The induction of the most common form of LTP is well known to involve activation of N-methyl-D-aspartate receptors. However, considerable evidence has also shown that certain forms of LTP induction at excitatory synapses onto both principle cells and interneurons are dependent on activation of metabotropic glutamate receptors (mGluRs). mCluR-dependent UP occurs in widespread areas of the brain including the neocortex, hippocampus, striatum and nucleus accumbens. mGluR-dependent forms of UP have been found to be diverse, involving activation of mGluR1 or mGluR5 and can be of AMPAR-mediated transmission or of WDAR-mediated transmission. Furthermore, the mGluR-dependent UP may involve activation of other receptors, in particular, activation of NMDAR, dopamine and adenosine receptors. mGluR-dependent UP can be expressed presynaptically or postsynaptically, and can involve a range of intracellular mediators including protein kinase C (PKC) and protein kinase A (PKA), tyrosine kinase Src and nitric oxide (NO). (C) 2009 Published by Elsevier Ltd.