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This chapter reviews models of generalized seizures induced by systemic administration of chemical agents in adult rodents. Models of acute seizures induced by chemoconvulsants still represent a valuable research tool used for screening of putative antiseizure drugs, in the toxicology research investigating convulsant properties of naturally occurring and man-made toxins, as well as for studies on mechanisms of action of these convulsant drugs. Models using drugs affecting GABA-A receptor and GABA synthesis, excitatory amino acids, cholinergic agents including organophosphorus compounds, and other drugs, such as strychnine and aminophylline are presented and their major features are described. Information regarding solubility, dosing, and appropriate routes of administration are discussed and examples of seizure outcome are presented including EEG samples recorded in mice and rats.

The aim of this study was to evaluate how endocannabinoids interact with excitotoxic processes both in vitro, using primary neural cell cultures, and in vivo, in the TMEV-IDD model of multiple sclerosis. First, we observed that neuronal cells respond to excitotoxic challenges by the production of endocannabinoid molecules which in turn exerted neuroprotective effects against excitotoxicity. The inhibitor of endocannabinoid uptake, UCM707, protected specifically against AMPA-induced excitotoxicity, by activating CB1 and CB2 cannabinoid receptors, as well as the nuclear factor, PPARγ. This neuroprotective effect was reverted by blocking the glial glutamate transporter, GLT-1. Mice subjected to the model of multiple sclerosis showed a decrease in the expression of GLT-1. UCM707 reversed this loss of GLT-1 and induced a therapeutic effect. Our data indicate that the enhancement of the endocannabinoid tone leads to neuroprotection against AMPA-induced excitotoxicity and provides therapeutic effects in this model of multiple sclerosis. © 2009 Elsevier Inc. All rights reserved.

Brain glutamate uptake is catalyzed by a family of Excitatory Amino Acid Transporter (EAAT) proteins present in the plasma membranes, for review see …

The amino acid glutamate is considered to be the major excitatory neurotransmitter in the mammalian …

Brain glutamate uptake is catalyzed by a family of Excitatory Amino Acid Transporter (EAAT) proteins present in the plasma membranes, for review see …

Brain glutamate uptake is catalyzed by a family of Excitatory Amino Acid Transporter (EAAT) proteins present in the plasma membranes, for review see …

Brain glutamate uptake is catalyzed by a family of Excitatory Amino Acid Transporter (EAAT) proteins present in the plasma membranes, for review see …

Brain glutamate uptake is catalyzed by a family of Excitatory Amino Acid Transporter (EAAT) proteins present in the plasma membranes, for review see …

Publisher Summary This chapter discusses the methods used to study the pharmacological properties of L-[ 3 H]glutamate transport in crude synaptosomes and the limitations of this approach. Synaptosomes are a membrane fraction enriched in synaptic nerve terminals that have pinched off from the cell bodies and resealed. Based on electron microscopic studies, the synaptosomes contain mitochondria and are presumably capable of generating ATP, which maintains the electrochemical gradients required for transporter activity. Although this membrane fraction is enriched in nerve terminals, these preparations are generally thought to be contaminated with glial elements. These glial elements can reseal to form gliosome. Therefore, it is possible that the transport activities in these preparations are caused by an uptake into neuronal or glial elements. For glutamate transporters, this may be a significant issue because there are different subtypes of transporters expressed by glia and by neurons.

Publisher Summary The value of conformationally constrained analogs rests with the hypothesis that restricting the number of attainable conformations of a flexible, acyclic molecule, such as L-glutamate, should limit the number of glutamate binding sites with which the analog can interact, thereby increasing its selectivity as a pharmacological probe. Pharmacophore models have become tools in the development of the next generation analogs that is used to refine the models and identify more selectively acting agents, such as those that can distinguish among closely related transporter subtypes. This chapter explains the calculation of low energy conformations of acidic amino acids. To compare the structures of the active transport inhibitors, computational libraries of the energetically accessible conformations of each must be generated. From a practical point of view, this task must be carried out using molecular mechanics rather than higher levels of theory.

Antisense ODN are highly effective tools to selectively inhibit synthesis of glutamate transporter subtypes. They have been used to evaluate the biology of individual transporter subtypes in vivo and in vitro. Appropriate use of antisense ODN, however, requires a number of important controls to validate the specificity of their effects. Ultimately, the efficacy at inhibiting the synthesis of transporters proteins reflects several variables: the actual efficacy of the antisense to directly inhibit synthesis, the rate of degradation of the ODN, the rate of intracellular penetration of the ODN, the rate of new protein synthesis for the transporter subtype, and the actual penetration of the ODN into CNS tissue. The methods described in this chapter will help one to optimize each of these parameters.

Publisher Summary This chapter explores strategies approaches to in vitro neurotoxicity. The most obvious way to study neurotoxicity in vitro is to begin by examining the effects of known toxic agents. These substances are from a chemically diverse group, and this necessitates and allows a multipronged approach, which may elucidate a few final discrete common pathways leading to cell death. An in vitro test of neurotoxicity, which is simple to assay, yet physiologically complex and therefore, composed of a series of discrete biochemically definable steps, such as neurite outgrowth, is needed to test for the neurotoxic potential of such a wide range of substances. This chapter elaborates the effect of some known toxic substances including free radicals, excitatory amino acids, metals and metal complexes, acrylamide, etc. The chapter discusses in detail information on the postulated mode of action of some of the well-known neurotoxic compounds. The chapter also discusses use of disease models for Parkinsonism, amyotrophic lateral sclerosis and lathyrism, and some other diseases. The role of trophic factors in neuronal well-being is also discussed.

Publisher Summary For a rational drug design, it is essential to know (1) the physiological roles of glutamate transporters, (2) whether the transporters are subject to regulation, and (3) whether the transporters are heterogeneous in terms of functional properties and cellular and regional distributions. These issues are addressed in this chapter. The maintenance of a low level of external glutamate is one obvious function of the glutamate transporter. This function is crucial as glutamate becomes neurotoxic when its extracellular concentration exceeds a certain level. From the studies, it is suggested that the role of glutamate transporters is restricted to that of maintaining a favorable gradient for glutamate diffusion from the synaptic cleft. Because perturbations of the concentration of extracellular glutamate may be involved in many diseases, there is a need for drugs that can counteract such perturbations. Glutamate transporters are appropriate targets for such drugs as they play a central role in the maintenance of the extracellular glutamate level.

Publisher Summary Considerable evidence suggests that the cell dense region surrounding the midbrain aqueduct, the midbrain periaqueductal gray region (PAG), is a crucial neural substrate for the integration of an animal's reactions to threatening or stressful stimuli. This chapter describes the great diversity of PAG output functions that make an understanding of its functional organization prerequisite to the study of its neural organization. It considers the results of studies from laboratory that have employed the technique of intracerebral stimulation with excitatory amino acids (EAA) to map the diverse functional output zones that exist within the PAG. Results of anatomical studies of the PAG efferents, which may mediate certain outputs, have been considered in the chapter. Data pertaining to the afferent regulation of the functionally diverse PAG regions have also been discussed.

Publisher Summary This chapter describes the methods that have proved to be useful in the laboratory for injecting excitatory amino acids into discrete brain regions of rodents and for determining the extent of the resulting lesions. The chapter first presents the injection procedure. Because of its great potency, kainic acid (KA) has most frequently been employed to make localized excitotoxin lesions in the brain. The extent of the lesion can be controlled by varying the concentration of the amino acid solution, the volume of solution injected, and the rate of injection. Restricted excitotoxin lesions could be made equally well by microiontophoresis or with commercially available micropressure devices. Another method is the staining procedure. This procedure predominantly visualizes degenerating terminals and lysosomes. The rapid accumulation of lysosomes within degenerating somata presumably explains the ability of this procedure to visualize these structures as well. Few degenerating axons stain under the conditions described in the chapter. The procedure is very sensitive. One serious disadvantage is that only tissue that has been fixed in situ can currently be stained with this procedure. Therefore this method cannot be use ordinarily to verify lesions in animals from which tissue is taken for biochemical analysis.

Publisher Summary This chapter describes the methods that have proved to be useful in the laboratory for injecting excitatory amino acids into discrete brain regions of rodents and for determining the extent of the resulting lesions. The chapter first presents the injection procedure. Because of its great potency, kainic acid (KA) has most frequently been employed to make localized excitotoxin lesions in the brain. The extent of the lesion can be controlled by varying the concentration of the amino acid solution, the volume of solution injected, and the rate of injection. Restricted excitotoxin lesions could be made equally well by microiontophoresis or with commercially available micropressure devices. Another method is the staining procedure. This procedure predominantly visualizes degenerating terminals and lysosomes. The rapid accumulation of lysosomes within degenerating somata presumably explains the ability of this procedure to visualize these structures as well. Few degenerating axons stain under the conditions described in the chapter. The procedure is very sensitive. One serious disadvantage is that only tissue that has been fixed in situ can currently be stained with this procedure. Therefore this method cannot be use ordinarily to verify lesions in animals from which tissue is taken for biochemical analysis.

Publisher Summary This chapter discusses the metabolic imbalance and nerve cell damage in the brain. The chapter provides observations on the effects of excitatory amino acids (EAA) in model systems in vitro , because the relatively well-controlled experimental conditions may facilitate the better understanding of mechanisms underlying the neurotoxic action of EAA. Concerning the potential use of such agents in the treatment of perinatal brain damage, the trophic action of EAA transmitters on developing nerve cells must also be taken into account. This is evidently an over-simplification, as the different disorders have, besides common features, specific characteristics that must be taken into account and will influence treatment. Recent observations indicating that EAA during development may also have a trophic influence were described and it was emphasized that the effect of EAA (trophic or toxic or eliciting no response) depends on the stage of maturation of the nerve cells. Promising results from animal experiments indicate that information on mechanisms involved in cell injury induced by metabolic stress in the brain has important therapeutic implications.