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“The neonatal intraventricular injection of adeno-associated virus has been shown to transduce neurons widely throughout the brain, CP-868596 in vitro but its full potential for experimental neuroscience has not been adequately explored. We report a detailed analysis of the method’s versatility with an emphasis on experimental applications where tools for genetic manipulation are currently lacking. Viral injection into the neonatal mouse brain is fast, easy, and accesses regions of the brain including the cerebellum and brainstem

that have been difficult to target with other techniques such as electroporation. We show that viral transduction produces an inherently mosaic expression pattern that can be exploited by varying the titer to transduce isolated neurons or densely-packed populations. We demonstrate that the expression of virally-encoded proteins is active much sooner than previously believed, allowing genetic perturbation during critical periods of neuronal plasticity, but is also long-lasting and stable, allowing chronic studies of aging. We harness these features to visualise and manipulate neurons in the hindbrain that have been recalcitrant to approaches commonly applied in the cortex. We show that viral labeling aids the analysis of postnatal dendritic maturation in cerebellar Purkinje neurons by allowing individual

cells to be readily distinguished, and then demonstrate that the same sparse labeling allows live in vivo imaging of mature Purkinje neurons at a resolution sufficient for complete analytical reconstruction. DAPT concentration Given the rising availability of viral constructs, packaging services, and genetically modified animals, these techniques should facilitate a wide range of experiments into brain development, function, and degeneration. The ability to create mosaic animal models in which selected cell populations are both genetically altered and

permanently labeled has yielded new insight into cell-autonomous and non-autonomous actions of many normal and disease-associated proteins (Davy & Soriano, 2005; C-X-C chemokine receptor type 7 (CXCR-7) Holtmaat & Svoboda, 2009; Holtmaat et al., 2009; Kanning et al., 2010; Park & Bowers, 2010; Warr et al., 2011). In parallel, the introduction of transgenic mice with sparse mosaic expression of fluorescent proteins (Feng et al., 2000) has afforded unprecedented views of neuronal morphology in vivo that have revised our understanding of structural plasticity in the brain following environmental stimulation and pathophysiological insult. Flexible yet precise control of mosaicism is needed in both of these settings, but serious challenges limit the use of current techniques. Modified genetic elements and fluorescent tags can be easily introduced by in-utero or neonatal electroporation, but the range of transfection is limited by the direction of the electric field and the diffusion of DNA (De Vry et al., 2010).