Neuronal and glial morphology in olfactory systems: Significance for information-processing and underlying developmental mechanisms

The shapes of neurons and glial cells dictate many important aspects of their functions. In olfactory systems, certain architectural features are characteristics of these two cell types across a wide variety of species. The accumulated evidence suggests that these common features may play fundamental roles in olfactory information processing. For instance, the primary olfactory neuropil in most vertebrate and invertebrate olfactory systems is organized into discrete modules called glomeruli. Inside each glomerulus, sensory axons and CNS neurons branch and synapse in patterns that are repeated across species. In many species, moreover, the glomeruli are enveloped by a thin and ordered layer of glial processes. The glomerular arrangement reflects the processing of odor information in modules that encode the discrete molecular attributes of odorant stimuli being processed. Recent studies of the mechanisms that guide the development of olfactory neurons and glial cells have revealed complex reciprocal interactions between these two cell types, which may be necessary for the establishment of modular compartments. Collectively, the findings reviewed here suggest that specialized cellular architecture plays key functional roles in the detection, analysis, and discrimination of odors at early steps in olfactory processing.