The Journal of Neuroscience, March 1, 2002, 22(5):1807-1815
Extended Plasticity of Visual Cortex in Dark-Reared Animals May
Result from Prolonged Expression of cpg15-Like Genes
Wei-Chung Allen
Lee and
Elly
Nedivi
Center for Learning and Memory, Departments of Brain and Cognitive
Sciences and Biology, Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139
cpg15 is an activity-regulated gene that encodes a
membrane-bound ligand that coordinately regulates growth of apposing
dendritic and axonal arbors and the maturation of their synapses. These properties make it an attractive candidate for participating in plasticity of the mammalian visual system. Here we compare
cpg15 expression during normal development of the rat
visual system with that seen in response to dark rearing, monocular
blockade of retinal action potentials, or monocular deprivation. Our
results show that the onset of cpg15 expression in the
visual cortex is coincident with eye opening, and it increases until
the peak of the critical period at postnatal day 28 (P28). This
early expression is independent of both retinal activity and visual
experience. After P28, a component of cpg15 expression
in the visual cortex, lateral geniculate nucleus (LGN), and superior
colliculus (SC) develops a progressively stronger dependence on
retinally driven action potentials. Dark rearing does not affect
cpg15 mRNA expression in the LGN and SC at any age, but
it does significantly affect its expression in the visual cortex from
the peak of the critical period and into adulthood. In dark-reared
rats, the peak level of cpg15 expression in the visual
cortex at P28 is lower than in controls. Rather than showing the normal
decline with maturation, these levels are maintained in dark-reared
animals. We suggest that the prolonged plasticity in the visual cortex
that is seen in dark-reared animals may result from failure to
downregulate genes such as cpg15 that could promote
structural remodeling and synaptic maturation.
Key words:
dark rearing; visual system; cpg15; critical period; cortex; plasticity; TTX; monocular deprivation
Copyright © 2002 Society for Neuroscience 0270-6474/02/2251807-09$05.00/0