Localization of mu class glutathione-S-transferase in the forebrains of neonatal and young rats: implications for astrocyte development.

The Yb (Mu class) isoform of glutathione-S-transferase has recently been localized in ependymal cells, subependymal cells, and astrocytes in the forebrains of rats 3 weeks to adult in age. It was not known, however, at what age Mu might first be observed during postnatal development and whether the first cells in which it was found would be immature astrocytes or some less differentiated glial precursor cell, if the latter were present in vivo. Tissue sections from the forebrains of neonatal to 16 day old rats were immunostained with antibodies against Mu. In neonates Mu was observed in vimentin-positive cells and their processes adjacent to the lateral ventricles, and in the corpus striatum. The colocalization with vimentin suggested that these were subependymal cells and radial glia. In the corpus striatum the radial glia, while still vimentin-positive, rapidly lost Mu from their radial cell processes, whereas the cell-bodies remained Mu-positive. During the first postnatal week the Mu-positive, glial-fibrillary-acidic-protein (GFAP)-positive cell bodies of immature astrocytes appeared in the corpus striatum. The earliest Mu-positive cells in the immature white matter of the corpus callosum were vimentin-positive and had striking longitudinal processes that also were vimentin- and Mu-positive. Like the processes of radial glia, the longitudinal processes lost their Mu-immunoreactivity, only later and more gradually. Mu-positive, GFAP-positive cells appeared later in the corpus callosum than in the corpus striatum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recovery of axonal myelination sheath and axonal caliber in the mouse corpus callosum following damage induced by N,N-diethyldithiocarbamate

Disulfiram is an aldehyde dehydrogenase inhibitor used for the treatment of alcohol dependence and of cocaine addiction. It has been demonstrated that subchronic administration of disulfiram or N,N-diethyldithiocarbamate (DEDTC), the main derivative of disulfiram, to rats can produce central-peripheral distal axonopathy. However, few data regarding the axonal effects of these compounds in the central nervous system exist. Our previous studies have revealed DEDTC-induced axonal damage in the mouse brain during the course of postnatal development, together with alterations in axonal pathfinding and in the myelination process, with partial recovery during the post-treatment period. In order to gather new data about how this axonal damage and recovery occurs in the central nervous system, we performed an ultrastructural analysis of the axons located in the corpus callosum from mice treated with DEDTC during postnatal development. The axonal caliber throughout the axonal area, the maximum axonal diameter, the maximum fiber diameter, and the axonal circularity, at different postnatal stages [from postnatal day (P)9 to P30], were analyzed. In addition, parameters related to the myelinization process (number of myelinated axons, sheath thickness, and the ratio of myelinated axons to total axons) were evaluated. A reduction in the average value of axonal caliber during treatment and a delay in the axonal myelination process were detected. Whereas early recovery of individual axons occurred after treatment (P22), complete recovery of myelinated axons occurred at late postnatal stages (P42). Therefore, chronic treatment with dithiocarbamates requires periods of rest to encourage the recovery of myelinated axons.     

脑白质损害新生大鼠的电镜超微结构观察

目的：应用Han方法建立脑白质损害（WMD）新生大鼠模型,电镜观察大鼠脑内髓鞘成熟度及突触超微结构改变。方法：2日龄新生SD大鼠39只,随机分为对照组(n=12)、假手术组(n=12)及WMD组(n=15)。WMD组大鼠在乙醚麻醉下行右颈总动脉结扎术,术后吸含6%氧气的氮氧混合气4h,制作新生大鼠WMD模型。各组均正常饲养至1月龄时经灌注固定后行电镜检查,同时行HE染色观察。 结果：电镜观察可见WMD组患侧海马CA1区胶质细胞受损及髓鞘形成延迟。WMD组大鼠海马CA1区突触活性区长度、突触间隙宽度、突触后致密物厚度及突触界面曲率与对照组及假手术组无显著性差异（P>0.05）;HE染色可见实验组白质疏松。结论 从超微结构方面观察,此方法对新生大鼠脑白质损害特异性高,突触损害轻微,模型效果可靠。     

Carbonic anhydrase in distinct precursors of astrocytes and oligodendrocytes in the forebrains of neonatal and young rats.

Carbonic anhydrase is present in oligodendrocytes and astrocytes in the mature rat brain. Whereas carbonic anhydrase-positive oligodendrocyte precursors had been identified during the first postnatal week, no information was available about the earliest occurrence of carbonic anhydrase in the astrocytic cell line, nor had carbonic anhydrase been detected in astrocytes in neonatal rat brains. Beginning on the first postnatal day, rat brains were double immunostained with anti-carbonic anhydrase II and respective 'markers' for immature and mature astrocytes and oligodendrocytes. During the first postnatal week there were intensely carbonic anhydrase-positive cells which were ovoid or had broad processes. On the basis of their shapes and antigen contents these were considered to be precursors of oligodendrocytes. Beginning on the first postnatal day carbonic anhydrase II was also observed in some vimentin-positive radial glia and in other vimentin-positive cells that differed in their appearance from the immature oligodendrocytes. The vimentin-positive, carbonic anhydrase-positive cells were less smooth-surfaced, and had much finer processes, than the oligodendrocyte precursors. By the third postnatal day there appeared carbonic anhydrase-positive, glial fibrillary acidic protein (GFAP)-positive cells that resembled the vimentin-positive cells. It is concluded that the latter are immature astrocytes and that carbonic anhydrase is in distinct precursors of oligodendrocytes and astrocytes as early as the first postnatal day.     

Long-term survival of mouse corpus callosum grafts in neonatal rat recipients, and the effect of host sensitization.

Previous studies have suggested that the incidence of spontaneous rejection among immunogenetically mismatched neural transplants in neonatal recipients varies significantly depending on the cellular composition of the graft material. For example, neuron-rich grafts of embryonic mouse retina generally survive for extended periods without showing signs of rejection after implantation into neonatal rats, whereas cortical xenografts, which contain abundant glial and endothelial cells as well as neurons, typically undergo rejection 4-6 weeks after implantation. To determine whether the presence of donor glia is responsible for this high incidence of spontaneous rejection, we examined the fate of a non-neuronal graft material composed predominantly of xenogeneic glial cells (post-natal day 3, PD3, CD-1 mouse corpus callosum) implanted into the mesencephalon of PD1 Sprague-Dawley rats. The distribution and survival of donor astrocytes were assessed using a monoclonal antibody specific for a mouse astrocyte surface antigen, M2. Thirteen of 16 animals sacrificed within 2 months of implantation had detectable transplants. In these animals, M2-positive cells frequently migrated well away from body of the graft, clustering in large numbers in several characteristic regions of the host brain. Unlike cortical grafts of similar age, the vast majority (93%) of callosal transplants showed no histological signs of rejection or major histocompatibility complex antigen expression in and around the transplant-derived cells. As previously noted in the neonatal retinal transplant paradigm, however, well-integrated 1-month-old corpus callosum grafts could be induced to reject by appropriate sensitization of the host immune system, implying that the host was not immunologically tolerant to the foreign neural graft. With longer survival times in unsensitized hosts, a progressively smaller percentage of animals had detectable donor astrocytes (5 of 10 animals at 3 months postimplantation and 4 of 16 animals at 4 months); in those 9 animals with surviving grafts, only small numbers of M2-positive cells were seen within the graft bed and surrounding host brain. However, only 2 of the 26 "long-term" animals showed evidence of graft rejection. These results indicate that mouse astrocytes show characteristic patterns of migration into the host brain when implanted into neonatal rats; however, these xenogeneic cells have a limited duration of survival. The infrequency with which even subtle signs of spontaneous rejection were detected in animals that had received corpus callosum xenografts suggests that an immune-mediated process is unlikely to be responsible for the time-dependent elimination of the donor astrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)     

The distribution of the callosal projection to the occipital visual cortex in rats and mice

The principal finding in this study is that the callosal projection to the occipital cortex in rats and mice follows a complex and highly reproducible pattern which has not previously been described in detail. In some regions, the callosal projection is associated with well defined cytoarchitectonic boundaries such as the border between areas 17 and 18a. However, extrastriate cortex lateral to area 17 receives callosal inputs which are not related to previously defined cytoarchitectonic boundaries. Following intraocular injections of [³H]fucose, transneuronal label occupies area 17 and mainly the posterior part of area 18a. A region in posterolateral area 18a which is ‘subdivided’ into callosal and sparsely callosal regions appears to receive an input from the lateral geniculate nucleus, based on transneuronal autoradiography. Comparison of the distribution of callosal axons and transneuronal label suggests that regions of murid cortex similar to areas 18, 19 and lateral suprasylvian cortex in cats may be located posteriorly in area 18a.     

Organization of callosal connections in the visual cortex of the rabbit following neonatal enucleation, dark rearing, and strobe rearing.

The organization of visual callosal projections was studied in (1) normal adult rabbits; (2) adult rabbits which had undergone monocular enucleation (ME) or binocular enucleation (BE) at birth; and (3) adult rabbits which had been deprived of normal visual experience during development by dark rearing (DR) or strobe rearing (SR). Previously published observations (Murphy and Grigonis, Behav Brain Res 30:151, 1988) on callosal organization in adult rabbits in which retinal ganglion cell activity was eliminated during development by intraocular tetrodotoxin (TTX) injections, are also summarized for comparison with these data. The tangential extent of the callosal cell zone was significantly larger than normal in DR, TTX, and ME rabbits, was unchanged in BE rabbits, and was significantly reduced in SR rabbits. An analysis of the laminar distribution of the callosal cells revealed a significant increase in the percentage of callosal cells in lamina IV in ME, DR, and TTX animals. Measurements of density of callosal cells showed a significant increase in the density of the callosal projection in ME and SR rabbits and a decrease in density in BE rabbits compared with normal. The data suggest that the mechanisms involved in the development of the tangential and laminar organization of the callosal cell zone are different. In addition, the data suggest that the mechanisms involved in the maintenance of callosal projections are different from the mechanisms involved in the elimination of callosal projections during development. The effects of these developmental manipulations on callosal organization in other mammals are reviewed and compared with the effects in rabbits. The data suggest that species differences in the degree of maturity of the visual system at birth and in the extent of callosal development at the time of eye opening, may underlie species differences in the effects of these manipulations on the organization of visual callosal projections during development.     

Agenesis of the corpus callosum: symptoms consistent with developmental disability in two siblings

Agenesis of the corpus callosum (AgCC) is a congenital disorder that disrupts the development of neurological structures connecting the right and left hemispheres of the brain. In addition to neurological symptoms, many individuals with AgCC demonstrate marked deficits in social, communication, and adaptive skills. This paper presents two case studies of congenital AgCC in siblings with socioemotional and behavioral symptoms consistent with developmental disability, but with notably different symptom presentations and clinical needs. Conclusions from these cases suggest that unique symptom profiles of individuals with AgCC warrant careful consideration for referral to appropriate academic and habilitative services.     

Visuotactile interactions in the congenitally acallosal brain: evidence for early cerebral plasticity

Studies in patients with an isolated, congenital agenesis of the corpus callosum have documented potentials and limits of brain plasticity. Literature suggests that early reorganization mechanisms can compensate for the absence of the corpus callosum in unisensory tasks that involve interhemispheric transfer. It is unknown, however, how the congenitally acallosal brain processes multisensory information, which presumably requires interhemispheric transfer of modality-specific input. Therefore, we tested five patients with total and one patient with partial agenesis of the corpus callosum in a visuotactile interference task (the “crossmodal congruency task”) with uncrossed and crossed hands and compared their performance to that of 31 healthy controls. We found that congruency effects followed the hands in space not only in healthy, but also in congenitally acallosal individuals. Remarkably, this was also true when patients’ hands crossed the vertical visual meridian and stimuli were presented at the same hand. These results suggest that callosal connectivity is not required for remapping of visuotactile space. We conclude that early brain plasticity allows for compensation of the developmental absence of the corpus callosum in a visuotactile interference task.     

Organization,Development and Enucleation-induced Alterations in the Visual Callosal Projection of the Hamster: Single Axon Tracing with Phaseolus vulgaris leucoagglutinin and Di-I

The distribution of callosal axons interconnecting lateral area 17 and medial area 18 of the rodent's occipital cortex is dramatically altered by neonatal enucleation, but it is not known how this manipulation affects the morphology of individual callosal axons or whether the enucleation-induced changes in this pathway reflect maintenance of a transient developmental state by these fibres. In the present study, these questions were addressed by tracing the individual callosal axons in normal adult and neonatally enucleated adult hamsters with Phaseolus vulgaris leucoagglutinin (PHAL) and by anterograde labelling of developing callosal axons with the carbocyanine dye, Di-I. In normal adults, injections of PHAL into the region of the 17 - 18a border produced dense labelling in all layers in the region of the contralateral 17 - 18a border. Larger injections resulted in callosal labelling that extended across the lateral one-half of area 17, primarily in layers I and V. Thirty-four callosal axons from normal adult hamsters were reconstructed through all the cortical laminae. Most of these had very simple terminal arbors. They gave off short collaterals in the infragranular layers and branched more extensively in the uppermost part of layer II - III and in lamina I. Small injections of PHAL into the occipital cortex of neonatally enucleated adult hamsters resulted in labelled axons throughout most of areas 17 and 18a in the contralateral hemisphere. The terminal arbors of most individual callosal axons in eyeless hamsters were not appreciably different from those in sighted animals. However, 26.8% of 28 fibres reconstructed through all cortical laminae in the neonatally enucleated hamsters had much more widespread branches than any of the axons recovered from normal hamsters. As a result, the average total length of the callosal axons from the blinded hamsters was significantly greater than that for such fibres from the sighted animals. Anterograde labelling with Di-I demonstrated axons in the anterior commissure and anterior part of the corpus callosum on P-0. Labelled fibres extended into the white matter underlying the occipital cortex on P-1 and entered the cortical plate on P-2. Some of these axons reached into the marginal layer. Many developing callosal axons had short branches in the white matter, but generally extended only a single collateral into the cortical grey matter. Callosal axons in perinatal animals branched very little within the cortex and, in this respect, resembled fibres labelled with PHAL in adult hamsters. These results support the conclusion that the expanded tangential distribution of the occipital callosal projection in neonatally enucleated adult hamsters results, at least in part, from individual axons with abnormally widespread terminal arbors which are not present in large numbers at any time during normal development.     

Autosomal recessive hereditary spastic paraplegia with thin corpus callosum: a novel mutation in the SPG11 gene and further evidence for genetic heterogeneity

Background and purpose:  Autosomal Recessive Hereditary Spastic Paraplegia with Thin Corpus Callosum (AR-HSPTCC) is a clinically and genetically heterogeneous complicated form of spastic paraplegia. Two AR-HSPTCC loci have been assigned to chromosome 15q13-15 ( SPG11 ) and chromosome 8p12-p11.21 respectively. Mutations in the SPG11 gene, encoding the spatacsin protein, have been found in the majority of SPG11 families. In this study, involvement of the SPG11 or 8p12-p11.21 loci was investigated in five Italian families, of which four consanguineous.
Methods:  Families were tested for linkage to the SPG11 or 8p12-p11.21 loci and the SPG11 gene was screened in all the affected individuals.
Results:  Linkage was excluded in the four consanguineous families. In the only SPG11 -linked family the same homozygous haplotype 4.2 cM across the SPG11 locus was shared by all the three affected siblings. A novel c.2608A>G mutation predicted to affect the splicing was found in exon 14 of the SPG11 gene.
Discussion:  This collection of families contributes to highlight the intra and inter locus heterogeneity in AR-HSPTCC, already remarked in previous reports. In particular, it confirms heterogeneity amongst Italian families and reports a new mutation predicted to affect splicing in the spatacsin gene.     

The value of diffusion-weighted imaging in the diagnosis of Marchiafava-Bignami disease: apropos of a case.

Marchiafava-Bignami disease (MBD) is characterized by demyelination and necrosis of corpus callosum encountered in chronic alcoholic patients. Etiology is the deficiency of vitamin B complex. Magnetic resonance imaging (MRI) in MBD typically reveals focal lesions of high T2 and FLAIR signal intensity in the corpus callosum. We here present a 42-year-old male alcoholic diagnosed as MBD on the basis of MRI and diffusion-weighted imaging (DWI) features. The patient totally recovered following appropriate vitamin B complex replacement therapy, despite reduced diffusion in the initial setting. This case report emphasizes on the important role played by MRI and DWI in the early diagnosis and follow-up of this potentially fatal disease.     

Interhemispheric pathways of the hippocampal formation, presubiculum, and entorhinal and posterior parahippocampal cortices in the rhesus monkey: the structure and organization of the hippocampal commissures

The interhemispheric pathways originating in the hippocampal formation, presubiculum, and entorhinal and posterior parahippocampal cortices and coursing through the fornix system were investigated by autoradiographic tracing in 29 rhesus monkeys (Macaca mulatta). The results revealed that crossing fibers are segregated into three contiguous systems. A ventral hippocampal commissure lies at the transition between the body and anterior columns of the fornix in the vicinity of the subfornical organ and the interventricular foramina of Monro; it is formed by axons arising in the most anterior (uncal and genual) subdivisions of the hippocampal formation. A dorsal hippocampal commissure lies inferior to the posterior end of the body of the corpus callosum; it is formed by axons arising in the presubiculum and entorhinal cortex of the anterior parahippocampal gyrus and the proisocortical and neocortical subdivisions of the posterior parahippocampal gyrus but not in the hippocampal formation. A hippocampal decussation lies between the ventral hippocampal commissure and dorsal hippocampal commissure; it is formed by axons arising in the body of the hippocampal formation. In contrast to the fibers of the ventral hippocampal commissure and dorsal hippocampal commissure, which terminate in contralateral cortical areas, these decussating fibers terminate in the contralateral septum. Thus, the ventral hippocampal commissure and dorsal hippocampal commissure of the rhesus monkey appear to be homologous to similarly designated structures in other mammals. To the extent that these observations also apply to the interhemispheric fibers of the human hippocampal formation and parahippocampal areas, their possible preservation must be considered when interpreting the effect of callosal transection on seizures and the results of "split-brain" studies, since callosal transection may fail to sever the hippocampal commissures in their entirety.     

Topographic organization of the middle temporal visual area in the macaque monkey: representational biases and the relationship to callosal connections and myeloarchitectonic boundaries

We have used physiological and anatomical techniques to address three general issues concerning the topographic organization of the middle temporal visual area (MT) of the macaque monkey. First, we carried out a quantitative analysis of irregularities and asymmetries in the visual representation in MT. This analysis revealed a striking overemphasis on a restricted portion of the visual field that runs obliquely through the inferior contralateral quadrant and largely avoids both the horizontal meridian and the inferior vertical meridian. This corresponds to the portion of the visual field that would be maximally stimulated during visually guided hand movements. Second, the physiologically determined topographic organization of MT was compared to the pattern of callosal inputs in the same hemisphere, which are known to be distributed irregularly within MT. Callosal inputs tended to be densest near the representation of the vertical meridian, but there were numerous exceptions to this trend. Thus, topographic irregularities account for only part of the irregularities in callosal inputs to MT. Finally, comparison of these data with previous reports shows a strong correlation between body weight and the average size of MT. The representation in myeloarchitectonically defined MT was found to include much of the visual periphery, although it is unclear from our data whether this representation is invariably complete.     

Characterization of the optic nerve and retinal ganglion cell layer in the dysmyelinated adult Long Evans Shaker rat: evidence for axonal sprouting

Myelin in the central nervous system (CNS) is hypothesized to help guide the growth of developing axons by inhibiting sprouting of aberrant neurites. Previous studies using animal models lacking CNS myelin have reported that increasing capacity for sprouting axons is negatively correlated with the degree of myelination. In the present study, we investigated the optic nerves of the recently identified Long Evans Shaker (LES) rat with prolonged dysmyelination of adult axons to determine whether the lack of myelin basic protein (MBP) in adult LES rats could manifest as increases in the population of CNS axons. We observed numerous small, unmyelinated axon profiles (<0.3 microm in diameter) clustered in bundles alongside normal caliber axons in dysmyelinated LES rats but not in normal myelinated Long Evans (LE) rats. These putative axon profiles resembled sprouting axons previously described in the CNS. Moreover, the high number of small putative axon profiles could not be accounted for by any significant increases in the number of ganglion cells and displaced amacrine cells in the ganglion cell layer when compared with normal rats as evaluated by using a variety of techniques. This finding suggests that the observed clusters of putative axon profiles were not due to developmental abnormalities in the retina but to the lack of myelin in the optic nerves of LES rats. The adult LES rat, therefore, may serve as a useful model to study the role of myelin in regulating axon development or axon regeneration after CNS injury in the adult mammalian system.     

Spastic paraplegia with thin corpus callosum: description of 20 new families, refinement of the SPG11 locus, candidate gene analysis and evidence of genetic heterogeneity

We studied 20 Mediterranean families (40 patients) with autosomal recessive hereditary spastic paraplegia and thin corpus callosum (ARHSP-TCC, MIM 604360) to characterize their clinical and genetic features. In six families (17 patients) of Algerian Italian, Moroccan, and Portuguese ancestry, we found data consistent with linkage to the SPG11 locus on chromosome 15q13–15, whereas, in four families (nine patients of Italian, French, and Portuguese ancestry) linkage to the SPG11 locus could firmly be excluded, reinforcing the notion that ARHSP-TCC is genetically heterogeneous. Patients from linked and unlinked families could not be distinguished on the basis of clinical features alone. In SPG11-linked kindred, haplotype reconstruction allowed significant refinement to 6 cM, of the minimal chromosomal interval, but analysis of two genes (MAP1A and SEMA6D) in this region did not identify causative mutations. Our findings suggest that ARHSP-TCC is the most frequent form of ARHSP in Mediterranean countries and that it is particularly frequent in Italy.Electronic Supplementary Material  Supplementary material is available for this article at     

Molecular tunnels and boundaries for growing axons in the anterior commissure of hamster embryos

We have analyzed the immunohistochemical expression of chondroitin sulfate proteoglycan (CSPG), fibronectin (FN), laminin (LN), tenascin (TN), and glial fibrillary acidic protein (GFAP) along the anterior commissure (AC) of hamster embryos (n = 175; from embryonic day (E)12 to E16). Frozen sections were cut at different planes from embryonic brains between E12 and E16, treated for immunohistochemistry, and observed under epifluorescence microscopy. During the pre-crossing stage (E12–E13), CSPG was expressed as a sagittal stratum between the interhemispheric fissure and the prospective AC region. TN appeared rostral to the third ventricle and along the medial subventricular zone of the lateral ventricles. LN and FN both presented a faint expression, and GFAP was not detected. Although AC axons started crossing the midline region (E13.5–E14), CSPG, FN, LN, and, much less intensely, GFAP circumscribed the AC bundle, forming a tunnel through which AC fibers elongate. TN was no longer seen at the midplane but remained visible laterally. During the post-crossing stage (E14.5–E16), CSPG and TN were no longer seen at the midline, although both could be observed between the AC limbs, seeming to form boundaries for AC lateral growth. LN and FN were then absent near the AC bundle. During this late stage, GFAP expression became most intense, forming a distinct tunnel around the AC. We have shown that the expression of extracellular matrix molecules and GFAP follow a time- and space-regulated course related to AC development, plausibly representing influential factors for growth and guidance of commissural fibers. J. Comp. Neurol. 399:176–188, 1998. © 1998 Wiley-Liss, Inc.