NMDA receptor‐mediated pilocarpine‐induced seizures: characterization in freely moving rats by microdialysis

Abstract

1 Pilocarpine administration has been used as an animal model for temporal lobe epilepsy since it produces several morphological and synaptic features in common with human complex partial seizures. Little is known about changes in extracellular neurotransmitter concentrations during the seizures provoked by pilocarpine, a non-selective muscarinic agonist. 2 Focally evoked pilocarpine-induced seizures in freely moving rats were provoked by intrahippocampal pilocarpine (10 mM for 40 min at a¯ow rate of 2 ml min 71 ) administration via a microdialysis probe. Concomitant changes in extracellular hippocampal glutamate, g-aminobutyric acid (GABA) and dopamine levels were monitored and simultaneous electrocorticography was performed. The animal model was characterized by intrahippocampal perfusion with the muscarinic receptor antagonist atropine (20 mM), the sodium channel blocker tetrodotoxin (1 mM) and the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (dizocilpine maleate, 100 mM). The e ectiveness of locally (600 mM) or systemically (10 mg kg 71 day 71 ) applied lamotrigine against the pilocarpine-induced convulsions was evaluated.3 Pilocarpine initially decreased extracellular hippocampal glutamate and GABA levels. During the subsequent pilocarpine-induced limbic convulsions extracellular glutamate, GABA and dopamine concentrations in hippocampus were signi®cantly increased. Atropine blocked all changes in extracellular transmitter levels during and after co-administration of pilocarpine. All pilocarpine-induced increases were completely prevented by simultaneous tetrodotoxin perfusion. Intrahippocampal administration of MK-801 and lamotrigine resulted in an elevation of hippocampal dopamine levels and protected the rats from the pilocarpine-induced seizures. Pilocarpine-induced convulsions developed in the rats which received lamotrigine perorally. 4 Pilocarpine-induced seizures are initiated via muscarinic receptors and further mediated via NMDA receptors. Sustained increases in extracellular glutamate levels after pilocarpine perfusion are related to the limbic seizures. These are arguments in favour of earlier described NMDA receptor-mediated excitotoxicity. Hippocampal dopamine release may be functionally important in epileptogenesis and may participate in the anticonvulsant e ects of MK-801 and lamotrigine. The pilocarpine-stimulated hippocampal GABA, glutamate and dopamine levels re¯ect neuronal vesicular release.

Cellular mechanisms underlying acquired epilepsy: The calcium hypothesis of the induction and maintainance of epilepsy

“…Using microdialysis in humans prior to neurological surgery, a clear association between potentially neurotoxic levels of glutamate and seizure progression has been demonstrated (During & Spencer, 1993;Wilson et al, 1996). Multiple studies in animals have similarly demonstrated an elevation in extracellular glutamate during SE (Liu et al, 1997;Smolders et al, 1997;Pena & Tapia, 1999;Ueda et al, 2002). This increase in glutamate has been implicated in the neuronal death observed after SE in these models, as antagonism of specific glutamate receptors during SE has shown to be neuroprotective (Meldrum, 1997;Rice & DeLorenzo, 1998;Hort et al, 1999;Ebert et al, 2002).…”

Variations of ATP and its metabolites in the hippocampus of rats subjected to pilocarpine-induced temporal lobe epilepsy

“…The actions exerted by ATP metabolites have not been completely understood, especially those of ADP and AMP. Increased ATP metabolism during SE may indicate increased glutamate release, which can contribute to cell death in this model [25].…”

In vitro status epilepticus but not spontaneous recurrent seizures cause cell death in cultured hippocampal neurons

“…Thus, it is important to stop ongoing SE and limit neuronal death. Microdialysis studies in humans (During and Spencer, 1993;Wilson et al, 1996) and animals (Smolders et al, 1997;Ueda et al, 2002) have shown significant elevations in extracellular glutamate during SE. On the other hand, there are also many microdialysis studies that failed to show increases in extracellular glutamate during SE (Bruhn et al, 1992;Millan et al, 1993).…”