Induction of LTD but not LTP through metabotropic glutamate receptors in visual cortex.

Long-term potentiation (LTP) and long-term depression (LTD), often used as essential components in synaptic models for learning, memory and forgetting, can be produced in cortical tissue by repetitive activation of neural pathways under different stimulus conditions. The involvement of metabotropic glutamate receptors (mGluRs) has been postulated to be necessary for the establishment of either or both forms of synaptic plasticity in hippocampus. The recent introduction of a specific antagonist for mGluRs, (+/-)-alpha-methyl-4-carboxyphenylglycine, prompted the investigation of the respective involvement of this receptor population in the induction of LTP and LTD in visual cortex of the rat in vitro. The results suggest the critical involvement of mGluRs in producing LTD but not LTP.