Pharmacological profiling of native group II metabotropic glutamate receptors in primary cortical neuronal cultures using a FLIPR.

The group II metabotropic glutamate (mGlu) receptors comprised of the mGlu2 and mGlu3 receptor subtypes have gained recognition in recent years as potential targets for psychiatric disorders, including anxiety and schizophrenia. In addition to studies already indicating which subtype mediates the anxiolytic and anti-psychotic effects observed in disease models, studies to help further define the preferred properties of selective group II mGlu receptor ligands will be essential. Comparison of the in vitro properties of these ligands to their in vivo efficacy and tolerance profiles may help provide these additional insights. We have developed a relatively high-throughput native group II mGlu receptor functional assay to aid this characterisation. We have utilised dissociated primary cortical neuronal cultures, which after 7 days in vitro have formed functional synaptic connections and display periodic and spontaneous synchronised calcium (Ca(2+)) oscillations in response to intrinsic action potential bursts. We herein demonstrate that in addition to non-selective group II mGlu receptor agonists, (2R,4R)-APDC, LY379268 and DCG-IV, a selective mGlu2 agonist, LY541850, and mGlu2 positive allosteric modulators, BINA and CBiPES, inhibit the frequency of synchronised Ca(2+) oscillations in primary cultures of rat and mouse cortical neurons. Use of cultures from wild-type, mGlu2(-/-), mGlu3(-/-) and mGlu2/3(-/-) mice allowed us to further probe the contribution of mGlu2 and mGlu3, and revealed LY541850 to be a partial mGlu2 agonist and a full mGlu3 antagonist. Overnight pre-treatment of cultures with these ligands revealed a preferred desensitisation profile after treatment with a positive allosteric modulator. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.