Differentiation of radial glia-like cells from embryonic stem cells

Radial glial cells play important roles in neural development. They provide support and guidance for neuronal migration and give rise to neurons and glia. In vitro, neurons, astrocytes, and oligodendrocytes can be generated from neural and embryonic stem cells, but the generation of radial glial cells from these stem cells has not yet been reported. Since the differentiation of radial glial cells is indispensable during brain development, we hypothesize that stem cells also generate radial glial cells during in vitro neural differentiation. To test this hypothesis, we utilized five different clones of mouse embryonic (ES) and embryonal carcinoma (EC) stem cell lines to investigate the differentiation of radial glial cells during in vitro neural differentiation. Here, we demonstrate that radial glia-like cells can be generated from ES/EC cell lines. These ES/EC cell-derived radial glia-like cells are similar in morphology to radial glial cells in vivo, i.e., they are bipolar with an unbranched long process and a short process. They also express several cytoskeletal markers, such as nestin, RC2, and/or GFAP, that are characteristics of radial glial cells in vivo. The processes of these in vitro generated radial glia-like cells are organized into parallel arrays that resemble the radial glial scaffolds in neocortical development. Since radial glia-like cells were observed in all five clones of ES/EC cells tested, we suggest that the differentiation of radial glial cells may be a common pathway during in vitro neural differentiation of ES cells. This novel in vitro model system should facilitate the investigation of regulation of radial glial cell differentiation and its biological function.     

Constructing Circuits: Neurogenesis and Migration in the Developing Neocortex

Summary:  Our knowledge of the proliferation, migration, and differentiation of neurons has changed dramatically over the last 10 years. Whereas traditionally it was thought that glial and neuronal cells were separate cell lines with different lineages, we now know that this is not true. Radial glia are a type of neural stem cell that generate excitatory pyramidal neurons directly through asymmetric cell division in the ventricular zone (VZ) of the telencephalon and indirectly through the symmetric division of daughter intermediate precursor cells that divide in the subventricular zone (SVZ). Moreover, pyramidal neurons, once thought to migrate only along radial guide fibers to the developing layers of the cortex, have been shown to proceed through four distinct stages of migration during which they change shape, direction, and speed. Gamma-aminobutyric acid (GABAergic) inhibitory interneurons, on the other hand, are generated not in the cortex, but in the medial ganglionic eminence and migrate tangentially to their final cortical destinations. Evidence suggests that GABA activation may play a role in coordinating the generation and migration of both pyramidal and interneuron populations. At the end of neurogenesis, radial glial cells translocate to the cortex and transform into astrocytes. Although they do not actively divide in the adult brain, astrocytes may retain the potential to generate new neurons. These new findings have increased our understanding of the mechanisms underlying certain developmental disorders and, in doing so, reveal potentially useful modes of therapeutic intervention.     

Simple method for the culture of glial cells from embryonic rat brain: implications for regional heterogeneity and the radial glial lineage

A simple method is described for the production of glial cell cultures from specific regions of the day 13-15 embryonic rat brainstem and midbrain based on differential cell attachment to a relatively nonadhesive substrate, which inhibits the growth of neurons. Regional differences in the ability of specific populations of brainstem and midbrain cells to attach and spread on the substrate suggest that embryonic glial populations may differ in their cell surface properties even when they derive from the same general area of the developing brain. Based on observations of the spatiotemporal distribution of radial-like glial cells and astrocytes with time in vitro, we suggest that this culture system may prove useful for investigation of the radial glial lineage.     

Balance between neurogenesis and gliogenesis in the adult hippocampus: role for reelin

The extracellular matrix protein reelin is essential for the proper radial migration of cortical neurons. In reeler mice lacking reelin, there is a malformation of the radial glial scaffold required for granule cell migration. Immunostaining for glial fibrillary acidic protein (GFAP) reveals abundant radial glial cells with long fibers traversing the granular layer in the wild type, but almost exclusively astrocytes in the reeler mutant. With the concept that radial glial cells are precursors of neurons, we hypothesized that the balance between neurogenesis and gliogenesis is altered in the reeler mutant. To this end, adult reeler mutants and their wild-type littermates were injected with bromodeoxyuridine (BrdU), a marker of newly generated cells. When compared to wild-type animals, we found a reduction in the number of BrdU-labeled cells in the adult reeler dentate gyrus. Moreover, whereas there was a dramatic decrease in the number of newly generated granule cells identified by double labeling for BrdU and NeuN, the number of BrdU-labeled, GFAP-positive astrocytes had increased. Decreased neurogenesis in the adult reeler dentate gyrus was confirmed by immunostaining for doublecortin, a marker of newly generated neurons. These results indicate that adult neurogenesis is altered in the reeler dentate gyrus and that newly generated cells preferentially differentiate into astrocytes.     

The non-pyramidal cells in layer III of cat primary auditory cortex (AI)

The form and location of non-pyramidal neurons in layer III of the primary auditory cortex (AI) of adult cats is described in Golgi, Nissl, and other material. The cells were compared to the profiles of retrogradely labeled, commissurally interconnected cells. A principal finding is that certain non-pyramidal and pyramidal cells project interhemispherically to AI; a second conclusion is that the retrogradely labeled commissural cells form small clusters or narrow strips separated by unlabeled patches even after massive injections in the opposite AI. The non-pyramidal cells of origin have not yet been conclusively identified, but they must include one (or more) of the following six types of cells observed in Golgi-impregnated material: tufted or bitufted cells with a radially elongated dendritic arbor; sparsely spinous stellate neurons with thin, smooth dendrites and vertically disposed axonal branches; small stellate cells with varicose dendrites, a restricted dendritic field, and a profusely branched local axon; bipolar neurons with long, thin dendrites; medium-sized multipolar cells with radiating, sparsely branched dendrites; and small stellate neurons with smooth dendrites and a tiny dendritic field. These non-pyramidal cells are found throughout layer III but are more numerous in the upper part, layer IIIa, where they mingle with the small pyramidal neurons. As a rule the axonal branches of non-pyramidal cells are more numerous than those arising from layer III pyramidal neurons, and although they have many axonal collaterals, most project locally and vertically in narrow radial strips. In contrast, pyramidal cell axons have ascending and descending components which invade large, lateral territories in many cortical layers. Layer III non-pyramidal neurons are similar to those in layer IV in certain respects, although their dendritic fields are more spherical and less tufted than those of layer IV cells, and their axons have more local, limited targets. These axons appear to contribute but little to the conspicuous, lateral fiber striae in layer III. The primary intrinsic targets of non-pyramidal cell axons appear to be the apical dendrites of medium-sized and large layer III pyramidal cells, and recurrent branches to the parent cell; their fine, distal branches fortify the vertical plexus in layer III, and certain axons may descend into layer IV. Since layer III in AI receives both commissural and thalamic input, it is possible that these parallel, afferent channels are to some degree segregated, and to some degree convergent, onto particular types of cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

The Specification of Neuronal Fate: A Common Precursor for Neurotransmitter Subtypes in the Rat Cerebral Cortex In Vitro

Neurotransmitter choice is a crucial step in neural development. In the cerebral cortex, pyramidal neurons use the excitatory neurotransmitter glutamate, whereas non-pyramidal cells use the inhibitory neurotransmitter GABA. We are interested in how these two neuronal types are generated. We labelled precursor cells from embryonic rat cerebral cortex with a retroviral vector in dissociated cell cultures, and examined the neurotransmitter phenotype of their progeny immunohistochemically after 2 weeks in vitro. We discovered, first, that precursor cells in culture generate glutamatergic and GABAergic neurons in proportions similar to those in vivo. Second, we found that neuronal precursor cells gave rise to both GABAergic and glutamatergic neurons. These results suggest that neuronal precursor cells in the cerebral cortex have the potential to generate both neuronal subtypes. Moreover, these data are consistent with a stochastic model of neurotransmitter specification.     

Immunoperoxidase localization of glial fibrillary acidic protein in radial glial cells and astrocytes of the developing rhesus monkey brain

Peroxidase-antiperoxidase (PAP) immunohistochemical staining, utilizing a specific antibody to the glial fibrillary acidic protein (GFA), was employed to analyze gliogenesis in the central nervous system of rhesus monkeys ranging in age from embryonic day 38(E38) to birth (E165) and through the second postnatal month. All major subdivisions of the brain contain glial cells, recognized by the presence of dark brown horseradish peroxidase (HRP) reaction product. Neuronal elements are not stained with this immunocytochemical technique. The first class of glial cell to appear during development are the radial glial cells; the radial glial fibers fan out from the ventricular and subventricular zones, where their cell bodies reside, to the pial surface where they terminate with conical endfeet. These glial cells appear within the first third of gestation, being present in the spinal cord and brainstem by E41; in the diencephalon by E45; and in the telencephalon and cerebellum by E47. The next class of glia to appear is the Bergmann glial cell of the cerebellar cortex, which can be stained by E54. Bergmann glial cells located below the Purkinje cell layer issue parallel processes which extend up to the pial surface. Within each major subdivision of the brain, massive numbers of elongated glial fibers continually alter their distinctive patterns to maintain constant ventricular-pial surface relationships during the major tectogenetic changes which occur throughout embryonic development. In Nissl-counterstained sections columns of migrating neurons are observed juxtaposed to GFA-positive radial and Bergmann glial fibers. Radial glial cells assume a variety of transitional forms during the process of their transformation into mature astrocytes. This transformation occurs in each structure at specific embryonic ages and is initiated after neuronal migration has begun to subside. The number of astroglial cells increases at an accelerated pace after neurogenesis is complete. The immunohistochemical localization of radial glial fibers at relatively early stages of embryonic development indicates that glial cells are present concomitantly with neurons, raising the possibility that at least two distinct populations of cell precursors compose the proliferative zones. Furthermore, the demonstration of large numbers of radial glial cells in all brain regions during the peak of neuronal migration and a close structural relationship between elongated glial fibers and migrating neurons support the concept that glia play a significant role in the guidance and compartmentalization of neuronal elements during development.     

Organization of radial and non-radial glia in the developing rat thalamus

The organization of glia and its relationship with migrating neurons were studied in the rat developing thalamus with immunocytochemistry by using light, confocal, and electron microscopy. Carbocyanine labeling in cultured slice of the embryonic diencephalon was also used. At embryonic day (E) 14, vimentin immunoreactivity was observed in radial fascicles spanning the neuroepithelium and extending from the ventricular zone to the lateral surface of the diencephalic vesicle. Vimentin-immunopositive fibers orthogonal to the radial ones were also detected at subsequent developmental stages. At E16, radial and non-radial processes were clearly associated with migrating neurons identified by the neuronal markers calretinin and gamma-aminobutyric acid. Non-radial glial fibers were no longer evident by E19. Radial fibers were gradually replaced by immature astrocytes at the end of embryonic development. In the perinatal period, vimentin immunoreactivity labeled immature astrocytes and then gradually decreased; vimentin-immunopositive cells were only found in the internal capsule by the second postnatal week. Glial fibrillary acidic protein immunoreactivity appeared at birth in astrocytes of the internal capsule, but was not evident in most of the adult thalamic nuclei. Confocal and immunoelectron microscopy allowed direct examination of the relationships between neurons and glial processes in the embryonic thalamus, showing the coupling of neuronal membranes with both radial and non-radial glia during migration. Peculiar ultrastructural features of radial glia processes were observed. The occurrence of non-radial migration was confirmed by carbocyanine-labeled neuroblasts in E15 cultured slices. The data provide evidence that migrating thalamic cells follow both radial and non-radial glial pathways toward their destination.     

The fate of neural progenitor cells expressing astrocytic and radial glial markers in the postnatal rat dentate gyrus

In the dentate gyrus neurons continue to be generated from late embryonic to adult stage. Recent extensive studies have unveiled several key aspects of the adult neurogenesis, but only few attempts have so far been made on the analysis of the early postnatal neurogenenesis, a transition state between the embryonic and adult neurogenesis. Here, we focus on the early postnatal neurogenesis and examine the nature and development of neural progenitor cells in Wistar rats. Immunohistochemistry for Ki67, a cell cycle marker, and 5-bromo-2-deoxyuridine (BrdU) labelling show that cell proliferation occurs mainly in the hilus and partly in the subgranular zone. A majority of the proliferating cells express S100beta and astrocyte-specific glutamate transporter (GLAST) and the subpopulation are also positive for glial fibrillary acidic protein (GFAP) and nestin. Tracing with BrdU and our modified retrovirus vector carrying enhanced green fluorescent protein (GFP) indicate that a substantial population of the proliferating cells differentiate into proliferative neuroblasts and immature neurons in the hilus, which then migrate to the granule cell layer (66.8%), leaving a long axon-like process behind in the hilus, and the others mainly become star-shaped astrocytes (12.0%) and radial glia-like cells (4.7%) in the subgranular zone. These results suggest that the progenitors of the granule cells expressing astrocytic and radial glial markers, proliferate and differentiate into neurons mainly in the hilus during the early postnatal period.     

Radial glia phenotype: origin, regulation, and transdifferentiation

Radial glial cells play a major guidance role for migrating neurons during central nervous system (CNS) histogenesis but also play many other crucial roles in early brain development. Being among the earliest cells to differentiate in the early CNS, they provide support for neuronal migration during embryonic brain development; provide instructive and neurotrophic signals required for the survival, proliferation, and differentiation of neurons; and may be multipotential progenitor cells that give rise to various cell types, including neurons. Radial glial cells constitute a major cell type of the developing brain in numerous nonmammalian and mammalian vertebrates, increasing in complexity in parallel with the organization of the nervous tissue they help to build. In mammalian species, these cells transdifferentiate into astrocytes when neuronal migration is completed, whereas, in nonmammalian species, they persist into adulthood as a radial component of astroglia. Thus, our perception of radial glia may have to change from that of path-defining cells to that of specialized precursor cells transiently fulfilling a guidance role during brain histogenesis. In that respect, their apparent change of phenotype from radial fiber to astrocyte probably constitutes one of the most common transdifferentiation events in mammalian development.     

Immunohistochemical investigation of caspase-1 and effect of caspase-1 inhibitor in delayed neuronal death after transient cerebral ischemia

The localization of caspase-1 protein, interleukin-1beta (IL-1beta)-converting enzyme, was immunohistochemically examined in the hippocampal CA-1 subfield by a transient occlusion of bilateral common carotid arteries in Mongolian gerbils. Immunoreactivities for caspase-1 were found in microglias, astrocytes, endothelial cells of capillaries and some non-pyramidal neurons. Immunopositive microglias increased in number from 3 days until 7 days from the transient ischemia, and astrocytes also increased in number from 3 days until 28 days. At the electron microscopic level, caspase-1 immunoreaction endproducts were associated with Golgi apparatus in glial cells, endothelial cells of blood vessels and non-pyramidal neurons. The delayed neuronal death of CA-1 pyramidal cells was significantly protected by the treatment of specific caspase-1 inhibitor (Ac-WEHD-CHO) or broad caspase family inhibitor (z-VAD-FMK). Cell death was protected in a dose dependent manner by the former by 43-57%, and by the latter by 66-91% when injected at 1 and 10 microg, respectively. On the other hand, the protective effect of specific caspase-3 inhibitor (Ac-DMQD-CHO) was less significant at higher dose (10 microg) by 33% (P<0.05), and not detectable at lower dose (1 microg) by 13% (P=0.27). Furthermore, a significant decrease of microglias and astrocytes was found in the CA-1 as well as the reduction of IL-1beta and caspase-1 immunoreactivities by the treatment of Ac-WEHD-CHO. Extravasation of serum albumin was also extremely reduced by this treatment. These findings suggest that the inhibition of caspase-1 activity ameliorates the ischemic injury by inhibiting the activity of IL-1beta.     

Transcallosal non-pyramidal cell projections from visual cortex in the cat

Non-pyramidal cells with transcallosal projections were identified in the area 17/18 border region of the cat by retrograde transport of horseradish peroxidase injected into border region of the opposite hemisphere. From several hundred neurons filled with a Golgi-like diaminobenzidine (DAB) reaction product, seven cells were identified by their radially oriented smooth dendrites as possible non-pyramidal cells. Following thin-sectioning and examination with the electron microscope, four of the neurons proved to be layer IV spiny stellate cells with incompletely filled dendritic spines, and two proved to be layer III pyramidal cells with an incompletely labelled apical dendrite and dendritic spines. The remaining neuron was a non-pyramidal cell whose essentially smooth dendrites were covered with synapses, and whose cell body formed both symmetric and asymmetric synapses with presynaptic terminals. To better assess how many non-pyramidal cells might be labelled, thin sections of the area 17/18 border were surveyed using material processed with tetramethylbenzidine (TMB), and another five labelled non-pyramidal cells with transcallosal projections were identified by the needle-like crystals of TMB reaction product they contained. During the study it became evident that both the DAB and TMB reaction products in the lightly labelled neurons tended to be associated with granules that are 0.5 microns or larger in diameter and that had the characteristics of lysosomes. These granules are also visible in the light microscope as dark puncta. The numbers of puncta in profiles of pyramidal and of non-pyramidal cells in layers II/III and IVa of the area 17/18 border region and in the control acallosal region of area 17 were counted and compared. These comparisons revealed that labelled transcallosally projecting non-pyramidal cells may constitute 10-32% of the non-pyramidal cell population at the area 17/18 border region. Similar values were also obtained for pyramidal cells in this region. Consequently, it is concluded that significant numbers of non-pyramidal cells have axons that project through the corpus callosum to the contralateral hemisphere.     

Physiological characterization of layer III non-pyramidal neurons in piriform (olfactory) cortex of rat

We performed whole-cell recordings of layer III non-pyramidal neurons in the piriform cortex of Sprague–Dawley rats. For comparison purposes, recordings were made from deep pyramidal cells, which are also present in layer III. These two cell types could be distinguished both anatomically and physiologically. Anatomically, the layer III non-pyramidal neuron displayed smooth beady dendrites, while deep pyramidal cells showed thicker dendrites with spines. The dendrites of the layer III non-pyramidal neuron also tended to be restricted to layer III while deep pyramidal cells had long apical dendrites that spanned layers I and II. Although the resting membrane potentials of both cell types were very similar, significant differences were noted in other physiological measures. Layer III non-pyramidal neurons typically displayed higher input resistances, faster time constants, smaller spike amplitudes, shorter spike widths, and higher spike thresholds. In addition, layer III non-pyramidal neurons were able to spike at much higher rates when stimulated with the same level of threshold normalized current injection. The most dramatic differences in physiology were seen in the pattern of spiking in response to increasing levels of positive constant current pulses. Layer III non-pyramidal neurons showed qualitatively different responses at low and high levels of stimulation. At low levels, spikes occurred with long latency and the firing frequency increased throughout the duration of the current pulse. At high levels, non-pyramidal neurons started spiking with short latency, followed by a decrease in firing frequency, which in turn was followed by an increase in firing frequency. Deep pyramidal neurons differed dramatically from this pattern, displaying a qualitatively similar response at all levels of current injection. This response was characterized by short latency spikes and spike adaptation for the duration of the current pulse.     

Differentiation of radial glia from radial precursor cells and transformation into astrocytes in the developing rat spinal cord

Radial glial cell origins and functions have been studied extensively in the brain; however, questions remain relating to their origin and fate in the spinal cord. In the present study, radial glia are investigated in vivo using the neuroepithelial markers nestin and vimentin and the gliogenic markers GLAST, BLBP, 3CB2, and glial fibrillary acidic protein (GFAP). This has revealed heterogeneity among nestin/vimentin-positive precursor cells and suggests a lineage progression from neuroepithelial cell through to astrocyte in the developing spinal cord. A population of self-renewing radial cells, distinct from an earlier pseudo-stratified neuroepithelium, that resemble radial glial cells in morphology but do not express GLAST, BLBP, or 3CB2, is revealed. These radial cells arise directly from the spinal cord neuroepithelium and are probably the progenitors of neurons and the earliest appearing radial glial cells. GLAST/BLBP-positive radial glia first appear in the ventral cord at E14, and these cells gradually transform through one or more intermediate stages into differentiated astrocytes. Few if any neurons appear to be derived from radial glial cells, which are instead the major sources of astrocytes in the spinal cord. Evidence for the nonradial glial cell origins of some white matter astrocytes is also presented.     

Radial and tangential neuronal migration disorder in ibotenate-induced cortical lesions in hamsters: immunohistochemical study of reelin, vimentin, and calretinin

To investigate the mechanisms of radial and tangential neuronal migration disorders, immunohistochemical expressions of reelin, vimentin, and calretinin were examined in brain lesions induced by ibotenate (an agonist of the N-methyl-D-aspartate [NMDA] complex receptor) in hamsters. Thirty-four newborn hamsters were subjected to intracerebral injections of ibotenate, and 12 animals served as the control. These hamsters were examined at 1, 2, 3, 5, and 7 days after injections. The cortical lesions observed after ibotenate injections had a strong resemblance to the following neuronal migration disorders: (1) microgyria, (2) focal subcortical heterotopia, and (3) leptomeningeal glioneuronal heterotopia. In microgyria, the radial glial fibers were sparsely distributed, but in leptomeningeal glioneuronal heterotopia, vimentin-positive fibers extended into this abnormal neural tissue. Calretinin-immunoreactive neurons and fibers were present along the lesion forming the microgyria and abnormal neuronal arrangement. Focal subcortical heterotopia also included a small number of calretinin-expressing neurons originating from the subplate neuronal population. These results imply that the neuronal migration disorders produced by ibotenate show not only the migrational arrest of neurons but also interference from the termination of the migration process. We also suggest that the heterotopic neurons constituting the focal subcortical heterotopia originate in the lateral or medial ganglionic eminence of the ventral telencephalon, probably caused by the abnormal tangential neuronal migration.     

Ultrastructural study of cholecystokinin-immunoreactive cells and processes in area CA1 of the rat hippocampus

We used light and electron microscopic immunocytochemical methods to examine the structure of neuronal perikarya and processes containing cholecystokinin-like immunoreactivity (CCK-IR) in area CA1 of the rat hippocampus. The morphology of stained perikarya, their positions within all laminae, and the orientation of their dendrites indicate that CCK-IR is located in interneurons. These cells were seen in the electron microscope to have deeply folded nuclei and to receive both symmetric and asymmetric synaptic junctions on their cell somata and dendritic shafts. Their dendrites are essentially spine-free, but form bulges at the site of some asymmetric synaptic junctions. Axonal varicosities containing CCK-IR make symmetric synaptic junctions with cell somata and dendritic shafts of both pyramidal and non-pyramidal neurons. In addition, CCK-IR varicosities form symmetric junctions with unstained non-pyramidal neurons and with CCK-IR cells, suggesting either recurrent innervation of one cell on itself or interaction between interneurons. The presence of CCK-IR varicosities and synaptic junctions on pyramidal cells is in agreement with physiological data which indicate that CCK has a direct postsynaptic action. The observation of CCK-IR varicosities forming synaptic junctions on non-pyramidal cells suggests that CCK might also modify the response of interneurons.     

A Golgi study of the brain malformation in Zellweger's cerebro-hepato-renal disease

Summary Characteristic neuronal heterotopias in two cases of Zellweger's cerebro-hepato-renal disease were studied with the Golgi method.In the corona radiata, heterotopias consist of large fields of small or medium-sized radial pyramids, and of dense clusters containing larger, randomly oriented pyramidal cells and multipolar neurons, some of which resemble granule cells. The latter type of heterotopia could result from a focal destructive process at a relatively early stage of neuronal migration.In the cerebellar white matter, heterotopic masses contain Purkinje cells and possibly Golgi neurons but no granule or basket cells. The mispositioned Purkinje cells resemble the subcortical and intragranular Purkinje cells of the reeler mutant mouse and those of the weaver mutant. The morphology of neurons in the abnormally convoluted olivary nucleus is normal.     

Neurogenesis in the adult brain: the demise of a dogma and the advent of new treatments

Since the early sixties, many concepts concerning neurogenesis have been progressively ruled out. Proof of the persistence of a physiological neurogenesis in adult mammals, including humans, raised the concept of a unique precursor cell giving birth to neurons and glial cells. According to this concept, a real continuum between neuroepithelial cells, radial glia and astrocytes exists from the embryonic period to adult age and generates both neurons and glial cells. Different factors, either secreted in situ or transported by blood, can influence this physiological neurogenesis process. The targets and role of newborn neurons are not clearly understood. In pathological conditions (ischemia, epilepsy, lesions), the physiological neurogenesis process is enhanced; however the significance of this neurogenesis excess (beneficial or deleterious) is not completely known. Advances in understanding the regulation of neurogenesis in these different conditions represent hopes of new therapeutic procedures, not only by improving the control of differentiation and survival of transplanted stem cells, but also by the possibility of modifying the processes of "endogenous neurogenesis".     

GFAP-expressing radial glia-like cell bodies are involved in a one-to-one relationship with doublecortin-immunolabeled newborn neurons in the adult dentate gyrus

The present study examined the relationship between radial glial cells and newborn neurons in the adult dentate gyrus using three different methods. Single labeling immunocytochemistry for newly born neurons using doublecortin, as well as double labeling using an additional antibody to glial fibrillary acidic protein (GFAP) to label astrocytes were used at the light microscopic level. Furthermore, doublecortin immunoelectron microscopy was used to examine the ultrastructural relationship between newborn neurons and astrocytes in the adult dentate gyrus. These data showed an intimate one-to-one relationship between GFAP-expressing radial glia-like cell bodies and their non-radial processes that wrap around the basal and lateral sides of newborn neurons to cradle them in the subgranular zone. A similar relationship is observed for the newborn neurons at the base of the granule cell layer, but the cell body of the GFAP-expressing radial glia-like cells is not as intimately associated with the cell body of the newborn neurons at this site. Furthermore, newborn neurons with apical dendritic processes and growth cones in the granule cell layer extend them along radial glial processes. These newborn neurons do not receive axosomatic or axodendritic synapses indicating the absence of basket cell innervation. These data show that GFAP-expressing radial glia-like cells in the dentate gyrus cradle newborn neurons in the subgranular zone and that their radial processes provide a scaffold for neuronal process outgrowth.