Orientation tuning and receptive field structure in cat striate neurons during local blockade of intracortical inhibition

• Published in: Neuroscience Vol. 84; no. 1; pp. 25 - 36
• Main Authors: Eysel, U.T, Shevelev, I.A, Lazareva, N.A, Sharaev, G.A
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-05-1998; Elsevier
• Subjects: Animals; bicuculline; Bicuculline - pharmacology; cat; Cats; Dose-Response Relationship, Drug; Electrophysiology; GABA Antagonists - pharmacology; inhibition; Neural Inhibition - drug effects; Neural Inhibition - physiology; Neurons - physiology; Orientation - physiology; orientation tuning; Photic Stimulation - methods; receptive fields; visual cortex; Visual Cortex - cytology; Visual Cortex - physiology; Visual Fields - physiology; orientation tuning; visual cortex; bicuculline; cat; receptive fields; inhibition; PSTH, peristimulus time histogram; V1, area 17 of the visual cortex; RF, receptive field; OT, orientation tuning
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(97)00378-3

The contribution of intracortical inhibition to orientation tuning in the cat striate cortex (area 17) was studied by responses to flashing light bars of different orientations and lengths in 68 single-units before and during microiontophoretical application of bicuculline, a GABA
A antagonist, A three-fold increase in the background activity (13.3±1.3 vs 4.4±0.5
imp/s) and 4.4-fold increase in the maximal discharge frequency (264.4±22.3 vs 60.6±5.3
imp/s) was found in 96.0% of the cells studied during microiontophoresis. In most units all characteristics of orientation tuning significantly changed during application of bicuculline: i) tuning width increased in 76.3% of cells from 52.7±2.8° in control to 85.2±4.6°, ii) tuning selectivity diminished in 63.6% of cells by a factor of 1.5, and iii) tuning quality dropped in 68.5% of cases by a factor of 2.5. The threshold ejection current of bicuculline for widening of tuning was in 2/3 of the cells in the range from +10 to +40
nA (+31.0±4.5
nA) and the maximum effect was obtained in 3/4 of units with +30–+100
nA (+67.1±6.0
nA).
Unmasking of additional excitatory inputs to the studied cells due to blockade of the inputs from inhibitory interneurons is considered as the main mechanism of the described bicuculline effects.