[Abstract Title]. - Society for Neuroscience

Max-Planck Society
The Rockefeller University Women & Science Fellowship
Title: Axonal sprouting of horizontal connections in adult mouse somatosensory cortex follows
whisker trimming
Authors: *S. A. MARIK 1 , H. YAMAHACHI 1 , W. DENK 2 , C. D. GILBERT 1 ;
1 Lab. of Neurobio., The Rockefeller Univ., New York, NY; 2 Dept. of Biomed. Optics, Max-
Planck Inst. for Med. Res., Heidelberg, Germany
Abstract: Neural circuits in the adult brain can be rewired to recover function that is lost after
stroke, sensory deprivation or neurodegenerative diseases. Evidence for this rewiring can be seen
at the functional level through changes in receptive fields and at the anatomical level by
synaptogenesis following sensory loss. Layer II/III cortical neurons are key players in cortical
reorganization since their long range horizontal axons allow for communication between
topographically distant cortical regions, and they are responsible for an increase in axonal
density in response to sensory deprivation. To determine the circuit mechanisms underlying map
reorganization in the mouse somatosensory cortex, we applied a technique that allowed us to
explore the dynamics of axons and boutons in vivo. Specifically, we employed the use of viral
vectors that were genetically engineered with the gene encoding YFP, which allowed us to
fluorescently label neurons located in specific barrels. The structural dynamics of labeled
neuronal processes were observed with two-photon imaging. We used the adult mouse
somatosensory cortex as a model to examine the structural changes of axons undergoing cortical
reorganization. Chronic whisker plucking reliably induces an expansion of the cortical
representation of adjacent whiskers. The receptive fields of the barrel cortex were mapped
electrophysiologically, and inputs from horizontal connections in the superficial cortical layers of
the deprived whisker barrel were labeled by injecting the virus into the adjacent, non-deprived
barrels. After full expression of the virus, the same labeled axons were imaged before whisker
plucking and at varying times following the initiation of chronic whisker plucking. Over a period
of weeks, there was a progressive sprouting of new axon collaterals into the deprived whisker
barrels. At the same time, other parts of the original axonal arbors projecting to this region were
pruned. Overall there was a net increase in axonal density from the non-deprived whisker barrel
into the deprived barrels. The functional remapping of the whisker barrel system is likely due to
this change in the plexus of horizontal connections.
Disclosures: S.A. Marik, None; H. Yamahachi, None; W. Denk, None; C.D. Gilbert, None.
Poster
239. Structural Plasticity at Synapses I
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm