Glial cells in the developing and adult olfactory lobe of the moth Manducasexta

The antennal lobe of the moth contains several classes of glial cells that are likely to play functional roles in both the developing and mature lobe. In this study, confocal and electron microscopy were used to examine in de tail the morphology of two classes of glial cells, those associated with ol factory receptor axons as they course to their targets in the lobe and thos e that form borders around the synaptic neuropil of the olfactory glomeruli . The former, the nerve-layer glia, have long processes with multiple expan sions that enwrap axon fascicles; the latter, the neuropil glia, constitute two sub-groups: complex glia with large cell bodies and branching, vellate arbors; and simple glia, with multiple, mostly unbranched processes with m any lamellate expansions along their lengths. The processes of complex glia appear to be closely associated with axon fascicles as they enter the glom eruli, while those of the simple glia surround the glomeruli as part of a m ulti-lamellar glial envelope, their processes rarely invading the synaptic neuropil of the body of the glomerulus. The full morphological development of antennal-lobe glial cells requires more than two-thirds of metamorphic d evelopment. During this period, cells that began as cuboidal or spindle-sha ped cells that were extensively dye-coupled to one another gradually assume their adult form and, at least under nonstimulated conditions, greatly red uce their coupling. These changes are only weakly dependent on the presence of olfactory receptor axons. Glial processes are somewhat shorter and less branched in the absence of these axons, but basic structure and degree of dye-coupling are unchanged.