Semaphorin 3C is not required for the establishment and target specificity of the GABAergic septohippocampal pathway in vitro

The septohippocampal (SH) pathway comprises cholinergic and GABAergic fibers. Whereas the former establish synaptic contacts with all types of hippocampal neurons, the latter form complex baskets specifically on interneurons. The GABAergic SH function is associated with the control of hippocampal synchronous networks. Little is known about the mechanisms involved in the formation of the GABAergic SH pathway. Semaphorin (Sema) 3C is expressed in most hippocampal interneurons targeted by these axons. To ascertain whether Sema 3C influences the formation of the SH pathway, we analyzed the development of this connection in Sema 3C-deficient mice. As these animals die at birth, we developed an in vitro organotypic co-culture model reproducing the postnatal development of the SH pathway. In these SH co-cultures, the GABAergic SH pathway developed with target specificity similar to that present in vivo. SH axons formed incipient baskets on several types of hippocampal interneurons at 7 days in vitro, which increased their complexity by 18-25 days in vitro. These SH fibers formed symmetric synaptic contacts on GABAergic interneurons. This synaptic specificity was not influenced by the absence of entorhinal afferents. Finally, the absence of Sema 3C in target neurons or its blockage by neuropilin-1 and -2 ectodomains in slice co-cultures did not lead to major changes in either the target specificity of the GABAergic SH pathway or its density of innervation. We conclude that the formation and synaptic specificity of the GABAergic SH pathway relies on robust molecular mechanisms, independent of Sema 3C, that are retained in our in vitro co-culture model.     

GLUT2-mediated glucose uptake and availability are required for embryonic brain development in zebrafish

Glucose transporter 2 (GLUT2; gene name SLC2A2) has a key role in the regulation of glucose dynamics in organs central to metabolism. Although GLUT2 has been studied in the context of its participation in peripheral and central glucose sensing, its role in the brain is not well understood. To decipher the role of GLUT2 in brain development, we knocked down slc2a2 (glut2), the functional ortholog of human GLUT2, in zebrafish. Abrogation of glut2 led to defective brain organogenesis, reduced glucose uptake and increased programmed cell death in the brain. Coinciding with the observed localization of glut2 expression in the zebrafish hindbrain, glut2 deficiency affected the development of neural progenitor cells expressing the proneural genes atoh1b and ptf1a but not those expressing neurod. Specificity of the morphant phenotype was demonstrated by the restoration of brain organogenesis, whole-embryo glucose uptake, brain apoptosis, and expression of proneural markers in rescue experiments. These results indicate that glut2 has an essential role during brain development by facilitating the uptake and availability of glucose and support the involvement of glut2 in brain glucose sensing.     

红藻氨酸致颞叶癫痫大鼠海马内Semaphorin3C、Semaphorin3F基因表达的研究

目的研究神经轴索导向分子Sem aphorin3C(Sem a3C),Sem aphorin3F(Sem a3F)mRNA对颞叶癫痫(TLE)大鼠海马神经轴索环路重建的调控作用。方法采用侧脑室内注射红藻氨酸(KA)制作TLE大鼠模型,用N issl染色及原位杂交的方法,分别检测致痫后1d、1w、2w、3w、4w大鼠海马的齿状回(DG),CA1区、CA3区神经细胞丢失程度以及Sem a3C、Sem a3F mRNA的表达。结果KA致痫后1d始出现神经元丢失,至4w神经元丢失明显增多。KA致痫后1w,Sem a3C、Sem a3F mRNA在海马的CA1区、Sem a3F mRNA在海马的CA3区表达明显下降,持续至3w(P<0.01),4w时恢复至正常(P>0.05);Sem a3C、Sem a3F mRNA在DG的表达,Sem a3C在CA3区的表达,实验组与对照组均无明显差别(P>0.05)。结论KA致痫后海马CA1区神经元下调Sem a3C、Sem a3F mRNA的表达,CA3区神经元下调Sem a3F mRNA的表达,可能促进TLE大鼠海马神经轴索环路重建。     

Prolidase enzyme is required for extracellular matrix integrity and impacts on postnatal cerebellar cortex development

The extracellular matrix is essential for brain development, lamination, and synaptogenesis. In particular, the basement membrane below the pial meninx (pBM) is required for correct cortical development. The last step in the catabolism of the most abundant protein in pBM, collagen Type IV, requires prolidase, an exopeptidase cleaving the imidodipeptides containing pro or hyp at the C-terminal end. Mutations impairing prolidase activity lead in humans to the rare disease prolidase deficiency characterized by severe skin ulcers and mental impairment. Thus, the dark-like (dal) mouse, in which the prolidase is knocked-out, was used to investigate whether the deficiency of prolidase affects the neuronal maturation during development of a brain cortex area. Focusing on the cerebellar cortex, thinner collagen fibers and disorganized pBM were found. Aberrant cortical granule cell proliferation and migration occurred, associated to defects in brain lamination, and in particular in maturation of Purkinje neurons and formation of synaptic contacts. This study deeply elucidates a link between prolidase activity and neuronal maturation shedding new light on the molecular basis of functional aspects in the prolidase deficiency.     

C9ORF72 G4C2-repeat expansion and frontotemporal dementia first reported case in Argentina

ABSTRACT

We present a female patient aged 51 who developed behavioral disorders followed by cognitive impairment over 3 years. Neuropsychological, neuropsychiatric, and radiological features suggested a probable behavioral variant of frontotemporal dementia (bvFTD). A family history of amyotrophic lateral sclerosis and parkinsonism suggested the hexanucleotide repeat expansion G₄C₂ in C9ORF72 . We set up a two-step genotyping algorithm for the detection of the expansion using fragment-length analysis polymerase chain reaction (PCR) and repeat-primed PCR with fluorescent primers. We confirmed the presence of an expanded G₄C₂ allele in the patient. This represents the first documented case of bvFTD due to a C9ORF72 expansion in Argentina.     

The roles of testicular orphan nuclear receptor 4 (TR4) in cerebellar development

Since Testicular Receptor 4 (TR4) was cloned, efforts have been made to elucidate its physiological function. To examine the putative functions of TR4, the conventional TR4 knockout (TR4^−/−) mouse model was generated. Throughout postnatal and adult stages, TR4^−/− mice exhibited behavioral deficits in motor coordination, suggesting impaired cerebellar function. Histological examination of the postnatal and adult TR4^−/− cerebellum revealed gross abnormalities in foliation. Further analyses demonstrated changes in the lamination of the TR4^−/− cerebellar cortex, including reduction in the thickness of both the molecular layer (ML) and the internal granule layer (IGL). Analyses of the developing TR4^−/− cerebellum indicate that the lamination irregularities observed may result from disrupted granule cell proliferation within the external granule cell layer (EGL), delayed inward migration of post-mitotic granule cells, and increased apoptosis during cerebellar development. In addition, abnormal development of Purkinje cells was observed in the postnatal TR4^−/− cerebellum, as indicated by aberrant dendritic arborization. In postnatal, neuronal-specific TR4 knockout mice, architectural changes in the cerebellum were similar to those seen in TR4^−/− animals, suggesting that TR4 function in neuronal lineages might be important for cerebellar morphogenesis, and that the effect on Purkinje cell development is likely mediated by changes elsewhere, such as in granule cells, or is highly dependent on developmental stage. Together, our findings from various TR4 knockout mouse models suggest that TR4 is required for normal cerebellar development and that failure to establish proper cytoarchitecture results in dysfunction of the cerebellum and leads to abnormal behavior.     

The glutamate receptor delta 2 in relation to cerebellar development and plasticity

Understanding what are the mechanisms that strengthen, stabilize and restrict synaptic innervation is a relevant topic in glutamate receptor delta 2 (GluRδ2)-related research. It also involves targeting and selection of afferent input during formation of the neuronal circuitry in the cerebellar cortex and its functioning. This review will focus on the role of GluRδ2, one of the main players in this field. Special emphasis will be placed on the processes that regulate the rapid translocation from climbing fibres to parallel fibres of GluRδ2 and the role of GluRδ2 in the reduction of supernumerary climbing fibre contacts on a single Purkinje cell. Furthermore, GluRδ2 knockout mice show ataxia and impaired motor coordination, suggesting that the presence of GluRδ2 plays an important role in controlling cerebellar functioning.     

Microglia are required for astroglial Toll-like receptor 4 response and for optimal TLR2 and TLR3 response

Within the central nervous system, astrocytes and microglia are the primary responders to endogenous ligands released upon injury and stress, as well as to infectious pathogens. Toll-like receptors (TLRs) are implicated in recognition of both types of stimulus. Whether astrocytes respond as strongly as microglia to TLR agonists remains contentious. In this study, we have rigorously purified astrocytes to determine their capacity for autonomous TLR response, in absence of microglia. We used flow cytometry and differential adhesion as well as a myeloid lineage-specific suicide gene to purify astrocytes from mixed glial cultures and measured their response to TLR agonists. Our results show that the response of astrocytes to TLR2 and TLR3 agonists is greatly enhanced by, and response to TLR4 agonists is completely dependent on, the presence of functional microglia. In the case of the TLR4 response to lipopolysaccharide, microglia exert their effect on astrocytes at least partially through release of soluble mediators that directly activate or facilitate astrocyte responses. Our findings underline the contribution of glial crosstalk in CNS responses to injury or inflammation.     

Laminin-like proteins are differentially regulated during cerebellar development and stimulate granule cell neurite outgrowth in vitro

The basement membrane glycoprotein laminin-1 is a potent stimulator of neurite outgrowth. Although a variety of laminin isoforms have been described in recent years, the role of alternative laminin isoforms in neural development remains largely uncharacterized. We found that a polyclonal antibody raised against the α1, β1, and γ1 chains of laminin-1 and a monoclonal antibody raised against the α2 chain of laminin-2 detect immunoreactive material in neuronal cell bodies in the developing mouse cerebellum. In addition, laminin-1-like immunoreactivity was found in cell types throughout the cerebellum, but laminin-α2-like immunoreactivity was restricted to the Purkinje cells. Purified laminin-1 and laminin-2 stimulated neurite outgrowth in primary cultures of mouse cerebellar granule neurons to a similar extent, whereas the synthetic peptides tested appeared to be active only for cell adhesion and not for stimulation of neurite outgrowth. The E8 proteolytic fragment of laminin-1 contained full neurite outgrowth activity. The identity of laminins expressed in granule neurons was also examined by Western blotting; laminin-like complexes were associated with the cell and appeared to have novel compositions. These results suggest that laminin-like complexes play important roles in cerebellar development. J. Neurosci. Res. 54:233–247, 1998. © 1998 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.     

红藻氨酸致颞叶癫(癎)大鼠脑内Semaphorin3A、Semaphorin4C基因表达的研究

目的研究轴索导向分子Semaphorin3A(Sema3A)、4C(Sema4C)对癫大鼠海马苔藓纤维重建的调控作用及对皮层神经元的保护作用。方法大鼠侧脑室内注射红藻氨酸制备颞叶癫模型,原位杂交法检测致痫间后1d,1、2、3、4周大鼠脑内Sema3A/Sema4C mRNA表达。结果致痫间后1周Sema3A、Sema4CmRNA分别在齿状回(DG),CA3区表达明显下降(P<0.01),持续至3、4周时恢复至正常(P>0.05);致痫间后1d Sema3A mRNA在皮层表达明显下降(P<0.01),持续至1、2周后恢复至正常(P>0.05)。结论红藻氨酸致痫间后DG及CA3区神经元分别下调Sema3A/Sema4C mRNA的表达,促进癫大鼠苔藓纤维重建;皮层神经元通过下调Sema3A mRNA的表达来维持自身存活。     

The role of CYP2C9 polymorphisms in phenytoin-related cerebellar atrophy

PurposePhenytoin is known to be able to induce cerebellar atrophy in patients with epilepsy. It is also known that a CYP2C9 mutation (*2 or *3) reduces phenytoin metabolism by 25–50% and can increase the risk of phenytoin-related side effects. We examined the influence of CYP2C9 polymorphisms on total cerebellar volume and cerebellar gray and white matter volumes in patients with epilepsy taking phenytoin.MethodsFor the genotyping, 100 adult patients with documented epilepsy who had been taking phenytoin for >1 year were selected. From this group, we randomly selected 19 mutant individuals (MT group; CYP2C9*2 and *3) for a whole-brain volume measurement using MRI and 19 wild-type individuals (group WT; CYP2C9*1) with similar clinical and demographic characteristics to those in the MT group for comparison. Total intracranial volume measurements were used to normalize the acquired volumes, which were separated into gray matter volume, white matter volume, and total volume.ResultsThe MT group exhibited a significant reduction in cerebellar white matter volume (p = 0.002) but not in total cerebellar volume.ConclusionOur study is the first to report evidence linking CYP2C9 polymorphism and a reduction in cerebellar volume in epileptic users of phenytoin.     

Expression of LPP3 in Bergmann glia is required for proper cerebellar sphingosine-1-phosphate metabolism/signaling and development

Bioactive lipids serve as intracellular and extracellular mediators in cell signaling in normal and pathological conditions. Here we describe that an important regulator of some of these lipids, the lipid phosphate phosphatase-3 (LPP3), is abundantly expressed in specific plasma membrane domains of Bergmann glia (BG), a specialized type of astrocyte with key roles in cerebellum development and physiology. Mice selectively lacking expression of LPP3/Ppap2b in the nervous system are viable and fertile but exhibit defects in postnatal cerebellum development and modifications in the cytoarchitecture and arrangement of BG with a mild non-progressive motor coordination defect. Lipid and gene profiling studies in combination with pharmacological treatments suggest that most of these effects are associated with alterations in sphingosine-1-phosphate (S1P) metabolism and signaling. Altogether our data indicate that LPP3 participates in several aspects of neuron-glia communication required for proper cerebellum development.     

Phospholipase Cbeta4 expression reveals the continuity of cerebellar topography through development

Mediolateral boundaries divide the mouse cerebellar cortex into four transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. Various expression markers reveal this complexity, and detailed maps have been constructed based on the differential expression of zebrin II/aldolase C in a Purkinje cell subset. Recently, phospholipase (PL) Cbeta4 expression in adult mice was shown to be restricted to, and coextensive with, the zebrin II-immunonegative Purkinje cell subset. The Purkinje cell expression of PLCbeta4 during embryogenesis and postnatal development begins just before birth in a subset of Purkinje cells that are clustered to form a reproducible array of parasagittal stripes. Double label and serial section immunocytochemistry revealed that the early PLCbeta4-immunoreactive clusters in the neonate are complementary to those previously identified by neurogranin expression. The PLCbeta4 expression pattern can be traced continuously from embryo to adult, revealing the continuity of the topographical map from perinatal to adult cerebella. The only exception, as has been seen for other antigenic markers, is that transient PLCbeta4 expression (which subsequently disappears) is seen in some Purkinje cell stripes during the second postnatal week. Furthermore, the data confirm that some adult Purkinje cell stripes are composite in origin, being derived from two or more distinct embryonic clusters. Thus, the zone and stripe topography of the cerebellum is conserved from embryo to adult, confirming that the early- and late-antigenic markers share a common cerebellar topography.     

The SDF-1/CXCR4 pathway and the development of the cerebellar system

Mice deficient for the chemokine receptor CXCR4 show premature translocation of granule cell neuroblasts from their germinal zone into the nascent cerebellum [Y.-R. Zuo et al. (1998) Nature, 393, 595-599]. Here, we used CXCR4-null mice to analyse the early development of cerebellar cortical inhibitory interneurons and pontine neurons which, in the adult, are synaptically integrated with granule cells. Cortical inhibitory interneuronal precursors normally invade the cerebellar anlage of CXCR4-deficient mice, but their dispersal is impeded by dislocated foci of proliferating granule cells, from which they are excluded. This is reminiscent of the strict exclusion of inhibitory interneuronal precursors from the superficial external granule cell layer. As inhibitory interneuronal precursors readily mingle with post-mitotic granule cells both in wild-type and CXCR4-null mice, these findings indicate that the developmentally regulated interactions between granule and inhibitory interneuronal precursors are independent of SDF-1/CXCR4 signalling. In contrast, the transit of pontine neurons from the rhombic lip through the anterior extramural stream to the basilar pons is disrupted in CXCR4-deficient animals. Migrating pontine neurons express CXCR4, and in CXCR4-null animals these cells are found displaced deep into the brainstem. Consequently, nascent pontine nuclei in CXCR4-deficient animals are hypoplastic. Moreover, they fail to express plexin D1, suggesting that SDF-1/CXCR4 signalling may also impinge on axon guidance critical to the orderly formation of granule cell mossy fibre afferents.     

Long experimental durations are required for double label [C]- and [H]2-deoxyglucose autoradiographic methods

Double-label 2-deoxyglucose (2-DG) studies using sequential [¹⁴C]- and [³H]2-DG injections demonstrate increased [¹⁴C]2-DG uptake durating the first and second stimulation periods. To understand why this occurs, the rat mystacial vibrissae were stimulated at various times following [¹⁴C]2-DG injection. Local cerebral glucose utilization (LCGU) increased when whisker stimulation was performed at 0–90 min following [¹⁴C]2-DG injection. LCGU did not increase when whisker stimulation was performed at 90–150 min following [¹⁴C]2-DG injection. To minimize contamination of the two tracers in double label 2-DG mapping studies, the time between [¹⁴C]- and [³H]2-DG administration should be increased to 90 min.     

Rab4 and Rab5 GTPase are required for directional mobility of endocytic vesicles in astrocytes

Rab4 and Rab5 GTPases are key players in the regulation of endocytosis. Although their role has been studied intensively in the past, it is still unclear how they regulate vesicle mobility. In particular, in astrocytes, the most abundant glial cells in the brain, vesicles have been shown to exhibit nondirectional and directional mobility, which can be intermittent, but the underlying switching mechanisms are not known. By using quantitative imaging, we studied the dynamics of single vesicle movements in astrocytes in real time, by transfecting them with different GDP- and GTP-locked mutants of Rab4 and Rab5. Along with the localization of Rab4 and Rab5 on early and late endocytic compartments, we measured the apparent vesicle size by monitoring the area of fluorescent puncta and determined the patterns of vesicle mobility in the presence of wild-type and Rab mutants. Dominant-negative and dominant-positive mutants, Rab4 S22N, Rab5 S34N and Rab4 Q67L, Rab5 Q79L, induced an increase in the apparent vesicle size, especially Rab5 mutants. These mutants also significantly reduced vesicle mobility in terms of vesicle track length, maximal displacement, and speed. In addition, significant reductions in the fraction of vesicles exhibiting directional mobility were observed in cells expressing Rab4 S22N, Rab4 Q67L, Rab5 S34N, and Rab5 Q79L. Our data indicate that changes in the GDP-GTP switch apparently not only affect fusion events in endocytosis and recycling, as already proposed, but also affect the molecular interactions determining directional vesicle mobility, likely involving motor proteins and the cytoskeleton.