| Objective:To explore the neuronal mechanism of strabismic amblyopia through observing the functional and morphologic changes in area 21a of strabismc amblyopic cats by extracellular recording with microelectrode and synaptic quantitative means. Methods:Nine kittens were randomly divided into 2 groups, in which 5 kittens were used as strabismic amblyopic group (Group S) and 4 as control (Group N). Tenotomy of the lateral rectus muscles of the right eyes of the kittens in Group S were performed to induce esotropic strabismus at the postnatal forth week. Cellular electrophysiological detection is performed after confirmation of the development of amblyopia by pattern visual evoked potential.The binocularity and ocular dominance of cortical neurons in area 21a of 5 amblyopic cats and 4 normal cats receiving drifting sinusoidal grating stimulus were compared after detecting the firing level by microelectrode recording.Two cats were randomly selected from the above each group, respectively. At the end of the recording session, each cat was given deep anaesthesia and perfused transcardially with a physiological saline followed by paraform PBS. The brain tissue of visual cortex area 21a was cut and doubly fixed with 2.5% glutaraldehyde and 1% osmium tetroxide, dehydrated with ethyl alcohol, and embedded with araldite. The prepared tissue was cut at 500A and stained with uranyl acetate andlead citrate, and then observed under JEM-100CX transmission electron microscope and photographed. The following parameters of Gray I synaptic interface in area 21a of the normal cats and strabismic amblyopic cats were quantified with image analysis software:(l) the width of synaptic cleft, (2) the thickness of the postsynaptic density, (3) the length of the active zones, (4) the curvature of the synaptic interface, (5)the numerical density(Nv) and the surface density(Sv), and (6)the proportion of synaptic types. Results:1. Ocular dominance of neurons in area 21 a of strabismic amblyopic cats The firing level of 172 units in normal cats and 170 units in strabismicamblyopic cats were recorded by extracellular microelectrode. Through data analysis, the proportion of binocular cells in area 21a of the Group N was 88.9%~93.2%, while the Group S is 17.9%~24.5% that was reduced when compared with the Group N (f=41.78, PO.001). The distribution of ocular dominance of the Group N was rather symmetric, while that of the Group S showed an obvious bias towards the non-deviating eye. In addition, the proportion of cells monocularly driven by the non-deviated eye reached 69.4%~79.5%, while the one of cells monocularly driven by the amblyopic eye was only around 5%. There was a significant difference between the distribution of ocular dominance in area 21a of the two groups (Kolmogorov-Smirnov test, Z=6.368, PO.001).2. Changes of synaptic ultrastructure of neurons in area 21a of strabismic amblyopic catsIn comparison with the Group N, the synaptic cleft width of the Group N was not found obvious change (t=-0.03, P>0.05), but the length of synaptic active zone showed shrinkage (t=2.41, PO.05) , the curvature of synaptic interface was... |
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