Neuronal activity plays an important role in the development and structural-functional maintenance of the brain as well as in its life-long plastic response to changes in sensory stimulation. We characterized the impact of unilateral 15°laser lesions in the temporal lower visual field of the retina, on visually driven neuronal activity in the afferent visual pathway of adult mice using in situ hybridization for the activity reporter gene zif268. In the first days post-lesion, we detected a discrete zone of reduced zif268 expression in the contralateral hemisphere, spanning the border between the monocular segment of the primary visual cortex (V1) with extrastriate visual area V2M. We could not detect a clear lesion projection zone (LPZ) in areas lateral to V1 whereas medial to V2M, agranular and granular retrosplenial cortex showed decreased zif268 levels over their full extent. All affected areas displayed a return to normal zif268 levels, and this was faster in higher order visual areas than in V1. The lesion did, however, induce a permanent LPZ in the retinorecipient layers of the superior colliculus. We identified a retinotopy-based intrinsic capacity of adult mouse visual cortex to recover from restricted vision loss, with recovery speed reflecting the areal cortical magnification factor. Our observations predict incomplete visual field representations for areas lateral to V1 vs. lack of retinotopic organization for areas medial to V2M. The validation of this mouse model paves the way for future interrogations of cortical region-and cell-type-specific contributions to functional recovery, up to microcircuit level.

In this study we used incorporation of the DNA synthesis marker 5-bromo-2′-deoxyuridine or BrdU to visualize cell proliferation in the visual system of the adult mouse as a response to monocular enucleation. We detected new BrdU-labeled cells in different subcortical retinal target regions and we established a specific time frame in which this cell proliferation occurred. By performing immunofluorescent double stainings for BrdU and different vascular (glucose transporter type 1, collagen type IV), glial (thymosin β4, glial fibrillary acidic protein) and neuronal (Neuronal Nuclei, doublecortin) markers, we identified these proliferating cells as activated microglia. Additional immunohistochemical stainings for thymosin β4 and glial fibrillary acidic protein also revealed reactive astrocytes in the different retinorecipient nuclei and allowed us to delineate a time frame for microglial and astroglial activation. A PCR array experiment further showed increased levels of cytokines, chemokines, growth factors and enzymes that play an important role in microglial-astroglial communication during the glial activation process in response to the deafferentation.

Abstract:We here report on the immunolocalization of Dynamin I (Dyn I) in neurons of the visual system of the cat. The lateral geniculate nucleus (LGN) complex displayed abundant Dyn I immunoreactivity in typical relay cells of the X-, Y-and W-pathway. The superficial and deep layers of the superior colliculus were also populated by Dyn I-immunoreactive projection neurons of the W-and Y-cell system. In primary visual areas 17 and 18, many densely packed layer VI neurons were intensely stained. A clear Dyn I signal was also demonstrated in pyramidal neurons of supragranular layers II and III, while layer IV displayed low Dyn I immunoreactivity. Additionally, area 18 displayed larger border pyramidal neurons in layer III compared to area 17. Generally, Dyn I was localized to the cell body and dendrites of neurons, to the neuropil and sometimes also to axon bundles. Typically, the Dyn I signal was not always uniformly distributed within the somatodendritic compartment. Based on its widespread distribution mainly in projection neurons Dyn I may play a fundamental role in mature neurons of different cortical and subcortical structures of the adult mammalian brain.