Immunohistochemical co-localization of S-100b and the glial fibrillary acidic protein in rat brain

An Extensive Study Regarding the Microscopic Anatomy of the Early Fetal Human Optic Nerve

The development of the optic nerve and its surrounding tissues during the early fetal period is a convoluted period because it spans both the organogenesis period and the fetal period. This study details the microscopic anatomy and histoembryology of the optic nerve in embryos during the early fetal period, including the second half of the first trimester of pregnancy. Serial sections through the orbit of variously aged embryos allowed us to analyze the nerve in both longitudinal and transverse aspects. A histological assessment and description of the structures surrounding and inside the nerve were performed, highlighting the cellular subtypes involved. By employing immunohistochemical techniques, we could characterize the presence and distribution of astrocytes within the optic nerve. Our findings suggest that by the 8th gestational week (WG) the structures are homologs to all the adult ones but with an early appearance so that maturation processes take place afterward. By this age, the axons forming the nerve are definitive adult axons. The glial cells do not yet exhibit adult phenotype, but their aspect becomes adult toward the 13th week. During its development the optic nerve increases in size then, at 14 weeks, it shrinks considerably, possibly through its neural maturation process. The morphological primordium of the blood-nerve barrier can be first noted at 10 WG and at 13 WG the morphological blood-nerve barrier is definitive. The meningeal primordium can be first noted as a layer of agglomerated fibroblasts, later toward 13 WG splitting in pachymeninx and leptomeninges and leaving space for intrinsic blood vessels.

Quantity, distribution and phenotype of newly generated cells in the intact spinal cord of adult macaque monkeys

The existence of proliferating cells in the intact spinal cord, their distribution and phenotype, are well studied in rodents. A limited number of studies also address the proliferation after spinal cord injury, in non-human primates. However, a detailed description of the quantity, distribution and phenotype of proliferating cells at different anatomical levels of the intact adult non-human primate spinal cord is lacking at present. In the present study, we analyzed normal spinal cord tissues from adult macaque monkeys (Macaca fuscata), infused with Bromo-2'-deoxyuridine (BrdU), and euthanized at 2h, 2 weeks, 5 weeks and 10 weeks after BrdU. We found a significantly higher density of BrdU + cells in the gray matter of cervical segments as compared to thoracic or lumbar segments, and a significantly higher density of proliferating cells in the posterior as compared to the anterior horn of the gray matter. BrdU + cells exhibited phenotype of microglia or endothelial cells (∼50%) or astroglial and oligodendroglial cells (∼40%), including glial progenitor phenotypes marked by the transcription factors Sox9 and Sox10. BrdU + cells also co-expressed other transcription factors known for their involvement in embryonic development, including Emx2, Sox1, Sox2, Ngn1, Olig1, Olig2, Olig3. In the central canal, BrdU + cells were located along the dorso-ventral axis and co-labeled for the markers Vimentin and Nestin. These results reveal the extent of cellular plasticity in the spinal cord of non-human primates under normal conditions.

Utilization of ethanolamine phosphate phospholyase as a unique astrocytic marker

Astrocytes play diverse roles in the central nervous system (CNS) in both physiological and pathological conditions. Previous studies have identified many markers of astrocytes to analyze their complicated roles. Recently, closure of the critical period by mature astrocytes has been revealed, and the need for finding mature astrocyte-specific markers has been growing. We previously found that Ethanolamine phosphate phospholyase (Etnppl) was almost not expressed in the developing neonatal spinal cord, and its expression level slightly decreased after pyramidotomy in adult mice, which showed weak axonal sprouting, suggesting that its expression level negatively correlates with axonal elongation. Although the expression of Etnppl in astrocytes in adult is known, its utility as an astrocytic marker has not yet been investigated in detail. Here, we showed that Etnppl was selectively expressed in astrocytes in adult. Re-analyses using published RNA-sequencing datasets revealed changes in Etnppl expression in spinal cord injury, stroke, or systemic inflammation models. We produced high-quality monoclonal antibodies against ETNPPL and characterized ETNPPL localization in neonatal and adult mice. Expression of ETNPPL was very weak in neonatal mice, except in the ventricular and subventricular zones, and it was heterogeneously expressed in adult mice, with the highest expression in the cerebellum, olfactory bulb, and hypothalamus and the lowest in white matter. Subcellular localization of ETNPPL was dominant in the nuclei with weak expression in the cytosol in the minor population. Using the antibody, astrocytes in adult were selectively labeled in the cerebral cortex or spinal cord, and changes in astrocytes were detected in the spinal cord after pyramidotomy. ETNPPL is expressed in a subset of Gjb6 ⁺ astrocytes in the spinal cord. The monoclonal antibodies we created, as well as fundamental knowledge characterized in this study, will be valuable resources in the scientific community and will expand our understanding of astrocytes and their complicated responses in many pathological conditions in future analyses.

Immunological Markers for Central Nervous System Glia

Glial cells in the central nervous system (CNS) are composed of oligodendrocytes, astrocytes and microglia. They contribute more than half of the total cells of the CNS, and are essential for neural development and functioning. Studies on the fate specification, differentiation, and functional diversification of glial cells mainly rely on the proper use of cell- or stage-specific molecular markers. However, as cellular markers often exhibit different specificity and sensitivity, careful consideration must be given prior to their application to avoid possible confusion. Here, we provide an updated overview of a list of well-established immunological markers for the labeling of central glia, and discuss the cell-type specificity and stage dependency of their expression.

Effect of senescence on the tyrosine hydroxylase and S100B immunoreactivity in the nigrostriatal pathway of the rat

Senescence is a natural and progressive physiological event that leads to a series of morphophysiological alterations in the organism. The brain is the most vulnerable organ to both structural and functional changes during this process. Dopamine is a key neurotransmitter for the proper functioning of the brain, directly involved in circuitries related with emotions, learning, motivation and reward. One of the main dopamine- producing nuclei is the substantia nigra pars compacta (SNpc), which establish connections with the striatum forming the so-called nigrostriatal pathway. S100B is a calcium binding protein mainly expressed by astrocytes, involved in both intracellular and extracellular processes, and whose expression is increased following injury in the nervous tissue, being a useful marker in altered status of central nervous system. The present study aimed to analyze the impact of senescence on the cells immunoreactive for tyrosine hydroxylase (TH) and S100B along the nigrostriatal pathway of the rat. Our results show an decreased expression of S100B⁺ cells in SNpc. In addition, there was a significant decrease in TH immunoreactivity in both projection fibers and TH⁺ cell bodies. In the striatum, a decrease in TH immunoreactivity was also observed, as well as an enlargement of the white matter bundles. Our findings point out that senescence is related to the anatomical and neurochemical changes observed throughout the nigrostriatal pathway.

Neural Stem Cells in Adult Mammals are not Astrocytes

At the turn of the 21st century studies of the cells that resided in the adult mammalian subventricular zone (SVZ) characterized the neural stem cells (NSCs) as a subtype of astrocyte. Over the ensuing years, numerous studies have further characterized the properties of these NSCs and compared them to parenchymal astrocytes. Here we have evaluated the evidence collected to date to establish whether classifying the NSCs as astrocytes is appropriate and useful. We also performed a meta-analysis with 4 previously published datasets that used cell sorting and unbiased single-cell RNAseq to highlight the distinct gene expression profiles of adult murine NSCs and niche astrocytes. On the basis of our understanding of the properties and functions of astrocytes versus the properties and functions of NSCs, and from our comparative transcriptomic analyses we conclude that classifying the adult mammalian NSC as an astrocyte is potentially misleading. From our vantage point, it is more appropriate to refer to the cells in the adult mammalian SVZ that retain the capacity to produce new neurons and macroglia as NSCs without attaching the term "astrocyte-like."

S100B is selectively expressed by gray matter protoplasmic astrocytes and myelinating oligodendrocytes in the developing CNS

Studies on the development of central nervous system (CNS) primarily rely on the use of specific molecular markers for different types of neural cells. S100B is widely being used as a specific marker for astrocytes in the CNS. However, the specificity of its expression in astrocyte lineage has not been systematically investigated and thus has remained a lingering issue. In this study, we provide several lines of molecular and genetic evidences that S100B is expressed in both protoplasmic astrocytes and myelinating oligodendrocytes. In the developing spinal cord, S100B is first expressed in the ventral neuroepithelial cells, and later in ALDH1L1+/GS+ astrocytes in the gray matter. Meanwhile, nearly all the S100B+ cells in the white matter are SOX10+/MYRF+ oligodendrocytes. Consistent with this observation, S100B expression is selectively lost in the white matter in Olig2-null mutants in which oligodendrocyte progenitor cells (OPCs) are not produced, and dramatically reduced in Myrf-conditional knockout mutants in which OPCs fail to differentiate. Similar expression patterns of S100B are observed in the developing forebrain. Based on these molecular and genetic studies, we conclude that S100B is not a specific marker for astrocyte lineage; instead, it marks protoplasmic astrocytes in the gray matter and differentiating oligodendrocytes.

Characterization of cell type-specific S100B expression in the mouse olfactory bulb

S100B is an EF-hand type Ca2+-binding protein of the S100 family, known to support neurogenesis and to promote the interactions between brain's nervous and immune systems. Here, we characterized the expression of S100B in the mouse olfactory bulb, a neurogenic niche comprising mature and adult-born neurons, astrocytes, oligodendrocytes and microglia. Besides astrocytes, for which S100B is a classical marker, S100B was also expressed in NG2 cells and, surprisingly, in APC-positive myelinating oligodendrocytes but not in mature/adult-born neurons or microglia. Various layers of the bulb differed substantially in the composition of S100B-positive cells, with the highest fraction of the APC-positive oligodendrocytes found in the granule cell layer. Across all layers, ∼50 % of NG2 cells were S100B-negative. Finally, our data revealed a strong correlation between the fraction of myelinating oligodendrocytes among the S100B-positive cells and the oligodendrocyte density in different brain areas, underscoring the importance of S100B for the establishment and maintenance of myelin sheaths.

Activated forms of astrocytes with higher GLT-1 expression are associated with cognitive normal subjects with Alzheimer pathology in human brain

Although the cognitive impairment in Alzheimer's disease (AD) is believed to be caused by amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), several postmortem studies have reported cognitive normal subjects with AD brain pathology. As the mechanism underlying these discrepancies has not been clarified, we focused the neuroprotective role of astrocytes. After examining 47 donated brains, we classified brains into 3 groups, no AD pathology with no dementia (N-N), AD pathology with no dementia (AD-N), and AD pathology with dementia (AD-D), which represented 41%, 21%, and 38% of brains, respectively. No differences were found in the accumulation of Aβ plaques or NFTs in the entorhinal cortex (EC) between AD-N and AD-D. Number of neurons and synaptic density were increased in AD-N compared to those in AD-D. The astrocytes in AD-N possessed longer or thicker processes, while those in AD-D possessed shorter or thinner processes in layer I/II of the EC. Astrocytes in all layers of the EC in AD-N showed enhanced GLT-1 expression in comparison to those in AD-D. Therefore these activated forms of astrocytes with increased GLT-1 expression may exert beneficial roles in preserving cognitive function, even in the presence of Aβ and NFTs.

Long-term effects of autoimmune CNS inflammation on adult hippocampal neurogenesis

Neurogenesis is a well-characterized phenomenon within the dentate gyrus (DG) of the adult hippocampus. Aging and chronic degenerative disorders have been shown to impair hippocampal neurogenesis, but the consequence of chronic inflammation remains controversial. In this study the chronic experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis was used to investigate the long-term effects of T cell-mediated central nervous system inflammation on hippocampal neurogenesis. 5-Bromodeoxyuridine (BrdU)-labeled subpopulations of hippocampal cells in EAE and control mice (coexpressing GFAP, doublecortin, NeuN, calretinin, and S100) were quantified at the recovery phase, 21 days after BrdU administration, to estimate alterations on the rate and differentiation pattern of the neurogenesis process. The core features of EAE mice DG are (i) elevated number of newborn (BrdU+) cells indicating vigorous proliferation, which in the long term subsided; (ii) enhanced migration of newborn cells into the granule cell layer; (iii) increased level of immature neuronal markers (including calretinin and doublecortin); (iv) trending decrease in the percentage of newborn mature neurons; and (v) augmented gliogenesis and differentiation of newborn neural precursor cells (NPCs) to mature astrocytes (BrdU+/S100+). Although the inflammatory environment in the brain of EAE mice enhances the proliferation of hippocampal NPCs, in the long term neurogenesis is progressively depleted, giving prominence to gliogenesis. The discrepancy between the high number of immature cells and the low number of mature newborn cells could be the result of a caused defect in the maturation pathway. © 2016 Wiley Periodicals, Inc.

Roles for DSCAM and DSCAML1 in central nervous system development and disease

DSCAMs (Down syndrome cell adhesion molecules) are a group of immunoglobulin-like transmembrane proteins that contain fibronectin III domains. The founding member of the family was isolated in a positional cloning study that sought to identify genes located on chromosome 21 at the locus 21q22.2-q22.3 that is implicated in the neurological and cardiac phenotypes associated with Down's syndrome. In Drosophila, Dscam proteins are involved in neuronal wiring, while in vertebrates, the role of these cell adhesion molecules in neurogenesis, dendritogenesis, axonal outgrowth, synaptogenesis, and synaptic plasticity is only just beginning to be understood. In this chapter, we will review the functions ascribed to the two paralogous proteins found in humans, DSCAM and DSCAML1 (DSCAM-like 1), based on findings in knockout mice. The signaling pathways downstream of DSCAM activation and the role of DSCAM miss-expression in disease will be also discussed, particularly with regard to the intellectual disability in Down's syndrome.

Astrocytosis in parkinsonism: considering tripartite striatal synapses in physiopathology?

The current concept of basal ganglia organization and function in physiological and pathophysiological conditions excludes the most numerous cells in the brain, i.e., the astrocytes, present with a ratio of 10:1 neuron. Their role in neurodegenerative condition such as Parkinson's disease (PD) remains to be elucidated. Before embarking into physiological investigations of the yet-to-be-identified "tripartite" synapses in the basal ganglia in general and the striatum in particular, we therefore characterized anatomically the PD-related modifications in astrocytic morphology, the changes in astrocytic network connections and the consequences on the spatial relationship between astrocytic processes and asymmetric synapses in normal and PD-like conditions in experimental and human PD. Our results unravel a dramatic regulation of striatal astrocytosis supporting the hypothesis of a key role in (dys) regulating corticostriatal transmission. Astrocytes and their various properties might thus represent a therapeutic target in PD.

Transgenic rat model of Huntington's disease: a histopathological study and correlations with neurodegenerative process in the brain of HD patients

Rats transgenic for Huntington's disease (tgHD51 CAG rats), surviving up to two years, represent an animal model of HD similar to the late-onset form of human disease. This enables us to follow histopathological changes in course of neurodegenerative process (NDP) within the striatum and compare them with postmortem samples of human HD brains. A basic difference between HD pathology in human and tgHD51 rats is in the rate of NDP progression that originates primarily from slow neuronal degeneration consequently resulting in lesser extent of concomitant reactive gliosis in the brain of tgHD51 rats. Although larger amount of striatal neurons displays only gradual decrease in their size, their number is significantly reduced in the oldest tgHD51 rats. Our quantitative analysis proved that the end of the first year represents the turn in the development of morphological changes related to the progression of NDP in tgHD51 rats. Our data also support the view that all types of CNS glial cells play an important, irreplaceable role in NDP. To the best of our knowledge, our findings are the first to document that tgHD51 CAG rats can be used as a valid animal model for detailed histopathological studies related to HD in human.

Regulation of S100B in white adipose tissue by obesity in mice

S100B is a calcium binding protein found in adipose tissue; however, relatively little is known about the physiologic regulation or distribution of the protein within this organ. We examined plasma S100B concentration and white adipose tissue (WAT) s100b mRNA levels in lean and diet-induced obese (DIO) mice. Plasma S100B levels were increased by obesity. In WAT, s100b gene expression was also significantly increased by obesity and this increase was reversed following weight-loss. s100b gene expression was detected in both the adipocyte-enriched and stromal-vascular fractions of WAT; however, the increase in s100b gene expression in obese animals was only detected in the adipocyte-enriched fraction. Our results support published in vitro data indicating that WAT S100B may contribute to obesity-associated inflammation.

Prenatal MAM administration affects histone H3 methylation in postnatal life in the rat medial prefrontal cortex

Several findings have indicated that schizophrenia may be connected with the impaired epigenetic regulation of gene transcription. The present study investigated the epigenetic modifications connected with histone H3 methylation at lysine (K)4 and K9 in the medial prefrontal cortex (mPFC) in a neurodevelopmental model of schizophrenia based on prenatal administration of methylazoxymethanol (MAM) at embryonic day 17, which impairs the sensorimotor gating process in adult but not adolescent animals. The effect of MAM was determined at different postnatal ages, pre-puberty (P15, P30 and P45) and post-puberty (P60 and P70), using western blot analyses. MAM treatment altered the levels of H3K9me2 before puberty. H3K9me2 was decreased at P15 and P45 but was increased at P30. In contrast, H3K4me3 was noticeably decreased in adult rats. Immunofluorescence experiments revealed that H3K9me2 protein levels were increased in neuronal cells at P30 and that H3K4me3 levels were decreased in astrocytes at P60 after MAM administration. Decreases in the methyltransferase ASH2L protein levels at P45, P60 and P70 were also observed, while the protein levels of the methyltransferase G9a did not change. In addition, levels of the demethylases LSD1 and JARID1c were analysed after MAM administration. LSD1 protein levels were increased at P15 but decreased at P30. JARID1c protein levels were increased in the MAM-treated animals at P60. Decreased Gad1 mRNA levels were found in adult MAM-treated animals, similar to alternation observed in schizophrenia. The present study indicates that prenatal MAM administration evokes changes in the methylation patterns of histone H3 during postnatal life.

Phosphodiesterase-4D knock-out and RNA interference-mediated knock-down enhance memory and increase hippocampal neurogenesis via increased cAMP signaling

Phosphodiesterase-4 (PDE4) plays an important role in mediating memory via the control of intracellular cAMP signaling; inhibition of PDE4 enhances memory. However, development of PDE4 inhibitors as memory enhancers has been hampered by their major side effect of emesis. PDE4 has four subtypes (PDE4A-D) consisting of 25 splice variants. Mice deficient in PDE4D displayed memory enhancement in radial arm maze, water maze, and object recognition tests. These effects were mimicked by repeated treatment with rolipram in wild-type mice. In addition, similarly as rolipram-treated wild-type mice, PDE4D-deficient mice also displayed increased hippocampal neurogenesis and phosphorylated cAMP response element-binding protein (pCREB). Furthermore, microinfusion of lentiviral vectors that contained microRNAs (miRNAs) targeting long-form PDE4D isoforms into bilateral dentate gyri of the mouse hippocampus downregulated PDE4D4 and PDE4D5, enhanced memory, and increased hippocampal neurogenesis and pCREB. Finally, while rolipram and PDE4D deficiency shortened α2 adrenergic receptor-mediated anesthesia, a surrogate measure of emesis, miRNA-mediated PDE4D knock-down in the hippocampus did not. The present results suggest that PDE4D, in particular long-form PDE4D, plays a critical role in the mediation of memory and hippocampal neurogenesis, which are mediated by cAMP/CREB signaling; reduced expression of PDE4D, or at least PDE4D4 and PDE4D5, in the hippocampus enhances memory but appears not to cause emesis. These novel findings will aid in the development of PDE4 subtype- or variant-selective inhibitors for treatment of disorders involving impaired cognition, including Alzheimer's disease.

Intermittent hypoxia promotes hippocampal neurogenesis and produces antidepressant-like effects in adult rats

Increasing evidence indicates that stimulating hippocampal neurogenesis could provide novel avenues for the treatment of depression, and recent studies have shown that in vitro neurogenesis is enhanced by hypoxia. The aim of this study was to investigate the potential regulatory capacity of an intermittent hypobaric hypoxia (IH) regimen on hippocampal neurogenesis and its possible antidepressant-like effect. Here, we show that IH promotes the proliferation of endogenous neuroprogenitors leading to more newborn neurons in hippocampus in adult rats. Importantly, IH produces antidepressant-like effects in multiple animal models screening for antidepressant activity, including the forced swimming test, chronic mild stress paradigm, and novelty-suppressed feeding test. Hippocampal x-ray irradiation blocked both the neurogenic and behavioral effects of IH, indicating that IH likely produces antidepressant-like effects via promoting neurogenesis in adult hippocampus. Furthermore, IH stably enhanced the expression of BDNF in hippocampus; both the antidepressant-like effect and the enhancement of cell proliferation induced by IH were totally blocked by pharmacological and biological inhibition of BDNF-TrkB (tyrosine receptor kinase B) signaling, suggesting that the neurogenic and antidepressant-like effects of IH may involve BDNF signaling. These observations might contribute to both a better understanding of physiological responses to IH and to developing IH as a novel therapeutic approach for depression.

Adipocytes as an Important Source of Serum S100B and Possible Roles of This Protein in Adipose Tissue

Adipocytes contain high levels of S100B and in vitro assays indicate a modulated secretion of this protein by hormones that regulate lipolysis, such as glucagon, adrenaline, and insulin. A connection between lipolysis and S100B release has been proposed but definitive evidence is lacking. Although the biological significance of extracellular S100B from adipose tissue is still unclear, it is likely that this tissue might be an important source of serum S100B in situations related, or not, to brain damage. Current knowledge does not preclude the use of this protein in serum as a marker of brain injury or astroglial activation, but caution is recommended when discussing the significance of changes in serum levels where S100B may function as an adipokine, a neurotrophic cytokine, or an alarmin.

Antidepressant- and anxiolytic-like effects of the phosphodiesterase-4 inhibitor rolipram on behavior depend on cyclic AMP response element binding protein-mediated neurogenesis in the hippocampus

Inhibition of phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP (cAMP), increases phosphorylation of the cAMP response element binding protein (pCREB) and hippocampal neurogenesis, and produces antidepressant-like effects on behavior; however, causal links among these actions have not been established. In this study, chronic administration of rolipram (0.31-1.25 mg/kg, 16-23 days) produced antidepressant- and anxiolytic-like effects on behavior in mice. It also increased cAMP and pCREB levels in the hippocampus and prefrontal cortex, but increased Sox2, a marker for mitotic progenitor cells, only in the hippocampus. Chronic rolipram treatment also increased hippocampal neurogenesis, as evidenced by increased bromodeoxyuridine (BrdU)-positive cells in the hippocampal dentate gyrus. Methylazoxymethanol (MAM), which is toxic to proliferating cells, reversed rolipram-induced increases in BrdU-positive cells and pCREB in the hippocampus and partially blocked its behavioral effects. Approximately 84% of BrdU-positive cells became newborn neurons, 93% of which co-expressed pCREB; these proportions were not altered by rolipram or MAM, either alone or in combination. Finally, 3 weeks after the end of the MAM treatment, when neurogenesis was no longer inhibited, rolipram again increased hippocampal pCREB and its antidepressant- and anxiolytic-like effects were restored. Overall, these results suggest that rolipram produces its effects on behavior in a manner that at least partially depends on its neurogenic action in the hippocampus, targeting mitotic progenitor cells rather than newborn or mature neurons; cAMP/CREB signaling in hippocampal newborn neurons is critical for neurogenesis and contributes to the behavioral effects of rolipram.

Immunohistochemical analysis of brain lesions using S100B and glial fibrillary acidic protein antibodies in arundic acid- (ONO-2506) treated stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive rats (SHRSP) used as a model of essential hypertension cause a high incidence of brain stroke on the course of hypertension. Incidences and sizes of brain lesions are known to relate to the astrocyte activities. Therefore, relation between brain damage and the expression profile of the astrocytes was investigated with morphometric and immunohistochemical analyses using astrocyte marker antibodies of S100B and glial fibrillary acidic protein (GFAP) with or without arundic acid administration, a suppressor on the activation of astrocytes. Arundic acid extended the average life span of SHRSP. An increase in brain tissue weight was inhibited concomitant with a lower rate of gliosis/hemosiderin deposit/scarring in brain lesions. S100B- or GFAP-positive dot and filamentous structures were decreased in arundic acid-treated SHRSP, and this effect was most pronounced in the cerebral cortex, white matter, and pons, and less so in the hippocampus, diencephalon, midbrain, and cerebellum. Blood pressure decreased after administration of arundic acid in the high-dose group (100 mg/kg/day arundic acid), but not in the low-dose group (30 mg/kg/day). These data indicate that arundic acid can prevent hypertension-induced stroke, and may inhibit the enlargement of the stroke lesion by preventing the inflammatory changes caused by overproduction of the S100B protein in the astrocytes.

Determinants of regional and local diversity within the astroglial lineage of the normal central nervous system

Astrocytes are a major component of the resident non-neuronal glial cell population of the CNS. They are ubiquitously distributed throughout the brain and spinal cord, where they were initially thought to function in both structural and homeostatic capacities, providing the framework and environment in which neurons performed their parenchymal duties. However, this stroma-like view of astrocytes is no longer satisfactory. Mounting evidence particularly within the last decade indicates that astrocytes do not simply support neuronal activity but directly contribute to it. Congruent with this evolving view of astrocyte function in information processing is the emergent notion that these glial cells are not a homogeneous population of cells. Thus, astrocytes in various anatomically distinct regions of the normal CNS possess unique phenotypic characteristics that may directly influence the particular neuronal activities that define these regions. Remarkably, regional populations of astrocytes appear to exhibit local heterogeneity as well. Many phenotypic traits of the astrocyte lineage are responsive to local environmental cues (i.e., are adaptable), suggesting that plasticity contributes to this diversity. However, compelling evidence suggests that astrocytes arise from multiple distinct progenitor pools in the developing CNS, raising the intriguing possibility that some astrocyte heterogeneity may result from intrinsic differences between these progenitors. The purpose of this review is to explore the evidence for and mechanistic determinants of regional and local astrocyte diversity.

Postinjury niches induce temporal shifts in progenitor fates to direct lesion repair after spinal cord injury

Progenitors that express NG2-proteoglycan are the predominant self-renewing cells within the CNS. NG2 progenitors replenish oligodendrocyte populations within the intact stem cell niche, and cycling NG2 cells are among the first cells to react to CNS insults. We investigated the role of NG2 progenitors after spinal cord injury and how bone morphogen protein signals remodel the progressive postinjury (PI) niche. Progeny labeled by an NG2-specific reporter virus undergo a coordinated shift in differentiation profile. NG2 progeny born 24 h PI produce scar-forming astrocytes and transient populations of novel phagocytic astrocytes shown to contain denatured myelin within cathepsin-D-labeled endosomes, but NG2 progenitors born 7 d PI differentiate into oligodendrocytes and express myelin on processes that wrap axons. Analysis of spinal cord mRNA shows a temporal shift in the niche transcriptome of ligands that affect PI remodeling and direct progenitor differentiation. We conclude that NG2 progeny are diverse lineages that obey progressive cues after trauma to replenish the injured niche.

Regional differences in the temporal expression of non-apoptotic caspase-3-positive bergmann glial cells in the developing rat cerebellum

Although caspases have been intimately linked to apoptotic events, some of the pro-apoptotic caspases also may regulate differentiation. We previously demonstrated that active caspase-3 is expressed and has an apparent non-apoptotic function during the development of cerebellar Bergmann glia. The current study seeks to further correlate active/cleaved caspase-3 expression with the developmental phenotype of Bergmann glia by examining regional differences in the temporal pattern of expression of cleaved caspase-3 immunoreactivity in lobules of the cerebellar vermis. In general, we found that the expression pattern of cleaved caspase-3 corresponds to the reported developmental temporal profile of the lobes and that its levels peak at 15 days and declines thereafter. Compared to intermediate or late maturing lobules, early maturing lobules had higher levels of active caspase-3 at earlier postnatal times. This period of postnatal development is precisely the time during which Bergmann glia initiate differentiation.

Quantitative analysis of mitotic Olig2 cells in adult human brain and gliomas: implications for glioma histogenesis and biology

The capacity of adult human glial progenitor cells (AGPs), to proliferate and undergo multipotent differentiation, positions them as ideal candidate cells of origin for human gliomas. To investigate this potential role we identified AGPs as mitotically active Olig2 cells in nonneoplastic adult human brain and gliomas. We conservatively estimated that one in 5,000 human temporal lobe neocortical gray or subcortical white matter cells is mitotic. Extrapolating from a mean Olig2/Mib-1 labeling index (LI) of 52% and total cell number of 100 billion, we estimated the overall prevalence of mitotic Olig2 AGPs in nonneoplastic human brain parenchyma at 10 million. These data identify a large reservoir of Olig2 AGPs which could be potential targets for human gliomagenesis. The vast majority of mitotic cells in Grade II and Grade III gliomas of all histologic subtypes expressed Olig2 (mean LI 75%) but rarely S100B (LI 0.6%), identifying the Olig2 cell as a distinct contributor to the proliferating cell population of human gliomas of both oligodendroglial and astrocytic lineages. In the most malignant Grade IV glioma, or glioblastoma multiforme (GBM), the prevalence of Olig2/Mib-1 cells was significantly decreased (24.5%). The significantly lower Olig2/Mib-1 LI in GBMs suggests that a decrease in the prevalence of Olig2 cells to the total mitotic cell pool accompanies increasing malignancy. The novel framework provided by this quantitative and comparative analysis supports future studies to examine the histogenetic role of Olig2 AGPs in adult gliomas, their potential contribution to the tumor stroma and the molecular role of Olig2 in glioma pathogenesis.

Connexin43 and bergmann glial gap junctions in cerebellar function

Connexin43 (Cx43), a major component of astrocytic gap junctions, is abundantly expressed in Bergmann glial cells (BGCs) in the cerebellum, but the function of Cx43 in BGCs is largely unknown. BGCs are specialized astrocytes closely associated with Purkinje cells. Here, we review our recent studies of the role of Cx43 in gap junctional coupling between BGCs and in cerebellar function. We generated Cx43 conditional knockout mice with an S100b-Cre transgenic line (Cx43^fl/fl:S100b-Cre), in which there was a significant postnatal loss of Cx43 in BGCs and cerebellar astrocytes. Gap junctional coupling between BGCs measured by dye coupling was virtually abolished in Cx43^fl/fl:S100b-Cre mice. Electrophysiologic and behavioral analyses suggested that Cx43-mediated gap junctions and Cx43 hemichannels in BGCs are not necessary for the neuron-glia interactions required for cerebellum-dependent motor coordination and motor learning. These findings raise questions regarding the regional differences in the impact of the loss of Cx43 in the brain.

Aging-related changes in astrocytes in the rat retina: imbalance between cell proliferation and cell death reduces astrocyte availability

The aim of this study was to investigate changes in astrocyte density, morphology, proliferation and apoptosis occurring in the central nervous system during physiological aging. Astrocytes in retinal whole-mount preparations from Wistar rats aged 3 (young adult) to 25 months (aged) were investigated qualitatively and quantitatively following immunofluorohistochemistry. Glial fibrillary acidic protein (GFAP), S100 and Pax2 were used to identify astrocytes, and blood vessels were localized using Griffonia simplicifolia isolectin B4. Cell proliferation was assessed by bromodeoxyuridine incorporation and cell death by TUNEL-labelling and immunolocalization of the apoptosis markers active caspase 3 and endonuclease G. The density and total number of parenchymal astrocytes in the retina increased between 3 and 9 months of age but decreased markedly between 9 and 12 months. Proliferation of astrocytes was detected at 3 months but virtually ceased beyond that age, whereas the proportion of astrocytes that were TUNEL positive and relative expression of active caspase 3 and endonuclease G increased progressively with aging. In addition, in aged retinas astrocytes exhibited gliosis-like morphology and loss of Pax2 reactivity. A small population of Pax2(+)/GFAP(-) cells was detected in both young adult and aged retinas. The reduction in the availability of astrocytes in aged retinas and other aging-related changes reported here may have a significant impact on the ability of astrocytes to maintain homeostasis and support neuronal function in old age.

Early involvement of synapsin III in neural progenitor cell development in the adult hippocampus

Synapsin III is a synaptic vesicle-associated protein that is expressed in cells of the subgranular layer of the hippocampal dentate gyrus, a brain region known to sustain substantial levels of neurogenesis into adulthood. Here we tested the hypothesis that synapsin III plays a role in adult neurogenesis with synapsin III knockout and wild-type mice. Immunocytochemistry of the adult hippocampal dentate gyrus revealed that synapsin III colocalizes with markers of neural progenitor cell development (nestin, PSA-NCAM, NeuN, and Tuj1) but did not colocalize with markers of mitosis (Ki67 and PCNA). Because neurogenesis consists of a number of stages, the proliferation, survival, and differentiation of neural progenitor cells were systematically quantitated in the hippocampal dentate gyrus of adult synapsin III knockout and wild-type mice. We found a 30% decrease in proliferation and a 55% increase in survival of neural progenitor cells in synapsin III knockout mice. We also observed a 6% increase in the number of neural progenitor cells that differentiated into neurons. No difference in the volume of the dentate gyrus was observed between synapsin III knockout and wild-type mice. Collectively, our results demonstrate a novel role for synapsin III in regulating the proliferation of neural progenitor cells in the adult hippocampal dentate gyrus. These findings suggest a distinct function for this synaptic vesicle protein, in addition to its role in neurotransmission.

Immunohistochemical markers for quantitative studies of neurons and glia in human neocortex

Reproducible visualization of neurons and glia in human brain is essential for quantitative studies of the cellular changes in neurological disease. However, immunohistochemistry in human brain specimens is often compromised because of prolonged fixation. To select cell lineage-specific antibodies for quantitative studies of neurons and the major types of glia, we used 29 different antibodies, different epitope retrieval methods, and different detection systems to stain tissue arrays of formalin-fixed human brain. The screening pointed at CD45/leukocyte common antigen (LCA), CD68(KP1), 2',3' cyclic nucleotide phosphatase (CNPase), glial fibrillary acidic protein (GFAP), HLA-DR, Ki67, neuronal nuclei (NeuN), p25alpha-antigen, and S100beta as candidates for future cell counting purposes, because these markers visualized specific neuronal and glial cell bodies. However, significant negative correlation between staining result and formalin fixation was observed by blinded scoring of staining for CD45/LCA, CNPase, GFAP, and NeuN in brain specimens fixed by immersion and stored up to 10 years in 4% formalin solution at room temperature, independent of donor sex and postmortem interval. In contrast, improved preservation of NeuN and CNPase staining, and full preservation of GFAP and CD45/LCA staining in tissue fixed by perfusion and stored for up to 3 years in 0.1% paraformaldehyde solution at 4C, indicated that immunohistochemistry can be performed in well-preserved biobank material.

Immune cell involvement in dorsal root ganglia and spinal cord after chronic constriction or transection of the rat sciatic nerve

Chronic constriction injury (CCI) of the sciatic nerve in rodents produces mechanical and thermal hyperalgesia and is a common model of neuropathic pain. Here we compare the inflammatory responses in L4/5 dorsal root ganglia (DRGs) and spinal segments after CCI with those after transection and ligation at the same site. Expression of ATF3 after one week implied that 75% of sensory and 100% of motor neurones had been axotomized after CCI. Macrophage invasion of DRGs and microglial and astrocytic activation in the spinal cord were qualitatively similar but quantitatively distinct between the lesions. The macrophage and glial reactions around neurone somata in DRGs and ventral horn were slightly greater after transection than CCI while, in the dorsal horn, microglial activation (using markers OX-42(for CD11b) and ED1(for CD68)) was greater after CCI. In DRGs, macrophages positive for OX-42(CD11b), CD4, MHC II and ED1(CD68) more frequently formed perineuronal rings beneath the glial sheath of ATF3+ medium to large neurone somata after CCI. There were more invading MHC II+ macrophages lacking OX-42(CD11b)/CD4/ED1(CD68) after transection. MHC I was expressed in DRGs and in spinal sciatic territories to a similar extent after both lesions. CD8+ T-lymphocytes aggregated to a greater extent both in DRGs and the dorsal horn after CCI, but in the ventral horn after transection. This occurred mainly by migration, additional T-cells being recruited only after CCI. Some of these were probably CD4+. It appears that inflammation of the peripheral nerve trunk after CCI triggers an adaptive immune response not seen after axotomy.

S100B protein is released from rat neonatal neurons, astrocytes, and microglia by in vitro trauma and anti-S100 increases trauma-induced delayed neuronal injury and negates the protective effect of exogenous S100B on neurons

S100B protein is found in brain, has been used as a marker for brain injury and is neurotrophic. Using a well-characterized in vitro model of brain cell trauma, we have previously shown that strain injury causes S100B release from neonatal rat neuronal plus glial cultures and that exogenous S100B reduces delayed post-traumatic neuronal damage even when given at 6 or 24 h post-trauma. The purpose of the current studies was to measure post-traumatic S100B release by specific brain cell types and to examine the effect of an antibody to S100 on post-traumatic delayed (48 h) neuronal injury and the protective effect of exogenous S100B. Neonatal rat cortical cells grown on a deformable elastic membrane were subjected to a strain (stretch) injury produced by a 50 ms displacement of the membrane. S100B was measured with an ELISA kit. Trauma released S100B from pure cultures of astrocytes, microglia, and neurons. Anti-S100 reduced released S100B to below detectable levels, increased delayed neuronal injury in traumatized cells and negated the protective effect of exogenous S100B on injured cells. Heat denatured anti-S100 did not exacerbate injury. These studies provide further evidence for a protective role for S100B following neuronal trauma.

Serum S100B protein is increased in fasting rats

BACKGROUND

S100B is a calcium-binding protein expressed and secreted by astrocytes; serum and cerebrospinal fluid (CSF) S100B elevation has been proposed as an index of brain damage. However, other tissues are shown to produce this protein and the clinical significance of serum S100B elevation has been discussed.

METHODS

We investigated the levels of serum and CSF S100B in fasting Wistar rats. Animals were divided into two groups, control and fasting for 48 h, and S100B levels in serum and CSF were determined by ELISA. S100B secretion in dissociated epididymal fat cells was investigated in the presence of epinephrine.

RESULTS

We observed a significant >2-fold increase of S100B levels in serum of fasting rats, without changes in its CSF content. Moreover, we demonstrated in vitro epinephrine stimulated S100B release from fat cells.

CONCLUSIONS

Present results reinforce that extracerebral sources of S100B, particularly adipocytes, contribute to its serum levels and support the idea that caution is needed when interpreting serum S100B increase as a clinical marker of brain damage.

Astrocyte end-feet in germinal matrix, cerebral cortex, and white matter in developing infants

Astrocyte end-feet ensheathe blood vessels in the brain and are believed to provide structural integrity to the cerebral vasculature. We sought to determine in developing infants whether the coverage of blood vessels by astrocyte end-feet is decreased in germinal matrix (GM) compared with cerebral cortex and white matter (WM), which may cause fragility of the GM vasculature. Therefore, we evaluated the perivascular coverage by astrocyte end-feet in these areas. We double-labeled the brain sections with astroglial markers [glial fibrillary acidic protein (GFAP), aquaporin-4 (AQP4), and S-100beta] and a vascular marker, laminin. Perivascular coverage by GFAP+ astrocyte end-feet increased consistently as a function of gestational age (GA) in cortex and WM from 19 to 40 wk. Compared with GFAP, AQP4+ astrocyte end-feet developed at an earlier GA, ensheathing about 63% of blood vessels for 23-40 wk in cortex, WM, and GM. Coverage by GFAP+ perivascular end-feet was decreased in GM compared with cortex and WM from 23 to 34 wk. There was no difference in the coverage by AQP4+ end-feet among the three areas in these infants. The expression of AQP4, a water channel molecule, in the astrocyte end-feet was not significantly different between premature and mature infants, suggesting similar risk of brain edema in preterm and term infants in pathologic conditions. More importantly, the lesser degree of GFAP expression in astrocyte end-feet of GM compared with cortex and WM may reflect a cytoskeletal structural difference that contributes to the fragility of GM vasculature and propensity to hemorrhage.

Localization of equilibrative nucleoside transporters in the rat brain

Adenosine is a recognized inhibitory neuromodulator and neuroprotective agent in the central nervous system. It is produced both intra- and extracellularly and transported across the cell membrane. Nucleoside transporters thus have a major impact on the extracellular adenosine levels, and consequently adenosine signalling. We have raised and characterized polyclonal antibodies against both the equilibrative nucleoside transporters 1 and 2, and report for the first time their distribution in rat brain at the cellular level. Double staining studies were performed to assess the localization of the transporters in neural and glial cells. Both transporters were present in practically all neurons. Some astrocytes showed equilibrative nucleoside transporter 1 staining, while equilibrative nucleoside transporter 2 staining on astrocytes was observed only sporadically.

Corticosterone-induced inhibition of gliogenesis in rat hippocampus is counteracted by electroconvulsive seizures

BACKGROUND

Volumetric changes and glial pathology have been reported in the central nervous system (CNS) of patients with depressive disorder, an illness often associated with elevated glucocorticoid levels. Glucocorticoids reduce gliogenesis in the adult rat CNS. Electroconvulsive seizure (ECS)-treatment, an animal model for the antidepressant treatment electroconvulsive therapy, can enhance proliferation of glial cells. This study examined glial cell proliferation in response to ECS in rats whose glucocorticoid levels were elevated to mimic the conditions seen in depression.

METHODS

Rats were injected daily for seven days with either corticosterone or vehicle. ECS- or sham- treatment was given once daily during the first five days. Proliferating cells in the hippocampus were labeled with bromodeoxyuridine and analyzed for co-labeling with the glial cell markers NG2, Ox42, S-100beta and Rip.

RESULTS

ECS counteracted the glucocorticoid-induced inhibition of NG2+, Ox42+ and Rip+ cell proliferation, and the gliogenesis rate was restored to baseline levels. Volumetric changes in rats treated with ECS were detected.

CONCLUSIONS

Our results show that ECS-treatment affects the proliferation of glial cells even in the presence of elevated levels of glucocorticoids. This result adds to an increasing number of studies suggesting that antidepressant treatment can counteract degenerative processes associated with major depression.

Differential cellular distribution of tonicity-induced expression of transcription factor TonEBP in the rat brain following prolonged systemic hypertonicity

In a previous work performed on cerebral cortex and hippocampus we reported that tonicity-responsive enhancer binding protein (TonEBP), originally identified as a transactivator of osmoprotective genes involved in osmoadaptation of renal cells, was induced in neurons only, but to varying levels, following acute systemic hypertonicity. Whether or not this cellular specificity reflected a unique ability of neurons or a differential time course among brain cells for tonicity-induction of TonEBP was investigated throughout the brain in this study by subjecting the animals to prolonged systemic hypertonicity. In normal rats, TonEBP immunolabeling and TonEBP-mRNA in situ hybridization labeling showed a widespread, uneven and parallel distribution. TonEBP was expressed primarily in the cell nuclei of neurons, where it was heterogeneously distributed in a nucleoplasmic and a granular pool. In rats subjected to prolonged systemic hypertonicity, TonEBP labeling increased in the cell nuclei of neurons only. The tonicity-induced expression of TonEBP for a given cell group of neurons was rather uniform but varied greatly among neuronal cell groups and was positively correlated with the average size of the cell nuclei, as determined by quantitative analysis of digitized images. The detailed distribution of tonicity-induced expression of TonEBP is reported throughout the brain. In normal rats, a very minor proportion of non-neuronal cells, identified as a subset of astrocytes and possibly oligodendrocytes, showed faint nuclear immunolabeling, which however did not increase in hypertonic animals. Ependymocytes, capillary endothelial cells, and microglial cells showed no TonEBP labeling, even in hypertonic animals. Altogether our data indicate that neurons, albeit possibly to a varying extent, are the only brain cells able to use TonEBP-mediated processes for adaptation to a systemic hyperosmotic unbalance.

Implication of “Down syndrome cell adhesion molecule” in the hippocampal neurogenesis of ischemic monkeys

Molecular signals regulating adult neurogenesis in primates are largely unknown. Here the authors used differential display to analyze gene expression changes that occur in dentate gyrus of adult monkeys after transient global cerebral ischemia. Among 14 genes upregulated, the authors focused on Down syndrome cell adhesion molecule (DSCAM) known to play crucial role during neuronal development, and characterized its expression pattern at the protein level. In contrast with approximately threefold upregulation of Dscam gene on days 5 and 7, immunoblotting and immunofluorescence analyses using specific antibodies showed a gradual decrease of DSCAM after ischemia until day 9 followed by recovery on day 15. In the control, immunofluorescence reactivity of DSCAM was detected in dentate gyrus granule cells and CA4 neurons but decreased after ischemia, being compatible with the immunoblotting data. However, in the subgranular zone, cerebral ischemia led to a marked increase of DSCAM-positive cells on days 9 and 15. DSCAM upregulation was seen in two cell types: one is immature neurons positive for polysialylated neural cell adhesion molecule or betaIII-tubulin, while another is astrocytes positive for S100beta. Young astrocytes were in intimate contact with newly generated neurons in the subgranular zone. These data suggest implication of DSCAM in the adult neurogenesis of primate hippocampus upregulated after ischemia.

Non-lethal active caspase-3 expression in Bergmann glia of postnatal rat cerebellum

Caspase-3, an apoptotic executor, has been shown in recent years to mediate non-lethal events like cellular proliferation and differentiation, primarily in studies related to non-neural tissue. In central nervous system development, the role of active caspase-3 is still unclear. We provide the first evidence for a potential new role of active (cleaved) caspase-3 in promoting differentiation of Bergmann glia. This study was predicated on the hypothesis that active caspase-3 is important for the differentiation of glia. We addressed the hypothesis through the following specific aims: (1) to establish the expression of active caspase-3 in glia; (2) to determine the developmental phenotype of the active caspase-3-expressing glia; and (3) to confirm that active caspase-3 expression is not mediating an apoptotic event. Through a temporal investigation from postnatal day 8 to 21, we observed that Bergmann glia express active caspase-3 without compromising their survival. Potential apoptotic fate of active caspase-3-positive Bergmann glia were ruled out based on immunohistochemical exclusion of phosphatidylserine exposure (Annexin V), DNA fragmentation (TUNEL), and DNA compaction (TOPRO-3). More than 90% of the active caspase-3-positive cells lacked colabeling for one of the apoptotic markers. Correlative studies using a proliferation marker Ki67 and a differentiation marker brain lipid-binding protein suggest that the expression of active caspase-3 was mostly associated with differentiating rather than proliferating Bergmann glia at all ages. Thus, this study supports the hypothesis that active caspase-3 may be regulating both differentiation of Bergmann glia by allowing the cells to exit the cell cycle and their morphogenesis.

Thalamocortical neuron loss and localized astrocytosis in the Cln3Δex7/8 knock-in mouse model of Batten disease

Juvenile neuronal ceroid lipofuscinosis (JNCL) is the result of mutations in the Cln3 gene. The Cln3 knock-in mouse (Cln3Deltaex7/8) reproduces the most common Cln3 mutation and we have now characterized the CNS of these mice at 12 months of age. With the exception of the thalamus, Cln3Deltaex7/8 homozygotes displayed no significant regional atrophy, but a range of changes in individual laminar thickness that resulted in variable cortical thinning across subfields. Stereological analysis revealed a pronounced loss of neurons within individual laminae of somatosensory cortex of affected mice and the novel finding of a loss of sensory relay thalamic neurons. These affected mice also exhibited profound astrocytic reactions that were most pronounced in the neocortex and thalamus, but diminished in other brain regions. These data provide the first direct evidence for neurodegenerative and reactive changes in the thalamocortical system in JNCL and emphasize the localized nature of these events.

Ciliary neurotrophic factor is expressed in the magnocellular neurosecretory system of the rat in vivo: evidence for injury- and activity-induced upregulation

Although ciliary neurotrophic factor (CNTF) has been shown to promote the survival of magnocellular neurons when applied exogenously to explants of the paraventricular and supraoptic nuclei (SON) in vitro, little is known regarding its expression or regulation in the adult magnocellular neurosecretory system (MNS) following injury in vivo. Therefore, we utilized in situ hybridization and immunocytochemical analysis in conjunction with quantitative optical densitometric analysis to identify the cellular source of CNTF and examine the temporal pattern of its expression, following unilateral transection of the hypothalamo-neurohypophysial tract in the adult rat. In intact rats, CNTF immunoreactivity (CNTF-ir) was predominantly localized within identified astrocytes within the ventral glial limitans subjacent to the SON. Quantitative optical densitometric analysis of CNTF-ir levels in the axotomized SON demonstrated that the proportional area of CNTF-ir was significantly elevated between 3 and 30 days following injury. A significant but more limited increase was also observed in the non-injured contralateral SON. In situ hybridization confirmed the expression and upregulation of CNTF in the axotomized SON. These results demonstrate the expression of CNTF in the adult rodent MNS in vivo and provide evidence that levels of CNTF are upregulated in response to both direct injury, and heightened metabolic activity, within the lesioned and sprouting SON, respectively.

S100B protein is released by in vitro trauma and reduces delayed neuronal injury

S100B protein in brain is produced primarily by astrocytes, has been used as a marker for brain injury and has also been shown to be neurotrophic and neuroprotective. Using a well characterized in vitro model of brain cell trauma, we examined the potential role of exogenous S100B in preventing delayed neuronal injury. Neuronal plus glial cultures were grown on a deformable Silastic membrane and then subjected to strain (stretch) injury produced by a 50 ms displacement of the membrane. We have previously shown that this injury causes an immediate, but transient, nuclear uptake of the fluorescent dye propidium iodide by astrocytes and a 24-48 h delayed uptake by neurons. Strain injury caused immediate release of S100-beta with further release by 24 and 48 h. Adding 10 or 100 nm S100B to injured cultures at 15 s, 6 h or 24 h after injury reduced delayed neuronal injury measured at 48 h. Exogenous S100B was present in the cultures through 48 h. These studies directly demonstrate the release and neuroprotective role of S100B after traumatic injury and that, unlike most receptor antagonists used for the treatment of trauma, S100B is neuroprotective when given at later, more therapeutically relevant time points.

Electroconvulsive seizures induce proliferation of NG2-expressing glial cells in adult rat amygdala

BACKGROUND

Volumetric changes and glial pathology have been reported in the amygdala in patients with major depressive disorder. Here we report an analysis of glial cell proliferation in response to electroconvulsive seizures (ECS), clinically used for the treatment of severe depression.

METHODS

Male Wistar rats were subjected to five ECS-treatments and then injected with bromodeoxyuridine (BrdU) to detect cell proliferation in the amygdala. The animals were transcardially perfused either 12 hours or 3 weeks after the last BrdU injection. Tissue sections were double-stained for BrdU and the cell-type markers NG2, OX-42, RIP, S-100beta, Doublecortin, or NeuN.

RESULTS

Electroconvulsive seizures dramatically increased the proliferation of amygdala cells expressing the oligodendrocyte progenitor marker NG2. Bromodeoxyuridine-labeled NG2-expressing cells were still present after 3 weeks of survival, and a small proportion of the proliferating cells had differentiated into mature oligodendrocytes.

CONCLUSIONS

Major depression has been associated with a reduction of glial cells. Our results show that ECS, an antidepressant treatment, significantly increases the number of NG2+ glial cells and mature oligodendrocytes in the adult rat amygdala.

Exercise increases hippocampal neurogenesis to high levels but does not improve spatial learning in mice bred for increased voluntary wheel running

The hippocampus is important for the acquisition of new memories. It is also one of the few regions in the adult mammalian brain that can generate new nerve cells. The authors tested the hypothesis that voluntary exercise increases neurogenesis and enhances spatial learning in mice selectively bred for high levels of wheel running (S mice). Female S mice and outbred control (C) mice were housed with and without running wheels for 40 days. 5-Bromodeoxyuridine was used to label dividing cells. The Morris water maze was used to measure spatial learning. C runners showed a strong positive correlation between running distance and new cell number, as well as improved learning. In S runners, neurogenesis increased to high levels that reached a plateau, but no improvement in learning occurred. This is the first evidence that neurogenesis can occur without learning enhancement. The authors propose an alternative function of neurogenesis in the control of motor behavior.

Transcription factor tonicity-responsive enhancer-binding protein (tonebp) which transactivates osmoprotective genes is expressed and upregulated following acute systemic hypertonicity in neurons in brain

Tonicity-responsive enhancer-binding protein (TonEBP) was initially identified as a transcription factor involved in adaptation of renal cells to hypertonicity by activation of osmoprotective genes encoding proteins for accumulation of compatible osmolytes. Since brain osmoadaptation is observed in relationship to neurological disorders resulting from pathological osmotic disbalances of blood plasma we have investigated through immunocytochemistry TonEBP expression in cerebral cortex and hippocampus of normal rat and rats submitted to an acute systemic hypertonicity or to a prolonged systemic hypotonicity. TonEBP-expressing cells were identified using double immunofluorescence and appropriate cell type markers. Their relative proportion was determined by quantitative image analysis. In normal rats TonEBP expressed primarily in neurons where it was strictly located in the cell nucleus but heterogeneously distributed into a nucleoplasmic pool and a granular pool. In animals made acutely hypertonic TonEBP labeling increased dramatically exclusively in the nuclei of neurons and reached a maximum within 1 h. In hypertonic animals TonEBP labeling covered the whole cell nucleus of virtually all neurons, appeared finely punctuated but was no more granular. Optical density of the labeling as determined by image analysis correlated linearly with the increased plasma osmolality. In animals made hypotonic for several days no conspicuous decrease of TonEBP labeling was observed. In normal animals a very minor proportion of non-neuronal cells showed a faint TonEBP nuclear labeling. This proportion increased slightly in hypertonic animals. Nevertheless these non-neuronal TonEBP-positive nuclei which belonged to oligodendrocytes and to a small subpopulation of astrocytes remained always very weakly labeled when compared with neuron nuclei. Brain capillary endothelial cells as well as microglial cells showed no TonEBP-labeling even in hypertonic animals. Our data demonstrate that in brain TonEBP is significantly expressed and tonicity-overexpressed in neurons and accordingly suggest that neurons only among brain cells accumulate compatible osmolytes through TonEBP-mediated activation of osmoprotective genes to adapt to acute systemic hypertonicity.

Electroconvulsive seizures induce proliferation of NG2-expressing glial cells in adult rat hippocampus

BACKGROUND

Analysis of postmortem tissue from patients with major depression and bipolar disorder has revealed structural changes in several brain regions. We have shown that electroconvulsive seizure (ECS), used for the treatment of severe depression, induces proliferation of both neuronal and nonneuronal cells in the adult rat hippocampus.

METHODS

Male Wistar rats were subjected to one or several ECS treatments, then injected with bromodeoxyuridine (BrdU) to detect cell proliferation. Animals were perfused either 1 day or 3 weeks following the last BrdU injection. Cells were double stained for BrdU and the cell type markers chondroitin sulfate proteoglycan (NG2), complement 3-receptor OX-42, 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), Ca(+) binding protein S100-beta, or neuron-specific nuclear protein (NeuN).

RESULTS

We identified NG2-expressing cells as a major cell type proliferating in the rat dentate gyrus in response to ECS. A sharp increase in NG2-positive cell proliferation was seen 2 days after ECS, and a large number of NG2-expressing cells persisted at 3 weeks.

CONCLUSIONS

Our results show that antidepressant treatment can induce a strong proliferation of glial progenitor cells in the adult rat hippocampus. We propose that this may counteract degenerative changes found in depression and be an important neurobiological event underlying the clinical effect of electroconvulsive seizures.

Roles of the mammalian subventricular zone in brain development

There has been enormous progress in uncovering the contributions of the subventricular zone (SVZ) to the developing brain. Here, we review the roles of four anatomically defined embryologic divisions of the SVZ of the mammalian brain: the lateral ganglionic eminence (LGE), the medial ganglionic eminence (MGE), the caudal ganglionic eminence (CGE), and the fetal neocortical SVZ (SVZn), as well as the roles of the two major anatomically defined regions of the postnatal SVZ, the anterior SVZ (SVZa) and the dorsolateral SVZ (SVZdl). We describe the types of cells within each subdivision of the SVZ, the types of brain cells that they generate during embryonic, fetal, and perinatal development, and when known the mechanisms that regulate their differentiation. This review provides a critical analysis of the literature, from which current and future studies on the SVZ can be formulated and evaluated.

Growth hormone and aging

In elderly people, vascular alterations and degenerative alterations of the Central Nervous System (CNS) are two of the most common reasons for illness and death. Lipid pattern modifications and menopause in women are some of the causes for the appearance of these alterations. Vascular endothelium is in part responsible for vascular homeostasis, through the production of several vasoactive factors. Growth hormone (GH) exerts effects on the CNS and on the vascular endothelium, since GH deficient subjects exhibit endothelium-dependent alterations, which recover under substitutive GH treatment. Growth hormone has important actions on lipid metabolism that also play a role on vascular and endothelial function. Moreover, cardiac function improves when GH is associated to angiotensin II receptor blockers. Elderly people exhibit a physiological GH deficiency that could affect their vascular and cerebral functions. A study was carried out using old Wistar rats to clarify the effects of GH on the vessels under chronic "in vivo" conditions. The response to various vasoactive substances in aortic rings has been evaluated. An increase in the aortic media thickness was seen in old rats, which showed also a reduction in the vasodilator response to isoprenaline as compared to young animals. GH treatment partially restored the vasodilator response and reduced media thickness. Neuronal population was reduced in the hypocampus of old rats as compared to young ones and GH treatment was able to significantly enhance the number. Neurotransmitters were measured in several cerebral areas to establish differences between young and old GH-treated or untreated animals. Glutamine, Arginine and Aspartate were reduced in old animals whereas Citruline was increased. GH treatment restored in all cases the levels corresponding to young rats.