The role of GABAergic inhibition in the cortical effects of monocular deprivation

Abstract

In cats and monkeys, monocular deprivation in early life results in an extensive reduction of the capability of the deprived eye to activate visual cortical cells¹, apparently because of changes taking place in the visual cortex itself rather than at an earlier stage in the visual pathway². The nature of the change taking place in the cortex is the subject of some controversy. One line of evidence favours a redistribution of the excitatory terminals relating to the two eye inputs^3–5 whilst another suggests that the deprived eye input is in some way suppressed⁶, possibly by γ-aminobutyric acid (GABA)-mediated intracortical inhibition⁷. We have now sought to clarify the role of this type of inhibitory influence in monocularly deprived cats, by ascertaining whether there is an enhancement of the deprived eye input to visual cortical cells during the iontophoretic application of the GABA antagonist, N-methyl-bicuculline (NMB). Our experiments show that although intracortical inhibition may submerge the deprived eye input to some cells, it is unlikely to precipitate the cortical effects of monocular deprivation. The redistribution of excitatory terminals would seem to be a more significant factor.