Neurogenesis in the striatum of the quinolinic acid lesion model of Huntington's disease

The presence of ongoing neurogenesis in the adult mammalian brain raises the exciting possibility that endogenous progenitor cells may be able to generate new neurons to replace cells lost through brain injury or neurodegenerative disease. We have recently demonstrated increased cell proliferation and the generation of new neurons in the Huntington's disease human brain. In order to better understand the potential role of endogenous neuronal replacement in neurodegenerative disorders and extend our initial observations in the human Huntington's disease brain, we examined the effect of striatal cell loss on neurogenesis in the subventricular zone (SVZ) of the adult rodent forebrain using the quinolinic acid (QA) lesion rat model of Huntington's disease. Cell proliferation and neurogenesis were assessed with bromodeoxyuridine (BrdU) labeling and immunocytochemistry for cell type-specific markers. BrdU labeling demonstrated increased cell proliferation in the SVZ ipsilateral to the QA-lesioned striatum, resulting in expansion of the SVZ in the lesioned hemisphere. Quantification revealed that QA lesion-induced striatal cell loss produced a significant increase in the area of BrdU-immunoreactivity in the SVZ ipsilateral to the lesioned hemisphere between 1 and 14 days post-lesion compared with sham-lesioned animals, with the greatest increase observed at 7 days post-lesion. These changes were associated with an increase in cells in the anterior SVZ ipsilateral to the lesioned striatum expressing the antigenic marker for SVZ neuroblasts, doublecortin (Dcx). Importantly, we observed Dcx-positive cells extending from the SVZ into the QA-lesioned striatum where a subpopulation of newly generated cells expressed markers for immature and mature neurons. This study demonstrates that loss of GABAergic medium spiny projection neurons following QA striatal lesioning of the adult rat brain increases SVZ neurogenesis, leading to the putative migration of neuroblasts to damaged areas of the striatum and the formation of new neurons.     

Chemoattractive activity of sonic hedgehog in the adult subventricular zone modulates the number of neural precursors reaching the olfactory bulb

The adult subventricular zone (SVZ) supports neural stem cell self-renewal and differentiation and continually gives rise to new neurons throughout adult life. The mechanisms orienting the migration of neuroblasts from the SVZ to the olfactory bulb (OB) via the rostral migratory stream (RMS) have been extensively studied, but factors controlling neuroblast exit from the SVZ remain poorly explored. The morphogen Sonic Hedgehog (Shh) displays proliferative and survival activities toward neural stem cells and is an axonal chemoattractant implicated in guidance of commissural axons during development. We identify here the presence of Shh protein in SVZ extracts and in the cerebrospinal fluid of adult mice, and we demonstrate that migrating neuroblasts in the SVZ and RMS express the Shh receptor Patched. We show that Shh displays a chemoattractive activity in vitro on SVZ-derived neuronal progenitors, an effect blocked by Cur61414, a Smoothened antagonist. Interestingly, Shh-expressing cells grafted above the RMS of adult mice exert a chemoattractive activity on migrating neuroblasts in vivo, thus inducing their accumulation and deviation from their normal migratory pathway. Furthermore, the adenoviral transfer of Shh into the lateral ventricle or the blocking of Shh present in the SVZ of adult mice using its physiological antagonist Hedgehog interacting protein or neutralizing Shh antibodies provides in vivo evidence that Shh can retain SVZ-derived neuroblasts. The ability to modulate the number of neuroblasts leaving the SVZ and reaching the OB through the chemoattractive activity of Shh suggests a novel degree of plasticity in cell migration of this adult stem cell niche.     

Age-dependent regional changes in the rostral migratory stream

Throughout life the subventricular zone (SVZ) is a source of new olfactory bulb (OB) interneurons. From the SVZ, neuroblasts migrate tangentially through the rostral migratory stream (RMS), a restricted route approximately 5 mm long in mice, reaching the OB within 10–14 days. Within the OB, neuroblasts migrate radially to the granule and glomerular layers where they differentiate into granule and periglomerular (PG) cells and integrate into existing synaptic circuits. SVZ neurogenesis decreases with age, and might be a factor in age-related olfactory deficits. However, the effect of aging on the RMS and on the differentiation of interneuron subpopulations remains poorly understood. Here, we examine RMS cytoarchitecture, neuroblast proliferation and clearance from the RMS, and PG cell subpopulations at 6, 12, 18, and 23 months of age. We find that aging affects the area occupied by newly generated cells within the RMS and regional proliferation, and the clearance of neuroblasts from the RMS and PG cell subpopulations and distribution remain stable.     

Nanofibrous scaffolds releasing a small molecule BDNF-mimetic for the re-direction of endogenous neuroblast migration in the brain

Brain tissue engineering has the potential to harness existing elements of neurogenesis within the adult brain to overcome a microenvironment that is otherwise inhibitory to regeneration, especially following severe tissue damage. This study investigates the ability of electrospun poly ε-caprolactone (PCL) to re-direct the migratory pathway of endogenous neuroblasts from the disrupted subventricular zone (SVZ). A small molecule non-peptide ligand (BDNF-mimetic) that mimicked the trophic properties of brain-derived neurotrophic factor (BDNF) was incorporated into electrospun PCL scaffolds to improve neuroblast survival and promote neuroblast migration towards the implant. PCL scaffolds were able to support neuroblast infiltration and migration along the implant tract. In the presence of the BDNF-mimetic, neuroblasts were able to migrate towards the implant via the parenchyma, and their persistence within the implants was prolonged. In addition, the BDNF-mimetic improved implant integration and increased local neuronal plasticity by increasing neurite sprouting at the tissue-implant interface. SMI32+ neurites were observed inside scaffolds at 21 days but not 8 days post implantation, indicating that at least some of the infiltrated neuroblasts had differentiated into neurons.     

Deprivation of sensory inputs to the olfactory bulb up-regulates cell death and proliferation in the subventricular zone of adult mice

The main olfactory bulb (MOB) is the first relay on the olfactory sensory pathway and the target of the neural progenitor cells generated in the subventricular zone (SVZ) lining the lateral ventricles and which migrate along the rostral extension of the SVZ, also called the rostral migratory stream (RMS). Within the MOB, the neuroblasts differentiate into granular and periglomerular interneurons. A reduction in the number of granule cells during sensory deprivation suggests that neurogenesis may be influenced by afferent activity. Here, we show that unilateral sensory deafferentation of the MOB by axotomy of the olfactory receptor neurons increases apoptotic cell death in the SVZ and along the rostro-caudal extent of the RMS. The vast majority of dying cells in the RMS are migrating neuroblasts as indicated by double Terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick-end labeling/PSA-NCAM labeling. Counting bromodeoxyuridine-labeled cells in animals killed immediately or 4 days after tracer administration showed a bilateral increase in proliferation in the SVZ and RMS which was balanced by cell death on the operated side. These data suggest that olfactory inputs are required for the survival of newborn neural progenitors. The greatest enhancement in proliferation occurred in the extension of the RMS located in the MOB, revealing a population of local precursors mitotically stimulated following axotomy. Together, these findings indicate that olfactory inputs may strongly modulate the balance between neurogenesis and apoptosis in the SVZ and RMS and provide a model for further investigation of the underlying molecular mechanisms of this activity-dependent neuronal plasticity.     

Tonic activation of GLUK5 kainate receptors decreases neuroblast migration in whole-mounts of the subventricular zone

In the postnatal subventricular zone (SVZ), neuroblasts migrate in chains along the lateral ventricle towards the olfactory bulb. AMPA/kainate receptors as well as metabotropic glutamate receptors subtype 5 (mGluR5) are expressed in SVZ cells. However, the cells expressing these receptors and the function of these receptors remain unexplored. We thus examined whether SVZ neuroblasts express mGluR5 and Ca(2+)-permeable kainate receptors in mouse slices. Doublecortin (DCX)-immunopositive cells (i.e. neuroblasts) immunostained positive for mGluR5 and GLU(K5-7)-containing kainate receptors. RT-PCR from approximately 10 GFP-fluorescent cell aspirates obtained in acute slices from transgenic mice expressing green fluorescent protein (GFP) under the DCX promoter showed mGluR5 and GLU(K5) receptor mRNA in SVZ neuroblasts. Patch-clamp data suggest that approximately 60% of neuroblasts express functional GLU(K5)-containing receptors. Activation of mGluR5 and GLU(K5)-containing receptors induced Ca(2+) increases in 50% and 60% of SVZ neuroblasts, respectively, while most neuroblasts displayed GABA(A)-mediated Ca(2+) responses. To examine the effects of these receptors on the speed of neuroblast migration, we developed a whole-mount preparation of the entire lateral ventricle from postnatal day (P) 20-25 DCX-GFP mice. The GABA(A) receptor (GABA(A)R) antagonist bicuculline increased the speed of neuroblast migration by 27%, as previously reported in acute slices. While the mGluR5 antagonist MPEP did not affect the speed of neuroblast migration, the homomeric and heteromeric GLU(K5) receptor antagonists, NS3763 and UB302, respectively, increased the migration speed by 38%. These data show that although both GLU(K5) receptor and mGluR5 activations increase Ca(2+) in neuroblasts, only GLU(K5) receptors tonically reduce the speed of neuroblast migration along the lateral ventricle.     

Putrescine as an important source of GABA in the postnatal rat subventricular zone

The subventricular zone (SVZ) is a neurogenic region that continually gives rise to olfactory bulb (OB) GABAergic interneurons in mammals. The newly generated neuroblasts already express GABA while migrating to this structure along the rostral migratory stream (RMS). Here, we investigate in early postnatal rat if SVZ/RMS cells undertake the same synthetic pathway by which GABA is produced in differentiated neurons, i.e. the decarboxylation of glutamate by the glutamic acid decarboxylase (GAD), or, if an alternative pathway, the conversion of putrescine into GABA, also contributes to GABA synthesis. We show here that GAD immunoreactivity is not significantly detectable within the SVZ/RMS. However, strong immunolabeling is found within the OB. Nevertheless, low GAD enzymatic activity (as compared with OB) is detected in the SVZ/RMS. SVZ/RMS explants convert approximately 30% of all captured radiolabeled putrescine into GABA in vitro, showing that this pathway is important for GABA synthesis in the SVZ. We also show that SVZ/RMS, OB and choroid plexus explants are able to synthesize putrescine, as analyzed by ornithine decarboxylase (ODC) activity, providing neuroblasts with different sources of putrescine for GABA production. During early stages of neuroblast differentiation, in which neurotransmitter choice may still be undefined, an alternative pathway for GABA synthesis guarantees the production of GABA, necessary for neuroblast proliferation and migration in the SVZ/RMS.     

Expression of ezrin radixin moesin proteins in the adult subventricular zone and the rostral migratory stream

Continuous proliferation occurs in the adult subventricular zone (SVZ) of the lateral ventricles throughout life. In the SVZ, progenitor cells differentiate into neuroblasts, which migrate tangentially along the rostral migratory stream (RMS) to reach their final destination in the olfactory bulb. These progenitor cells mature and integrate into the existing neural network of the olfactory bulb. Long distance migration of neuroblasts in the RMS requires a highly dynamic cytoskeleton with the ability to respond to surrounding stimuli. Radixin is a member of the ERM (Ezrin, Radixin, Moesin) family, which connect the actin cytoskeleton to the extracellular matrix through transmembrane proteins. The membrane-cytoskeleton linker proteins of the ERM family may regulate cellular events with a high demand on cytoskeleton plasticity, such as cell motility. Recently, specific expression of the ERM protein ezrin was shown in the RMS. Radixin however has not been characterized in this region. Here we used immunohistochemistry and confocal microscopy to examine the expression of radixin in the different cell types of the adult subventricular zone niche and in the RMS. Our findings indicate that radixin is strongly expressed in neuroblasts of the adult RMS and subventricular zone, and also in Olig2-positive cells. We also demonstrate the presence of radixin in the cerebral cortex, striatum, cerebellum, thalamus, hippocampus as well as the granular and periglomerular layers of the olfactory bulb. Our studies also reveal the localization of radixin in neurosphere culture studies and we reveal the specificity of our labeling using Western blotting. The expression pattern demonstrated here suggests a role for radixin in neuronal migration and differentiation in the adult RMS. Understanding how adult neuronal migration is regulated is of importance for the development of new therapeutic interventions using endogenous repair for neurodegenerative diseases.     

Adult neural stem cells from the mouse subventricular zone are limited in migratory ability compared to progenitor cells of similar origin

The subventricular zone (SVZ) in the forebrain is the largest source of neural stem cells and progenitor cells in the adult CNS. To assess the ability of adult neural stem cells to survive, differentiate and migrate, we have compared the behavior of dissociated, neurosphere-derived stem cells with that of progenitor cells in transplantation experiments. This ability was first tested in vivo, offering the stem cells the possibility to migrate along the rostral migratory stream (RMS), their specific pathway. In addition, the differential behaviors of the two classes of cells were also compared in vitro by grafting them into organotypic slice cultures containing either tangential (embryonic cerebral cortex) or radial (early postnatal cerebellar cortex) migratory routes. Most of the grafted adult neurosphere-derived stem cells survived and integrated in vivo, and a proportion of them differentiate into neurons, oligodendrocytes or astrocytes. However, they were unable to migrate along the RMS and remained in the vicinity of the injection site. In contrast, SVZ progenitor cells were able to migrate toward the olfactory bulb and, once there, to acquire the phenotype of granule cells, as previously reported. In vitro, neural stem cells exhibited a better migratory ability, although they only migrated for short distances, particularly, in forebrain slices. Nevertheless, the average distance covered by progenitor cells was a two-fold longer than that covered by neural stem cells, corroborating that this class of more specified cells has higher migratory ability. These results suggest that the in vitro conditions of expanding SVZ-derived stem cells, required to maintain them in an immature stage might modify their intrinsic properties, preventing their differentiation into neuroblasts and their subsequent migration.     

The age-dependent change in Olfactory periglomerular neuronal populations is not affected by interrupting subventricular neuroblast migration in adult rats

The olfactory bulb (OB) is rich in the number and variety of neurotransmitter and neuropeptide containing cells, in particular in the glomerular layer. Several reports suggest that numbers of some periglomerular phenotypes could change depending on age. However, it is unclear whether the different classes of periglomerular interneurons are modified or are maintained stable throughout life. Thus, our first objective was to obtain the absolute number of cells belonging to the different periglomerular phenotypes at adulthood. On the other hand, the olfactory bulb is continously supplied with newly generated periglomerular neurons produced by stem cells located in the subventricular zone (SVZ) and rostral migratory stream. Previously, we demonstrated that the implantation of a physical barrier completely prevents SVZ neuroblast migration towards the OB. Then, another objective of this study was to evaluate whether stopping the continuous supply of SVZ neuroblasts modified the different periglomerular populations throughout time. In summary, we estimated the total number of TH-IR, CalB-IR, CalR-IR and GAD-IR cells in the OB glomerular layer at several time points in control and barrier implanted adult rats. In addition, we estimated the volume of glomerular, granular and complete OB. Our main finding was that the number of the four main periglomerular populations is age-dependent, even after impairment of subventricular neuroblast migration. Furthermore, we established that these changes do not correlate with changes in the volume of glomerular layer.     

Beta-catenin signaling promotes proliferation of progenitor cells in the adult mouse subventricular zone

The subventricular zone (SVZ) is the largest germinal zone in the mature rodent brain, and it continuously produces young neurons that migrate to the olfactory bulb. Neural stem cells in this region generate migratory neuroblasts via highly proliferative transit-amplifying cells. The Wnt/beta-catenin signaling pathway partially regulates the proliferation and neuronal differentiation of neural progenitor cells in the embryonic brain. Here, we studied the role of beta-catenin signaling in the adult mouse SVZ. beta-Catenin-dependent expression of a destabilized form of green fluorescent protein was detected in progenitor cells in the adult SVZ of Axin2-d2EGFP reporter mice. Retrovirus-mediated expression of a stabilized beta-catenin promoted the proliferation of Mash1+ cells and inhibited their differentiation into neuroblasts. Conversely, the expression of Dkk1, an inhibitor of Wnt signaling, reduced the proliferation of Mash1+ cells. In addition, an inhibitor of GSK3 beta promoted the proliferation of Mash1+ cells and increased the number of new neurons in the olfactory bulb 14 days later. These results suggest that beta-catenin signaling plays a role in the proliferation of progenitor cells in the SVZ of the adult mouse brain.     

Fate mapping and lineage analyses demonstrate the production of a large number of striatal neuroblasts after transforming growth factor alpha and noggin striatal infusions into the dopamine-depleted striatum

Infusion of transforming growth factor alpha (TGFalpha) into the adult dopamine (DA)-depleted striatum generates a local population of nestin(+)/proliferating cell nuclear antigen (PCNA)(+) newborn cells. The precise origin and fate of these new striatal cells are unknown, making it difficult to direct them for neural repair in Parkinson's disease. Experiments in rats using 5-bromo-2'-deoxyuridine (BrdU) to label neural progenitor cells showed that during TGFalpha infusion in the DA-depleted striatum, newborn striatal cells formed a homogeneous population of precursors, with the majority coexpressing nestin, Mash1, Olig2, and epidermal growth factor receptor, consistent with the phenotype of multipotent C cells. Upon TGFalpha pump withdrawal, the subventricular zone (SVZ) was repopulated by neuroblasts. Strikingly, during this period, numerous clusters of doublecortin(+)/polysialylated neuronal cell adhesion molecule(+) neuroblasts were also produced in the ipsilateral medial striatum. In parallel, striatal BrdU(+)/glial fibrillary acidic protein(+) astrocytes were generated, but no BrdU(+)/O4(+)/CNPase(+) oligodendrocytes were generated. Infusion of the neuralizing bone morphogenetic protein antagonist noggin after TGFalpha pump withdrawal increased the neuroblast-to-astrocyte ratio among new striatal cells by blocking glial differentiation but did not alter striatal neurogenesis. At no time or treatment condition were differentiated neurons generated, including DA neurons. Using 6-hydroxydopamine-lesioned nestin-CreER(T2)/R26R-YFP mice that allow genetic fate-mapping of SVZ nestin(+) cells, we show that TGFalpha-generated striatal cells originate from SVZ nestin(+) precursors that confirmed data from the rats on the phenotype and fate of striatal nestin(+)/PCNA(+) cells upon TGFalpha withdrawal. This work demonstrates that a large population of multipotent striatal C-like cells can be generated in the DA-depleted striatum that do not spontaneously differentiate into DA neurons.     

Intravenous administration of human neural stem cells induces functional recovery in Huntington's disease rat model

An animal model induced by striatal quinolinic acid (QA) injection shows ongoing striatal degeneration mimicking Huntington's disease. To study the migratory ability and the neuroprotective effect of human neural stem cells (NSCs) in this model, we transplanted NSCs (5 x 10(6)) or saline intravenously at 7 days after unilateral QA injection. NSCs-group exhibited the reduced apomorphine-induced rotation and the reduced striatal atrophy compared to the control. PCR analysis for the human-specific ERV-3 gene supported an evidence of the engraftment of human NSCs in the rat brain. X-gal+ cells were found in and around the damaged striatum and migrated NSCs differentiated into neurons and glias. This result indicates that intravenously injected human NSCs can migrate into the striatal lesion, decrease the following striatal atrophy, and induce long-term functional improvement in a glutamate toxicity-induced striatal degeneration model.     

Endogenous matrix metalloproteinase (MMP)-3 and MMP-9 promote the differentiation and migration of adult neural progenitor cells in response to chemokines

Adult neurogenesis is regulated by both intrinsic programs and extrinsic stimuli. The enhanced proliferation of adult neural stem/progenitor cells (aNPCs) in the subventricular zone and the migration of neuroblasts toward the ischemic region in adult brains present a unique challenge as well as an opportunity to understand the molecular mechanisms underlying the extrinsic cue-induced neurogenic responses. Matrix metalloproteinases (MMPs) are a family of proteinases known to play a role in extracellular matrix remodeling and cell migration. However, their presence in aNPCs and their potential function in injury-induced aNPC migration remain largely unexplored. Here we demonstrate that in response to two injury-induced chemokines, stromal cell-derived factor 1 (SDF-1) and vascular endothelial growth factor, aNPCs differentiated into migratory cells that expressed increased levels of MMP-3 and MMP-9. Whereas differentiated neuroblasts and a subpopulation of astrocytes migrated toward the chemokines, undifferentiated progenitors did not migrate. Blocking the expression of MMP-3 or MMP-9 in aNPCs interfered with both the differentiation of aNPCs and chemokine-induced cell migration. Thus, endogenous MMPs expressed by aNPCs are important for mediating their neurogenic response to extrinsic signals.     

成年鼠大脑皮质损伤后神经前体细胞的增殖、迁移和分化

探讨皮质损伤后室管膜下区(SVZ)神经前体细胞增殖、迁移和分化的变化。在立体定位仪上纵切SD大鼠的大脑皮质,于手术后10d腹腔注射BrdU,分别于术后10、13、16、19和21d处死动物。用BrdU、nestin、GFAP和NSE免疫组化单标或双标染色方法,观察损伤后神经前体细胞增殖、迁移和分化的情况。结果显示:损伤后第10d,除损伤区出现大量BrdU阳性细胞外,SVZ背外侧角也聚集大量BrdU阳性细胞;第13d时,SVZ背外侧角的BrdU阳性细胞开始沿胼胝体向损伤区迁移;至第16d和19d,BrdU阳性细胞已迁移到SVZ背外侧角和损伤区之间;第21d时,BrdU阳性细胞已进到损伤区;BrdU阳性细胞为神经前体细胞,但未见分化为星形胶质细胞和神经元。结果提示机械性大脑皮质损伤可诱导SVZ背外侧角神经前体细胞增殖并引导向损伤区迁移,可能参与脑损伤后的修复。     

Enhanced neurogenesis in the ischemic striatum following EGF-induced expansion of transit-amplifying cells in the subventricular zone

In the subventricular zone (SVZ) of the adult mammalian brain, neural stem cells continually produce transit-amplifying precursors, which generate neuroblasts migrating into the olfactory bulb. Previous studies have suggested that SVZ cells also have the capacity to generate some striatal neurons after cerebral ischemia. The infusion of epidermal growth factor (EGF) has been demonstrated to increase the number of these regenerated neurons. However, which cell types in the SVZ are stimulated to proliferate or differentiate after EGF infusion remains unknown. In this paper, we demonstrated that cerebral ischemia results in an increase in the number of EGF receptor (EGFR)-positive transit-amplifying cells in the SVZ. EGF infusion into the ischemic brain caused the number of transit-amplifying cells to increase and the number of neuroblasts to decrease. On the other hand, after an interval of 6 days after the discontinuation of EGF infusion, a significant increase in the number of neuroblasts was found, both in the striatum and the SVZ. These results suggest that the replacement of neurons in injured striatum can be enhanced by an EGF-induced expansion of transit-amplifying cells in the SVZ.     

成年大鼠去皮层血管引起前脑室下区祖细胞增殖迁移并形成迁移路至损伤部位(二)来自背外侧脑室下区的祖细胞形成迁移路经胼胝体至损伤部位

近年来很多实验证明各种脑损伤和中枢神经疾病都能促进神经干细胞或祖细胞向非嗅球区域迁移,本研究将成年大鼠一侧大脑皮层血管去除,用免疫组化方法标记前脑室下区正在分裂的细胞、神经元祖细胞和胶质细胞祖细胞。结果证明:损伤侧及对侧的背外侧脑室下区各类祖细胞明显增多并向胼胝体迁移,在胼胝体内它们分别形成迁移路至损伤部位;迁移路内的各种祖细胞具有典型的不成熟的迁移细胞特点,胞体细长,一般首尾各有一突起,其引导突皆朝向损伤区。本研究结果提示去皮层血管增殖的前脑室下区神经元祖细胞和胶质细胞祖细胞通过放射状迁移路至损伤部位可能参与修复机制。     

Increased progenitor cell proliferation and astrogenesis in the partial progressive 6-hydroxydopamine model of Parkinson's disease

The existence of endogenous progenitor cells in the adult mammalian brain presents an exciting and attractive alternative to existing therapeutic options for treating neurodegenerative diseases such as Parkinson's disease (PD). However, prior to designing endogenous cell therapies, the effect of PD neuropathology on endogenous progenitor cell proliferation and their neurogenic potential must be investigated. This study examined the effect of dopaminergic cell loss on the proliferation and differentiation of subventricular zone- (SVZ) and midbrain-derived progenitor cells in the adult rodent brain, using the partial progressive 6-hydroxydopamine (6-OHDA) lesion model of PD. Cell proliferation and differentiation were assessed with 5-bromo-2'-deoxyuridine (BrdU) labeling and immunohistochemistry for cell type-specific markers. Tyrosine hydroxylase immunohistochemistry demonstrated a complete loss of nigrostriatal projections in the striatum and a subsequent progressive loss of dopamine (DA) cells in the SN. Quantification indicated that 6-OHDA lesion-induced cell degeneration produced a significant increase in BrdU immunoreactivity in the SVZ, ipsilateral to the lesioned hemisphere from 3 to 21 days post-lesion, compared with sham-lesioned animals. Similarly, in the striatum we observed a significant increase in the total number of BrdU positive cells in 6-OHDA-lesioned animals at all time points examined. More importantly, a significant increase in midbrain-derived BrdU positive cells was demonstrated in 6-OHDA-lesioned animals 28 days post-lesion. While we did not detect neurogenesis, BrdU labeled cells co-expressing the astrocytic marker glial fibrillary acidic protein (GFAP) were widely distributed throughout the 6-OHDA-lesioned striatum at all time points. In contrast, BrdU-labeled cells in the SN of 6-OHDA-lesioned animals did not co-express neural markers. These results demonstrate that DA-ergic neurodegeneration in the partial progressive 6-OHDA-lesioned rat brain increases SVZ- and midbrain-derived progenitor cell proliferation. While, newborn striatal progenitors undergo robust astrogenesis, newborn midbrain-derived progenitors remain in an undifferentiated state suggesting local environments differentially regulate endogenous progenitor cell populations in PD.     

Dynamic imaging reveals that brain-derived neurotrophic factor can independently regulate motility and direction of neuroblasts within the rostral migratory stream

Neuronal precursors generated in the subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB). Although, the mechanisms regulating this migration remain largely unknown. Studies have shown that molecular factors, such as brain-derived neurotrophic factor (BDNF) emanating from the OB, may function as chemoattractants drawing neuroblasts toward their target. To better understand the role of BDNF in RMS migration, we used an acute slice preparation from early postnatal mice to track the tangential migration of GAD65-GFP labeled RMS neuroblasts with confocal time-lapse imaging. By quantifying the cell dynamics using specific directional and motility criteria, our results showed that removal of the OB did not alter the overall directional trajectory of neuroblasts, but did reduce their motility. This suggested that additional guidance factors present locally within the RMS region also contribute to this migration. Here we report that BDNF and its high affinity receptor, tyrosine kinase receptor type 2 (TrkB), are indeed heterogeneously expressed within the RMS at postnatal day 7. By altering BDNF levels within the entire pathway, we showed that reduced BDNF signaling changes both neuroblast motility and direction, while increased BDNF levels changes only motility. Together these data reveal that during this early postnatal period BDNF plays a complex role in regulating both the motility and direction of RMS flow, and that BDNF comes from sources within the RMS itself, as well as from the olfactory bulb.