Peripheral metabotropic glutamate receptors as drug targets for pain relief.

The relatively new family of G-protein-coupled metabotropic glutamate receptors (mGluRs) is comprised of eight cloned subtypes, which are classified into three groups based on their sequence homology, signal transduction mechanisms and receptor pharmacology. It is now well-established that mGluRs in the central nervous system are essential for neuroplasticity associated with normal brain functions but are also critically involved in various neurological and psychiatric disorders. Recent anatomical and behavioural evidence suggests an important role of mGluRs in peripheral tissues in animal models of inflammatory and neuropathic pain. Once the cellular effects of peripheral mGluR activation and inhibition are better understood, certain peripheral mGluR subtypes may become important novel therapeutic targets for the relief of pain associated with peripheral tissue injury. Peripherally acting drugs that modulate nociceptive processing through mGluRs should have the advantage of lacking the central side effects commonly observed with drugs interfering with glutamatergic transmission in the central nervous system.