Modification of orientation sensitivity of cat visual cortex neurons by removal of GABA-mediated inhibition

Abstract

The effects of an inhibitor of GABA synthesis, 3-mercaptopropionic acid (MP), and of the GABA antagonist bicuculline (BIC), on the direction and orientation sensitivity of visual cortical neurons were investigated using a computer-controlled stimulus presentation system. Intravenous administration of MP, which was usually more effective than if administered microelectrophoretically, induced a slight, but significant reduction in these properties of about half of the neurons tested. The effect of electrophoretic BIC was in the same direction but clearer than that of MP. In 71% of the simple cells, direction sensitivity was virtually lost during administration of BIC while orientation sensitivity was never completely eliminated in any neuron tested. Simultaneous administration of both drugs (MP systemically, BIC electrophoretically) caused more complete modification of the sensitivities than single administration of each. In four out of thirteen neurons tested, orientation sensitivity was completely abolished. The excitatory receptive fields slightly increased in size and became virtually round. The response magnitude to the optimal stimulus was increased by each drug along and by both. The present results further support the hypothesis that intracortical inhibition plays a major if not an exclusive role for the orientation and direction sensitivity of cortical cells.

GABAergic Interneurons Implications for Understanding Schizophrenia and Bipolar Disorder

“…Growing evidence supports the hypothesis that cortical interneurons can influence the discriminative responses of pyramidal neurons. For example, in the visual system, GABAergic interneurons play a key role in modulating the activity of geniculate inputs to the primary visual cortex and defining the orientation selectivity of its neurons (Sillito 1975(Sillito , 1984Tsumoto et al 1979). Support for a role of interneurons in shaping of receptor fields has been extended to other cortical areas such as the somatosensory cortex (Alloway et al 1989;Alloway and Burton 1991;Wilson et al 1994;Kyriazi et al 1996).…”

GABAergic Neurons Are Less Selective to Stimulus Orientation than Excitatory Neurons in Layer II/III of Visual Cortex, as Revealed byIn VivoFunctional Ca2+Imaging in Transgenic Mice

“…One of the principal functions of GABAergic neurons is considered to be the sharpening of specific functional properties of cortical neurons. In the visual cortex, for example, GABAergic neurons were proposed to play a role in rendering cortical neurons selective to a particular orientation of visual stimuli, although this view still remains highly controversial (Sillito, 1975;Tsumoto et al, 1979;Ferster, 1986;Chapman et al, 1991;Somers et al, 1995;Shevelev et al, 1998;Anderson et al, 2000;Teich and Qian, 2006). If GABAergic neurons play such a role, they are assumed to have the preferred orientation orthogonal to or different from that of neighboring excitatory neurons to curb nonpreferred inputs or to have no or poor selectivity to generally suppress orientationbiased inputs to excitatory neurons (for review, see Vidyasagar et al, 1996;Sompolinsky and Shapley, 1997;Ferster and Miller, 2000).…”

Effects of vigabatrin on evoked potentials in dogs.

“…Numerous studies point to the failure of GABAergie inhibition as a key factor in local and global seizures (see Roberts, 1986 for review). Reduction in the efficacy of the GABA system, such as that produced by interference with GABA synthesis or blockage of GABA receptors, has been associated with altered physiology and ultimately with seizures (Roberts, 1976;Tsumoto et al, 1979;Sillito, 1984). Conversely, drugs that interfere with GABA-transaminase (GABA-T), blocking the major catabolic route for GABA, probably would increase available GABA and be efficacious for the treatment of epilepsy.…”