Metabotropic glutamate receptors: novel targets for pain relief.

Metabotropic glutamate receptors (mGluRs) are a relatively new family of G-protein coupled receptors that can be activated by the major excitatory neurotransmitter, L-glutamate. The eight known mGluR subtypes are classified into three groups based on their sequence homology, signal transduction mechanisms and receptor pharmacology. Extensive research has implicated mGluRs in neuroplasticity associated with normal brain functions, but also in various neurological and psychiatric disorders. Evidence is accumulating to suggest an important role of mGluRs in nociception and pain. With the availability in recent years of selective pharmacological tools, behavioral and electrophysiological studies have shown that mGluR subgroups and subtypes mediate and modulate nociceptive processing at different levels of the nervous system: periphery, spinal cord and brain. Thus, mGluRs may provide important novel therapeutic targets for the relief of pain associated with altered neurotransmission and neuronal excitability.