Quantitative analysis of AChR aggregate parameters. The stimulus protocols for all panels are shown at the bottom: C control (no stimulus), A agrin, L laminin-1, AL agrin and laminin, A>L agrin followed by laminin, L>A laminin followed by agrin. See Table 2 for protocol details. A-D, numbers at the top indicate statistical groupings based on one factor ANOVA F tests, p < .05. A, expression of receptors (arbitrary units). Both agrin and LN1 increased the label intensity of AChRs significantly, and agrin clearly more so than LN1. In all combinations assayed the effects of agrin and LN1 on receptor expression were additive. B, number of aggregates detected per cell. On this basis LN1 alone was similar to control cells, while agrin alone or in combination gave similarly increased numbers of aggregates. C, aggregate size in micrometers. In this case both agrin and laminin, alone or in combination, produced similarly enhanced aggregate size compared to control cells. D, aggregate density (arbitrary units). With regard to this metric agrin alone was indistinguishable from control cells, while laminin alone or in combination showed a significant increase in density. E, the mean Z corresponding to the average separation between aggregates. For random distributions this metric has an expected value of 0. Significant deviations from random separation (p < .01) are marked with *. When significant, negative values indicate that aggregates are closer together than random distributions, and positive values would indicate aggregates farther apart than average (see Materials and Methods). In this set of experiments controls showed a small but significant deviation from randomness, and agrin alone showed a large deviation. In both cases the aggregates were found to be further apart than expected at random.