Innexin Gap Junctions

Morphology of the adult brain: mushroom body glia

Confocal image of adult brain showing mushroom body neurons and a number of glial types

Figure legend: Neurons and glia in the adult Drosophila brain. A, Single confocal section near the front of the brain corresponding to the region of the oulined box in the brain illustration above. Glia (green) and mushroom body (MB) neurons (purple) are shown in the region of the MB lobes (α, β/γ). B, Confocal image from the same brain. This optical section is from the middle of the brain. CG, cortex glia. NG, neuropile glia. P, pedunculus (seen as a cross-section through the axonal tract). EB, ellipsoid body. Glia express UAS-mCD8-GFP (green) under the transcriptional control of nrv2-GAL4. Neurons are revealed by antibody staining with α-FasII antibodies (purple). Arrowheads indicate where neuropile glial processes are closely associated with MB neuronal tracts (in the lobes and the pedunculus) and also with neurons of other brain structures such as the central complex ellipsoid body (EB).

nervana 2 is the Drosophila homolog of the vertebrate protein 'Adhesion Molecule on Glia' (AMOG) (Gloor et al. 1990). The nervana 2 enhancer trap line nrv2-GAL4 (Sun et al, 1999) drives reporter expression in two types of glial cell, cortex and neuropile glia, in the adult brain. Cortex glia are present near the brain surface and extend glial processes around the neuronal and glial cell bodies that exist at the outer edge of the brain (the cortex). This produces a mesh-like structure, as seen in image A above (also image: Cortex glia honeycomb near the protocerebral bridge). Neuropile glia cell bodies and processes are located within the brain and they ensheath various neuronal structures including the mushroom bodies and central complex (detailed descriptions of these structures can found at Flybrain). Individual neuropile glia processes can be observed almost throughout the brain (when you look very closely) but can't be seen in image B above because of the 'full moon effect' that renders it impossible to visualize very strong and very weak fluorescent signals in the same image (Ito et al. 2003). Because of this, only the strongest glial staining, corresponding to large aggregations of glial processes (Image: Neuropile glial processes ensheathing a section of the MB pedunculus), can be seen in image B. A third type of glial cell, called surface glia (Image: Putative surface glia revealed by an Inx2-GAL4 enhancer trap line), cover the exterior of the brain but are not revealed by nrv2-GAL4 (Dumstrei et al. 2003).

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