Neuronal heterotopias in the developing cerebral cortex produced by neurotrophin-4.

The marginal zone (MZ) of embryonic neocortex is crucial to its normal development. We report that neurotrophin-4 (but not NT3 or NGF), applied to embryonic rodent cortex in vitro or in vivo, produces heterotopic accumulations of neurons in the MZ. Although heterotopia production is TrkB mediated, BDNF is >10-fold less effective than NT4. Heterotopic neurons have the same birth date and phenotype as normal MZ neurons; they are not the result of NT4-induced proliferation or rescue from apoptosis. We suggest that NT4 causes excess neurons to migrate into the MZ and thus may play a role in normal MZ formation as well as in the pathogenesis of certain human cortical dysplasias.

Two modes of radial migration in early development of the cerebral cortex.

Layer formation in the developing cerebral cortex requires the movement of neurons from their site of origin to their final laminar position. We demonstrate, using time-lapse imaging of acute cortical slices, that two distinct forms of cell movement, locomotion and somal translocation, are responsible for the radial migration of cortical neurons. These modes are distinguished by their dynamic properties and morphological features. Locomotion and translocation are not cell-type specific; although at early ages some cells may move by translocation only, locomoting cells also translocate once their leading process reaches the marginal zone. The existence of two modes of radial migration may account for the differential effects of certain genetic mutations on cortical development.

New directions for neuronal migration.

Analysis of genetic mutations that lead to abnormal migration and layer formation in the developing cerebral cortex of mice and humans has led to important new discoveries regarding the molecular mechanisms that underlie these processes. Genetic manipulation and experimental analysis have demonstrated significant tangential migrations of cortical neurons, some arriving from very distant noncortical sites.

Clinical considerations in cerebral palsy and spasticity.

The ultimate goal for management of patients with cerebral palsy is to help them grow up to become as independent as possible, learn to make their own choices in life, and pursue their own dreams. Optimal mobility is crucial to achieving independence and is also necessary for better health and quality of life in these patients. This article discusses the treatment of spasticity in cerebral palsy, addresses tone management issues in relationship to mobility and physical fitness, and introduces the reader to a comprehensive approach to the management of patients with cerebral palsy.

Expanded spectrum of herpes simplex encephalitis in childhood.

We designed a polymerase chain reaction method to detect herpes simplex virus (HSV) DNA in spinal fluid from patients with encephalitis. The polymerase chain reaction amplified a 211 base-pair segment of the HSV DNA polymerase gene. Applying this method, we diagnosed HSV type 1 infection in three young children, aged 7 to 13 months, who had atypical forms of the illness. On the basis of magnetic resonance imaging, their disease was diffuse or multifocal in two cases and, in all three, lacked the temporal lobe involvement considered characteristic of HSV encephalitis beyond the neonatal period. Most of the diffuse or multifocal abnormalities detected by magnetic resonance imaging were not apparent by computed tomography. Restriction enzyme analysis of the polymerase chain reaction products from all three patients indicated that their disease was caused by HSV type 1. We conclude that in preschool-age children beyond the neonatal period, the spectrum of HSV encephalitis includes multifocal or diffuse involvement of the brain, which may be detected most efficiently by magnetic resonance imaging. The polymerase chain reaction method has the potential for providing an early diagnosis, but further studies are required to define the sensitivity and specificity of the polymerase chain reaction before it can be used for routine clinical decision making.

Motor benefit from levodopa in spastic quadriplegic cerebral palsy.

We report on a 16-year-old girl with spastic quadriplegic cerebral palsy associated with premature birth and typical periventricular leukomalacia, who had a dramatic improvement in motor function after treatment with carbidopa/levodopa. Kinematic and electromyographic analyses of reaching movements demonstrate that levodopa decreased muscle co-contraction, decreased unwanted movements, and improved her ability to maintain a steady arm posture. These findings suggest that levodopa be considered as an adjunct therapy for the treatment of spastic quadriplegic cerebral palsy.

Automated recognition and mapping of immunolabelled neurons in the developing brain.

The cerebral cortex is distinguished by layers of neurons of different morphologies and densities. The layers are formed by the migration of newly generated neurons from the ventricular zone to the cortical plate near the outer (pial) boundary of the cortex, along radial paths approximately perpendicular to the cortical surface. Immunochemical labelling makes these cells' patterns visible in brightfield microscopy so that layer formation can be studied. We developed a suite of programs that automatically digitize the entire cortex, identify the labelled cells and compute cell densities along local radial paths. Cell identification used supervised classification on all the significantly stained objects corresponding to maxima in lowpass filtered versions of the digital microgrphs. Classification of all the stained objects as cells or noncell objects was made by a decision rule based on morphometric and grey-level texture features, including features based on Gabor functions. Detection sensitivity and classification accuracy were jointly maximized on training data consisting of about 3000 expert-identified neurons in micrographs. Total program performance was tested on a separate (test) set of labelled neurons the same size as the training data set. The program detected 85% of the cells in the test set with a total error of 0.19. The identified cells' locations were used to compute population densities along normals to the cortical layers, and these densities served as a measure of neuronal migration. Transcortical density profiles obtained by computation and by manual cell counting were very similar. The cell identification program was built on well-established methods in statistical pattern recognition and image analysis and should generalize readily to other histological preparations.

Neuronal production of fibronectin in the cerebral cortex during migration and layer formation is unique to specific cortical domains.

The distribution of fibronectin (FN) changes rapidly during early development of the cerebral cortex, but its cellular source is not known. With in situ hybridization we find two spatially and temporally distinct periods of FN mRNA expression in the embryonic and early postnatal cortex of the mouse. Before and during formation of the preplate by the first postmitotic neurons, FN mRNA levels are high throughout the telencephalic vesicle, deep in the neuroepithelial proliferative zone that contains dividing cells and the cell bodies of radial glia; expression in the cortical proliferative zone is limited to the period of neurogenesis. Just after the cortical plate is formed within the preplate, FN mRNA is expressed in the intermediate zone, which contains migrating neurons, and in the cortical plate, where neurons migrate past their predecessors to form layers. Brefeldin A treatment of an organotypic slice preparation demonstrates FN production in the intermediate zone and cortical plate, in locations that correspond exactly to the distribution of FN mRNA by in situ hybridization. FN-producing cells immunolabel with neuron-specific markers; in the intermediate zone and lower cortical plate they have morphological features characteristic of migrating neurons and are closely apposed to radial glia. FN mRNA expression and protein production continue in neurons of the cortical plate through the period of layer formation and then are downregulated. Examination of dissociated cortical cells by laser confocal microscopy confirms that FN accumulation after brefeldin A treatment is intracellular in neurons as well as in glia. Neuroepithelial expression of FN mRNA takes place throughout the telencephalon; FN produced by neurons is restricted to cells migrating toward and into specific cortical domains that include neocortex, insular and perirhinal cortex, and subiculum. Thus FN may be involved initially in supporting the cell division and fate determination that takes place in the neuroepithelium; later production by migrating neurons may play a role in the selection of radial glial pathways that lead to specific cortical regions, and in interactions between neurons as they form cortical layers within these regions.