Morphogen and proinflammatory cytokine release kinetics from PRGF-Endoret fibrin scaffolds: evaluation of the effect of leukocyte inclusion

The potential influence of leukocyte incorporation in the kinetic release of growth factors from platelet-rich plasma (PRP) may explain the conflicting efficiency of leukocyte platelet-rich plasma (L-PRP) scaffolds in tissue regeneration. To assess this hypothesis, leukocyte-free (PRGF-Endoret) and L-PRP fibrin scaffolds were prepared, and both morphogen and proinflammatory cytokine release kinetics were analyzed. Clots were incubated with culture medium to monitor protein release over 8 days. Furthermore, the different fibrin scaffolds were morphologically characterized. Results show that leukocyte-free fibrin matrices were homogenous while leukocyte-containing ones were heterogeneous, loose and cellular. Leukocyte incorporation produced a significant increase in the contents of proinflammatory cytokines interleukin (IL)-1β and IL-16 but not in the platelet-derived growth factors release (<1.5-fold). Surprisingly, the availability of vascular endothelial growth factor suffered an important decrease after 3 days of incubation in the case of L-PRP matrices. While the release of proinflammatory cytokines was almost absent or very low from PRGF-Endoret, the inclusion of leukocytes induced a major increase in these cytokines, which was characterized by the presence of a latent period. The PRGF-Endoret matrices were stable during the 8 days of incubation. The inclusion of leukocytes alters the growth factors release profile and also increased the dose of proinflammatory cytokines.

Visualizing CD4 T-cell migration into inflamed skin and its inhibition by CCR4/CCR10 blockades using in vivo imaging model

BACKGROUND

Chemokines are critical mediators of T-cell homing into inflamed skin. The complex nature of this multicellular response makes it difficult to analyse mechanisms mediating the early responses in vivo.

OBJECTIVES

To visualize directly T-cell homing into inflamed skin and its inhibition by blockades using a unique noninvasive confocal microscopy.

MATERIALS AND METHODS

A mouse model of allergic contact dermatitis was used. T cells from oxazolone-sensitized and -challenged Balb/c mice were first analysed phenotypically in vitro. CD4 T cells were then labelled with a tracker dye and transferred into Balb/c-SCID mice. The recipient mice were challenged with oxazolone and CD4 T-cell homing into inflamed skin was visualized.

RESULTS

T cells with the skin homing receptors CCR4 and CCR10 were increased in the affected skin and draining lymph nodes, and effectively attracted by their specific chemokines CCL17, CCL22 and CCL27 in vitro. Using in vivo imaging, T-cell migration into the inflamed skin was observed at 2 h after application, peaking at 12 h and continuing for 48 h. Simultaneous systemic administration of neutralizing antibodies against CCR4 ligands (CCL17 and CCL22) and CCR10 ligand (CCL27) led to a significant suppression of T-cell migration and skin inflammation.

CONCLUSIONS

Our data indicate that these tissue-selective adhesion molecules and chemokine/receptor pathways act in concert to attract specialized T-cell populations to mediate cutaneous inflammation. The in vivo imaging technique can be applicable to other models of cutaneous diseases to help with better understanding of the pathogenesis and monitoring the therapeutic effects.

The herbicide paraquat induces alterations in the elemental and biochemical composition of non-target microalgal species

Huge quantities of pesticides are dispersed in the environment, affecting non-target organisms. Since paraquat affects the photosynthetic process, the biochemical composition of affected species should be altered. The effect of paraquat on Chlamydomonas moewusii, a freshwater non-target species, was studied. After 48 h of herbicide exposure, growth rate, dry weight, and chlorophyll a and protein content were affected by paraquat concentrations above 0.05 microM. C/N ratio was also affected due to a decrease in nitrogen content in the dry biomass, while the carbon content remained constant for all paraquat concentrations assayed. Enzymes involved in nitrogen assimilation were affected by paraquat, being nitrate reductase activity more sensitive to paraquat than nitrite reductase. Based on the results obtained in the present study, paraquat exerts adverse effects upon a common freshwater green microalga, thus the application of this herbicide for weed control must be carried out very carefully, so that any disturbance affecting algae will have severe repercussions on higher trophic levels and on the elemental biogeochemical cycles.

Fibroblastic response to treatment with different preparations rich in growth factors

OBJECTIVES

Preparations rich in growth factors (PRGF) release them plus bioactive proteins at localized sites, with the aim of triggering healing and regenerative processes. The prevailing paradigm suggests that their influence on proliferation, angiogenesis and the extracellular matrix synthesis is minimal. However, variations in their composition and impact on different cell phenotypes have not been examined.

MATERIALS AND METHODS

Sixteen fibroblast cultures obtained from three different anatomical sites (skin, synovium and tendon) of 16 donors were exposed to the molecular pool released from PRGF scaffolds, with increasing amounts of platelets. We evaluated cell proliferation, secretion of angiogenic growth factors (VEGF and HGF), synthesis of type I collagen and hyaluronic acid (HA), considering platelet dose and anatomical origin of the cells. Activity of transforming growth factor-beta (TGF-beta) in type I procollagen and HA synthesis was examined by adding exogenous TGF-beta to plasma preparations.

RESULTS

All plasma preparations induced a significant proliferative response compared to non-stimulated cells (P < 0.05). Maximum proliferation rate was obtained with PRGF with 2-fold or 4-fold platelet concentration. Exposure to PRGF stimulated VEGF synthesis exclusively in tendon cells (P < 0.05), which also exhibited a different pattern of HGF production (P < 0.05). PRGF enhanced HA synthesis (P < 0.05), but did not alter collagen I production. Platelet-secreted TGF-beta may be involved in HA, but not in type I procollagen synthesis.

CONCLUSIONS

Optimizing composition and use of platelet-rich products is crucial to enhancing the therapeutic potential of this technology. Our data show that the biological effects of PRGF may depend on concentration of platelets and on the anatomical source of the cells.

Comparison of the sensitivity of different toxicity test endpoints in a microalga exposed to the herbicide paraquat

The use of herbicides constitutes the principal method of weed control but the introduction of these compounds into the aquatic environment can provoke severe consequences for non-target organisms such as microalgae. Toxic effects of these pollutants on microalgae are generally evaluated using phytotoxicity tests based on growth inhibition, a population-based parameter. However, physiological cellular endpoints could allow early detection of cell stress and elucidate underlying toxicity mechanisms. Effects of the herbicide paraquat on the freshwater microalga Chlamydomonas moewusii were studied to evaluate growth rate and cellular parameters such as cellular viability and metabolic activity assayed by flow cytometry and DNA damage assayed by the comet assay. Sensitivity of growth and parameters assayed by flow cytometry were similar, showing a significant effect in cultures exposed to a paraquat concentration of 0.1 microM or higher, although in cultures exposed during 48 h to 0.05 microM, a significant stimulation of cellular fluorescein fluorescence was observed, related to cellular metabolic activity. After only 24 h of herbicide exposure significant DNA damage was observed in microalgal cells exposed to all paraquat concentrations assayed, with a 23.67% of comets in cultures exposed to 0.05 microM, revealing the genotoxicity of this herbicide. Taking into account the results obtained, comet assay provides a sensitive and rapid system for measuring primary DNA damage in Chlamydomonas moewusii, which could be an important aspect of environmental genotoxicity monitoring in surface waters.

Population growth study of the rotifer Brachionus sp. fed with triazine-exposed microalgae

Few data exist on potential toxic effects that pollutants may have on zooplankton fed microalgae exposed to pesticides. For that reason, microalgal cultures were exposed to different concentrations of the triazine herbicide terbutryn, and used as exclusive food source to Brachionus sp. females, with the aim to evaluate potential deleterious effects upon population growth, survival, reproduction and feeding of the rotifer. Chlorella vulgaris cells were able to accumulate terbutryn, removing more than 90% of the total amount of herbicide in all the exposed cultures. Growth curves of Brachionus sp. showed that population density decreased as terbutryn concentration increased in the microalgal cells. In fact, this species of rotifer did not survive beyond four days when fed with microalgae exposed to 500 nM terbutryn. Percentage of reproductive females in rotifer populations fed with terbutryn-exposed microalgae decreased significantly as herbicide concentration increased. In control cultures, reproductive females laid a maximum of three eggs per individual; whereas in 100 nM cultures, reproductive females laid only one egg per individual throughout the treatment period. Terbutryn accumulated in C. vulgaris provoked a decrease in the feeding rate of Brachionus sp. cultures fed with these microalgae with respect to control cultures. After this treatment period, all the rotifer populations, except those fed with 500 nM terbutryn-exposed microalgae, showed recovery patterns when they were returned to fresh medium containing herbicide-free microalga. Taking into account the results obtained, uptake of pesticides by phytoplankton can directly affect higher trophic levels.

Salt and solvent effects on the kinetics and thermodynamics of the inclusion of the ruthenium complex [Ru(NH3)5(4,4'-bpy)]2+ in beta-cyclodextrin

The influences of solvents (in water-cosolvent mixtures) and salts on the kinetics and thermodynamics of the inclusion of [Ru(NH3)5(4,4'-bpy)]2+ in beta-cyclodextrin (beta-CD) have been studied. Solvent effects on the kinetics can be described as a consequence of the competition of the cosolvent for the beta-CD cavity. The salt effects on the kinetics depend on the ion pairing of the anions with the [Ru(NH3)5(4,4'-bpy)]2+ complex. On the other hand, the solvent effects on the equilibrium constant depend on the stabilization of the 4,4'-bipyridine ligand in the water-cosolvent mixture relative to water. Finally, salt effects on the equilibrium constant are interpreted as a consequence of ion pairing between the anion of the salt and the inclusion complex.

Studies on medicinal plants of Ivory Coast: investigation of Sida acuta for in vitro antiplasmodial activities and identification of an active constituent

Sida acuta Burm. (Malvaceae) originating from Ivory Coast was selected after an ethnobotanical survey: traditional healers of malaria commonly used this plant for the treatment. Extracts were tested on two strains of Plasmodium falciparum: FcM29-Cameroon (chloroquine-resistant strain) and a Nigerian chloroquine-sensitive strain. Extracts were obtained by preparing decoction in water of the powdered plant, the technique used by most of the traditional healers. An ethanol extract was then made and tested. The IC50 values obtained for these extracts ranged from 3.9 to -5.4 microg/ml. Purification of this active fraction led to the identification of cryptolepine as the active antiplasmodial constituent of the plant.

Hyperbaric oxygen therapy protects against mitochondrial dysfunction and delays onset of motor neuron disease in Wobbler mice

The Wobbler mouse is a model of human motor neuron disease. Recently we reported the impairment of mitochondrial complex IV in Wobbler mouse CNS, including motor cortex and spinal cord. The present study was designed to test the effect of hyperbaric oxygen therapy (HBOT) on (1) mitochondrial functions in young Wobbler mice, and (2) the onset and progression of the disease with aging. HBOT was carried out at 2 atmospheres absolute (2 ATA) oxygen for 1 h/day for 30 days. Control groups consisted of both untreated Wobbler mice and non-diseased Wobbler mice. The rate of respiration for complex IV in mitochondria isolated from motor cortex was improved by 40% (P<0.05) after HBOT. The onset and progression of the disease in the Wobbler mice was studied using litters of pups from proven heterozygous breeding pairs, which were treated from birth with 2 ATA HBOT for 1 h/day 6 days a week for the animals' lifetime. A "blinded" observer examined the onset and progression of the Wobbler phenotype, including walking capabilities ranging from normal walking to jaw walking (unable to use forepaws), and the paw condition (from normal to curled wrists and forelimb fixed to the chest). These data indicate that the onset of disease in untreated Wobbler mice averaged 36+/-4.3 days in terms of walking and 40+/-5.7 days in terms of paw condition. HBOT significantly delayed (P<0.001 for both paw condition and walking) the onset of disease to 59+/-8.2 days (in terms of walking) and 63+/-7.6 days (in terms of paw condition). Our data suggest that HBOT significantly ameliorates mitochondrial dysfunction in the motor cortex and spinal cord and greatly delays the onset of the disease in an animal model of motor neuron disease.

In vitro antiplasmodial activity of extracts of Alchornea cordifolia and identification of an active constituent: ellagic acid

Extracts of leaves of Alchornea cordifolia were studied for their antiplasmodial activities. Chloroformic and ether extracts were found to be inactive while the ethanolic extract exhibited mild in vitro activity against Plasmodium falciparum. Fractionation of this extract led us to isolate ellagic acid as the active constituent of the extract with IC(50) in the range of 0.2-0.5 microM. Cytotoxicity of ethanolic fraction and ellagic acid was also estimated on human fibroblasts cells (IC(50) on Hela cells = 7.3 microM at 24 h for ellagic acid).

EEG effects of ECT: implications for rTMS

Electroconvulsive therapy (ECT) involves the use of electrical stimulation to elicit a series of generalized tonic-clonic seizures for therapeutic purposes and is the most effective treatment known for major depression. These treatments have significant neurophysiologic effects, many of which are manifest in the electroencephalogram (EEG). The relationship between EEG data and the response to ECT has been studied since the 1940s, but for many years no consistent correlates were found. Recent studies indicate that a number of specific EEG features recorded during the induced seizures (ictal EEG) as well as before and after a course of treatment (interictal EEG) are related to both the therapeutic efficacy and cognitive side effects. Similar to ECT, repetitive transcranial magnetic stimulation (rTMS), which involves focal electromagnetic stimulation of cortical neurons, has also been studied as an antidepressant therapy and also appears to have neurophysiologic effects, although these have not been as fully investigated as is the case with ECT. Given the similarity of these treatments, it is natural to consider whether advances in understanding the electrophysiologic correlates of the ECT response might have implications for rTMS. The present article reviews the literature on the EEG effects of ECT and discusses the implications in terms of the likely efficacy and side effects associated with rTMS in specific anatomic locations, the potential for producing an antidepressant response with rTMS without eliciting seizure activity, eliciting focal seizures with rTMS, and the possibility of using rTMS to focally modulate seizure induction and spread with ECT to optimize treatment.

Thromboembolic events lead to cortical spreading depression and expression of c-fos, brain-derived neurotrophic factor, glial fibrillary acidic protein, and heat shock protein 70 mRNA in rats

The hypotheses that cerebral embolic events lead to repetitive episodes of cortical spreading depression (CSD) and that these propagating waves trigger the expression of c-fos, brain-derived neurotrophic factor (BDNF), glial fibrillary acidic protein (GFAP), and heat shock protein 70 (HSP70) mRNA were tested. Wistar rats underwent photochemically induced right common carotid artery thrombosis (CCAT) (n = 18) or sham (n = 8) procedures. In a subgroup of rats (n = 5), laser-Doppler flowmetry probes were placed overlying the right parietal cortex to record CSD-like changes in cortical blood flow during the initial 2-hour postinjury period. Rats were killed by decapitation at 2 or 24 hours after CCAT, and brains were processed for in situ localization of the gene expression. Two to five intermittent transient hyperemic episodes lasting 1 to 2 minutes were recorded ipsilaterally after CCAT. At 2 hours after CCAT, the widespread expression of c-fos and BDNF mRNAs was observed throughout the ipsilateral cerebral cortex. Pretreatment with the N-methyl-D-aspartate receptor blocker MK-801 (2 mg/kg) 1 hour before CCAT reduced the expression of BDNF mRNA expression at 2 hours. At 24 hours after CCAT, increased expression of GFAP mRNA was present in cortical and subcortical regions. In contrast, multifocal regions of HSP70 expression scattered throughout the thrombosed hemisphere were apparent at both 2 and 24 hours after injury. These data indicate that thromboembolic events lead to episodes of CSD and time-dependent alterations in gene expression. The ability of embolic processes to induce widespread molecular responses in neurons and glia may be important in the pathogenesis of transient ischemic attacks and may influence the susceptibility of the postembolic brain to subsequent insults including stroke.

New methods of time series analysis of non-stationary EEG data: eigenstructure decompositions of time varying autoregressions

OBJECTIVE

Those who analyze EEG data require quantitative techniques that can be validly applied to time series exhibiting ranges of non-stationary behavior. Our objective is to introduce a new analysis technique based on formal non-stationary time series models. This novel method provides a decomposition of the time series into a set of 'latent' components with time-varying frequency content. The identification of these components can lead to practical insights and quantitative comparisons of changes in frequency structure over time in EEG time series.

METHODS

The technique begins with the development of time-varying autoregressive models of the EEG time series. Such models have been previously used in EEG analysis but we extend their utility by the introduction of eigenstructure decomposition methods. We review the basis and implementation of this method and report on the analysis of two channel EEG data recorded during 3 generalized tonic-clonic seizures induced in an individual as part of a course of electroconvulsive therapy for major depression.

RESULTS

This technique identified EEG patterns consistent with prior reports. In addition, it quantified a decrease in dominant frequency content over the seizures and suggested for the first time that this decrease is continuous across the end of the seizures. The analysis also suggested that the seizure EEG may be best modeled by the combination of multiple processes, whereas post-ictally there appears to be one dominant process. There was also preliminary evidence that these features may differ as a function of ECT therapeutic effectiveness.

CONCLUSIONS

Eigenanalysis of time-varying autoregressive models has promise for improving the analysis of EEG time series.

Delayed hypovolemic hypotension exacerbates the hemodynamic and histopathologic consequences of thromboembolic stroke in rats

Abnormalities in cerebrovascular reactivity or hemodynamic reserve are risk factors for stroke. The authors determined whether hemodynamic reserve is reduced in an experimental model of thromboembolic stroke. Nonocclusive common carotid artery thrombosis (CCAT) was produced in rats by a rose bengal-mediated photochemical insult, and moderate hypotension (60 mm Hg/30 min) was induced 1 hour later by hemorrhage. Alterations in local cerebral blood flow (ICBF) were assessed immediately after the hypotensive period by 14C-iodoantipyrine autoradiography, and histopathologic outcome was determined 3 days after CCAT. Compared to normotensive CCAT rats (n = 5), induced hypotension after CCAT (n = 7) led to enlarged regions of severe ischemia (i.e., mean ICBF < 0.24 mL/g/min) in the ipsilateral hemisphere. For example, induced hypotension increased the volume of severely ischemic sites from 16 +/- 4 mm3 (mean +/- SD) to 126 +/- 99 mm3 (P < 0.05). Histopathologic data also showed a larger volume of ischemic damage with secondary hypotension (n = 7) compared to normotension (22 +/- 15 mm3 versus 5 +/- 5 mm3, P < .05). Both hypotension-induced decreases in ICBF and ischemic pathology were commonly detected within cortical anterior and posterior borderzone areas and within the ipsilateral striatum and hippocampus. In contrast to CCAT, mechanical ligation of the common carotid artery plus hypotension (n = 8) did not produce significant histopathologic damage. Nonocclusive CCAT with secondary hypotension therefore predisposes the post-thrombotic brain to hemodynamic stress and structural damage.

Thromboembolic events predispose the brain to widespread cerebral infarction after delayed transient global ischemia in rats

BACKGROUND AND PURPOSE

Transient distal platelet accumulation after common carotid artery thrombosis (CCAT) leads to hemodynamic, metabolic, and molecular events that may influence the response of the postthrombotic brain to secondary insults. We investigated how a thromboembolic insult would affect histopathological outcome when combined with an ischemic insult induced 24 hours later.

METHODS

Three groups of rats underwent either (1) CCAT+10 minutes of normothermic 2-vessel occlusion (n=6), (2) CCAT+sham ischemia procedures (n=6), or (3) sham CCAT procedures+10 minutes of 2-vessel occlusion (n=6). At 7 days, rats were perfused for quantitative histopathological and immunocytochemical analysis.

RESULTS

Rats undergoing combined insults (group 1) had significantly larger areas of ischemic injury (P<0.05) within the cerebral cortex, striatum, and thalamus compared with the other, single-injury groups. Increased ischemic damage included selective neuronal necrosis, infarction, and focal hemorrhage. By means of glial fibrillary acidic protein immunocytochemistry and lectin histochemistry, reactive astrocytes and microglia were found to be associated with widespread tissue necrosis. In contrast, infrequent infarction or CA1 hippocampal neuronal necrosis was observed in groups 2 and 3, respectively.

CONCLUSIONS

A prior thromboembolic event is a risk factor for widespread cerebral infarction and hemorrhage when combined with a delayed ischemic insult. The understanding of what factors enhance the susceptibility of the postthrombotic brain to secondary insults may aid in the development of neuroprotective strategies to be applied after transient ischemic attacks to prevent the initiation of stroke.

Ritanserin, a 5-HT2 receptor antagonist, increases subcortical blood flow following photothrombotic middle cerebral artery occlusion in rats

It has been proposed that the reversal of serotonin-mediated vasoconstriction accounts for the neuroprotective effect of serotonin (5-HT2) receptor blockade in focal cerebral ischemia. We investigated the effect of pretreatment with ritanserin, a 5-HT2 receptor antagonist, on cerebral blood flow in a model of photothrombotic middle cerebral artery occlusion in rats. Local cerebral blood flow was measured by iodoantipyrine autoradiography 30 minutes after induction of ischemia. Using a novel image-alignment algorithm, 3-dimensional reconstructions of averaged cerebral blood flow were calculated. The difference-image of local cerebral blood flow between ritanserin and vehicle-treated animals revealed a subcortical zone underlying the ischemic cortex where cerebral blood flow was markedly enhanced indicating a beneficial hemodynamic effect of ritanserin. Three-dimensional image analysis provides a powerful tool to detect inter-group differences of cerebral blood flow which are underestimated by conventional types of data analysis.

Posttraumatic cerebral ischemia after fluid percussion brain injury: an autoradiographic and histopathological study in rats

OBJECTIVES

Mild-to-moderate reductions in local cerebral blood flow (ICBF) have been reported to occur in rats after moderate (1.7-2.2 atm) fluid percussion brain injury. The purpose of this study was to determine whether evidence for severe ischemia (i.e., mean ICBF < 0.25 ml/g/min) could be demonstrated after severe brain injury. In addition, patterns of indium-labeled platelet accumulation and histopathological outcome were correlated with the hemodynamic alterations.

METHODS

Sprague-Dawley rats (n = 23), anesthetized with halothane and maintained on a 70:30 mixture of nitrous oxide:oxygen and 0.5% halothane, underwent normothermic (37 degrees C) parasagittal fluid percussion brain injury (2.4-2.6 atm). Indium-111-tropolone-labeled platelets were injected 30 minutes before traumatic brain injury (TBI), while 14C-iodoantipyrine was infused 30 minutes after trauma for ICBF determination. Sham-operated animals (n = 8) underwent similar surgical procedures but were not injured. For histopathological analysis, traumatized rats (n = 5) were perfusion-fixed 3 days after TBI.

RESULTS

In autoradiographic images of indium-labeled platelets, abnormal platelet accumulation that was most pronounced overlying the pial surface was commonly associated with severe reductions in ICBF within underlying cortical regions 30 minutes after TBI. For example, within the lateral parietal cortex, ICBF was significantly reduced from 1.67 +/- 0.11 ml/g per minute (mean +/- standard error of the mean) in sham-operated animals to 0.23 +/- 0.03 ml/g per minute within the traumatized group. In addition to focal severe ischemia, moderate reductions in ICBF were detected throughout the traumatized hemisphere, including the frontal and occipital cortices, hippocampus, thalamus, and striatum. Mild decreases in ICBF were also observed throughout the contralateral cerebral cortex. At 3 days after severe TBI, histopathology demonstrated intracerebral and subarachnoid hemorrhage associated with cerebral contusion and selective neuronal necrosis.

CONCLUSION

These data indicate that multiple cerebrovascular abnormalities, including subarachnoid hemorrhage, focal platelet accumulation, and severe ischemia, are important early events in the pathogenesis of cortical contusion formation after TBI. Injury severity is expected to be a critical factor in determining what therapeutic strategies are attempted in the clinical setting.

White matter alterations following thromboembolic stroke: a beta-amyloid precursor protein immunocytochemical study in rats

Thromboembolic stroke in rats leads to a well-described pattern of histopathological and behavioral abnormalities. However, limited data are available in animal models concerning the response of the white matter to embolic events. The purpose of this study was to document patterns of white matter abnormalities using beta-amyloid precursor protein (betaAPP) immunocytochemistry as a marker of axonal damage. Twelve male Wistar rats underwent photochemically induced right common carotid artery thrombosis (CCAT) or sham procedures. At 3 days after CCAT, rats were perfusion-fixed and sections immunostained for the visualization of betaAPP or stained with hematoxylin and eosin for routine histopathological analysis. As previously described, CCAT produced small ipsilateral embolic infarcts and ischemic cell change within gray matter structures including the medial cerebral cortex, striatum, hippocampus and thalamus. In areas of frank infarction, numerous reactive profiles were observed within borderzones of the damaged site. However, betaAPP immunocytochemistry also revealed reactive axonal profiles within various white matter tracts including the corpus callosum, external capsule and fimbria of the hippocampus. In many cases, the presence of axonal damage could not be appreciated with routine hematoxylin and eosin staining. These data indicate that CCAT leading to platelet embolization to the brain not only produces embolic infarcts but also produces more subtle white matter abnormalities. Previously undetected white matter damage would be expected to participate in the sensorimotor and cognitive behavioral deficits following embolic stroke.

The effect of nitric oxide synthase inhibition on acute platelet accumulation and hemodynamic depression in a rat model of thromboembolic stroke

The relative importance of hemodynamic factors in the pathogenesis of thrombotic or embolic stroke is unclear. Of particular therapeutic interest are those substances that facilitate vasodilation and the clearance of platelet aggregates in the compromised microvasculature. A likely contributor to these functions is nitric oxide because it is known to inhibit platelet aggregability and promote vascular relaxation. To investigate the involvement of nitric oxide in the hemodynamic changes after experimental ischemia, photochemically induced nonocclusive common carotid artery thrombosis (CCAT) was studied. CCAT is a rat model of unilateral carotid artery stenosis and platelet embolization to the brain. This study characterized the acute hemodynamic consequences of CCAT and the resultant pattern of platelet deposits with and without nitric oxide synthase inhibition by nitro-L-arginine methyl ester (L-NAME). In addition, the subacute local cerebral blood flow changes were studied at 24 hours. Right CCAT was produced in 30 male Wistar rats injected with (111)In-labeled platelets. Between 5 and 15 minutes after thrombosis, rats were treated with either 15 mg/kg of L-NAME (intravenously) or saline vehicle. Hemodynamic changes were studied 30 to 45 minutes after thrombosis using [14C]iodoantipyrine autoradiography. Eight coronal levels were analyzed, and cortical and subcortical regions of interest were defined. Significant increases were observed in total platelets in the ipsilateral hemisphere after L-NAME treatment, and in the distribution of platelets in the anterior frontal and occipital cortices with nitric oxide synthase inhibition, encompassing the anterior and posterior border zone areas of the ipsilateral cortex. Otherwise, foci of labeled platelets were detected throughout the ipsilateral and contralateral hemispheres. Mean local cerebral blood flow images (n = 5) revealed a moderate bilateral global reduction in flow acutely, which normalized in the untreated thrombosed group by 24 hours. In contrast, the L-NAME-treated groups (sham and experimental) had lasting, widespread reductions in flow of approximately 25%. Pairwise comparisons between groups showed that CCAT/L-NAME was significantly different from shams in the corpus callosum and different from L-NAME shams in the internal capsule (P < 0.05) These hemodynamic and platelet accumulation changes may partially account for the aggravation of cognitive and sensorimotor deficits previously reported in this model of thromboembolic stroke.

The role of nitric oxide in the pathophysiology of thromboembolic stroke in the rat

Although nitric oxide (NO) has been shown to play an important role in the pathophysiology of cerebral ischemia, its contribution to the pathogenesis of experimentally induced thromboembolic stroke is unknown. In this study, we pharmacologically manipulated NO levels in the acute post-thrombotic stage and determined the effects on behavior and histopathology. The following drugs were used: nitro-L-arginine-methyl ester (L-NAME), a non-specific endothelial and neuronal nitric oxide synthase (eNOS and nNOS) inhibitor, 3-bromo-7-nitroindazole (7-NI), a specific inhibitor for nNOS, the NO precursor, exogenous L-arginine and the NO-donor, 3-morpholino-sydnonimine (SIN-1). Male Wistar rats (n = 76) were randomly assigned to receive vehicle or drug immediately after common carotid artery thrombosis (CCAT). Regional measurements of cortical NOS activity using the [3H]L-arginine to [3H]L-citrulline conversion assay were decreased 1 h after treatment with L-NAME and 7-NI by 50 and 65%, respectively; hippocampal NOS activity was reduced with L-NAME by 35% and with 7-NI by 65%. L-NAME significantly worsened forelimb placing as compared to other groups. 7-NI accelerated sensorimotor recovery. Water maze retention deficits were noted 48 h after CCAT and these were exacerbated by L-NAME treatment. Histopathological protection was conferred in the hippocampus by 7-NI and SIN-1; conversely, L-NAME increased neuronal injury in the contralateral cortex. L-arginine had no effect on these outcomes. In conclusion, both structural and functional consequences of CCAT can be aggravated by limiting endothelial NO production in the acutely post-thrombotic brain. In contrast, inhibition of nNOS and infusion of an NO donor has a beneficial effect on pathology.

Cerebral protection by intermittent reperfusion during temporary focal ischemia in the rat

Temporary arterial occlusion has been routinely used as an adjunct in intracranial aneurysm surgery. This has commonly been performed using a protocol of multiple short periods of occlusion alternating with periods of restoration of normal circulation. Recently, the logical basis of this method has come under scrutiny. There is extensive experimental evidence to suggest that repetitive, brief periods of global ischemia may cause more severe cerebral injury than an equivalent single period of global ischemia. Only recently has this issue begun to be addressed with regard to focal ischemia. Hence, despite the common use of temporary clipping, little experimental data are available regarding the ischemic consequences of temporary arterial occlusion with periods of reperfusion versus uninterrupted temporary occlusion. To investigate this issue, a protocol of occlusion/reperfusion that simulates the temporal profile that occurs during surgery was performed in a rat model of focal ischemia. Sixteen anesthetized Sprague-Dawley rats were divided into two groups. The animals in Group I underwent 60 minutes of uninterrupted middle cerebral artery occlusion and the animals in Group II were subjected to six separate 10-minute occlusion periods with 5 minutes of reperfusion between occlusions. Histopathological analysis was performed 72 hours postischemia. Group I had significantly increased mean infarction volumes (50.0 +/- 12.1 mm3) compared to Group II (8.7 +/- 3.1 mm3) (p = 0.008). Injuries in Group I occurred in both the cortex and striatum, whereas Group II showed only striatal injuries. Furthermore, the extent of the injuries in Group II was less severe, characterized by ischemic neuronal injury rather than frank infarction. The results indicate that intermittent reperfusion is neuroprotective during temporary focal ischemia and support the hypothesis that intermittent reperfusion is beneficial if temporary clipping is required during aneurysm repair.

L-arginine does not improve cortical perfusion or histopathological outcome in spontaneously hypertensive rats subjected to distal middle cerebral artery photothrombotic occlusion

The potential of nitric oxide (NO) to influence positively or negatively the outcome of mechanically induced focal cerebral ischemia is still controversial. Recent evidence suggests that NO of vascular origin, whether synthesized from exogenously administered L-arginine (L-Arg) or from NO donor compounds, is beneficial but that of neuronal origin is not. However, the therapeutic potential of NO to ameliorate stroke induced by arterial thrombosis has not been reported. We assessed the therapeutic effect of L-Arg administration in spontaneously hypertensive rats (SHR) subjected to permanent photothrombotic occlusion of the distal middle cerebral artery (dMCA). The ipsilateral carotid artery was left unligated to enhance L-Arg delivery into the putative penumbral region. Local CBF (LCBF) was assessed at 30 min by the [14C]iodoantipyrine technique (n = 9), while histological infarct volumes and index of peripheral ischemic cell change were determined at 3 days (n = 7). Rats (n = 9) given 300 mg/kg L-Arg at 18 and 3 h before photothrombotic dMCA occlusion and at 5 min afterward displayed no significant differences in LCBF compared with animals (n = 8) injected with water (the carrier vehicle) and similarly irradiated. Infarct volumes were also similar, being 37.0 +/- 9.7 mm3 (SD) in the vehicle-treated and 49.1 +/- 17.2 mm3 (SD) in the L-Arg-treated groups (both n = 7), as were assessments of ischemic neuronal density in the penumbra. In contrast, L-Arg administered intravenously in a dose of 300 mg/kg to nonischemic SHR (n = 5) increased cortical CBF by approximately 75% during a 70-min observation period. We conclude that thrombotic processes superimposed upon cerebral ischemia may facilitate tissue reactions that offset the potentially beneficial effect of L-Arg, and this caveat must be considered when proposing L-Arg for clinical treatment of focal thrombotic stroke.

Depiction of infarct frequency distribution by computer-assisted image mapping in rat brains with middle cerebral artery occlusion. Comparison of photothrombotic and intraluminal suture models

BACKGROUND AND PURPOSE

Histopathologic analysis of experimental brain damage has traditionally been performed by measuring areas of infarction and/or selective neuronal alterations on a section-by-section basis in individual animals. For series containing multiple replicate animals, quantitation of tissue injury is typically performed at similar coronal levels throughout an experimental group. A means of facilitating pictorial group comparisons of these histopathologic alterations between different series of replicate studies is highly desirable.

METHODS

We introduce a newly designed approach to achieve this goal, based on a linear affine transformation that is used to map corresponding sections at the same anatomic level into a common template to yield a frequency distribution map depicting the aggregate data set. We have applied this approach to compare the histopathologic features of two models of middle cerebral artery (MCA) occlusion in rats: (1) photothrombotically induced permanent distal MCA occlusion in spontaneously hypertensive rats (SHR) and (2) temporary MCA occlusion by intraluminal suture in Wistar rats.

RESULTS

The brains of SHR rats with permanent distal MCA occlusion showed a high frequency of infarction involving the dorsolateral and lateral portions of the ipsilateral neocortex, whereas Wistar rats with 90-minute MCA suture occlusion showed a zone of infarction largely concentrated in the dorsolateral portion of the ipsilateral caudoputamen. Infarct frequency distributions for the two animal groups were compared statistically at three corresponding anatomic levels by Fisher's exact test; the resulting statistical parametric maps are shown.

CONCLUSIONS

With the use of frequency distribution maps, the pattern of trends within a group can be observed coronally or three-dimensionally. One can directly access data as to numbers of rats with infarction for any point on the map. Studies performed under different experimental conditions can also be compared with one another by means of the generated data sets.

Widespread hemodynamic depression and focal platelet accumulation after fluid percussion brain injury: a double-label autoradiographic study in rats

Cerebrovascular damage leading to subsequent reductions in local cerebral blood flow (lCBF) may represent an important secondary injury mechanism following traumatic brain injury (TBI). We determined whether patterns of 111-indium-labeled platelet accumulation were spatially related to alterations in lCBF determined autoradiographically 30 min after TBI. Sprague-Dawley rats (n = 8), anesthetized with halothane and maintained on a 70:30 (vol/vol) mixture of nitrous oxide/oxygen and 0.5% halothane, underwent parasagittal fluid percussion brain injury (1.7-2.2 atm). 111-Indium-tropolone-labeled platelets were injected 30 min prior to TBI while [14C]-iodoantipyrine was infused 30 min after trauma. Sham-operated animals (n = 7) underwent similar surgical procedures but were not injured. In autoradiographic images of the indium-labeled platelets, focal sites of platelet accumulation within the traumatized hemisphere were restricted to the pial surface (five of eight rats), the external capsule underlying the lateral parietal cortex (five of eight rats), and within cerebrospinal fluid (CSF) compartments (six of eight rats). In contrast, mild-to-moderate reductions in lCBF, not restricted to sites of platelet accumulation, were seen throughout the traumatized hemisphere. Flow reductions were most severe in coronal sections underlying the impact site. For example, within the lateral parietal cortex and hippocampus, lCBF was significantly reduced [p <0.01; analysis of variance (ANOVA)] from 1.71 +/- 0.34 (mean +/- SD) and 0.78 +/- 0.12 ml/g/min, respectively, versus 0.72 +/- 0.17 and 0.41 +/- 0.06 ml/g/min within the traumatized hemisphere. Significant flow reductions were also seen in remote cortical and subcortical areas, including the right frontal cortex and striatum. These results indicate that focal platelet accumulation and widespread hemodynamic depression are both early consequences of TBI. Therapeutic strategies directed at these early microvascular consequences of TBI may be neuroprotective by attenuating secondary ischemic processes.

Nonocclusive common carotid artery thrombosis in the rat results in reversible sensorimotor and cognitive behavioral deficits

BACKGROUND AND PURPOSE

Microemboli released during transient ischemic attack, stroke, and cardiac surgery are thought to cause a variety of functional deficits in humans. The purpose of this study was to characterize the type and extent of neurobehavioral deficits present after photochemically induced common carotid artery thrombosis (CCAT), a thromboembolic model of stroke in the rat that results in a platelet emboli shower.

METHODS

Thirty-two male Wistar rats were assigned to four groups. Groups 1 (n = 8) and 3 (n = 8) were long-term (6-week survival) and short-term (2-week survival) experimental groups subjected to right CCAT with the use of the photochemical technique. Groups 2 (n = 8) and 4 (n = 8) served as sham-operated controls for each experimental group. A battery of behavioral tests was applied daily beginning 24 hours after thrombosis; this consisted of elicited forelimb placing, postural reflex, beam balance, beam walking, and open field activity. Cognitive testing with a water maze task was performed on post-CCAT days 30 to 33 for groups 1 and 2 and on post-CCAT day 2 for groups 3 and 4. Ten-micrometer coronal brain sections were stained with hematoxylin and eosin, and infarct location and frequency were determined.

RESULTS

Significant sensorimotor deficits were observed, which recovered within 2 weeks after CCAT. The data that follow are derived by combining the two experimental groups and comparing these with the two sham groups. The following tests showed significant effects after CCAT: contralateral elicited forelimb placing, ipsilateral elicited forelimb placing, beam balance, and beam walking score. Cognitive dysfunction was seen acutely (group 3 animals) at 2 days after CCAT; Morris water maze length and latency to target were significantly greater in the experimental group. No deficits were seen in postural reflex, open field activity, or delayed cognitive testing. Histopathological assessment revealed small infarcts in 11 of 16 thrombosed rats. However, a strong relationship between neurobehavioral deficits and infarct location was not consistently demonstrated.

CONCLUSIONS

CCAT produces consistent sensorimotor and cognitive behavioral deficits that recover within 2 weeks of injury. Behavioral outcome was not necessarily associated with overt histopathological damage, suggesting that reversible injury mechanisms, both vascular and neuronal, may be partly responsible for the temporary loss of function. These data strengthen the role of CCAT as a clinically relevant model of thromboembolic stroke.

A dual role for nitric oxide in NMDA-mediated toxicity in vivo

Nitric oxide has been implicated in N-methyl-D-aspartate (NMDA)-mediated damage in vitro; however, its role in excitotoxic damage in vivo is not clear. In the present study we evaluated the histopathological and hemodynamic consequences of intrastriatal injections of various doses of NMDA and determined the effects of nitric oxide synthase inhibition on these changes. NMDA was injected into the striatum at doses of 50, 150, and 300 nmol with or without N omega-nitro-L-arginine methyl ester (L-NAME; 100 micrograms, locally). Three days following injections histopathological assessment was performed by morphometric analysis of the lesion area in multiple sections taken from the anterior to the posterior borders of the lesion. In animals injected with 150 and 300 nmol of NMDA (+/- L-NAME), local CBF (lCBF) was determined 30 min following injections using 14C-iodoantipyrine autoradiography. All NMDA-treated animals showed a well-demarcated lesion extending beyond the injection site. The volume of the lesion correlated significantly with the NMDA dose injected. The effects of L-NAME on lesion size were dependent on the dose of the NMDA. The lesion induced by 50 nmol of NMDA was not affected by L-NAME. With a dose of 150 nmol of NMDA, L-NAME induced a 43% increase in lesion volume. In contrast, a 38% decrease in lesion size was observed in animals treated with 300 nmol of NMDA combined with L-NAME. At a dose of 150 nmol, NMDA induced a significant elevation in lCBF, which was restricted to regions close to the injection site including the center areas of the anterior and middle striatum. The increase in lCBF observed with 150 nmol of NMDA was significantly attenuated in the NMDA + L-NAME-treated group. The lCBF changes induced by 300 nmol of NMDA were not significantly different from those in the 150-nmol group; however, the extent of the regions involved was larger. The increases in lCBF were observed in all striatal regions including the central and peripheral areas. L-NAME did not have a significant effect on the lCBF changes induced by NMDA at a dose of 300 nmol. These data suggest that in vivo the involvement of nitric oxide in NMDA toxicity depends on the NMDA dose and on the participation of hemodynamic mechanisms secondary to NMDA exposure.

Ischemia-induced changes in extracellular levels of striatal cyclic GMP: role of nitric oxide

Using microdialysis, we evaluated temporal changes in striatal extracellular cGMP level following ischemia and its relationship to nitric oxide (NO) production. In untreated animals, significant elevation of cGMP was observed during ischemia and during 4 h of recirculation. In animals treated with L-NAME ischemia induced a modest increase in the cGMP level, but this level was significantly lower than that observed in the untreated animals. These results demonstrate first, that the microdialysis technique can be used to detect changes in extracellular cGMP levels during ischemia and second, that ischemia and recirculation induce a rise in cGMP which is diminished by nitric oxide synthase inhibition, suggesting a linkage to NO production.

A photothrombotic 'ring' model of rat stroke-in-evolution displaying putative penumbral inversion

BACKGROUND AND PURPOSE

To facilitate reproducible and rigorous study of a tissue zone at risk of encroaching ischemic damage, we propose a new model in which the potentially compromised tissue lies within rather than perifocal to an ischemic locus. The perimeter of the "zone at risk" is defined by a photothrombotically produced cortical lesion in the shape of a toroid (or "ring").

METHODS

The exposed crania of erythrosin B-injected rats were irradiated with a 514.5-nm laser beam, configured as a 5-mm-diameter ring, to yield a ring-shaped lesion caused by photochemically induced platelet occlusion of cortical vasculature. Developing perfusion deficits in the interior region were revealed by carbon black infusion. Tissue damage and infarct volumes were assessed by light and electron microscopy, and blood-brain barrier integrity was assessed with Evans blue dye and horseradish peroxidase as tracers.

RESULTS

For rats injected with 17 mg/kg erythrosin B and irradiated for 2 minutes with a ring beam intensity of 0.92 W/cm2 (beam power of 65 mW), carbon black infusion at times up to 4 hours demonstrated a shallow cortical ring lesion encircling a fully patent zone at risk, which by 24 hours evinced an essentially complete perfusion deficit. At times up to 24 hours, the ring lesion was penetrated at the pial surface by distal branches of the middle cerebral and anterior cerebral arteries. Stereotaxically based histopathological assessment showed that by 24 hours the lesion spanned the cortical thickness. Lesion volume increased from 14.5 +/- 8.0 mm3 (mean +/- SD) (n = 8) to 46.2 +/- 15.6 mm3 (n = 8) between 4 and 24 hours after irradiation (P < .01), but the anteroposterior lesion diameter did not change significantly between 4 hours (6.00 +/- 1.03 mm; n = 9) and 24 hours (6.75 +/- 1.15 mm; n = 9).

CONCLUSIONS

The present model of slowly developing but inevitable cortical tissue death in a sequestered area should facilitate more precise observations of the evolution of tissue metabolic responses, from the impending onset of ischemia to the threshold of irreversible damage. This system may prove efficient for evaluating treatments intended to salvage a penumbral region.

Acadesine reduces indium-labeled platelet deposition after photothrombosis of the common carotid artery in rats

BACKGROUND AND PURPOSE

The adenosine-regulating agent acadesine has been shown to reduce the incidence of myocardial infarction and stroke after cardiopulmonary bypass surgery. The present study examined the effect of acadesine on the accumulation of indium-labeled platelet emboli and infarct size after photothrombosis of the common carotid artery.

METHODS

Rats were anesthetized with halothane and preloaded with 111In-tropolone-labeled platelets (50 to 80 microCi) 30 minutes before nonocclusive common carotid artery thrombosis induced by a rose bengal-mediated photochemical insult. Intravenous infusion of acadesine (0.5, 1, or 2 mg/kg per minute) or vehicle was begun 30 minutes before right common carotid artery thrombosis and continued for an additional 15 minutes. Rats were then killed and brains processed for the autoradiographic quantitation of labeled platelet aggregates. In a separate group of rats, infarct areas and volumes were determined in treated (acadesine 1 mg/kg per minute) (n = 9) and nontreated (n = 9) rats 7 days after thrombosis.

RESULTS

Although the ratio of right-to-left common carotid artery radioactivity was not affected by treatment, acadesine at 1 and 2 mg/kg per minute significantly decreased (P < .01) platelet deposition within the right cerebral cortex, hippocampus, and striatum. For example, within the frontoparietal cortex, numbers of platelet aggregates were 11.8 +/- 1.8 (mean +/- SEM), 6.1 +/- 1.4, 2.3 +/- 0.6, and 3.2 +/- 0.8 in rats infused with vehicle, 0.5, 1, and 2 mg/kg per minute acadesine, respectively. In addition, infarct volume was reduced by 48% in acadesine-treated (1 mg/kg per minute) rats, with a significant reduction in infarct area at the coronal level 3.7 mm anterior to bregma (P < .01).

CONCLUSIONS

These results support a prophylactic role for acadesine in reducing the accumulation of platelet emboli during vascular thrombosis and subsequent brain infarction. Acadesine treatment in patients at risk for embolic stroke could potentially lead to cerebral protection.

Glutamate antagonist MK-801 attenuates incomplete but not complete infarction in thrombotic distal middle cerebral artery occlusion in Wistar rats

The purpose of this study was to investigate the effects of a non-competitive N-methyl-D-aspartate antagonist, MK-801, on incomplete infarction (selective neuronal necrosis), a zone of which had been found previously in a thrombotic distal middle cerebral artery (MCA) occlusion model in Wistar rats. Male Wistar rats were treated with 1 mg/kg of MK-801 or saline 30 min before MCA occlusion. Laser irradiation with intravenous administration of Rose Bengal dye was used to cause thrombotic distal MCA occlusion. The ipsilateral common carotid artery was occluded permanently and the contralateral carotid artery for 60 min. Head temperature was controlled at 36 degrees C. Cerebral blood flow (CBF) was determined with laser-Doppler flowmetry. Three days after the ischemic insult, brains were perfusion-fixed and volumes of cortical (complete and incomplete) infarction were determined. There were no significant differences in physiological variables or CBF between the two groups. Volumes of complete infarction were equivalent between the two groups (94.9 +/- 15.6 mm3 and 91.6 +/- 14.0 mm3 in the control and MK-801 treated groups, respectively). In MK-801 treated group, the volume of incomplete infarction was reduced by 44% (6.4 +/- 1.7 mm3 vs. 3.6 +/- 2.1 mm3 in control and MK-801 treated groups, respectively, P < 0.05). Although the zone responsive to MK-801 was small in this thrombotic MCA occlusion model, our present study revealed that MK-801 has a beneficial effect on the tissue zone containing selective neuronal alterations (incomplete infarction). Our results support the concept that this drug is effective in the area of less severe ischemia.

Dendritic development in neocortex of infants with early postnatal life undernutrition

The structure of large pyramidal cells from layer V of the motor cortex of undernourished and well-nourished infants was studied to determine the effects of postnatal nutrition on cortical dendritic development. In undernourished infants, the arborization and span of the basilar dendrites were decreased in comparison to controls. These findings indicated that undernutrition experienced during the first months of postnatal life could affect the growth of pyramidal cells, especially the formation of basilar dendrites.

Transient platelet accumulation in the rat brain after common carotid artery thrombosis. An 111In-labeled platelet study

BACKGROUND AND PURPOSE

Thromboembolic events are a major cause of ischemic stroke. To obtain evidence for platelet embolization after cerebrovascular injury, the accumulation of indium-labeled platelets was documented after photothrombosis of the rat common carotid artery.

METHODS

Heterologous blood was collected from donor rats, and the isolated platelets were labeled with 111In-tropolone. Labeled platelets were then infused into Wistar rats 30 minutes before right carotid artery thrombosis. Nonocclusive common carotid artery thrombosis was induced by a laser-driven rose bengal-mediated photochemical insult to the vascular endothelium, and the rats were killed 15 minutes or 3 hours later. Carotid arteries and brains were immediately removed and dissected for regional radioactivity assessment or sectioned for the autoradiographic visualization of platelet emboli.

RESULTS

At 15 minutes after thrombosis, the ratio of right-to-left common carotid artery radioactivity was significantly elevated compared with control (33 +/- 12 [mean +/- SEM] versus 0.97 +/- 0.2). Within individual brain regions, including the frontal and frontoparietal cortices and hippocampus, significant elevations in right-to-left radioactivity ratios were also documented. Autoradiographic images revealed multiple foci of 111In-labeled platelets throughout the thrombosed hemisphere. At the level of the frontal cortex, bilateral platelet accumulation was seen. Regional counts demonstrated significantly increased platelet density within selective cortical and subcortical regions. In contrast to the 15-minute findings, right-to-left ratios of carotid arteries or brain regional radioactivities were not significantly elevated at 3 hours after injury. In addition, the areal densities of autoradiographically visualized platelets in the 3-hour group were not different from control except in the right frontal cortex.

CONCLUSIONS

These data demonstrate (1) the acute accumulation of labeled platelets in downstream vessels after nonocclusive common carotid artery thrombosis, (2) that platelet accumulation is widespread and also involves contralateral areas, and (3) that platelet accumulation within the thrombosed carotid artery and brain is largely transient.

Selective brain cooling increases cortical cerebral blood flow in rats

To evaluate the effect of selective brain cooling on cortical cerebral blood flow, we reduced brain temperature in nitrous oxide anesthetized adult rats using a high speed fan while keeping rectal temperature at 37-38 degrees C. During selective brain cooling, cortical cerebral blood flow, as measured by laser-Doppler flowmetry, increased to 215 +/- 26% (mean +/- SE) of baseline at a cortical brain temperature of 30.9 +/- 0.5 degrees C and a rectal temperature of 37.5 +/- 0.1 degrees C. During rewarming, as brain temperature increased, cortical cerebral blood flow decreased. The cerebral vasodilatory response to hypothermia may explain its protective effects during and after cerebral ischemia.

Microvascular and neuronal consequences of common carotid artery thrombosis and platelet embolization in rats

The microvascular and neuronal consequences of nonocclusive common carotid artery (CCA) thrombosis were documented in rats. Thrombosis of the CCA was produced by a rose bengal-mediated photochemical insult and regional patterns of blood-brain barrier (BBB) disruption were documented by horseradish peroxidase (HRP) histochemistry at 15 min (n = 12), 4 h (n = 3), 1 day (n = 5) or 7 days (n = 5) after vascular injury. At 15 min and 4 h after thrombosis, multiple foci of BBB disruption were present throughout the thrombosed hemisphere; protein leakage was occasionally detected contralaterally. Extravasated HRP was associated with well-perfused arterioles and arterioles containing luminal platelet aggregates at different stages of degranulation. Evidence for local platelet adhesion and aggregation or endothelial disruption at these sites was not detected. However, HRP-containing endothelial plasmalemmal vesicles were present at leaky sites. Variable degrees of parenchymal injury were documented including dendritic and astrocytic swelling with neuronal necrosis. By 1 day after CCA thrombosis, the overall frequency of permeable sites, more commonly associated with luminal leukocytes and parenchymal necrosis, was reduced. At 7 days, vessels permeable to HRP were associated with tissue necrosis, reactive astrocytes and microglial infiltration. Arteriole wall thickening and leukocyte accumulation within arterioles and venules were also detected. Widespread platelet embolization leading to variable degrees of BBB disruption and tissue injury occurs after CCA thrombosis. Acute abnormalities in vascular permeability are thus hypothesized to play an important role in the acute pathogenesis of cerebrovascular thrombosis. Delayed leukocyte accumulation in this model of embolic infarction may represent a secondary insult to the injured brain.

Effects of nitric oxide synthase inhibition on cerebral blood flow following bilateral carotid artery occlusion and recirculation in the rat

The effects of bilateral carotid artery occlusion/recirculation on cortical CBF (cCBF) were studied in rats following the intravenous administration of either the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester hydrochloride (L-NAME; 30 mg/kg) or an equivalent volume of saline (500 microliters). Induction of bilateral carotid occlusion (BCO) in L-NAME-treated animals resulted in a reduction of cCBF to 30% of baseline. During recirculation subsequent to 20 min of BCO, cCBF in L-NAME-infused animals remained at 30% of baseline. In contrast, cCBF in saline-treated control animals returned to the original baseline level following a similar reduction to 30-40% of baseline during BCO. These results indicate that inhibition of nitric oxide generation limits normalization of regional cortical perfusion following occlusion of proximal large cerebral vessels.

Failure of MK-801 to reduce infarct volume in thrombotic middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

We examined the effects of the noncompetitive N-methyl-D-aspartate receptor antagonist MK-801 using a newly developed stroke model of thrombotic distal middle cerebral artery occlusion under conditions of carefully controlled head temperature.

METHODS

Male Sprague-Dawley rats were treated with 1 mg/kg of MK-801 or saline before the induction of ischemia. An argon laser-activated dye laser (562 nm) was used to cause thrombotic distal middle cerebral artery occlusion. In experiments 1 and 2, the single laser beam (20 mW) was separated into three beams. Each beam was positioned onto the distal middle cerebral artery at three sites along the vessel. The photosensitizing dye rose bengal (20 mg/kg) was administered intravenously over 2 minutes; the three points were then irradiated for 3 minutes. In experiment 3, higher power of the laser (three separate irradiations using a single beam of 20 mW) was used. The ipsilateral common carotid artery was occluded permanently, and the contralateral carotid artery was occluded for 60 minutes. Head temperature was controlled at 36 degrees C in experiment 1 and not controlled in experiments 2 and 3. Three days after the ischemic insult, brains were perfusion-fixed and infarct volumes were determined.

RESULTS

Head temperature was mildly hypothermic (34-35 degrees C before ischemia, with a further decrease of 1-2 degrees C during the initial 60 minutes of ischemia) in experiment 2. However, no differences were observed in head temperature between the MK-801-treated and control groups. Cortical infarct volume in experiment 1 was 89 +/- 29 mm3 (mean +/- SD) in the treated group, which was not different from the control value of 84 +/- 40 mm3. Infarct volumes were smaller (58 +/- 35 mm3 and 54 +/- 14 mm3) in the control groups of experiments 2 and 3, respectively. However, MK-801 also failed to reduce infarct volumes in experiments 2 and 3.

CONCLUSIONS

MK-801 is not effective in this stroke model of focal thrombotic infarction under conditions of either controlled (normothermic) or uncontrolled (mildly hypothermic) head temperature.

Comparative histopathologic consequences of photothrombotic occlusion of the distal middle cerebral artery in Sprague-Dawley and Wistar rats

BACKGROUND AND PURPOSE

We have developed a minimally invasive model of photothrombotic occlusion of the distal middle cerebral artery in rats and have evaluated the patterns and features of the resulting histopathologic injury in two normotensive strains.

METHODS

Food-deprived male Sprague-Dawley (n = 14) and Wistar (n = 10) rats anesthetized with halothane/nitrous oxide underwent a small craniotomy to expose the right distal middle cerebral artery just above the rhinal fissure. The animals were injected intravenously with the photosensitizing dye rose bengal, and the distal middle cerebral artery was irradiated with light from an argon laser-activated dye laser at three separate points to induce thrombotic occlusion. The ipsilateral common carotid artery was then permanently occluded, and the contralateral common carotid artery was occluded for 60 minutes. Three days later, the brains were perfusion-fixed and prepared for histopathologic examination, and infarct volume was determined by quantitative planimetry.

RESULTS

In Sprague-Dawley rats, a large consistent temporoparietal cortical infarct was observed; mean +/- SD infarct volume was 130.5 +/- 40.0 mm3 (coefficient of variation, 30.7%) and a relatively small adjacent zone of selective neuronal necrosis ("incomplete infarction"), amounting to only 9.1% of the total injury volume, was also seen. By contrast, Wistar rats had smaller and more variable cortical infarcts (volume, 48.4 +/- 26.9 mm3; coefficient of variation, 55.6%) but displayed a much more substantial zone of incomplete cortical infarction (volume, 20.8 +/- 10.1 mm3; 30.1% of the total injury volume). In neither strain was infarct size related to alterations of blood pressure. In both strains, infarcts were limited to the cortex, typically involving the parietal cortex, somatosensory cortex, and forelimb region. Three rats exhibited infarcts in the contralateral hemisphere.

CONCLUSIONS

This model has the advantages of necessitating only minimal surgery, allowing the dura to remain intact, and avoiding mechanical trauma to the brain surface. In Sprague-Dawley rats, the resulting large cortical infarct exhibited relatively small interanimal variation, making the model suitable, for example, for replicate studies of pharmacotherapy. In Wistar rats, the large zone of incomplete infarction, a unique feature heretofore undescribed in rodent models of permanent focal ischemia, lends the model to the study of the pathomechanisms underlying graded cortical ischemic injury.

Ischemia-induced changes in extracellular levels of striatal cyclic AMP: role of dopamine neurotransmission

Dopamine has been demonstrated to be involved in the development of ischemic neuronal damage in the striatum. This detrimental effect of dopamine may involve activation of second messenger systems, such as the cyclic AMP (cAMP) cascade, which may enhance the susceptibility of striatal neurons to ischemia. In the present study, we have evaluated the relationship between ischemia-induced changes in cAMP and dopamine neurotransmission. Microdialysis probes were implanted in both striata, and a D1 antagonist (SCH-23390, 100 microM) was administered through one probe and modified Ringer's solution through the other. After a stabilization period, rats (n = 6) were subjected to 20 min of ischemia by two-vessel occlusion plus hypotension. Extracellular samples were collected from both striata, before, during, and after ischemia, and analyzed for cAMP by radioimmunoassay. Ischemia induced a significant increase in extracellular cAMP (means +/- SE, fmol/microliter; baseline: 4.35 +/- 1.1, ischemia: 12.2 +/- 1.98), which was also observed at 4 h of recirculation (mean level of 8.45 +/- 1.14). Treatment with the D1 antagonist significantly inhibited the rise in extracellular cAMP during ischemia and recirculation. These results indicate that an ischemia-induced surge in dopamine and activation of D1 receptors are involved in the generation of cAMP during ischemia and recirculation. Because activation of the adenylate cyclase cascade may modulate the effects of glutamate, generation of cAMP through this pathway may play a role in facilitating the injurious effects of dopamine during ischemia.