Neuronal migration, cerebral cortical development, and cerebral cortical anomalies

Curvature analysis of perisylvian epilepsy

PURPOSE

We assess whether alterations in the convolutional anatomy of the deep perisylvian area (DPSA) might indicate focal epileptogenicity.

MATERIALS AND METHODS

The DPSA of each hemisphere was segmented on MRI and a 3D gray-white matter interface (GWMI) geometrical model was constructed. Comparative visual and quantitative assessment of the convolutional anatomy of both the left and right DPSA models was performed. Both the density of thorn-like contours (peak percentage) and coarse interface curvatures was computed using Gaussian curvature and shape index, respectively. The proposed method was applied to a total of 14 subjects; 7 patients with an epileptogenic DPSA and 7 non-epileptic subjects.

RESULTS

A high peak percentage correlated well with the epileptogenic DPSA. It distinguished between patients and non-epileptic subjects (P = 0.029) and identified laterality of the epileptic focus in all but one case. A diminished regional curvature also identified epileptogenicity (P = 0.016) and, moreover, its laterality (P = 0.001).

CONCLUSION

An increased peak percentage from a global view of the GWMI of the DPSA provides some indication of a propensity toward a focal or regional DPSA epileptogenicity. A diminished convolutional anatomy (i.e., smoothing effect) appears also to coincide with the epileptogenic site in the DPSA and to distinguish laterality.

p75NTR prevents the onset of cerebellar granule cell migration via RhoA activation

Neuronal migration is one of the fundamental processes during brain development. Several neurodevelopmental disorders can be traced back to dysregulated migration. Although substantial efforts have been placed in identifying molecular signals that stimulate migration, little is known about potential mechanisms that restrict migration. These restrictive mechanisms are essential for proper development since it helps coordinate the timing for each neuronal population to arrive and establish proper connections. Moreover, preventing migration away from a proliferative niche is necessary in maintaining a pool of proliferating cells until the proper number of neuronal progenitors is attained. Here, using mice and rats, we identify an anti-migratory role for the p75 neurotrophin receptor (p75NTR) in cerebellar development. Our results show that granule cell precursors (GCPs) robustly express p75NTR in the external granule layer (EGL) when they are proliferating during postnatal development, however, they do not express p75NTR when they migrate either from the rhombic lip during embryonic development or from the EGL during postnatal development. We show that p75NTR prevented GCP migration by maintaining elevated levels of active RhoA. The expression of p75NTR was sufficient to prevent the migration of the granule cells even in the presence of BDNF (brain-derived neurotrophic factor), a well-established chemotactic signal for this cell population. Our findings suggest that the expression of p75NTR might be a critical signal that stops and maintains the GCPs in the proliferative niche of the EGL, by promoting the clonal expansion of cerebellar granule neurons.

Seizures and EEG characteristics in a cohort of pediatric patients with dystroglycanopathies

PURPOSE

To delineate the seizure type, phenotype and V-EEG patterns of dystroglycanopathy (DGP) and correlate them with the neuroradiological and genetic results.

METHODS

Patients with seizures were screened from our dystroglycanopathy database from January 2010 to March 2021. Detailed clinical information, including seizure type, brain magnetic resonance imaging (MRI), EEG and genetic analysis, was collected.

RESULTS

Thirteen patients (15.1%, 13/86) had seizures. Most patients had a severe phenotype. The mean age at first seizure onset was 2 years and 8 months. The most common seizure type was generalized tonic-clonic seizure (GTCS), with 92.3% (12/13) induced by fever. Three patients were diagnosed with epilepsy. Most patients did not take any medicine. A few patients had irregular use of antiseizure medications (ASMs). Of the 13 patients, seven patients were diagnosed with MEB, four patients with POMGNT1 mutations, two with ISPD mutations, and one with POMT1 mutation. Three patients were diagnosed with FCMD with FKTN mutations. Two patients were diagnosed with CMD-MR, one patient with ISPD mutation, and one with POMT1 mutation. One patient was diagnosed with LGMD with FKRP mutation. Nine patients underwent EEG examination, and eight patients had abnormal EEG results, including abnormal background activities in three patients, abnormal background activities combined with paroxysmal discharges in three patients, pure paroxysmal discharges in one patient and positive phase sharp waves in the occipital region in one patient. For radiology, brain MRI was available for 12 patients. The brain MRI of nine patients showed type II lissencephaly. Two patients showed cerebellar hypoplasia and brainstem hypoplasia. One patient had a normal brain MRI result. Patients with type II lissencephaly usually had abnormal background activities and paroxysmal discharges.

CONCLUSION

The seizure phenotype of dystroglycanopathy (DGP) is characterized by GTCS, which was the most common seizure type, while focal seizures and epileptic spasms could also occur in DGP patients. Most seizures were induced by fever. Seizures were relatively more frequent in severe phenotypes of DGP, such as FCMD and MEB. Abnormal background activities were the most common EEG patterns, which were closely related to type II lissencephaly.

The Epigenome in Neurodevelopmental Disorders

Neurodevelopmental diseases (NDDs), such as autism spectrum disorders, epilepsy, and schizophrenia, are characterized by diverse facets of neurological and psychiatric symptoms, differing in etiology, onset and severity. Such symptoms include mental delay, cognitive and language impairments, or restrictions to adaptive and social behavior. Nevertheless, all have in common that critical milestones of brain development are disrupted, leading to functional deficits of the central nervous system and clinical manifestation in child- or adulthood. To approach how the different development-associated neuropathologies can occur and which risk factors or critical processes are involved in provoking higher susceptibility for such diseases, a detailed understanding of the mechanisms underlying proper brain formation is required. NDDs rely on deficits in neuronal identity, proportion or function, whereby a defective development of the cerebral cortex, the seat of higher cognitive functions, is implicated in numerous disorders. Such deficits can be provoked by genetic and environmental factors during corticogenesis. Thereby, epigenetic mechanisms can act as an interface between external stimuli and the genome, since they are known to be responsive to external stimuli also in cortical neurons. In line with that, DNA methylation, histone modifications/variants, ATP-dependent chromatin remodeling, as well as regulatory non-coding RNAs regulate diverse aspects of neuronal development, and alterations in epigenomic marks have been associated with NDDs of varying phenotypes. Here, we provide an overview of essential steps of mammalian corticogenesis, and discuss the role of epigenetic mechanisms assumed to contribute to pathophysiological aspects of NDDs, when being disrupted.

Superparamagnetic Iron Oxide Nanoparticles: Cytotoxicity, Metabolism, and Cellular Behavior in Biomedicine Applications

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely investigated and applied in the field of biomedicine due to their excellent superparamagnetic properties and reliable traceability. However, with the optimization of core composition, shell types and transfection agents, the cytotoxicity and metabolism of different SPIONs have great differences, and the labeled cells also show different cellular behaviors. Therefore, a holistic review of the construction and application of SPIONs is desired. This review focuses the advances of SPIONs in the field of biomedicine in recent years. After summarizing the toxicity of different SPIONs, the uptake, distribution and metabolism of SPIONs in vitro were discussed. Then, the regulation of labeled-cells behavior is outlined. Furthermore, the major challenges in the optimization process of SPIONs and insights on its future developments are proposed.

Caffeine and adenosine A2A receptors rescue neuronal development in vitro of frontal cortical neurons in a rat model of attention deficit and hyperactivity disorder

Although some studies have supported the effects of caffeine for treatment of Attention deficit and hyperactivity disorder (ADHD), there were no evidences about its effects at the neuronal level. In this study, we sought to find morphological alterations during in vitro development of frontal cortical neurons from Spontaneoulsy hypertensive rats (SHR, an ADHD rat model) and Wistar-Kyoto rats (WKY, control strain). Further, we investigated the effects of caffeine and adenosine A₁ and A_2A receptors (A₁R and A_2AR) signaling. Cultured cortical neurons from WKY and SHR were analyzed by immunostaining of microtubule-associated protein 2 (MAP-2) and tau protein after treatment with either caffeine, or A₁R and A_2AR agonists or antagonists. Besides, the involvement of PI3K and not PKA signaling was also assessed. Neurons from ADHD model displayed less neurite branching, shorter maximal neurite length and decreased axonal outgrowth. While caffeine recovered neurite branching and elongation from ADHD neurons via both PKA and PI3K signaling, A_2AR agonist (CGS 21680) promoted more neurite branching via PKA signaling. The selective A_2AR antagonist (SCH 58261) was efficient in recovering axonal outgrowth from ADHD neurons through PI3K and not PKA signaling. For the first time, frontal cortical neurons were isolated from ADHD model and they presented disturbances in the differentiation and outgrowth. By showing that caffeine and A_2AR may act at neuronal level rescuing ADHD neurons outgrowth, our findings strengthen the potential of caffeine and A_2AR receptors as an adjuvant for ADHD treatment.

Deprivation of Muscleblind-Like Proteins Causes Deficits in Cortical Neuron Distribution and Morphological Changes in Dendritic Spines and Postsynaptic Densities

Myotonic dystrophy (Dystrophia Myotonica; DM) is the most common adult-onset muscular dystrophy and its brain symptoms seriously affect patients’ quality of life. It is caused by extended (CTG)_n expansions at 3′-UTR of DMPK gene (DM type 1, DM1) or (CCTG)_n repeats in the intron 1 of CNBP gene (DM type 2, DM2) and the sequestration of Muscleblind-like (MBNL) family proteins by transcribed (CUG)_n RNA hairpin is the main pathogenic mechanism for DM. The MBNL proteins are splicing factors regulating posttranscriptional RNA during development. Previously, Mbnl knockout (KO) mouse lines showed molecular and phenotypic evidence that recapitulate DM brains, however, detailed morphological study has not yet been accomplished. In our studies, control (Mbnl1^+/+; Mbnl2^cond/cond; Nestin-Cre^−/−), Mbnl2 conditional KO (2KO, Mbnl1^+/+; Mbnl2^cond/cond; Nestin-Cre^+/−) and Mbnl1/2 double KO (DKO, Mbnl1^ΔE3/ΔE3; Mbnl2^cond/cond; Nestin-Cre^+/−) mice were generated by crossing three individual lines. Immunohistochemistry for evaluating density and distribution of cortical neurons; Golgi staining for depicting the dendrites/dendritic spines; and electron microscopy for analyzing postsynaptic ultrastructure were performed. We found distributional defects in cortical neurons, reduction in dendritic complexity, immature dendritic spines and alterations of postsynaptic densities (PSDs) in the mutants. In conclusion, loss of function of Mbnl1/2 caused fundamental defects affecting neuronal distribution, dendritic morphology and postsynaptic architectures that are reminiscent of predominantly immature and fetal phenotypes in DM patients.

Separating chemotherapy-related developmental neurotoxicity from cytotoxicity in monolayer and neurosphere cultures of human fetal brain cells

Chemotherapy-induced neurotoxicity can reduce the quality of life of patients by affecting their intelligence, senses and mobility. Ten percent of safety-related late-stage clinical failures are due to neurological side effects. Animal models are poor in predicting human neurotoxicity due to interspecies differences and most in vitro assays cannot distinguish neurotoxicity from general cytotoxicity for chemotherapeutics. We developed in vitro assays capable of quantifying the paediatric neurotoxic potential for cytotoxic drugs. Mixed cultures of human fetal brain cells were differentiated in monolayers and as 3D-neurospheres in the presence of non-neurotoxic chemotherapeutics (etoposide, teniposide) or neurotoxicants (methylmercury). The cytotoxic potency towards dividing progenitors versus differentiated neurons and astrocytes was compared using: (1) immunohistochemistry staining and cell counts in monolayers; (2) through quantitative Western blots in neurospheres; and (3) neurosphere migration assays. Etoposide and teniposide, were 5-10 times less toxic to differentiated neurons compared to the mix of all cells in monolayer cultures. In contrast, the neurotoxicant methylmercury did not exhibit selectivity and killed all cells with the same potency. In 3D neurospheres, etoposide and teniposide were 24 to 10 times less active against neurons compared to all cells. These assays can be used prioritise drugs for local drug delivery to brain tumours.

GAP-independent functions of DLC1 in metastasis

Metastases are responsible for most cancer-related deaths. One of the hallmarks of metastatic cells is increased motility and migration through extracellular matrixes. These processes rely on specific small GTPases, in particular those of the Rho family. Deleted in liver cancer-1 (DLC1) is a tumor suppressor that bears a RhoGAP activity. This protein is lost in most cancers, allowing malignant cells to proliferate and disseminate in a Rho-dependent manner. However, DLC1 is also a scaffold protein involved in alternative pathways leading to tumor and metastasis suppressor activities. Recently, substantial information has been gathered on these mechanisms and this review is aiming at describing the potential and known alternative GAP-independent mechanisms allowing DLC1 to impair migration, invasion, and metastasis formation.

Ultrasmall superparamagnetic iron oxide nanoparticle prelabelling of human neural precursor cells

Stem cells prelabelled with iron oxide nanoparticles can be visualised using magnetic resonance imaging (MRI). This technique allows for noninvasive long-term monitoring of migration, integration and stem cell fate following transplantation into living animals. In order to determine biocompatibility, the present study investigated the biological impact of introducing ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) into primary human fetal neural precursor cells (hNPCs) in vitro. USPIOs with a mean diameter of 10-15 nm maghemite iron oxide core were sterically stabilised by 95% methoxy-poly(ethylene glycol) (MPEG) and either 5% cationic (NH2) end-functionalised, or 5% Rhodamine B end-functionalised, polyacrylamide. The stabilising polymer diblocks were synthesised by reversible addition-fragmentation chain transfer (RAFT) polymerisation. Upon loading, cellular viability, total iron capacity, differentiation, average distance of migration and changes in intracellular calcium ion concentration were measured to determine optimal loading conditions. Taken together we demonstrate that prelabelling of hNPCs with USPIOs has no significant detrimental effect on cell biology and that USPIOs, when utilised at an optimised dosage, are an effective means of noninvasively tracking prelabelled hNPCs.

Effects of ethanol exposure on nervous system development in zebrafish

Alcohol (ethanol) is a teratogen that adversely affects nervous system development in a wide range of animal species. In humans numerous congenital abnormalities arise as a result of fetal alcohol exposure, leading to a spectrum of disorders referred to as fetal alcohol spectrum disorder (FASD). These abnormalities include craniofacial defects as well as neurological defects that affect a variety of behaviors. These human FASD phenotypes are reproduced in the rodent central nervous system (CNS) following prenatal ethanol exposure. While the study of ethanol effects on zebrafish development has been more limited, several studies have shown that different strains of zebrafish exhibit differential susceptibility to ethanol-induced cyclopia, as well as behavioral deficits. Molecular mechanisms underlying the effects of ethanol on CNS development also appear to be shared between rodent and zebrafish. Thus, zebrafish appear to recapitulate the observed effects of ethanol on human and mouse CNS development, indicating that zebrafish can serve as a complimentary developmental model system to study the molecular basis of FASD. Recent studies examining the effect of ethanol exposure on zebrafish nervous system development are reviewed, with an emphasis on attempts to elucidate possible molecular pathways that may be impacted by developmental ethanol exposure. Recent work from our laboratories supports a role for perturbed extracellular matrix function in the pathology of ethanol exposure during zebrafish CNS development. The use of the zebrafish model to assess the effects of ethanol exposure on adult nervous system function as manifested by changes in zebrafish behavior is also discussed.

Hereditary lissencephaly and cerebellar hypoplasia in Churra lambs

Background

Lissencephaly is a rare developmental brain disorder in veterinary and human medicine associated with defects in neuronal migration leading to a characteristic marked reduction or absence of the convolutional pattern of the cerebral hemispheres. In many human cases the disease has a genetic basis. In sheep, brain malformations, mainly cerebellar hypoplasia and forms of hydrocephalus, are frequently due to in utero viral infections. Although breed-related malformations of the brain have been described in sheep, breed-related lissencephaly has not been previously recorded in a peer reviewed publication.

Results

Here we report neuropathological findings in 42 newborn lambs from a pure Churra breed flock, with clinical signs of weakness, inability to walk, difficulty in sucking and muscular rigidity observed immediately after birth. All the lambs showed near-total agyria with only a rudimentary formation of few sulci and gyri, and a severe cerebellar hypoplasia. On coronal section, the cerebral grey matter was markedly thicker than that of age-matched unaffected lambs and the ventricular system was moderately dilated. Histologically, the normal layers of the cerebral cortex were disorganized and, using an immunohistochemical technique against neurofilaments, three layers were identified instead of the six present in normal brains. The hippocampus was also markedly disorganised and the number and size of lobules were reduced in the cerebellum. Heterotopic neurons were present in different areas of the white matter. The remainder of the brain structures appeared normal. The pathological features reported are consistent with the type LCH-b (lissencephaly with cerebellar hypoplasia group b) defined in human medicine. No involvement of pestivirus or bluetongue virus was detected by immunohistochemistry. An analysis of pedigree data was consistent with a monogenic autosomal recessive pattern inheritance.

Conclusions

The study describes the clinical and pathological findings of lissencephaly with cerebellar hypoplasia in Churra lambs for which an autosomal recessive inheritance was the most likely cause. Histopathological features observed in the cerebral cortex and hippocampus are consistent with a possible failure in neuronal migration during brain development. This report suggests that lissencephaly should be considered in the differential diagnosis of congenital neurological disease in newborn lambs showing weakness, inability to walk and difficulty sucking.

Dystroglycan on radial glia end feet is required for pial basement membrane integrity and columnar organization of the developing cerebral cortex

Interactions between the embryonic pial basement membrane (PBM) and radial glia (RG) are essential for morphogenesis of the cerebral cortex because disrupted interactions cause cobblestone malformations. To elucidate the role of dystroglycan (DG) in PBM-RG interactions, we studied the expression of DG protein and Dag1 mRNA (which encodes DG protein) in developing cerebral cortex and analyzed cortical phenotypes in Dag1 CNS conditional mutant mice. In normal embryonic cortex, Dag1 mRNA was expressed in the ventricular zone, which contains RG nuclei, whereas DG protein was expressed at the cortical surface on RG end feet. Breaches of PBM continuity appeared during early neurogenesis in Dag1 mutants. Diverse cellular elements streamed through the breaches to form leptomeningeal heterotopia that were confluent with the underlying residual cortical plate and contained variably truncated RG fibers, many types of cortical neurons, and radial and intermediate progenitor cells. Nevertheless, layer-specific molecular expression seemed normal in heterotopic neurons, and axons projected to appropriate targets. Dendrites, however, were excessively tortuous and lacked radial orientation. These findings indicate that DG is required on RG end feet to maintain PBM integrity and suggest that cobblestone malformations involve disturbances of RG structure, progenitor distribution, and dendrite orientation, in addition to neuronal "overmigration."

Sonographic assessment of normal and abnormal patterns of fetal cerebral lamination

OBJECTIVES

Prenatal development of the brain is characterized by gestational age-specific changes in the laminar structure of the brain parenchyma before 30 gestational weeks. Cerebral lamination patterns of normal fetal brain development have been described histologically, by postmortem in-vitro magnetic resonance imaging (MRI) and by in-vivo fetal MRI. The purpose of this study was to evaluate the sonographic appearance of laminar organization of the cerebral wall in normal and abnormal brain development.

METHODS

This was a retrospective study of ultrasound findings in 92 normal fetuses and 68 fetuses with abnormal cerebral lamination patterns for gestational age, at 17-38 weeks' gestation. We investigated the visibility of the subplate zone relative to the intermediate zone and correlated characteristic sonographic findings of cerebral lamination with gestational age in order to evaluate transient structures.

RESULTS

In the normal cohort, the subplate zone-intermediate zone interface was identified as early as 17 weeks, and in all 57 fetuses examined up to 28 weeks. In all of these fetuses, the subplate zone appeared anechoic and the intermediate zone appeared homogeneously more echogenic than did the subplate zone. In the 22 fetuses between 28 and 34 weeks, there was a transition period when lamination disappeared in a variable fashion. The subplate zone-intermediate zone interface was not identified in any fetus after 34 weeks (n=13). There were three patterns of abnormal cerebral lamination: (1) no normal laminar pattern before 28 weeks (n=32), in association with severe ventriculomegaly, diffuse ischemia, microcephaly, teratogen exposure or lissencephaly; (2) focal disruption of lamination before 28 weeks (n=24), associated with hemorrhage, porencephaly, stroke, migrational abnormalities, thanatophoric dysplasia, meningomyelocele or encephalocele; (3) increased prominence and echogenicity of the intermediate zone before 28 weeks and/or persistence of a laminar pattern beyond 33 weeks (n=10), associated with Type 1 lissencephaly or CMV infection. There was a mixed focal/diffuse pattern in two fetuses. In CMV infection, the earliest indication of the infection was focal heterogeneity and increased echogenicity of the intermediate zone, which predated the development of microcephaly, ventriculomegaly and intracranial calcification.

CONCLUSIONS

The fetal subplate and intermediate zones can be demonstrated reliably on routine sonography before 28 weeks and disappear after 34 weeks. These findings represent normal gestational age-dependent transient laminar patterns of cerebral development and are consistent with histological studies. Abnormal fetal cerebral lamination patterns for gestational age are also visible on sonography, and may indicate abnormal brain development.

Sall1 regulates cortical neurogenesis and laminar fate specification in mice: implications for neural abnormalities in Townes-Brocks syndrome

Progenitor cells in the cerebral cortex undergo dynamic cellular and molecular changes during development. Sall1 is a putative transcription factor that is highly expressed in progenitor cells during development. In humans, the autosomal dominant developmental disorder Townes-Brocks syndrome (TBS) is associated with mutations of the SALL1 gene. TBS is characterized by renal, anal, limb and auditory abnormalities. Although neural deficits have not been recognized as a diagnostic characteristic of the disease, ∼10% of patients exhibit neural or behavioral abnormalities. We demonstrate that, in addition to being expressed in peripheral organs, Sall1 is robustly expressed in progenitor cells of the central nervous system in mice. Both classical- and conditional-knockout mouse studies indicate that the cerebral cortex is particularly sensitive to loss of Sall1. In the absence of Sall1, both the surface area and depth of the cerebral cortex were decreased at embryonic day 18.5 (E18.5). These deficiencies are associated with changes in progenitor cell properties during development. In early cortical progenitor cells, Sall1 promotes proliferative over neurogenic division, whereas, at later developmental stages, Sall1 regulates the production and differentiation of intermediate progenitor cells. Furthermore, Sall1 influences the temporal specification of cortical laminae. These findings present novel insights into the function of Sall1 in the developing mouse cortex and provide avenues for future research into potential neural deficits in individuals with TBS.

Neurodevelopmental and neurofunctional outcomes in children with congenital diaphragmatic hernia

The objective of this review was to provide a critical overview of our current understanding on the neurocognitive, neuromotor, and neurobehavioral development in congenital diaphragmatic hernia (CDH) patients, focusing on three interrelated clinical issues: (1) comprehensive outcome studies, (2) characterization of important predictors of adverse outcome, and (3) the pathophysiological mechanism contributing to neurodevelopmental disabilities in infants with CDH. Improved survival for CDH has led to an increasing focus on longer-term outcomes. Neurodevelopmental dysfunction has been recognized as the most common and potentially most disabling outcome of CDH and its treatment. While increased neuromotor dysfunction is a common problem during infancy, behavioral problems, hearing impairment and quality of life related issues are frequently found in older children and adolescence. Intelligence appears to be in the low normal range. Patient and disease specific predictors of adverse neurodevelopmental outcome have been defined. Imaging studies have revealed a high incidence of structural brain abnormalities. An improved understanding of the pathophysiological pathways and the neurodevelopmental consequences will allow earlier and possibly more targeted therapeutic interventions. Continuous assessment and follow-up as provided by an interdisciplinary team of medical, surgical and developmental specialists should become standard of care for all CDH children to identify and treat morbidities before additional disabilities evolve and to reduce adverse outcomes.

Impact of ethanol on the developing GABAergic system

Alcohol intake during pregnancy has a tremendous impact on the developing brain. Embryonic and early postnatal alcohol exposures have been investigated experimentally to elucidate the fetal alcohol spectrum disorders' (FASD) milieu, and new data have emerged to support a devastating effect on the GABAergic system in the adult and developing nervous system. GABA is a predominantly inhibitory neurotransmitter that during development excites neurons and orchestrates several developmental processes such as proliferation, migration, differentiation, and synaptogenesis. This review summarizes and brings new data on neurodevelopmental aspects of the GABAergic system with FASD in experimental telencephalic models.

Disruption of neural progenitors along the ventricular and subventricular zones in periventricular heterotopia

Periventricular heterotopia (PH) is a disorder characterized by neuronal nodules, ectopically positioned along the lateral ventricles of the cerebral cortex. Mutations in either of two human genes, Filamin A (FLNA) or ADP-ribosylation factor guanine exchange factor 2 (ARFGEF2), cause PH (Fox et al. in 'Mutations in filamin 1 prevent migration of cerebral cortical neurons in human periventricular heterotopia'. Neuron, 21, 1315-1325, 1998; Sheen et al. in 'Mutations in ARFGEF2 implicate vesicle trafficking in neural progenitor proliferation and migration in the human cerebral cortex'. Nat. Genet., 36, 69-76, 2004). Recent studies have shown that mutations in mitogen-activated protein kinase kinase kinase-4 (Mekk4), an indirect interactor with FlnA, also lead to periventricular nodule formation in mice (Sarkisian et al. in 'MEKK4 signaling regulates filamin expression and neuronal migration'. Neuron, 52, 789-801, 2006). Here we show that neurons in post-mortem human PH brains migrated appropriately into the cortex, that periventricular nodules were primarily composed of later-born neurons, and that the neuroependyma was disrupted in all PH cases. As studied in the mouse, loss of FlnA or Big2 function in neural precursors impaired neuronal migration from the germinal zone, disrupted cell adhesion and compromised neuroepithelial integrity. Finally, the hydrocephalus with hop gait (hyh) mouse, which harbors a mutation in Napa [encoding N-ethylmaleimide-sensitive factor attachment protein alpha (alpha-SNAP)], also develops a progressive denudation of the neuroepithelium, leading to periventricular nodule formation. Previous studies have shown that Arfgef2 and Napa direct vesicle trafficking and fusion, whereas FlnA associates dynamically with the Golgi membranes during budding and trafficking of transport vesicles. Our current findings suggest that PH formation arises from a final common pathway involving disruption of vesicle trafficking, leading to impaired cell adhesion and loss of neuroependymal integrity.

Characteristic behavioral anomalies in rats prenatally exposed to 5-bromo-2'-deoxyuridine

The aim of the present study was to characterize behavioral anomalies in rats prenatally exposed to 5-bromo-2'-deoxyuridine, a useful model of hyperactive disorder. Rats were treated with BrdU at 50mg/kg IP or carboxymethylcellulose, its vehicle, on gestational Days 9 through 15, and their offsprings were subjected to behavioral tests. Rats prenatally exposed to 5-bromo-2'-deoxyuridine showed higher locomotor activity levels when the lights were turned off, and these levels kept increasing throughout the dark cycle. In an elevated plus maze, the rats prenatally exposed to 5-bromo-2'-deoxyuridine exhibited decreased anxiety-related behavior, including higher open arm entries and a longer time spent per one open arm entry when compared with rats prenatally exposed to carboxymethylcellulose. Methylphenidate, a psychostimulant that suppresses hyperactivity in humans with attention-deficit hyperactivity disorder, increased locomotor activity in both rats, with a greater sensitivity in rats prenatally exposed to 5-bromo-2'-deoxyuridine. Desipramine, a specific noradrenaline uptake inhibitor, normalized the hyperactivity of rats prenatally exposed to 5-bromo-2'-deoxyuridine. Paroxetine, a selective serotonin reuptake inhibitor, also normalized the hyperactivity and the low anxiety-related behavior in the elevated plus maze. These results suggest that rats prenatally exposed to 5-bromo-2'-deoxyuridine are hyperactive and exhibit a lower anxiety level. Dysfunctional monoaminergic neurons may be, at least in part, the cause of the behavioral anomalies.

Neuronal migration defect: a case of subcortical heterotopia in a California sea lion

A 2 and a half-year-old male California sea lion (Zalophus californianus) presented with a history of intermittent generalized seizures. Magnetic resonance imaging revealed a large focal mass occupying the right cerebral hemisphere with moderate dilatation of the contralateral lateral ventricle. At necropsy, the right cerebral hemispheric white matter was expanded by numerous irregularly shaped, pale pink nodules up to 10 mm in diameter. The overlying cortex was characterized by increased numbers of small, poorly developed gyri with shallow, often indistinct, sulci (polymicrogyria). Microscopically, nodules were composed of neurons, oligodendroglia, microglia, and supporting neuropil and were well delineated from the surrounding white matter. The gross, histological, and immunohistochemical features of this lesion are consistent with a neuronal migration defect resulting in unilateral subcortical heterotopia.

Differential activation of mononuclear phagocytes in cerebellar malformation associated with Walker-Warburg syndrome

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder with alterations affecting the CNS that are characteristic of type-II lissencephaly and dysplasia/hypoplasia of the cerebellum. Other than these features, WWS is typically also accompanied by muscular dystrophy and abnormalities affecting the eyes. There is at present little information on the state of microglial and mononuclear phagocytic cell responses within the brain in WWS. In this case report, we present evidence for focal and differential activation of mononuclear phagocytes specifically confined to the dysplastic cerebellum of an infant at 5 months of age, diagnosed with WWS.

Histological and magnetic resonance imaging assessment of cortical layering and thickness in autism spectrum disorders

BACKGROUND

Qualitative reports of the cerebral cortex in a small number of autism spectrum disorder (ASD) cases have suggested an increase in thickness and disruptions in migration and lamination patterns.

METHODS

We examined postmortem ASD individuals and age-matched controls using magnetic resonance imaging (MRI) to evaluate total cortical thickness, and histological samples to evaluate the pattern of cortical layering.

RESULTS

Overall, thickness measures from ASD subjects were equivalent to control cases. Individual regions showed marginal but nonsignificant thickness differences in the temporal lobes. Cortical thickness values in ASD subjects decreased significantly with age. Quantitative examination of proportional layer thickness in histological sections indicated that the pattern of cortical layering was largely undisturbed, while qualitative examination of these same samples revealed evidence of cell clustering and supernumerary cells in layer I and the subplate. These features were not severe and were never found in a majority of cases.

CONCLUSIONS

These findings support limited disturbances in cortical cell patterning, but do not indicate a major deficit in the orderly migration of cortical neuroblasts during development, or their subsequent aggregation into the laminar pattern found in typically developing individuals.

A new method of embryonic culture for assessing global changes in brain organization

While dissociated, reaggregated cells and organotypic slice cultures are useful models for understanding brain development, they only partially mimic the processes and organization that exist in vivo. Towards bridging the gap between in vitro and in vivo paradigms, a method for culturing intact brain tissue was developed using whole cerebral cortical hemispheres in which the anatomical and cellular organization of nervous system tissue is preserved. Single, free-floating telencephalic hemispheres were dissected from embryonic mice and placed into defined culture medium on an orbital shaker. Orbital shaking was necessary for optimal growth, and cortices grown under these conditions closely approximated in vivo parameters of cell division, differentiation, migration and cell death for up to 24 h. In addition to wild-type cultures, the method was compatible with genetically altered tissues. One particular advantage of this method is its ability to reveal global anatomical alterations in the embryonic brain following exposure to soluble growth factors. This method should thus be helpful for assessing a wide range of soluble molecules for their systemic effects on the embryonic brain.

Cortical dysplasia: neuropathological aspects

INTRODUCTION

Malformations of the cerebral cortex are a frequent cause of pharmacoresistant epilepsies and developmental disorders.

EPIDEMIOLOGY AND GENETICS

The incidence of cortical dysplasias in epilepsy surgical series varies from 12 to 40% and focal cortical dysplasias (FCD) are one of the most common neuropathological findings in resection specimens from pediatric patients undergoing cortical resections for the treatment of refractory epilepsy.

MACROSCOPY AND HISTOPATHOLOGY

Surgical specimens in FCD may appear normal macroscopically, but in some cases, widening of the cortex with poor demarcation from the underlying white matter is noted. In milder dysplasias, the main pathological feature is disorganization of the cortical architecture ("dislamination") with less striking neuronal and glial cytopathology. Histopathology shows an excess of neurons in layer I, including Cajal-Retzius cells, clusters of neurons, marginal glioneuronal heterotopias, and a persistent subpial granule cell layer. The hallmarks of FCD are disorganization of the laminar architecture and of the cytology of individual neurons. In many cases, layer I remains hypocellular and distinct from deeper laminae, but lower cortical layers may be ill-defined or broken up by the presence of many large and randomly located abnormal and cytomegalic neurons; depending on their morphology, referred to as "giant neurons," "immature neurons," or "dysmorphic neurons." The other pathognomonic cell type associated with FCD is the "balloon cell." These cells were originally considered to be of astrocytic lineage; however, there is evidence that they are in effect "balloon neurons."

IMMUNOHISTOCHEMISTRY AND STRUCTURAL FINDINGS

Immunohistochemistry is not essential in making the diagnosis of FCD or microdysgenesis but allows further characterization of cell types.

Neuropathological analysis of an asymptomatic adult case with Dandy-Walker variant

The Dandy-Walker (DW) complex is a rare posterior fossa malformation, usually observed during the prenatal period or the early infancy. Clinically, it is characterized by mental retardation, seizures, cerebellar ataxia as well as symptoms of hydrocephalus. Structural imaging reveal a hypoplasia or agenesis of the cerebellar vermis, enlargement of the fourth ventricle with a posterior fossa cyst. Additional neurodevelopmental changes such as agenesis of the corpus callosum, lissencephaly and cortical dysplasia are also present. We report the first neuropathological analysis of an adult asymptomatic DW case. Brain computerized tomography showed a massive posterior fossa cyst and hypoplasia of the cerebellum. An Ehlers-Danlos syndrome type IV characterized by repetitive intestinal perforations and a saccular aneurysm on the left posterior communicating artery was also present. Macroscopic brain examination revealed hypoplasia of both cerebellar hemispheres and posterior part of the vermis, as well as dilatation of the fourth ventricle without hydrocephalus. The posterior fossa cyst wall was formed by an external arachnoid layer, middle layer with loose connective tissue and an internal layer of ependymal cells. There were two foci of cerebellar cortical dysplasia but no ectopic neurons, neuronal loss or gliosis in both cerebellum and cerebral cortex. No vascular or significant neurodegenerative lesions were observed. In comparison with previous reports in DW infants, this adult case displayed milder brain abnormalities compatible with a diagnosis of DW variant. The preservation of the cortical cytoarchitecture as well as the paucity of additional neurodevelopmental changes may explain the absence of clinical expression.

Central nervous system findings by magnetic resonance in children with profound sensorineural hearing loss

INTRODUCTION

High-resolution magnetic resonance studies are an important tool in the investigation of the etiology of childhood sensorineural hearing loss. An added benefit with magnetic resonance is the ability to screen the central nervous system for findings which may adversely affect the neurodevelopmental outcome of these children.

OBJECTIVE

To determine the proportion of cases and significance of associated intracranial abnormalities as detected by central nervous system high-resolution magnetic resonance imaging in children with profound sensorineural hearing loss.

METHODS

Retrospective chart review of children undergoing evaluation for cochlear implantation in a tertiary care academic children's hospital with high-resolution magnetic resonance of the temporal bone and brain during a 21 month period. Magnetic resonance studies were interpreted by an experienced senior neuroradiologist blinded to the identity and clinical data of the patients.

RESULTS

Forty patients were identified. All had the same magnetic resonance study consisting of a 3D high-resolution sequence through the temporal bone as well as a T1 sagittal and T2 axial screening sequence of the brain. Eight patients (20%) showed significant brain abnormalities by magnetic resonance imaging ranging from myelination delays to migrational anomalies. Temporal bone abnormalities were not seen. Three patients with Connexin-26 mutations had no associated brain abnormalities by magnetic resonance.

CONCLUSIONS

A significant proportion of our patients being investigated by magnetic resonance imaging for profound sensorineural hearing loss show migrational abnormalities of the central nervous system, suggesting a central origin to their hearing loss. Some of these findings may result in neurodevelopmental delay and hence, negatively impact the success of cochlear implantation. We propose that magnetic resonance imaging of the temporal bone as part of the evaluation protocol for cochlear implantation in children should include central nervous system screening.

Degeneration of monoaminergic fibers in the aged micrencephalic rat

Age-related changes in the monoaminergic neuron systems in the brains of methylazoxymethanol acetate (MAM)-induced micrencephalic rats were studied. Neurochemical analysis revealed high levels of serotonin, norepinephrine and associated metabolites in several brain areas of MAM-treated rats. In particular, serotonin levels in the frontal cortex, cingulate cortex and hippocampus of 12-month-old (12 M) MAM-treated rats were significantly higher than in corresponding age-matched controls. Immunohistochemical analysis demonstrated numerous aberrant serotonin-immunoreactive fibers and small numbers of aberrant tyrosine hydroxylase-immunoreactive fibers in the septum, caudate putamen, thalamus, cerebral cortex, hippocampus and midbrain tegmentum of 12 M MAM-treated rats. Aberrant monoaminergic fibers characterized by swollen varicosities and thickening of intervaricose segments were common compared to 12 M control rats. In the cortex and hippocampus of 12 M MAM-treated rats, aberrant fibers were observed near cortical heterotopic tissue. These results indicate early onset of age-related degeneration of monoaminergic fibers in micrencephalic rats. Aged MAM-treated rats may thus offer a good model for studying age-related monoaminergic changes in the cortical heterotopic tissue of human cortical malformations.

Neuronal migration in developmental disorders

Normal central nervous system development is dependent on extensive cell migration. Cells born in the proliferative ventricular zone migrate radially along specialized glial processes to their final locations. In contrast, most inhibitory interneurons found in the adult mammalian cerebral cortex and some other structures migrate along a nonradial pathway and on substrates only recently defined. Defects in radial cell migration have been implicated in several distinct human syndromes in which patients often present with epilepsy and mental retardation and have characteristic cerebral abnormalities. The identification of several genes responsible for human neural cell migration defects has led to a better understanding of the cellular and molecular interactions necessary for normal migration and the pathogenesis of these disorders. The prototypic cell migration disorder in humans is type I lissencephaly. Although type 1 lissencephaly is clearly a defect in radial cell migration, recent data from two model systems (Lis1 and ARX mutant mice) indicate that a defect in non-radial cell migration also exists. Thus, the result of a LIS1 mutation appears to have broader implications than a radial cell migration defect alone. Furthermore, it is likely that the observed defect in non-radial cell migration contributes to the clinical phenotype observed in these patients. Herein we discuss the role of normal non-radial cell migration in cortical development, as well as how perturbations in both radial and nonradial migration result in developmental anomalies.

Interneuron deficits in patients with the Miller-Dieker syndrome

Lissencephaly is characterized by a thickened cortex and loss of gyri, resulting in the brain having a smooth surface. Patients with lissencephaly frequently exhibit epilepsy and mental retardation, conditions often associated with a defect in inhibitory neurons. While lissencephaly has traditionally been considered a disorder of radial migration, recent data indicate interneurons migrate non-radially, while projection neurons migrate radially. To determine if an interneuron defect, and therefore a non-radial migration defect, exists in patients with lissencephaly, we studied the calretinin-expressing interneuron subpopulation in the brains from two fetuses and two children with lissencephaly and a deletion involving 17p13 deletion (Miller-Dieker syndrome) along with age-matched controls. Our data indicate fetuses with the Miller-Dieker syndrome have a significant (tenfold) reduction in the number of calretinin-expressing interneurons present, whereas minimal reductions in the number of calretinin-expressing interneurons are present in children with this disorder. These data parallel those seen in the Lis1(+/-) mouse model of human lissencephaly, and are consistent with a non-radial cell migration defect in humans. Thus, when considering the pathogenesis of human lissencephaly and the clinical manifestations in these patients, defects in both non-radial cell migration (inhibitory interneurons) and radial migration (excitatory projection neurons) must be considered.

Neurodevelopment, neuroplasticity, and new genes for schizophrenia

Schizophrenia is a complex, debilitating neuropsychiatric disorder. Epidemiological, clinical, neuropsychological, and neurophysiological studies have provided substantial evidence that abnormalities in brain development and ongoing neuroplasticity play important roles in the pathogenesis of the disorder. Complementing these clinical studies, a range of cytoarchitectural, morphometric, ultrastructural, immunochemical, and gene expression methods have been applied in investigations of postmortem brain tissues to characterize the cellular and molecular profile of putative developmental and plastic abnormalities in schizophrenia. While findings have been diverse and many are in need of replication, investigations focusing on higher cortical and limbic brain regions are increasingly demonstrating abnormalities in the structural and molecular integrity of the synaptic complex as well as glutamate-related receptors and signal transduction pathways that play critical roles in brain development, synaptogenesis, and synaptic plasticity. Most exciting have been recent associations of schizophrenia with specific genes, such as neuregulin-1, dysbindin-1, and AKT-1, which are vital to synaptic development, neurotransmission, and plasticity.

Axon mediated interneuron migration

Mammalian forebrain development requires extensive cell migration for cells to reach their appropriate location in the adult brain. Defects in this migration result in human malformations and neurologic deficits. Thus, understanding the mechanisms underlying normal cell migration during development is essential to understanding the pathogenesis of human malformations. Radial glia are known to support radial cell migration, while axons have been proposed as substrate for some non-radially migrating cells. Herein we have directly tested the hypothesis that axons can support non-radial cell migration. One population of cells known to migrate non-radially is the inhibitory interneurons that move from the ganglionic eminence to the cerebral cortex. We first show that early born GABAergic cells colocalize with TAG-1-positive (TAG-1+) axons, while later born cells colocalize with intermediate weight neurofilament-positive, TAG-1-negative (TAG-1-) processes, suggesting temporal differences in substrate specificities. We next developed an in vitro assay that allows us to observe cell migration on axons in culture. Using this assay we find that early born medial ganglionic eminence-derived interneurons migrate preferentially on TAG-1+ axons, while later born cells only migrate on neurofilament-positive/TAG-1- processes. These data provide the first direct evidence that ganglionic eminence cells migrate on axons and that there is an age-dependent substrate preference. Furthermore, the assay developed and characterized herein provides a robust method to further study the molecular substrates and guidance cues of axonophilic cell migration in neural development.

Lis1 is necessary for normal non-radial migration of inhibitory interneurons

Type I lissencephaly is a central nervous system (CNS) malformation characterized by mental retardation and epilepsy. These clinical features suggest a deficit in inhibitory neurons may, in part, underlie the pathogenesis of this disorder. Mutations in, or deletions of, LIS1 are the most commonly recognized genetic anomaly associated with type I lissencephaly. The pathogenesis of type I lissencephaly is believed to be a defect in radial neuronal migration, a process requiring LIS1. In contrast the inhibitory neurons migrate non-radially from the basal forebrain to the neocortex and hippocampus. Given that Lis1 is expressed in all neurons, we hypothesized that Lis1 also functions in non-radial migrating inhibitory neurons. To test this hypothesis we used a combination of in vivo and in vitro studies with Lis1 mutant mice and found non-radial cell migration is also affected. Our data indicate Lis1 is required for normal non-radial neural migration and that the Lis1 requirement is primarily cell autonomous, although a small cell non-autonomous effect could not be excluded. These data indicate inhibitory neuron migration is slowed but not absent, similar to that found for radial cell migration. We propose that the defect in non-radial cell migration is likely to contribute to the clinical phenotype observed in individuals with a LIS1 mutation.

Neocortical neuronal arrangement in LIS1 and DCX lissencephaly may be different

In type I or classical lissencephaly, two genetic causes, namely the LIS1 gene mapping at 17p13.3 and the DCX (doublecortin on X) gene mapping at Xq22.3 are involved. These are considered to act during corticogenesis on radial migratory pathways. The prevailing view is that heterozygous mutations in the LIS1 gene and hemizygous mutations in the DCX gene produce similar histological pattern. The present detailed neuropathological study in two unrelated fetuses with respectively a mutation in the LIS1 and the DCX genes do not confirm this view. In LIS1 mutation, the cortical ribbon displays a characteristic inverted organization, also called "four layered cortex" while in DCX mutation, the cortex displays a roughly ordered "six layered" lamination. Our hypothesis is that mutations of the LIS1 and DCX genes, may not affect the same neuronal arrangement in the neocortex. Because the pathology of proven XLIS is rarely documented, further detailed neuropathological analysis in other cases identified through molecular study would be of a great help in the recognition of neuronal population involved in these migrational disorders and their underlying molecular mechanism.

Cortical dysplasia and epilepsy: animal models

Cortical dysplasia syndromes--those conditions of abnormal brain structure/organization that arise during aberrant brain development--frequently involve epileptic seizures. Neuropathological and neuroradiological analyses have provided descriptions and categorizations based on gross anatomical and cellular histological features (e.g., lissencephaly, heterotopia, giant cells), as well as on the developmental mechanisms likely to be involved in the abnormality (e.g., cell proliferation, migration). Recently, the genes responsible for several cortical dysplastic conditions have been identified and the underlying molecular processes investigated. However, it is still unclear how the various structural abnormalities associated with cortical dysplasia are related to (i.e., "cause") chronic seizures. To elucidate these relationships, a number of animal models of cortical dysplasia have been developed in rats and mice. Some models are based on laboratory manipulations that injure the brain (e.g., freeze, undercut, irradiation, teratogen exposure) of immature animals; others are based on spontaneous genetic mutations or on gene manipulations (knockouts/transgenics) that give rise to abnormal cortical structures. Such models of cortical dysplasia provide a means by which investigators can not only study the developmental mechanisms that give rise to these brain lesions, but also examine the cause-effect relationships between structural abnormalities and epileptogenesis.