Figure 7. Comparison of length density of VIP-immunostained nerves (L_V VIP) expressed x10^-5 µm^-2, after logarithmic transformation, among prostate regions (ducts, ampular, dorsal, and ventral) for pubertals, young adults, and aged adults. In each graph, the letters over each error bar indicate the significance: Bars affected by different letters show significant differences (P < .05).