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The Journal of Neuroscience, November 1, 2006, 26(44):11257-11266; doi:10.1523/JNEUROSCI.2805-06.2006

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Development/Plasticity/Repair
Activity-Dependent Plasticity in the Olfactory Intrabulbar Map

Carolyn A. Marks, Kai Cheng, Diana M. Cummings, and Leonardo Belluscio

Developmental Neural Plasticity Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892

Correspondence should be addressed 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. Email: belluscl{at}ninds.nih.gov

In mammals, each olfactory bulb contains two mirror-symmetric glomerular maps. Isofunctional glomeruli within each bulb are specifically linked through a set of reciprocal intrabulbar projections (IBPs) to form an intrabulbar map. We injected neural tracers into the glomerular layer on one side of the bulb and examined the resulting projection on the opposite side. In adult mice, the size of the projection tuft is directly proportional to the size of the injected region. Using this ratio as a measure of IBP maturity, we find an immature 5:1 projection to injection ratio at 1 week of age that gradually refines to a mature 1:1 by 7 weeks. Moreover, whereas the glomerular map is able to form despite the elimination of odorant-induced activity, the intrabulbar map shows clear activity dependence for its precise formation. Here we show through experiments with both naris-occluded and anosmic mice that odorant-induced activity is not required to establish IBPs but is crucial for projection refinement. In contrast, increased glomerular activation through exposure to distinct odorants during map development can accelerate the refinement of projections associated with the activated glomeruli. These findings illustrate a clear role for odorant-induced activity in shaping the internal circuitry of the bulb. Interestingly, activity deprivation can alter the organization of both the developing and the mature map to the same degree, demonstrating that intrabulbar map plasticity is maintained into adulthood with no discernible critical period.

Key words: external tufted cell; olfactory bulb; development; neural tracer; axon targeting; mouse

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Received June 30, 2006; revised Sept. 5, 2006; accepted Sept. 19, 2006.

Correspondence should be addressed 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. Email: belluscl{at}ninds.nih.gov

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				S. V. Jones, D. C. Choi, M. Davis, and K. J. Ressler Learning-Dependent Structural Plasticity in the Adult Olfactory Pathway J. Neurosci., December 3, 2008; 28(49): 13106 - 13111. [Abstract] [Full Text] [PDF]

				L. Belluscio and D. M. Cummings Charting Plasticity in the Regenerating Maps of the Mammalian Olfactory Bulb Neuroscientist, June 1, 2008; 14(3): 251 - 263. [Abstract] [PDF]

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