H. Yu*; A. Majewska; M. Sur
Picower Center for Learning & Memory, MIT, Cambridge, MA, USA

Dendritic spines are small protrusions on dendritic processes. They contain the postsynaptic domains of most of the excitatory synapses in cortex, and are therefore well poised to subserve functional neuronal plasticity. Previous studies have revealed that dendritic spine morphology is very dynamic and plastic, indicating that spines have the potential to consolidate the functional plasticity at the micro-structural level. In this study, we examine whether changes in visually-driven activity elicit the modification of dendritic spine morphology in ferret visual cortex. In order to compare changes in subcellular structure to changes in network activity over time, structural two-photon imaging and functional intrinsic optical imaging are performed in the same piece of cortex in vivo. A modified Sindbis virus (Jeromin et al 2003) delivering Green Fluorescence Protein (GFP) is focally injected into the superficial layers of ferret primary visual cortex, and a transparent window is made above the injected cortex to allow chronic two-photon and optical imaging. We find that GFP labeled neuronal structures, including dendritic spines, can be clearly imaged two days after virus injection, and the label remains stable and can be repeatedly imaged for a couple of days. Optical imaging demonstrates a strong ocular dominance and orientation map in both injected and non-injected regions. These maps remain unchanged over a month in control animals. In order to examine visually-driven functional and structural changes, we monocularly deprive P40-50 ferrets by suturing the contralateral eyelids, and ocular dominance significantly shifts to the ipsilateral eye in a matter of days. During this time, the same groups of dendritic spines are repeatedly examined day by day in the deprived and non-deprived eye dominated regions, and the spine dynamics are compared with the simultaneous functional shift in ocular dominance.

(Supported by NIH grants EY07023, EY15068 & Whiteman Fund).