect on GGR, while p21 loss had only a marginal effect, determined by measurements of repair synthesis (unscheduled DNA synthesis), by immunoassays to detect removal of UV photoproducts from genomic DNA, and by assays determining strand-specific removal of CPDs from the mouse dhfr gene. Taken together, the evidence suggests a role for Gadd45, but relatively little role for p21, in DNA repair responses to UV radiation. Recent evidence suggests that Gadd45 binds to UV-damaged chromatin and may affect lesion accessibility. MEFs lacking p53 or gadd45 genes exhibited decreased colony-forming ability after UV radiation and cisplatin compared to wild-type MEFs, indicating their sensitivity to DNA damage. We provide evidence that Gadd45 affects chromatin remodelling of templates concurrent with DNA repair, thus indicating that Gadd45 may participate in the coupling between chromatin assembly and DNA repair.

Bcl-2 family proteins are essential for platelet survival

Platelets are relatively short-lived, anucleated cells that are essential for proper hemostasis. The regulation of platelet survival in the circulation remains poorly understood. The process of platelet activation and senescence in vivo is associated with processes similar to those observed during apoptosis in nucleated cells, including loss of mitochondrial membrane potential, caspase activation, phosphatidylserine (PS) externalization, and cell shrinkage. ABT-737, a potent antagonist of Bcl-2, Bcl-X(L), and Bcl-w, induces apoptosis in nucleated cells dependent on these proteins for survival. In vivo, ABT-737 induces a reduction of circulating platelets that is maintained during drug therapy, followed by recovery to normal levels within several days after treatment cessation. Whole body scintography utilizing ([111])Indium-labeled platelets in dogs shows that ABT-737-induced platelet clearance is primarily mediated by the liver. In vitro, ABT-737 treatment leads to activation of key apoptotic processes including cytochrome c release, caspase-3 activation, and PS externalization in isolated platelets. Despite these changes, ABT-737 is ineffective in promoting platelet activation as measured by granule release markers and platelet aggregation. Taken together, these data suggest that ABT-737 induces an apoptosis-like response in platelets that is distinct from platelet activation and results in enhanced clearance in vivo by the reticuloendothelial system.

Increased production of the TrkB protein tyrosine kinase receptor after brain insults

The protein-tyrosine kinases Trk, TrkB, and TrkC are signal-transducing receptors for a family of neurotrophic factors known as the neurotrophins. Here we show that seizures induced by hippocampal kindling lead to a rapid, transient increase of trkB mRNA and protein in the hippocampus. TrkB is a component of a high affinity receptor for brain-derived neurotrophic factor (BDNF). No change was detected in mRNAs for Trk or TrkC, components of the high affinity nerve growth factor or neurotrophin-3 receptors, respectively. trkB mRNA was also transiently increased in the dentate gyrus following cerebral ischemia and hypoglycemic coma; these treatments had no effect on trk and trkC mRNAs. The increase in trkB mRNA and protein showed the same time course and distribution as the increase in BDNF mRNA. These data suggest that BDNF and its receptor may play a local role within the hippocampus in kindling-associated neural plasticity and in neuronal protection following epileptic, ischemic, and hypoglycemic insults.

The influence of mild body and brain hypothermia on ischemic brain damage

The influence of brain and body temperature on ischemic brain damage, notably on the density and distribution of selective neuronal vulnerability, was studied in SPF-Wistar rats subjected to 15 min of forebrain ischemia induced by bilateral occlusion of the common carotid arteries combined with arterial hypotension (50 mm Hg) in a room air environment. In one group of animals, the body temperature was maintained at 37 degrees C but no attempt was made to prevent heat losses from the ischemic brain; i.e., the head was not heated during ischemia. Under those conditions the temperature of the caudoputamen and at a subcutaneous site over the skull bone spontaneously fell to approximately 32 degrees C. In four other groups, both the rectal and the subcutaneous skull temperatures were maintained at 38, 37, 35, and 33 degrees C during the ischemia. Our results confirm those recently reported when brain temperature was varied during 20 min of ischemia, with body temperature kept constant. Thus, the histopathological outcome of the brain damage, as assessed after 7 days of recovery, was strongly temperature dependent. Whereas ischemia at 37-38 degrees C consistently caused neuronal necrosis in the hippocampus, neocortex, and caudoputamen, spontaneous cooling of the brain during ischemia at a rectal temperature of 37 degrees C significantly reduced the ischemic damage. Intentional lowering of temperature to 35 degrees C markedly reduced and to 33 degrees C virtually prevented neuronal necrosis in some but not all of the regions studied. While damage to the caudoputamen was extremely temperature sensitive, that affecting the CA1 sector of the hippocampus, and particularly the lateral reticular nucleus of the thalamus, was less so. Our results suggest that whatever biochemical events are responsible for selective neuronal vulnerability, they are temperature sensitive; however, since there are differences in sensitivity between different parts of the brain, more than one mechanism may be involved.

Ischemic penumbra in a model of reversible middle cerebral artery occlusion in the rat

It has become increasingly clear that a stroke lesion usually consists of a densely ischemic focus and of perifocal areas with better upheld flow rates. At least in rats and cats, some of these perifocal ("penumbral") areas subsequently become recruited in the infarction process. The mechanisms may involve an aberrant cellular calcium metabolism and enhanced production of free radicals. In general, though, the metabolic perturbation in the penumbra requires better characterization. The objective of this article was to define flow distribution in a rat model of reversible middle cerebral artery (MCA) occlusion, so as to allow delineation of the metabolic aberrations responsible for the subsequent infarction. We modified the intraluminal filament occlusion model recently developed by Koizumi et al. (1986), and described in more detail by Nagasawa and Kogure (1989), adopting it for use in both spontaneously breathing and artificially ventilated rats. Successful occlusion of the MCA (achieved in about 9/10 rats) was judged by unilateral EEG depression in ventilated rats, and neurological deficits, such as circling, in spontaneously breathing ones. CBF in the ipsilateral hemisphere was reduced to nearly constant values after 20, 60, and 120 min of occlusion, flow rates in the focus being about 10% and in the perifocal ipsilateral areas about 15-20% of control (contralateral side). When the filament was left in place (permanent occlusion) 2,3,5-triphenyl tetrazolium chloride (TTC) staining and histopathology after 24 h showed a massive infarct on the occluded side, extending from caudoputamen and overlaying cortex to the occipital striate cortex. Animals recirculated after 60 min of MCA occlusion, and allowed to survive 7 days for histopathology, showed infarction of the caudoputamen (lateral part or whole nucleus) in 5/6 animals and selective neuronal necrosis in one animal. The neocortex showed either infarcts, selective neuronal necrosis, or no damage. There was some overlap between neocortical areas which were infarcted and those which were salvaged by reperfusion. In general, though, both the CBF data and the recovery studies with a histopathological endpoint define large parts of the neocortex as perifocal (penumbral) areas which lend themselves to studies of metabolic events leading to infarction.

Right hippocampal impairment in the recall of spatial location: encoding deficit or rapid forgetting?

The recall of spatial location in patients with left or right temporal-lobe lesions was studied in two experiments, in which recall was tested either immediately after presentation of an array of objects, or after an intervening verbal task, a spatial task or an unfilled interval. Deficits were found only in patients with right temporal-lobe lesions that included extensive removal of the hippocampal region, and only when recall was tested after a delay. The presence of an intervening task in the delay interval did not accentuate the deficit. The results show that, despite a normal ability to encode location, patients with large right hippocampal lesions demonstrate an abnormally rapid forgetting of such information.

Changes in extra- and intracellular pH in the brain during and following ischemia in hyperglycemic and in moderately hypoglycemic rats

Incomplete forebrain ischemia of 15-min duration was induced in rats made hyperglycemic or moderately hypoglycemic prior to ischemia. Tissue CO2 tension, CO2 content, labile tissue metabolites, and extracellular pH (pHe) were measured, and intracellular pH (pHi) was derived by calculation on the assumption that cerebral intracellular fluids can be lumped into one space. In hypoglycemic animals, mean tissue lactate content increased from 2 to 10 mumol g-1. Tissue CO2 content was virtually unchanged and the CO2 tension increased from approximately 50 to approximately 145 mm Hg. In hyperglycemic animals, tissue lactate content rose to 20 mumol g-1, and the CO2 content decreased by 25%, demonstrating that some CO2 was lost to the blood supplied by the remaining perfusion. Accordingly, tissue CO2 tension did not rise above 200 mm Hg. pHe was reduced in proportion to the amount of lactate accumulated, the values obtained in hypo- and hyperglycemic animals showing relatively little scatter (6.76 +/- 0.03 and 6.25 +/- 0.04, respectively). In hypoglycemic animals the extracellular HCO-3 concentration was virtually unchanged, demonstrating that any influx of lactic acid from the cells must have been accompanied by H+ efflux and/or HCO-3 influx via independent routes. In hyperglycemic animals [HCO-3]e fell by greater than 10 mumol ml-1. In both groups [HCO-3]e was reduced during the first 5 min of recovery. Recovery of pHe was slower in hyper- than in hypoglycemic animals. During ischemia calculated pHi fell to 6.37 +/- 0.04 and 5.95 +/- 0.06 in hypo- and hyperglycemic animals, respectively. Differences in pHi were maintained for the first 15 min of recovery, but in both hypo- and hyperglycemic animals pHi had normalized after 30 min. It is concluded that preischemic hyperglycemia leads to a more pronounced intra- and extracellular acidosis than normo- and hypoglycemia, an acidosis that also resolves more slowly during recirculation.

Regulation of brain-derived neurotrophic factor gene expression after transient middle cerebral artery occlusion with and without brain damage

Levels of mRNA for c-fos, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), TrkB, and TrkC were studied using in situ hybridization in the rat brain at different reperfusion times after unilateral middle cerebral artery occlusion (MCAO). Short-term (15 min) MCAO, which does not cause neuronal death, induced elevated BDNF mRNA expression confined to ipsilateral frontal and cingulate cortices outside the ischemic area. With a longer duration of MCAO (2 h), which leads to cortical infarction, the increase was more marked and elevated BDNF mRNA levels were also detected bilaterally in dentate granule cells and CA1 and CA3 pyramidal neurons. Maximum expression was found after 2 h of reperfusion. At 24 h BDNF mRNA expression had returned to control values. In the ischemic core of the parietal cortex only scattered neurons were expressing high levels of BDNF mRNA after 15 min and 2 h of MCAO. Analysis of different BDNF transcripts showed that MCAO induced a marked increase of exon III mRNA but only small increases of exon I and II mRNAs in cortex and hippocampus. In contrast to BDNF mRNA, elevated expression of c-fos mRNA was observed in the entire ipsilateral cerebral cortex, including the ischemic core, after both 15 min and 2 h of MCAO. Two hours of MCAO also induced transient, bilateral increases of NGF and TrkB mRNA levels and a decrease of NT-3 mRNA expression, confined to dentate granule cells. The upregulation of BDNF mRNA expression in cortical neurons after MCAO is probably triggered by glutamate through a spreading depression-like mechanism. The lack of response of the BDNF gene in the ischemic core may be due to suppression of signal transduction or transcription factor synthesis caused by the ischemia. The observed pattern of gene expression after MCAO agrees well with a neuroprotective role of BDNF in cortical neurons. However, elevated levels of NGF and BDNF protein could also increase synaptic efficacy in the postischemic phase, which may promote epileptogenesis.

The effect of non-steroidal anti-inflammatory drugs on human colorectal cancer cells: evidence of different mechanisms of action

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit proliferation and induce apoptosis in human colorectal cancer cells in vitro. It remains unclear whether individual NSAIDs act by cyclooxygenase-2 (COX-2) inhibition and how NSAIDs exert their anti-proliferative effects. We investigated the effects of NS-398 (a selective COX-2 inhibitor), indomethacin (a non-selective COX inhibitor) and aspirin on four human colorectal cancer cell lines (HT29.Fu, HCA-7, SW480 and HCT116). NS-398 completely inhibited proliferation, induced G1 arrest and promoted apoptosis in COX-2-expressing cells (HT29.Fu and HCA-7). However, indomethacin had similar effects on all cells, regardless of COX-2 expression. NS-398 also had anti-proliferative activity on COX-2-negative cell lines (SW480 and HCT116). Aspirin inhibited proliferation of all cell lines but did not induce apoptosis. Indomethacin decreased beta-catenin protein expression in all cells (unlike NS-398 or aspirin). NSAIDs act on human colorectal cancer cells via different mechanisms. Decreased beta-catenin protein expression may mediate the anti-proliferative effects of indomethacin.

Neuroprotective effects of a novel nitrone, NXY-059, after transient focal cerebral ischemia in the rat

Recent results have demonstrated that the spin trapping agent alpha-phenyl-N-tert-butyl nitrone (PBN) reduces infarct volume in rats subjected to 2 hours of middle cerebral artery occlusion, even when given 1 to 3 hours after the start of recirculation. In the current study, the authors assessed the effect of NXY-059, a novel nitrone that is more soluble than PBN. Loading doses were given of 0.30, 3.0, or 30 mg x kg(-1) followed by 0.30, 3.0, or 30 mg x kg(-1) x h(-1) for 24 or 48 hours. Dose-response studies showed that when treatment was begun 1 hour after recirculation, 0.30 mg x kg(-1) had a small and 30 mg x kg(-1) a marked effect on infarct volume. At equimolar doses (3.0 mg x kg(-1) for NXY-059 and 1.4 mg x kg(-1) for PBN), NXY-059 was more efficacious than PBN. Similar results were obtained when a recovery period of 7 days was allowed. The window of therapeutic opportunity for NXY-059 was 3 to 6 hours after the start of recirculation. Studies of the transfer constant of [14C]NXY-059 showed that, in contrast to PBN, this more soluble nitrone penetrates the blood-brain barrier less extensively. This fact, and the pronounced antiischemic effect of NXY-059, suggest that the delayed events leading to infarction may be influenced by reactions occurring at the blood-endothelial interface.

The neurochemical and metabolic cascade following brain injury: moving from animal models to man

Experimental traumatic brain injury produces a series of cellular events contributing to a neurochemical and neurometabolic cascade. This cascade is defined by the release of neurotransmitters resulting in a massive ionic flux, which, consequently, produces an increase in glycolysis. This increase in glycolysis is followed by a metabolic diaschisis, which is related to the degree and extent of behavioral deficits. Clinical efforts have now determined that a similar cascade occurs in human head injury, validating the animal model as well as providing new assessment strategies for the management and treatment of brain injury.

Exercise training bradycardia: the role of autonomic balance

We used an algebraic model of resting heart rate (HRr), HRr-mn (HRo), to compare resting parasympathetic (n) and sympathetic (m) influence, intrinsic heart rate (HRo), and resting autonomic balance (Abal) in ten endurance-trained (ET) and ten nontrained (NT) men. The values of m, n, and Abal were determined by selective pharmacological blockade with atropine and metoprolol. HRo was obtained during double blockade with atropine and metoprolol. HRo and HRr were significantly lower (P less than or equal to 0.04 and P less than or equal to 0.01, respectively) in the ET subjects (79.5 +/- 2.8 beats.min-1 and 54.7 +/- 3.0 beats.min-1, respectively) when compared to the NT subjects (86.6 +/- 2.5 beats.min1 and 70.2 +/- 3.1 beats.min-1, respectively). Parasympathetic influence (n) was greater in the ET subjects (P less than or equal to 0.04), while sympathetic influence (m) was slightly (P less than or equal to 0.05) less in the ET subjects. Consequently, the value of Abal was significantly less in the ET subjects (P less than or equal to 0.02), indicating that resting parasympathetic predominance was significantly greater in the ET subjects. We concluded that the exercise training bradycardia, observed in this group of subjects, was due to both a lower HRo and an Abal with an augmented parasympathetic dominance.

Regional hippocampal alteration associated with cognitive deficit following experimental brain injury: a systems, network and cellular evaluation

Cognitive deficits persist in patients who survive traumatic brain injury (TBI). Lateral fluid percussion brain injury in the mouse, a model of human TBI, results in hippocampal-dependent cognitive impairment, similar to retrograde amnesia often associated with TBI. To identify potential substrates of the cognitive impairment, we evaluated regional neuronal loss, regional hippocampal excitability and inhibitory synaptic transmission. Design-based stereology demonstrated an approximate 40% loss of neurons through all subregions of the hippocampus following injury compared with sham. Input/output curves recorded in slices of injured brain demonstrated increased net synaptic efficacy in the dentate gyrus in concert with decreased net synaptic efficacy and excitatory postsynaptic potential-spike relationship in area CA1 compared with sham slices. Pharmacological agents modulating inhibitory transmission partially restored regional injury-induced alterations in net synaptic efficacy. Both evoked and spontaneous miniature inhibitory postsynaptic currents (mIPSCs) recorded in surviving dentate granule neurons were smaller and less frequent in injured brains than in uninjured brains. Conversely, both evoked and spontaneous mIPSCs recorded in surviving area CA1 pyramidal neurons were larger in injured brains than in uninjured brains. Together, these alterations suggest that regional hippocampal function is altered in the injured brain. This study demonstrates for the first time that brain injury selectively disrupts hippocampal function by causing uniform neuronal loss, inhibitory synaptic dysfunction, and regional, but opposing, shifts in circuit excitability. These changes may contribute to the cognitive impairments that result from brain injury.