Figure 1.

Plexus morphology of NOS-expressing fibers in the brain of a vertebrate (rat; A, B) and an insect (locust; C, D). Both groups of animals have convergently adopted an NO source architecture in which extensive meshworks of exceedingly fine fibers arise from comparatively few neurons. A, The plexus of NOS-expressing fibers in the rat cerebral cortex arises from a scattered population of neurons. Targets include both an extensive volume of (synaptic) gray matter and the blood vessels within it (small arrows in A). B, High-power image of the region indicated by the black frame in A reveals the ubiquity of exceedingly fine fibers that constitute the plexus. C, The plexus of NOS-expressing fibers in the medulla of the locust optic lobe is similarly derived from few neurons and pervades an extensive volume of synaptic neuropil. D, High-power view of the region indicated by the black frame in C.