[Electron microscopic analysis of expression of NMDA-R1 in the developmental process of visual cortex in strabismic amblyopic cat].

OBJECTIVE: To investigate the expression and distribution of N-methyl-D-aspartate receptor subunit 1 (NMDA-R1) in neuronal ultrastructure in visual cortex of strabismic amblyopic cat during development.

METHODS: Eleven kittens were used for this study. Esotropia in six kittens had been made monocularly by tenotomy at two weeks of age. Two pairs of normal and strabismic kittens were sacrificed in three weeks of age, one week after tenotomy. Another two pairs of normal and strabismic kittens were sacrificed in five weeks of age, three weeks after tenotomy. One normal and two strabismic amblyopic cats were sacrificed after 6 months of age. Animals were deeply anaesthetized and perfused transcardially with 4% paraformaldehyde. Cryostat sections of frontal central area P5-P0 were cut to 25 micro m thickness. The mouse anti-NMDA-R1 monoclonal antibody (mAb54.1, PharMingen) was used. After stained, a light microscope was used to select regions of layer II-III, layer IV and layer V-VI of visual cortex area 17 for re-embedding. HITACHI H-7000 transmission electron microscope at magnifications ranging from 30 000 - 300 000 X was used for observation.

RESULTS: Three hundred and twenty-eight neurons of strait cortex were observed. NMDA-R1 receptor was located at the nuclei, Nissl body, cytoplasm, plasma membrane and the postsynaptic element of axons and dendrites. The ultrastructural morphology, including the mitochondrion, smooth endoplasmic reticulum, rough endoplasmic reticulum, and the Golgi apparatus, was not significantly different in the comparison between the cells in visual cortex of normal and strabismic groups. In the entire normal group, the percentage density of NMDA-R1 labeled cells was higher than that of strabismic groups (chi(2) = 4.280, 4.41, 4.89; P < 0.05). One thousand and three hundred and twenty NMDA-R1 immunopositive synapses were counted. The NMDA-R1 immunopositive synapses were dominated in layer II-III of visual cortex and increased during the development of normal kittens (F = 3.28, P < 0.05). There was no significant difference of NMDA-R1 immunopositive synapse distribution between the normal and strabismic kitten at 3 weeks (one week after operation) of age (F = 0.17, P > 0.05). The reduction of NMDA-R1 immunopositive synapse of plasma membrane in visual cortex of strabismic kitten was started at 5 weeks (threes weeks after surgery) of age. It was decreased significantly in strabismic amblyopic cat compared with that of the normal cat (F = 26.94, 47.01; P < 0.001). The ratios of nuclear membrane invagination of cells in visual cortex of normal and strabismic cat were higher than those of normal and squint kittens (chi(2) = 36.24, P < 0.01), but the ratio was not significantly different between the normal and strabismic group.

CONCLUSION: (1) In the normal developmental process of cat, the plasticity of the neuronal synapsis in II and III layer of visual cortex is relatively great. (2) In the strabismus amblyopia occurring in the plastic critical period of visual development, no pathological changes of neuronal organelle in the visual cortex are found, but there are changes at molecular level in the neuronal synapsis.