Intrahippocampal cholinesterase inhibition induces epileptogenesis in mice without evidence of neurodegenerative events.

The mechanisms of epileptogenesis remain largely unknown and are probably diverse. The aim of this study was to investigate the role of focal cholinergic imbalance in epileptogenesis. To address this question, we monitored electroencephalogram (EEG) activity up to 12 weeks after the injection of a potent cholinesterase (ChE) inhibitor (soman) at different doses (0.53, 0.75, 1, 2, 2.8, 4 and 11 nmol) into the right dorsal hippocampus of C57BL/6 mice. Different parameters were used to choose the dose for a focal model of epileptogenesis (mainly electrographic patterns and peripheral ChE inhibition). The pattern of neuronal activation was studied by Fos immunohistochemistry (IHC). Brain damage was evaluated by hemalun-phloxin, neuronal nuclei antigen IHC and silver staining. Glial fibrillary acidic protein IHC was used to evaluate astroglial reaction. Finally, long-term behavioral consequences were characterized. At the highest dose (11 nmol), soman quickly evoked severe signs, including initial seizures and promoted epileptogenesis in the absence of tissue damage. With lower doses, late-onset seizures were evidenced, after 1-4 weeks depending on the dose, despite the absence of initial overt seizures and of brain damage. Only a weak astroglial reaction was observed. Following injection of 1 nmol, Fos changes were first evidenced in the ipsilateral hippocampus and then spread to extrahippocampal areas. A selective deficit in contextual fear conditioning was also evidenced two months after injection. Our data show that focal hypercholinergy may be a sufficient initial event to promote epilepsy and that major brain tissue changes (cellular damage, edema, neuroinflammation) are not necessary conditions.

Molecular events involved in neuronal death induced in the mouse hippocampus by in-vivo injection of kainic acid.

Apoptosis results from the activation of a programmed cellular cascade involving several mechanisms. In the present study, we have investigated the implication of three molecules of this cascade, p53, Bax and caspase-3, in neuronal death induced by kainic acid (KA) administration in mouse hippocampus. Using immunocytochemistry, western blot and quantification of enzyme activity, we observed in p53+/+ and p53-/- animals that KA induced neuronal death by both p53-dependent and independent pathways. Moreover, apoptosis (labeled by TUNEL) and the increase of bax and caspase-3 protein expression after the neurotoxic insult appeared to clearly depend on p53 expression.

Acute exposure to a low or mild dose of soman: biochemical, behavioral and histopathological effects.

Effects of low to mild doses of soman on central and blood cholinesterase (ChE) activities and anxiety behavior were studied in mice 30 min, 24 h and 7 days after poisoning. At these two latter time points, histopathological consequences of soman intoxication were also studied. The 30-microg/kg dose of soman produced 30 min after intoxication, about 35% of central ChE inhibition, and an anxiolytic effect without toxic signs or histopathological changes. The 50-microg/kg dose of soman produced at the same time, about 56% of central ChE inhibition, slight clinical signs of poisoning without convulsions, an anxiogenic effect with a slight hypolocomotion but no brain damage. A mild dose of soman (90 microg/kg) produced at this same time point about 80% of central ChE inhibition, and led to ataxia and tremors in every mouse and to convulsions in some of them. Thirty minutes and 24 h after poisoning, the behavioral tests revealed neither anxiolytic nor anxiogenic responses despite a clear hypolocomotion. Only mice that experienced long-lasting convulsions developed neuropathological changes. The functional implication of our results, as well as the biological relevance of blood vs. brain ChE levels, as an index of intoxication severity are discussed.

p53 and Bax implication in NMDA induced-apoptosis in mouse hippocampus.

Seven days after in vivo intrahippocampal administration of NMDA, 3'-OH DNA fragmentations and Bax protein expression were detected in hippocampal neurons of p53+/+ but not p53-/- transgenic mice. Interestingly, neurons showing pycnosis, an early apoptotic phenomena, were present in all genotypes. These results confirm that apoptotic 3'OH DNA fragmentations and Bax protein induction during NMDA-induced apoptosis in adult hippocampal neurons are p53 dependent.

Medical management of organophosphate-induced seizures.

Recent studies concerning management of soman-induced seizures are reviewed. While drugs classically used against epilepsy in hospital appear ineffective against soman, muscarinic receptor blockers are shown to be able to prevent or stop seizures within the first 5 min after their onset. Benzodiazepine could also be considered as an emergency treatment useful during the first 10 min of seizure. Comparatively NMDA antagonists appear to be able to terminate soman-induced seizures even if the treatment is delayed after 40 min of epileptic activity. Drugs with both antimuscarinic and anti-NMDA properties may represent the most adequate pharmacological treatment to treat soman intoxication. However, the results obtained until now with these drugs must be completed in relation with their possible efficacy after i.m. administration. Propositions for future studies are reviewed.

c-fos antisense oligonucleotide prevents delayed induction of hsp70 mRNA after soman-induced seizures.

Previous studies have shown the successive expression of c-fos and hsp70 genes, especially in the hippocampal formation, during soman-induced seizures. In order to detect a possible link between the induction of these two genes, antisense strategies have been used. First, the ability of unilateral intrahippocampal infusion of c-fos antisense oligonucleotides to inhibit ipsilateral, seizure-related, c-FOS-like immunoreactivity, was verified. Second, induction of hsp70 mRNA was investigated using in situ hybridization. Unilateral inhibition of c-fos induction clearly reduced levels of hsp70 mRNA in the c-fos antisense-infused hippocampus relative to the non-infused contralateral side. Infusion of c-fos sense probe or vehicle did not affect bsp70 mRNA induction. This study suggests a role of c-FOS in regulating bsp70 mRNA induction.

Study of endemic scrapie in a flock of "Ile de France" sheep.

An "Ile de France" flock was studied over a period of 5 years. The authors found similar results concerning incidence and age of onset of scrapie to those found in the English literature. A close relationship was established between the age of the dam at parturition and the age of the progeny at onset of scrapie. In the later years of our study, scrapie was detected in younger animals than in the earlier years, suggesting a phenomenon of genetic "anticipation". Increased fecundity in this endemically affected flock might represent a form of selection which favorises the occurrence and maintenance of the disease within the flock.

[Blood serotonin and histamine in sheep with endemic scrapie: initial results]. / Sérotoninémie et histaminémie chez des ovins endémiquement atteints de tremblante (scrapie): premiers résultats.

The whole blood histamine levels of sheep without clinical scrapie but living in infected farms, control, and scrapie infected sheep are not significantly different. By contrast whole blood serotonin is decreased both in sheep living in infected farms and in scrapie-infected sheep as compared to controls. Thrombopenia may account for the hyposerotoninemia of sheep living in infected farms except those genetically linked to scrapie-infected sheep for which, as for scrapie-infected sheep, platelet serotonin appears also to be diminished. Whole blood serotonin determination might therefore be useful to detect sheep living in infected farms (these sheep probably play an important role in scrapie infection) and perhaps also humans with high susceptibility to Creutzfeldt-Jakob disease.

[The OLA major histocompatibility complex of sheep. Genetic frequencies compared in Prélpe sheep with and without scrapie]. / Le complexe majeur d'histocompatibilité OLA des ovins. Fréquences géniques comparées chez des moutons Préalpes atteints ou non de tremblante (scrapie).

The OLA genic frequencies were studied in both normal "Préalpe" Sheep and those affected with Scrapie. In the non-affected Sheep of contaminated flocks, frequencies were generally decreased, compared with frequencies of the same factors in sick Sheep or in non-infected controls. Three OLA-A genes significantly decreased; at this locus, results in "Préalpe" and "Ile-de-France" Sheep were inversed. This observation excludes OLA genes being involved in pathogeny or resistance to the disease, but suggests the existence of a linkage between the OLA loci and at least one resistance or susceptibility locus.