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.

Recent studies have shown that several receptor populations in cat visual cortex undergo alterations in their laminar distributions during postnatal development (Shaw et al., 1984a, b; 1986b). These redistributions occur during the first few months of postnatal life, coincident with the physiologically defined critical period for cortical plasticity. In the present communication, we demonstrate that receptor redistributions can be prevented from occurring, or progressing once started, by surgically isolating the visual cortex at appropriate postnatal ages. These data suggest that the maturation of the chemical circuitry of the visual cortex is dependent on factors of extrinsic origin.