NGFI-A Expression in Response to an EE
We have recently demonstrated that exposure of animals for 1 hour/day to an EE setting for 3 weeks, a procedure that induces plasticity in the cerebral cortex, is capable of inducing the IEGs NGFI-A and arc in discrete regions of the retina, a region of the CNS previously thought to be incapable, or have limited capabilities, of undergoing reorganizational changes (Chernenko and West, 1976; Pinaud, 2004).
We showed that undisturbed (UD) rats, which remained housed in standard laboratory cages, and handled-only (HO) controls displayed only a few immunolabeled cells in the inner nuclear layer (INL) and ganglion cell layer (GCL), when compared to animals exposed to an EE (Pinaud et al., 2002b) (Fig. 5.1). Animals in the latter group had a marked increase of NGFI-A labeling in these retinal layers. In addition, Arc immunoreactivity was found in an upregulated fashion in the inner and outer plexiform layers of EE animals, but not in UD and HO controls (discussed below) (Fig. 5.1). These findings suggest that enhanced complexity of the visual environment triggers a cascade of gene expression that might be correlated with circuit rewiring. We postulate that these putative wiring modifications may be associated with the optimization of information capture and processing and thus, increased functional capacity. In fact, it has been demonstrated that exposure of mice to an enriched environment does enhance visual acuity by 18%, as compared to control animals (Prusky et al., 2000). It remains to be investigated whether the enhanced functional performance of visual circuitry is related to optimization of neural networks at the level of the retina or higher brain areas.
In our experiments, increased NGFI-A immunoreactivity was also found in the GCL, even though it is possible that some of the labeled neurons were amacrine cells. Since the different classes of amacrine cells were not explored in these experiments, it is difficult to speculate about the type of neuromodulation
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