, 1999). Owing to the fact that only few inhibitory neurons carry spines, studies of structural plasticity in cortical inhibitory neurons thus far have primarily focused on changes to the branch tips of dendrites (Chen et al., 2011, Lee et al., 2006 and Lee et al., 2008). The potential plasticity of dendritic spines on cortical inhibitory neurons in both the naive brain and following sensory deprivation is still unexplored.

Similarly, axonal boutons can serve as a structural marker for presynaptic components in chronic in vivo imaging experiments (De Paola et al., 2006 and Stettler et al., 2006). These studies have shown that axonal boutons of excitatory Talazoparib clinical trial cells display a baseline turnover in the unperturbed cortex (De Paola et al., 2006 and Stettler et al., 2006) and that, like spines, bouton dynamics increase following sensory deprivation in both excitatory (Yamahachi et al., 2009) and inhibitory (Chen et al., 2011 and Marik et al., 2010) neurons.

While the importance of inhibitory circuits in cortical plasticity is well established in juvenile animals during the critical period (Hensch, 2005), the role of inhibition is less understood in adult animals. In both functional (Froemke et al., 2007) and anatomical (Chen et al., 2011, Hendry and Jones, 1988 and Rosier et al., 1995) studies in adult animals, changes in inhibition seem to occur prior to changes in excitatory connections, over time courses Tryptophan synthase ranging from seconds (Froemke et al., 2007) to days (Chen et al., 2011 and Rosier et al., 1995) to months (Hendry and Jones, 1988), suggesting a possible role of reduced inhibition find more in enhancing plasticity of excitatory connections. In previous work, we have introduced a retinal lesion paradigm in mice (Keck et al., 2008), which leads to functional alterations in the visual cortex. Permanent ablation of a small part of the retina leaves a region of the monocular

visual cortex temporarily unresponsive. As had been described previously (Calford et al., 2003, Giannikopoulos and Eysel, 2006, Gilbert and Wiesel, 1992, Heinen and Skavenski, 1991 and Kaas et al., 1990), in the weeks and months following the retinal lesion, the cortical “lesion projection zone” (LPZ) reorganizes functionally and regains responsiveness to visual stimuli. The functional reorganization is believed to occur largely within the cortex (Gilbert and Wiesel, 1992), as there is only very restricted recovery in the lateral geniculate nucleus (LGN, Eysel, 1982). Reorganization is accompanied by cortical structural plasticity, such as increased spine dynamics in layer 5 pyramidal neurons in the LPZ (Keck et al., 2008) and axonal sprouting of layer 2/3 pyramidal cells into the LPZ from adjacent regions of cortex (Darian-Smith and Gilbert, 1994 and Yamahachi et al., 2009). Here, we use chronic two-photon imaging to examine the structural plasticity of inhibitory neurons following retinal lesions.