Mechanisms of Convulsant Action of Intrahippocampally Infused Pregnenolone Sulfate in Rats.
Abstract number :
1.034
Submission category :
Year :
2001
Submission ID :
2193
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
Z. Mtchedlishvili, PhD, Neurology, University of Virginia, Charlottesville, VA; W. Yen, College of Arts and Sciences, University of Virginia, Charlottesville, VA; J. Labrie, College of Arts and Sciences, University of Virginia, Charlottesville, VA; J. Wil
RATIONALE: Neuroactive steroid pregnenolone sulfate (PS) is present in nanomolar concentrations and synthesized from steroid precursors in the hippocampus. Intracerebroventricular and intrahippocampal injections of PS improve memory. Intracerebroventricular infusion of PS also induces seizures in mice. PS appears to have nongenomic action on excitatory and inhibitory transmission. Convulsant action of PS in the hippocampus has not been yet studied.
METHODS: Adult naive rats were implanted with canula in left ventral hippocampus and increasing doses of PS (300pM [ndash] 4[mu]M) in 40[mu]l dextran were infused with microsyringe into hippocampi of 8 groups of rats. 5 rats received infusion of dextran alone, as a control. Latency of seizure onset, seizure score and duration were assessed with EEG and behavioral monitoring. PS modulation of GABA evoked currents was studied in dentate granule cells (DGCs), acutely isolated from adult rats. Neurons were voltage clamped to 0mV and drugs were applied with U-tube application system. PS modulation of NMDA receptor currents was studied in cultured hippocampal neurons voltage clamped to -70mV.
RESULTS: Threshold dose for occurrence of electrographic seizure was 10nM PS. Increasing doses of PS evoked seizures in larger fraction of animals and increased intensity of seizures. Half-maximal dose of PS for seizure occurrence (ED[sub]50[/sub]) was 68nM. Increasing concentrations of PS evoked status epilepticus with ED[sub]50[/sub] = 142nM. In DGCs, application of increasing concentrations of PS (300nM - 300[mu]m) with 30[mu]M GABA inhibited GABA[sub]A[/sub]R currents with EC[sub]50[/sub] = 13.1[mu]M (n = 14) and the maximal inhibition was 92.3% [plusminus] 1.3, (n = 8). In cultured hippocampal cells PS (3 - 300[mu]M) enhanced NMDA elicited currents with the EC[sub]50[/sub] = 15.7mM (n = 8), and the maximal enhancement was 89.4% [plusminus] 14, (n = 8).
CONCLUSIONS: This study demonstrated that intrahippocampaly infused PS has potent convulsant properties, in nanomolar concentration. Latency of seizure onset decreased and duration and intensity increased at increasing doses of PS. The convulsant action of PS is mediated by its modulation of GABA[sub]A[/sub] and NMDA receptors present on hippocampal cells.
Support: AES and NINDS.