Short-term effects of pilocarpine on rat hippocampal neurons in culture.
OBJECTIVE
Status epilepticus (SE) has been considered an epileptogenic factor in humans. In the pilocarpine (PILO) model, after a brief period marked by SE, the rats exhibit recurrent spontaneous seizures, mimicking the clinical features of temporal lobe epilepsy. The aim of our study was to identify the molecular actions of PILO that could account for its ability to induce SE.


METHODS
Whole-cell mode of the patch-clamp technique was applied to cultured hippocampal neurons (2-3 weeks old) in the absence and in the presence of PILO (1-10 microM), to study the spontaneous activity, the evoked, and the miniature postsynaptic currents. The postsynaptic currents were isolated pharmacologically.


RESULTS
PILO (1 and 10 microM) caused an initial increase followed by a decrease in the frequency of spontaneous activity. The increase in the frequency of excitatory postsynaptic currents (EPSCs) and inhibitory PSCs (IPSCs) was blocked by atropine (1 microM), indicating that this effect is mediated through muscarinic receptors. PILO also promoted a brief increase of the amplitude of IPSCs indirectly evoked by stimulation of a neuron synaptically connected to the neuron under study. Conversely, PILO promoted a sustained increase on the amplitude of electrically evoked EPSCs. In presence of tetrodotoxin (TTX; 300 nM), PILO (1 microM) increased the frequency of miniature EPSCs and IPSCs without changing their amplitude during the first 3 min of application.


CONCLUSIONS
These results indicate that PILO acting through muscarinic receptor causes an imbalance between excitatory and inhibitory transmission that can result in the generation of SE observed in animals acutely treated with PILO.
School of Medicine, University of Maryland, Baltimore, MD, USA. priel.nexp@epm.br
M R
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Priel
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Albuquerque
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002478:Cells, Cultured; D003292:Convulsants / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000187:drug effects*; D010862:Pilocarpine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D009435:Synaptic Transmission / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D003292:Convulsants; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010862:Pilocarpine; D013779:Tetrodotoxin; D001285:Atropine