GABAB-receptor-mediated inhibition reduces the orientation selectivity of the sustained response of striate cortical neurons in cats.
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.
Allison
J D
JD
Department of Cell Biology, Vanderbilt University, Nashville, TN 37235, USA.
Kabara
J F
JF
Snider
R K
RK
Casagrande
V A
VA
Bonds
A B
AB
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology; D002415:Cats; D018756:GABA Antagonists / Q000494:pharmacology; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D011930:Reaction Time / Q000187:drug effects; D018080:Receptors, GABA-B / Q000502:physiology*; D014793:Visual Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D018756:GABA Antagonists; D018080:Receptors, GABA-B; D001418:Baclofen; C057491:2-hydroxysaclofen