Dentate Gyrus Of Adult Mice Research Articles

Increased efficiency of the GABAA and GABAB receptor-mediated neurotransmission in the Ts65Dn mouse model of Down syndrome

Cognitive impairment in Down syndrome (DS) involves the hippocampus. In the Ts65Dn mouse model of DS, deficits in hippocampus-dependent learning and synaptic plasticity were linked to enhanced inhibition. However, the mechanistic basis of changes in inhibitory efficiency remains largely unexplored, and efficiency of the GABAergic synaptic neurotransmission has not yet been investigated in direct electrophysiological experiments. To investigate this important feature of neurobiology of DS, we examined synaptic and molecular properties of the GABAergic system in the dentate gyrus (DG) of adult Ts65Dn mice. Both GABAA and GABAB receptor-mediated components of evoked inhibitory postsynaptic currents (IPSCs) were significantly increased in Ts65Dn vs. control (2N) DG granule cells. These changes were unaccompanied by alterations in hippocampal levels of GABAA (α1, α2, α3, α5 and γ2) or GABAB (Gbr1a and Gbr1b) receptor subunits. Immunoreactivity for GAD65, a marker for GABAergic terminals, was also unchanged. In contrast, there was a marked change in functional parameters of GABAergic synapses. Paired stimulations showed reduced paired-pulse ratios of both GABAA and GABAB receptor-mediated IPSC components (IPSC2/IPSC1), suggesting an increase in presynaptic release of GABA. Consistent with increased gene dose, the level of the Kir3.2 subunit of potassium channels, effectors for postsynaptic GABAB receptors, was increased. This change was associated with enhanced postsynaptic GABAB/Kir3.2 signaling following application of the GABAB receptor agonist baclofen. Thus, both GABAA and GABAB receptor-mediated synaptic efficiency is increased in the Ts65Dn DG, thus likely contributing to deficient synaptic plasticity and poor learning in DS.

Properties of Doublecortin-(DCX)-Expressing Cells in the Piriform Cortex Compared to the Neurogenic Dentate Gyrus of Adult Mice

The piriform cortex receives input from the olfactory bulb and (via the entorhinal cortex) sends efferents to the hippocampus, thereby connecting the two canonical neurogenic regions of the adult rodent brain. Doublecortin (DCX) is a cytoskeleton-associated protein that is expressed transiently in the course of adult neurogenesis. Interestingly, the adult piriform cortex, which is usually considered non-neurogenic (even though some reports exist that state otherwise), also contains an abundant population of DCX-positive cells. We asked how similar these cells would be to DCX-positive cells in the course of adult hippocampal neurogenesis. Using BAC-generated transgenic mice that express GFP under the DCX promoter, we studied DCX-expression and electrophysiological properties of DCX-positive cells in the mouse piriform cortex in comparison with the dentate gyrus. While one class of cells in the piriform cortex indeed showed features similar to newly generated immature granule neurons, the majority of DCX cells in the piriform cortex was mature and revealed large Na+ currents and multiple action potentials. Furthermore, when proliferative activity was assessed, we found that all DCX-expressing cells in the piriform cortex were strictly postmitotic, suggesting that no DCX-positive “neuroblasts” exist here as they do in the dentate gyrus. We conclude that DCX in the piriform cortex marks a unique population of postmitotic neurons with a subpopulation that retains immature characteristics associated with synaptic plasticity. DCX is thus, per se, no marker of neurogenesis but might be associated more broadly with plasticity.

Deficiency of DGCR8 gene, a potential gene for 22q11 deletion syndrome, decreases proliferation of neural stem cell in hippocampal dentate gyrus of adult mice

Deficiency of DGCR8 gene, a potential gene for 22q11 deletion syndrome, decreases proliferation of neural stem cell in hippocampal dentate gyrus of adult mice

The Adult Mouse Dentate Gyrus Contains Populations of Committed Progenitor Cells that are Distinct from Subependymal Zone Neural Stem Cells

There is currently a debate as to whether or not a neural stem cell (NSC) exists in the adult mammalian hippocampus. Clonal colony-forming assays allow single cells to cells to be evaluated for stem cell properties: self-renewal and multipotentiality. In these in vitro assays, single cells from the subependymal zone (SEZ) of the adult lateral ventricle yield large colonies which self-renew and are multipotential, while single cells from the adult dentate gyrus (DG) produce small, unipotent, and nonself-renewing colonies. We find that multipotential and long-term self-renewing colonies can be isolated only from the early embryonic hippocampus, before the formation of the DG. No movement of progenitors from the postnatal SEZ to the newly forming DG subgranular zone is detected and adult DG colonies in vitro originate from the embryonic hippocampal primordium. These data support a model where embryonic hippocampal NSCs change their properties as the organism ages. When adult DG spheres are cocultured with embryonic brain slices, self-renewal (but not multipotentiality) is restored and maintained for several passages off of slices. Adult clonal DG spheres grown on embryonic brain slices or transplanted into brains of neonatal mice do not give rise to neurons. Neurons arise from separate, small clones that are approximately 10 times more frequent than sphere colonies in vitro and may be responsible for maintaining neurogenesis in the adult in vivo. We propose that there are separate glial and neuronal clones in the adult hippocampus, with glial progenitors being the most proliferative in culture.

Spatiotemporal specificity of GABAA receptor-mediated regulation of adult hippocampal neurogenesis

GABAergic transmission regulates adult neurogenesis by exerting negative feedback on cell proliferation and enabling dendrite formation and outgrowth. Further, GABAergic synapses target differentiating dentate gyrus granule cells prior to formation of glutamatergic connections. GABA(A) receptors (GABA(A) Rs) mediating tonic (extrasynaptic) and phasic (synaptic) transmission are molecularly and functionally distinct, but their specific role in regulating adult neurogenesis is unknown. Using global and single-cell targeted gene deletion of subunits contributing to the assembly of GABA(A) Rs mediating tonic (α4, δ) or phasic (α2) GABAergic transmission, we demonstrate here in the dentate gyrus of adult mice that GABA(A) Rs containing α4, but not δ, subunits mediate GABAergic effects on cell proliferation, initial migration and early dendritic development. In contrast, α2-GABA(A) Rs cell-autonomously signal to control positioning of newborn neurons and regulate late maturation of their dendritic tree. In particular, we observed pruning of distal dendrites in immature granule cells lacking the α2 subunit. This alteration could be prevented by pharmacological inhibition of thrombospondin signaling with chronic gabapentin treatment, shown previously to reduce glutamatergic synaptogenesis. These observations point to homeostatic regulation of inhibitory and excitatory inputs onto newborn granule cells under the control of α2-GABA(A) Rs. Taken together, the availability of distinct GABA(A) R subtypes provides a molecular mechanism endowing spatiotemporal specificity to GABAergic control of neuronal maturation in adult brain.

Leucine-Rich Repeat Kinase 2 Modulates Retinoic Acid-Induced Neuronal Differentiation of Murine Embryonic Stem Cells

BackgroundDominant mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most prevalent cause of Parkinson's disease, however, little is known about the biological function of LRRK2 protein. LRRK2 is expressed in neural precursor cells suggesting a role in neurodevelopment.Methodology/Principal FindingsIn the present study, differential gene expression profiling revealed a faster silencing of pluripotency-associated genes, like Nanog, Oct4, and Lin28, during retinoic acid-induced neuronal differentiation of LRRK2-deficient mouse embryonic stem cells compared to wildtype cultures. By contrast, expression of neurotransmitter receptors and neurotransmitter release was increased in LRRK2+/− cultures indicating that LRRK2 promotes neuronal differentiation. Consistently, the number of neural progenitor cells was higher in the hippocampal dentate gyrus of adult LRRK2-deficient mice. Alterations in phosphorylation of the putative LRRK2 substrates, translation initiation factor 4E binding protein 1 and moesin, do not appear to be involved in altered differentiation, rather there is indirect evidence that a regulatory signaling network comprising retinoic acid receptors, let-7 miRNA and downstream target genes/mRNAs may be affected in LRRK2-deficient stem cells in culture.Conclusion/SignificanceParkinson's disease-linked LRRK2 mutations that associated with enhanced kinase activity may affect retinoic acid receptor signaling during neurodevelopment and/or neuronal maintenance as has been shown in other mouse models of chronic neurodegenerative diseases.

In Vivo Clonal Analysis Reveals Self-Renewing and Multipotent Adult Neural Stem Cell Characteristics

Neurogenesis and gliogenesis continue in discrete regions of the adult mammalian brain. A fundamental question remains whether cell genesis occurs from distinct lineage-restricted progenitors or from self-renewing and multipotent neural stem cells in the adult brain. Here, we developed a genetic marking strategy for lineage tracing of individual, quiescent, and nestin-expressing radial glia-like (RGL) precursors in the adult mouse dentate gyrus. Clonal analysis identified multiple modes of RGL activation, including asymmetric and symmetric self-renewal. Long-term lineage tracing invivo revealed a significant percentage of clones that contained RGL(s), neurons, and astrocytes, indicating capacity of individual RGLs for both self-renewal and multilineage differentiation. Furthermore, conditional Pten deletion in RGLs initially promotes their activation and symmetric self-renewal but ultimately leads to terminal astrocytic differentiation and RGL depletion in the adult hippocampus. Our study identifies RGLs as self-renewing and multipotent neural stem cells and provides novel insights into invivo properties of adult neural stem cells.

Early and adult hippocampal TGF-β1 overexpression have opposite effects on behavior

TGF-β1 is an anti-inflammatory cytokine that is augmented in the brain of autistic patients and that can affect brain development. In this work, we studied the effects of overexpressing TGF-β1 in the dentate gyrus of adult or young mice on behavior. TGF-β1 overexpression during postnatal development led to a long-term decrease in social interaction and to long-term increases in self-grooming and depression-related behaviors. Our analysis shows that these behavioral changes correlate with the long-term downregulation of TGF-β1 and IL-6 expression in the dentate gyrus, as well as to decreases in the mRNA levels of the synaptic protein neuroligin 3 and in the number of Reelin-positive neurons in the dentate gyrus. In contrast, chronic expression of TGF-β1 during adulthood led to transient opposite effects on these behaviors. These results show a central role of hippocampal TGF-β1 in the programming and modulation of social interaction, repetitive behavior and depression-related behavior. Finally, our data suggest a role of hippocampal TGF-β1 and early-life neuroinflammation in the development of the behavioral alterations observed in autism spectrum disorders.

Comparison of the dose-response relationship of radiation-induced apoptosis in the hippocampal dentate gyrus and intestinal crypt of adult mice

The present study compared the dose-response curves for the frequency of apoptosis in mouse hippocampal dentate gyrus (DG) and intestinal crypt using whole-body gamma irradiation. The incidence of gamma-ray-induced apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end-labelling (TUNEL) method. TUNEL-positive apoptotic nuclei in the DG and intestinal crypt were increased in a dose-dependent pattern (0-2 Gy). The dose-response curves were linear-quadratic, with a significant relationship between the appearance of apoptosis and irradiation dose. The slopes of the dose-response curves in the DG were much steeper (~5-6-fold) than those in the intestinal crypt within the range of 0-1 Gy exposure. Hippocampal DG might be a more effective and sensitive evaluation structure than the intestinal crypt to estimate the degree of radiation exposure in damaged organs of adult mice exposed to low irradiation dose.

Hydroxylation of 5-Methylcytosine by TET1 Promotes Active DNA Demethylation in the Adult Brain

Cytosine methylation is the major covalent modification of mammalian genomic DNA and plays important roles in transcriptional regulation. The molecular mechanism underlying the enzymatic removal of this epigenetic mark, however, remains elusive. Here, we show that 5-methylcytosine (5mC) hydroxylase TET1, by converting 5mCs to 5-hydroxymethylcytosines (5hmCs), promotes DNA demethylation in mammalian cells through a process that requires the base excision repair pathway. Though expression of the 12 known human DNA glycosylases individually did not enhance removal of 5hmCs in mammalian cells, demethylation of both exogenously introduced and endogenous 5hmCs is promoted by the AID (activation-induced deaminase)/APOBEC (apolipoprotein B mRNA-editing enzyme complex) family of cytidine deaminases. Furthermore, Tet1 and Apobec1 are involved in neuronal activity-induced, region-specific, active DNA demethylation and subsequent gene expression in the dentate gyrus of the adult mouse brain in vivo. Our study suggests a TET1-induced oxidation-deamination mechanism for active DNA demethylation in mammals.

Galectin-1 is expressed in early-type neural progenitor cells and down-regulates neurogenesis in the adult hippocampus

BackgroundIn the adult mammalian brain, neural stem cells (NSCs) proliferate in the dentate gyrus (DG) of the hippocampus and generate new neurons throughout life. A multimodal protein, Galectin-1, is expressed in neural progenitor cells (NPCs) and implicated in the proliferation of the NPCs in the DG. However, little is known about its detailed expression profile in the NPCs and functions in adult neurogenesis in the DG.ResultsOur immunohistochemical and morphological analysis showed that Galectin-1 was expressed in the type 1 and 2a cells, which are putative NSCs, in the subgranular zone (SGZ) of the adult mouse DG. To study Galectin-1's function in adult hippocampal neurogenesis, we made galectin-1 knock-out mice on the C57BL6 background and characterized the effects on neurogenesis. In the SGZ of the galectin-1 knock-out mice, increased numbers of type 1 cells, DCX-positive immature progenitors, and NeuN-positive newborn neurons were observed. Using triple-labeling immunohistochemistry and morphological analyses, we found that the proliferation of the type-1 cells was increased in the SGZ of the galectin-1 knock-out mice, and we propose that this proliferation is the mechanism for the net increase in the adult neurogenesis in these knock-out mice DG.ConclusionsGalectin-1 is expressed in the neural stem cells and down-regulates neurogenesis in the adult hippocampus.

Abnormal neurogenesis in the dentate gyrus of adult mice lacking 1,25‐dihydroxy vitamin D3(1,25‐(OH)2D3)

In this study, we employed 1α-hydroxylase knockout (1α-(OH)ase(-/-) ) mice to investigate the influence of 1,25-dihydroxy vitamin D(3) (1,25-(OH)(2) D(3) ) deficiency on the adult neurogenesis in the hippocampal dentate gyrus (DG). The numbers of both 24-hr-old BrdU(+) cells and proliferating cell nuclear antigen positive cells in 8-week-old 1α-(OH)ase(-/-) mice increased approximately twofold compared with wild-type littermates. In contrast, the numbers of 7- and 28-day-old BrdU(+) cells in 1α-(OH)ase(-/-) mice decreased by 50% compared with wild-type mice, while the proportion of BrdU(+) /NeuN(+) cells in BrdU(+) population showed no difference between 1α-(OH)ase(-/-) and wild-type mice. Apoptotic cells in the subgranular zone (SGZ) of DG markedly increased in 1α-(OH)ase(-/-) mice. Replenishment of 1,25-(OH)(2) D(3) , but not correction of serum calcium and phosphorus levels, completely prevented changes in the neurogenesis in 1α-(OH)ase(-/-) mice. The absence of 1,25-(OH)(2) D(3) led to an increase in the expression of L-type voltage-gated calcium channel (L-VGCC) and a decrease in the nerve growth factor (NGF) mRNA level. Treatment with the L-VGCC inhibitor nifedipine blocked the increased cell proliferations by 1,25-(OH)(2) D(3) deficiency. Administration of NGF significantly attenuated the loss of newborn neurons in 1α-(OH)ase(-/-) mice.

NMDA receptor hypofunction in the dentate gyrus and impaired context discrimination in adult Fmr1 knockout mice

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability in humans. This X-linked disorder is caused by the transcriptional repression of a single gene, Fmr1. The loss of Fmr1 transcription prevents the production of Fragile X mental retardation protein (FMRP) which in turn disrupts the expression of a variety of key synaptic proteins that appear to be important for intellectual ability. A clear link between synaptic dysfunction and behavioral impairment has been elusive, despite the fact that several animal models of FXS have been generated. Here we report that Fmr1 knockout mice exhibit impaired bidirectional synaptic plasticity in the dentate gyrus (DG) of the hippocampus. These deficits are associated with a novel decrease in functional NMDARs (N-methyl-D-aspartate receptors). In addition, mice lacking the Fmr1 gene show impaired performance in a context discrimination task that normally requires functional NMDARs in the DG. These data indicate that Fmr1 deletion results in significant NMDAR-dependent electrophysiological and behavioral impairments specific to the DG.

Genetically targeting new neurons in the adult hippocampus

Neurogenesis, the birth of new neurons from neural stem cells, is known to occur throughout life in two specific regions of the adult mammalian brain, the subgranular zone/hippocampal dentate gyrus and the subventricular zone/olfactory bulb 1, 2, 3. Adult neurogenesis is a multi-step process (Figure 1), which includes proliferation and fate specification of adult neural stem cells, morphogenesis, migration, axonal and dendritic development, survival, and synaptic integration by newborn neurons 4. Understanding the basic process and molecular mechanisms of adult neurogenesis not only enriches our general knowledge about this unique type of structural and functional plasticity in the mature brain, but also has significant implications for cell replacement therapy after injury or degenerative neurological disorders. The rapid progress made in understanding adult neurogenesis has been driven by new analytical tools introduced to the field, including labeling of proliferating progenitors using nucleotide analogs, such as Bromodeoxyuridine (BrdU), or 5-ethynyl-2′-deoxyuridine (EdU), and oncoretroviruses for quantitative analysis of cell proliferation, fate mapping and neuronal development 5. In this issue of Cell Research, Xiong and colleagues bring a significant new addition to our tool box with a genetic approach, based on inducible Cre/loxP recombinase, for pulse labeling, long-term tracing and genetic manipulation of newborn neurons in the dentate gyrus of adult mice in vivo 6.

Pulse labeling and long-term tracing of newborn neurons in the adult subgranular zone

Research over the past decades has demonstrated that adult brain produces neural progenitor cells which proliferate and differentiate to newborn neurons that integrate into the existing circuit. However, detailed differentiation processes and underlying mechanisms of newly generated neurons are largely unknown due to the limitation of available methods for labeling and manipulating neural progenitor cells and newborn neurons. In this study, we designed a tightly controlled, noninvasive system based on Cre/loxP recombination to achieve long-term tracing and genetic manipulation of adult neurons in vivo. In this system, tamoxifen-inducible recombinase, CreER(T2), was driven by BAC-based promoter of doublecortin (DCX, a marker of newborn neurons). By crossing this Cre line with reporter mouse, we found that newborn neurons in the dentate gyrus (DG) could be selectively pulse-labeled by tamoxifen-induced expression of yellow fluorescent protein (YFP). YFP-positive neurons were identified by coimmunostaining with cell type-specific markers and characterized by electrophysiological recording. Furthermore, analysis of the migration of these neurons showed that the majority of these labeled neurons migrated to the inner part of granule cell layer. Moreover, spine growth of inner molecular layer of newborn granule neurons takes a dynamic pattern of invert U-shape, in contrast to the wedge-shaped change in the outer molecular layer. Our transgenic tool provides an efficient way to selectively label and manipulate newborn neuron in adult mouse DG.

Expression of tryptophan 2,3-dioxygenase in mature granule cells of the adult mouse dentate gyrus

New granule cells are continuously generated in the dentate gyrus of the adult hippocampus. During granule cell maturation, the mechanisms that differentiate new cells not only describe the degree of cell differentiation, but also crucially regulate the progression of cell differentiation. Here, we describe a gene, tryptophan 2,3-dioxygenase (TDO), whose expression distinguishes stem cells from more differentiated cells among the granule cells of the adult mouse dentate gyrus. The use of markers for proliferation, neural progenitors, and immature and mature granule cells indicated that TDO was expressed in mature cells and in some immature cells. In mice heterozygous for the alpha-isoform of calcium/calmodulin-dependent protein kinase II, in which dentate gyrus granule cells fail to mature normally, TDO immunoreactivity was substantially downregulated in the dentate gyrus granule cells. Moreover, a 5-bromo-2'-deoxyuridine labeling experiment revealed that new neurons began to express TDO between 2 and 4 wk after the neurons were generated, when the axons and dendrites of the granule cells developed and synaptogenesis occurred. These findings indicate that TDO might be required at a late-stage of granule cell development, such as during axonal and dendritic growth, synaptogenesis and its maturation.

Exposure to extremely low-frequency (50 Hz) electromagnetic fields enhances adult hippocampal neurogenesis in C57BL/6 mice

Throughout life, new neurons are continuously generated in the hippocampus, which is therefore a major site of structural plasticity in the adult brain. We recently demonstrated that extremely low-frequency electromagnetic fields (ELFEFs) promote the neuronal differentiation of neural stem cells in vitro by up-regulating Ca v1-channel activity. The aim of the present study was to determine whether 50-Hz/1 mT ELFEF stimulation also affects adult hippocampal neurogenesis in vivo, and if so, to identify the molecular mechanisms underlying this action and its functional impact on synaptic plasticity. ELFEF exposure (1 to 7 h/day for 7 days) significantly enhanced neurogenesis in the dentate gyrus (DG) of adult mice, as documented by increased numbers of cells double-labeled for 5-bromo-deoxyuridine (BrdU) and doublecortin. Quantitative RT-PCR analysis of hippocampal extracts revealed significant ELFEF exposure-induced increases in the transcription of pro-neuronal genes ( Mash1, NeuroD2, Hes1) and genes encoding Ca v1.2 channel α 1C subunits. Increased expression of NeuroD1, NeuroD2 and Ca v1 channels was also documented by Western blot analysis. Immunofluorescence experiments showed that, 30 days after ELFEF stimulation, roughly half of the newly generated immature neurons had survived and become mature dentate granule cells (as shown by their immunoreactivity for both BrdU and NeuN) and were integrated into the granule cell layer of the DG. Electrophysiological experiments demonstrated that the new mature neurons influenced hippocampal synaptic plasticity, as reflected by increased long-term potentiation. Our findings show that ELFEF exposure can be an effective tool for increasing in vivo neurogenesis, and they could lead to the development of novel therapeutic approaches in regenerative medicine.

Alterations in discrete glutamate receptor subunits in adult mouse dentate gyrus granule cells following perforant path transection

Custom-designed microarray analysis was utilized to evaluate expression levels of glutamate receptors (GluRs) and GluR-interacting protein genes within isolated dentate gyrus granule cells following axotomy of the principal input, the perforant path (PP). Dentate gyrus granule cells were evaluated by microdissection via laser capture microdissection, terminal continuation RNA amplification, and microarray analysis following unilateral PP transections at seven time points. Expression profiles garnered from granule cells on the side ipsilateral to PP transections were compared and contrasted with naive subjects and mice subjected to unilateral occipital cortex lesions. Selected microarray observations were validated by real-time quantitative PCR analysis. Postlesion time-dependent alterations in specific alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors, kainate receptors, N-methyl-D-aspartate (NMDA) receptors, and GluR-interacting protein genes were found across the time course of the study, suggesting a neuroplasticity response associated with the transsynaptic granule cell alterations following axotomy of incoming PP terminals.

(‐)‐epigallocatechin‐3‐gallate increases cell proliferation and neuroblasts in the subgranular zone of the dentate gyrus in adult mice

Neurogenesis is regulated by several factors such as age, stress and pharmacological agents. We observed the effects of (-)-epigallocatechin-3-gallate (EGCG), a major catechin of green tea, on neurogenesis in mice. The animals were orally administered EGCG for 4 weeks. Brain sections were stained using a marker for cell proliferation (Ki67 and BrdU) and neuroblasts (doublecortin, DCX). In all groups, Ki67, BrdU and DCX immunoreaction were observed in the subgranular zone of the dentate gyrus. Oral administration of EGCG significantly increased the number of Ki67-, BrdU- and DCX-immunoreactive cells as well as BrdU/DCX-colabled cells in the subgranular zone when compared to those in the vehicle-treated group. These results indicate that oral administration of EGCG can enhance cell proliferation and increase the number of neuroblasts in mice hippocampal dentate gyrus.

Localization of Retinoic Acid Receptor RARα in Adult Mouse Hippocampal Dentate Gyrus Neurons

Retinoids (Vitamin A) play an important role in differentiation and patterning in the developing nervous system. Retinoids bind to specific nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs), in order to mediate cellular effects. Three subtypes of RAR receptor, RARα, β and γ, have been identified. Evidence has emerged that retinoid signaling required for synaptic plasticity, learning and memory behaviors, and for adult neurogenesis. In this study, we investigated the expression pattern of RARα in adult mouse hippocampus. We hypothesized that the receptor may have a developmental‐dependent expression in the new neurons of the dentate gyrus. Co‐labeling experiments were performed with markers for immature and mature neurons (Doublecortin, Calretinin, NeuN) and for astrocytes/stem cells (nestin, GFAP). We found that RARα expression was located at several different areas in the mouse hippocampus, CA1‐CA3, the granule cell layer, hillus and granule cell layer of DG. RARα immunohistochemical stain was clearly visualized in cell cytoplasm, but not in nucleus. There was colocalization of RARα in DG with NeuN, but not with astrocyte/stem cell markers GFAP or Nestin. RARα immunohistochemical stain was not colocalized with immature granule cell markers doublecortin and calretinin. Our results provide the first evidence for identify RARα localized only in mature granular neurons of adult mouse dentate gyrus.