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.
Pernot
F
F
Département de Toxicologie, Centre de Recherches du Service de Santé des Armées, CRSSA, 24 Avenue des Maquis du Grésivaudan, B.P. 87, 38702 La Tronche cedex, France.
Carpentier
P
P
Baille
V
V
Testylier
G
G
Beaup
C
C
Foquin
A
A
Filliat
P
P
Liscia
P
P
Coutan
M
M
Piérard
C
C
Béracochea
D
D
Dorandeu
F
F
D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000473:pathology; D002800:Cholinesterase Inhibitors; D003213:Conditioning, Psychological; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography; D004827:Epilepsy / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D005239:Fear; D017781:Genes, Immediate-Early; D006624:Hippocampus / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D018782:Maze Learning; D051379:Mice; D008810:Mice, Inbred C57BL; D010507:Periodicity; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis / Q000235:genetics; D045442:Rotarod Performance Test; D012640:Seizures / Q000139:chemically induced / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology; D012999:Soman; D013997:Time Factors
D002800:Cholinesterase Inhibitors; D016760:Proto-Oncogene Proteins c-fos; D012999:Soman; D000110:Acetylcholinesterase