Géza Ádám

Blood-Brain Barrier Damage during the Acute Stage of Subarachnoid Hemorrhage, as Exemplified by a New Animal Model

Models have been devised and characterized in the laboratory rat for studying the neuropathology of subarachnoid hemorrhage. Several ways of injecting blood via different routes have been tried; cortical subarachnoid administration is the most reproducible suitable model. The location of injected blood was detected in histological sections. In this rat model for subarachnoid hemorrhage, the arterial blood pressure and the intracranial pressure did not elevate significantly, and the influence of major ischemic components in the development of brain edema could also be ruled out. Measurements performed on the water, electrolyte, and albumin contents of brain tissue have clearly indicated that the brain edema developing in the acute stage of rat experimental subarachnoid hemorrhage could be classified as having a primarily vasogenic component as well. These findings may have implications in the treatment of subarachnoid hemorrhage.

Actinomycin D suppresses the protective effect of dexamethasone in rats affected by global cerebral ischemia.

Simultaneous occlusion of both common carotid arteries in female Sprague-Dawley CFY rats produced characteristic symptoms of global cerebral ischemia, such as staggering, circling, convulsions, followed by coma and death. A close correlation existed among these symptoms and the elevation of water and Na+ content, appearing at the stage of staggering; Evans blue extravasation and diminution of K+ content, detected at circling; and the increase in Ca2+ content in the total brain tissue, manifesting itself at the phase of convulsions, indicating the development of cerebral edema due to ischemia. Dexamethasone given subcutaneously in a single 2.0 mg kg-1 dose 5 hours prior to the induction of global cerebral ischemia reduced considerably the morbidity and mortality, the alterations in water and electrolyte content, and albumin leakage in the brain tissue. Actinomycin D, in a dose of 0.5 mg kg-1 injected intravenously 1 hour before steroid treatment, abolished the beneficial effect. This finding suggests that de novo protein synthesis is involved in the cerebroprotective effect of dexamethasone.

Cerebroprotective effect of dexamethasone by increasing the tolerance to hypoxia and preventing brain oedema in newborn piglets with experimental pneumothorax

The effect of dexamethasone (DXM) pretreatment in newborn piglets with experimental pneumothorax (EPT) was studied. Neither low DXM doses nor those administered 1 or 2 h prior to the induction of EPT were found to be effective against its course. In contrast, 5 mg/kg of body wt. of DXM given subcutaneously 4 h prior to EPT improved significantly both the tolerance and laboratory data of the animals. The extent of brain oedema, measured 4 h after recovery, was also considerably lowered. Actinomycin D pretreatment prevented almost completely the beneficial effect offered by DXM suggesting the involvement of newly synthesized protein(s) in the cerebroprotective effect of DXM.

Increased vulnerability of the blood-brain barrier to experimental subarachnoid hemorrhage in spontaneously hypertensive rats.

The influence of chronic arterial hypertension upon the permeability to albumin of the cerebral capillaries, i.e. the blood-brain barrier, was studied in normotensive Wistar and spontaneously hypertensive Wistar rats with experimental subarachnoid hemorrhage. The blood-brain barrier permeability to albumin was assessed quantitatively by spectrophotometric determination of Evans blue extravasation. Subarachnoid hemorrhage was produced by injecting autologous blood into the cortical subarachnoid space. A significant increase of Evans blue albumin extravasation was found in the spontaneously hypertensive rats with subarachnoid hemorrhage as compared with normotensive animals suffering from subarachnoid hemorrhage. Subarachnoid hemorrhage in this model alone caused a significant Evans blue extravasation, whereas sham-operation did not. These findings emphasize the necessity for effective attempts to reduce the leakage of the capillary system in the early stage of subarachnoid hemorrhage.

Kainic acid neurotoxicity: Characterization of blood-brain barrier damage

The alterations in the water, sodium (Na) and potassium (K) contents of the frontoparietal cortex, hippocampus and thalamus as well as the protein permeability of the blood-brain barrier were investigated in rats 4 h after systemic kainic acid administration. Increases in the water and Na contents and a decrease in the K content were observed together with Evans blue extravasation in the thalamus area indicating the development of vasogenic brain edema. Changes observed in the ion contents of the frontoparietal cortex and hippocampus may be due to a general cell membrane permeability damage but are not caused by a primary disturbance of the blood-brain barrier.

Effects of acute hypoxia on the adenylate cyclase and evans blue transport of brain microvessels

Kinetic parameters of the albumin transport were measured during and after an acute hypoxic insult evoked in newborn piglets by experimental bilateral pneumothorax. Adenylate cyclase activity was determined in the cerebral microvessels isolated by ultracentrifugation from different stages of brain damage. A decrease of the adenylate cyclase activity was observed in the cerebral microvessels of animals with acute hypoxic condition. However, the adenylate cyclase activity was found to be increased significantly in the microvessels during recirculation. The activation of adenylate cyclase in the microvessel wall may be of pathogenetic importance in the development of vasogenic brain oedema.

Prevention by macrocortin of global cerebral ischemia in sprague-dawley rats

We have previously shown that dexamethasone protects female Sprague-Dawley CFY rats against global cerebral ischemia induced by bilateral carotid artery ligation. In the present study, macrocortin derived from rat peritoneal cells exposed to dexamethasone was found to exhibit antiphospholipase A2 activity and to provide significant protection against the fatal consequences of carotid artery ligation. These results suggest that the cerebroprotective effect of glucocorticoids may be related to macrocortin production.

Microtubule-associated cyclic AMP-dependent protein kinase in Drosophila melanogaster

Abstract: Microtubules were prepared from head extracts of the adult fruit fly, Drosophila melanogaster, by one‐step, taxol‐assisted polymerization. The microtubular fraction displayed cyclic AMP‐dependent protein kinase (protein kinase A) activity, as witnessed by endogenous protein phosphorylation and by protein kinase assay. Microtubule‐bound protein kinase A amounts to 4–5% of total soluble kinase activity, which is almost an order of magnitude less than in mammals. The high‐molecular‐weight microtu‐bule‐associated protein‐2 (MAP‐2), the main binding species for protein kinase A in mammalian brain microtubules, is not detectable in the fly system by protein staining and immunoblotting with anti‐pig MAP‐2 serum, as well as by hybridization of fly DNA with a cDNA probe for human MAP‐2. Cyclic AMP removes a major part of the regulatory (R) subunit of the enzyme from Drosophila microtubules, as demonstrated by enzyme assay, autophosphoryla‐tion of R subunit, and quantitating cyclic AMP binding sites. It is proposed that permanently elevated cyclic AMP levels may elute protein kinase A from crucial intracellular binding sites, thereby interfering with signal transduction.

Casein kinases I and II bound to pig brain microtubules

Summary1.Microtubules prepared from pig brain by two cycles of assembly-disassembly comprise cyclic nucleotide-independent protein kinase activity with phosvitin and troponin T as substrates.2.Phosphocellulose chromatography resolved two phosvitin kinase activity peaks, one of which coincided with the troponin T kinase peak.3.The activity peak corresponding to troponin T kinase was inhibited by heparin (I50 = 0.06µg/ml), whereas the other phosvitin kinase peak was unaffected.4.Both kinase fractions phosphorylated tubulin and microtubule-associated protein (MAP-2).5.It is concluded that pig brain microtubules contain bound casein kinases I and II. The association may target the action of these kinases toward microtubular proteinsin vivo.

CalpB modulates border cell migration in Drosophila egg chambers

BackgroundCalpains are calcium regulated intracellular cysteine proteases implicated in a variety of physiological functions and pathological conditions. The Drosophila melanogaster genome contains only two genes, CalpA and CalpB coding for canonical, active calpain enzymes. The movement of the border cells in Drosophila egg chambers is a well characterized model of the eukaryotic cell migration. Using this genetically pliable model we can investigate the physiological role of calpains in cell motility.ResultsWe demonstrate at the whole organism level that CalpB is implicated in cell migration, while the structurally related CalpA paralog can not fulfill the same function. The downregulation of the CalpB gene by mutations or RNA interference results in a delayed migration of the border cells in Drosophila egg chambers. This phenotype is significantly enhanced when the focal adhesion complex genes encoding for α-PS2 integrin ( if), β-PS integrin ( mys) and talin ( rhea) are silenced. The reduction of CalpB activity diminishes the release of integrins from the rear end of the border cells. The delayed migration and the reduced integrin release phenotypes can be suppressed by expressing wild-type talin-head in the border cells but not talin-headR367A, a mutant form which is not able to bind β-PS integrin. CalpB can cleave talin in vitro, and the two proteins coimmunoprecipitate from Drosophila extracts.ConclusionsThe physiological function of CalpB in border cell motility has been demonstrated in vivo. The genetic interaction between the CalpB and the if, mys, as well as rhea genes, the involvement of active talin head-domains in the process, and the fact that CalpB and talin interact with each other collectively suggest that the limited proteolytic cleavage of talin is one of the possible mechanisms through which CalpB regulates cell migration.