Potent and specific action of the mGlu1 antagonists YM-298198 and JNJ16259685 on synaptic transmission in rat cerebellar slices

Background and purpose: Specific and selective inhibitors for mGlu1 receptors are presently inadequate. A new generation of non-competitive mGlu1 antagonists with low nanomolar potencies is emerging. We evaluated two new compounds, YM-298198 and JNJ16259685, for effectiveness, potency and specificity for the first time in a brain slice preparation.

Experimental approach: Patch-clamp recording of Purkinje neurones in cerebellar slices were obtained. The slow mGlu1-mediated EPSP was used to establish a concentration-response curve. Fast excitatory synaptic inputs were tested for non-specific effects.

Key results: YM-298198 and JNJ16259685 inhibited the synaptic activation of mGlu1 in a concentration-dependent manner (IC(50) values of 24 nM and 19 nM, respectively). The antagonists were slow to inhibit and to reverse on washout, probably due to their lipophilic nature. There were no non-specific effects on fast AMPA receptor-mediated synaptic transmission in the cerebellum.

Conclusions and implications: These compounds are more than a thousand-fold more potent than previously available compounds. Their selectivity and specificity will be very useful for studying the role of mGlu1 receptors both in vitro and in vivo.