dizocilpine-maleate and trimethyltin

The organotin trimethyltin (TMT) is known to cause neuronal degeneration in the central nervous system. A systemic injection of TMT produced neuronal damage in the cerebral frontal cortex of mice. To elucidate the mechanism(s) underlying the toxicity of TMT toward neurons, we prepared primary cultures of neurons from the cerebral cortex of mouse embryos for use in this study. Microscopic observations revealed that a continuous exposure to TMT produced neuronal damage with nuclear condensation in an incubation time-dependent manner up to 48 h. The neuronal damage induced by TMT was not blocked by N-methyl-D-aspartate receptor channel-blocker MK-801. The exposure to TMT produced an elevation of the phosphorylation level of c-Jun N-terminal kinase (JNK)(p46), but not JNK(p54), prior to neuronal death. Under the same conditions, a significant elevation was seen in the phosphorylation level of stress-activated protein kinase 1, which activates JNKs. Furthermore, TMT enhanced the expression and phosphorylation of c-Jun during a continuous exposure. The JNK inhibitor SP600125 was effective in significantly but only partially attenuating the TMT-induced nuclear condensation and accumulation of lactate dehydrogenase in the culture medium. Taken together, our data suggest that the neuronal damage induced by TMT was independent of excitotoxicity but that at least some of it was dependent on the JNK cascades in primary cultures of cortical neurons.

Topics: Animals; Anthracenes; Cell Survival; Cells, Cultured; Cerebral Cortex; Dizocilpine Maleate; Enzyme Activation; Fungicides, Industrial; Immunoblotting; Injections, Intraperitoneal; JNK Mitogen-Activated Protein Kinases; Male; MAP Kinase Kinase 4; Mice; Mice, Inbred Strains; N-Methylaspartate; Nerve Degeneration; Neurons; Phosphorylation; Time Factors; Trimethyltin Compounds

Activation of NMDA receptors has been shown to induce either neuronal cell death or neuroprotection against excitotoxicity in cultured cerebellar granule neurons in vitro. We have investigated the effects of pretreatment with NMDA on kainate-induced neuronal cell death in mouse hippocampus in vivo. The systemic administration of kainate (30 mg/kg), but not NMDA (100 mg/kg), induced severe damage in pyramidal neurons of the hippocampal CA1 and CA3 subfields 3-7 days later, without affecting granule neurons in the dentate gyrus. An immunohistochemical study using an anti-single-stranded DNA antibody and TdT-mediated dUTP nick end labeling analysis both revealed that kainate, but not NMDA, induced DNA fragmentation in the CA1 and CA3 pyramidal neurons 1-3 days after administration. Kainate-induced neuronal loss was completely prevented by the systemic administration of NMDA (100 mg/kg) 1 h to 1 day previously. No pyramidal neuron was seen with fragmented DNA in the hippocampus of animals injected with kainate 1 day after NMDA treatment. The neuroprotection mediated by NMDA was prevented by the non-competitive NMDA receptor antagonist MK-801. Taken together these results indicate that in vivo activation of NMDA receptors is capable of protecting against kainate-induced neuronal damage through blockade of DNA fragmentation in murine hippocampus.

Topics: Animals; Behavior, Animal; Cytoprotection; Dizocilpine Maleate; DNA Fragmentation; Excitatory Amino Acid Antagonists; Hippocampus; Injections, Intraperitoneal; Kainic Acid; Male; Mice; Mice, Inbred Strains; N-Methylaspartate; Neuroprotective Agents; Neurotoxins; Pyramidal Cells; Receptors, N-Methyl-D-Aspartate; Transcription Factor AP-1; Trimethyltin Compounds

In evaluating mechanisms of trimethyltin (TMT)-initiated neuronal damage, the present study focused on involvement of reactive oxygen species, protein kinase C (PKC), and glutamate receptors. Exposure of cerebellar granule cells to TMT (0.01-0.1 microM) produced primarily apoptosis, but higher concentrations were associated with cellular lactate dehydrogenase efflux and necrosis. TMT increased generation of cellular reactive oxygen species, which was inhibited by either L-NAME (inhibitor of nitric oxide synthase, NOS) or catalase, indicating that both NO and H(2)O(2) are formed on TMT exposure. Since chelerythrine (selective PKC inhibitor) also inhibited oxidative species generation, PKC appears to play a significant role in TMT-induced oxidative stress. The metabotropic glutamate receptor antagonist, MCPG, (but not MK-801) prevented oxidative species generation, indicating significant involvement of metabotropic receptors (but not NMDA receptors) in TMT-induced oxidative stress. NOS involvement in the action of TMT was confirmed through measurement of nitrite, which increased concentration dependently. Nitrite accumulation was blocked by L-NAME, chelerythrine, or MCPG, showing that NO is generated by TMT and that associated changes in NOS are regulated by a PKC-mediated mechanism. Oxidative damage by TMT was demonstrated by detection of elevated malondialdehyde levels. It was concluded that low concentrations of TMT (0.01-0.1 microM) cause apoptotic cell death in which oxidative signaling is an important event. Higher concentrations of TMT initiate necrotic death, which involves both an oxidative and a non-oxidative component. TMT-induced necrosis but not apoptosis in granule cells is mediated by glutamate receptors.

Topics: Alkaloids; Animals; Apoptosis; Benzophenanthridines; Catalase; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; In Situ Nick-End Labeling; L-Lactate Dehydrogenase; Necrosis; Neurons; NG-Nitroarginine Methyl Ester; Nitrites; Phenanthridines; Protein Kinase C; Rats; Reactive Oxygen Species; Receptors, Glutamate; Tetradecanoylphorbol Acetate; Thiobarbituric Acid Reactive Substances; Trimethyltin Compounds

In the present study we examined the presumable changes in the distribution of N-methyl-D-aspartate (NMDA) receptors in the hippocampus of rat exposed to a potent neurotoxic drug, trimethyltin (TMT). Using in vitro receptor binding autoradiography, [3H]MK801 labelling was determined at 7, 14, 21, 30 and 60 days after treatment with TMT (single dose of 8 mg/kg, i.p.) in various hippocampal areas thought to be affected by the neurotoxin. At 21-60 days after exposure, a decrease in receptor binding was observed in CA1 hippocampal subfield (10-20%, P< 0.05). A reduction in binding density also occurred in CA4/ CA3c, where labelling vanished completely at longer times. In the molecular layer (ML) of the dentate gyrus (DG), however, 16-37% (P<0.05) increase in receptor binding was found at 14-60 days postexposure. These results suggest that exposure to TMT leads to an altered topography of NMDA receptor density sites in the rat hippocampus. Dynamics of the reduction in receptor binding in CA4/CA3c and CA1 followed the development of the well-known degenerative effects induced by the neurotoxin. In contrast, the enhanced binding density in the ML of the DG may be a part of a mechanism of plastic response of granule cells to denervation/reinnervation.

Topics: Animals; Autoradiography; Dizocilpine Maleate; Hippocampus; Male; Neurons; Neurotoxins; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Time Factors; Trimethyltin Compounds; Tritium

Topics: Administration, Oral; Animals; Dizocilpine Maleate; Hippocampus; Male; Neurons; Pentylenetetrazole; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Seizures; Spermine; Trimethyltin Compounds