Charting Plasticity in the Regenerating Maps of the Mammalian Olfactory Bulb

Abstract

The anatomical organization of a neural system can offer a glimpse into its functional logic. The basic premise is that by understanding how something is put together one can figure out how it works. Unfortunately, organization is not always represented purely at an anatomical level and is sometimes best revealed through molecular or functional studies. The mammalian olfactory system exhibits organizational features at all these levels including 1) anatomically distinct structural layers in the olfactory bulb, 2) molecular maps based upon odorant receptor expression, and 3) functional local circuits giving rise to odor columns that provide a contextual logic for an intrabulbar map. In addition, various forms of cellular plasticity have been shown to play an integral role in shaping the structural properties of most neural systems and must be considered when assessing each system's anatomical organization. Interestingly, the olfactory system invokes an added level of complexity for understanding organization in that it regenerates both at the peripheral and the central levels. Thus, olfaction offers a rare opportunity to study both the structural and the functional properties of a regenerating sensory system in direct response to environmental stimuli. In this review, we discuss neural organization in the form of maps and explore the relationship between regeneration and plasticity. KeywordsOlfactory system; Map; Sensory neurons; Olfactory bulb; Intrabulbar map Sensory Systems and MapsSensory systems serve to translate the external environment into neural representations and signals that allow organisms to survive. In each sensory modality the outside world is transposed onto the central nervous system via a series of maps that generally serve to refine information as it travels from a peripheral receptive field to the cortex. In the visual system specialized light-sensing neurons, the rods and cones, reside in the retina and are capable of detecting a single photon of light that is converted to electrical signals that are relayed through the thalamus and then transmitted to the primary visual cortex. Within the retina these rods and cones are arranged in a two-dimensional array where nearest neighbor relations are critical to faithfully transpose images of the external world so that they are accurately deciphered by the brain. The resulting map generated by the retina is then reproduced several times, first by retinal projections to the lateral geniculate nucleus (LGN) and then through LGN projections to the visual cortex. Similarly, in the auditory system tonotopic maps exist that transpose the Address correspondence to: Leonardo Belluscio, Developmental Neural Plasticity Unit, National Institute of Neurological Disorders and Stroke, Porter Neuroscience Research Center, Building 35, Room 3A-116, 35 Convent Drive, MSC 3703, Bethesda, MD 20892-3703 (belluscl@ninds.nih.gov). NIH Public Access Author ManuscriptNeuroscientist. Author manuscript; available in PMC 2010 November 5. NIH-PA Author ManuscriptNI...

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