Patterns Of Light-mediated C-fos Activity In The Medial Visual Cortex Of Mice Lacking Both Rods And Cones

Abstract

 

Purpose:

 

Retinal melanopsin cells are capable of activating the visual cortex in mice (Brown et al., 2010; Ecker et al., 2010). In order to investigate the anatomical extent of this response we have examined light-driven c-fos expression in the medial visual cortex of mice lacking rods/cones (rd/rd cl).

 

Methods:

 

Mice were dark-adapted overnight and either sacrificed in darkness or following 90 minutes light (250µW/cm2). Coronal sections through the brain were immunostained for c-fos together with the cytoarchitectural markers SMI-32, calretinin, calbindin, parvalbumin and GAD67. Light-induced neural activation was measured across the rostro-caudal extent of visual cortex by quantification of c-fos positive cells. In both the dark-adapted and light-exposed groups, analysis was restricted to a region of interest in medial V1 / V2.

 

Results:

 

There was a marked elevation in c-fos positive cells in the visual cortex of rd/rd cl mice following light exposure. This effect achieved statistical significance towards more caudal regions of medial visual cortex (p<0.05). While light-driven cortical activation was observed throughout all layers of visual cortex (I-VI), there was a marked response in layer IV (input) and the deepest layer (VI). The c-fos positive cells were associated with immunoreactivity for GAD67 and a small subpopulation expressed the inhibitory interneuron marker calbindin.

 

Conclusions:

 

Using the functional anatomical marker c-fos, we provide evidence that the melanopsin system is capable of activating more middle-caudal regions of visual cortex in retinal degenerate mice. A subset of activated neurons express markers consistent with inhibitory neurotransmission and the activation in layer VI may suggest a role for melanopsin in the modulation of dLGN sensitivity / visual object recognition.  

 

Keywords: ganglion cells • visual cortex • retina