GABAergic inhibition already operates on a group of neurons in the kitten visual cortex at the time of eye opening.

Effects of iontophoretic application of gamma-aminobutyric acid (GABA) and its antagonist, N-methyl-bicuculline (BIC), on visual responses of striate cortical neurons were studied in kittens 6-13 days old. Visually responsive cells were classified into 3 groups, i.e., orientation-selective, orientational bias and non-oriented cells. In almost all of the orientation-selective cells their responses were completely suppressed by GABA while the majority of the others were not significantly or only weakly suppressed. BIC abolished or reduced the selectivity of all the orientation-selective cells while it did not affect any of the non-oriented cells tested. These results suggest that GABAergic inhibition already operates on a group of cortical neurons to make them orientation-selective at the time of eye opening.