Animals exposed to an enriched environment display increased brain volume, an enhanced number of dendritic spines and enlarged synapses. These are all features of the phenomenon known as neural plasticity.
Now there is a report that includes the first description of molecular plasticity in the mammalian retina, as revealed by gene expression.
This is the first evidence that genes are regulated in the adult mammalian retina by non-invasive -- and biologically meaningful -- stimulation of the sensory pathway.
As the authors put it, "A marked upregulation of both NGFI-A and Arc, two candidate-plasticity genes, was observed in adult rats that had been exposed to an enriched environment for 3 weeks. This increase was paralleled by an increase in the expression of the late genes GAP-43 and Synapsin I, which also indicated changes in retinal connectivity.
"Our results suggest that both NGFI-A and Arc may regulate mechanisms of plasticity that had been invoked by heightened complexity of the visual environment."
The report was presented at the Society for Neuroscience meeting in San Diego November 10-15 by Raphael Pinaud, Liisa A. Tremere, Marsha R. Penner, Steven Barnes and Harold A. Robertson of Dalhousie University, Halifax, Nova Scotia, Canada; and Felipe F. Hess of Dalhousie and the Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
In the case of the retina, neural plasticity refers to the capability of neurons there to undergo genetically-mediated changes in functional connectivity as a result of particular sets of sensory experience.
In their experiments, the authors tested retinal plasticity as a result of exposure to an enriched environment.
The plastic nature of central nervous system tissue has only recently become accepted into the dogma of neuroscience. This makes it extremely interesting that the entire mammalian visual system, including the retina, appears to be capable of experience-dependent reorganization, presumably to enhance the resolution and fidelity of visual information processing.
The implications of rewiring in the retina for more complex processing of visual information will be tested in the upcoming months by the same team. But enriched environment exposure has generally been linked to enhanced performance in skill learning and memory. Therefore, the authors anticipate that molecular plasticity in these early stages of visual processing represent exciting mechanisms by which an organism improves its ability to extract and digest sensory information that activates the visual pathway.
The paper has been accepted for publication in Molecular Brain Research and will appear online approximately one month from now.
[Contact: R. William Currie Ph.D., Raphael Pinaud]