Migration and fate of newly born cells after focal cortical ischemia in adult rats

Neural cell migration and differentiation may participate in neural repair after adult brain injury; however, the survival and differentiation of newly born cells after different brain lesions are poorly understood. We have examined the migration and fate of bromodeoxyuridine (BrdU)-labeled cells after a highly reproducible focal ischemic lesion restricted to the frontoparietal cortex in adult rats. Thermocoagulation of pial blood vessels induces a circumscribed degeneration of all cortical layers while sparing the corpus callosum and striatum and increases cell proliferation in the subventricular zone (SVZ) and rostral migratory stream (RMS) within 7 days. We now show that, although the rostral migration of the newly born SVZ cells and their differentiation into neurons in the olfactory bulb were not affected by the lesion, numerous cells expressing the neuroblast marker doublecortin migrated laterally in the striatum and corpus callosum 5 days postinjury. In addition to the SVZ, BrdU-labeled cells were seen in the striatum, in the corpus callosum, and around the lesion. One month later, BrdU-labeled cells in the corpus callosum expressed transferrin and the pi isoform of glutathione-S-transferase (GST-pi), markers of oligodendrocytes. Other BrdU+ cells expressed a marker of astrocytes, but none expressed neuronal markers, suggesting that new neurons do not form or survive under these conditions. Numerous BrdU-labeled cells were still observed in the SVZ and RMS. The data show that focal cortical ischemia does not lead to the long-term survival of new neurons in the striatum or cortex but induces long-term alterations in the SVZ and the production of new oligodendrocytes that may contribute to neural repair.     

Progenitor cells of the adult mouse subventricular zone proliferate, migrate and differentiate into oligodendrocytes after demyelination

Identifying a source of cells with the capacity to generate oligodendrocytes in the adult CNS would help in the development of strategies to promote remyelination. In the present study, we examined the ability of the precursor cells of the adult mouse subventricular zone (SVZ) to differentiate into remyelinating oligodendrocytes. After lysolecithin-induced demyelination of the corpus callosum, progenitors of the rostral SVZ (SVZa) and the rostral migratory pathway (RMS), expressing the embryonic polysialylated form of the neural cell adhesion molecule (PSA-NCAM), increased progressively with a maximal expansion occurring after 2 weeks. This observation correlated with an increase in the proliferation activity of the neural progenitors located in the SVZa and RMS. Moreover, polysialic acid (PSA)-NCAM-immunoreactive cells arizing from the SVZa were detected in the lesioned corpus callosum and within the lesion. Tracing of the constitutively cycling cells of the adult SVZ and RMS with 3H-thymidine labelling showed their migration toward the lesion and their differentiation into oligodendrocytes and astrocytes but not neurons. These data indicate that, in addition to the resident population of quiescent oligodendrocyte progenitors of the adult CNS, neural precursors from the adult SVZ constitute a source of oligodendrocytes for myelin repair.     

Doublecortin-expressing cells in the ischemic penumbra of a small-vessel stroke

A cortical lesion was induced by disrupting the medium-size pial vessels, which led to a cone-shaped cortical lesion and turned into a fluid-filled cavity surrounded by a glial acidic fibrillary protein-positive (GFAP(+)) glia limitans 21 days after injury. Therefore, it mimics conditions of lacunar infarctions, one of the most frequent human stroke pathologies. Doublecortin (DCX)-positive cells were present in the neocortex and corpus callosum at the base of the lesion. The number of DCX-positive cells in the corpus callosum was significantly increased from day 5 to day 14 compared with the control group. In contrast, there were no DCX-positive cells in neocortex of control animals; the DCX-positive cells appeared in the neocortex after lesioning and were maintained until 14 days postlesioning. Some of the DCX-positive cells were also immunoreactive for beta III-tubulin, another marker of immature neurons. They did not stain positively for markers of glia cells. The presence of these DCX-positive cells near the lesion might indicate a migratory pathway for developing neuroblasts from the subventricular zone (SVZ) through the corpus callosum to the lesion. SVZ cells were labeled with a lipophilic molecule, 5- (and 6-) carboxyfluorescein diacetate succinimidyl ester (CFSE) stereotaxical injections. Although rostral migratory stream and olfactory bulb were intensely labeled, no CFSE-containing cells were found in the cortex beneath the lesion. These results do not support the idea that the DCX-positive cells were originating from neural precursors of the SVZ, but they might be generated from local progenitor cells.     

Growth factor treatment promotes mobilization of young but not aged adult subventricular zone precursors in response to demyelination

Precursor cells of the adult mouse subventricular zone (SVZ) are mobilized and recruited by a lysolecithin (LPC)-induced demyelination of the corpus callosum. Because age decreases the proliferation of the SVZ neural precursors as well as the potential for myelin repair of the adult central nervous system, we have compared the ability of young and aged adult neural precursors to respond to LPC-induced demyelination. With age, the SVZ cells lost their capacity to proliferate and to be recruited by the lesion. Whereas a single injection of fibroblast growth factor-2 or transforming growth factor-alpha stimulated the proliferation of SVZ and rostral migratory stream precursors in both groups of animals after demyelination, they favored recruitment at the lesion in young mice but not in aged ones. In vitro experiments using neurospheres derived from young and aged animals indicated that both populations have the same migratory performances. Our in vivo data thus suggest that aged neural precursors may loose their intrinsic capacities to respond to demyelination-induced signals. Alternatively, their function may be altered by modification of the aged extracellular environment.     

Id1, Id2, and Id3 gene expression in neural cells during development

Id1, Id2, and Id3 mRNA are expressed mainly in the proliferating ependymal cell zone of the mouse brain during embryogenesis. In this study, the expression pattern and cell phenotypes of the Id family mRNA were examined in postnatal and adult rat brain. The expression of Id1 and Id3 mRNA in rat brain was observed in the cortex layer 1, corpus callosum, ventricular/ subventricular zone (VZ/ SVZ), and the CA1-4 layers of the hippocampus at postnatal day 1 (P1) through P14, whereby it declined at 2 months. In general, the developmental pattern of Id1 mRNA coincided with the pattern observed for Id3 mRNA. Similar to Id1 and Id3, Id2 mRNA was highly expressed in the corpus callosum, VZ/ SVZ, and the hippocampus. Examination of Id2 mRNA revealed high levels in the cortex and caudate putamen at P1 through P14, whereas a decline was observed in its expression in the adult cortex. In P5 rat cerebellum, all Id mRNA examined were found in the internal granular cell layers; however, at this time point, only Id2 mRNA expression was detected in the differentiating zone of the external granular cell layers, preferentially localizing to adult Purkinje cells. Furthermore, only Id2 mRNA expression in brain was observed in NF+ neurons at P5. Examination of S100α+ and GFAP+ astrocytes, revealed the presence of all three mRNAs, whereas the expression of Id2 and Id3 mRNA was absent in O4+ immature oligodendrocytes. These data suggest that the spatial and temporal kinetic patterns during development, as well as cellular specificity, of the Id gene family may play a critical role in neural precursor cell proliferation and cell divergence. GLIA 24:372–381, 1998. © 1998 Wiley-Liss, Inc.     

Responses of microglia and neural progenitors to mechanical brain injury.

Neural cells have distinct responses to CNS injury; however, neural progenitor response to CNS injury is not yet documented. Stab injury combined with injection of bromodeoxyuridine (BrdU), a thymidine analog, into adult rat cortex above the lateral ventricle for 10 min resulted in activated microglia/macrophage infiltration along with nuclear factor kappa B (NF kappa B)/p65 activation at the lesion site. Most NF kappa B/p65+ cells displayed a phagocytic morphology. Under these conditions, profound cell apoptosis took place in the injured corpus callosum, but not in the subventricular/ventricular zone (SVZ/VZ). The SVZ/VZ-derived neural progenitors in both injected and non-injected contralateral hemispheres showed strong BrdU immunostaining, indicating that SVZ/VZ-derived neural progenitors of both hemispheres may undergo DNA synthesis in response to unilateral brain injury.     

Migration patterns of subventricular zone cells in adult mice change after cerebral cortex injury

The subventricular zone (SVZ) generates the largest number of migratory cells in the adult brain. SVZ neuroblasts migrate to the olfactory bulbs (OB) in the adult, whereas during development, SVZ cells migrate into many adjacent nuclei. Previously, we showed that cerebral cortex injury in the adult causes molecular and cellular changes which may recapitulate the developmental migratory directions. Consistent with this, growth factors, as well as models of illness or injury can cause adult SVZ cells to migrate into non-olfactory bulb nuclei. Here, we tested the hypothesis that cerebral cortex injury in the adult mouse induces changes in migration, by labeling adult SVZ cells with a retroviral vector and examining the distribution of cells 4 days and 3 weeks later. Four days after cortical lesions, disproportionately fewer retrovirally-labeled cells had migrated to the olfactory bulb in lesioned mice than in controls. Conversely, the number of cells found in non-olfactory bulb regions (primarily the area of the lesion and the corpus callosum) was increased in lesioned mice. The morphology of these emigrated cells suggested that they were differentiating into glial cells. Three weeks after cortical injury, the majority of retrovirally-labeled cells in both groups of mice had migrated into the granule and periglomerular layers of the olfactory bulb. At 3 weeks, we still observed retrovirally-labeled glial cells in the corpus callosum and in the area of the injury in lesioned mice. These results suggest that cortical lesions cause a transient change in migration patterns of SVZ progeny, which is characterized by decreases in migration to the olfactory bulb but increased migration towards the injury. Our studies also suggest that cortical lesions induce the production of new glial cells which survive for at least 3 weeks after injury. The data support the concept that in the adult, SVZ cells can generate progeny that migrate towards injured areas and thus potentially be harnessed for neural repair.     

Cellular proliferation and migration following a controlled cortical impact in the mouse

Neurogenesis following neural degeneration has been demonstrated in many models of disease and injury. The present study further examines the early proliferative and migratory response of the brain to a controlled cortical impact (CCI) model of traumatic brain injury. The CCI was centered over the forelimb sensorimotor cortex, unilaterally, in the adult mouse. To examine proliferation, bromo-deoxyuridine (BrdU) was injected i.p. immediately post-injury and on post-injury days 1, 2, and 3. To assess migration, we labeled SVZ cells with inert latex microspheres immediately post-injury. By combining microsphere labeling with BrdU, we determined if migrating cells had gone through the S-phase of the cell cycle after the lesion. In addition, we used a marker of neurogenesis and migration, doublecortin, to further characterize the response of the SVZ to the injury. Lastly, we determined whether subregions of the SVZ respond differentially to injury. The current study demonstrates that 3 days following CCI cellular proliferation is seen around the cortex, in the SVZ, corpus callosum, and subcortical areas anatomically connected to, but not directly damaged by the impact. It delineates that an increase in proliferation occurs in the dorsal-most aspect of the ipsilateral SVZ following impact. Lastly, it demonstrates that proliferating cells migrate from the SVZ to cortical and subcortical structures affected by the injury and that some of these cells are migrating neuroblasts.     

Subventricular zone neuroblasts emigrate toward cortical lesions

Adult subventricular zone (SVZ) neuroblasts migrate in the rostral migratory stream to the olfactory bulbs. Brain lesions generally increase SVZ neurogenesis or gliogenesis and cause SVZ cell emigration to ectopic locations. We showed previously that glia emigrate from the SVZ toward mechanical injuries of the somatosensory cerebral cortex in mice. Here we tested the hypotheses that SVZ neurogenesis increases, that neuroblasts emigrate, and that epidermal growth factor expression increases after cortical injuries. Using immunohistochemistry for phenotypic markers and BrdU, we show that newborn doublecortin-positive SVZ neuroblasts emigrated toward cerebral cortex lesions. However, the number of doublecortin-positive cells in the olfactory bulbs remained constant, suggesting that dorsal emigration was not at the expense of rostral migration. Although newborn neuroblasts emigrated, rates of SVZ neurogenesis did not increase after cortical lesions. Finally, we examined molecules that may regulate emigration and neurogenesis after cortical lesions and found that epidermal growth factor was increased in the SVZ, corpus callosum, and cerebral cortex. These results suggest that after injuries to the cerebral cortex, neuroblasts emigrate from the SVZ, that emigration does not depend either on redirection of SVZ cells or on increased neurogenesis, and that epidermal growth factor may induce SVZ emigration.     

Postnatal cellular contributions of the hippocampus subventricular zone to the dentate gyrus, corpus callosum, fimbria, and cerebral cortex

The rodent dentate gyrus (DG) is formed in the embryo when progenitor cells migrate from the dentate neuroepithelium to establish a germinal zone in the hilus and a secondary germinal matrix, near the fimbria, called the hippocampal subventricular zone (HSVZ). The developmental plasticity of progenitors within the HSVZ is not well understood. To delineate the migratory routes and fates of progenitors within this zone, we injected a replication-incompetent retrovirus, encoding the enhanced green fluorescent protein (EGFP), into the HSVZ of postnatal day 5 (P5) mice. Between P6 and P45, retrovirally-infected EGFP(+) of progenitors migrated into the DG, established a reservoir of progenitor cells, and differentiated into neurons and glia. By P6-7, EGFP(+) cells were observed migrating into the DG. Subsets of these EGFP(+) cells expressed Sox2 and Musashi-1, characteristic of neural stem cells. By P10, EGFP(+) cells assumed positions within the DG and expressed immature neuronal markers. By P20, many EGFP(+) cells expressed the homeobox prospero-like protein Prox1, an early and specific granule cell marker in the CNS, and extended mossy fiber projections into the CA3. A subset of non-neuronal EGFP(+) cells in the dentate gyrus acquired the morphology of astrocytes. Another subset included EGFP(+)/RIP(+) oligodendrocytes that migrated into the fimbria, corpus callosum, and cerebral cortex. Retroviral injections on P15 labeled very few cells, suggesting depletion of HSVZ progenitors by this age. These findings suggest that the early postnatal HSVZ progenitors are multipotent and migratory, and contribute to both dentate gyrus neurogenesis as well as forebrain gliogenesis.     

Chronic lithium treatment decreases NG2 cell proliferation in rat dentate hilus,amygdala and corpus callosum

An increasing number of investigations suggest volumetric changes and glial pathology in several brain regions of patients with bipolar disorder. Lithium, used in the treatment of this disorder, has been reported to be neuroprotective and increase brain volume. Here we investigate the effect of lithium on the proliferation and survival of glial cells positive for the chondroitin sulphate proteoglycan NG2 (NG2 cells); a continuously dividing cell type implicated in remyelination and suggested to be involved in regulation of neuronal signaling and axonal outgrowth. Adult male rats were treated with lithium for four weeks and injected with the proliferation marker bromodeoxyuridine (BrdU) before or at the end of the treatment period. Immunohistochemical analysis of brain sections was performed to estimate the number of newly born (BrdU-labeled) NG2 cells and oligodendrocytes in hippocampus, basolateral nuclei of amygdala and corpus callosum. Lithium significantly decreased the proliferation of NG2 cells in dentate hilus of hippocampus, amygdala and corpus callosum, but not in the molecular layer or the cornu ammonis (CA) regions of hippocampus. The effect was more pronounced in the corpus callosum. No effect of lithium on the survival of newborn cells or the number of newly generated oligodendrocytes could be detected. Our results demonstrate that in both white and gray matter brain regions implicated in the pathophysiology of bipolar disorder, chronic lithium treatment significantly decreases the proliferation rate of NG2 cells; the major proliferating cell type of the adult brain.     

Endogenous and exogenous ciliary neurotrophic factor enhances forebrain neurogenesis in adult mice

Neurogenesis in the adult mammalian CNS occurs in the subventricular zone (SVZ) and dentate gyrus. The receptor for ciliary neurotrophic factor (CNTF), CNTFRalpha, is expressed in the adult subventricular zone. Because the in vitro effects of CNTF on neural precursors have been varied, including proliferation and differentiation into neurons or glia, we investigated its role in vivo. Injection of CNTF in the adult C57BL/6 mice forebrain increased the number of cells labeled with ip BrdU in both neurogenic regions. In the dentate gyrus, CNTF also appeared to enhance differentiation of precursors into neurons, i.e., increased the proportion of NeuN+/BrdU+ cells from approximately 14 to approximately 29%, but did not affect differentiation into astrocytes (GFAP+) or oligodendrocytes (CNPase+). In the SVZ, CNTF increased the proportion of GFAP+/BrdU+ cells from approximately 1 to approximately 2%. CNTF enhanced the distance of migration of new neurons into the granule cell layer. Intraventricular injection of neutralizing anti-CNTF antibodies reduced the number of BrdU-labeled cells in the SVZ. These results suggest that endogenous CNTF regulates adult neurogenesis by increasing proliferation of neural stem cells and/or precursors. Alternatively, CNTF could maintain cells longer in the S-phase, resulting in increased BrdU labeling. In the neurogenic region of the SVZ, CNTFRalpha was exclusively present in GFAP-positive process-bearing cells, suggesting that CNTF affects neurogenesis indirectly via neighboring astroglia. Alternatively, these cells may be part of the neural precursor lineage. The restricted expression of CNTF within the nervous system makes it a potential selective drug target for cell replacement strategies.     

PARP-1 deletion promotes subventricular zone neural stem cells toward a glial fate

Identification of critical factors involved in oligodendroglial fate specification from endogenous neural stem cells is relevant to the development of therapeutic interventions that aim to promote remyelination. Here we report a novel role of the DNA repair protein poly-ADP-ribose polymerase-1 (PARP-1) in regulating the neural stem cell profile in the postnatal mouse forebrain subventricular zone (SVZ). We observed increased expression of Sox2 and Sox10 in the SVZ of postnatal day 11 (P11) PARP-1 knockout mice. This increase corresponded to increased Olig2 expression in Sox2-positive cells of the PARP-1 knockout mouse SVZ and decreased Map2abc expression compared with Sox2/Olig2 and Sox2/Map2abc expression in wild-type mice. We noted enhanced expression of proliferating oligodendrocyte progenitor cells (OPCs) at the expense of proliferating neuroblasts in the SVZ of PARP-1 knockout mice, by using Olig1/Ki67/DCX, NG2/Ki67/DCX, and PDGFR/BrdU/TuJ1 immunofluorescence labeling. In addition, the percentage of BrdU/Olig2 double-labeled cells increased in the SVZ and corpus callosum of PARP-1 knockout mice compared with wild-type mice. We also observed a decrease in DCX-positive cells without a decrease in the overall SVZ area in PARP-1 knockout mice, further indicating a switch from neuroblast to OPC fate. PARP-1 knockout mice displayed thinning of MBP expression in the corpus callosum and external capsule, suggesting that the enhanced OPC proliferation in the SVZ might compensate for deficiency in myelination. Together, our results show that PARP-1 deletion promotes SVZ neural stem cells toward a glial fate and suggest that future studies target PARP-1 as a potential therapeutic strategy for demyelinating diseases.     

Cell and molecular analysis of the developing and adult mouse subventricular zone of the cerebral hemispheres

The subventricular zone (SVZ) of the lateral ventricle remains mitotically active in the adult mammalian central nervous system (CNS). Recent studies have suggested that this region may contain neuroñal precursors (neural stem cells) in adult rodents. A variety of neuronal and glial markers as well as three extracellular matrix (ECM) markers were examined with the hope of understanding factors that may affect the growth and migration of neurons from this region throughout development and in the adult. This study has characterized the subventricular zone of late embryonic, postnatal, and adult mice using several neuronal markers [TuJ1, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), neuron- specific enolase (NSE)], glial markers [RC-2, vimentin, glial fibrillary acidic protein (GFAP), galactocerebroside (Gal-C)], ECM markers [tenascin-C (TN-C), chondroitin sulfate, a chondroi tin sulfate proteoglycan termed dermatan sulfate-dependent proteoglycan-1 (DSD-1-PG)], stem-cell marker (nestin), and proliferation-specific marker [bromodeoxyuridine (BrdU)]. TuJ1⁺ and nestin⁺ cells (neurons and stem cells, respectively) persist in the region into adulthood, although the numbers of these cells become more sparse as the animal develops, and they appear to be immature compared to the cells in surrounding forebrain structures (e. g., not expressing NSE and having few, if any, processes). Likewise, NADPH-d⁺ cells are found in and around the SVZ during early postnatal development but become more sparse in the prolifera tive zone through maturity, and, by adulthood, only a few labeled cells can be found at the border between the SVZ and surrounding forebrain structures (e. g., the striatum), and even smaller numbers of positive cells can be found within the adult SVZ proper. BrdU labeling also seems to decrease significantly after the first postnatal week, but it still persists in the SVZ of adult animals. The disappearance of RC-2⁺ (radial) glia during postnatal development and the persistence of glial-derived ECM molecules such as tenascin and chondroitin sulfate proteoglycans (as well as other “boundary” molecules) in the adult SVZ may be associated with a persistence of immaturity, cell death, and a lack of cell emigration from the SVZ in the adult. © 1995 Wiley-Liss, Inc.     

Postischemic exercise attenuates whereas enriched environment has certain enhancing effects on lesion-induced subventricular zone activation in the adult rat

Experimental stroke increases cell proliferation and neurogenesis in the subventricular zone (SVZ) and in the dentate gyrus subgranular zone (SGZ) in the adult mammalian brain. This study examined the effects of postischemic voluntary exercise (running wheel) and environmental enrichment on the SVZ and SGZ 1 week after focal cortical ischemia in adult spontaneously hypertensive rats. Immunohistochemical labeling was performed for incorporation of specific cell markers such as Ki67 and 5-bromodeoxyuridine (proliferating and newborn cells), terminal deoxynucleotidyl transferase-mediated dUTP in situ nick-end labeling (apoptotic cells), Sox-2 and glial fibrillary acidic protein (neural stem and progenitor cells), polysialylated neural cell adhesion molecule and doublecortin (neuroblasts). Postischemic exercise and environmental enrichment differentially modulated SVZ cell genesis but lacked effects on the SGZ. Lesion-induced proliferation of neural stem/progenitor cells and neuronal precursors was attenuated in stroke runners without any effects on apoptosis or neuronal migration in the forebrain. Running activity did not affect the SVZ in intact rats. In contrast to postischemic wheel running, postischemic environmental enrichment did not have attenuating effects on the ipsilateral SVZ and increased proliferating putative neural stem cells and neuronal precursors contralaterally. A significant functional improvement, assessed using a rotating pole, was observed only in the postischemically enriched group and was likely due to other types of plasticity than neuronal replacement at this early time point. It may be concluded that in contrast to enriched environment, exercise during the first postischemic week might be detrimental for regenerative processes initiated in the SVZ after stroke.     

Differential effects of distinct central nervous system regions on cell migration and axonal extension of neural precursor transplants

Transplantation of neural precursor cells (NPCs) is a promising therapeutic strategy in CNS injury. However, the adult CNS lacks instructive signals present during development and, depending on the region and type of transplant, may be inhibitory for neuron generation and axonal growth. We examined the effects of the white matter in different regions of the adult CNS on the properties of NPC transplants with respect to cell survival, differentiation, migration, and axonal growth. NPCs were prepared from day 13.5 embryonic spinal cord of transgenic rats that express the human placental alkaline phosphatase (AP) reporter. These NPCs were injected unilaterally into the cervical spinal cord white matter and into the corpus callosum of adult rats and were analyzed immunohistochemically 2 weeks later. NPCs survived in both regions and differentiated into astrocytes, oligodendrocytes, and neurons, with no apparent differences in survival or phenotypic composition. However, in the spinal cord white matter, graft‐derived cells, identified as precursors and glial cells, migrated from the injection site rostrally and caudally, whereas, in the corpus callosum, graft‐derived cells did not migrate and remained at the injection site. Importantly, graft‐derived neurons extended axons from the grafting site along the corpus callosum past the midline, entering into the contralateral side of the corpus callosum. These results demonstrate dramatic differences between white matter regions in the spinal cord and brain with respect to cell migration and axonal growth and underscore the importance of considering the effects of the local CNS environment in the design of effective transplantation strategies. © 2012 Wiley Periodicals, Inc.     

Distinguishing features of progenitor cells in the late embryonic and adult hippocampus

Adult neurogenesis occurs within the subgranular layer of the hippocampal dentate gyrus. In this study, we examined dividing cells in the late embryonic and adult rat hippocampus to identify distinguishing characteristics and potential neural stem cell population(s), as identified by the putative neural stem cell markers FGFR4 and Sox1. In embryonic hippocampal cells in primary culture, basic fibroblast factor caused cell proliferation, increased telomerase activity and upregulation of FGFR4 mRNA. In both the embryonic and adult brains, proliferating cells express Sox1, as well as markers for neuronal- and glial-restricted precursors. However, the cell markers associated with cells expressing proliferative cell nuclear antigen (PCNA) and Sox1 differed between late embryonic and adult hippocampus, suggesting that there are important differences between adult and embryonic neurogenesis.     

Trimethyltin intoxication induces the migration of ventricular/subventricular zone cells to the injured murine hippocampus

Following the postnatal decline of cell proliferation in the mammalian central nervous system, the adult brain retains progenitor cells with stem cell-like properties in the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampus. Brain injury can stimulate proliferation and redirect the migration pattern of SVZ precursor cells to the injury site. Sublethal exposure to the neurotoxicant trimethyltin (TMT) causes dose-dependent necrosis and apoptosis in the hippocampus dentate gyrus and increases SGZ stem cell proliferation to generate new granule cells. To determine whether SVZ cells also contribute to the repopulation of the TMT-damaged dentate gyrus, 6-8 week old male C3H mice were injected with the carbocyanine dye spDiI and bromodeoxyuridine (80 mg/kg; ip.) to label ventricular cells prior to TMT exposure. The presence of labeled cells in hippocampus was determined 7 and 28 days after TMT exposure. No significant change in the number of BrdU⁺ and spDiI⁺ cells was observed in the dentate gyrus 7 days after TMT treatment. However, 28 days after TMT treatment there was a 3–4 fold increase in the number of spDiI-labeled cells in the hippocampal hilus and dentate gyrus. Few spDiI⁺ cells stained positive for the mature phenotypic markers NeuN or GFAP, suggesting they may represent undifferentiated cells. A small percentage of migrating cells were BrdU⁺/spDiI⁺, indicating some newly produced, SVZ- derived precursors migrated to the hippocampus. Taken together, these data suggest that TMT-induced injury of the hippocampus can stimulate the migration of ventricular zone-derived cells to injured dentate gyrus.