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Plasticity of Neural Connections

Overview

Dynamic alterations of adult brain function, or neural plasticity, can occur at the level of metabolites, protein chemistry, synaptic morphology, systems-level activation or anatomical rearrangement. Frank Anatomical Plasticity in the adult mammalian CNS is minimal in comparison to the developing and adolescent brain. Classically, one of the last stages in neural development is the "critical period," during which activity has a pronounced effect on connectivity, prior to entering the anantomically static adult stage. We are exploring the molecular basis for restriction of anatomical plasticity in the adult brain and spinal cord.

Nogo Receptor in Plasticity

Monocular deprivation normally alters ocular dominance in the visual cortex only during a postnatal critical period (20 to 32 days postnatal in mice). This is a period when intracortical myelination is reaching adult levels. Therefore, we focused on the role of the myelin inhibitor pathway in plasticity. Mutations in the Nogo-66 receptor (NgR1) affect cessation of ocular dominance plasticity. In NgR1-/- mice, plasticity during the critical period is normal, but it continues abnormally, such that ocular dominance at 45 or 120 days postnatal is subject to the same plasticity as at juvenile ages. Thus, physiological NgR signaling from myelin-derived Nogo, MAG, and OMgp consolidates the neural circuitry established during experience-dependent plasticity.

Our ongoing work explores the anatomical basis of NgR1-regulated plasticity. We hypothesize that alterations in anatomical plasticity underlie the electrophysiological evidence of increased cortical plasticity. We are using in vivo imaging and conditional NgR1 alleles to test the ability of this pathway to titrate adult anatomical plasticity in the mouse brain. This pathway plays a role in fear extinction and recovery from neurological trauma, as well as in ocular dominance plasticity.