RESUMO
Many neurons in the cat primary visual cortex reveal sensitivity to cruciform and corner figures as well as to local orientation discontinuities. We investigated this sensitivity in 85 V1 neurons before and after the local blockade of GABA(A)ergic inhibition by microiontophoretic application of bicuculline and observed two opposite effects: a decrease or disappearance of sensitivity to crosses in about half of the neurons and its increase or appearance in about one third of the units. The results indicate substantial and drastically different contribution of intracortical inhibition to sensitivity to line-crossings in the visual cortical neurons. Some possible mechanisms of this difference are discussed.
Assuntos
Inibição Neural/fisiologia , Neurônios/fisiologia , Córtex Visual/fisiologia , Animais , Bicuculina/farmacologia , Gatos , Antagonistas GABAérgicos/farmacologia , Antagonistas de Receptores de GABA-A , Microeletrodos , Inibição Neural/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Estimulação Luminosa/métodos , Receptores de GABA-A/efeitos dos fármacos , Receptores de GABA-A/fisiologia , Córtex Visual/efeitos dos fármacosRESUMO
Many neurons in the cat primary visual cortex are sensitive to cruciform and corner figures consisting of two oriented lines. To determine the contribution of inhibition to this property we investigated 85 V1 neurons before and after local blockade of GABAergic inhibition by microiontophoretic application of bicuculline. Cross sensitivity was generated or enhanced by inhibition in roughly 1/3 and suppressed or diminished in another 1/3 of the cells. In the remaining 1/3 cross sensitivity was either absent or not influenced by inhibition. The results demonstrate a substantial contribution of intracortical inhibition to either establish sharp single bar orientation tuning or to generate or modulate the sensitivity of visual cortical neurons to line crossings.
Assuntos
Inibição Neural/fisiologia , Córtex Visual/química , Córtex Visual/fisiologia , Ácido gama-Aminobutírico/fisiologia , Animais , Bicuculina/farmacologia , Química Encefálica/efeitos dos fármacos , Gatos , Eletrofisiologia , Antagonistas GABAérgicos/farmacologia , Orientação/fisiologia , Receptores de GABA-A/fisiologia , Visão Monocular/fisiologiaRESUMO
Receptive fields (RFs) in the visual cortex are characterized by spatiotemporal profiles that have been described in detail for area 17 simple cells. In this study, we analyse spatial and temporal RF properties of simple and complex cells in layer II/III of area 18 of the anaesthetized adult cat, using the reverse correlation method with brief 50 ms presentations of flashing bright and dark bars. Stimuli were presented with preferred orientation as previously determined by moving bars. Simple cell RFs were characterized by spatially and temporally separable ON and OFF subfields, while in complex cells ON and OFF subfields were superimposed. To discriminate possible contributions of GABAergic inhibition to RF structure and response dynamics in area 18, we have used three-barrelled micropipettes for single cell recordings and microiontophoresis, and have documented ON and OFF responses before, during and after application of bicuculline methiodide for blockade of GABAA receptors. During blockade of GABAergic inhibition, the stimulus-induced and resting discharge frequency increased, and in about 50% of the cells both ON and OFF subfields changed significantly in space and/or time in a reversible manner. In space, blockade of inhibition widened RF subfields, whereas in time, it shortened the duration of the excitatory cell response in simple and complex cells. ON and OFF subfields separated in space and time (simple cells), or time (complex cells) became less isolated or even superimposed. The results indicate substantial local inhibitory processing contributing to spatiotemporal RF properties in layers II/III of area 18 of the cat.
Assuntos
Mapeamento Encefálico , Inibição Neural/fisiologia , Córtex Visual/fisiologia , Campos Visuais/fisiologia , Ácido gama-Aminobutírico/fisiologia , Animais , Bicuculina/farmacologia , Gatos , Eletrofisiologia , Antagonistas GABAérgicos/farmacologia , Iontoforese , Potenciais da Membrana/efeitos dos fármacos , Inibição Neural/efeitos dos fármacos , Neurônios Aferentes/fisiologia , Receptores de GABA/fisiologia , Fatores de Tempo , Córtex Visual/química , Córtex Visual/citologiaAssuntos
Percepção de Forma , Inibição Neural , Neurônios/fisiologia , Córtex Visual/fisiologia , Animais , Bicuculina/farmacologia , Gatos , Percepção de Forma/efeitos dos fármacos , Antagonistas GABAérgicos/farmacologia , Inibição Neural/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Estimulação Luminosa , Córtex Visual/efeitos dos fármacosRESUMO
The effects of prostaglandin (PG) E2 and the nitric oxide (NO) donor SIN-1 on leukotriene (LT) release from formyl-methionyl-leucyl-phenylalanine (fMLP) (100 nM)-stimulated rat peritoneal neutrophils (RPN) and on thrombin-induced aggregation of washed human platelets were investigated. Both PGE2 (1-100 nM) and SIN-1 (30-300 microM) inhibited release of LTB4 and cysteinyl-LT from RPN in a concentration-dependent manner. The combined effects of PGE2 and SIN-1 were not greater than expected by summation. On the other hand, the inhibitory effect of SIN-1 (0.5 or 1.0 microM) on platelet aggregation was potentiated by PGE2 (0.3-5 microM) in a concentration-dependent manner, while PGE2 alone in the concentrations used had only marginal effects. The results suggest differential regulation of platelet and leukocyte functions by the mediators PGE2 and NO, which could be relevant for various physiological and pathophysiological conditions.