Regulation of neurotransmitter release by metabotropic glutamate receptors

The G protein-coupled metabotropic glutamate (mGlu) receptors are different ially localized at various synapses throughout the brain. Depending on the receptor subtype, they appear to be localized at presynaptic and/or postsyn aptic sites, including glial as well as neuronal elements. The heterogeneou s distribution of these receptors on glutamate and nonglutamate neurons/cel ls thus allows modulation of synaptic transmission by a number of different mechanisms, Electrophysiological studies have demonstrated that the activa tion of mGlu receptors can modulate the activity of Ca2+ or K+ channels, or interfere with release processes downstream of Ca2+ entry, and consequentl y regulate neuronal synaptic activity. Such changes evoked by mGlu receptor s can ultimately regulate transmitter release at both glutamatergic and non glulamatergic synapses, Increasing neurochemical evidence has emerged, obta ined from in vitro and in vivo studies, showing modulation of the release o f a variety of transmitters by mGlu receptors, This review addresses the ne urochemical evidence for mGlu receptor-mediated regulation of neurotransmit ters, such as excitatory and inhibitory amino acids, monoamines, and neurop eptides.