Subventricular zone neural progenitors protect striatal neurons from glutamatergic excitotoxicity

Improving Sensitivity and Longevity of In Vivo Glutamate Sensors with Electrodeposited NanoPt

In vivo glutamate sensing has provided valuable insight into the physiology and pathology of the brain. Electrochemical glutamate biosensors, constructed by cross-linking glutamate oxidase onto an electrode and oxidizing H2O2 as a proxy for glutamate, are the gold standard for in vivo glutamate measurements for many applications. While glutamate sensors have been employed ubiquitously for acute measurements, there are almost no reports of long-term, chronic glutamate sensing in vivo, despite demonstrations of glutamate sensors lasting for weeks in vitro. To address this, we utilized a platinum electrode with nanometer-scale roughness (nanoPt) to improve the glutamate sensors' sensitivity and longevity. NanoPt improved the GLU sensitivity by 67.4% and the sensors were stable in vitro for 3 weeks. In vivo, nanoPt glutamate sensors had a measurable signal above a control electrode on the same array for 7 days. We demonstrate the utility of the nanoPt sensors by studying the effect of traumatic brain injury on glutamate in the rat striatum with a flexible electrode array and report measurements of glutamate taken during the injury itself. We also show the flexibility of the nanoPt platform to be applied to other oxidase enzyme-based biosensors by measuring γ-aminobutyric acid in the porcine spinal cord. NanoPt is a simple, effective way to build high sensitivity, robust biosensors harnessing enzymes to detect neurotransmitters in vivo.

Functional correlates of cognitive abilities vary with age in pediatric multiple sclerosis

BACKGROUND

Pediatric multiple sclerosis (PedMS) can hamper brain maturation. Aim of this study was to assess the neuropsychological profile of PedMS patients and their resting-state functional connectivity (RS FC).

METHODS

We assessed intelligence quotient (IQ), executive speed, and language in 76 PedMS patients. On a 3.0T scanner RS FC of brain networks was estimated with a seed-based analysis (subset of 58 right-handed PedMS patients and 22 matched healthy controls). Comparisons were run between controls and PedMS (whole cohort and by age).

RESULTS

Ninety-five% of patients had normal IQ. The highest rate of failure was observed in executive speed. PedMS showed reduced RS FC in all networks than controls, especially in the basal ganglia. In younger patients (<16-year-old, n = 32) reduced RS FC in the basal ganglia, language, and sensorimotor networks associated with poorer cognitive performance (p < 0.05; r range: 0.39; 0.56). Older patients (≥16-year-old, n = 26) showed increased RS FC in the basal ganglia, default-mode, sensorimotor, executive, and language networks, associated with poorer performance in executive speed and language abilities (p < 0.05; r range: -0.40; -0.59). In both groups, lower RS FC of the caudate nucleus associated with poorer executive speed.

CONCLUSIONS

The effect of PedMS on RS FC is clinically relevant and differs according to patients' age.

Age-induced alterations of granulopoiesis generate atypical neutrophils that aggravate stroke pathology

Aging accounts for increased risk and dismal outcome of ischemic stroke. Here, we investigated the impact of age-related changes in the immune system on stroke. Upon experimental stroke, compared with young mice, aged mice had increased neutrophil clogging of the ischemic brain microcirculation, leading to worse no-reflow and outcomes. Aged mice showed an enhanced granulopoietic response to stroke that led to the accumulation of CD101+CD62Llo mature and CD177hiCD101loCD62Llo and CD177loCD101loCD62Lhi immature atypical neutrophils in the blood, endowed with increased oxidative stress, phagocytosis and procoagulant features. Production of CXCL3 by CD62Llo neutrophils of the aged had a key role in the development and pathogenicity of aging-associated neutrophils. Hematopoietic stem cell rejuvenation reverted aging-associated neutropoiesis and improved stroke outcome. In elderly patients with ischemic stroke, single-cell proteome profile of blood leukocytes identified CD62Llo neutrophil subsets associated with worse reperfusion and outcome. Our results unveil how stroke in aging leads to a dysregulated emergency granulopoiesis impacting neurological outcome.

Fast-Specific Fluorescent Probes to Visualize Norepinephrine Signaling Pathways and Its Flux in the Epileptic Mice Brain

Norepinephrine (NE) is synthesized in the locus coeruleus and widely projected throughout the brain and spinal cord. It regulates various actions and consciousness linked to a variety of neurological diseases. A "hunting-shooting" strategy was proposed in this work to improve the specificity and response rate of an NE fluorescent probe: 2-(cyclohex-2-en-1-ylidene)malononitrile derivatives were chosen as a fluorophore. To create a dual-site probe, an aldehyde group was added to the ortho of the ester group (or benzene sulfonate). Because of its excellent electrophilic activity, the aldehyde group could rapidly "hunt" the amino group and then form an intramolecular five-membered ring via the nucleophilic reaction with the β-hydroxyl group. The -NH- in the five-membered ring "shoots" the adjacent ester group, releasing the fluorophore and allowing for rapid and specific NE detection. The NE release and reuptake ″emetic″-″swallow″ transient process is captured and visualized under the action of the primary NE receptor drug. Furthermore, by introducing halogen into the fluorophore to lengthen the absorption wavelength, improve lipid solubility, and adjust the pK_a appropriately, the probe successfully penetrated the blood-brain barrier (BBB). In situ synchronous probe imaging was used to detect the NE level in the brains of epileptic and normal mice, and abnormal expression of NE in the brain was discovered during epilepsy. Brain anatomy was used to examine the distribution and level changes of NE in various brain regions before and after epilepsy. This research provides useful tools and a theoretical foundation for diagnosing and treating central nervous system diseases early.

Regulation of microglia function by neural stem cells

Neural stem and precursor cells (NPCs) build and regenerate the central nervous system (CNS) by maintaining their pool (self-renewal) and differentiating into neurons, astrocytes, and oligodendrocytes (multipotency) throughout life. This has inspired research into pro-regenerative therapies that utilize transplantation of exogenous NPCs or recruitment of endogenous adult NPCs for CNS regeneration and repair. Recent advances in single-cell RNA sequencing and other "omics" have revealed that NPCs express not just traditional progenitor-related genes, but also genes involved in immune function. Here, we review how NPCs exert immunomodulatory function by regulating the biology of microglia, immune cells that are present in NPC niches and throughout the CNS. We discuss the role of transplanted and endogenous NPCs in regulating microglia fates, such as survival, proliferation, migration, phagocytosis and activation, in the developing, injured and degenerating CNS. We also provide a literature review on NPC-specific mediators that are responsible for modulating microglia biology. Our review highlights the immunomodulatory properties of NPCs and the significance of these findings in the context of designing pro-regenerative therapies for degenerating and diseased CNS.

Neural precursor cells tune striatal connectivity through the release of IGFBPL1

The adult brain retains over life endogenous neural stem/precursor cells (eNPCs) within the subventricular zone (SVZ). Whether or not these cells exert physiological functions is still unclear. In the present work, we provide evidence that SVZ-eNPCs tune structural, electrophysiological, and behavioural aspects of striatal function via secretion of insulin-like growth factor binding protein-like 1 (IGFBPL1). In mice, selective ablation of SVZ-eNPCs or selective abrogation of IGFBPL1 determined an impairment of striatal medium spiny neuron morphology, a higher failure rate in GABAergic transmission mediated by fast-spiking interneurons, and striatum-related behavioural dysfunctions. We also found IGFBPL1 expression in the human SVZ, foetal and induced-pluripotent stem cell-derived NPCs. Finally, we found a significant correlation between SVZ damage, reduction of striatum volume, and impairment of information processing speed in neurological patients. Our results highlight the physiological role of adult SVZ-eNPCs in supporting cognitive functions by regulating striatal neuronal activity.

Prenatal exposure to Cannabis smoke induces early and lasting damage to the brain

Cannabis is the most widely used illegal drug during pregnancy, however, the effects of gestational exposure to Cannabis smoke (CS) on the central nervous system development remain uncharacterised. This study investigates the effects of maternal CS inhalation on brain function in the offspring. Pregnant mice were exposed daily to 5 min of CS during gestational days (GD) 5.5-17.5. On GD 18.5 half of the dams were euthanized for foetus removal. The offspring from the remaining dams were euthanized on postnatal days (PND) 20 and 60 for evaluation. Brain volume, cortex cell number, SOX2, histone-H3, parvalbumin, NeuN, and BDNF immunoreactivity were assessed in all groups. In addition, levels of NeuN, CB1 receptor, and BDNF expression were assessed and cortical primary neurons from rats were treated with Cannabis smoke extract (CSE) for assessment of cell viability. We found that male foetuses from the CS exposed group had decreased brain volume, whereas mice at PND 60 from the exposed group presented with increased brain volume. Olfactory bulb and diencephalon volume were found lower in foetuses exposed to CS. Mice at PND 60 from the exposed group had a smaller volume in the thalamus and hypothalamus while the cerebellum presented with a greater volume. Also, there was an increase in cortical BDNF immunoreactivity in CS exposed mice at PND 60. Protein expression analysis showed an increase in pro-BDNF in foetus brains exposed to CS. Mice at PND 60 presented an increase in mature BDNF in the prefrontal cortex (PFC) in the exposed group and a higher CB1 receptor expression in the PFC. Moreover, hippocampal NeuN expression was higher in adult animals from the exposed group. Lastly, treatment of cortical primary neurons with doses of CSE resulted in decreased cell viability. These findings highlight the potential negative neurodevelopmental outcomes induced by gestational CS exposure.

NPC transplantation rescues sci-driven cAMP/EPAC2 alterations, leading to neuroprotection and microglial modulation

Neural progenitor cell (NPC) transplantation represents a promising treatment strategy for spinal cord injury (SCI); however, the underlying therapeutic mechanisms remain incompletely understood. We demonstrate that severe spinal contusion in adult rats causes transcriptional dysregulation, which persists from early subacute to chronic stages of SCI and affects nearly 20,000 genes in total tissue extracts. Functional analysis of this dysregulated transcriptome reveals the significant downregulation of cAMP signalling components immediately after SCI, involving genes such as EPAC2 (exchange protein directly activated by cAMP), PKA, BDNF, and CAMKK2. The ectopic transplantation of spinal cord-derived NPCs at acute or subacute stages of SCI induces a significant transcriptional impact in spinal tissue, as evidenced by the normalized expression of a large proportion of SCI-affected genes. The transcriptional modulation pattern driven by NPC transplantation includes the rescued expression of cAMP signalling genes, including EPAC2. We also explore how the sustained in vivo inhibition of EPAC2 downstream signalling via the intrathecal administration of ESI-05 for 1 week impacts therapeutic mechanisms involved in the NPC-mediated treatment of SCI. NPC transplantation in SCI rats in the presence and absence of ESI-05 administration prompts increased rostral cAMP levels; however, NPC and ESI-05 treated animals exhibit a significant reduction in EPAC2 mRNA levels compared to animals receiving only NPCs treatment. Compared with transplanted animals, NPCs + ESI-05 treatment increases the scar area (as shown by GFAP staining), polarizes microglia into an inflammatory phenotype, and increases the magnitude of the gap between NeuN + cells across the lesion. Overall, our results indicate that the NPC-associated therapeutic mechanisms in the context of SCI involve the cAMP pathway, which reduces inflammation and provides a more neuropermissive environment through an EPAC2-dependent mechanism.

Inhibition of CSPG receptor PTPσ promotes migration of newly born neuroblasts, axonal sprouting, and recovery from stroke

In addition to neuroprotective strategies, neuroregenerative processes could provide targets for stroke recovery. However, the upregulation of inhibitory chondroitin sulfate proteoglycans (CSPGs) impedes innate regenerative efforts. Here, we examine the regulatory role of PTPσ (a major proteoglycan receptor) in dampening post-stroke recovery. Use of a receptor modulatory peptide (ISP) or Ptprs gene deletion leads to increased neurite outgrowth and enhanced NSCs migration upon inhibitory CSPG substrates. Post-stroke ISP treatment results in increased axonal sprouting as well as neuroblast migration deeply into the lesion scar with a transcriptional signature reflective of repair. Lastly, peptide treatment post-stroke (initiated acutely or more chronically at 7 days) results in improved behavioral recovery in both motor and cognitive functions. Therefore, we propose that CSPGs induced by stroke play a predominant role in the regulation of neural repair and that blocking CSPG signaling pathways will lead to enhanced neurorepair and functional recovery in stroke.

Orexin-A and endocannabinoids are involved in obesity-associated alteration of hippocampal neurogenesis, plasticity, and episodic memory in mice

The mammalian brain stores and distinguishes among episodic memories, i.e. memories formed during the personal experience, through a mechanism of pattern separation computed in the hippocampal dentate gyrus. Decision-making for food-related behaviors, such as the choice and intake of food, might be affected in obese subjects by alterations in the retrieval of episodic memories. Adult neurogenesis in the dentate gyrus regulates the pattern separation. Several molecular factors affect adult neurogenesis and exert a critical role in the development and plasticity of newborn neurons. Orexin-A/hypocretin-1 and downstream endocannabinoid 2-arachidonoylglycerol signaling are altered in obese mice. Here, we show that excessive orexin-A/2-arachidonoylglycerol/cannabinoid receptor type-1 signaling leads to the dysfunction of adult hippocampal neurogenesis and the subsequent inhibition of plasticity and impairment of pattern separation. By inhibiting orexin-A action at orexin-1 receptors we rescued both plasticity and pattern separation impairment in obese mice, thus providing a molecular and functional mechanism to explain alterations in episodic memory in obesity.

The authors show that adult hippocampal neurogenesis is altered in the dentate gyrus of obese mice with subsequent inhibition of long-term potentiation and impairment of pattern separation. Inhibition of orexin-A action at orexin-1 receptors rescued both impairments in obese mice.

Post-stroke Neurogenesis: Friend or Foe?

The substantial clinical burden and disability after stroke injury urges the need to explore therapeutic solutions. Recent compelling evidence supports that neurogenesis persists in the adult mammalian brain and is amenable to regulation in both physiological and pathological situations. Its ability to generate new neurons implies a potential to contribute to recovery after brain injury. However, post-stroke neurogenic response may have different functional consequences. On the one hand, the capacity of newborn neurons to replenish the damaged tissue may be limited. In addition, aberrant forms of neurogenesis have been identified in several insult settings. All these data suggest that adult neurogenesis is at a crossroads between the physiological and the pathological regulation of the neurological function in the injured central nervous system (CNS). Given the complexity of the CNS together with its interaction with the periphery, we ultimately lack in-depth understanding of the key cell types, cell-cell interactions, and molecular pathways involved in the neurogenic response after brain damage and their positive or otherwise deleterious impact. Here we will review the evidence on the stroke-induced neurogenic response and on its potential repercussions on functional outcome. First, we will briefly describe subventricular zone (SVZ) neurogenesis after stroke beside the main evidence supporting its positive role on functional restoration after stroke. Then, we will focus on hippocampal subgranular zone (SGZ) neurogenesis due to the relevance of hippocampus in cognitive functions; we will outline compelling evidence that supports that, after stroke, SGZ neurogenesis may adopt a maladaptive plasticity response further contributing to the development of post-stroke cognitive impairment and dementia. Finally, we will discuss the therapeutic potential of specific steps in the neurogenic cascade that might ameliorate brain malfunctioning and the development of post-stroke cognitive impairment in the chronic phase.

Blocking Notch-Signaling Increases Neurogenesis in the Striatum after Stroke

Stroke triggers neurogenesis in the striatum in mice, with new neurons deriving in part from the nearby subventricular zone and in part from parenchymal astrocytes. The initiation of neurogenesis by astrocytes within the striatum is triggered by reduced Notch-signaling, and blocking this signaling pathway by deletion of the gene encoding the obligate Notch coactivator Rbpj is sufficient to activate neurogenesis by striatal astrocytes in the absence of an injury. Here we report that blocking Notch-signaling in stroke increases the neurogenic response to stroke 3.5-fold in mice. Deletion of Rbpj results in the recruitment of a larger number of parenchymal astrocytes to neurogenesis and over larger areas of the striatum. These data suggest inhibition of Notch-signaling as a potential translational strategy to promote neuronal regeneration after stroke.

Endogenous neural precursor cells in health and disease

Neurogenesis persists in the adult brain of mammals in the subventricular zone (SVZ) of the lateral ventricles and in the subgranular zone (SGZ) of the dentate gyrus (DG). The complex interactions between intrinsic and extrinsic signals provided by cells in the niche but also from distant sources regulate the fate of neural stem/progenitor cells (NPCs) in these sites. This fine regulation is perturbed in aging and in pathological conditions leading to a different NPC behavior, tailored to the specific physio-pathological features. Indeed, NPCs exert in physiological and pathological conditions important neurogenic and non-neurogenic regulatory functions and participate in maintaining and protecting brain tissue homeostasis. In this review, we discuss intrinsic and extrinsic signals that regulate NPC activation and NPC functional role in various homeostatic and non-homeostatic conditions.

Static Magnetic Field Exposure In Vivo Enhances the Generation of New Doublecortin-expressing Cells in the Sub-ventricular Zone and Neocortex of Adult Rats

Static magnetic field (SMF) is gaining interest as a potential technique for modulating CNS neuronal activity. Previous studies have shown a pro-neurogenic effect of short periods of extremely low frequency pulsatile magnetic fields (PMF) in vivo and pro-survival effect of low intensity SMF in cultured neurons in vitro, but little is known about the in vivo effects of low to moderate intensity SMF on brain functions. We investigated the effect of continuously-applied SMF on subventricular zone (SVZ) neurogenesis and immature doublecortin (DCX)-expressing cells in the neocortex of young adult rats and in primary cultures of cortical neurons in vitro. A small (3 mm diameter) magnetic disc was implanted on the skull of rats at bregma, producing an average field strength of 4.3 mT at SVZ and 12.9 mT at inner neocortex. Levels of proliferation of SVZ stem cells were determined by 5-ethynyl-2'-deoxyuridine (EdU) labelling, and early neuronal phenotype development was determined by expression of doublecortin (DCX). To determine the effect of SMF on neurogenesis in vitro, permanent magnets were placed beneath the culture dishes. We found that low intensity SMF exposure enhances cell proliferation in SVZ and new DCX-expressing cells in neocortical regions of young adult rats. In primary cortical neuronal cultures, SMF exposure increased the expression of newly generated cells co-labelled with EdU and DCX or the mature neuronal marker NeuN, while activating a set of pro neuronal bHLH genes. SMF exposure has potential for treatment of neurodegenerative disease and conditions such as CNS trauma and affective disorders in which increased neurogenesis is desirable.

Functions of subventricular zone neural precursor cells in stroke recovery

The proliferation and ectopic migration of neural precursor cells (NPCs) in response to ischemic brain injury was first reported two decades ago. Since then, studies of brain injury-induced subventricular zone cytogenesis, primarily in rodent models, have provided insight into the cellular and molecular determinants of this phenomenon and its modulation by various factors. However, despite considerable correlational evidence-and some direct evidence-to support contributions of NPCs to behavioral recovery after stroke, the causal mechanisms have not been identified. Here we discuss the subventricular zone cytogenic response and its possible roles in brain injury and disease, focusing on rodent models of stroke. Emerging evidence suggests that NPCs can modulate harmful responses and enhance reparative responses to neurologic diseases. We speculatively identify four broad functions of NPCs in the context of stroke: cell replacement, cytoprotection, remodeling of residual tissue, and immunomodulation. Thus, NPCs may have pleiotropic functions in supporting behavioral recovery after stroke.

Obesity-induced type 2 diabetes impairs neurological recovery after stroke in correlation with decreased neurogenesis and persistent atrophy of parvalbumin-positive interneurons

Type 2 diabetes (T2D) hampers stroke recovery though largely undetermined mechanisms. Few preclinical studies have investigated the effect of genetic/toxin-induced diabetes on long-term stroke recovery. However, the effects of obesity-induced T2D are mostly unknown. We aimed to investigate whether obesity-induced T2D worsens long-term stroke recovery through the impairment of brain's self-repair mechanisms - stroke-induced neurogenesis and parvalbumin (PV)+ interneurons-mediated neuroplasticity. To mimic obesity-induced T2D in the middle-age, C57bl/6j mice were fed 12 months with high-fat diet (HFD) and subjected to transient middle cerebral artery occlusion (tMCAO). We evaluated neurological recovery by upper-limb grip strength at 1 and 6 weeks after tMCAO. Gray and white matter damage, stroke-induced neurogenesis, and survival and potential atrophy of PV-interneurons were quantitated by immunohistochemistry (IHC) at 2 and 6 weeks after tMCAO. Obesity/T2D impaired neurological function without exacerbating brain damage. Moreover, obesity/T2D diminished stroke-induced neural stem cell (NSC) proliferation and neuroblast formation in striatum and hippocampus at 2 weeks after tMCAO and abolished stroke-induced neurogenesis in hippocampus at 6 weeks. Finally, stroke resulted in the atrophy of surviving PV-interneurons 2 weeks after stroke in both non-diabetic and obese/T2D mice. However, after 6 weeks, this effect selectively persisted in obese/T2D mice. We show in a preclinical setting of clinical relevance that obesity/T2D impairs neurological functions in the stroke recovery phase in correlation with reduced neurogenesis and persistent atrophy of PV-interneurons, suggesting impaired neuroplasticity. These findings shed light on the mechanisms behind impaired stroke recovery in T2D and could facilitate the development of new stroke rehabilitative strategies for obese/T2D patients.

Neural Stem Cells of the Subventricular Zone Contribute to Neuroprotection of the Corpus Callosum after Cuprizone-Induced Demyelination

Myelin loss occurring in demyelinating diseases, including multiple sclerosis, is the leading cause of long-lasting neurological disability in adults. While endogenous remyelination, driven by resident oligodendrocyte precursor cells (OPCs), might partially compensate myelin loss in the early phases of demyelinating disorders, this spontaneous reparative potential fails at later stages. To investigate the cellular mechanisms sustaining endogenous remyelination in demyelinating disorders, we focused our attention on endogenous neural precursor cells (eNPCs) located within the subventricular zone (SVZ) since this latter area is considered one of the primary sources of new OPCs in the adult forebrain. First, we fate mapped SVZ-eNPCs in cuprizone-induced demyelination and found that SVZ endogenous neural stem/precursor cells are recruited during the remyelination phase to the corpus callosum (CC) and are capable of forming new oligodendrocytes. When we ablated SVZ-derived eNPCs during cuprizone-induced demyelination in female mice, the animals displayed reduced numbers of oligodendrocytes within the lesioned CC. Although this reduction in oligodendrocytes did not impact the ensuing remyelination, eNPC-ablated mice experienced increased axonal loss. Our results indicate that, in toxic models of demyelination, SVZ-derived eNPCs contribute to support axonal survival.SIGNIFICANCE STATEMENT One of the significant challenges in MS research is to understand the detrimental mechanisms leading to the failure of CNS tissue regeneration during disease progression. One possible explanation is the inability of recruited oligodendrocyte precursor cells (OPCs) to complete remyelination and to sustain axonal survival. The contribution of endogenous neural precursor cells (eNPCs) located in the subventricular zone (SVZ) to generate new OPCs in the lesion site has been debated. Using transgenic mice to fate map and to selectively kill SVZ-derived eNPCs in the cuprizone demyelination model, we observed migration of SVZ-eNPCs after injury and their contribution to oligodendrogenesis and axonal survival. We found that eNPCs are dispensable for remyelination but protect partially from increased axonal loss.

Adaptive neurogenesis in the cerebral cortex and contralateral subventricular zone induced by unilateral cortical devascularization: Possible modulation by dopamine neurotransmission

Understanding endogenous neurogenesis and neuronal replacement to mature circuits is a topic of discussion as a therapeutic alternative under acute and chronic neurodegenerative disorders. Adaptive neurogenic response may result as a result of ischemia which could support long-term recovery of behavioral functions. Endogenous sources of neural progenitors may be stimulated by changes in blood flow or neuromodulation. Using a mouse model of unilateral cortical devascularization, we have observed reactive neurogenesis in the perilesional cortex and subventricular zone neurogenic niche. C57BL/6L 4 weeks old male mice were craneotomized at 1 mm caudal from frontal suture and 1 mm lateral from midline to generate a window of 3 mm side. Brain injury was produced by removal of the meninges and superficial vasculature of dorsal parietal cortex. BrdU agent (50 mg/kg, ip) was injected to lesioned and sham animals, during days 0 and 1 after surgery. Sagittal sections were analyzed at 1, 4, 7, and 10 days post-injury. A time-dependent increase in BrdU⁺ cells in the perilesional parietal cortex was accompanied by augmented BrdU⁺ cells in the sub ventricular and rostral migratory stream of ipsilateral and contralateral hemispheres. Neural progenitors and neuroblasts proliferated in the lesioned and non-lesioned subventricular zone and rostral migratory stream on day 4 after injury. Augmented contralateral neurogenesis was associated with an increase in vesicular monoamine transporter 2 protein in the striosomal sub ventricular neurogenic niche of non-lesioned hemisphere.

Transplanting Mesenchymal Stem Cells for Treatment of Ischemic Stroke

Stroke is a major disease that leads to high mortality and morbidity. Given the ageing population and the potential risk factors, the prevalence of stroke and socioeconomic burden associated with stroke are expected to increase. During the past decade, both prophylactic and therapeutic strategies for stroke have made significant progress. However, current therapies still cannot adequately improve the outcomes of stroke and may not apply to all patients. One of the significant advances in modern medicine is cell-derived neurovascular regeneration and neuronal repair. Progress in stem cell biology has greatly contributed to ameliorating stroke-related brain injuries in preclinical studies and demonstrated clinical potential in stroke treatment. Mesenchymal stem cells (MSCs) have the differentiating potential of chondrocytes, adipocytes, and osteoblasts, and they have the ability to transdifferentiate into endothelial cells, glial cells, and neurons. Due to their great plasticity, MSCs have drawn much attention from the scientific community. This review will focus on MSCs, stem cells widely utilized in current medical research, and evaluate their effect and potential of improving outcomes in ischemic stroke.

Mesenchymal Stem Cell Protection of Neurons against Glutamate Excitotoxicity Involves Reduction of NMDA-Triggered Calcium Responses and Surface GluR1, and Is Partly Mediated by TNF

Mesenchymal stem cells (MSC) provide therapeutic effects in experimental CNS disease models and show promise as cell-based therapies for humans, but their modes of action are not well understood. We previously show that MSC protect rodent neurons against glutamate excitotoxicity in vitro, and in vivo in an epilepsy model. Neuroprotection is associated with reduced NMDA glutamate receptor (NMDAR) subunit expression and neuronal glutamate-induced calcium (Ca²⁺) responses, and increased expression of stem cell-associated genes. Here, to investigate whether MSC-secreted factors modulate neuronal AMPA glutamate receptors (AMPAR) and gene expression, we performed longitudinal studies of enriched mouse cortical neurons treated with MSC conditioned medium (CM). MSC CM did not alter total levels of GluR1 AMPAR subunit in neurons, but its distribution, reducing cell surface levels compared to non-treated neurons. Proportions of NeuN-positive neurons, and of GFAP- and NG2-positive glia, were equal in untreated and MSC CM-treated cultures over time suggesting that neurons, rather than differentially-expanded glia, account for the immature gene profile previously reported in MSC CM-treated cultures. Lastly, MSC CM contained measurable amounts of tumor necrosis factor (TNF) bioactivity and pre-treatment of MSC CM with the TNF inhibitor etanercept reduced its ability to protect neurons. Together these results indicate that MSC-mediated neuroprotection against glutamate excitotoxicity involves reduced NMDAR and GluR1-containing AMPAR function, and TNF-mediated neuroprotection.

Selective killing of spinal cord neural stem cells impairs locomotor recovery in a mouse model of spinal cord injury

Background

Spinal cord injury (SCI) is a devastating condition mainly deriving from a traumatic damage of the spinal cord (SC). Immune cells and endogenous SC-neural stem cells (SC-NSCs) play a critical role in wound healing processes, although both are ineffective to completely restore tissue functioning. The role of SC-NSCs in SCI and, in particular, whether such cells can interplay with the immune response are poorly investigated issues, although mechanisms governing such interactions might open new avenues to develop novel therapeutic approaches.

Methods

We used two transgenic mouse lines to trace as well as to kill SC-NSCs in mice receiving SCI. We used Nestin CreERT2 mice to trace SC-NSCs descendants in the spinal cord of mice subjected to SCI. While mice carrying the suicide gene thymidine kinase (TK) along with the GFP reporter, under the control of the Nestin promoter regions (Nestin^TK mice) were used to label and selectively kill SC-NSCs.

Results

We found that SC-NSCs are capable to self-activate after SCI. In addition, a significant worsening of clinical and pathological features of SCI was observed in the Nestin^TK mice, upon selective ablation of SC-NSCs before the injury induction. Finally, mice lacking in SC-NSCs and receiving SCI displayed reduced levels of different neurotrophic factors in the SC and significantly higher number of M1-like myeloid cells.

Conclusion

Our data show that SC-NSCs undergo cell proliferation in response to traumatic spinal cord injury. Mice lacking SC-NSCs display overt microglia activation and exaggerate expression of pro-inflammatory cytokines. The absence of SC-NSCs impaired functional recovery as well as neuronal and oligodendrocyte cell survival. Collectively our data indicate that SC-NSCs can interact with microglia/macrophages modulating their activation/responses and that such interaction is importantly involved in mechanisms leading tissue recovery.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1085-9) contains supplementary material, which is available to authorized users.

Human Neural Stem Cells for Ischemic Stroke Treatment

Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. It takes place when the brain does not receive sufficient blood supply due to the blood clot in the vessels or narrowing of vessels' inner space due to accumulation of fat products. Apart from thrombolysis (dissolving of blood clot) and thrombectomy (surgical removal of blood clot or widening of vessel inner area) during the first hours after an ischemic stroke, no effective treatment to improve functional recovery exists in the post-ischemic phase. Due to their narrow therapeutic time window, thrombolysis and thrombectomy are unavailable to more than 80% of stroke patients.Many experimental studies carried out in animal models of stroke have demonstrated that stem cell transplantation may become a new therapeutic strategy in stroke. Transplantation of stem cells of different origin and stage of development has been shown to lead to improvement in experimental models of stroke through several mechanisms including neuronal replacement, modulation of cellular and synaptic plasticity and inflammation, neuroprotection and stimulation of angiogenesis. Several clinical studies and trials based on stem cell delivery in stroke patients are in progress with goal of improvements of functional recovery through mechanisms other than neuronal replacement. These approaches may provide therapeutic benefit, but generation of specific neurons for reconstruction of stroke-injured neural circuitry remains ultimate challenge. For this purpose, neural stem cells could be developed from multiple sources and fated to adopt required neuronal phenotype.

Intertwining extracellular nucleotides and their receptors with Ca2+ in determining adult neural stem cell survival, proliferation and final fate

In the central nervous system (CNS), during both brain and spinal cord development, purinergic and pyrimidinergic signalling molecules (ATP, UTP and adenosine) act synergistically with peptidic growth factors in regulating the synchronized proliferation and final specification of multipotent neural stem cells (NSCs) to neurons, astrocytes or oligodendrocytes, the myelin-forming cells. Some NSCs still persist throughout adulthood in both specific 'neurogenic' areas and in brain and spinal cord parenchyma, retaining the potentiality to generate all the three main types of adult CNS cells. Once CNS anatomical structures are defined, purinergic molecules participate in calcium-dependent neuron-to-glia communication and also control the behaviour of adult NSCs. After development, some purinergic mechanisms are silenced, but can be resumed after injury, suggesting a role for purinergic signalling in regeneration and self-repair also via the reactivation of adult NSCs. In this respect, at least three different types of adult NSCs participate in the response of the adult brain and spinal cord to insults: stem-like cells residing in classical neurogenic niches, in particular, in the ventricular-subventricular zone (V-SVZ), parenchymal oligodendrocyte precursor cells (OPCs, also known as NG2-glia) and parenchymal injury-activated astrocytes (reactive astrocytes). Here, we shall review and discuss the purinergic regulation of these three main adult NSCs, with particular focus on how and to what extent modulation of intracellular calcium levels by purinoceptors is mandatory to determine their survival, proliferation and final fate.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.

Olfactory function in an excitotoxic model for secondary neuronal degeneration: Role of dopaminergic interneurons

Secondary neuronal degeneration (SND) occurring in Traumatic brain injury (TBI) consists in downstream destructive events affecting cells that were not or only marginally affected by the initial wound, further increasing the effects of the primary injury. Glutamate excitotoxicity is hypothesized to play an important role in SND. TBI is a common cause of olfactory dysfunction that may be spontaneous and partially recovered. The role of the glutamate excitotoxicity in the TBI-induced olfactory dysfunction is still unknown. We investigated the effects of excitotoxicity induced by bilateral N-Methyl-D-Aspartate (NMDA) OB administration in the olfactory function, OB volumes, and subventricular zone (SVZ) and OB neurogenesis in rats. NMDA OB administration induced a decrease in the number of correct choices in the olfactory discrimination tests one week after lesions (p<0.01), and a spontaneous recovery of the olfactory deficit two weeks after lesions (p<0.05). A lack of correlation between OB volumes and olfactory function was observed. An increase in SVZ neurogenesis (Ki67+ cells, PSANCAM+ cells (p<0.01) associated with an increase in OB glomerular dopaminergic immunostaining (p<0.05) were related to olfactory function recovery. The present results show that changes in OB volumes cannot explain the recovery of the olfactory function and suggest a relevant role for dopaminergic OB interneurons in the pathophysiology of recovery of loss of smell in TBI.

Neural Stem Cell Transplantation Induces Stroke Recovery by Upregulating Glutamate Transporter GLT-1 in Astrocytes

Ischemic stroke is the leading cause of disability, but effective therapies are currently widely lacking. Recovery from stroke is very much dependent on the possibility to develop treatments able to both halt the neurodegenerative process as well as to foster adaptive tissue plasticity. Here we show that ischemic mice treated with neural precursor cell (NPC) transplantation had on neurophysiological analysis, early after treatment, reduced presynaptic release of glutamate within the ipsilesional corticospinal tract (CST), and an enhanced NMDA-mediated excitatory transmission in the contralesional CST. Concurrently, NPC-treated mice displayed a reduced CST degeneration, increased axonal rewiring, and augmented dendritic arborization, resulting in long-term functional amelioration persisting up to 60 d after ischemia. The enhanced functional and structural plasticity relied on the capacity of transplanted NPCs to localize in the peri-ischemic and ischemic area, to promote the upregulation of the glial glutamate transporter 1 (GLT-1) on astrocytes and to reduce peri-ischemic extracellular glutamate. The upregulation of GLT-1 induced by transplanted NPCs was found to rely on the secretion of VEGF by NPCs. Blocking VEGF during the first week after stroke reduced GLT-1 upregulation as well as long-term behavioral recovery in NPC-treated mice. Our results show that NPC transplantation, by modulating the excitatory-inhibitory balance and stroke microenvironment, is a promising therapy to ameliorate disability, to promote tissue recovery and plasticity processes after stroke.

SIGNIFICANCE STATEMENT

Tissue damage and loss of function occurring after stroke can be constrained by fostering plasticity processes of the brain. Over the past years, stem cell transplantation for repair of the CNS has received increasing interest, although underlying mechanism remain elusive. We here show that neural stem/precursor cell transplantation after ischemic stroke is able to foster axonal rewiring and dendritic plasticity and to induce long-term functional recovery. The observed therapeutic effect of neural precursor cells seems to underlie their capacity to upregulate the glial glutamate transporter on astrocytes through the vascular endothelial growth factor inducing favorable changes in the electrical and molecular stroke microenvironment. Cell-based approaches able to influence plasticity seem particularly suited to favor poststroke recovery.

Neural Stem Cell Plasticity: Advantages in Therapy for the Injured Central Nervous System

The physiological and pathological properties of the neural germinal stem cell niche have been well-studied in the past 30 years, mainly in animals and within given limits in humans, and knowledge is available for the cyto-architectonic structure, the cellular components, the timing of development and the energetic maintenance of the niche, as well as for the therapeutic potential and the cross talk between neural and immune cells. In recent years we have gained detailed understanding of the potentiality of neural stem cells (NSCs), although we are only beginning to understand their molecular, metabolic, and epigenetic profile in physiopathology and, further, more can be invested to measure quantitatively the activity of those cells, to model in vitro their therapeutic responses or to predict interactions in silico. Information in this direction has been put forward for other organs but is still limited in the complex and very less accessible context of the brain. A comprehensive understanding of the behavior of endogenous NSCs will help to tune or model them toward a desired response in order to treat complex neurodegenerative diseases. NSCs have the ability to modulate multiple cellular functions and exploiting their plasticity might make them into potent and versatile cellular drugs.

Neurogenesis upregulation on the healthy hemisphere after stroke enhances compensation for age-dependent decrease of basal neurogenesis

Stroke is a leading cause of death and disability worldwide with no treatment for the chronic phase available. Interestingly, an endogenous repair program comprising inflammation and neurogenesis is known to modulate stroke outcome. Several studies have shown that neurogenesis decreases with age but the therapeutic importance of endogenous neurogenesis for recovery from cerebral diseases has been indicated as its ablation leads to stroke aggravation and worsened outcome. A detailed characterization of the neurogenic response after stroke related to ageing would help to develop novel and targeted therapies. In an innovative approach, we used the DCX-Luc mouse, a transgenic model expressing luciferase in doublecortin-positive neuroblasts, to monitor the neurogenic response following middle cerebral artery occlusion over three weeks in three age groups (2, 6, 12months) by optical imaging while the stroke lesion was monitored by quantitative MRI. The individual longitudinal and noninvasive time profiles provided exclusive insight into age-dependent decrease in basal neurogenesis and neurogenic upregulation in response to stroke which are not accessible by conventional BrdU-based measures of cell proliferation. For cortico-striatal strokes the maximal upregulation occurred at 4days post stroke followed by a continuous decrease to basal levels by three weeks post stroke. Older animals effectively compensated for reduced basal neurogenesis by an enhanced sensitivity to the cerebral lesion, resulting in upregulated neurogenesis levels approaching those measured in young mice. In middle aged and older mice, but not in the youngest ones, additional upregulation of neurogenesis was observed in the contralateral healthy hemisphere. This further substantiates the increased propensity of older brains to respond to lesion situation. Our results clearly support the therapeutic relevance of endogenous neurogenesis for stroke recovery and particularly in older brains.

Cannabinoid Type-2 Receptor Drives Neurogenesis and Improves Functional Outcome After Stroke

BACKGROUND AND PURPOSE

Stroke is a leading cause of adult disability characterized by physical, cognitive, and emotional disturbances. Unfortunately, pharmacological options are scarce. The cannabinoid type-2 receptor (CB2R) is neuroprotective in acute experimental stroke by anti-inflammatory mechanisms. However, its role in chronic stroke is still unknown.

METHODS

Stroke was induced by permanent middle cerebral artery occlusion in mice; CB2R modulation was assessed by administering the CB2R agonist JWH133 ((6aR,10aR)-3-(1,1-dimethylbutyl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran) or the CB2R antagonist SR144528 (N-[(1S)-endo-1,3,3-trimethylbicyclo-[2.2.1]-heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide) once daily from day 3 to the end of the experiment or by CB2R genetic deletion. Analysis of immunofluorescence-labeled brain sections, 5-bromo-2´-deoxyuridine (BrdU) staining, fluorescence-activated cell sorter analysis of brain cell suspensions, and behavioral tests were performed.

RESULTS

SR144528 decreased neuroblast migration toward the boundary of the infarct area when compared with vehicle-treated mice 14 days after middle cerebral artery occlusion. Consistently, mice on this pharmacological treatment, like mice with CB2R genetic deletion, displayed a lower number of new neurons (NeuN⁺/BrdU⁺ cells) in peri-infarct cortex 28 days after stroke when compared with vehicle-treated group, an effect accompanied by a worse sensorimotor performance in behavioral tests. The CB2R agonist did not affect neurogenesis or outcome in vivo, but increased the migration of neural progenitor cells in vitro; the CB2R antagonist alone did not affect in vitro migration.

CONCLUSIONS

Our data support that CB2R is fundamental for driving neuroblast migration and suggest that an endocannabinoid tone is required for poststroke neurogenesis by promoting neuroblast migration toward the injured brain tissue, increasing the number of new cortical neurons and, conceivably, enhancing motor functional recovery after stroke.

Beneficial Effects of Co-Ultramicronized Palmitoylethanolamide/Luteolin in a Mouse Model of Autism and in a Case Report of Autism

AIMS

Autism spectrum disorder (ASD) is a condition defined by social communication deficits and repetitive restrictive behaviors. Association of the fatty acid amide palmitoylethanolamide (PEA) with the flavonoid luteolin displays neuroprotective and antiinflammatory actions in different models of central nervous system pathologies. We hypothesized that association of PEA with luteolin might have therapeutic utility in ASD, and we employed a well-recognized autism animal model, namely sodium valproate administration, to evaluate cognitive and motor deficits.

METHODS

Two sets of experiments were conducted. In the first, we investigated the effect of association of ultramicronized PEA with luteolin, co-ultramicronized PEA-LUT® (co-ultraPEA-LUT®) in a murine model of autistic behaviors, while in the second, the effect of co-ultraPEA-LUT® in a patient affected by ASD was examined.

RESULTS

Co-ultraPEA-LUT® treatment ameliorated social and nonsocial behaviors in valproic acid-induced autistic mice and improved clinical picture with reduction in stereotypes in a 10-year-old male child.

CONCLUSION

These data suggest that ASD symptomatology may be improved by agents documented to control activation of mast cells and microglia. Co-ultraPEA-LUT® might be a valid and safe therapy for the symptoms of ASD alone or in combination with other used drugs.

Glutamate Increases In Vitro Survival and Proliferation and Attenuates Oxidative Stress-Induced Cell Death in Adult Spinal Cord-Derived Neural Stem/Progenitor Cells via Non-NMDA Ionotropic Glutamate Receptors

Traumatic spinal cord injury (SCI) leads to a cascade of secondary chemical insults, including oxidative stress and glutamate excitotoxicity, which damage host neurons and glia. Transplantation of exogenous neural stem/progenitor cells (NSPCs) has shown promise in enhancing regeneration after SCI, although survival of transplanted cells remains poor. Understanding the response of NSPCs to the chemical mediators of secondary injury is essential in finding therapies to enhance survival. We examined the in vitro effects of glutamate and glutamate receptor agonists on adult rat spinal cord-derived NSPCs. NSPCs isolated from the periventricular region of the adult rat spinal cord were exposed to various concentrations of glutamate for 96 h. We found that glutamate treatment (500 μM) for 96 h significantly increased live cell numbers, reduced cell death, and increased proliferation, but did not significantly alter cell phenotype. Concurrent glutamate treatment (500 μM) in the setting of H2O2 exposure (500 μM) for 10 h increased NSPC survival compared to H2O2 exposure alone. The effects of glutamate on NSPCs were blocked by the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonist GYKI-52466, but not by the N-methyl-D-aspartic acid receptor antagonist MK-801 or DL-AP5, or the mGluR3 antagonist LY-341495. Furthermore, treatment of NSPCs with AMPA, kainic acid, or the kainate receptor-specific agonist (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid mimicked the responses seen with glutamate both alone and in the setting of oxidative stress. These findings offer important insights into potential mechanisms to enhance NSPC survival and implicate a potential role for glutamate in promoting NSPC survival and proliferation after traumatic SCI.

Co-Ultramicronized Palmitoylethanolamide/Luteolin Promotes Neuronal Regeneration after Spinal Cord Injury

Spinal cord injury (SCI) stimulates activation of astrocytes and infiltration of immune cells at the lesion site; however, the mechanism that promotes the birth of new neurons is still under debate. Neuronal regeneration is restricted after spinal cord injury, but can be stimulated by experimental intervention. Previously we demonstrated that treatment co-ultramicronized palmitoylethanolamide and luteolin, namely co-ultraPEALut, reduced inflammation. The present study was designed to explore the neuroregenerative properties of co-ultraPEALut in an estabished murine model of SCI. A vascular clip was applied to the spinal cord dura at T5-T8 to provoke injury. Mice were treated with co-ultraPEALut (1 mg/kg, intraperitoneally) daily for 72 h after SCI. Co-ultraPEALut increased the numbers of both bromodeoxyuridine-positive nuclei and doublecortin-immunoreactive cells in the spinal cord of injured mice. To correlate neuronal development with synaptic plasticity a Golgi method was employed to analyze dendritic spine density. Co-ultraPEALut administration stimulated expression of the neurotrophic factors brain-derived neurotrophic factor, glial cell-derived neurotrophic factor, nerve growth factor, and neurotrophin-3. These findings show a prominent effect of co-ultraPEALut administration in the management of survival and differentiation of new neurons and spine maturation, and may represent a therapeutic treatment for spinal cord and other traumatic diseases.

Neurogenesis following Stroke Affecting the Adult Brain

A bulk of experimental evidence supports the idea that the stroke-damaged adult brain makes an attempt to repair itself by producing new neurons also in areas where neurogenesis does not normally occur (e.g., the striatum and cerebral cortex). Knowledge about mechanisms regulating the different steps of neurogenesis after stroke is rapidly increasing but still incomplete. The functional consequences of stroke-induced neurogenesis and the level of integration of the new neurons into existing neural circuitries are poorly understood. To have a substantial impact on the recovery after stroke, this potential mechanism for self-repair needs to be enhanced, primarily by increasing the survival and differentiation of the generated neuroblasts. Moreover, for efficient repair, optimization of neurogenesis most likely needs to be combined with promotion of other endogenous neuroregenerative responses (e.g., protection and sprouting of remaining mature neurons, transplantation of neural stem/progenitor cells [NSPC]-derived neurons and glia cells, and modulation of inflammation).

Prenatal exposure to cannabinoids evokes long-lasting functional alterations by targeting CB1 receptors on developing cortical neurons

The CB1 cannabinoid receptor, the main target of Δ(9)-tetrahydrocannabinol (THC), the most prominent psychoactive compound of marijuana, plays a crucial regulatory role in brain development as evidenced by the neurodevelopmental consequences of its manipulation in animal models. Likewise, recreational cannabis use during pregnancy affects brain structure and function of the progeny. However, the precise neurobiological substrates underlying the consequences of prenatal THC exposure remain unknown. As CB1 signaling is known to modulate long-range corticofugal connectivity, we analyzed the impact of THC exposure on cortical projection neuron development. THC administration to pregnant mice in a restricted time window interfered with subcerebral projection neuron generation, thereby altering corticospinal connectivity, and produced long-lasting alterations in the fine motor performance of the adult offspring. Consequences of THC exposure were reminiscent of those elicited by CB1 receptor genetic ablation, and CB1-null mice were resistant to THC-induced alterations. The identity of embryonic THC neuronal targets was determined by a Cre-mediated, lineage-specific, CB1 expression-rescue strategy in a CB1-null background. Early and selective CB1 reexpression in dorsal telencephalic glutamatergic neurons but not forebrain GABAergic neurons rescued the deficits in corticospinal motor neuron development of CB1-null mice and restored susceptibility to THC-induced motor alterations. In addition, THC administration induced an increase in seizure susceptibility that was mediated by its interference with CB1-dependent regulation of both glutamatergic and GABAergic neuron development. These findings demonstrate that prenatal exposure to THC has long-lasting deleterious consequences in the adult offspring solely mediated by its ability to disrupt the neurodevelopmental role of CB1 signaling.

Subventricular zone neural progenitors reverse TNF-alpha effects in cortical neurons

INTRODUCTION

Tumor necrosis factor alpha (TNFα) plays a physiological role in controlling synaptic transmission and plasticity in the healthy central nervous system by modulating glutamate receptor trafficking to the plasma membrane. TNFα expression is also rapidly induced in response to tissue injury and infection. By promoting the insertion of Ca(2+) permeable-AMPA receptors into the neuronal plasma membrane, this cytokine may cause excessive Ca(2+) influx into neurons, thus enhancing neuronal death.

METHODS

Primary cultures of cortical neurons were obtained from E18 foetal mice and incubated for 24 h with adult neural stem cells (aNPCs) either stimulated with lipopolysaccharide (LPS(+)aNPCs) or not (aNPCs). Cultures were treated with TNFα (100 ng/ml), and electrophysiological recordings were performed in different conditions to evaluate the effect of the cytokine on neuronal transmission.

RESULTS

In this study, we demonstrate that aNPCs from the subventricular zone reverse the effects induced by the cytokine. Moreover, we show that the effect of aNPCs on cortical neurons is mediated by cannabinoid CB1 receptor activation.

CONCLUSION

These data suggest that the role of aNPCs in preventing excitatory neurotransmission potentiation induced by TNFα on cortical neurons may have important implications for pathologies characterized by an inflammatory component affecting cortical neurons such as Alzheimer's disease.

The role of cannabinoids in adult neurogenesis

The processes underpinning post-developmental neurogenesis in the mammalian brain continue to be defined. Such processes involve the proliferation of neural stem cells and neural progenitor cells (NPCs), neuronal migration, differentiation and integration into a network of functional synapses within the brain. Both intrinsic (cell signalling cascades) and extrinsic (neurotrophins, neurotransmitters, cytokines, hormones) signalling molecules are intimately associated with adult neurogenesis and largely dictate the proliferative activity and differentiation capacity of neural cells. Cannabinoids are a unique class of chemical compounds incorporating plant-derived cannabinoids (the active components of Cannabis sativa), the endogenous cannabinoids and synthetic cannabinoid ligands, and these compounds are becoming increasingly recognized for their roles in neural developmental processes. Indeed, cannabinoids have clear modulatory roles in adult neurogenesis, probably through activation of both CB1 and CB2 receptors. In recent years, a large body of literature has deciphered the signalling networks involved in cannabinoid-mediated regulation of neurogenesis. This timely review summarizes the evidence that the cannabinoid system is intricately associated with neuronal differentiation and maturation of NPCs and highlights intrinsic/extrinsic signalling mechanisms that are cannabinoid targets. Overall, these findings identify the central role of the cannabinoid system in adult neurogenesis in the hippocampus and the lateral ventricles and hence provide insight into the processes underlying post-developmental neurogenesis in the mammalian brain.

The potential use of mesenchymal stem cells in stroke therapy--From bench to bedside

Stroke is the second main cause of morbidity and mortality worldwide. The rationale for the use of mesenchymal stem cells (MSCs) in stroke is based on the capacity of MSCs to secrete a large variety of bioactive molecules such as growth factors, cytokines and chemokines leading to reduction of inflammation, increased neurogenesis from the germinative niches of central nervous system, increased angiogenesis, effects on astrocytes, oligodendrocytes and axons. This review presents the data derived from experimental studies and the evidence available from clinical trials about the use of MSCs in stroke therapy.

Endogenous neural stem/progenitor cells stabilize the cortical microenvironment after traumatic brain injury

Although a myriad of pathological responses contribute to traumatic brain injury (TBI), cerebral dysfunction has been closely linked to cell death mechanisms. A number of therapeutic strategies have been studied in an attempt to minimize or ameliorate tissue damage; however, few studies have evaluated the inherent protective capacity of the brain. Endogenous neural stem/progenitor cells (NSPCs) reside in distinct brain regions and have been shown to respond to tissue damage by migrating to regions of injury. Until now, it remained unknown whether these cells have the capacity to promote endogenous repair. We ablated NSPCs in the subventricular zone to examine their contribution to the injury microenvironment after controlled cortical impact (CCI) injury. Studies were performed in transgenic mice expressing the herpes simplex virus thymidine kinase gene under the control of the nestin(δ) promoter exposed to CCI injury. Two weeks after CCI injury, mice deficient in NSPCs had reduced neuronal survival in the perilesional cortex and fewer Iba-1-positive and glial fibrillary acidic protein-positive glial cells but increased glial hypertrophy at the injury site. These findings suggest that the presence of NSPCs play a supportive role in the cortex to promote neuronal survival and glial cell expansion after TBI injury, which corresponds with improvements in motor function. We conclude that enhancing this endogenous response may have acute protective roles after TBI.

Programming of neural cells by (endo)cannabinoids: from physiological rules to emerging therapies

Among the many signalling lipids, endocannabinoids are increasingly recognized for their important roles in neuronal and glial development. Recent experimental evidence suggests that, during neuronal differentiation, endocannabinoid signalling undergoes a fundamental switch from the prenatal determination of cell fate to the homeostatic regulation of synaptic neurotransmission and bioenergetics in the mature nervous system. These studies also offer novel insights into neuropsychiatric disease mechanisms and contribute to the public debate about the benefits and the risks of cannabis use during pregnancy and in adolescence.

Endogenous neurogenesis following ischaemic brain injury: insights for therapeutic strategies

Ischaemic stroke is among the most common yet most intractable types of central nervous system (CNS) injury in the adult human population. In the acute stages of disease, neurons in the ischaemic lesion rapidly die and other neuronal populations in the ischaemic penumbra are vulnerable to secondary injury. Multiple parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. Accumulating evidence indicates that cerebral ischaemia initiates an endogenous regenerative response within the adult brain that potentiates adult neurogenesis from populations of neural stem and progenitor cells. A major research focus has been to understand the cellular and molecular mechanisms that underlie the potentiation of adult neurogenesis and to appreciate how interventions designed to modulate these processes could enhance neural regeneration in the post-ischaemic brain. In this review, we highlight recent advances over the last 5 years that help unravel the cellular and molecular mechanisms that potentiate endogenous neurogenesis following cerebral ischaemia and are dissecting the functional importance of this regenerative mechanism following brain injury. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.

Inflammation in neurodegenerative diseases--an update

Neurodegeneration, the progressive dysfunction and loss of neurons in the central nervous system (CNS), is the major cause of cognitive and motor dysfunction. While neuronal degeneration is well-known in Alzheimer's and Parkinson's diseases, it is also observed in neurotrophic infections, traumatic brain and spinal cord injury, stroke, neoplastic disorders, prion diseases, multiple sclerosis and amyotrophic lateral sclerosis, as well as neuropsychiatric disorders and genetic disorders. A common link between these diseases is chronic activation of innate immune responses including those mediated by microglia, the resident CNS macrophages. Such activation can trigger neurotoxic pathways leading to progressive degeneration. Yet, microglia are also crucial for controlling inflammatory processes, and repair and regeneration. The adaptive immune response is implicated in neurodegenerative diseases contributing to tissue damage, but also plays important roles in resolving inflammation and mediating neuroprotection and repair. The growing awareness that the immune system is inextricably involved in mediating damage as well as regeneration and repair in neurodegenerative disorders, has prompted novel approaches to modulate the immune system, although it remains whether these approaches can be used in humans. Additional factors in humans include ageing and exposure to environmental factors such as systemic infections that provide additional clues that may be human specific and therefore difficult to translate from animal models. Nevertheless, a better understanding of how immune responses are involved in neuronal damage and regeneration, as reviewed here, will be essential to develop effective therapies to improve quality of life, and mitigate the personal, economic and social impact of these diseases.

Juvenile cannabinoid treatment induces frontostriatal gliogenesis in Lewis rats

Cannabis abuse in adolescence is associated with a broad array of phenotypical consequences, including a higher risk for schizophrenia and other mental disturbances related to dopamine (DA) imbalances. The great variability of these sequelae likely depends on the key influence of diverse genetic vulnerability factors. Inbred rodent strains afford a highly informative tool to study the contribution of genetic determinants to the long-term effects of juvenile cannabinoid exposure. In this study, we analyzed the phenotypical impact of the synthetic cannabinoid agonist WIN 55,212-2 (WIN; 2mg/kg/day from postnatal day 35-48) in adolescent Lewis rats, an inbred strain exhibiting resistance to psychotomimetic effects of environmental manipulations. At the end of this treatment, WIN-injected animals displayed increased survival of new cells (mainly oligodendroglia precursors) in the striatum and prefrontal cortex (PFC), two key terminal fields of DAergic pathways. To test whether these changes may be associated with enduring behavioral alterations, we examined the consequences of adolescent WIN treatment in adulthood (postnatal days 60-70), with respect to DA levels and metabolism as well as multiple behavioral paradigms. Rats injected with WIN exhibited increased turnover, but not levels, of striatal DA. In addition, cannabinoid-treated animals displayed increases in acoustic startle latency and novel-object exploration; however, WIN treatment failed to induce overt deficits of sensorimotor gating and social interaction. These results indicate that, in Lewis rats, juvenile cannabinoid exposure leads to alterations in frontostriatal gliogenesis, as well as select behavioral alterations time-locked to high DAergic metabolism, but not overt schizophrenia-related deficits.

Beyond cell replacement: unresolved roles of NG2-expressing progenitors

NG2-expressing parenchymal precursors (NG2+p) serve as primary source of myelinating oligodendrocytes in both the developing and adult Central Nervous System (CNS). However, their abundance, limited differentiation potential at adult stages along with stereotypic reaction to injury independent of the extent of myelin loss suggest that NG2+p exert functions additional to myelin production. In support of this view, NG2+p express a complex battery of molecules known to exert neuromodulatory and neuroprotective functions. Further, they establish intimate physical associations with the other CNS cell types, receive functional synaptic contacts and possess ion channels apt to constantly sense the electrical activity of surrounding neurons. These latter features could endow NG2+p with the capability to affect neuronal functions with potential homeostatic outcomes. Here we summarize and discuss current evidence favoring the view that NG2+p can participate in circuit formation, modulate neuronal activity and survival in the healthy and injured CNS, and propose perspectives for studies that may complete our understanding of NG2+p roles in physiology and pathology.