Rearrangement of dendritic spines during short term monocular deprivation in the primary visual cortex of the ferret in vivo.

H. Yu*, A. Majewska & M. Sur.

Picower Center for Learning & Memory, Dept. Brain & Cognitive Sciences, M.I.T., Cambridge, MA 02139

Spines are small protrusions on dendrites that receive excitatory synapses. Previous studies have revealed that dendritic spines are dynamic, indicating that spines have the potential to consolidate functional cortical plasticity at the micro-structural level. In this study, we examined whether changes in visually-driven activity elicit rapid modifications of dendritic spine morphology in ferret primary visual cortex (V1). In order to compare changes in subcellular structure to changes in network activity, structural two-photon imaging of GFP-labeled neurons and functional intrinsic signal optical imaging were performed in the same cortex in vivo. Monocular deprivation (MD) for 3-6 hours can induce a significant shift of the ocular dominance map in V1 of a critical period ferret. The deprived eye response decreases, and this shift can be reversed by 3-6 hours of binocular visual experience. Functional changes after MD are accompanied by a significant loss of dendritic spines (control 5%; MD 20%), suggesting that the decrease in deprived eye responses may be mediated by a rapid loss of cortical connections subserving the deprived eye. This hypothesis is supported by the observation that in regions dominated by the deprived eye, spine loss is more pronounced than in the binocular zone. Importantly, the spine number recovers after 1 day of binocular vision, partially due to the reappearance of some spines that were lost following MD, and also due to the appearance of spines at new sites. Spines that are likely to turn over during MD and recovery include small mushroom spines, stubby spines and filopodia; large mushroom spines rarely turn over. The correlation between dendritic spine turnover and the magnitudes and timescales of ocular dominance shifts at the same loci suggests that rapid structural changes at synapses are closely tied to functional remodeling elicited by visual activity.

(Supported by NIH grants EY07023, EY15068 & the Burroughs Wellcome Fund).