In vitro analyses of interactions between olfactory receptor growth cones and glial cells that mediate axon sorting and glomerulus formation

Abstract

During development, the axons of olfactory receptor neurons project to the CNS and converge on glomerular targets. For vertebrate and invertebrate olfactory systems, neuron-glia interactions have been hypothesized to regulate the sorting and targeting of olfactory receptor axons and the development of glomeruli. In the moth Manduca sexta, glial reduction experiments have directly implicated two types of central olfactory glia, the sorting zone- and neuropil-associated glia, in key events in olfactory development, including axon sorting and glomerulus stabilization. By using cocultures containing central olfactory glial cells and explants of olfactory receptor epithelium, we show that olfactory receptor growth cones elaborate extensively and cease advancement following contact with sorting zone- and neuropil-associated glial cells. These effects on growth cone behavior were specific to central olfactory glia; peripheral glial cells of the olfactory nerve failed to elicit similar responses in olfactory receptor growth cones. We propose that sorting zone- and neuropil-associated glial cells similarly modify axon behavior in vitro by altering the adhesive properties and cytoskeleton of olfactory receptor growth cones and that these in vitro changes may underlie functionally relevant changes in growth cone behavior in vivo.

Sprouting interneurons in mushroom bodies of adult cricket brains

“…Enhanced cytoplasmic electron density either is found in sprouting neural and glial cells (this study; Salecker and Boeckh, 1995) or represents decaying degenerating material in these cell types (Schü rmann, 1987;Watts et al, 2003Watts et al, , 2004Brown and Strausfeld, 2006). The glial system has been demonstrated to be crucially involved in growth processes sorting the neuropil into subdivisions and to serve for intimate contact with nerve cells (Tolbert and Oland, 1990;Rössler et al, 1999;Tucker et al, 2004). Our ultrastructural data on the KC perikaryal layer also show that areas just peripheral to the core of inward-growing KC axons reveal an electron-dense matrix with interspersed glial cell extensions.…”

“…Phalloidin-f-actin occurs in the tips of growth cones clearly demonstrated in insect cell culture (Tucker et al, 2004). High f-actin contents in compact fiber bundles have been similarly found in sprouting KC proliferation centers of immature larval and nymphal forms of different species (Kurusu et al, 2002;Farris and Sinakevitch, 2003;Farris et al, 2004), reflecting fiber growth and potential motility.…”

“…The antibody has been successfully employed to detect acetylated ␣-tubulins from various organisms, including protista, plants, invertebrates, and vertebrates (Le Dizet and Piperno, 1987). It stains selectively tubulins in arthropods (Harzsch et al, 1997;Tucker et al, 2004) and annelids (Voronenzhskaya et al, 2002), especially in nerve cell somata and in axonal fibers with gathered microtubuli. Therefore, tracts and nerves can be visualized and traced similarly to tracing in silver-or gold-stained insect nervous systems (see Strausfeld, 1976).…”

Embryonic origin of theDrosophila brain neuropile

“…Glial-neuronal interactions in the context of neuropile formation have been studied at the greatest level of resolution in the antennal lobe of Manduca and other insects (Malun et al, 1994;Baumann et al, 1996;Oland and Tolbert, 2003;Tucker et al, 2004). The antennal lobe is characterized by neuropilar "microcompartments," the glomeruli.…”

Insect neuronal cultures: an experimental vehicle for studies of physiology, pharmacology and cell interactions

“…In contrast centrally derived glia from the sorting-zone and neuropile-associated glia from the antennal lobe never form arrays in vitro and growth cone-glial cell encounters halt axon elongation and cause permanent elaborations in growth cone morphology. It is proposed that antennal nerve glia play a role in supporting axon elongation while sorting and targeting roles are played by central glia by altering the adhesive properties and cytoskeletal elements of the olfactory receptor growth cones (Tucker and Tolbert 2003;Tucker et al 2004). The interactions between neurones and glia during the development of the insect nervous system and the contribution made by in vitro studies have been reviewed by Oland and Tolbert (2003).…”