Biomedical subjects

E T MacKenzie

Publications and source records attributed to E T MacKenzie.

At least 19 recordsLinked to original sources

PubMed2003

Desflurane affords greater protection than halothane against focal cerebral ischaemia in the rat.

BACKGROUND: We studied the potential neuroprotective effects of halothane and desflurane, compared with the awake state, on infarct size following 2 h of intraluminal middle cerebral artery occlusion (MCAo) and 22 h of reperfusion. METHODS: Male Sprague-Dawley rats were anaesthetized with desflurane or halothane, intubated, and mechanically ventilated. Mean arterial pressure (MAP), blood gases, and pH were controlled. Body temperature was maintained at 37.5-38 degrees C. Animals were assigned to one of four groups according to the anaesthetic type (halothane or desflurane) and the duration of anaesthesia: "short-duration", during the preparation only; "long-duration", during both preparation and ischaemia. Twenty-four hours after MCAo, infarcts were visualized by staining with 2,3,5-triphenyltetrazolium chloride. Two additional groups of rats were subjected to the same protocol as that of long-duration halothane and long-duration desflurane with additional pericranial temperature measurements made. RESULTS: Physiological parameters were comparable between the groups but MAP was higher (P<0.0001) in the short-duration groups. In the short-duration groups, cerebral infarct volumes were not significantly different between anaesthetics (short-duration halothane: 288 (61) mm(3), mean (SD); short-duration desflurane: 269 (71) mm(3), P>0.56). Compared with the awake state (short-duration groups), halothane and desflurane significantly reduced infarct volumes (long-duration halothane: 199 (54) mm(3), P<0.0047 vs short-duration halothane; long-duration desflurane: 121 (55) mm(3), P<0.0001 vs short-duration desflurane). The mean infarct volume in the long-duration desflurane group was significantly lower than that in the long-duration halothane group (P<0.0053). Pericranial temperatures were similar in the desflurane and halothane long-duration groups (P>0.17). CONCLUSIONS: In rats, desflurane-induced neuroprotection against focal cerebral ischaemia was greater than that conferred by halothane.

Analysis of Variance↗

PubMed2001

A soluble transforming growth factor-beta (TGF-beta ) type I receptor mimics TGF-beta responses.

Transforming growth factor-beta (TGF-beta) signaling requires a ligand-dependent interaction of TGF-beta receptors Tau beta R-I and Tau beta R-II. It has been previously demonstrated that a soluble TGF-beta type II receptor could be used as a TGF-beta antagonist. Here we have generated and investigated the biochemical and signaling properties of a soluble TGF-beta type I receptor (Tau beta RIs-Fc). As reported for the wild-type receptor, the soluble Tau beta R-I does not bind TGF-beta 1 on its own. Surprisingly, in the absence of TGF-beta1, the Tau beta RIs-Fc mimicked TGF-beta 1-induced transcriptional and growth responses in mink lung epithelial cells (Mv1Lu). Signaling induced by the soluble TGF-beta type I receptor is mediated via the obligatory presence of both TGF-beta type I and type II receptors at the cell surface since no signal was observed in Mv1Lu-derivated mutants for TGF-beta receptors R-1B and DR-26. The comparison between the structures of TGF-betas and a three-dimensional model of the extracellular domain of Tau beta RI has shown that five residues of the supposed binding site of TGF-beta 1 (Lys(31), His(34), Glu(5), Tyr(91), and Lys(94)) were found with equivalent biochemical properties and similar spatial positions.

Amino Acid Sequence↗

PubMed2001

Inhibition of neuronal nitric oxide synthase by 7-methoxyindazole and related substituted indazoles.

The synthesis and pharmacological evaluation of methoxyindazoles as new inhibitors of neuronal nitric oxide synthase are presented. The 7-methoxyindazole, although less potent than 7-NI, is the most active compound of the series in an in vitro enzymatic assay of neuronal nitric oxide synthase activity. This result shows that the nitro-substitution is not indispensable to the biological activity of the indazole ring. 7-Methoxyindazole possesses in vivo NOS inhibitory as well and related antinociceptive properties.

Analgesics↗

PubMed2001

Neuroprotection mediated by glial cell line-derived neurotrophic factor: involvement of a reduction of NMDA-induced calcium influx by the mitogen-activated protein kinase pathway.

The glial cell line-derived neurotrophic factor (GDNF) is first characterized for its trophic activity on dopaminergic neurons. Recent data suggested that GDNF could modulate the neuronal death induced by ischemia. The purpose of this study was to characterize the influence of GDNF on cultured cortical neurons subjected to two paradigms of injury (necrosis and apoptosis) that have been identified during cerebral ischemia and to determine the molecular mechanisms involved. First, we demonstrated that both neurons and astrocytes express the mRNA and the protein for GDNF and its receptor complex (GFRalpha-1 and c-Ret). Next, we showed that the application of recombinant human GDNF to cortical neurons and astrocytes induces the activation of the MAP kinase (MAPK) pathway, as visualized by an increase in the phosphorylated forms of extracellular signal-regulated kinases (ERKs). Thereafter, we demonstrated that GDNF fails to prevent apoptotic neuronal death but selectively attenuates slowly triggered NMDA-induced excitotoxic neuronal death via a direct effect on cortical neurons. To further characterize the neuroprotective mechanisms of GDNF against NMDA-mediated neuronal death, we showed that a pretreatment with GDNF reduces NMDA-induced calcium influx. This effect likely results from a reduction of NMDA receptor activity rather than an enhanced buffering or extrusion capacity for calcium. Finally, we also demonstrated that an ERKs activation pathway is necessary for GDNF-mediated reduction of the NMDA-induced calcium response. Together, these results describe a novel mechanism by which the activation of MAPK induced by GDNF modulates NMDA receptor activity, a mechanism that could be responsible for the neuroprotective effect of GDNF in acute brain injury.

Animals↗

PubMed2001

Complement anaphylatoxin C3a is selectively protective against NMDA-induced neuronal cell death.

The anaphylatoxin C3a is a potent inflammatory polypeptide released at sites of complement activation. To test whether C3a might alter neuronal outcome following an ischemic insult, we determined the effects of purified human C3a on murine primary cortical cell cultures exposed to apoptotic or excitotoxic paradigms. C3a prevented neither serum deprivation-induced apoptotic neuronal death, nor AMPA/kainate-mediated excitotoxicity. However, in mixed cultures of neurons and astrocytes, C3a dose-dependently protected neurons against NMDA toxicity (47% neuroprotection using 100 nM C3a, p < 0.01, n = 12). The neuroprotective effect of C3a was observable only in the presence of astrocytes. These observations suggest that C3a is involved in excitotoxicity-mediated neuronal death through astrocyte stimulation and extend its role beyond immune functions.

Anaphylatoxins↗

PubMed2001

The proteolytic activity of tissue-plasminogen activator enhances NMDA receptor-mediated signaling.

Tissue-plasminogen activator (t-PA) is now available for the treatment of thrombo-embolic stroke but adverse effects have been reported in some patients, particularly hemorrhaging. In contrast, the results of animal studies have indicated that t-PA could increase neuronal damage after focal cerebral ischemia. Here we report for the first time that t-PA potentiates signaling mediated by glutamatergic receptors by modifying the properties of the N-methyl-D-aspartate (NMDA) receptor. When depolarized, cortical neurons release bio-active t-PA that interacts with and cleaves the NR1 subunit of the NMDA receptor. Moreover, the treatment with recombinant t-PA leads to a 37% increase in NMDA-stimulated fura-2 fluorescence, which may reflect an increased NMDA-receptor function. These results were confirmed in vivo by the intrastriatal injection of recombinant-PA, which potentiated the excitotoxic lesions induced by NMDA. These data provide insight into the regulation of NMDA-receptor-mediated signaling and could initiate therapeutic strategies to improve the efficacy of t-PA treatment in man.

Animals↗

PubMed2001

Increased expression of transforming growth factor-beta after cerebral ischemia in the baboon: an endogenous marker of neuronal stress?

There has been an increasing interest in recent years in the evaluation of the neuronal and glial responses to ischemic insult. Some cytokines, including transforming growth factor-beta (TGF-beta), that are overexpressed after experimental stroke in rodents are thought to be implicated in the neuronal processes that lead to necrosis. Thus, such cytokines could predict tissue fate after stroke in humans, although data are currently sparse for gyrencephalic species. The current study addressed the expression pattern of TGF-beta1 in a nonhuman primate model of middle cerebral artery occlusion. Focal permanent ischemia was induced for 1 or 7 days in 6 baboons and the following investigations were undertaken: cerebral oxygen metabolism (CMRO2) positron emission tomography studies, magnetic resonance imaging, postmortem histology, and reverse transcription-polymerase chain reaction. The aim of the current study was to correlate the expression of TGF-beta1 to the underlying metabolic and histologic state of the threatened cerebral parenchyma. The authors evidenced increased TGF-beta1 mRNA levels (up to 25-fold) in those regions displaying a moderate (20% to 49%) reduction in CMRO2. The current findings suggest that the greatly enhanced expression of TGF-beta1 in the penumbral zones that surround tissue destined to infarction may represent a robust index of potentially salvageable brain. The current investigation, in the nonhuman primate, strengthens the authors' hypothesis, derived from rodent models, that TGF-beta1 may be involved in the physiopathology of human stroke.

Animals↗

PubMed2001

The ischaemic penumbra.

The concept of an ischaemic penumbra, surrounding a focal cerebral lesion, is now widely accepted, although no universal definition of the 'penumbra' exists. In the present review, we consider the penumbra as that volume of brain tissue at the periphery of a focal, irreversibly damaged area that is threatened by recruitment into necrosis. Implicit to such a definition are several secondary concepts. First, the penumbra is both spatial, in that it surrounds the densely ischaemic core, but it is also temporal, in that its evolution toward infarction is a relatively progressive phenomenon. The pertinent literature is summarized. Second, penumbral tissue is potentially salvageable; the most recent animal studies are reviewed. Third, because electrically silent and pathologically damaged tissues have identical functional characteristics, it is evident that most clinical rating scales, be they neurological, behavioural, or psychological, are poorly adapted to address the problem of the penumbra. Finally, the penumbral tissue is remarkably and intensively 'active': multiple processes of cell death and repair occur and involve molecular mechanisms, electrophysiology and the vasculature.

Animals↗

PubMed2000

Haemodynamic correlates of penumbral depolarization following focal cerebral ischaemia.

Transient ischaemic depolarizations (IDs) are thought to play a key role in the pathogenesis of focal cerebral ischaemia. Most transient IDs are akin to spreading depression (SD), although a negative DC shift is not observed in half the cases. The other IDs may represent transient anoxic depolarizations. Using cortical DC and blood flow recordings, following middle cerebral artery occlusion in rats, we show here that: (i) these later depolarizations do indeed represent transient anoxic depolarizations; (ii) SD-like IDs, DC and haemodynamic parameters are similar to those of SDs when blood flow remains close to base line and; (iii) when blood flow decreases, the hyperaemia associated with SD-like IDs is largely reduced and there is an increasing proportion of cortical sites which fail to display a DC shift. These data demonstrate the coexistence of two mechanisms of IDs, and yield new information as to the flow-dependence of DC and haemodynamic correlates of SD-like IDs, the pathophysiological significance of which remains to be determined.

Analysis of Variance↗

PubMed2000

Glial responses, clusterin, and complement in permanent focal cerebral ischemia in the mouse.

There is considerable evidence that complement activation occurs within the CNS in inflammatory and degenerative disorders, but little is known about its involvement in the pathophysiology of cerebral ischemia. Our study sought to characterize the glial response and the expression of complement factors after permanent focal cerebral ischemia in the mouse, using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemistry. mRNA expression of glial fibrillary acidic protein (GFAP) increased at day 1 and peaked 3 days after middle cerebral artery (MCA) occlusion in the perifocal area. Immunohistochemical staining for GFAP indicated that astroglia were activated the day after MCA occlusion. Microglial activation, as assessed by lectin-binding experiments, increased by 1 day after MCA occlusion in the perifocal area and peaked at 3 days postocclusion. RT-PCR experiments demonstrated an increased expression of clusterin, C1qB, and C4 mRNA in the ischemic cortex, with a peak level at 3 days after MCA occlusion. Clusterin, C1qB, and C4 mRNA were located in the perifocal area, as assessed by in situ hybridization. Reactive astrocytes within the cortex medial to the ischemic lesion were found to be strongly immunoreactive for clusterin. In addition, we observed C1q-positive macrophage-like cells within the infarcted core at 3 days postocclusion. At 7 days after the onset of ischemia, increased C4 immunostaining was restricted to perifocal neurons. We conclude that local expression of complement components may contribute to the inflammation observed in this model, thereby representing an important process in secondary injury mechanisms after focal cerebral ischemia.

Animals↗

PubMed2000

Expression of receptors for complement anaphylatoxins C3a and C5a following permanent focal cerebral ischemia in the mouse.

In the present study, we have examined the expression of anaphylatoxin C3a and C5a receptors (C3aR and C5aR) at the mRNA and protein levels in ischemic brain tissues following permanent middle cerebral artery (MCA) occlusion in the mouse. C3aR and C5aR mRNAs were both detected by semiquantitative reverse transcription and polymerase chain reaction (RT-PCR) and the cellular distribution of each receptor was analyzed by immunohistochemistry. Significant increases in the expression of C3aR and C5aR mRNAs in the ischemic cortex were observed; the expression of both reached a peak at 2 days after MCA occlusion (4.3- and 3.4-fold increases, respectively, compared with nonoperated control cortical samples; P < 0.00625 with Bonferroni's correction, n = 3). C3aR and C5aR stainings were found constitutively on neurons and astrocytes. In ischemic tissues, we observed that C3aR and C5aR were expressed de novo on endothelial cells of blood vessels, at 6 h and 2 days after MCA occlusion, respectively. C3aR and C5aR immunostaining was increased in macrophage-like cells and reactive astrocytes 7 days postocclusion. C3a and C5a may play an important role in promoting inflammatory and/or repair processes in the ischemic brain by regulating glial cell activation and chemotaxis.

Animals↗

PubMed2000

Exofocal alterations in opioidergic receptor densities following focal cerebral ischemia in the mouse.

In previous studies of our group, we have reported differential alterations in opioidergic receptor subtypes densities in infarcted and periinfarcted brain tissue following middle cerebral artery occlusion (MCAO) in mice. Other studies have also described subcortical alterations consecutive to focal cortical ischemia. For a better understanding of ischemic processes in exofocal areas, we have investigated the evolution of opioidergic receptors following focal cortical ischemia through the quantification of relative binding densities, B(max) and K(d) values for the mu, delta, and kappa subtypes. Our results demonstrate that opioid receptor subtypes exhibit adaptations at distance from the ischemic core, mainly in the striatum, the thalamus, and the substantia nigra. Indeed, mu and delta B(max) values were increased in ventral thalamic nuclei, while kappa relative binding densities were transiently increased in nucleus medialis dorsalis and nucleus lateralis, pars posterior. Moreover, the B(max) of mu and delta receptors were transiently decreased at 6 h post-MCAO in ipsi- and contralateral patches and matrices of the striatum. Conversely, the mu B(max) values were increased in ipsi- and contralateral substantia nigra, pars compacta, and pars reticulata, 24 h following MCAO. In contralateral substantia nigra, pars compacta, kappa B(max) was found to be decreased at 24 h post-MCAO. These alterations could reflect neuronal dysfunction in exofocal brain structures, consecutively to the degeneration of defined neuroanatomical pathways. Our study indicates that opioidergic receptors could be used as markers of the neuronal reorganization that take place in subcortical areas following an ischemic insult of the brain cortex.

Analysis of Variance↗

PubMed2000

The use of cerebral blood flow as an index of neuronal activity in functional neuroimaging: experimental and pathophysiological considerations.

Over recent years, activation studies that have been undertaken using brain imaging techniques, such as functional magnetic resonance imaging, positron emission tomography or near infrared spectroscopy, have greatly improved our knowledge of the functional anatomy of the brain. Nevertheless, activation studies do not directly quantify the variations of synaptic transmission (neuronal activity) but detect it indirectly either through the visualisation of changes in cerebral blood flow, oxidative or glycolytic metabolism (for positron emission tomography), or through the measurement of a global index that is dependent on both cerebral blood flow and oxidative metabolism (for functional magnetic resonance imaging and near infrared spectroscopy). Such approaches are based on the concept of a tight parallelism--termed coupling--between variations in neuronal activity, metabolism and cerebral blood flow. However, several "uncoupled" situations between these parameters have been reported over the last decade through experimental, pharmacological and pathophysiological studies. The aim of this review is to focus on these data that have to be taken into account for the interpretation of the results obtained in activation paradigms.

Alzheimer Disease↗

PubMed2000

Ischemia-induced interleukin-6 as a potential endogenous neuroprotective cytokine against NMDA receptor-mediated excitotoxicity in the brain.

In the brain, the expression of the pleiotropic cytokine interleukin-6 (IL-6) is enhanced in various chronic or acute central nervous system disorders. However, the significance of IL-6 production in such neuropathologic states remains controversial. The present study investigated the role of IL-6 after cerebral ischemia. First, the authors showed that focal cerebral ischemia in rats early up-regulated the expression of IL-6 mRNA, without affecting the transcription of its receptors (IL-6Ralpha and gp130). Similarly, the striatal injection of N-methyl-D-aspartate (NMDA) in rats, a paradigm of excitotoxic injury, activated the expression of IL-6 mRNA. The involvement of glutamatergic receptor activation was further investigated by incubating cortical neurons with NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA). NMDA and ionomycin (a calcium ionophore) up-regulated IL-6 mRNA, suggesting that neurons may produce IL-6 in response to the calcium influx mediated through NMDA receptors. The potential role of IL-6 during ischemic/excitotoxic insults was then studied by testing the effect of IL-6 against apoptotic or excitotoxic challenges in cortical cultures. IL-6 did not prevent serum deprivation- or staurosporine-induced apoptotic neuronal death, or AMPA/kainate-mediated excitotoxicity. However, in both mixed and pure neuronal cultures, IL-6 dose-dependently protected neurons against NMDA toxicity. This effect was blocked by a competitive inhibitor of IL-6. Overall, the results suggest that the up-regulation of IL-6 induced by cerebral ischemia could represent an endogenous neuroprotective mechanism against NMDA receptor-mediated injury.

Animals↗

PubMed1999

The nature of penumbral depolarizations following focal cerebral ischemia in the rat.

It has been previously suggested that the transient ischemic depolarizations (IDs), thought involved in the gradual expansion of ischemic injury in the first hours following middle cerebral artery occlusion (MCAo), are akin to spreading depression (SD). However, previous studies indicate that the characteristics of these events are heterogeneous (unlike those of SDs). We therefore sought to determine whether different types of IDs exist or not. Using four cortical microelectrodes, we compared the spatial and the temporal characteristics of IDs that occur following intraluminal MCAo in halothane-anesthetized rats to those of electrically induced SDs. An average 4.6+/-3.2 series of events, sequentially affecting the four electrodes, were recorded in 5 h following the induction of ischemia. The distribution of ID duration disclosed two types: short IDs (<7 min, 53% of all events) and long IDs (>7 min; 9% of all events). Most long IDs occurred within the first 30 min and as the initial electrophysiological event. Later on and often restricted to a single or reduced number of recording sites, intermittent IDs were of reduced amplitude or even replaced entirely by suppressed electrocorticographic activity (38% of all events). While the amplitude, duration and spreading characteristics were similar between short IDs and SDs provoked in the cortex of non-ischemic rats, those of long IDs were markedly different. Our results indicate that two types of IDs exist and confirm that most IDs (short ones) are similar in nature to SDs. Long IDs may represent a penumbral anoxic depolarization (AD), reversed by an improvement of perfusion, in the early stages of ischemia. Furthermore, we show that intermittent blockade of depolarization waves occurs and that its incidence increases with time. This blockade may reflect adaptive mechanisms which take place to prevent further depolarizations, the nature of which remains to be determined. The present description of electrophysiological abnormalities might have implications for anti-depolarization therapy in focal cerebral ischemia and to interpret the results of non-invasive techniques which enable the imaging of depolarized areas following stroke.

Animals↗

PubMed1999

Neurochemical stimulation of the rat substantia innominata increases cerebral blood flow (but not glucose use) through the parallel activation of cholinergic and non-cholinergic pathways.

Neurochemical activation of the substantia innominata (SI) in the rat, through the direct injection of the cholinergic agonist carbachol, has been reported to induce large increases in cerebral blood flow (CBF) throughout cortical and subcortical projection regions. The present study aimed to determine whether the vasomotor responses to cholinergic stimulation of the SI were, or were not, the consequence of an increase in metabolic activity. To this end, coupled measurements of CBF and cerebral glucose use (CGU) were undertaken during carbachol-elicited stimulation of the SI. Infusion of carbachol into the basal forebrain induced significant CBF increases in several ipsilateral cortical and subcortical areas including the amygdala. In contrast, CGU increased only in the ipsilateral amygdala and SI. Thus, we tested the hypothesis of a direct neurogenic, rather than metabolic, contribution of the basalocortical system. In this respect, carbachol-elicited stimulation resulted in significant increases in extracellular acetylcholine concentrations in the ipsilateral parietal cortex; systemic pretreatment with the muscarinic receptor antagonist scopolamine completely abolished the increase in cortical CBF elicited by cholinergic stimulation of the SI in the ipsilateral frontoparietal motor cortex while it failed to affect the increase observed in the ipsilateral temporal cortex. Several conclusions can be drawn from the present study. The stimulation of the SI by carbachol induces an increase in CBF that can be dissociated from changes in underlying glucose metabolism. Secondly, these induced changes in cortical CBF are paralleled by an increase in acetylcholine release. Lastly, the failure of scopolamine to block the flow response in all cortical regions would suggest that SI stimulation will evoke the release of vasodilatatory neurotransmitter(s) as well as acetylcholine itself.

Acetylcholine↗

PubMed1999

Cerebrovascular evidence for a GABAergic modulation of the cholinergic vasodilatatory basalocortical system in the rat.

The present work is aimed to study the functional relevance of GABAergic-cholinergic interactions on the modulation of cerebral blood flow (CBF) exerted by the basalocortical system. Injections of GABA into the substantia innominata (SI) induce increases in blood flow in several cortical areas and inhibit partly the increases in cortical blood flow induced by cholinergic activation of this structure. Blockade of local GABAergic receptors by picrotoxin induced almost similar effects. These findings suggest that local GABAergic neurones of the SI exert a complex cortical cerebrovascular modulation at a resting and an activated state.

Animals↗

PubMed1999

Focal cerebral ischaemia induces a decrease in activity and a shift in ouabain affinity of Na+, K+-ATPase isoforms without modifications in mRNA and protein expression.

In a mouse model of focal cerebral ischaemia, we observed after 1 h of ischaemia, that the total Na+, K+-ATPase activity was decreased by 39.4%, and then did not vary significantly up to 6 h post-occlusion. In the sham group, the dose-response curves for ouabain disclosed three inhibitory sites of low (LA), high (HA) and very high (VHA) affinity. In ischaemic animals, we detected the presence of only two inhibitory sites for ouabain. After 1 h of permanent occlusion, the first site exhibited a low affinity while the second site presented an affinity intermediate between those of HA and VHA sites, which evolved after 3 h and 6 h of occlusion towards that of the VHA site. The presence of only two ouabain sites for Na+, K+-ATPase after ischaemia could result from a change in ouabain affinity of both HA and VHA sites (alpha2 and alpha3 isoforms, respectively) to form a unique component. Irrespective of the duration of ischaemia, the smaller activity of this second site accounted entirely for the loss in total activity. Surprisingly, no modifications in protein and mRNA expression of any alpha or beta isoforms of the enzyme were observed, thus suggesting that ischaemia could induce intrinsic modifications of the Na+, K+-ATPase.

Animals↗