Dendritic spines are the postsynaptic components of most excitatory synapses in the mammalian brain. Spines accumulate rapidly during early postnatal development and undergo a substantial loss as animals mature into adulthood. In past decades, studies have revealed that the number and size of dendritic spines are regulated by a variety of gene products and environmental factors, underscoring the dynamic nature of spines and their importance to brain plasticity. Recently, in vivo time-lapse imaging of dendritic spines in the cerebral cortex suggests that, although spines are highly plastic during development, they are remarkably stable in adulthood, and most of them last throughout life. Therefore, dendritic spines may provide a structural basis for lifelong information storage, in addition to their well-established role in brain plasticity. Because dendritic spines are the key elements for information acquisition and retention, understanding how spines are formed and maintained, particularly in the intact brain, will likely provide fundamental insights into how the brain possesses the extraordinary capacity to learn and to remember.

Neurons in the human central nervous system (CNS) are unable to regenerate, as a result of both an inhibitory environment and their inherent inability to regrow. In contrast, the CNS environment in fish is permissive for growth, yet some neurons still cannot regenerate. Fish thus offer an opportunity to study molecules that might surmount the intrinsic limitations they share with mammals, without the complication of an inhibitory environment. We show by in vivo imaging in zebrafish that post-injury application of cyclic adenosine monophosphate can transform severed CNS neurons into ones that regenerate and restore function, thus overcoming intrinsic limitations to regeneration in a vertebrate.

Most studies of spinal interneurons in vertebrate motor circuits have focused on the activity of interneurons in a single motor behavior. As a result, relatively little is known about the extent to which particular classes of spinal interneurons participate in different behaviors. Similarities between the morphology and connections of interneurons activated in swimming and escape movements in different fish and amphibians led to the hypothesis that spinal interneurons might be shared by these behaviors. To test this hypothesis, we took advantage of the optical transparency of zebrafish larvae and developed a new preparation in which we could use confocal calcium imaging to monitor the activity of individual identified interneurons noninvasively, while we simultaneously filmed the movements of the fish with a high-speed digital camera. With this approach, we could directly examine the involvement of individual interneurons in different motor behaviors. Our work revealed unexpected differences in the interneurons activated in swimming and escape behaviors. The observations lead to predictions of different behavioral roles for particular classes of spinal interneurons that can eventually be tested directly in zebrafish by using laser ablations or mutant lines with interneuronal deficits.

The myelin sheath insulates axons in the vertebrate nervous system, allowing rapid propagation of action potentials via saltatory conduction. Specialized glial cells, termed Schwann cells in the PNS and oligodendrocytes in the CNS, wrap axons to form myelin, a compacted, multilayered sheath comprising specific proteins and lipids. Disruption of myelinated axons causes human diseases, including multiple sclerosis and Charcot-Marie-Tooth peripheral neuropathies. Despite the progress in identifying human disease genes and other mutations disrupting glial development and myelination, many important unanswered questions remain about the mechanisms that coordinate the development of myelinated axons. To address these questions, we began a genetic dissection of myelination in zebrafish. Here we report a genetic screen that identified 13 mutations, which define 10 genes, disrupting the development of myelinated axons. We present the initial characterization of seven of these mutations, defining six different genes, along with additional characterization of mutations that we have described previously. The different mutations affect the PNS, the CNS, or both, and phenotypic analyses indicate that the genes affect a wide range of steps in glial development, from fate specification through terminal differentiation. The analysis of these mutations will advance our understanding of myelination, and the mutants will serve as models of human diseases of myelin.

Animals can produce movements of widely varying speed and strength by changing the recruitment of motoneurons according to the well-known size principle. Much less is known about patterns of recruitment in the spinal interneurons that control motoneurons because of the difficulties of monitoring activity simultaneously in multiple interneurons of an identified class. Here we use electrophysiology in combination with in vivo calcium imaging of groups of identified excitatory spinal interneurons in larval zebrafish to explore how they are recruited during different forms of the escape response that fish use to avoid predators. Our evidence indicates that escape movements are graded largely by differences in the level of activity within an active pool of interneurons rather than by the recruitment of an inactive subset.

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Objective:Paresthesias can result from metabolic disorders, nerve entrapment following repetitive motions, hyperventilation pursuant to anxiety, or exposure to neurotoxins. We analyzed data from community members exposed to the World Trade Center (WTC) disaster of September 11, 2001, to evaluate whether exposure to the disaster was associated with paresthesias.Methods:Analysis of data from 3141 patients of the WTC Environmental Health Center.Results:Fifty-six percent of patients reported paresthesias at enrollment 7 to 15 years following the WTC disaster. After controlling for potential confounders, paresthesias were associated with severity of exposure to the WTC dust cloud and working in a job requiring cleaning of WTC dust.Conclusions:This study suggests that paresthesias were commonly associated with WTC-related exposures or post-WTC cleaning work. Further studies should objectively characterize these paresthesias and seek to identify relevant neurotoxins or paresthesia-inducing activities.

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