GABAergic inhibition and orientation selectivity 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 three groups, i.e. orientation-selective, orientation-bias and nonoriented 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. An application of BIC abolished or reduced the selectivity of all the orientation-selective cells but did not affect any of the nonoriented 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, but such an action of GABA on other groups of neurons develops later.