Retraction of Active Axons Figure 5. Quantitative analysis of arbor morphology. Scattergrams show a plot of two measures, total length (A) and number of branch points (B), for all arbors in this study together with the measures obtained under various experimental conditions published previously [9,10,17]. Total length (A) is calculated by adding the lengths of all axon segments constituting the terminal field of an arbor. The number of branch points (B) indicates the total number of axonal bifurcations. Only portions above the layer IV and V border are considered for these analyses. Each symbol represents the data of an arbor, and short horizontal lines indicate the means of individual groups. Red and blue symbols represent open-eye and deprived-eye arbors, respectively. The data obtained in the BoNT/E- and muscimol-treated cortex are indicated by the shaded and striped areas, respectively. The duration of cortical treatment is indicated at the top. Arbor and animal groups are indicated at the bottom as follows: Norm, arbors of animals with normal vision; BD, arbors of binocularly deprived animals; ND and D of MD, nondeprived-eye and deprived-eye arbors of monocularly deprived animals; P30, P40 and P50, arbors of normal animals on postnatal days 30, 40 and 50. doi:10.1371/journal.pone.0004193.g005 might directly affect intracellular signals leading to morphological changes. Active afferents might have greater Ca2+ influx at their terminals than deprived-eye afferents. The difference in Ca2+ concentration might regulate axon behavior, as demonstrated in the guidance of growth cones [22]. Alternatively, presynaptic activity might regulate the response of axons to a repulsive signal in the cortex. For example, recent experiments demonstrated that p75 neurotrophin receptors mediate axon retraction during Table 1. Statistical comparison of geniculocortical arbors. Cortical treatment Arbor Groups Total length BoNT/E-norm BoNT/E-BD BoNT/E-norm BoNT/E-BD Number of branch points BoNT/E BD (P48–50) 0.001 Q - - 0.027 Q Muscimol (1w) Muscimol (2w) MD-ND (P47–53) ns ns ns ns MD-ND (P42–43) 0.001 q 0.0001 q 0.002 q 0.0001 q MD-D (P41–45) 0.034Q ns ns 0.041Q Norm (P40–46) ns 0.0001 q 0.003 q ,0.0001 q BD (P40–46) 0.001Q ns 0.001Q 0.021Q None P30 0.002Q ns ns ns P40 P50 0.001 Q 0.004 Q 0.003 Q ns 0.002 Q 0.003 Q 0.002 Q 0.003Q Statistical comparisons among arbor groups are provided as p values (Wilcoxon rank sum test). ns, not significant (p.0.05). Arrows for the p values indicate whether each of the two measures of the BoNT/E-norm and BoNT/E-BD groups shown on the left is larger (q) or smaller (Q) than those of the arbor groups shown on the top. Arbor and animal groups: norm and BD, arbors of normal-vision and BD animals, respectively. MD-ND and MD-D, nondeprived-eye and deprived-eye arbors of MD animals, respectively. The ages of the animals in each group at perfusion are given in parentheses below each experimental condition. doi:10.1371/journal.pone.0004193.t001 PLoS ONE | www.plosone.org 6 January 2009 | Volume 4 | Issue 1 | e4193