Telomerase expression in the glial scar of rats with spinal cord injury

A rat model of spinal cord injury was established using the weight drop method. A cavity formed 14 days following spinal cord injury, and compact scar tissue formed by 56 days. Enzyme-linked immunosorbent assay and polymerase chain reaction enzyme-linked immunosorbent assay results demonstrated that glial fibrillary acidic protein and telomerase expression increased gradually after injury, peaked at 28 days, and then gradually decreased. Spearman rank correlation showed a positive correlation between glial fibrillary acidic protein expression and telomerase expression in the glial scar. These results suggest that telomerase promotes glial scar formation.     

Spinal cord injury-induced lesional expression of the repulsive guidance molecule (RGM)

The repulsive guidance molecule (RGM) is involved in the formation of the central nervous system (CNS) during development by modulating guidance of growing axons. However, a role of RGM in CNS injury remains to be established. We studied the expression of RGM in the spinal cord of rats with spinal cord injury (SCI). After SCI, RGM+ cells accumulated in lesions and peri-lesional areas. During the first days after SCI, RGM expression was confined to neurons, ballooned neurite fibers/retraction bulbs, smooth muscle/endothelial cells, and to leucocytes infiltrating the lesion. Lesional RGM expression was frequently confined to hypertrophic beta-APP+ and RhoA+ neurites/retraction bulbs. With maturation of the lesion, we observed RGM expression by components of the developing scar tissue (cicatrix), such as fibroblastoid cells, reactive astrocytes and in addition a pronounced extracellular RGM deposition resembling neo-laminae. Frequent RGM+, RhoA+ coexpression by lesional retraction bulbs represent first preliminary evidence of RGM to exert growth inhibitory effects by the second messenger system RhoA. To date, RGM is one of the most potent axonal growth inhibitors identified and present in axonal growth impediments (i) oligodendrocytes; (ii) the plexus choroideus and (iii) components of the developing scar.     

Examining the properties and therapeutic potential of glial restricted precursors in spinal cord injury

In the aftermath of spinal cord injury, glial restricted precursors (GRPs) and immature astrocytes offer the potential to modulate the inlfammatory environment of the injured spinal cord and promote host axon re-generation. Nevertheless clinical application of cellular therapy for the repair of spinal cord injury requires strict quality-assured protocols for large-scale production and preservation that necessitates long-term in vitro expansion. Importantly, such processes have the potential to alter the phenotypic and functional properties and thus therapeutic potential of these cells. Furthermore, clinical use of cellular therapies may be limited by the inlfammatory microenvironment of the injured spinal cord, altering the phenotypic and functional properties of grafted cells. This report simulates the process of large-scale GRP production and demonstrates the permissive properties of GRP following long-termin vitro culture. Furthermore, we de-ifned the phenotypic and functional properties of GRP in the presence of inlfammatory factors, and call attention to the importance of the microenvironment of grafted cells, underscoring the importance of modulating the environment of the injured spinal cord.     

Spinal cord injury induces expression of RGS7 in microglia/macrophages in rats

RGS proteins regulate G protein-mediated signalling pathways through direct interaction with the Galpha subunits and facilitation of GTP hydrolysis. An RGS subfamily consisting of RGS 6, 7, 9, and 11 also interacts with the G protein beta subunit Gbeta5 via a characteristic Ggamma-like domain. Thus far, these complexes were found only in neurons, with RGS7 being the most widely distributed in the brain. Here we confirm the expression of RGS7 in spinal neurons and show as a novel finding that following an experimental spinal cord injury in rats, expression of RGS7 is induced in a subpopulation of other cells. Immunofluorescent confocal microscopy using a series of cell specific antibodies identified these RGS7 positive cells as activated microglia and/or invading peripheral macrophages. To rule out interference from the adjacent neurons and confirm the presence of RGS7-Gbeta5 complex in inflammatory cells, we performed immunocytochemistry, RT-PCR, Western blot, and immunoprecipitation using microglial (BV2) and peripheral macrophage (RAW) cell lines. Expression of RGS7 mRNA and protein are nearly undetectable in non-stimulated BV2 and RAW cells, but remarkably increased after stimulation with LPS or TNF-alpha In addition, RGS7-positive cells were also found in the perinodular rim in the rat spleen. Our findings show that RGS7-Gbeta5 complex is expressed in immunocompetent cells such as resident microglia and peripheral macrophages following spinal cord injury. This expression might contribute to the post-traumatic inflammatory responses in the central nervous system.     

Differential expression of sPLA2 following spinal cord injury and a functional role for sPLA2‐IIA in mediating oligodendrocyte death

After the initial mechanical insult of spinal cord injury (SCI), secondary mediators propagate a massive loss of oligodendrocytes. We previously showed that following SCI both the total phospholipase activity and cytosolic PLA₂‐IVα protein expression increased. However, the expression of secreted isoforms of PLA₂ (sPLA₂) and their possible roles in oligodendrocyte death following SCI remained unclear. Here we report that mRNAs extracted 15 min, 4 h, 1 day, or 1 month after cervical SCI show marked upregulation of sPLA₂‐IIA and IIE at 4 h after injury. In contrast, SCI induced down regulation of sPLA₂‐X, and no change in sPLA₂‐IB, IIC, V, and XIIA expression. At the lesion site, sPLA₂‐IIA and IIE expression were localized to oligodendrocytes. Recombinant human sPLA₂‐IIA (0.01, 0.1, or 2 μM) induced a dose‐dependent cytotoxicity in differentiated adult oligodendrocyte precursor cells but not primary astrocytes or Schwann cells in vitro. Most importantly, pretreatment with S3319, a sPLA₂‐IIA inhibitor, before a 30 min H₂O₂ injury (1 or 10 mM) significantly reduced oligodendrocyte cell death at 48 h. Similarly, pretreatment with S3319 before injury with IL‐1β and TNFα prevented cell death and loss of oligodendrocyte processes at 72 h. Collectively, these findings suggest that sPLA₂‐IIA and IIE are increased following SCI, that increased sPLA₂‐IIA can be cytotoxic to oligodendrocytes, and that in vitro blockade of sPLA₂ can create sparing of oligodendrocytes in two distinct injury models. Therefore, sPLA₂‐IIA may be an important mediator of oligodendrocyte death and a novel target for therapeutic intervention following SCI. © 2009 Wiley‐Liss, Inc.     

Sphingosine 1-phosphate induces the production of glial cell line-derived neurotrophic factor and cellular proliferation in astrocytes

Sphingosine 1-phosphate (S1P) is a platelet-derived bioactive sphingolipid that evokes a variety of biological responses. To understand the role of S1P in the central nervous system, we have examined the effect of S1P on the production of glial cell line-derived neurotrophic factor (GDNF) and growth regulation of cortical astrocytes from rat embryo. Moreover, we examined the possibility that the expression of GDNF is regulated differently in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) than in those from Wistar kyoto rats (WKY). The mRNA expression was quantitated by RT-PCR based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay. S1P induced the expression of GDNF mRNA and the production of GDNF protein in a dose-dependent manner in WKY astrocytes. Moreover, S1P increased cell numbers and induced the proliferation of astrocytes. In addition, the level of mRNA expression and protein production of GDNF was significantly lower in SHRSP than WKY astrocytes following exposure to S1P. These findings revealed that S1P augments GDNF protein production and cellular growth in astrocytes. Also, our results indicate that production in SHRSP astrocytes was attenuated in response to S1P compared with that observed in WKY. We conclude that S1P specifically triggers a cascade of events that regulate the production of GDNF and cell growth in astrocytes. Our results also suggest that the reduced expression of GDNF caused by S1P is a factor in the stroke proneness of SHRSP.     

A new in vitro model of the glial scar inhibits axon growth

Astrocytes respond to central nervous system (CNS) injury with reactive astrogliosis and participate in the formation of the glial scar, an inhibitory barrier for axonal regeneration. Little is known about the injury-induced mechanisms underlying astrocyte reactivity and subsequent development of an axon-inhibitory scar. We combined two key aspects of CNS injury, mechanical trauma and co-culture with meningeal cells, to produce an in vitro model of the scar from cultures of highly differentiated astrocytes. Our model displayed widespread morphological signs of astrocyte reactivity, increases in expression of glial fibrillary acidic protein (GFAP), and accumulation of GFAP in astrocytic processes. Expression levels of scar-associated markers, phosphacan, neurocan, and tenascins, were also increased. Importantly, neurite growth from various CNS neuronal populations was significantly reduced when neurons were seeded on the scar-like cultures, compared with growth on cultures of mature astrocytes. Quantification of neurite growth parameters on the scar model demonstrated significant reductions in neuronal adhesion and neurite lengths. Interestingly, neurite outgrowth of postnatal neurons was reduced to a greater extent than that of embryonic neurons, and outgrowth inhibition varied among neuronal populations. Scar-like reactive sites and neurite-inhibitory patches were found throughout these cultures, creating a patchwork of growth-inhibitory areas mimicking a CNS injury site. Thus, our model showed relevant aspects of scar formation and produced widespread inhibition of axonal regeneration; it should be useful both for examining mechanisms underlying scar formation and to assess various treatments for their potential to improve regeneration after CNS injury. (c) 2008 Wiley-Liss, Inc.     

Evidence that Sema3A and Sema3F regulate the migration of GABAergic neurons in the developing neocortex

The ganglionic eminence (GE) supplies neurons containing gamma-aminobutyric acid (GABA) to the pallium of the telencephalon. We investigated the molecular guidance mechanisms of GE cell migration in the neocortex and found neuropilin-1 (Npn-1) or neuropilin-2 (Npn-2) on the GE cells. Ectopic Sema3A or -3F expression by COS1 cell clusters placed on embryo neocortical slices reduced the cell migration but did not block it completely. However, the cell migration was almost completely blocked by COS1 cell clusters expressing both Sema3A and -3F. The direction of cell migration could be reversed by placing Sema3A- and -3F-coexpressing COS1 cell clusters at the distal cut end of the neocortical slices. Further slice experiments revealed that migration of half of the GE cells in the neocortex was regulated by Sema3A and that migration of the other half of the GE cells in the neocortex was regulated by Sema3F. When the cells responding to Sema3A were diverted by ectopic Sema3A expression in vivo, Dlx2-positive cells were found predominantly in the lower intermediate zone (IZ). When the cells responding to Sema3F were diverted by ectopic Sema3F expression in vivo, Dlx2-positive cells were found predominantly in the upper IZ. It was speculated that the semaphorin-neuropilin interactions distribute the GABAergic GE cells evenly in the neocortex as well as guide the GE cells from the GE to the neocortex. The Sema3A expression site under the subplate extended dorsally as the embryo developed. The Sema3A expression seemed to block the Npn-1-positive GE cells in the neocortex from entering the cortical plate (CP) and guide them to the dorsal cortex and the hippocampus. Sema3F expression in the CP continued through the embryonic stages. The expression seemed to block Npn-2-positive GE cells in the neocortex from entering the CP and make them migrate into the lower IZ. Finally, the semaphorin-neuropilin interactions sorted GABAergic inteneurons into the CP and white matter neurons into the IZ.     

Binding and complementary expression patterns of semaphorin 3E and plexin D1 in the mature neocortices of mice and monkeys

Although axon guidance molecules play critical roles in neural circuit formation during development, their roles in the adult circuit are not well understood. In this study we examined the expression patterns of Semaphorin 3E (Sema3E), a member of the semaphorin family, in the mature neocortices of monkeys and mice by in situ hybridization (ISH). We found that Sema3E mRNA is highly specific to layer VI throughout the macaque monkey neocortex. We further examined the ratio of Sema3E+ cells among the layer VI excitatory neurons in areas M1, S1, TE, and V1 by fluorescence double ISH, using the vesicular glutamate transporter 1 (VGluT1) gene as a specific marker for excitatory neurons. Among these areas, 34-63% of the VGluT1+ neurons expressed Sema3E mRNA. In the mouse cortex, two significant differences were observed in the pattern of Sema3E mRNA distribution. 1) Sema3E mRNA was expressed in layer Vb, in addition to layer VI in mice. 2) A subset of GABAergic interneurons expressed Sema3E mRNA in mice. By an in vitro binding experiment, we provide evidence that Plexin D1 is the specific receptor for Sema3E. Plexin D1 mRNA was preferentially expressed in layers II-V in both monkey and mouse cortices. The detailed lamina analysis by double ISH, however, revealed that Plexin D1 mRNA is expressed in layers II-Va, but not in layer Vb in the mouse cortex. Thus, the Plexin D1 and Sema3E mRNAs exhibit conserved complementary lamina patterns in mice and monkeys, despite the species differences in the pattern of each gene.     

Neuronal expression of Nogo-A mRNA and protein during neurite outgrowth in the developing rat olfactory system

The major impediments to axonal regeneration in the central nervous system are growth-inhibitory proteins present in the myelin sheath, and Nogo-A is one of the most potent inhibitors synthesized by oligodendrocytes. However, neuronal expression of Nogo-A during development suggests that it may have an additional role. The spatio-temporal regulation of both Nogo-A mRNA and protein expression was examined by in situ hybridization and immunohistochemistry in the developing rat olfactory system. During embryonic and postnatal development (from E13 to P6), Nogo-A mRNA and protein were strongly expressed by differentiating neurons in the olfactory epithelium and in the olfactory bulb. From the second postnatal week, a progressive down-regulation of both Nogo-A mRNA and protein occurred, such that only a weak expression persisted in the adult olfactory system. Using double-immunostainings in the adult olfactory epithelium, we determined that Nogo-A was preferentially expressed by immature olfactory receptor neurons extending axonal processes toward the olfactory bulb. At all developmental stages, Nogo-A protein was preferentially targeted in olfactory axons emerging from the olfactory epithelium. Using an in vitro model of olfactory axon growth, we demonstrated that, in addition to its presence along the entire axon length, Nogo-A accumulated in axonal growth cone and at axonal branching points, with a distribution similar to that of microtubule-associated proteins. Moreover, Nogo-A was transiently expressed in dendritic processes in the postnatal olfactory bulb. Together, our data suggest that, in non-pathological conditions, Nogo-A may be involved in the processes of axonal growth and dendritic modeling through the regulation of microtubule dynamics.     

Interleukin 15 expression in the CNS: blockade of its activity prevents glial activation after an inflammatory injury

Although reactive glia formation after neuronal degeneration or traumatic damage is one of the hallmarks of central nervous system (CNS) injury, we have little information on the signals that direct activation of resting glia. IL-15, a pro-inflammatory cytokine involved in regulating the response of T and B cells, may be also key for the regulation of early inflammatory events in the nervous system. IL-15 was expressed in the CNS, most abundantly in cerebellum and hippocampus, mainly in astrocytes and in some projection neurons. Using a rodent model of acute inflammatory injury [lipopolysaccharide (LPS) injection], we found enhanced expression of IL-15 in both reactive astroglia and microglia, soon after CNS injury. Blockade of IL-15 activity with an antibody to the cytokine, reversed activation of both glial types, suggesting that IL-15 has a major role in the generation of gliotic tissue and in the regulation of neuroimmune responses. Because IL-15 appears to modulate the inflammatory environment acutely generated after CNS injury, regulating IL-15 expression seems a clear antiinflammatory therapy to improve the outcome of neurodegenerative diseases and CNS trauma.     

Hyperactive glial cells contribute to axonal pathologies in the spinal cord of Npc1 mutant mice

Niemann‐Pick disease type C1 (NPC1) is a neurodegenerative disease with various progressive pathological features, for example, neuronal loss, dysmyelination, abnormal axon swelling, and gliosis, in the brain. Pathological activation of p38‐mitogen‐activated protein kinase (MAPK) results in hyperphosphorylation of tau protein, which contributes to the development of neurodegenerative diseases. In this study, axonal varicosities or spheroids and presynaptic aggregates in the spinal cord of the Npc1 mutant mice were found from postnatal day (P) 35 onwards, as indicated by the increased hyperphosphorylated neurofilament and synaptophysin immunoreactivity as well as the findings from electron microscopy. However, activities of astrocytes and microglia in the Npc1 mutant spinal cord were progressively increased earlier from P10 onwards, accompanied by increased expression of interleukin‐1β and apolipoprotein E, as well as up‐regulated p38‐MAPK activity and enhanced phosphorylated tau protein, but not cyclin‐dependent kinase 5/p35 complex and glycogen synthase kinase‐3β. Taken together, our data suggest that the axonal pathologies in the Npc1 mutant spinal cord are strongly correlated with the increase of activated glial cells, which produce IL‐1β and ApoE, resulting in the activation of p38‐MAPK signaling pathway and enhanced phosphorylated tau protein. GLIA 2014;62:1024–1040     

Distribution and differentiation of A2B5+ glial precursors in the developing rat spinal cord

In many regions of the rat central nervous system, oligodendrocytes develop from migratory A2B5⁺ precursor cells. In the rat spinal cord, during early embryonic development the capacity for oligodendrogenesis appears to be restricted to ventral regions of the spinal cord, while cultures of postnatal rat spinal cord contain a distinct population of A2B5⁺ astrocyte precursors. To determine if, as in other regions of the CNS, spinal cord A2B5⁺ cells give rise directly to oligodendrocytes and astrocytes, the initial distribution, and subsequent dispersion, proliferation, and differentiation of spinal cord A2B5⁺ cells have been examined in both explant and dissociated cell cultures. Spinal cord oligodendrocytes develop from A2B5⁺ cells. At E14, A2B5⁺ cells are restricted to ventral regions of the spinal cord and as development proceeds they become more uniformly distributed throughout the spinal cord. In explant cultures, greater than 95% of the explants that contain oligodendrocytes also contain A2B5⁺ cells and a proportion of mature oligodendrocytes retain detectable A2B5 immunoreactivity briefly on their surface. The maturation of spinal cord oligodendrocyte precursors occurs in a number of distinct stages characterized by the expression of O4 immunoreactivity, which first appears at E16, and GC immunoreactivity, which first appears at E18. As spinal cord oligodendrocyte precursors acquire O4 immunoreactivity they appear to lose the ability to proliferate in response to PDGF but retain the ability to proliferate in response to bFGF, suggesting that the control of proliferation of oligodendrocyte precursors is, in part, dependent on their maturational state. In the presence of high serum, spinal cord A2B5⁺ cells fail to develop in isolated E14 dorsal spinal cord cultures, while in ventral cultures they subsequently differentiate into A2B5⁺ astrocytes suggesting that A2B5⁺ astrocyte precursors are also initially ventrally located. Unlike oligodendrocyte differentiation, however, the differentiation of spinal cord A2B5⁺ cells into astrocytes is delayed in early embryonic-derived cultures compared to those from older animals. These observations suggest that local influences may regulate the timing of spinal cord A2B5⁺ astrocyte development, but not spinal cord oligodendrocyte development. © 1994 Wiley-Liss, Inc.     

Extracellular ATP induces graded reactive response of astrocytes and strengthens their antioxidative defense in vitro

It is widely accepted that adenosine triphosphate (ATP) acts as a universal danger‐associated molecular pattern with several known mechanisms for immune cell activation. In the central nervous system, ATP activates microglia and astrocytes and induces a neuroinflammatory response. The aim of the present study was to describe responses of isolated astrocytes to increasing concentrations of ATP (5 µM to 1 mM), which were intended to mimic graded intensity of the extracellular stimulus. The results show that ATP induces graded activation response of astrocytes in terms of the cell proliferation, stellation, shape remodeling, and underlying actin and GFAP filament rearrangement, although the changes occurred without an apparent increase in GFAP and actin protein expression. On the other hand, ATP in the range of applied concentrations did not evoke IL‐1β release from cultured astrocytes, nor did it modify the release from LPS and LPS+IFN‐γ–primed astrocytes. ATP did not promote astrocyte migration in the wound‐healing assay, nor did it increase production of reactive oxygen and nitrogen species and lipid peroxidation. Instead, ATP strengthened the antioxidative defense of astrocytes by inducing Cu/ZnSOD and MnSOD activities and by increasing their glutathione content. Our current results suggest that although ATP triggers several attributes of activated astrocytic phenotype with a magnitude that increases with the concentration, it is not sufficient to induce full‐blown reactive phenotype of astrocytes in vitro. © 2016 Wiley Periodicals, Inc.     

Nerve injury proximal or distal to the DRG induces similar spinal glial activation and selective cytokine expression but differential behavioral responses to pharmacologic treatment

The specific mechanisms by which nervous system injury becomes a chronic pain state remain undetermined. Historically, it has been believed that injuries proximal or distal to the dorsal root ganglion (DRG) produce distinct pathologies that manifest in different severity of symptoms. This study investigated the role of injury site relative to the DRG in (1) eliciting behavioral responses, (2) inducing spinal neuroimmune activation, and (3) responding to pharmacologic interventions. Rats received either an L5 spinal nerve transection distal to the DRG or an L5 nerve root injury proximal to the DRG. Comparative studies assessed behavioral nociceptive responses, spinal cytokine mRNA and protein expression, and glial activation after injury. In separate studies, intrathecal pharmacologic interventions by using selective cytokine antagonists (interleukin-1 [IL-1] receptor antagonist and soluble tumor necrosis factor [TNF] receptor) and a global immunosuppressant (leflunomide) were performed to determine their relative effectiveness in these injury paradigms. Behavioral responses assessed by mechanical allodynia and thermal hyperalgesia were almost identical in the two models of persistent pain, suggesting that behavioral testing may not be a sensitive measure of injury. Spinal IL-1beta, IL-6, IL-10, and TNF mRNA and IL-6 protein were significantly elevated in both injuries. The overall magnitude of expression and temporal patterns were similar in both models of injury. The degree of microglial and astrocytic activation in the L5 spinal cord was also similar for both injuries. In contrast, the pharmacologic treatments were more effective in alleviating mechanical allodynia for peripheral nerve injury than nerve root injury, suggesting that nerve root injury elicits a more robust, centrally mediated response than peripheral nerve injury. Overall, these data implicate alternate nociceptive mechanisms in these anatomically different injuries that are not distinguished by behavioral testing or the neuroimmune markers used in this study.     

Neuronal and glial localization of the cannabinoid-1 receptor in the superficial spinal dorsal horn of the rodent spinal cord

A long line of experimental evidence indicates that endogenous cannabinoid mechanisms play important roles in nociceptive information processing in various areas of the nervous system including the spinal cord. Although it is extensively documented that the cannabinoid‐1 receptor (CB₁‐R) is strongly expressed in the superficial spinal dorsal horn, its cellular distribution is poorly defined, hampering our interpretation of the effect of cannabinoids on pain processing spinal neural circuits. Thus, we investigated the cellular distribution of CB₁‐Rs in laminae I and II of the rodent spinal dorsal horn with immunocytochemical methods. Axonal varicosities revealed a strong immunoreactivity for CB₁‐R, but no CB₁‐R expression was observed on dendrites and perikarya of neurons. Investigating the co‐localization of CB₁‐R with markers of peptidergic and non‐peptidergic primary afferents, and axon terminals of putative glutamatergic and GABAergic spinal neurons we found that nearly half of the peptidergic (immunoreactive for calcitonin gene‐related peptide) and more than 20% of the non‐peptidergic (binding isolectin B4) nociceptive primary afferents, more than one‐third and approximately 20% of the axon terminals of putative glutamatergic (immunoreactive for vesicular glutamate transporter 2) and GABAergic (immunoreactive for glutamic acid decarboxylase; GAD65 and/or GAD67) spinal interneurons, respectively, were positively stained for CB₁‐R. In addition to axon terminals, almost half of the astrocytic (immunoreactive for glial fibrillary acidic protein) and nearly 80% of microglial (immunoreactive for CD11b) profiles were also immunolabeled for CB₁‐R. The findings suggest that the activity‐dependent release of endogenous cannabinoids activates a complex signaling mechanism in pain processing spinal neural circuits into which both neurons and glial cells may contribute.     

Origin,maturation, and astroglial transformation of secondary radial glial cells in the developing dentate gyrus

The dentate gyrus is a brain region where neurons are continuously born throughout life. In the adult, the role of its radial glia in neurogenesis has attracted much attention over the past years; however, little is known about the generation and differentiation of glial cells and their relationship to radial glia during the ontogenetic development of this brain structure. Here, we combine immunohistochemical phenotyping using antibodies against glial marker proteins with BrdU birthdating to characterize the development of the secondary radial glial scaffold in the dentate gyrus and its potential to differentiate into astrocytes. We demonstrate that the expression of brain lipid‐binding protein, GLAST, and glial fibrillary acidic protein (GFAP) characterizes immature differentiating cells confined to an astrocytic fate in the early postnatal dentate gyrus. On the basis of our studies, we propose a model where immature astrocytes migrate radially through the granule cell layer to adopt their final positions in the molecular layer of the dentate gyrus. Time‐lapse imaging of acute hippocampal slices from hGFAP‐eGFP transgenic mice provides direct evidence for such a migration mode of differentiating astroglial cells in the developing dentate gyrus. © 2010 Wiley‐Liss, Inc.