The diameters of the sampled dendrites and the number of total silver grains in each group were shown. Bars represented the mean percentage of KOPR-silver grains associated with the plasma membrane in rats intrathecally injected with dynorphin A (15 nmole), U50,488H (100 nmole) or saline. Values are mean ± SEM of data obtained from 3 rats per group, at least 150 dendrite profiles per rat.*, p<0.05, compared with saline group by Fisher’s exact test using the silver grain numbers categorized into on the surface or in the cytoplasm.