Neurosteroids and epileptogenesis in the pilocarpine model: evidence for a relationship between P450scc induction and length of the latent period.
OBJECTIVE
Cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc) catalyzes the initial step in the biosynthesis of neurosteroids within the brain. We sought to determine which cells express P450cc and whether neurosteroids play a role in the regulation of epileptogenesis following pilocarpine-induced status epilepticus (SE).


METHODS
Rats experienced uninterrupted SE or SE terminated with diazepam at 60, 120, and 180 min. P450scc induction in CA3 hippocampus was determined by double immunolabeling with P450scc antiserum and monoclonal antibodies against GFAP (astrocytes), RIP (oligodendrocytes), or heme oxygenase-1 (microglia).


RESULTS
SE was associated with P450scc induction in many astrocytes and a small number of microglia and oligodendrocytes in the hippocampal CA3 strata radiatum and lacunosum-moleculare. The extent of P450scc induction increased with increasing SE duration. Paradoxically, increased P450scc induction in rats experiencing SE for 180 min or more was associated with the delayed onset of spontaneous recurrent seizures. Treatment with the 5 alpha-reductase inhibitor finasteride (100 mg/kg/day for 25 days), which inhibits the synthesis of gamma-aminobutyric acid (GABA)(A) receptor modulating neurosteroids such as allopregnanolone, was associated with a significant reduction in time to the onset of spontaneous seizures in rats exposed to 180-min but not 90-min SE.


CONCLUSIONS
P450scc is induced by SE in a diverse population of hippocampal glia. Induction of P450scc is associated with the delayed onset of spontaneous seizures. Conversely, inhibition of neurosteroid synthesis accelerated the onset of spontaneous seizures, but only in animals exhibiting significant increases in P450scc. These findings suggest that induction of neurosteroid synthesis in reactive glial cells is associated with delayed onset of spontaneously recurrent seizures.
Biagini
Giuseppe
G
Dipartimento di Scienze Biomediche, Università di Modena e Reggio Emilia, Modena, Italy. gbiagini@unimore.it
Longo
Daniela
D
Baldelli
Enrica
E
Zoli
Michele
M
Rogawski
Michael A
MA
Bertazzoni
Giuliano
G
Avoli
Massimo
M
D000818:Animals; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000096:biosynthesis* / Q000502:physiology; D004195:Disease Models, Animal; D004790:Enzyme Induction / Q000187:drug effects / Q000502:physiology; D008297:Male; D018377:Neurotransmitter Agents / Q000096:biosynthesis* / Q000502:physiology; D010862:Pilocarpine / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology*; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000502:physiology; D012008:Recurrence; D012640:Seizures / Q000201:enzymology / Q000378:metabolism / Q000503:physiopathology; D013226:Status Epilepticus / Q000139:chemically induced / Q000201:enzymology* / Q000378:metabolism
D018377:Neurotransmitter Agents; D011963:Receptors, GABA-A; D010862:Pilocarpine; D002786:Cholesterol Side-Chain Cleavage Enzyme