Neurogenesis in the adult crayfish brain. A. Crayfish were exposed to BrdU for 6 hours followed by immediate sacrifice. Confocal image of a crayfish hemi-brain labeled immunocytochemically for BrdU (green) and glutamine synthetase (blue) and counterstained with propidium iodide (red), a marker of nucleic acids. BrdU-labeled cells are observed within both the lateral (LPZ) and medial (MPZ) proliferation zones. Precursor cells located in a niche (rectangle) generate daughter cells that migrate along the streams to either the LPZ or MPZ. B. Dextran-fluorescein (green) injections into the pericardial sinus show that the "vascular cavity" of the niche (arrowhead) is confluent with the vasculature. The niche lies on a blood vessel (arrows). Propidium iodide (red), and glutamine synthetase (blue) labeling are also shown. Sidebar shows each channel separately. C. A triple-labeled M-phase cell close to the niche is immunolabeled with glutamine synthetase (cyan), phophohistone-H3 (green) and BrdU (red). The asterisk marks the vascular cavity. [Image from 17] D. Model summarizing events leading to the production of olfactory and accessory lobe interneurons in adult crayfish brain [Image from 29]. 1st generation precursors reside within a neurogenic niche where they divide symmetrically. Both daughter cells appear to migrate to the proliferation zones towards either the LPZ or the MPZ. At least one more division will occur in the LPZ and MPZ before the progeny (third- and subsequent-generations) differentiate into neurons. Black arrows indicate direction of precursor cell migration; curved arrows indicate locations of cell divisions. Scale bars: A, 100 μm; B, 20 μm, side bar 20 μm; C, 20 μm; C inset, 10 μm.