Mechanisms of drug actions against neuronal damage caused by ischemia--an overview

Serum concentration-guided intravenous magnesium sulfate administration for neuroprotection in patients with aneurysmal subarachnoid hemorrhage: a retrospective evaluation of a 12-year single-center experience

Delayed cerebral infarction (DCI) is a major cause of morbidity and mortality in patients with aneurysmal subarachnoid hemorrhage (aSAH). The benefits of magnesium sulfate as an alternative treatment are controversial, and most previous studies examined its benefits only as adjunctive treatment to traditional nimodipine. We retrospectively analyzed aSAH patients records with magnesium sulfate between 2010 and 2021. We aimed for a serum magnesium concentration of 2-2.5 mmol/l between post-hemorrhage days 3 and 12. The patients were separated in three groups based on average serum magnesium concentration (magnesium >2 mmol/l, reduced magnesium 1.1-1.9 mmol/l, and no magnesium). Additionally, we assessed delayed cerebral infarction (DCI) and clinical outcome at follow-up, using the modified Rankin Scale (mRS), categorized in favorable (0-3) and unfavorable outcome (4-5). In this analysis, 548 patients were included. Hereof, radiological evidence of DCI could be found in 23.0% (n = 126) of patients. DCI rates were lower if patients' average serum magnesium was higher than 2 mmol/l (magnesium 18.8%, n = 85; reduced magnesium 38.3%, n = 23; no magnesium 51.4%, n = 18; p < 0.001). Also, at the last follow-up, patients in the group with a higher serum magnesium concentration had better outcome (favorable outcome: magnesium 64.7%, n = 293; reduced magnesium 50.0%, n = 30; no magnesium 34.3%, n = 12; p < 0.001). This 12-year study reveals the value of serum concentration-guided magnesium administration in aSAH patients. Our findings demonstrate the safety and efficacy when titrated to a serum concentration of 2-2.5 mmol/l. We observed higher rates of delayed cerebral infarction and unfavorable outcomes in patients with serum concentrations below 2 mmol/l.

Neonatal asphyxia as an inflammatory disease: Reactive oxygen species and cytokines

Neonatologists resuscitate asphyxiated neonates by every available means, including positive ventilation, oxygen therapy, and drugs. Asphyxiated neonates sometimes present symptoms that mimic those of inflammation, such as fever and edema. The main pathophysiology of the asphyxia is inflammation caused by hypoxic-ischemic reperfusion. At birth or in the perinatal period, neonates may suffer several, hypoxic insults, which can activate inflammatory cells and inflammatory mediator production leading to the release of larger quantities of reactive oxygen species (ROS). This in turn triggers the production of oxygen stress-induced high mobility group box-1 (HMGB-1), an endogenous damage-associated molecular patterns (DAMPs) protein bound to toll-like receptor (TLR) -4, which activates nuclear factor-kappa B (NF-κB), resulting in the production of excess inflammatory mediators. ROS and inflammatory mediators are produced not only in activated inflammatory cells but also in non-immune cells, such as endothelial cells. Hypothermia inhibits pro-inflammatory mediators. A combination therapy of hypothermia and medications, such as erythropoietin and melatonin, is attracting attention now. These medications have both anti-oxidant and anti-inflammatory effects. As the inflammatory response and oxidative stress play a critical role in the pathophysiology of neonatal asphyxia, these drugs may contribute to improving patient outcomes.

Neural dysfunctions following experimental permanent occlusions of bilateral common carotid arteries cause an increase of rat voluntary alcohol drinking behavior

We have previously reported that ischemic animal models treated with a respiratory inhibitor, rotenon, show an increased voluntary alcohol intake. Although it is clear that ischemic brain, as a result of reduced-blood flow, shows pathological events and/or neuro-degenerations apparently, little is known of causal relationship between the mechanism of neural dysfunction and voluntary alcohol consumption. Authors have investigated effects of permanent two-vessel occlusion (p2VO) on rat voluntary alcohol drinking behavior. In first experiment the p2VO-treated rats showed an increase of voluntary alcohol drinking behavior, as compared with sham controls. Using brain microdialysis technique, increases of only nucleus accumbens (ACC) dopamine (DA) releases were suppressed in the p2VO-treated rats significantly, following the high K⁺ (40 mM) perfusion through the microdialysis probe membrane. Alcohol (200 mM) perfusion-induced DA and serotonin (5-HT) releases in the ACC of the p2VO-treated rats were suppressed significantly in the second experiment, as compared with the sham-treated rats. In third experiment p2VO-treated rats showed significant decreases of the contents of DA, not 5-HT, in the ACC, caudate-putamen (C/P), ventral tegmental area-substantia nigra (VT/SN) and lateral hypothalamus (LH). Dopaminergic neurons in the ACC showed more functional vulnerability against the p2VO treatments, as compared with the serotonergic neurons. An increase of alcohol intake in the p2VO-treated rats means the compensation for the neural degeneration of the dopaminergic system in the ACC consisted brain rewarding system. It was likely suggested that neural disturbance of higher functions involved with incomplete global brain ischemia leads the risk of an abnormal alcohol drinking in human.

Targeting Sentinel Proteins and Extrasynaptic Glutamate Receptors: a Therapeutic Strategy for Preventing the Effects Elicited by Perinatal Asphyxia?

Perinatal asphyxia (PA) is a relevant cause of death at the time of labour, and when survival is stabilised, associated with short- and long-term developmental disabilities, requiring inordinate care by health systems and families. Its prevalence is high (1 to 10/1000 live births) worldwide. At present, there are few therapeutic options, apart from hypothermia, that regrettably provides only limited protection if applied shortly after the insult.PA implies a primary and a secondary insult. The primary insult relates to the lack of oxygen, and the secondary one to the oxidative stress triggered by re-oxygenation, formation of reactive oxygen (ROS) and reactive nitrogen (RNS) species, and overactivation of glutamate receptors and mitochondrial deficiencies. PA induces overactivation of a number of sentinel proteins, including hypoxia-induced factor-1α (HIF-1α) and the genome-protecting poly(ADP-ribose) polymerase-1 (PARP-1). Upon activation, PARP-1 consumes high amounts of ATP at a time when this metabolite is scarce, worsening in turn the energy crisis elicited by asphyxia. The energy crisis also impairs ATP-dependent transport, including glutamate re-uptake by astroglia. Nicotinamide, a PARP-1 inhibitor, protects against the metabolic cascade elicited by the primary stage, avoiding NAD+ exhaustion and the energetic crisis. Upon re-oxygenation, however, oxidative stress leads to nuclear translocation of the NF-κB subunit p65, overexpression of the pro-inflammatory cytokines IL-1β and TNF-α, and glutamate-excitotoxicity, due to impairment of glial-glutamate transport, extracellular glutamate overflow, and overactivation of NMDA receptors, mainly of the extrasynaptic type. This leads to calcium influx, mitochondrial impairment, and inactivation of antioxidant enzymes, increasing further the activity of pro-oxidant enzymes, thereby making the surviving neonate vulnerable to recurrent metabolic insults whenever oxidative stress is involved. Here, we discuss evidence showing that (i) inhibition of PARP-1 overactivation by nicotinamide and (ii) inhibition of extrasynaptic NMDA receptor overactivation by memantine can prevent the short- and long-term consequences of PA. These hypotheses have been evaluated in a rat preclinical model of PA, aiming to identify the metabolic cascades responsible for the long-term consequences induced by the insult, also assessing postnatal vulnerability to recurrent oxidative insults. Thus, we present and discuss evidence demonstrating that PA induces long-term changes in metabolic pathways related to energy and oxidative stress, priming vulnerability of cells with both the neuronal and the glial phenotype. The effects induced by PA are region dependent, the substantia nigra being particularly prone to cell death. The issue of short- and long-term consequences of PA provides a framework for addressing a fundamental issue referred to plasticity of the CNS, since the perinatal insult triggers a domino-like sequence of events making the developing individual vulnerable to recurrent adverse conditions, decreasing his/her coping repertoire because of a relevant insult occurring at birth.

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

Anesthetics, cerebral protection and preconditioning

BACKGROUND AND OBJECTIVES

Several studies demonstrate that cerebral preconditioning is a protective mechanism against a stressful situation. Preconditioning determinants are described, as well as the neuroprotection provided by anesthetic and non-anesthetics agents.

CONTENT

Review based on the main articles addressing the pathophysiology of ischemia-reperfusion and neuronal injury and pharmacological and non-pharmacological factors (inflammation, glycemia, and temperature) related to the change in response to ischemia-reperfusion, in addition to neuroprotection induced by anesthetic use.

CONCLUSIONS

The brain has the ability to protect itself against ischemia when stimulated. The elucidation of this mechanism enables the application of preconditioning inducing substances (some anesthetics), other drugs, and non-pharmacological measures, such as hypothermia, aimed at inducing tolerance to ischemic lesions.

Anesthetics, cerebral protection and preconditioning

BACKGROUND AND OBJECTIVES

Several studies demonstrate that cerebral preconditioning is a protective mechanism against a stressful situation. Preconditioning determinants are described, as well as the neuroprotection provided by anesthetic and non-anesthetics agents.

CONTENT

Review based on the main articles addressing the pathophysiology of ischemia-reperfusion and neuronal injury and pharmacological and non-pharmacological factors (inflammation, glycemia, and temperature) related to the change in response to ischemia-reperfusion, in addition to neuroprotection induced by anesthetic use.

CONCLUSIONS

The brain has the ability to protect itself against ischemia when stimulated. The elucidation of this mechanism enables the application of preconditioning inducing substances (some anesthetics), other drugs, and non-pharmacological measures, such as hypothermia, aimed at inducing tolerance to ischemic lesions.

Magnesium treatment for neuroprotection in ischemic diseases of the brain

This article reviews experimental and clinical data on the use of magnesium as a neuroprotective agent in various conditions of cerebral ischemia. Whereas magnesium has shown neuroprotective properties in animal models of global and focal cerebral ischemia, this effect could not be reproduced in a large human stroke trial. These conflicting results may be explained by the timing of treatment. While treatment can be started before or early after ischemia in experimental studies, there is an inevitable delay of treatment in human stroke. Magnesium administration to women at risk for preterm birth has been investigated in several randomized controlled trials and was found to reduce the risk of neurological deficits for the premature infant. Postnatal administration of magnesium to babies after perinatal asphyxia has been studied in a number of controlled clinical trials. The results are promising but the trials have, so far, been underpowered. In aneurysmal subarachnoid hemorrhage (SAH), cerebral ischemia arises with the onset of delayed cerebral vasospasm several days after aneurysm rupture. Similar to perinatal asphyxia in impending preterm delivery, treatment can be started prior to ischemia. The results of clinical trials are conflicting. Several clinical trials did not show an additive effect of magnesium with nimodipine, another calcium antagonist which is routinely administered to SAH patients in many centers. Other trials found a protective effect after magnesium therapy. Thus, it may still be a promising substance in the treatment of secondary cerebral ischemia after aneurysmal SAH. Future prospects of magnesium therapy are discussed.

Neutroprotective efficacy of sodium tanshinone B on hippocampus neuron in a rat model of focal cerebral ischemia

OBJECTIVE

To investigate the protective effects of sodium tanshinone B (STB) on brain damage following focal ischemia-reperfusion (I/R) injury through interfering with N-methyl-D-aspartic acid receptor (NMDAR) and excitatory and inhibitory amino acids, and evaluate the potential mechanisms of the neuroprotective activity of STB.

METHODS

Transient forebrain ischemia was induced by middle cerebral artery occlusion (MCAO). The rats were randomized into a sham operated group, a model group (I/R) and three STB different dose groups. Rats were pretreated with STB at the doses of 4, 8, 16 mg/kg (STB(1), STB(2), STB(3)) for 3 days before MCAO. The expression of NMDAR1 was detected by immunohistochemistry and Western blotting. The concentrations of glutamate and γ-aminobutyric acid (GABA) were analyzed using high performance liquid chromatography.

RESULTS

STB treatment reduced neurological defect scores, cerebral infarction volume and brain water content. The levels of NMDAR1 were significantly higher in the l/R and STB(1) groups than that of the sham and the STB(3) groups (P<0.01). Optical density of NMDAR1 was significantly increased in cornu ammonis (CA)1 region of the l/R group (P<0.05). STB treatment reduced NMDAR1 optical density in the CA1 region (P<0.01). The levels of glutamate were significantly lower in the hippocampus in the STB(3) group than that of the l/R, STB(1) and STB(2) groups (P<0.01).

CONCLUSION

Preconditioning with STB appears to be a simple and promising strategy to reduce or even prevent cerebral l/R injury and has potential for future clinical application.

Preclinical drug evaluation for combination therapy in acute stroke using systematic review, meta-analysis, and subsequent experimental testing

There is some evidence that in animal models of acute ischaemic stroke, combinations of neuroprotective agents might be more efficacious than the same agents administered alone. Hence, we developed pragmatic, empirical criteria based on therapeutic target, cost, availability, efficacy, administration, and safety to select drugs for testing in combination in animal models of acute stroke. Magnesium sulphate, melatonin, and minocycline were chosen from a library of neuroprotective agents, and were tested in a more 'realistic' model favoured by the STAIR (Stroke Therapy Academic Industry Roundtable). Outcome was assessed with infarct volume, neurologic score, and two newly developed scales measuring general health and physiologic homeostasis. Owing to the failure to achieve neuroprotection in aged, hypertensive animals with drug delivery at 3 hours, the bar was lowered in successive experiments to determine whether neuroprotection could be achieved under conditions more conducive to recovery. Testing in younger animals showed more favourable homeostasis and general health scores than did testing in older animals, but infarct volume and neurologic scores did not differ with age, and treatment efficacy was again not shown. Testing with shorter occlusions resulted in smaller infarct volumes; nevertheless, treatment efficacy was still not observed. It was concluded that this combination, in these stroke models, was not effective.

Altered responsiveness of the guinea-pig isolated ileum to smooth muscle stimulants and to electrical stimulation after in situ ischemia

1. We evaluated changes in contractility of the guinea-pig isolated ileum, using intact segments and myenteric plexus-longitudinal muscle (MPLM) preparations, after several times (5-160 min) of ischemia in situ. 2. Intestinal ischemia was produced by clamping the superior mesenteric artery. Ischemic and nonischemic segments, obtained from the same guinea-pig, were mounted in organ baths containing Krebs-bicarbonate (K-B) solution, maintained at 37 degrees C and gassed with 95% O2/5% CO2. The preparations were allowed to equilibrate for 60 min under continuous superfusion of warm K-B solution and then electrically stimulated at 40 V (0.3 Hz, 3.0 ms). Thereafter, complete noncumulative concentration-response curves were constructed for acetylcholine (ACh), histamine (HIS), potassium chloride (KCl), and barium chloride (BaCl2). Mean Emax (maximal response) values were calculated for each drug. 3. Our study shows that alterations of chemically and electrically evoked contractions are dependent on ischemic periods. It also demonstrates that contractile responses of ischemic tissues to neurogenic stimulation decreases earlier and to a significantly greater extent than the non-nerve mediated responses of the intestinal smooth muscle. Contractile responses to smooth muscle stimulants were all similarly affected by ischemia. Electron microscopy images indicated necrotic neuronal death. The decrease in reactivity of ischemic tissues to electrical stimulation was ameliorated by dexrazoxane, an antioxidant agent. 4. We consider the guinea-pig isolated ileum as a useful model system to study the processes involved in neuronal ischemia, and we propose that the reduction in maximal responses to electrical stimulation is a useful parameter to study neuroprotection.

Expression of clusterin in Müller cells of the rat retina after pressure-induced ischemia

We have investigated the expression and cellular localization of clusterin in the rat retina following ischemia induced by transiently increasing the intraocular pressure. In the normal retina, weak clusterin immunoreactivity was visible in Müller cell profiles located in the inner nuclear layer. Following ischemia and reperfusion, strong immunoreactivity appeared in Müller cell somata and processes up to 3 days postlesion. Quantitative evaluation by immunoblotting confirmed that clusterin expression continuously increased and showed a peak value at 3 days after ischemic injury (to 1300% of control levels), and then decreased again to 400% of controls at 4 weeks postlesion. Immunocytochemistry using antisera against clusterin or glutamine synthase combined with the TUNEL method or immunocytochemistry using antisera activated caspase 3 and electron microscopy revealed that some clusterin-labeled Müller cells underwent apoptotic cell death. Our findings demonstrate that some Müller cells die by apoptosis, and suggest that clusterin produced and released by Müller cell may play an important role in the pathogenesis of ischemic injury in the rat retina.

The beta-adrenoceptor antagonists metipranolol and timolol are retinal neuroprotectants: comparison with betaxolol

beta-adrenoceptor antagonists are used clinically to reduce elevated intraocular pressure in glaucoma which is characterised by a loss of retinal ganglion cells. Previous studies have shown that the beta(1)-selective adrenoceptor antagonist, betaxolol, is additionally able to protect retinal neurones in vitro and ganglion cells in vivo from the detrimental effects of either ischemia-reperfusion or from excitotoxicity, after topical application. The neuroprotective effect of betaxolol is thought not to be elicited through an interaction with beta-adrenoceptors, but by its ability to reduce influx of sodium and calcium through voltage-sensitive calcium and sodium channels. In the present study it is shown that the non-selective beta-adrenoceptor antagonists, metipranolol and timolol behave like betaxolol. When topically applied they all attenuate the detrimental effect of ischemia-reperfusion. Protection of the retina was determined by evaluating changes in the electroretinogram and by assessing the loss of mRNA for Thy-1, which is expressed in retinal ganglion cells. In addition, studies conducted on neurones in mixed retinal cultures demonstrated that metipranolol, betaxolol and timolol were all able to partially counteract anoxia-induced cell loss and viability reduction. The influence of timolol was, however, not significant. Within the confines of these investigations, an order of neuroprotective efficacy was delineated for the three beta-adrenoceptor antagonists: betaxolol>metipranolol>timolol. The ability of the beta-adrenoceptor antagonists to attenuate ligand-induced stimulation of calcium and sodium entry into neuronal preparations showed a similar order of effectiveness. In conclusion, the ability to confer neuroprotection to retinal neurones is a common feature of three ophthalmic beta-adrenoceptor antagonists (betaxolol, metipranolol and timolol). A comparison of the effectiveness of the individual compounds in protecting retinal cells in vivo was not possible in these studies. However, in vitro studies show that the capacity of the individual beta-adrenoceptor antagonists to act as neuroprotectants appears to relate to their capacity to attenuate neuronal calcium and sodium influx.

The regulatory expression of neuronal nitric oxide synthase in the ischemic rat retina

We investigated the expression and cellular localization of neuronal nitric oxide synthase (nNOS) in the rat retina, following ischemic injury induced by transient increase of intraocular pressure. In the normal retina, nNOS immunoreactivity was localized to certain populations of amacrine cells, displaced amacrine cells and a few bipolar cells. Following transient ischemia, retinal neurons expressing the immunoreactivity increased and peaked three days after reperfusion. Quantitative evaluation using immunoblotting confirmed that nNOS expression showed a peak value (500% of control levels) at 3 days, and then decreased again to 150% of controls by 4 weeks after reperfusion. Our findings suggest that this over-produced NO may act as a neurotoxic agent in the ischemic rat retina.

NMDA and AMPA/kainate glutamate receptors modulate dentate neurogenesis and CA3 synapsin-I in normal and ischemic hippocampus

The effect of N-methyl-D-aspartate (NMDA) and 2-(aminomethyl)phenylacetic acid/kainate (AMPA/kainate) glutamate receptors on dentate cell proliferation and hippocampal synapsin-I induction was examined after global ischemia. Cell proliferation was assessed using BrdU labeling, and synaptic responses were assessed using synapsin-I expression. Systemic glutamate receptor antagonists (MK-801 and NBQX) increased BrdU-labeled cells in the dentate subgranular zone (SGZ) of control adult gerbils (30% to 90%, P < 0.05). After global ischemia (at 15 days after 10 minutes of ischemia), most CA1 pyramidal neurons died, whereas the numbers of BrdU-labeled cells in the SGZ increased dramatically (>1000%, P < 0.0001). Systemic injections of MK801 or NBQX, as well as intrahippocampal injections of either drug, when given at the time of ischemia completely blocked the birth of cells in the SGZ and the death of CA1 pyramidal neurons at 15 days after ischemia. Glutamate receptor antagonists had little effect on cell birth and death when administered 7 days after ischemia. The induction of synapsin-I protein in stratum moleculare of CA3 at 7 and 15 days after global ischemia was blocked by pretreatment with systemic or intrahippocampal MK-801 or NBQX. It is proposed that decreased dentate glutamate receptor activation--produced by glutamate receptor antagonists in normal animals and by chronic ischemic hippocampal injury--may trigger dentate neurogenesis and synaptogenesis. The synapsin-I induction in mossy fiber terminals most likely represents re-modeling of dentate granule cell neuron presynaptic elements in CA3 in response to the ischemia. The dentate neurogenesis and synaptogenesis that occur after ischemia may contribute to memory recovery after hippocampal injury caused by global ischemia.

Nitric oxide is involved in sustained and delayed cell death of rat retina following transient ischemia

We have investigated the role of nitric oxide (NO) in the rat retina following ischemic injury induced by transient increase of intraocular pressure. The thickness of both the inner plexiform layer and inner nuclear layer decreased during early postischemic stages (up to 1 week). In late postischemic stages (2-4 weeks), the thickness of the outer nuclear layer (ONL) decreased markedly. Thus, mechanisms other than excitotoxic ones may contribute to postischemic retinal cell death. Treatment of rats with N(G)-nitro-L-arginine methyl ester, a nitric oxide synthase (NOS) inhibitor, significantly reduced ischemic damage. Our findings suggest that NO is involved in the mechanism of ischemic injury, and plays a key role in the delayed and sustained cell death in the ONL following transient retinal ischemia.

Cytotoxicity of tributyltin in rat hippocampal slice cultures

The neurotoxic effects of tributyltin (TBT), an endocrine-disrupting chemical, were evaluated in organotypic slice cultures of immature rat hippocampus. Confocal microscopy study with propidium iodide showed that TBT induced severe neuronal death in a concentration- and time-dependent manner with CA3 > CA1 > dentate gyrus ranking of vulnerability of the hippocampal subfields. Dead or damaged neurons exhibited chromatin condensation, which is one of the morphological characteristics of apoptosis, as revealed by acridine orange staining. TBT neurotoxicity was alleviated by application of free radical scavengers or antioxidants, such as catalase, superoxide dismutase, Trolox and alpha-tocopherol but not by ascorbic acid or N-acetyl-L-cysteine, which suggests an involvement of free radicals, particularly reactive oxygen species. Neurons displayed a long-lasting increase in intracellular Ca2+ concentrations after TBT treatment. Although neither N-methyl-D-aspartate (NMDA) receptor inhibitors nor voltage-sensitive Ca2+ channel blockers protected hippocampal neurons against TBT neurotoxicity, non-NMDA receptor antagonist completely prevented TBT-induced neurodegeneration. These data suggest that TBT provokes apoptosis-like neuronal cell death, which might be mediated by intracellular Ca2+ elevation and free radical generation via non-NMDA receptor activation.

Selective neuronal survival and upregulation of PCNA in the rat inner retina following transient ischemia

In this study we investigated the extent and time course of neuronal cell death and the regulation of the proliferating cell nuclear antigen (PCNA) in the different retinal cell layers following ischemia-reperfusion injury. Retinal ischemia was induced by controlled elevation of the intraocular pressure for a duration of 60 min. Changes in thickness and cell numbers in the retinal cell layers were analyzed at various time points (1 h to 4 weeks) after reperfusion. In parallel, apoptotic cell death was determined by the TUNEL method and the expression of PCNA analyzed by immunocytochemistry. In addition, we tested whether PCNA is expressed in neurons by double immunocytochemistry. The reduction in thickness was found to be less pronounced in the inner nuclear layer (INL). Correspondingly, cell numbers decreased by only 33% in the inner retina, but by more than 80% in the outer nuclear layer (ONL). Alterations in glial cell numbers did not contribute significantly to postischemic changes in the INL and ONL as assessed by using immunocytochemical markers for microglial and Müller cells. The time course of cell death determined by the TUNEL technique also differed markedly in the retinal layers being rapid and transient in the inner retina but delayed and prolonged in the ONL. PCNA immunoreactivity was undetectable in the normal retina, but was specifically induced in neurons of the inner retina within 1 h after reperfusion and was sustained for at least 4 weeks. We conclude that in contrast to photoreceptors in the ONL, a significant proportion of inner retinal neurons is resistant to ischemic insult induced by transiently increased intraocular pressure and that PCNA may possibly play a role in the selective postischemic survival of these cells.

Methylprednisolone therapy for retinal laser injury

OBJECTIVE

Laser photocoagulation treatment of the posterior pole of the retina is often complicated by immediate visual impairment, which is caused by the unavoidable laser-induced destruction of the normal tissue adjacent to the lesion. A neuroprotective therapy aimed at salvaging this normal tissue might enhance the benefit obtained from treatment and permit safe perifoveal photocoagulation. To determine whether corticosteroids can provide neuroprotection during photocoagulation, we examined the effect of methylprednisolone on laser-induced retinal injury in a rat model.

METHODS

Argon laser lesions were inflicted on the retinas of 36 rats and were followed immediately by intraperitoneal injections of high-dose methylprednisolone or saline. The animals were sacrificed after 3, 20, or 60 days, and their retinal lesions were evaluated histologically and morphometrically.

RESULTS

No histopathologic differences were observed between the treated and control animals. Methylprednisolone treatment was demonstrated to posses some neuroprotective effect for a short time after laser exposure, but was ineffective in ameliorating the long-term results of retinal laser injury.

CONCLUSIONS

On the basis of our results, we suggest that high-dose methylprednisolone treatment is ineffective in ameliorating laser-induced retinal injury. Other drugs should be investigated for their potential role as neuroprotective agents to prevent the spread of retinal laser damage.

Expression of CNTF in Müller cells of the rat retina after pressure-induced ischemia

We have investigated the expression and cellular localization of ciliary neurotrophic factor (CNTF) in the rat retina following ischemia induced by transiently increasing the intraocular pressure. In the normal retina, CNTF immunoreactivity was restricted to profiles in the ganglion cell layer. Following ischemia and reperfusion, immunoreactivity appeared in Müller cell somata and processes and its intensity increased between 1 day and 2 weeks post-lesion. Quantitative evaluation by immunoblotting confirmed that CNTF expression continuously increased up to 2 weeks after ischemic injury (to 600% of control levels), but had declined again to 250% of controls at 4 weeks post-lesion. Our findings suggest that CNTF supplied by Müller cells has a protective function for lesioned neurons following transient ischemia.

Carnosine: an endogenous neuroprotector in the ischemic brain

1. The biological effects of carnosine, a natural hydrophilic neuropeptide, on the reactive oxygen species (ROS) pathological generation are reviewed. 2. We describe direct antioxidant action observed in the in vitro experiments. 3. Carnosine was found to effect metabolism indirectly. These effects are reflected in ROS turnover regulation and lipid peroxidation (LPO) processes. 4. During brain ischemia carnosine acts as a neuroprotector, contributing to better cerebral blood flow restoration, electroencephalography (EEG) normalization, decreased lactate accumulation, and enzymatic protection against ROS. 5. The data presented demonstrate that carnosine is a specific regulator of essential metabolic pathways in neurons supporting brain homeostasis under unfavorable conditions.

Carvedilol in the treatment of hypertension--a review of the clinical data base

Carvedilol is a novel antihypertensive agent. It is a multiple-action neurohormonal antagonist with a beta-adrenoceptor blocking effect combined with a vasodilating action based on alpha1-adrenoceptor blockade. In addition, carvedilol exerts a number of well documented ancillary effects such as being a scavenger of free radicals. It also has an antiproliferative action on smooth muscle cells. This combination of effects opens up a number of interesting clinical perspectives. It is the purpose of this brief review to summarize some of the clinical studies that have been performed with carvedilol. Investigations in hypertensive patients will form the basis of this review, but special interest will also be devoted to other patient groups. In particular the therapeutic value of carvedilol will be discussed in patients with concomitant disorders such as atheromatosis, left ventricular hypertrophy, angina pectoris, myocardial infarction, congestive heart failure, arrhythmias, stroke, renal failure or diabetes. Finally, the usefulness of carvedilol in the treatment of elderly hypertensive patients will be reviewed. It is evident from the available scientific literature that carvedilol is an antihypertensive agent with a novel mode of action. It is effective in many of the subpopulations of patients alluded to above. It appears reasonable to assume that some of these therapeutic effects can be attributed to its ancillary properties.

Fe2+-induced inhibition of gerbil forebrain microsomal Ca2+-ATPase: effect of stobadine, glutathione and combination of both antioxidants

The incubation of the gerbil forebrain microsomes in the presence of ferrous sulphate and EDTA for either 30 min or for 60 min at a temperature of 37 degrees C led to the inhibition of Ca2+-ATPase in both a concentration- and time-dependent manner. The concentrations of Fe2+ which led to the inhibition of 50% of the Ca2+-ATPase activity (IC50-value) at these times were 0.59 mM and 0.07 mM, respectively. The preincubation of microsomes with 0.1 mM of stobadine prevented the inhibition of Ca2+-ATPase, however, the effectivity of prevention was dependent on the Fe2+ concentration. The net effect of stobadine was an increase in IC50-value to 0.76 mM. Unlike stobadine, reduced glutathione is a naturally occurring water soluble antioxidant. Glutathione at the concentration of 0.1 mM had no significant protective effect on the inhibition of Ca2+-ATPase. The protective effect of a stobadine-glutathione mixture was also investigated; 0.1 mM of stobadine in combination with 0.1 mM of glutathione was more potent in prevention of Fe2+-induced inhibition of Ca2+-ATPase than stobadine alone (IC50=1. 31 mM). In addition, we have investigated the effect of various stobadine-glutathione molar ratios (the total concentration of both antioxidants being 0.2 mM) on Fe2+-induced inhibition of Ca2+-ATPase. The results indicated that the best stobadine-glutathione ratio was close to 1 : 1. The effect of 0.04 mM stobadine in combination with 0.16 mM glutathione was comparable to the effect of 0.2 mM of stobadine alone, whereas 0.2 mM glutathione was almost ineffective. These results may suggest a possible role of membrane in Fe2+-induced inhibition of Ca2+-ATPase.

Neuroprotective effect of chronic verapamil treatment on cognitive and noncognitive deficits in an experimental Alzheimer's disease in rats

It is well known that disturbance of calcium homeostasis has a significant role in the development of neurodegenerative disorders, such as Alzheimer's disease (AD). Our recent data suggest that acute treatment with the calcium antagonist verapamil can improve some behavioral deficits in an experimental model of AD. Therefore, the present study was done to establish the effect of chronically administered verapamil on cognitive and noncognitive behavior of rats with bilateral electrolitical lesions of nucleus basalis manocellularis (NBM)--an animal model of AD. The NBM lesions produce a deficit in performance of diverse behavior tests: active avoidance (AA), low level of fear (the open field test) as well as aggressive (the test of foot-shock induced aggression) and depressive (the learned helplessness test) behavior. Verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg i.p.) or saline solution (1 ml/kg i.p.) were injected 24 hr after the lesion of NBM and then repeatedly administered during the next 8 days (twice a day). Performance of the two-way active avoidance test, the open field test, the foot shock-induced aggression test and the learned helplessness test were done on day 4 after the last verapamil or saline treatment (day 13 after the lesion). Verapamil in doses of 2.5 and 5.0 mg/kg significantly ameliorated the deficit in the performance of AA, the open field behavior, and the depression, but not the aggressive behavior. The obtained beneficial effect of chronic administered verapamil suggests that the regulation of calcium homeostasis during the early period after NBM lesions might be a reasonable way to prevent the behavioral deficits in an experimental model of AD.

Lisuride prevents learning and memory impairment and attenuates the increase in extracellular dopamine induced by transient global cerebral ischemia in rats

In this experiment, we tested the efficacy of neuroprotection with lisuride, a dopamine agonist, using the 4-vessel occlusion rat model. Functional improvement was evaluated with two behavior tests exploring learning and memorization capacity in the rat, the Morris water maze and the 14-unit T-maze, 18 days after ischemia. Extracellular dopamine levels during ischemia were determined in search of a possible neuroprotection mechanism. Dopamine and its metabolites, DOPAC and HVA, as well as the serotonin metabolite, 5-HIAA, were assayed with HPLC-EC, in striatal extracellular fluid obtained by in vivo microdialysis in the awake rat. Lisuride was administered at a total dose of 10 ng by continuous intrastriatal infusion or at the dose of 0.5 mg/kg by i.p. infusion, 160 minutes before onset of ischemia for the neurochemical study and at the dose of 0.5 mg/kg via i.p. infusion, 1 hour before occlusion of the carotid arteries, for the behavior tests. Behavioral testing showed significantly better recovery in both sets of behavioral tests, with more pronounced positive results with the 14-unit T-maze, in comparison with the saline-treated animals. Microdialysis confirmed a significant attenuation of the ischemia-induced dopamine surge, whatever the mode of administration, compared with saline-treated animals. These results show that lisuride offers significant neuroprotection from the effect of experimental transient global forebrain cerebral ischemia in the rat; the mechanism would imply, at least in part, reduced levels of extracellular dopamine.

Neuroprotective therapy for argon-laser induced retinal injury

Laser photocoagulation treatment of the central retina is often complicated by an immediate side effect of visual impairment, caused by the unavoidable laser-induced destruction of the normal tissue lying adjacent to the lesion and not affected directly by the laser beam. Furthermore, accidental laser injuries are at present untreatable. A neuroprotective therapy for salvaging the normal tissue might enhance the benefit obtained from treatment and allow safe perifoveal photocoagulation. We have developed a rat model for studying the efficacy of putative neuroprotective compounds in ameliorating laser-induced retinal damage. Four compounds were evaluated: the corticosteroid methylprednisolone, the glutamate-receptor blocker MK-801, the anti-oxidant enzyme superoxide dismutase, and the calcium-overload antagonist flunarizine. The study was carried out in two steps: in the first, the histopathological development of retinal laser injuries was studied. Argon laser lesions were inflicted in the retinas of 18 pigmented rats. The animals were killed after 3, 20 or 60 days and their retinal lesions were evaluated under the light microscope. The laser injury mainly involved the outer layers of the retina, where it destroyed significant numbers of photoreceptor cells. Over time, evidence of two major histopathological processes was observed: traction of adjacent normal retinal cells into the central area of the lesion forming an internal retinal bulging, and a retinal pigmented epithelial proliferative reaction associated with subretinal neovascularization and invasion of the retinal lesion site by phagocytes. The neuroprotective effects of each of the four compounds were verified in a second step of the study. For each drug tested, 12 rats were irradiated with argon laser inflictions: six of them received the tested agent while the other six were treated with the corresponding vehicle. Twenty days after laser exposure, the rats were killed and their lesions were subjected to image-analysis morphometry. The extent of retinal destruction was assessed by measuring the lesion diameter and the amount of photoreceptor cell loss in the outer nuclear layer. Methylprednisolone and MK-801 were shown to ameliorate laser-induced retinal damage, whereas both superoxide dismutase and flunarizine were ineffective. Furthermore, MK-801 diminished the proliferative reaction of the retinal pigment epithelial cells. On the basis of our results we suggest that the pigmented rat model is suitable for studying and screening various compounds for their neuroprotective efficacy in treating retinal laser injury. We further suggest that glutamate might play a key role in mediating retinal injury induced by laser irradiation.

Experimental spinal cord injury: Wallerian degeneration in the dorsal column is followed by revascularization, glial proliferation, and nerve regeneration

The presence of adequate blood supply is a critical factor in recovery from traumatic injuries. We have examined whether the revascularization of the injured tissues is as crucial a precondition for wound healing in the spinal cord as in other organs. The development of the initial primary lesion (PL) after spinal crush injury in rats is followed by the formation of a unique tunnel-like dorsal column lesion (DCL) that extends rostrocaudally for many millimeters from the primary injury site. The DCL has been shown to result from Wallerian degeneration of the long spinal tracts in the dorsal column. In this study, we compared the processes of revascularization, wound healing, and nerve regeneration in the PL and the DCL by light microscopy after a crush injury of the cord. The spinal cord of 54 adults rats was crushed at T8 with jewelers forceps. The rats were allowed to survive from 3 h up to 8 weeks after spinal cord injury. The PL appeared immediately after injury and the DCL began to develop 6 h later. Infiltration of neutrophils, which is the first sign of the inflammatory responses to injury, began several hours later in the DCL than in the PL. Secondary vascular injury then occurred which resulted in hemorrhage around the DCL and rapid enlargement of the lesion during the remainder of the first week. Subsequent changes in the PL and DCL were entirely different. The PL underwent progressive enlargement and cavitation such that by 8 weeks, the lesion contained only very few cells, vessels, and axons scattered between huge fluid-filled cavities. The DCL, on the other hand, was maximal in size at 1 week and declined significantly in size and cavitation thereafter. By 8 weeks it was highly vascularized, contained abundant nerve fibers, and lacked any trace of cavitation. These findings amplify the current view that ischemia plays a critical role in spinal cord trauma by showing that revascularization precedes tissue repair and nerve regeneration in the dorsal columns. We conclude (a) that a well-vascularized lesion permits the ingrowth of glial and other cells which give rise to a supportive matrix for the nerve regeneration and (b) that procedures which induce revascularization or angiogenesis will ameliorate the cascade of progressive tissue necrosis.

Retinal neurones containing kainate receptors are influenced by exogenous kainate and ischaemia while neurones lacking these receptors are not -- melatonin counteracts the effects of ischaemia and kainate

The present experiments were carried out on three types of neurone in primary rabbit retinal cultures. One cell-type, bipolar neurones, have glutamate APB-type metabotropic receptors and can be identified by the presence of thetaPKC-immunoreactivity. The other two cell-types are primarily amacrine cells and can be 'stained' for the localisation of GABA immunoreactivity or for serotonin taken up from the medium. Most of the serotonin-accumulating and GABA-containing neurones contain glutamate kainate-type receptors. Exposure of the cultures to treatment of kainate (50 microM) or experimental ischaemia (8 h followed by 16 h reoxygenation) produced essentially similar findings. The serotonin-accumulating and GABA cells were affected as they were drastically reduced in numbers while the numbers of thetaPKC-containing cells were unaffected. Inclusion of the kainate/AMPA antagonist CNQX (100 microM) or melatonin (100 microM) to the medium during kainate or ischaemia treatments largely prevented the detrimental influences on the serotonin-accumulating and GABA cells. It is concluded that during experimental ischaemia excessive glutamate is released to influence cells which contain kainate and APB-type receptors. However, only the neurones containing the kainate receptors are negatively affected with the generation of free radicals. Melatonin or CNQX protects against this effect by scavenging free radicals or acting at the receptor level, respectively.

Is chlormethiazole neuroprotective in experimental global cerebral ischemia? A microdialysis and behavioral study

Chlormethiazole, an anticonvulsive agent, has been shown to have a possible neuroprotective effect against cerebral ischemia. In addition, chlormethiazole inhibits methamphetamine-induced release of dopamine, protecting against this neurotransmitter's neurotoxicity. The aim of this work was to ascertain whether, in experimental cerebral ischemia, chlormethiazole administration attenuated the ischemia-induced rise of the extracellular concentration of aminergic neurotransmitters and whether it reduces ischemia-induced deficits in memory and learning. Histology for assessment of ischemic damage was a so included. The four-vessel occlusion rat model was used to induce global cerebral ischemia. Aminergic neurotransmitters and their metabolites in the striatal extracellular fluid obtained by microdialysis were assayed by high-performance liquid chromatography-electrochemical detection. The drug was administered either IP (50 mg/kg-1) or directly through the dialysis probe (30 microM) 80 min before ischemia. For the behavioral test and histology, the drug was given IP (100 mg/kg-1) 1 h postischemia. The results obtained did not demonstrate any statistically significant evidence that chlormethiazole has an effect on the ischemia-induced rise in extracellular dopamine and serotonin levels. There was also no variation in metabolite levels. Behavioral measures (learning, recall) were not changed appreciably by the treatment. We observed no significant cell protection in the hippocampus (CA1, CA1), striatum, and entorhinal cortex in animals treated with chlormethiazole. We conclude that, under our experimental conditions, chlormethiazole has little or no effect on the neurochemical, neurobehavioral, and histological consequences of global cerebral ischemia.

TGF-beta 1 protects hippocampal neurons against degeneration caused by transient global ischemia. Dose-response relationship and potential neuroprotective mechanisms

BACKGROUND AND PURPOSE

Transforming growth factor-beta 1 (TGF-beta 1) has been shown to rescue cultured neurons from excitotoxic and hypoxic cell death and to reduce infarct size after focal cerebral ischemia in mice and rabbits. The present study investigated the effects of TGF-beta 1 in a different pathophysiological setting and the delayed neuronal death of hippocampal pyramidal cells after transient global ischemia in rats, and evaluated the potential mechanisms of the neuroprotective activity of TGF-beta 1.

METHODS

Transient forebrain ischemia was induced in male adult Wistar rats with bilateral occlusion of both common carotid arteries combined with systemic hypotension for 10 minutes. Seven days after ischemia, brains were perfusion-fixed and stained for histological evaluation. TGF-beta 1 or vehicle was injected intracerebroventricularly (ICV; 0.5, 4, and 50 ng) or intrahippocampally (4 ng) 1 hour before ischemia. For in vitro studies, hippocampal neurons were derived from E17 rat embryos and cultured for 10 to 14 days. Cells were exposed to (1) S-nitrosocysteine (SNOC; 30 mumol/L) to induce nitric oxide-induced oxidative injury and (2) staurosporine (0.03 mumol/L) to induce apoptotic cell death.

RESULTS

Transient forebrain ischemia caused extensive degeneration of CA1 hippocampal pyramidal cells in vehicle-treated control animals. Ischemic injury was not significantly reduced after ICV administration of 0.5 ng TGF-beta 1 (71 +/- 7% damaged neurons versus 84 +/- 3% in vehicle-treated controls: n = 9 and 11, respectively; P = .07, Mann-Whitney U test). Administration of 4 ng TGF-beta 1 reduced the percentage of damaged CA1 pyramidal cells from 71 +/- 10% in controls to 52 +/- 7% in TGF-beta 1-treated animals (n = 11 and 12, respectively; P = .04). TGF-beta 1 (4 ng) also produced significant protection when injected directly into the hippocampal tissue. In contrast, ICV administration of 50 ng TGF-beta 1 failed to show a protective effect in two separate sets of experiments. In vitro, a 24-hour pretreatment of the cultured hippocampal neurons with TGF-beta 1 (0.1 to 10 ng/mL) significantly inhibited both nitric oxide and staurosporine neurotoxicity. Posttreatment with TGF-beta 1 (10 ng/mL) also inhibited staurosporine neurotoxicity but actually potentiated nitric oxide-induced neuronal injury.

CONCLUSIONS

We demonstrated that TGF-beta 1 in a surprisingly low dose range has the capacity to reduce injury to CA1 hippocampal neurons caused by transient global ischemia in rats. This protective action could well be associated with the antioxidative and antiapoptotic effects of TGF-beta 1 demonstrated in vitro.

Systemic NMDA receptor antagonist CGP-40116 does not impair memory acquisition but protects against NMDA neurotoxicity in rhesus monkeys

A widely accepted hypothesis is that long-term potentiation (LTP) is a synaptic mechanism of memory. NMDA receptors are critically involved in induction but not maintenance of LTP; therefore, their blockade should impair memory acquisition but not retrieval. In Experiment 1, we investigated the effect of a systemic NMDA receptor antagonist, CGP-40116 [D-isomer of CGP-37849: (E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (6 mg/kg, i.m.) 60 min before the testing session] on memory acquisition and retrieval by monkeys in the "object-in-place" visual memory task, an analog of human episodic memory. Only a small increase in error rate was produced (< 3%), and this increase was observed in both retention and acquisition tests. This deficit is substantially smaller than the previously reported deficit after fornix transection in the same task, and is not specific to memory acquisition. In Experiment 2, we investigated the neuroprotective effect of CGP-40116. NMDA (68 nmol) was injected into the right hippocampus, then CGP-40116 (6 mg/kg) was given intramuscularly, and then NMDA was injected into the left hippocampus. The area of cell loss in CA1 and CA3 fields was smaller in both hemispheres compared with unprotected monkeys (without CGP-40116). Thus, CGP-40116 provides both retrograde and anterograde protection against NMDA neurotoxicity. These data (1) demonstrate that acquisition of episodic memories remains almost intact when an NMDA receptor antagonist is given in a dose sufficient to block NMDA receptors in the hippocampus, and (2) indirectly oppose the hypothesis that NMDA receptor-dependent LTP plays the key role in memory.

Failure of isradipine to reduce infarct size in mouse, gerbil, and rat models of cerebral ischemia

BACKGROUND AND PURPOSE

The dihydropyridine L-type calcium channel blocker isradipine has been reported to exhibit neuroprotective properties in some, but not all, studies performed in the rat middle cerebral artery occlusion (MCAO) model. In the present study, we examined isradipine in several other models of focal and global ischemia: rat rose bengal, mouse MCAO, and gerbil bilateral carotid artery occlusion (BCAO). For comparison, a novel calcium channel blocker, SB201823A, that we have previously shown to be neuroprotective in rat and gerbil models was also examined in the mouse.

METHODS

In the gerbil BCAO model, isradipine was administered at 2.5 mg/kg i.p. as a single dose 60 minutes after ischemia (n = 10). Corresponding controls received vehicle (n = 10), and sham-operated animals received no treatment (n = 6). Locomotor activity and histological assessments were made at 4 days after ischemia. In the rat photothrombotic occlusion model, isradipine was administered at 2.5 mg/kg i.p. as a single dose 60 minutes after ischemia (n = 10), and corresponding controls (n = 10) received vehicle. Histological assessment was made at 7 days after ischemia. In the mouse MCAO model, isradipine was also administered at 2.5 mg/kg i.p. as a single dose 60 minutes after ischemia. Histological assessments were made at 1 (n = 13), 2 (n = 9), and 4 (n = 9) days after ischemia. Vehicle numbers were n = 10, n = 6, and n = 8, respectively. Isradipine and SB201823A were also examined using a combined preischemia and postischemia regimen. Isradipine was administered at 2.5 mg/kg i.p. before occlusion, 1.25 mg/kg i.p. 1 hour after occlusion, 1.25 mg/kg i.p. 2 hours after occlusion, and 2.5 mg/kg twice a day for 3 days after occlusion (n = 16). Corresponding controls received vehicle at the same time points (n = 14). SB201823A was administered 30 minutes before occlusion, 30 minutes after occlusion, and twice daily for 3 days (n = 12). Corresponding controls received vehicle (n = 9). Histological assessment was performed at 4 days after ischemia.

RESULTS

When given after ischemia, isradipine failed to affect lesion volume in both the rat and mouse models. In the gerbil, locomotor hyperactivity and hippocampal cell loss were unaffected. Given before and after ischemia in the mouse, isradipine was also ineffective, whereas SB201823A produced a significant reduction in lesion volume.

CONCLUSIONS

The L-type calcium channel blocker isradipine was devoid of neuroprotective activity in focal and global models of cerebral ischemia in three species of normotensive animals. These results were compared with data for the novel calcium channel blocker SB201823A, which exhibited a significant effect after pre- and postocclusion administration in the mouse model of permanent focal ischemia.

The influence of experimental ischaemia on protein kinase C and the GABAergic system in the rabbit retina

Pressure-induced ocular ischaemia followed by 25-28 hr of reperfusion to the rabbit retina drastically reduces or eliminates the b-wave of the electroretinogram and results in all the GABA from the amacrine cells being released, as judged by immunohistochemistry. Some of these GABA cells have the capacity to take-up exogenous serotonin and these GABA/serotonin cells have kainate/AMPA receptors. Previous studies have shown that an ischaemic insult causes these receptors to be stimulated to produce a release of the cells' GABA. The majority of the GABA/serotonin cells are also incapable of taking-up exogenous serotonin after ischaemia, which suggests that they are irreversibly damaged. However, there was still a minority of the cells which accumulated serotonin, which shows that neurones containing kainate/AMPA receptors are not irreversibly damaged at the same rate by ischaemia. The "staining" patterns for GABAA-receptor and GABA immunoreactivities in the rabbit retina are very similar and following ischaemia the GABAA-receptor immunoreactivity was reduced in intensity and became patchy in nature. It is not known whether this result reflects a down-regulation of the GABAA-receptors caused by the released GABA or a destruction of cells containing the GABAA-receptors. The ischaemic conditions used caused patchy, irregular and inconsistent signs of histological damage to the retina, even in areas of similar eccentricity, suggesting this parameter should be used with caution when judging the severity of an ischaemic insult. alpha-Protein kinase C (alpha PKC) present in the on-bipolar cells which have glutamate metabotropic APB receptors is both reduced or down-regulated and translocated by ischaemia. This is also the case for delta PKC which is absent from the on-bipolar cells. These data were established by a combination of immunohistochemistry and electrophoresis/blotting experiments. Enzyme analysis also showed that all PKC calcium-dependent and -independent isoenzymes, are translocated and reduced by ischaemia making it difficult to judge whether PKC inhibitors may be appropriate anti-ischaemic agents.

Antioxidant properties of phenyl styryl ketones

Phenolic and non phenolic derivatives of phenyl styryl ketones were synthesized and evaluated as in vitro inhibitors of iron and cumene hydroperoxide dependent lipid peroxidation in rat brain homogenates. The compounds were also tested for antioxidant activity in phosphatidylcholine liposomes. Phenyl 3,5-di-tert-butyl-4-hydroxystyryl ketone was found to be the most potent inhibitor of peroxidation among all the compounds tested. It was found to be more active than vitamin E. It also reduced the stable free radical 1,1-diphenyl-2-picrylhydrazyl to an appreciable extent.

Calcium activity and post-ischemic suppression of protein synthesis

Increase in intracellular calcium concentration is a prominent feature of ischemia and has been considered a major factor in the initiation of ischemic pathology, which involves inhibition of protein synthesis. A reduction of calcium ion activity during and immediately after in vitro ischemia did not prevent inhibition of protein synthesis in hippocampae slices. When slices were overloaded with calcium by NMDA receptor activation or by the calcium ionophore A23187, no significant inhibition of protein synthesis was observed. We conclude that calcium overload plays only a limited role in ischemic inhibition of protein synthesis.

Carvedilol, a new antihypertensive drug with unique antioxidant activity: potential role in cerebroprotection

The antioxidant activities of carvedilol have been demonstrated in a wide variety of test systems, including (i) physicochemical (EPR studies), (ii) biochemical (measurement of lipid peroxidation and endogenous antioxidant depletion), (iii) cellular, and (iv) in vivo. The antioxidant activity of carvedilol clearly emanates from the carbazole moiety which is unique to carvedilol. The antioxidant activity resides equally in both of the enantiomers of carvedilol, as well as in some of its metabolites which are devoid of either the alpha 1-adrenoceptor blocking activity or beta-adrenoceptor blocking activity. This novel antioxidant property of carvedilol may account, at least in part, for its cerebroprotection. The data discussed in this article suggest that carvedilol may not only provide effective and safe antihypertensive therapy and therefore reduce a major risk factor for stroke, but will also be better able to provide additional benefits to patients by protecting against oxygen free radicals generated during cerebral ischemia and stroke.

Antioxidant properties of dehydrozingerone and curcumin in rat brain homogenates

The present study investigates the inhibition of lipid peroxidation by dehydrozingerone and curcumin in rat brain homogenates. Both the test compounds inhibited the formation of conjugated dienes and spontaneous lipid peroxidation. These compounds also inhibited lipid peroxidation induced by ferrous ions, ferric-ascorbate and ferric-ADP-ascorbate. In all these cases, curcumin was more active than dehydrozingerone and dl-alpha-tocopherol.

Protein synthesis in the hippocampal slice: transient inhibition by glutamate and lasting inhibition by ischemia

Protein synthesis was measured in hippocampal slices which were exposed to glutamate (1 mM or 10 mM) or which were deprived of glucose and oxygen ('in vitro ischemia') for 15 min. Glutamate at 1 mM, a concentration estimated to occur during in vivo ischemia did not affect protein synthesis. Ten mM glutamate inhibited protein synthesis immediately after exposure (50% of control values) and reduced ATP levels to about 30% of the control. After two hours, slices fully recovered their protein synthesis and energy metabolism. The effect of 10 mM glutamate was not receptor-mediated, as NMDA, AMPA, or metabotropic receptor antagonists failed to block the glutamate effect. Immediately after ischemia, protein synthesis was reduced to 30% of control values, and 2 hours later it was still depressed to one-half of control values. Energy charge, however, recovered completely. Ischemic inhibition of protein synthesis was not reversed by glutamate receptor antagonists. The data indicate that inhibition of protein synthesis in hippocampal slices during ischemia is not glutamate-dependent.

Schizophrenia: an extended etiological explanation

Schizophrenia has become an elusive medical conundrum since it was first described at the turn of the 19th century. Over time, a variety of causal hypotheses have been advanced to explain the spectrum of schizophreniform disorders. This etiological explanation outlines the relationship that obtains between smoking, schizophrenia, and impaired glycometabolism which also includes disruption to the dopaminergic and serotinergic pathways. A possible genetic explanation for this disruption will be identified which links mental illness to a locus of genes contained on the short arm of chromosome 11. These genes are all essential to normal glucose transport which positron emission tomography (PET) scans show is seriously abnormal in schizophrenia. Thus, a redefinition of schizophrenia as 'cerebral diabetes' will be proposed since this term implies a diabetic brain state consistent with PET scans of schizophrenic patients.

Protective effects of 5-HT1A receptor agonists against neuronal damage demonstrated in vivo and in vitro

The aim of the present study was to evaluate the neuroprotective effect of the 5-hydroxytryptamine1A (5-HT1A) agonists, CM 57493 and urapidil, in vivo and in vitro, respectively. In vivo permanent occlusion of the middle cerebral artery (MCA) was performed in male Wistar rats. Forty-eight hours after electrocoagulation of the MCA the infarct volume was determined. Pretreatment of the rat with the 5-HT1A agonist urapidil significantly reduced infarct development. The neuroprotective effect of the agent was restricted to the cortical area; the striatal damage was not influenced. As the stimulation of the 5-HT1A receptor by serotonin is supposed to induce inhibitory, hyperpolarizing effects by opening of a Ca(2+)-independent neuronal K+ ionophore, the efficacy of agonistic drugs directly on the neuron was investigated in vitro. Cyanide-induced cytotoxic hypoxia as well as glutamate-induced excitotoxicity were performed using primary neuronal cell cultures from chick embryo cerebral hemispheres. Treatment with the 5-HT1A agonists urapidil and CM 57493 significantly increased protein content of hypoxic cultures. CM 57493 added to the culture medium (1-10 microM) during and up to 24 h after glutamate exposure ameliorated viability of the neurons. The results demonstrate neuroprotective potency of the 5-HT1A agonists, urapidil and CM 57493, when applied under hypoxic, excitotoxic and ischemic conditions in vivo and in vitro, respectively. Both, presynaptically induced inhibition of glutamate release as well as postsynaptically induced inhibition of neuronal excitability could be discussed as possible mechanisms of action of the 5-HT1A receptor agonism.

Primary cultures of neurons for testing neuroprotective drug effects

Primary cultures of neurons are widely used for the investigation of pathomechanisms of neuronal damage and for the evaluation of neuroprotective drug effects. The present paper gives a short survey of frequently used primary neuronal culture systems and of experimental measures for the induction of defined neuronal damage with particular respect to the pathomechanisms of cerebral ischemia. Neuroprotective drug effects as achieved under these conditions are reviewed, and the neuroprotective effects of glutamate antagonists, radical scavengers, and neural growth factors are discussed in some more detail.