Neuroprotective effects of tetrodotoxin as a Na+ channel modulator and glutamate release inhibitor in cultured rat cerebellar neurons and in gerbil global brain ischemia

Neural cell isolation from adult macaques for high-throughput analyses and neurosphere cultures

The low number of neural progenitor cells (NPCs) present in the adult and aged primate brains represents a challenge for generating high-yield and viable in vitro cultures of primary brain cells. Here we report a step-by-step approach for the fast and reproducible isolation of high-yield and viable primary brain cells, including mature neurons, immature cells and NPCs, from adult and aged macaques. We describe the anesthesia, transcardial perfusion and brain tissue preparation; the subsequent microdissection of the regions of interest and their enzymatic dissociation, leading to the separation of single cells. The cell isolation steps of our protocol can also be used for routine cell culturing, in particular for NPC expansion and differentiation, suitable for studies of hippocampal neurogenesis in the adult macaque brain. The purified primary brain cells are largely free from myelin debris and erythrocytes, paving the way for multiple downstream applications in vitro and in vivo. When combined with single-cell profiling techniques, this approach allows an unbiased and comprehensive mapping of cell states in the adult and aged macaque brain, which is needed to advance our understanding of human cognitive and neurological diseases. The neural cell isolation protocol requires 4 h and a team of four to six users with expertize in primary brain cell isolation to avoid tissue hypoxia during the time-sensitive steps of the procedure.

Ceftriaxone as a Novel Therapeutic Agent for Hyperglutamatergic States: Bridging the Gap Between Preclinical Results and Clinical Translation

Dysregulation of glutamate homeostasis is a well-established core feature of neuropsychiatric disorders. Extracellular glutamate concentration is regulated by glutamate transporter 1 (GLT-1). The discovery of a beta-lactam antibiotic, ceftriaxone (CEF), as a safe compound with unique ability to upregulate GLT-1 sparked the interest in testing its efficacy as a novel therapeutic agent in animal models of neuropsychiatric disorders with hyperglutamatergic states. Indeed, more than 100 preclinical studies have shown the efficacy of CEF in attenuating the behavioral manifestations of various hyperglutamatergic brain disorders such as ischemic stroke, amyotrophic lateral sclerosis (ALS), seizure, Huntington’s disease, and various aspects of drug use disorders. However, despite rich and promising preclinical data, only one large-scale clinical trial testing the efficacy of CEF in patients with ALS is reported. Unfortunately, in that study, there was no significant difference in survival between placebo- and CEF-treated patients. In this review, we discussed the translational potential of preclinical efficacy of CEF based on four different parameters: (1) initiation of CEF treatment in relation to induction of the hyperglutamatergic state, (2) onset of response in preclinical models in relation to onset of GLT-1 upregulation, (3) mechanisms of action of CEF on GLT-1 expression and function, and (4) non-GLT-1-mediated mechanisms for CEF. Our detailed review of the literature brings new insights into underlying molecular mechanisms correlating the preclinical efficacy of CEF. We concluded here that CEF may be clinically effective in selected cases in acute and transient hyperglutamatergic states such as early drug withdrawal conditions.

nNav1.5 expression is associated with glutamate level in breast cancer cells

Background

Glutamate and voltage-gated sodium channels, both have been the target of intense investigation for its involvement in carcinogenesis and progression of malignant disease. Breast cancer with increased level of glutamate often metastasize to other organs (especially bone), whilst re-expression of ‘neonatal’ Nav1.5, nNav1.5 in breast cancer is known to promote cell invasion in vitro, metastasis in vivo and positive lymph node metastasis in patients.

Methods

In this study, the role of nNav1.5 in regulating glutamate level in human breast cancer cells was examined using pharmacological approach (VGSCs specific blocker, TTX, glutamate release inhibitor, riluzole and siRNA-nNav1.5). Effect of these agents were evaluated based on endogenous and exogenous glutamate concentration using glutamate fluorometric assay, mRNA expression of nNav1.5 using qPCR and finally, invasion using 3D culture assay.

Results

Endogenous and exogenous glutamate levels were significantly higher in aggressive human breast cancer cells, MDA-MB-231 cells compared to less aggressive human breast cancer cells, MCF-7 and non-cancerous human breast epithelial cells, MCF-10A. Treatment with TTX to MDA-MB-231 cells resulted in significant reduction of endogenous and exogenous glutamate levels corresponded with significant suppression of cell invasion. Subsequently, downregulation of nNav1.5 gene was observed in TTX-treated cells.

Conclusions

An interesting link between nNav1.5 expression and glutamate level in aggressive breast cancer cells was detected and requires further investigation.

An Updated Review of Tetrodotoxin and Its Peculiarities

Tetrodotoxin (TTX) is a crystalline, weakly basic, colorless organic substance and is one of the most potent marine toxins known. Although TTX was first isolated from pufferfish, it has been found in numerous other marine organisms and a few terrestrial species. Moreover, tetrodotoxication is still an important health problem today, as TTX has no known antidote. TTX poisonings were most commonly reported from Japan, Thailand, and China, but today the risk of TTX poisoning is spreading around the world. Recent studies have shown that TTX-containing fish are being found in other regions of the Pacific and in the Indian Ocean, as well as the Mediterranean Sea. This review aims to summarize pertinent information available to date on the structure, origin, distribution, mechanism of action of TTX and analytical methods used for the detection of TTX, as well as on TTX-containing organisms, symptoms of TTX poisoning, and incidence worldwide.

Tetrabromobisphenol A-induced depolarization of rat cerebellar granule cells: ex vivo and in vitro studies

The brominated flame retardant tetrabromobisphenol A (TBBPA) is toxic to cultured brain neurons, and glutamate receptors partially mediate this effect; consequently, the depolarizing effect of TBBPA on neurons is to be expected, but it is yet to be actually demonstrated. The aim of this study was to detect TBBPA-evoked depolarization and identify the underlying mechanisms. The plasma membrane potential of rat cerebellar granule cells (CGC) in cerebellar slices or in primary cultures was measured using whole-cell current clamp recordings, or the fluorescent probe oxonol VI, respectively. The contribution of NMDA and AMPA receptors, voltage-gated sodium channels and intracellular calcium mobilization was tested using their selective antagonists or inhibitors. Direct interactions of TBBPA with NMDARs were tested by measuring the specific binding of radiolabeled NMDAR ligands to isolated rat cortical membrane fraction. TBBPA (25 μM) strongly depolarized CGC in cerebellar slices, and at ≥ 7.5 μM concentration-dependently depolarized primary CGC cultures. Depolarization of the primary CGC by 25 μM TBBPA was partly reduced when MK-801 was applied alone or in combination with either TTX or CNQX, or where bastadin 12 was applied in combination with ryanodine, whereas depolarization was completely prevented when MK-801, CNQX and TTX where combined. TBBPA had no effect on the specific binding of NMDAR radio-ligands to isolated cortical membranes. These results demonstrate the depolarizing effect of TBBPA on CGC, which is mainly mediated by ionotropic glutamate receptors, while voltage-gated sodium channels are also involved. We found no evidence for the direct activation of NMDARs by TBBPA.

The Influence of Tetrodotoxin (TTX) on the Distribution and Chemical Coding of Caudal Mesenteric Ganglion (CaMG) Neurons Supplying the Porcine Urinary Bladder

The treatment of micturition disorders creates a serious problem for urologists. Recently, new therapeutic agents, such as neurotoxins, are being considered for the therapy of urological patients. The present study investigated the chemical coding of caudal mesenteric ganglion (CaMG) neurons supplying the porcine urinary bladder after intravesical instillation of tetrodotoxin (TTX). The CaMG neurons were visualized with retrograde tracer Fast blue (FB) and their chemical profile was disclosed with double-labeling immunohistochemistry using antibodies against tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), calbindin (CB), galanin (GAL) and neuronal nitric oxide synthase (nNOS). It was found that in both the control (n = 6) and TTX-treated pigs (n = 6), the vast majority (92.6% ± 3.4% and 88.8% ± 2%, respectively) of FB-positive (FB+) nerve cells were TH+. TTX instillation caused a decrease in the number of FB+/TH+ neurons immunopositive to NPY (88.9% ± 5.3% in the control animals vs. 10.6% ± 5.3% in TTX-treated pigs) or VIP (1.7% ± 0.6% vs. 0%), and an increase in the number of FB+/TH+ neurons immunoreactive to SOM (8.8% ± 1.6% vs. 39% ± 12.8%), CB (1.8% ± 0.7% vs. 12.6% ± 2.7%), GAL (1.7% ± 0.8% vs. 10.9% ± 2.6%) or nNOS (0% vs. 1.1% ± 0.3%). The present study is the first to suggest that TTX modifies the chemical coding of CaMG neurons supplying the porcine urinary bladder.

Loss of α-Synuclein Does Not Affect Mitochondrial Bioenergetics in Rodent Neurons

Increased α-synuclein (αsyn) and mitochondrial dysfunction play central roles in the pathogenesis of Parkinson's disease (PD), and lowering αsyn is under intensive investigation as a therapeutic strategy for PD. Increased αsyn levels disrupt mitochondria and impair respiration, while reduced αsyn protects against mitochondrial toxins, suggesting that interactions between αsyn and mitochondria influences the pathologic and physiologic functions of αsyn. However, we do not know if αsyn affects normal mitochondrial function or if lowering αsyn levels impacts bioenergetic function, especially at the nerve terminal where αsyn is enriched. To determine if αsyn is required for normal mitochondrial function in neurons, we comprehensively evaluated how lowering αsyn affects mitochondrial function. We found that αsyn knockout (KO) does not affect the respiration of cultured hippocampal neurons or cortical and dopaminergic synaptosomes, and that neither loss of αsyn nor all three (α, β and γ) syn isoforms decreased mitochondria-derived ATP levels at the synapse. Similarly, neither αsyn KO nor knockdown altered the capacity of synaptic mitochondria to meet the energy requirements of synaptic vesicle cycling or influenced the localization of mitochondria to dopamine (DA) synapses in vivo. Finally, αsyn KO did not affect overall energy metabolism in mice assessed with a Comprehensive Lab Animal Monitoring System. These studies suggest either that αsyn has little or no significant physiological effect on mitochondrial bioenergetic function, or that any such functions are fully compensated for when lost. These results implicate that αsyn levels can be reduced in neurons without impairing (or improving) mitochondrial bioenergetics or distribution.

REVIEW ■ : Physical Injury of Neurons: Important Roles for Sodium and Chloride Ions

There is growing evidence that ions other than Ca2+ play important roles in the deterioration of neuronal elements in both gray and white matter after physical injury. This review features information gathered with a tissue culture model of dendrite transection regarding the contributions of Na+ and CI- to ultrastructural damage and neuronal death. This information and the results of other in vitro investigations of physical and ischemic/excitotoxic injuries indicate that elevation of internal Na+ is an early event that may contribute significantly to neuronal injury through effects on Na+-driven transport mechanisms. Proposed deleterious consequences include cytoplasmic acidification, reduced mitochondrial energy production, and elevation of intracellular Ca2+ and extracellular excitatory amino acids to toxic levels. Prevention of Na+ entry into neurons after injury has been found to limit ultrastructural damage, prevent death, and preserve electrophysiological function. Although the role of CI- in neuronal injury is less well defined, there is also evidence that elevation of intracellular CI- contributes to structural damage, particularly to the smooth endoplasmic reticulum. In terventions that limit Na+- and CI--mediated damage to injured neurons may have utility in neurosurgery and as acute phase treatments for nervous system trauma and other pathological states. NEURO SCIENTIST 3:89-101, 1997

An overview on the origin and production of tetrodotoxin, a potent neurotoxin

Tetrodotoxin (TTX) is a deadly neurotoxin which selectively inhibits Na(+) activation mechanism of nerve impulse, without affecting the permeability of K(+) ions. Because of this sodium channel blocking action, it is majorly being studied for biomedical applications. TTX is present in taxonomically diverse groups of animals inhabiting terrestrial, marine, fresh water and brackish water environments, still its origin remains unclear. The extensive study of the toxin has revealed a few possibilities of its origin. This review reports on the aspects of the origin of TTX, where the primary focus is on its exogenous origin. The significance of bacterial, cellular and environmental factors in its biogenesis and accumulation is also discussed. The possible facets for engineering the bacterial genomics to modulate the gene expression for TTX production are also outlined.

Do sodium channel blockers have neuroprotective effect after onset of ischemic insult?

OBJECTIVE

Cerebral ischemia causes a series of pathophysiologic events that may result in cerebral infarct. Some neurons are more vulnerable to ischemia, particularly pyramidal neurons in the hippocampal CA1 region. Pharmacologic intervention for treatment of cerebral ischemia aims to counteract secondary neurotoxic events or to interrupt the progression of this process. In the present study, we compare the neuroprotective effects of sodium channel blockers (mexiletine, riluzole and phenytoin) and investigate whether they have neuroprotective effect when given after ischemic insult.

METHODS

A transient global cerebral ischemia model was performed in this study by clipping bilateral common carotid arteries during 45 minutes. Riluzole (8 mg/kg), mexiletine (80 mg/kg) and phenytoin (200 mg/kg) were injected into the rats intraperitoneally 30 minutes before or after reperfusion. Lipid peroxidation levels and cerebral water contents were evaluated 24 hours after ischemia. Histopathologic assessment of hippocampal region was determined 7 days after ischemia.

RESULTS

Riluzole, mexiletine and phenytoin treatment after global ischemia significantly decreased water content of the ischemic brain (p<0.05 for each). No significant difference was observed in cerebral edema among the drug treatment groups (p>0.05). When pre-treatment and post-treatment groups were compared with each other, only riluzole pre-treatment group revealed better result for cerebral edema (p<0.05). Pre-treatment with these drugs revealed significantly better results for the malonyldialdehyde (MDA) level and the number of survival neuron on the hippocampal region than the post-treatment groups.

CONCLUSION

It is demonstrated that riluzole, mexiletine and phenytoin are potent neuroprotective agents in the rat model of transient global cerebral ischemia, but they are more effective when given before onset of the ischemia.

Therapeutic targets for neuroprotection in acute ischemic stroke: lost in translation?

The development of a suitable neuroprotective agent to treat ischemic stroke has failed when transitioned to the clinical setting. An understanding of the molecular mechanisms involved in neuronal injury during ischemic stroke is important, but must be placed in the clinical context. Current therapeutic targets have focused on the preservation of the ischemic penumbra in the hope of improving clinical outcomes. Unfortunately, most patients in the ultra-early time windows harbor penumbra but have tremendous variability in the size of the core infarct, the ultimate predictor of prognosis. Understanding this variability may allow for proper patient selection that may better correlate to bench models. Reperfusion therapies are rapidly evolving and have been shown to improve clinical outcomes. The use of neuroprotective agents to prolong time windows prior to reperfusion or to prevent reperfusion injury may present future therapeutic targets for the treatment of ischemic stroke. We review the molecular pathways and the clinical context from which future targets may be identified.

Effects of TRH and its analogues on primary cortical neuronal cell damage induced by various excitotoxic, necrotic and apoptotic agents

The tripeptide thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2) has been shown to possess neuroprotective activity in in vitro and in vivo models. Since its potential utility is limited by relatively rapid metabolism, metabolically stabilized analogues have been constructed. In the present study we investigated the influence of TRH and its three stable analogues: Montirelin (MON, CG-3703), RGH-2202 (L-6-keto-piperidine-2carbonyl-l-leucyl-l-prolinamide) and Z-TRH (N-carbobenzyloxy-pGlutamyl-Histydyl-Proline) in various models of mouse cortical neuronal cell injury. Twenty four hour pre-treatment with TRH and its analogues in low micromolar concentrations attenuated the neuronal cell death evoked by excitatory amino acids (EAAs: glutamate, NMDA, kainate, quisqualate) and hydrogen peroxide. All the peptides showed neuroprotective action on staurosporine (St)-evoked apoptotic neuronal cell death, but this effect was caspase-3 independent. Interestingly, in mixed neuronal-glial cell preparations only MON decreased St- and glutamate-evoked neurotoxicity. None of the peptides inhibited the doxorubicin- and lactacystin-induced neuronal cortical cell death, agents acting via activation of death receptor (FAS) or inhibition of proteasome function, respectively. Furthermore, we found that neither inhibitors of PI3-K (wortmannin, LY 294002) nor MAPK/ERK1/2 (PD 098059, U 0126) were able to inhibit neuroprotective properties of TRH and MON in St model of apoptosis. The protection mediated by TRH and MON it that model was also not connected with influence of peptides on the pro-apoptotic GSK-3beta and JNK protein kinase expression and activity. Further studies showed that calpains, calcium-activated proteases were induced by Glu, but not by St in cortical neurons. Moreover, the Glu-evoked increase in spectrin alpha II cleavage product induced by calpains was blocked by TRH. The obtained data showed that the potency of TRH and its analogues in inhibiting EAAs- and H(2)O(2)-induced neuronal cell death from the highest to lowest activity was: MON>TRH>Z-TRH>RHG. Interestingly, all peptides were active against St-induced apoptosis, however, on concentration basis MON was far more potent than the other peptides. None of the peptides inhibited Dox- and LC-evoked apoptotic cell death. Additionally, the data exclude potential role of pro-survival (PI3-K/Akt and MAPK/ERK1/2) and pro-apoptotic (GSK-3beta and JNK) pathways in neuroprotective effects of TRH and its analogues on St-induced neuronal apoptosis. Moreover, the results point to involvement of the inhibition of calpains in the TRH neuroprotective effect in Glu model of neuronal cell death.

Mechanism of the persistent sodium current activator veratridine-evoked Ca elevation: implication for epilepsy

Although the role of Na(+) in several aspects of Ca(2+) regulation has already been shown, the exact mechanism of intracellular Ca(2+) concentration ([Ca(2+)](i)) increase resulting from an enhancement in the persistent, non-inactivating Na(+) current (I(Na,P)), a decisive factor in certain forms of epilepsy, has yet to be resolved. Persistent Na(+) current, evoked by veratridine, induced bursts of action potentials and sustained membrane depolarization with monophasic intracellular Na(+) concentration ([Na(+)](i)) and biphasic [Ca(2+)](i) increase in CA1 pyramidal cells in acute hippocampal slices. The Ca(2+) response was tetrodotoxin- and extracellular Ca(2+)-dependent and ionotropic glutamate receptor-independent. The first phase of [Ca(2+)](i) rise was the net result of Ca(2+) influx through voltage-gated Ca(2+) channels and mitochondrial Ca(2+) sequestration. The robust second phase in addition involved reverse operation of the Na(+)-Ca(2+) exchanger and mitochondrial Ca(2+) release. We excluded contribution of the endoplasmic reticulum. These results demonstrate a complex interaction between persistent, non-inactivating Na(+) current and [Ca(2+)](i) regulation in CA1 pyramidal cells. The described cellular mechanisms are most likely part of the pathomechanism of certain forms of epilepsy that are associated with I(Na,P). Describing the magnitude, temporal pattern and sources of Ca(2+) increase induced by I(Na,P) may provide novel targets for antiepileptic drug therapy.

Extracellular guanosine and GTP promote expression of differentiation markers and induce S-phase cell-cycle arrest in human SH-SY5Y neuroblastoma cells

SH-SY5Y neuroblastoma cells, a model for studying neuronal differentiation, are able to differentiate into either cholinergic or dopaminergic/adrenergic phenotypes depending on media conditions. Using this system, we asked whether guanosine (Guo) or guanosine-5'-triphosphate (GTP) are able to drive differentiation towards one particular phenotype. Differentiation was determined by evaluating the frequency of cells bearing neurites and assessing neurite length after exposure to different concentrations of Guo or GTP for different durations. After 6 days, 0.3 mM Guo or GTP induced a significant increase in the number of cells bearing neurites and increased neurite length. Western blot analyses confirmed that purines induced differentiation; cells exposed to purines showed increases in the levels of GAP43, MAP2, and tyrosine hydroxylase. Proliferation assays and cytofluorimetric analyses indicated a significant anti-proliferative effect of purines, and a concentration-dependent accumulation of cells in S-phase, starting after 24 h of purine exposure and extending for up to 6 days. A transcriptional profile analysis using gene arrays showed that an up-regulation of cyclin E2/cdk2 evident after 24 h was responsible for S-phase entry, and a concurrent down-regulation of cell-cycle progression-promoting cyclin B1/B2 prevented S-phase exit. In addition, patch-clamp recordings revealed that 0.3 mM Guo or GTP, after 6 day incubation, significantly decreased Na(+) currents. In conclusion, we showed Guo- and GTP-induced cell-cycle arrest in neuroblastoma cells and suggest that this makes these cells more responsive to differentiation processes that favor the dopaminergic/adrenergic phenotype.

Tetrodotoxin Poisoning

Tetrodotoxin (TTX) is one of the most potent and oldest known neurotoxins. The poisoning cases due to ingestion of TTX-containing marine animals, especially for puffer, have frequently occurred in Asia since a long time ago. This chapter describes various topics on TTX poisoning including the tendency of poisoning incidents, typical case report, treatment and prevention, biology distribution, original source, infestation mechanism, detection methods, characteristics of chemistry and pharmacology, and therapeutic application. Furthermore, the protocols for how to make puffer safe to eat and how to prevent puffer products made from toxic puffers have been suggested. Finally, the biological significance and neurophysiological role of TTX have been elucidated and TTX may act as an important drug like anesthetic in future.

Neuroprotective effect of etomidate in the central nervous system of streptozotocin-induced diabetic rats

It is well known that hyperglycaemia due to diabetes mellitus leads to oxidative stress in the central nervous system. Oxidative stress plays important role in the pathogenesis of neurodegenerative changes. In the present study we investigated the possible neuroprotective effect of etomidate against streptozotocin-induced (STZ-induced) hyperglycaemia in the rat brain and spinal cord. A total of 40 rats were used in this study. Rats were divided into four groups: sham-control, diabetic, diabetic-etomidate treated and vehicle for etomidate treatment group. Diabetes mellitus was induced by a single injection of streptozotocin (60 mg/kg body weight). Three days after streptozotocin injection, etomidate (2 mg/kg) was injected intraperitoneally for etomidate group and lipid emulsion (10%) for vehicle group was injected with corresponding amount intraperitoneally every day for 6 weeks. Six weeks after streptozotocin injection, seven rats from each group were killed and brain, brain stem and cervical spinal cord were removed. The hippocampus, cortex, cerebellum, brain stem and spinal cord were dissected for the biochemical analysis (the level of malondialdehyde [MDA], total nitrite, reduced glutathione [GSH], and xanthine oxidase [XO] activity). STZ-induced diabetes resulted in significantly elevation of MDA, XO and nitrite levels in the hippocampus, cortex, cerebellum, brain stem and spinal cord of the rats (P < 0.05) while etomidate treatment provided significantly lower values (P < 0.05). This study demonstrated that etomidate have neuroprotective effect on the neuronal tissue against the diabetic oxidative damage.

Potential effects of tetrodotoxin exposure to human glial cells postulated using microarray approach

Sodium channels play an important role in many neurological disorders and also in prostate cancer. Tetrodotoxin (TTX), a blocker of voltage-gated sodium channels has been chiefly used as a molecular probe for the study and characterization of these channels. The regulation of gene expression in response for the exposure of TTX to glial cells which are reported to be involved in neurodegenerative process is poorly understood. Therefore, the present study aims to develop a repository of genes and map it on a few pivotal neurodegenerative pathways to speculate the effect of TTX. Using Affymetrix GeneChip (HG-U133A), we have selected a subset of 692 differentially expressed genes, several of which are-cullin 4A (CUL4A), ubiquitin carrier protein (E2-EPF), proteasome (prosome, macropain) subunit, beta type, 8 (large multifunctional protease 7) (PSMB8), protein tyrosine phosphatase type IVA (PTP4A1), intercellular adhesion molecule 1 (ICAM1), prostaglandin-endoperoxide synthase 2 (PTGS2), and caspase 1 (CASP1). These genes, which facilitate some of the neurodegenerative pathways, such as ubiquitin, proteasome, inflammation and kinases, were identified to be up- or down-regulated for the TTX treatment. Thus, the selected genes were further examined on ubiquitin-proteasome mediated inflammatory responses pathway as ample evidence for the role of glial cell-mediated inflammation in the neurodegenerative process are available. In summary, our result provides a basic understanding of the differentially expressed genes along with one of the possible pathway which may have been modulated by the exposure of TTX.

Neuroprotection and peptide toxins

Neurodegeneration induced by excitatory neurotransmitter glutamate is considered to be of particular relevance in several types of acute and chronic neurological impairments ranging from cerebral ischaemia to neuropathological conditions such as motor neuron disease, Alzheimer's, Parkinson's disease and epilepsy. The hyperexcitation of glutamate receptors coupled with calcium overload can be prevented or modulated by using well-established competitive and non-competitive antagonists targeting ion/receptor channels. The exponentially increasing body of pharmacological evidence over the years indicates potential applications of peptide toxins, due to their exquisite subtype selectivity on ion channels and receptors, as lead structures for the development of drugs for the treatment of wide variety of neurological disorders. This review comprehensively highlights the overview of the diversity in the molecular as well as neurobiological mechanisms of different peptide toxins derived from venomous animals with particular reference to neuroprotection. In addition, the potential applications of peptide toxins in the diagnosis and treatment of neurological disorders such as neuromuscular disorders, epilepsy, Alzheimer's and Parkinson's diseases, gliomas and ischaemic stroke and their future prospects in the diagnosis as well as in the therapy are addressed.

Characterization of hydroxyl radical generation in the striatum of free-moving rats due to carbon monoxide poisoning, as determined by in vivo microdialysis

Carbon monoxide (CO) poisoning caused by CO exposure at 3000 ppm for 40 min resulted in stimulation of hydroxyl radical (*OH) generation (estimated by measuring 2,3-dihydroxybenzoic acid (2,3-DHBA) production from salicylic acid) in the striatum of free-moving rats, as determined by means of brain microdialysis. Pretreatment with a voltage-dependent Na+ channel blocker, tetrodotoxin (TTX), lowered the basal level of 2,3-DHBA and strongly suppressed the increase in 2,3-DHBA induced by CO poisoning. CO poisoning significantly, though only slightly, increased extracellular glutamate in the striatum, and glutamate (Glu) receptor antagonists, such as MK-801 (dizocilpine) and NBQX, failed to suppress the CO-induced increase in 2,3-DHBA. These findings suggest that CO poisoning may induce Na+ influx via the voltage-dependent Na+ channels, resulting in stimulation of *OH generation in rat striatum. This effect may be independent of Glu receptor activation by increased extracellular Glu.

Neuronal NOS activation during oxygen and glucose deprivation triggers cerebellar granule cell death in the later reoxygenation phase

The present study investigated the temporal relationship between neuronal nitric oxide synthase (nNOS) activity and expression and the development of neuronal damage occurring during anoxia and anoxia followed by reoxygenation. For this purpose, cerebellar granule cells were exposed to 2 hr of oxygen and glucose deprivation (OGD) and 24 hr of reoxygenation. To clarify the consequences of nNOS activity inhibition on neuronal survival, cerebellar granule cells were exposed to OGD, both in the absence of extracellular Na(+) ([Na(+)](e)), a condition that by reducing intracellular Ca(2+) ([Ca(2+)](I)) prevents Ca(2+)-dependent nNOS activation, and in the presence of selective and nonselective nNOS inhibitors, such as N(omega)-L-allyl-L-arginine (L-ALA), N(omega)-propyl-L-arginine (NPLA), and L-nitro-arginine-methyl-ester (L-NAME), respectively. The results demonstrated that the removal of [Na(+)](e) hampered the [Ca(2+)](i) increase and decreased expression and activity of nNOS. Similarly, the increase of free radical production present in cerebellar neurons, exposed previously to OGD and OGD/reoxygenation, was abolished completely in the absence of [Na(+)](e). Furthermore, the absence of [Na(+)](e) in cerebellar neurons exposed to 2 hr of OGD led to the improvement of mitochondrial activity and neuronal survival, both after the OGD phase and after 24 hr of reoxygenation. Finally, the exposure of cerebellar neurons to L-ALA (200 nM), and L-NAME (500 microM) was able to effectively reduce NO(*) production and caused an increase in mitochondrial oxidative activity and an improvement of neuronal survival not only during OGD, but also during reoxygenation. Similar results during OGD were obtained also with NPLA (5 nM), another selective nNOS inhibitor. These data suggest that the activation of nNOS is highly accountable for the neuronal damage occurring during the OGD and reoxygenation phases.

RS-100642-198, a novel sodium channel blocker, provides differential neuroprotection against hypoxia/hypoglycemia, veratridine or glutamate-mediated neurotoxicity in primary cultures of rat cerebellar neurons

The present study investigated the effects of RS-100642-198 (a novel sodium channel blocker), and two related compounds (mexiletine and QX-314), in in vitro models of neurotoxicity. Neurotoxicity was produced in primary cerebellar cultures using hypoxia/hypoglycemia (H/H), veratridine or glutamate where, in vehicle-treated neurons, 65%, 60% and 75% neuronal injury was measured, respectively. Dose-response neuroprotection experiments were carried out using concentrations ranging from 0.1-500 micro M. All the sodium channel blockers were neuroprotective against H/H-induced injury, with each exhibiting similar potency and efficacy. However, against veratridine-induced neuronal injury only RS-100642-198 and mexiletine were 100% protective, whereas QX-314 neuroprotection was limited (i.e. only 54%). In contrast, RS-100642-198 and mexiletine had no effect against glutamate-induced injury, whereas QX-314 produced a consistent, but very limited (i.e. 25%), neuroprotection. Measurements of intraneuronal calcium [Ca(2+)]i) mobilization revealed that glutamate caused immediate and sustained increases in [Ca(2+)]i which were not affected by RS-100642-198 or mexiletine. However, both drugs decreased the initial amplitude and attenuated the sustained rise in [Ca(2+)]i mobilization produced by veratridine or KCl depolarization. QX-314 produced similar effects on glutamate-, veratridine- or KCl-induced [Ca(2+)]i dynamics, effectively decreasing the amplitude and delaying the initial spike in [Ca(2+)]i, and attenuating the sustained increase in [Ca(2+)]i mobilization. By using different in vitro models of excitotoxicity, a heterogeneous profile of neuroprotective effects resulting from sodium channel blockade has been described for RS-100642-198 and related drugs, suggesting that selective blockade of neuronal sodium channels in pathological conditions may provide therapeutic neuroprotection against depolarization/excitotoxicity via inhibition of voltage-dependent Na(+) channels.

Activation of voltage-sensitive sodium channels during oxygen deprivation leads to apoptotic neuronal death

Sodium (Na(+)) entry into neurons during hypoxia is known to be associated with cell death. However, it is not clear whether Na(+) entry causes cell death and by what mechanisms this increased Na(+) entry induces death. In this study we used cultures of rat neocortical neurons to show that an increase in intracellular sodium (Na(i)(+)) through voltage-sensitive sodium channels (VSSCs), during hypoxia contributes to apoptosis. Hypoxia increased Na(i)(+) and induced neuronal apoptosis, as assessed by electron microscopy, annexin V staining, and terminal UDP nick end labeling staining. Reducing Na(+) entry with the VSSC blocker, tetrodotoxin (TTX), attenuated apoptotic neuronal death via a reduction in caspase-3 activation. Since the attenuation of apoptosis by TTX during hypoxia suggested that the activation of VSSCs and Na(+) entry are crucial events in hypoxia-induced cell death, we also determined whether the activation of VSSCs per se could lead to apoptosis under resting conditions. Increasing Na(+) entry with the VSSC activator veratridine also induced neuronal apoptosis and caspase-3 activation. These data indicate that a) Na(+) entry via VSSCs during hypoxia leads to apoptotic cell death which is mediated, in part, by caspase-3 and b) activation of VSSCs during oxygen deprivation is a major event by which hypoxia induces cell death.

A comparison of Ca2+ channel blocking mode between gabapentin and verapamil: implication for protection against hypoxic injury in rat cerebrocortical slices

1 The mode of Ca(2+) channel blocking by gabapentin [1-(aminomethyl)cyclohexane acetic acid] was compared to those of other Ca(2+) channel blockers, and the potential role of Ca(2+) channel antagonists in providing protection against hypoxic injury was subsequently investigated in rat cerebrocortical slices. 2 mRNA for the alpha(2)delta subunits of Ca(2+) channels was found in rat cerebral cortex. 3 Nitric oxide (NO) synthesis estimated from cGMP formation was enhanced by KCl stimulation, which was mediated primarily by the activation of N- and P/Q-type Ca(2+) channels. Gabapentin blocked both types of Ca(2+) channels, and preferentially reversed the response to 30 mM K(+) stimulation compared with 50 mM K(+) stimulation. In contrast, verapamil preferentially inhibited the response to depolarization by the higher concentration (50 mM) of K(+). 4 Gabapentin inhibited KCl-induced elevation of intracellular Ca(2+) in primary neuronal culture. 5 Hypoxic injury was induced in cerebrocortical slices by oxygen deprivation in the absence (severe injury) or presence of 3 mM glucose (mild injury). Gabapentin preferentially inhibited mild injury, while verapamil suppressed only severe injury. omega-Conotoxin GVIA (omega-CTX) and omega-agatoxin IVA (omega-Aga) were effective in both models. 6 NO synthesis was enhanced in a manner dependent on the severity of hypoxic insults. Gabapentin reversed the NO synthesis induced by mild insults, while verapamil inhibited that elicited by severe insults. omega-CTX and omega-Aga were effective in both the cases. 7 Therefore, the data suggest that gabapentin and verapamil cause activity-dependent Ca(2+) channel blocking by different mechanisms, which are associated with their cerebroprotective actions and are dependent on the severity of hypoxic insults.

AM-36, a novel neuroprotective agent, profoundly reduces reactive oxygen species formation and dopamine release in the striatum of conscious rats after endothelin-1-induced middle cerebral artery occlusion

Elevated generation of reactive oxygen species (ROS) has been demonstrated during ischemia and reperfusion. Dopamine (DA) autooxidation may contribute to increased ROS generation. The novel neuroprotective agent AM-36 has antioxidant and Na(+) channel blocking activity and reduces neuronal damage in both cortex and striatum after middle cerebral artery (MCA) occlusion. Here we sought in vivo evidence of the ability of AM-36 to inhibit intrastriatal ROS generation and DA release after ischemia. Salicylate hydroxylation coupled with in vivo microdialysis in the striatum of conscious Long Evans rats was performed during MCA occlusion by perivascular microinjection of endothelin-1 (ET-1). AM-36 (6 mg/kg) was administered intraperitoneally 30 min after MCA occlusion. Dialysates were analysed using high performance liquid chromatography with electrochemical detection for the salicylate hydroxylation product, 2,3-dihydroxybenzoic acid (2,3 DHBA) and for DA and metabolites. MCA occlusion resulted in a marked increase in 2,3 DHBA and a secondary increase in all analytes, 180-300 min later. Increased DA release coincided with 2,3 DHBA formation. AM-36 significantly reduced ischemia induced increases in 2,3 DHBA and DA, and infarct volume in the striatum. Significant improvements in a battery of behavioural tests was also found in AM-36 treated rats. This study has demonstrated profound inhibition of ROS generation by a novel compound with antioxidant activity, administered post-ischemia in conscious rats.

DOPA cyclohexyl ester potently inhibits aglycemia-induced release of glutamate in rat striatal slices

Brain ischemic insult causes glutamate release and resultant neuronal cell death. We here show that L-3,4-dihydroxyphenylalanine (DOPA) is a positive regulatory factor for glutamate release elicited by a mild brain insult using in vitro superfused rat striatal slices as a model system. Glucose deprivation for 18 min elicited release of glutamate, DOPA and dopamine (DA). Either tetrodotoxin (TTX) (1 microM) or alpha-methyl-p-tyrosine (alpha-MPT) (1 mM), a tyrosine hydroxylase inhibitor reduced markedly each of these releases. NSD-1015 (20 microM), an aromatic L-amino acid decarboxylase inhibitor restored the inhibition by alpha-MPT of glutamate and DOPA but not DA release. DOPA cyclohexyl ester (DOPA CHE) (0.3-1 microM), a competitive DOPA antagonist, concentration-dependently suppressed aglycemia-induced glutamate release, the effect which was mimicked neither by S-sulpiride nor SCH23390, a DA D(1) or D(2) receptor antagonist, respectively. Zonisamide (1-1000 microM), an anticonvulsant or YM872 (1 microM), an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) a receptor antagonist produced no effect on aglycemia-induced glutamate release. DOPA CHE thus showed a relatively potent inhibitory action on aglycemia-induced glutamate release among several neuroprotective agents tested.

Pharmacology of ischemia-induced glutamate efflux from rat cerebral cortex in vitro

Simulated ischemic conditions (hypoxia-hypoglycaemia) in vitro enhanced glutamate efflux from rat cerebrocortical prisms. Here we characterised efflux mechanisms using pharmacological tools. The Na(+) channel blocker TTX (1 microM) did not affect ischemia-induced efflux, while sipatrigine (100 microM), a Na(+)/Ca(2+) channel blocker and omega-conotoxin MVIIC (2 microM), an N/P/Q type Ca(2+) channel blocker, inhibited efflux by fractions of 0.53 and 0.46, respectively (1.00 corresponding to total inhibition). Omission of extracellular Ca(2+) and addition of EGTA (2 mM) inhibited ischemia-induced efflux only during the first 25 min of incubation. A similar result was observed on omission of extracellular Ca(2+) together with addition of La(3+) (10 microM) and Mg(2+) (6 mM). TTX, sipatrigine and La(3+)/Mg(2+) all inhibited control efflux. Ischemia-induced efflux was sensitive to the volume activated anion channel inhibitor NPPB (100 microM) only after the first 25 min of incubation, with the maximal fraction inhibited being 0.54. The glutamate transporter inhibitor D,L-TBOA reduced ischemia-induced efflux throughout a 45-min incubation period, and enhanced efflux from control tissue. D,L-TBOA inhibited efflux at 30 min by a maximum fraction of 0.49, at 50 microM. These data indicate that the early phase of ischemia-induced glutamate efflux is in part Ca(2+) dependent, while the later phase involves volume activated anion currents and both phases involve excitatory amino acid transporters.

Down regulation of sodium channel Na(v)1.1 expression by veratridine and its reversal by a novel sodium channel blocker, RS100642, in primary neuronal cultures

This study investigated the effects of veratridine-induced neuronal toxicity on sodium channel gene (NaCh) expression in primary forebrain cultures enriched in neurons, and its reversal by a novel sodium channel blocker, RS100642. Using quantitative RT-PCR, our findings demonstrated the expression ratio of NaCh genes in normal fetal rat forebrain neurons to be Na(v)1.2 > Na(v)1.3 > Na(v)1.8 > Na(v)1.1 > Na(v)1.7 (rBII > rBIII > PN3 > rBI > PN1). Veratridine treatment of neuronal cells produced neurotoxicity in a dose-dependent manner (0.25-20 micro M). Neuronal injury caused by a dose of veratridine producing 80% cell death (2.5 micro M) significantly, and exclusively down-regulated the Na(v)1.1 gene. However, treatment of neurons with RS100642 (200 micro M) reversed the down-regulation of the Na(v)1.1 gene expression caused by veratridine. Our findings document for the first time quantitative and relative changes in the expression of various NaCh genes in neurons following injury produced by selective activation of voltage-gated sodium channels, and suggest that the Na(v)1.1 sodium channel gene may play a key role in the neuronal injury/recovery process.

Halothane attenuates the cerebroprotective action of several Na+ and Ca2+ channel blockers via reversal of their ion channel blockade

We have previously shown the involvement of Na(+) channel as well as N-type and P/Q-type Ca(2+) channels in the oxygen and glucose deprivation-induced injury in rat cerebrocortical slices. In the present study, we investigated the influence of halothane on the cerebroprotective effects of a variety of Na(+) and Ca(2+) channel blockers in rat cerebrocortical slices. The hypoxic injury was attenuated by Na(+) channel blockers including tetrodotoxin, lidocaine and dibucaine, and Ca(2+) channel blockers, such as verapamil, omega-agatoxin IVA and omega-conotoxin GVIA. Halothane abolished the protective effects of lidocaine, dibucaine and verapamil, all of which block the respective cation channels in a voltage-dependent manner, without affecting the actions of tetrodotoxin, omega-agatoxin IVA and omega-conotoxin GVIA, which reveal voltage-independent blockade. On the other hand, the nitric oxide synthesis estimated from the extracellular cyclic GMP formation was elevated during exposure to hypoxia. All channel blockers tested here attenuated hypoxia-evoked nitric oxide synthesis. Halothane blocked almost completely these actions of lidocaine and verapamil. Moreover, the Na(+) and Ca(2+) channel blockade by these compounds, as determined by veratridine- and KCl-stimulated nitric oxide synthesis, respectively, was also reversed by halothane. These findings suggest that an anesthetic agent halothane reversed the Na(+) and Ca(2+) channel blockade of several voltage-dependent ion channel blockers, leading to the attenuation of their cerebroprotective actions. Therefore, the influence of halothane anesthesia should be taken into consideration for the evaluation of neuroprotective action of Na(+) and Ca(2+) channel blockers.

Organotypic brain-slice cultures from adult rats: approaches for a prolonged culture time

Animal experiments are widely used in neurobiological and neuropharmacological research. Today, juvenile brain organotypic slice cultures have partially replaced in vivo experiments, but there is no adequate in vitro counterpart for the adult brain. The present study was aimed at the long-term culture of physiologically intact hippocampal slices from adult rats, by improving the conditions for preparation and culture, and the development of a new culture medium. A cerebrospinal fluid (CSF)-like medium was used, which was modified with a variety of supplements, including energy precursors, free-radical scavengers, and compounds known to inhibit neurotoxicity. The population spike amplitude (PSA) was used as a measure of viability, and amplitudes larger than 1mV indicated viable cultures. The addition of MK-801 during slice preparation improved PSA values during the first two days in vitro (DIV). Ascorbic acid and insulin prolonged the culture time up to DIV 4. FK-506 and vitamin E, alone or in combination, supported slice culture up to DIV 5. An increase in ATP, unless combined with vitamin E, and/or insulin, increased culture time up to DIV 6. Vitamins B(1), B(2), B(12) and D(2) had no effect. The modified CSF-like medium developed in this study permits the culture of adult hippocampal tissue for at least 6 days.

Molecular and pharmacological characterization of genes encoding urotensin-II peptides and their cognate G-protein-coupled receptors from the mouse and monkey

Urotensin-II (U-II) and its receptor (UT) represent novel therapeutic targets for management of a variety of cardiovascular diseases. To test such hypothesis, it will be necessary to develop experimental animal models for the manipulation of U-II/UT receptor system. The goal of this study was to clone mouse and primate preproU-II and UT for pharmacological profiling. Monkey and mouse preproU-II genes were identified to encode 123 and 125 amino acids. Monkey and mouse UT receptors were 389, and 386 amino acids, respectively. Genomic organization of mouse genes showed that the preproU-II has four exons, while the UT receptor has one exon. Although initially viewed by many exclusively as cardiovascular targets, the present study demonstrates expression of mouse and monkey U-II/UT receptor mRNA in extra-vascular tissue including lung, pancreas, skeletal muscle, kidney and liver. Ligand binding studies showed that [125I]h U-II bound to a single sites to the cloned receptors in a saturable/high affinity manner (Kd 654+/-154 and 214+/-65 pM and Bmax of 1011+/-125 and 497+/-68 fmol mg-1 for mouse and monkey UT receptors, respectively). Competition binding analysis demonstrated equipotent, high affinity binding of numerous mammalian, amphibian and piscine U-II isopeptides to these receptors (Ki=0.8 - 3 nM). Fluorescein isothiocyanate (FITC) labelled U-II, bound specifically to HEK-293 cells expressing mouse or monkey UT receptor, confirming cell surface expression of recombinant UT receptor. Exposure of these cells to human U-II resulted in an increase in intracellular [Ca2+] concentrations (EC50 3.2+/-0.8 and 1.1+/-0.3 nM for mouse and monkey UT receptors, respectively) and inositol phosphate (Ip) formation (EC50 7.2+/-1.8 and 0.9+/-0.2 nM for mouse and monkey UT receptors, respectively) consistent with the primary signalling pathway for UT receptor involving phospholipase C activation.

Differential pattern of expression of voltage-gated sodium channel genes following ischemic brain injury in rats

This study investigated the effects of brain ischemia on sodium channel gene (NaCh) expression in rats. Using quantitative RT-PCR, our findings demonstrated the expression ratio of NaCh genes in normal rat brain to be Na(v)1.1 > Na(v)1.8 > Na(v)1.3 > Na(v)1.7 (rBI > PN3 > rBIII > PN1). In contrast, brain injury caused by middle cerebral artery occlusion (MCAo) for 2 h followed by reperfusion significantly down-regulated Na(v)1.3 and Na(v)1.7 genes in both injured and contralateral hemispheres; whereas the Na(v)1.8 gene was down regulated in only the injured hemisphere (though only acutely at 2 or 2-6 h post-MCAo). However, the time-course of NaCh gene expression revealed a significant down-regulation of Na(v)1.1 only in the ischemic hemisphere beginning 6 h post-MCAo and measured out to 48 h post-MCAo. In a separate preliminary study Na(v)1.2 (rBII) gene was found to be expressed at levels greater than that of Na(v)1.1 in normal rats and was significantly down regulated at 24 h post-MCAo). Our findings document, for the first time, quantitative and relative changes in the expression of various NaCh genes following ischemic brain injury and suggest that the Na(v)1.1 sodium channel gene may play a key role in ischemic injury/recovery.

The AMPA receptor/Na(+) channel blocker BIIR 561 CL is protective in a model of global cerebral ischaemia

In this study, we investigated whether the novel neuroprotective compound dimethyl-[2-[2-(3-phenyl-[1,2,4]oxadiazol-5-yl)-phenoxy]-ethyl]-amine hydrochloride, BIIR 561 CL, a combined non-competitive antagonist of AMPA receptors and blocker of voltage-gated Na+ channels, is protective in a rat model of severe global ischaemia. BIIR 561 CL administered immediately after 10 min of ischaemia (occlusion of both carotid arteries plus reduction of arterial blood pressure to 38-40 mm Hg) significantly reduced hippocampal damage at 4 x 26.8 mg/kg (subcutaneous injections). The competitive AMPA receptor antagonist 2,3-dihydro-6-nitro-7-sulfamoyl-benz(F)quinoxaline, NBQX, was used as a reference compound and was protective at 3x30 mg/kg (intraperitoneal and/or subcutaneous administration). BIIR 561 CL significantly reduced the ischaemia-induced premature mortality from 33.6% in the controls to 14.3%, whereas NBQX treatment had no statistically significant effect.Thus, BIIR 561 CL could be shown to reduce hippocampal damage and premature mortality in a model of severe global ischaemia. A compound with these properties might be an interesting candidate for the treatment of disorders related to global cerebral ischaemia in man.

The use-dependent sodium channel blocker mexiletine is neuroprotective against global ischemic injury

Mechanisms responsible for anoxic/ischemic cell death in mammalian CNS grey and white matter involve an increase in intracellular Ca2+, however the routes of Ca2+ entry appear to differ. In white matter, pathological Ca2+ influx largely occurs as a result of reversal of Na+-Ca2+ exchange, due to increased intracellular Na+ and membrane depolarization. Na+ channel blockade has therefore been logically and successfully employed to protect white matter from ischemic injury. In grey matter ischemia, it has been traditionally presumed that activation of agonist (glutamate) operated and voltage dependent Ca2+ channels are the primary routes of Ca2+ entry. Less attention has been directed towards Na+-Ca2+ exchange and Na+ channel blockade as a protective strategy in grey matter. This study investigates mexiletine, a use-dependent sodium channel blocker known to provide significant ischemic neuroprotection to white matter, as a grey matter protectant. Pentobarbital (65 mg/kg) anesthetized, mechanically ventilated Sprague-Dawley rats were treated with mexiletine (80 mg/kg, i.p.). Then 25 min later the animals were subjected to 10 min of bilateral carotid occlusion plus controlled hypotension to 50 Torr by temporary partial exsanguination. Animals were sacrificed with perfusion fixation after 7 days. Ischemic and normal neurons were counted in standard H&E sections of hippocampal CA1 and the ratio of ischemic to total neurons calculated. Mexiletine pre-treatment reduced hippocampal damage by approximately half when compared to control animals receiving saline alone (45 vs. 88% damage, respectively; P<0.001). These results suggest that mexiletine (and perhaps other drugs of this class) can provide protection from ischemia to grey matter as well as white matter.

Characterization of endogenous amino acid efflux from hippocampal slices during chemically-induced ischemia

Using sodium (NaN3)-induced anoxia plus aglycaemia as a model of chemically-induced ischemia, we have characterized the endogenous release of excitatory and inhibitory amino acids from superfused hippocampal slices. Chemical ischemia produced an azide (1-30 mM) dose-dependent increase in the efflux of glutamate, aspartate and GABA. These increases were attenuated to varying degrees by removal of Ca2+, or the addition of the voltage dependent Na+-channel blocker tetrodotoxin (TTX), the selective Ca2+ channel blockers conotoxin MVIIA, MVIIC, and nifedipine, the NMDA antagonist MK801, the AMPA antagonist GYKI-52466. Similarly, addition of the GLT-1 glutamate transport inhibitor dihydrokainate (DHK) and the anti-estrogen/anion channel blocker tamoxifen also attenuated the efflux of glutamate and GABA. It would therefore appear that the increases in amino acid efflux induced by chemical ischemia originates from both the neuronal pool, via conventional exocytotic release, and glial sources via reversal of the GLT-1 transporter and anion channel regulated cell swelling.

Cerebroprotective action of a Na+/Ca2+ channel blocker NS-7. I. Effect on the cerebral infarction and edema at the acute stage of permanent middle cerebral artery occlusion in rats

The effect of a novel Na+/Ca2+ channel blocker NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride] on the cerebral infarction, edema and brain energy metabolism was investigated in rats after permanent middle cerebral artery occlusion (MCAO). The infarction and brain water content were evaluated at 48 h and 24 h after MCAO, respectively. A single bolus injection of NS-7 (0.03125-0.25 mg/kg) immediately after MCAO produced a dose-dependent reduction in the infarct volume as well as edema both in the cerebral cortex and striatum. Glycerol (4 g/kg) also decreased water content both in the occluded and non-occluded brain, but it did not reduce the size of cerebral infarction. Unlike glycerol, NS-7 did not change the water content in non-occluded brain. Moreover, a significant protective action was still observed even when NS-7 was injected once at 12 h after occlusion. In addition, NS-7 significantly reversed the decrease in tissue ATP content observed at 3 h but not at 0.5 h after MCAO. These findings suggest that a Na+/Ca2+ channel blocker NS-7 protects cerebral tissues against ischemic insults by improving the disturbance of cerebral energy metabolism and suppressing the cerebral edema.

Characterization of transient focal ischemia-induced increases in extracellular glutamate and aspartate in spontaneously hypertensive rats

Using middle cerebral artery occlusion (MCAO) and in vivo microdialysis, we have evaluated the changes in extracellular concentrations of the excitatory amino acids (EAA) glutamate and aspartate during varying periods of MCAO (0, 30, 60 min) in the striatum of spontaneously hypertensive rats (SHR). A positive correlation between occlusion time-dependent elevations in EAAs and the resulting ischemic injury was observed. This is the first demonstration of the temporal profile of EAA efflux during transient focal ischemia in SHRs. Possible sources and mechanisms of ischemia-induced EAA efflux were examined during 60 min of MCAO. Removal of Ca(2+) from the microdialysis infusion media significantly attenuated ischemia-induced increases in both glutamate (from ischemic peak of 4892 +/- 1298 to 1144 +/- 666% of preischemic values) and aspartate (from 2703 +/- 682 to 2090 +/- 599% of preischemic values). Similarly, infusion of the voltage dependent Na(+) channel blocker tetrodotoxin (TTX; 10 microM) significantly attenuated MCAO-induced increases in glutamate (to 1313 +/- 648%) and aspartate (to 359 +/- 114%). Infusion of the GLT-1 selective nontransportable inhibitor, dihydrokainate (DHK; 1 mM) also significantly attenuated the ischemia-induced increases in both EAAs (1285 +/- 508 and 1366 +/- 741% of the preischemic levels, respectively). These results indicate that during transient focal ischemia the increase in extracellular EAAs originates from both the neuronal pool, via conventional exocytotic release, and glial sources via the reversal of the GLT-1 transporter.

Role of sodium channel inhibition in neuroprotection: effect of vinpocetine

Vinpocetine (ethyl apovincaminate) discovered during the late 1960s has successfully been used in the treatment of central nervous system disorders of cerebrovascular origin for decades. The increase in the regional cerebral blood flow in response to vinpocetine administration is well established and strengthened by new diagnostical techniques (transcranial Doppler, near infrared spectroscopy, positron emission tomography). The latest in vitro studies have revealed the effect of the compound on Ca(2+)/calmodulin dependent cyclic guanosine monophosphate-phosphodiesterase 1, voltage-operated Ca(2+) channels, glutamate receptors and voltage dependent Na(+)-channels; the latest being especially relevant to the neuroprotective action of vinpocetine. The good brain penetration profile and heterogenous brain distribution pattern (mainly in the thalamus, basal ganglia and visual cortex) of labelled vinpocetin were demonstrated by positron emission tomography in primates and man. Multicentric, randomized, placebo-controlled clinical studies proved the efficacy of orally administered vinpocetin in patients with organic psychosyndrome. Recently positron emission tomography studies have proved that vinpocetine is able to redistribute regional cerebral blood flow and enhance glucose supply of brain tissue in ischemic post-stroke patients.

Broad-spectrum cation channel inhibition by LOE 908 MS reduces infarct volume in vivo and postmortem in focal cerebral ischemia in the rat

Cation channels conduct calcium, sodium and potassium, cations that are likely deleterious in the evolution of focal ischemic injury. We studied the effects of a novel, broad-spectrum inhibitor of several cation channels, LOE 908 MS, on acute ischemic lesion development with diffusion-weighted magnetic resonance imaging (DWI) and on cerebral perfusion with perfusion imaging (PI) in vivo and on cerebral infarct size using 2,3,5-triphenyltetrazolium chloride (TTC) staining postmortem. A total of 18 male Sprague-Dawley rats underwent 90 min of middle cerebral artery occlusion (MCAO) and were randomly and blindly assigned to either LOE 908 MS or vehicle starting 30 min after inducing focal ischemia and continuing for 4 h. Whole-brain DWI and multislice PI were done before initiation of treatment and repeated frequently for the next 3.5 h. DWI-derived lesion volume at 4 h showed a significant difference in favor of the drug treated group (P=0.03), whereas PI-derived perfusion deficit volumes did not significantly differ between the groups. The postmortem infarct volume at 24 h was significantly attenuated in the treated group in comparison to controls (P=0.0001) and neurological score was significantly better in the treated group (P<0.02). Blocking several distinct cation channels with LOE 908 MS significantly reduced infarct size and improved neurological outcome without observable adverse effects in this focal ischemia model.

Role of voltage-gated Na+ channels in hypoxia-induced neuronal injuries

1. Mammalian neurons in the central nervous system are vulnerable to oxygen deprivation. In clinical conditions, such as stroke or apnoea, permanent loss of neuronal functions can occur within minutes of severe hypoxia. 2. Recent studies have focused on the role of Na+ in acute neuronal responses to hypoxia. These studies have shown that the influx of extracellular Na+ is an important factor in hypoxia-induced injury and that blockade of voltage-gated Na+ channels reduces hypoxic responses and injury of neurons. Yet, the mechanism underlying the effect of blockade of Na+ channels on hypoxic injury is unclear. 3. The aim of the present review is to discuss the above topics given the current understanding of the role of Na+ channels in hypoxia and its implications on therapeutic strategy for preventing hypoxia-induced neurological damage. 4. It has been known that the maintenance of ionic homeostasis and membrane properties in neurons are improved by reducing the activity of voltaged-gated Na+ channels during acute hypoxia. 5. Recent studies suggest that persistent Na+ current and Na+-dependent exchangers may play a role in Na+ influx and neuronal injury during hypoxia. 6. The neuroprotective action of blockers of the Na+ channel may also be via the improved maintainance of intracellular energy levels because the action is dependent on cellular energy levels and extracellular glucose during hypoxia. 7. Hence, the blockade of voltage-gated Na+ channels reduces the excitability of neurons, Na+ influx and the accumulation of intracellular Na+. These improve the ionic homeostasis and cellular energy levels and, thus, prevent hypoxia-induced neuronal injury and neuronal damage mediated by Ca2+ overload.

T-477, a novel Ca(2+)- and Na(+) channel blocker, prevents veratridine-induced neuronal injury

To evaluate the effect of (R)-(+)-2-(4-chlorophenyl)-2, 3-dihydro-4-diethyl aminoacetyl-4H-1,4-benzothiazine hydrochloride (T-477), a novel Na(+)- and Ca(2+) channel blocker, on neuronal injury in vitro, we studied veratridine-induced injury in cultured rat hippocampal neurons. Neurons swelled extensively 10 min after the addition of veratridine, and returned to their initial size within 2 h. Intracellular Na(+) and Ca(2+) concentrations and amino acid release from the cells, in particular, that of glutamate, increased after the treatment with veratridine. Approximately 70% of neurons died within 24 h. T-477 inhibited both veratridine-induced swelling and death in a concentration-dependent manner. Moreover, T-477 concentration dependently reduced the increases in Na(+) and Ca(2+) influx and amino acid release. These results suggest that T-477 prevented the veratridine-induced influx of Na(+) and, thereby, reduced neuronal swelling. This, combined with the effects of T-477 on the inhibition of Ca(2+) influx and glutamate release, possibly by the blockade of Na(+) channels, may be the mechanism by which T-477 protects neurons from death induced by veratridine.

Quantitative evaluation of extracellular glutamate concentration in postischemic glutamate re-uptake, dependent on brain temperature, in the rat following severe global brain ischemia

Changes in brain temperature are known to modulate the marked neuronal damage caused by an approximately 10-min intra-ischemic period. Numerous studies have suggested that the extracellular glutamate concentration ([Glu](e)) in the intra-ischemic period and the initial postischemia period is strongly implicated in such damage. In this study, the effects of intra-ischemic brain temperature (32, 37, 39 degrees C) on [Glu](e) were investigated utilizing a dialysis electrode combined with ferrocene bovine serum albumin (BSA), which allows oxygen-independent real-time measurement of [Glu](e). This system allowed separate quantitative evaluation of intra-ischemic biphasic glutamate release from the neurotransmitter and metabolic pools, and of postischemic glutamate re-uptake in ischemia-reperfusion models. The biphasic [Glu](e) elevation in the intra-ischemic period did not differ markedly among intra-ischemic brain temperatures ranging from 32 to 39 degrees C. Intra-ischemic normothermia (37 degrees C) and mild hyperthermia (39 degrees C) markedly inhibited [Glu](e) re-uptake during the postischemic period, although the intra-ischemic [Glu](e) elevation did not differ from that during intra-ischemic hypothermia (32 degrees C). It was assumed that normothermia or mild hyperthermia in the intra-ischemic period influences intracellular functional abnormalities other than the intra-ischemic [Glu](e) elevation, thereby inhibiting glutamate re-uptake after reperfusion rather than directly modulating intra-ischemic [Glu](e) dynamics.

The protective action of tetrodotoxin and (+/-)-kavain on anaerobic glycolysis, ATP content and intracellular Na+ and Ca2+ of anoxic brain vesicles

Because recent reports point to Na+ channel blockers as protective agents directed against anoxia-induced neuronal damage including protection of anaerobic glycolysis, the influences of tetrodotoxin (TTX) and (+/-)-kavain on anoxic rat brain vesicles were investigated with respect to lactate synthesis, vesicular ATP content and cytosolic free Na+ and Ca2+ ([Na+]i, [Ca2+]i), both of the latter determined fluorometrically employing SBFI and FURA-2, respectively. After anoxia, basal lactate production was increased from 2.9 to 9.8 nmol lactate/min/mg protein. Although lactate synthesis seemed to be stable for at least 45 min of anoxia, as deduced from the linearity of lactate production, the ATP content declined continuously with a half life (tau 1/2) of 14.5 min, indicating that anaerobic glycolysis was insufficient to cover the energy demand of anoxic vesicles. Correspondingly, [Na+]i and [Ca2+]i increased persistently after anoxia by 22.1 mmol/l Na+ and 274.9 nmol/l Ca2+, determined 6.3 min after onset. An additional stimulation of vesicles with veratridine accelerated the drop of ATP (tau 1/2 = 5.1 min) and provoked a massive Na+ overload, which levelled off to 119 mmol/l Na+ within a few minutes. Concomitantly, [Ca2+]i increased linearly with a rate of 355 nmol Ca2+/l/min. Despite the massive perturbation of ion homeostasis, lactate production was unaffected during the first 8 min of veratridine stimulation. However, complete inhibition of lactate synthesis took place 30 min after veratridine was added. The Na+ channel blockers TTX and (+/-)-kavain, if applied before anoxia, preserved vesicular ATP content, diminished anoxia-induced increases in [Na+]i and [Ca2+]i and prevented both the veratridine-induced increases of [Na+]i and [Ca2+]i and the inhibition of lactate production. The data indicate a considerable Na+ influx via voltage-dependent Na+ channels during anoxia, which speeds up the decline in ATP and provokes an increase in [Ca2+]i. A massive Na+ and Ca2+ overload induced by veratridine failed to influence lactate synthesis directly, but initiated its inhibition.

Sodium overload through voltage-dependent Na(+) channels induces necrosis and apoptosis of rat superior cervical ganglion cells in vitro

Using the failure to exclude trypan blue as a criterion for cell death, we found that veratridine, the voltage-dependent Na(+) channel activator, exerted its toxicity to cultured sympathetic neurons in a dose-dependent manner (half-maximal toxicity occurred at 2 microM). The co-presence of tetrodotoxin completely reversed the toxicity only at concentrations of veratridine < 20 microM. Veratridine neurotoxicity was due to the influx of Na(+); a medium low in Na(+) (36 mM) completely abolished its neurotoxicity, whereas a Ca(2+)-free medium did not attenuate its neurotoxicity. Furthermore, the buffering action of 1, 2-Bis-(2-aminophenoxy)ethane-N,N,N',N',-tetraacetate (BAPTA) on veratridine-induced increase in intracellular Ca(2+) levels neither blocked veratridine neurotoxicity in normal medium, nor attenuated the low Na(+) effect. Elevated K(+) effectively blocked veratridine neurotoxicity in a Ca(2+)-dependent manner. Cytoplasmic pH measurements using a fluorescent pH indicator demonstrated that cellular acidification (from pH 7.0 to pH 6.5) occurred upon treatment with veratridine. Both veratridine-induced acidification and cell death were ameliorated by 5-(N-ethyl-N-isopropyl)amiloride, the specific inhibitor of the Na(+)/H(+) exchanger (IC(50) = 0.5 microM). Finally, necrosis occurred predominantly in veratridine neurotoxicity, but both staining with bis-benzimide and TUNEL analysis showed nuclear features of apoptosis in sympathetic neurons undergoing cell death.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Calcitonin gene-related peptide receptor independently stimulates 3',5'-cyclic adenosine monophosphate and Ca2+ signaling pathways

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse biological properties including potent vasodilating activity. Recently, we reported the cloning of complementary DNAs (cDNAs) encoding the human and porcine CGRP receptors which share significant amino acid sequence homology with the human calcitonin receptor, a member of the recently described novel subfamily of G-protein-coupled 7TM receptors. Activation of this family of receptors has been shown to result in an increase in intracellular cAMP accumulation and calcium release. In this study, we demonstrate that HEK-293 cells expressing recombinant CGRP receptors (HEK-293HR or PR) respond to CGRP with increased intracellular calcium release (EC50 = 1.6 nM) in addition to the activation of adenylyl cyclase (EC50 = 1.4 nM). The effect of CGRP on adenylyl cyclase activation and calcium release was inhibited by CGRP (8-37), a CGRP receptor antagonist. Both effects were mediated by cholera toxin-sensitive G-proteins, but these two signal transduction pathways were independent of each other. While cholera toxin pretreatment of HEK-293PR cells resulted in permanent activation of adenylyl cyclase, the same pretreatment resulted in an inhibition of CGRP-mediated [Ca2+]i release. Pertussis toxin was without effect on CGRP-mediated responses. In addition, CGRP-mediated calcium release appears to be due to release from a thapsigargin-sensitive intracellular calcium pool. These results show that the recombinant human as well as porcine CGRP receptor can independently increase both cAMP production and intracellular calcium release when stably expressed in the HEK-293 cell line.

Cellular protection mechanisms against extracellular heme. heme-hemopexin, but not free heme, activates the N-terminal c-jun kinase

Hemopexin protects cells lacking hemopexin receptors by tightly binding heme abrogating its deleterious effects and preventing nonspecific heme uptake, whereas cells with hemopexin receptors undergo a series of cellular events upon encountering heme-hemopexin. The biochemical responses to heme-hemopexin depend on its extracellular concentration and range from stimulation of cell growth at low levels to cell survival at otherwise toxic levels of heme. High (2-10 microM) but not low (0.01-1 microM) concentrations of heme-hemopexin increase, albeit transiently, the protein carbonyl content of mouse hepatoma (Hepa) cells. This is due to events associated with heme transport since cobalt-protoporphyrin IX-hemopexin, which binds to the receptor and activates signaling pathways without tetrapyrrole transport, does not increase carbonyl content. The N-terminal c-Jun kinase (JNK) is rapidly activated by 2-10 microM heme-hemopexin, yet the increased intracellular heme levels are neither toxic nor apoptotic. After 24 h exposure to 10 microM heme-hemopexin, Hepa cells become refractory to the growth stimulation seen with 0.1-0.75 microM heme-hemopexin but HO-1 remains responsive to induction by heme-hemopexin. Since free heme does not induce JNK, the signaling events, like phosphorylation of c-Jun via activation of JNK as well as the nuclear translocation of NFkappaB, G2/M arrest, and increased expression of p53 and of the cell cycle inhibitor p21(WAF1/CIP1/SDI1) generated by heme-hemopexin appear to be of paramount importance in cellular protection by heme-hemopexin.