Abstracts

Rationale: Glutamatergic synaptic transmission is mediated through three families of ionotropic glutamate receptors which include AMPA, NMDA, and kainate receptors (KARs). KARs have been implicated in epilepsy disorders, but their precise role has not been determined in part due to a lack of pharmacological compounds that selectively target KARs. Previous studies have shown that MSVIII-19 and 2,4-epi-neoDH, act as selective kainate receptor antagonists in in vitro recombinant receptor model systems. MSVIII-19 has selective antagonistic action on the GluR5 KAR subunit, while 2,4-epi-neoDH targets both the GluR5 and GluR6 subunits. IKM-159, a novel DH analog produces catalepsy in vivo and has antagonist activity for AMPA/KARs (Ikoma et al., 2008). These novel marine-derived compounds have never been tested on any neuronal system. Here, we assess if these novel pharmacological compounds have antagonistic activity on synaptic kainate receptors and determine their efficacy as anticonvulsants in in vitro models of epilepsy. Methods: We examined the potency of these novel compounds on kainate receptor synaptic currents using whole-cell patch clamp techniques in hippocampal slice preparations. Results: In mossy fiber-CA3 pyramidal cell synapses, whose principal KAR subunits include GluR6 and KA2, 100 µM 2,4-epi-neoDH inhibited kainate receptor mediated excitatory postsynaptic currents (EPSCs) by 34% and had no effect on the paired-pulse ratio (PPR) in hippocampal slice preparations. 10 µM MSVIII-19 failed to inhibit postsynaptic CA3 KAR-EPSCs, likely due to MSVIII-19 selectivity for the GluR5 kainate receptor subunit. It will be important to further test this compound on GluR5 activity, as GluR5 selective antagonists have been shown to attenuate and prevent seizure induction in pilocarpine induced seizure models. IKM-159 did not depress CA3 KAR-EPSCs, but showed a higher selectivity for AMPA-EPSCs. IKM-159 reduced AMPA/KAR-EPSCs evoked by stimulation of Schaffer collateral inputs to CA1 pyramidal neurons in acute slice preparations and also reduced bursts of AMPA/KA receptor mediated EPSCs in voltage clamp recordings from hippocampal neurons in culture. IKM-159 reduced spontaneous re-occurring epileptiform discharge (SRED) action potential firing in an in vitro model of stroke-induced epilepsy. Conclusions: Given the initial characterization of these compounds on synaptic kainate receptor function in hippocampal slice preparations and in vitro models of epilepsy, we propose that these selective kainate receptors antagonists can be further pursued as a new generation of selective target anticonvulsant therapies in treating epilepsy and seizure disorders.