Abstract: The present study examined the ultrastructure of synapses before and 80 min． after LTP produced in visual cortical brain slices of young rats aged 18—30 days． Double—blind scoring procedures were used to quantify the following parameters in electrophotographs with image analyzer：（1）the width of the synaptic cleft;（2）the thickness of the postsynaptic densities（PSD）；（3） the length of the active zones and（4） the curvature of the synaptic interface．The result suggested that the curvature of the synaptic interface and the length of active zones all increased significantly．

Key words: synapse, curvature, LTP