GABAB-receptor-mediated inhibition reduces the orientation selectivity of the sustained response of striate cortical neurons in cats

Vis Neurosci. May-Jun 1996;13(3):559-66. doi: 10.1017/s0952523800008233.

Abstract

Blocking GABAA-receptor-mediated inhibition reduces the selectivity of striate cortical neurons for the orientation of a light bar primarily by reducing the selectivity of their onset transient (initial 200 ms) response. Blocking GABAB-receptor-mediated inhibition with phaclofen, however, is not reported to reduce the orientation selectivity of these neurons when it is measured with a light bar. We hypothesized that blocking GABAB-receptor-mediated inhibition would instead affect the orientation selectivity of cortical neurons by reducing the selectivity of their sustained response to a prolonged stimulus. To test this hypothesis, we stimulated 21 striate cortical neurons with drifting sine-wave gratings and measured their orientation selectivity before, during, and after iontophoretic injection of 2-hydroxy-saclofen (2-OH-S), a selective GABAB-receptor antagonist. 2-OH-S reduced the orientation selectivity of six of eight simple cells by an average of 28.8 (+/- 13.2) % and reduced the orientation selectivity of eight of 13 complex cells by an average of 32.3 (+/- 27.4) %. As predicted, 2-OH-S reduced the orientation selectivity of the neurons' sustained response, but did not reduce the orientation selectivity of their onset transient response. 2-OH-S also increased the length of spike "bursts" (two or more spikes with interspike intervals < or = 8 ms) and eliminated the orientation selectivity of these bursts for six cells. These results are the first demonstration of a functional role for GABAB receptors in visual cortex and support the hypothesis that two GABA-mediated inhibitory mechanisms, one fast and the other slow, operate within the striate cortex to shape the response properties of individual neurons.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Baclofen / analogs & derivatives
  • Baclofen / pharmacology
  • Cats
  • GABA Antagonists / pharmacology
  • Neural Inhibition / physiology*
  • Neurons / drug effects
  • Neurons / physiology*
  • Orientation / physiology*
  • Reaction Time / drug effects
  • Receptors, GABA-B / physiology*
  • Visual Cortex / cytology
  • Visual Cortex / drug effects
  • Visual Cortex / physiology*

Substances

  • GABA Antagonists
  • Receptors, GABA-B
  • Baclofen
  • 2-hydroxysaclofen