Effects of felbamate on muscarinic and metabotropic-glutamate agonist-mediated responses and magnesium-free or 4-aminopyridine-induced epileptiform activity in guinea pig olfactory cortex neurons in vitro

The effects of the anticonvulsant agent felbamate (FBM) were examined on muscarinic and metabotropic-glutamate receptor agonist-induced responses and chemically induced epileptiform activity, in guinea pig olfactory cortex slices in vitro. FBM (100-500 mu M) had little effect on neuronal membrane proper ties and on postsynaptic potentials evoked by electrical stimulation of lateral olfactory tract terminals, whereas it reduced the duration of presumed Ca++ spikes induced by intracellular Cs+ loading. In contrast, the muscarinic receptor agonist oxotremorine-M (10 mu M) or the metabotropic glutamate receptor agonist 1-aminocyclopentane-1S-3R-dicarboxylic acid (10 mu M) induced a sustained membrane depolarization with repetitive firing, an increase in input resistance and the appearance of a slow poststimulus afterdepolarizing potential. These effects were reversibly reduced in the presence of FBM (100-500 mu M).