Effect of Pharmacological Modulation of Activity of Metabotropic Glutamate Receptors on Their Gene Expression after Excitotoxic Damage in Hippocampal Neurons.

Microinjection of kainic acid into rat hippocampus causes excitotoxic neuronal damage predominantly in the CA3 and CA1 fields. These lesions can be significantly reduced by simultaneous administration of MPEP, a negative allosteric modulator of type 5 metabotropic glutamate receptors, and LY354740, an agonist of type 2 metabotropic glutamate receptors. The decrease in neuronal death in the hippocampus during pharmacological modulation was paralleled by adaptive changes in gene expression. In the hippocampus, gene expression of type 5 postsynaptic metabotropic glutamate receptor was close to the control level, and in the frontal cortex expression of the gene of α1-subunit of the GABAA receptor returned to normal. In the frontal cortex, a reciprocal relationship was observed for type 2 metabotropic glutamate receptor: expression of the corresponding gene decreased in response to pharmacological activation.

Expression of metabotropic glutamate receptors after hippocampal injury.

The expression of metabotropic glutamate receptors (mGluR2, mGluR3, mGluR4, and mGluR5) and dendritic cytoplasmic BC1 RNA in the hippocampus and frontal neocortex of Wistar rats was studied 1 and 4 weeks after intrahippocampal microinjection of kainic acid. The efficiency of glutamatergic transmission was shown to change not only in the injured hippocampus, but also in the neocortex. It was associated with variations in the expression of presynaptic (mGluR2, mGluR3, and mGluR4) and postsynaptic receptors (mGluR5).

[Peculiarities of neurodegeneration in hippocampus fields after kainic acid action in rats].

Comparison between results of different ways of application of excitotoxin (kainic acid, KA), intrahippocampal (0.2 µg/µl) and intraventricular (0.6 µg/µl), was carried out in the course of investigations of the prolonged action of KA on the morphological state of various fields in dorsal hippocampus. Light microscopy with Cresyl Violet staining and fluorescent microscopy with staining by fluoro-jade B were used in our researches. The results revealed that KA, being injected intrahippocampally at a dose, which does not result in animal epileptization, caused obvious degenerative phenomena in hippocampus. Two weeks after KA injection the layers of pyramid cells in the fields CA3 and CA4 were absent, and in four weeks, degenerative changes and cell lysis were spread on the CA1 field as well. Four weeks after KA intraventricular administration in rats with epileptic status the damages of various levels were observed in hippocampus, from partial injuries of pyramid neurons in the fields CA3 and CA4 up to full loss of layers of pyramids in the fields CA1, CA3 and CA4. In both ways of KA injection, in the CA2 field the layer of cells mainly remained undamaged what indicates a special role of this field. After a single-time KA administration the both ways of injection led to the long-term damages of a neural tissue, possibly, of a general character, but differing in rates of neuron reactions in different fields to the damaging factor. An explanation of the prolonged action of KA excitotoxicity might be in the activation of GluR6-containing kainate receptors in pyramid neurons in CA3 field which brings to chronic character in single-time KA action and promotes the destruction of the remaining neurons by necrotic way while at the initial stage of KA influence the neurons perish by apoptotic way.

Memory disorders in rats after impairment of the dorsal hippocampal CA3 field with kainic acid.

We studied the possibility of conditioning of food-procuring response in animals after impairment of the dorsal hippocampal region with kainic acid. Histological studies of brain sections showed that the greater part of dorsal hippocampal CA3 pyramidal neurons were lyzed in 2 weeks after kainic acid microinjection into the hippocampus. Morphological signs of necrosis were found in CA2 and CA4 neurons at the interface with CA3 field. Preinjection of anti-inflammatory cytokine IL-10 virtually did not prevent neuronal death. Damage to the hippocampus impaired learning of experimental animals and they required more attempts for reliable performance of the skill than the controls. Short-term memory of experimental rats was retained, which was proven by the results of single-day training. It was hypothesized that memory dysfunctions in animals after damage to the dorsal hippocampal CA3 field and to the hippocampus in general are determined by impaired transition of short-term into long-term memory.

[Monoclonal antibodies to type A, B, E and F botulinum neurotoxins].

Mouse monoclonal antibodies against the most acutely toxic substances, botulinum neurotoxins (BoNTs) of types A, B, E, and F, was generated and characterized, that recognize their respective toxins in natural toxin complex. Based on these antibodies, we developed sandwich-ELISA for quantitative detection of these toxins. For each respective toxin the detection limit of the assay was: BoNT/A - 0.4 ng/ml, BoNT/B - 0.5 ng/ml; BoNT/E - 0.1 ng/ml; and for BoNT/F - 2.4 ng/ml. The developed assays permitted quantitative identification of the BoNTs in canned meat and vegetables. The BNTA-4.1 and BNTA-9.1 antibodies possessed neutralizing activity against natural complex of the botulinium toxin type A in vivo, both individually and in mixture, the mixture of the antibodies neutralized the higher dose of the toxin. The BNTA-4.1 antibody binds specifically the light chain (the chain with protease activity) of the toxin, whereas BNTA-9.1 interacts with the heavy chain. We believe that the BNTA-4.1 and BNTA-9.1 monoclonal antibodies are prospective candidates for development of humanized therapeutic antibodies for treatment of BoNT/A-caused botulism.

[Metabotropic glutamate receptors as targets for new drug development].

The review is devoted to experimental investigations of metabotropic glutamate receptors and the properties of drugs (ligands) belonging to agonists, antagonists, and modulators of the activity of these receptors. Possibilities of the treatment of neurodegenerative disorders, cognitive disturbances in schizophrenia patients, and narcotic dependency by using drugs of this class are considered.