The group III metabotropic glutamate receptor agonist, l-AP4, reduces EPSPs in some layers of rat visual cortex

The action of the specific Group III metabotropic glutamate receptor, l-2-amino-4-phosphonobutanoic acid (l-AP4) was tested in slices of rat visual cortex. When the predominant input to the cell was stimulated, l-AP4 generally reduced the EPSP that was produced. This result was specific to the layer: it was found when recording cells in layers II/III, V and VI, but not when recording cells in layer IV. The effect was the same when G-proteins in the cell recorded were inactivated. Also, l-AP4 had little effect on membrane potential and input impedance of the cell recorded, and little effect on the response to NMDA in that cell. Thus, Group III metabotropic glutamate receptors act presynaptically to reduce the release of glutamate onto cells in layers II/III, V and VI in visual cortex, but not cells in layer IV.