Activation of metabotropic glutamate receptors has different effects in different layers of cat visual cortex

Single neurons were recorded in cat primary visual cortex, and the effect of iontophoresis of the metabotropic glutamate agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid (ACPD) was observed. In nearly all cases (41/43), ACPD reduced the visual response. In some cases ACPD also reduced spontaneous activity (24/43), and in other cases ACPD increased spontaneous activity (18/43). Increases were generally seen in infragranular layers (V and VI), and decreases in supragranular layers (II and III). The reduction in the visual response was also largest in supragranular layers. We conclude that activation of metabotropic glutamate receptors has both facilitatory and depressive effects in visual cortex, and the effect depends on the layer of the cell recorded.