| ObjectiveSingle-cell extracellular recording techniques, Blood oxygenation level dependent-functional magnetic resonance imaging, immuno-histochemical and stereological quantitation method were used to study the changes of the spatial-temporal properties of striate cortical cells in strabismic amblyopia, and to deeper elucidate the pathogenetic mechanism of the strabismic amblyopia. Methods(1) After surgical creation of esotropic strabismus at the postnatal second week, some cats often develop amblyopia. The response properties of occipital cortex neurons in 17 amblyopic cats (6 mild amblyopes, 7 moderate amblyopes, 4 severe amblyopes) and 10 normal cats were studied with drifting sinusoidal gratings. The cortical binocularity and ocular dominance in strabismic amblyopic and normal cats were qualitatively analyzed. The optimal spatial frequency, optimal temporal frequency and integration time of the cortical neurons driven by two eyes of strabismic amblyopes were quantitatively measured.(2) Using an EPI gradient echo sequence in 1.5T MRI, calcarine activation by monocular viewing of checkerboard pattern with reversal were examined in 15 strabismic amblyopes and 10 normally-sighted controls. The cortex related to vision was located. The binocular voxel index of the activation in both groups and the average activation level of the neurons driven by two eyes of strabismic amblyopes were quantitatively analyzed. The relationship between the visual acuity and BOLD-fMRI signal intensity was studied.(3) The expression patterns of 5-HT2cR in occipital cortex in 8 normal cats and 8 strabismic cats were examined by immuno-histochemical methods using a monoclonal anti-5-HT2cR antibody. 5-HT2cR expression at postnatal 3 weeks, 6 weeks, 9 weeks and 6 months was compared between the two groups.(4) Using stereological electron microscopic methods, the amount and the structural parameter of synapses in occipital cortex were studied in 4 normal cats and 4 strabismic amblyopic cats. Synaptic cleft width, the thickness of the postsynaptic densities (PSD) , length of the active zones and curvature of the synaptic interface in occipital cortex were quantitatively compared between the two groups.Results(1) The cortical binocularity in the amblyopic group was lower than in the normal group, meanwhile, the distribution of ocular dominance was correlated to the severity of amblyopia. For example, a bias in ocular dominance favoring the contralateral eye was found in severe amblyope, but it wasn't found in mild and moderate amblyope. The optimal spatial frequency and the integration time of the cortical neurons driven by the amblyopic eye were substantially and significantly lower than for neurons driven by the non-amblyopic eye. But there are few differences of the temporal frequency tuning between the two eyes.(2 ) Occipital cortex, inferior temporal gyrus, and post parietal/gyrus angularis were activated in both groups. The most of the activated areas were located around the fissure of occipital cortex. Both the activated area and the binocular voxels index in the strabismic amblyopic group were lower than in the normal group. The activation by bigher-spatial-frequency stimuli was reduced in the strabismic amblyopic group, but not in the normal group. The visual acuity was not correlated to the BOLD-fMRI signal intensity.(3) The architecture of 5-HT2cR protein expression in normal occipital cortex was very clear. In spatial distribution, 5-HT2cR protein expression were found in all layers of the occipital cortex. The amount of expression was relatively higher in layers II-IV, and weaker in layers V-VI. In temporal distribution, at postnatal weeks 3, 5-HT2cR expression was pronounced in the normal cat occipital cortex, The expression were increased with peak at postnatal weeks 6 and decreased at postnatal weeks 9. The expression at postnatal weeks 9 was similar to adult level. 5-HT2cR protein was low expressed in strabismic amblyopia occipital cortex compared to the normal cortex. There was no significant difference...
|
PDF Full Text Request