An Integrated Micro- and Macroarchitectural Analysis of the Drosophila Brain by Computer-Assisted Serial Section Electron Microscopy
(A) Schematic depiction of cross-section of one brain hemisphere, showing outer cortex of neuronal cell bodies in central neuropile, formed by neuronal processes (neurites). One lineage of primary neurons is highlighted in purple color. Processes of glial cells (green) surround the cortex and neuropile and form boundaries around compartments within the neuropile. (B) Schematic of larval brain and ventral nerve cord, indicating positioning and orientation of serial sections. The first stack contains the neuropile of one brain hemisphere in two closely adjacent sets of 400 and 100 sections, respectively. The second stack includes 250 sections of the ventral nerve cord (corresponding to approximately two consecutive neuromeres). Colored lines represent axon tracts connecting brain and ventral nerve cord (after 69). (C, D) Electron micrographs of sections of neuropile illustrating resolution that can be achieved at 5,000× primary magnification. Arrow in (C) points at synapse; arrow in (D) indicates presynaptic vesicles; arrowhead shows obliquely sectioned microtubule. At a resolution of 4 nm per pixel, these structures can be clearly resolved. Scale bars: 1 µm (C); 350 nm (D).