A second subtype of glia, referred

to as Drosophila astrocytes, extends cellular processes deeply into the neuropil and associates closely with axons, dendrites, and synapses ( Awasaki et al., 2008 and Doherty et al., 2009). Selleckchem HIF inhibitor One might not think so, but fly CNS glia have evolved a complex association with the vasculature (containing hemolymph), likely to maintain neuronal health. Gas exchange in Drosophila occurs through a series of trachea, gas filled tubules that penetrate most tissues in the fly, including the CNS. Within the cell cortex, trachea are tightly surrounded by glial membranes, likely from cortex glia, and within the neuropil tracheal elements are in close proximity to astrocyte membranes ( Pereanu et al., MAPK inhibitor 2007). These glia-trachea contacts provide an obvious potential route of gas exchange between CNS neuronal cell bodies and the environment. And what about nutrient delivery? The Drosophila nervous system is surrounded by a multilayered BBB, which is composed of an outermost neural lamella (a carbohydrate-based extracellular matrix), a layer of glial cells termed perineurial glia, and then subperineurial glia (SPGs) ( DeSalvo et al., 2011). SPGs are flattened, surround the entire CNS, and form pleated septate junctions with one another that act as a BBB. The

entire BBB structure can be thought of as an inside-out blood vessel—hemolymph is on the outside and, to get in, the CNS molecules must pass through the neural lamella (a charge and size exclusion barrier). The PGs and SPGs (the latter sealed with tight junctions) are probably the site of exchange of ions, metabolites, growth factors, and other molecules that travel into and out of the CNS. The final subtype of CNS Mephenoxalone glia is ensheathing cells, which form a layer between the neuropil and cell cortex but also penetrate the neuropil to compartmentalize different regions of the brain. Rhombomeres of the vertebrate CNS are an example where compartmentalization of brain structures is important for segregating function;

whether this is also the case for Drosophila glial brain segregation remains for the moment speculative. Certainly these cells are critical to maintain brain health—after injury, ensheathing glia become “reactive” and extend membranes to sites of injury, where they phagocytose degenerating neuronal material ( MacDonald et al., 2006). Certain functional roles for glial cells in the fly are analogous to those defined in mammals. Drosophila CNS glia express glutamate transporters, glutamine synthetase, and GABA transporters presumably to aid in neurotransmitter recycling ( Rival et al., 2004 and Soustelle et al., 2002). They guide axon outgrowth, dendrite morphogenesis, and provide trophic support required for neuronal survival ( Edenfeld et al., 2005 and Freeman and Doherty, 2006). Peripheral glial cells are important for maintaining nerve health, NMJ integrity, and growth.