The child's brain is more malleable or plastic than that of adults and this accounts for the ability of children to learn new skills quickly or recovery from brain injuries. Several mechanisms contribute to this ability including overproduction and deletion of neurons and synapses, and activity-dependent stabilization of synapses. The molecular mechanisms for activity dependent synaptic plasticity are being discovered and this is leading to a better understanding of the pathogenesis of several disorders including neurofibromatosis, tuberous sclerosis, Fragile X syndrome and Rett syndrome. Many of the same pathways involved in synaptic plasticity, such as glutamate-mediated excitation, can also mediate brain injury when the brain is exposed to stress or energy failure such as hypoxia-ischemia. Recent evidence indicates that cell death pathways activated by injury differ between males and females. This new information about the molecular pathways involved in brain plasticity and injury are leading to insights that will provide better therapies for pediatric neurological disorders. KeywordsPlasticity; Injury; Fragile X Syndrome; Rett Syndrome; Hypoxia-Ischemia; NMDA; AMPA; Periventricular Leukomalacia Many disorders and injuries of the developing brain affect the basic mechanisms that allow the nervous system to be shaped by experience during childhood. These mechanisms provide the substrate for brain plasticity (kasosei in Japanese), which is much more active in children than in adults. Plasticity in the child's brain is enhanced because the organization of networks of *Correspondence: 707 North Broadway, Baltimore, MD 21205, Fax: 443-923-9317 Phone: 443-923-9315, Johnston@kennedykrieger.org. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. neuronal synapses as well as white matter pathways remain "under construction" well into adolescence and even later(1). Accordingly, the effects of intensive learning in school, exposure to a second language or practice in athletics has a much greater impact on children than adults. Several neurobiological mechanism contribute to brain plasticity, including an over-production of neurons in early development, apoptosis or programmed cell death of excessive neurons, overproduction and elimination of immature synapses in childhood, and continuous stabilization and strengthening of synaptic connections later in life(2). In this review we focus on some mechanisms for synaptic plasticity, and emerging evidence that these processes are disrupted in several pediatric neurological disorders. NIH Public Access Synaptic PlasticitySynaptic p...

Subcortical white matter (WM) is a frequent target of ischemic injury and extensive WM lesions are important substrates of vascular cognitive impairment (VCI) in humans. However, ischemic stroke rodent models have been shown to mainly induce cerebral infarcts in the gray matter, while cerebral hypoperfusion models show only WM rarefaction without infarcts. The lack of animal models consistently replicating WM infarct damage may partially explain why many neuroprotective drugs for ischemic stroke or VCI have failed clinically, despite earlier success in preclinical experiments. Here, we report a novel animal model of WM infarct damage with cognitive impairment can be generated by surgical implantation of different devices to the right and left common carotid artery (CCA) in C57BL/6J mice. Implantation of an ameroid constrictor to the right CCA resulted in gradual occlusion of the vessel over 28 d, whereas placement of a microcoil to the left CCA induced ϳ50% arterial stenosis. Arterial spin labeling showed a gradual reduction of cerebral blood flow over 28 d post operation. Such reductions were more marked in the right, compared with the left, hemisphere and in subcortical, rather than the cortical, areas. Histopathological analysis showed multiple infarct damage in right subcortical regions, including the corpus callosum, internal capsule, hippocampal fimbria, and caudoputamen, in 81% of mice. Mice displaying such damage performed significantly poorer in locomotor and cognitive tests. The current mouse model replicates the phenotypes of human subcortical VCI, including multiple WM infarcts with motor and cognitive impairment.

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