The anticonvulsant effects of intracerebral administration of the highly potent group II metabotropic glutamate receptor agonist, DCG-IV, were tested in fully kindled rats following daily electrical stimulation of the basolateral amygdala. The agonist caused a dose-dependent increase in the generalized seizure threshold (GST) of these seizure susceptible animals within the dose range tested (0. 01-1.0 nmol). The estimated GST100 value (dose causing a 100% increase in GST) for this effect was 0.22 nmol. The anti-seizure activity of DCG-IV was fully inhibited in the presence of the group II metabotropic glutamate receptor antagonist (2S,1'S, 2'S)-2-methyl-2-(carboxycyclopropyl)glycine (MCCG; 40 nmol), while MCCG alone showed no significant inhibitory effect on seizure activity. DCG-IV also powerfully inhibited depolarization-induced release of [3H]D-aspartate from rat cerebrocortical synaptosomes, with an IC50 value of 0.39 microM. In this respect, DCG-IV was approximately 70-fold more potent than the clinically effective anticonvulsant drug lamotrigine (IC50=27.7 microM), a proposed neurotransmitter release inhibitor known to inhibit glutamate release, also tested in this assay. These findings demonstrate the high potency of DCG-IV as an anticonvulsant agent and confirm a key role for group II metabotropic glutamate receptors in the control of seizure activity via their modulatory action on neuronal glutamate release.
Copyright 1998 Elsevier Science B.V.