Figure 8.

Signaling properties of coarse versus fine nitrergic plexus morphologies with random fiber distributions. A, An example of multiple nitrergic plexuses is found in the ocellar neuropil of the locust. Fine fibers arborize in a pseudorandom manner. Scale bar, 10 μm. B, C, NO signals generated by a finer plexus are less dependent on the details of the random plexus morphology, more homogeneous, and more centered relative to the synthesizing volume. Populations of model plexuses (n = 30) composed of 1- μm-diameter fibers (B) or 5- μm-diameter fibers (C) were grown by a random branching algorithm, yielding the same overall source density within a synthesizing region of 100 × 100 × 100 μm³. Three instances of each population are shown schematically in Bi, Ci (synthesizing region indicated by dashed gray outlines). Bii, Cii, After 1 s of NO synthesis, the frequency distribution of the NO concentrations encountered in the center is much narrower across the population of fine plexuses. This indicates greater independence from the morphological details of the plexus and greater homogeneity of the concentration distribution across the synthesizing volume. Biii, Ciii, Compare the concentration profiles across the center of random plexuses (fine gray lines; n = 30) with that across a homogeneous spherical source (heavy black line). The spherical source has the same overall source strength as each plexus and occupies the same volume as the synthesizing region within which the plexuses were grown. The signals from fine plexuses (Biii) approximate much more closely that of a homogeneous source than those generated by coarse plexuses (Ciii). Moreover, with finer plexus morphologies, the NO cloud is better centered over the synthesizing region. This is shown schematically in Bi and Ci by gray circles, indicating the clouds, and quantitatively in D by plotting the center-of-mass positions of the clouds across populations of fine (circles) and coarse (crosses) plexuses on a slice through the center of the synthesizing region.