Neuronal precursors within the adult rat subventricular zone differentiate into dopaminergic neurons after substantia nigra lesion and chromaffin cell transplant

Mechanisms Involved in Neuroprotective Effects of Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is widely used in neurophysiology to study cortical excitability. Research over the last few decades has highlighted its added value as a potential therapeutic tool in the treatment of a broad range of psychiatric disorders. More recently, a number of studies have reported beneficial and therapeutic effects for TMS in neurodegenerative conditions and strokes. Yet, despite its recognised clinical applications and considerable research using animal models, the molecular and physiological mechanisms through which TMS exerts its beneficial and therapeutic effects remain unclear. They are thought to involve biochemical-molecular events affecting membrane potential and gene expression. In this aspect, the dopaminergic system plays a special role. This is the most directly and selectively modulated neurotransmitter system, producing an increase in the flux of dopamine (DA) in various areas of the brain after the application of repetitive TMS (rTMS). Other neurotransmitters, such as glutamate and gamma-aminobutyric acid (GABA) have shown a paradoxical response to rTMS. In this way, their levels increased in the hippocampus and striatum but decreased in the hypothalamus and remained unchanged in the mesencephalon. Similarly, there are sufficient evidence that TMS up-regulates the gene expression of BDNF (one of the main brain neurotrophins). Something similar occurs with the expression of genes such as c-Fos and zif268 that encode trophic and regenerative action neuropeptides. Consequently, the application of TMS can promote the release of molecules involved in neuronal genesis and maintenance. This capacity may mean that TMS becomes a useful therapeutic resource to antagonize processes that underlie the previously mentioned neurodegenerative conditions.

Repetitive Deep TMS for Parkinson Disease: A 3-Month Double-Blind, Randomized Sham-Controlled Study

PURPOSE

To study the effects of a repetitive deep transcranial magnetic stimulation (rDTMS) in patients with Parkinson disease using the H5 coil for the low-frequency stimulation of the primary motor cortex, followed by the high-frequency rDTMS of the prefrontal cortex.

METHODS

The main outcome measures were the total and motor scores of the Unified Parkinson's Disease Rating Scale (UPDRS). Secondary measures included rating of depression and quantitative motor tasks.

RESULTS

Forty-eight patients were randomized 1:1 into real or sham rDTMS treatment arms. Analyses (n = 42) of both UPDRS scores revealed a significant main effect for time between baseline and day 90 (end of treatment), indicating that there was an improvement of both scores over time in the whole sample. Although effects of treatment and time-by-treatment were insignificant, simple effects analysis of both measures was significant in the rDTMS group and reached a P-value of 0.06 in the sham group. The response rate was higher in patients with longer disease duration and higher motor UPDRS scores. Side effects were more common in the rDTMS group but were transient and tolerable.

CONCLUSIONS

Although rDTMS treatment exhibited some motor improvements, we could not demonstrate an advantage for real treatment over sham. Further research is required to establish stimulation parameters that may induce potentially more beneficial outcomes, probably in patients with longer and more sever disease.

Neuroprotective Effect of Low Frequency-Pulsed Electromagnetic Fields in Ischemic Stroke

Low frequency-pulsed electromagnetic fields (LF-PEMFs) affect many biological processes; however, the fundamental mechanisms responsible for these effects remain unclear. Our study aimed to investigate the effect of LF-PEMFs on neuroprotection after ischemic stroke. C57B6 mice were exposed to LF-PEMF (F = 60 Hz, Bm = 10 mT) after photothrombotic occlusion. We measured the BDNF/TrkB/Akt signaling pathway, pro-apoptotic and pro-survival protein and gene expressions, and the expression of inflammatory mediators and performed behavioral tests in both LF-PEMF-treated and untreated ischemic stroke mice. Our results showed that LF-PEMF treatment promotes activation of the BDNF/TrkB/Akt signaling pathway. Subsequently, pro-survival proteins were significantly increased, while pro-apoptotic proteins and inflammatory mediators were decreased in ischemic stroke mice after LF-PEMF treatment. The results demonstrated that LF-PEMF exposure has a neuroprotective effect after ischemic stroke in mice during the recovery process.

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.

Neural stem cells in Parkinson's disease: a role for neurogenesis defects in onset and progression

Parkinson's disease (PD) is the second most common neurodegenerative disorder, leading to a variety of motor and non-motor symptoms. Interestingly, non-motor symptoms often appear a decade or more before the first signs of motor symptoms. Some of these non-motor symptoms are remarkably similar to those observed in cases of impaired neurogenesis and several PD-related genes have been shown to play a role in embryonic or adult neurogenesis. Indeed, animal models deficient in Nurr1, Pitx3, SNCA and PINK1 display deregulated embryonic neurogenesis and LRRK2 and VPS35 have been implicated in neuronal development-related processes such as Wnt/β-catenin signaling and neurite outgrowth. Moreover, adult neurogenesis is affected in both PD patients and PD animal models and is regulated by dopamine and dopaminergic (DA) receptors, by chronic neuroinflammation, such as that observed in PD, and by differential expression of wild-type or mutant forms of PD-related genes. Indeed, an increasing number of in vivo studies demonstrate a role for SNCA and LRRK2 in adult neurogenesis and in the generation and maintenance of DA neurons. Finally, the roles of PD-related genes, SNCA, LRRK2, VPS35, Parkin, PINK1 and DJ-1 have been studied in NSCs, progenitor cells and induced pluripotent stem cells, demonstrating a role for some of these genes in stem/progenitor cell proliferation and maintenance. Together, these studies strongly suggest a link between deregulated neurogenesis and the onset and progression of PD and present strong evidence that, in addition to a neurodegenerative disorder, PD can also be regarded as a developmental disorder.

Allopregnanolone and neurogenesis in the nigrostriatal tract

Reinstalling the neurobiological circuits to effectively change the debilitating course of neurodegenerative diseases is of utmost importance. This reinstallation requires generation of new cells which are able to differentiate into specific types of neurons and modification of the local environment suitable for integration of these new neurons into the neuronal circuits. Allopregnanolone (APα) seems to be involved in both of these processes, and therefore, is a potential neurotrophic agent. Loss of dopamine neurons in the substantia nigra (SN) is one of the main pathological features of Parkinson’s and also in, at least, a subset of Alzheimer’s patients. Therefore, reinstallation of the dopamine neurons in nigrostriatal tract is of unique importance for these neurodegenerative diseases. However, for the neurogenic status and the roles of allopregnanolone in the nigrostriatal tract, the evidence is accumulating and debating. This review summarizes recent studies regarding the neurogenic status in the nigrostriatal tract. Furthermore, special attention is placed on evidence suggesting that reductions in allopregnenalone levels are one of the major pathological features in PD and AD. This evidence has also been confirmed in brains of mice that were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or those bearing neurodegenerative mutations. Lastly, we highlight studies showing that allopregnanalone can augment the number of total cells and dopaminergic neurons via peripheral exogenous administration.

Effects of hypocretin/orexin cell transplantation on narcoleptic-like sleep behavior in rats

The sleep disorder narcolepsy is now considered a neurodegenerative disease because there is a massive loss of neurons containing the neuropeptide hypocretin/orexin (HCRT). In consequence, narcoleptic patients have very low cerebrospinal fluid (CSF) levels of HCRT. Studies in animal models of narcolepsy have shown the neurophysiological role of the HCRT system in the development of this disease. For example, the injection of the neurotoxin named hypocretin-2-saporin (HCRT2/SAP) into the lateral hypothalamus (LH) destroys the HCRT neurons, therefore diminishes the contents of HCRT in the CSF and induces narcoleptic-like behavior in rats. Transplants of various cell types have been used to induce recovery in a variety of neurodegenerative animal models. In models such as Parkinson's disease, cell survival has been shown to be small but satisfactory. Similarly, cell transplantation could be employed to implant grafts of HCRT cells into the LH or even other brain regions to treat narcolepsy. Here, we report for the first time that transplantation of HCRT neurons into the LH of HCRT2/SAP-lesioned rats diminishes narcoleptic-like sleep behavior. Therefore, cell transplantation may provide an effective method to treat narcolepsy.

Resident adult neural stem cells in Parkinson's disease--the brain's own repair system?

One important pathological process in the brain of Parkinson disease (PD) patients is the degeneration of the dopaminergic neurons in the substantia nigra, which leads to a decline in striatal dopamine levels and motor dysfunction. A major clinical problem is that this degenerative process currently cannot be stopped or reversed. Expectations from the restorative capacity of neural stem cells (NSCs) are high, as these cells can potentially replace the degenerating neurons. The discovery of the presence of NSCs in the adult human brain has instigated research into the potential of these cells as a resource to promote brain repair in neurodegenerative diseases. Neural stem and progenitor cells reside in the subventricular zone (SVZ), which is closely situated to the striatum, which is affected in PD. Therefore, restoring the dopamine levels in the striatum of PD patients through stimulating endogenous NSCs in the nearby SVZ to migrate into the striatum and differentiate into dopaminergic neurons might thus be an attractive future therapeutic approach. We will review the reported changes in NSCs in the SVZ of PD animal models and PD patients, which are due to a lack of striatal dopamine. Furthermore, we will summarise the reports that describe efforts to stimulate NSCs to replace dopaminergic cells in the SN and restore striatal dopamine levels. In our opinion, mobilizing the endogenous SVZ NSCs to replenish striatal dopamine is an attractive approach to alleviate the motor symptoms in PD patients, without the ethical and immunological challenges of transplantation of NSCs and foetal brain tissue.

Implications for preserving neural stem cells in whole brain radiotherapy and prophylactic cranial irradiation: a review of 2270 metastases in 488 patients

This study delineated the incidence of metastatic involvement of neural stem cell (NSC) regions and further aimed to explore the feasibility of selectively sparing the NSC compartments during whole brain radiotherapy (WBRT) and prophylactic cranial irradiation (PCI). A total of 2270 intracranial metastases in 488 patients were identified. Lesions were classified according to locations, including lesions in the NSC compartments (subventricular zone, SVZ, or hippocampus) and those in the rest of the brain/brainstem. The incidence of involvement of NSC regions was compared between oligometastatic patients (those with 1-4 lesions) and non-oligometastatic patients (those with 5 or more lesions) using a chi-square test. The volume of the NSC regions accounted for 2.23% of the whole brain, and the overall rate of metastatic lesions in NSC regions was 1.1% in 2270 metastases (25/2270), and 4.7% in 488 patients (23/488). Of the NSC region metastases, 7 (0.3%) involved the hippocampus and 18 (0.8%) occurred in the SVZ. Among the 7 hippocampal metastases identified in this study, 1/7 (14.3%) were found in oligometastatic patients, while 6/7 (85.7%) metastases were in non-oligometastatic patients. For metastases in the SVZ, all lesions occurred in non-oligometastatic patients with none in oligometastatic patients. Metastatic involvement of the NSC compartments was significantly lower in oligometastatic patients (0.15%, 1/670) than in non-oligometastatic patients (1.5%, 24/1600) (P < 0.001). Our retrospective review of 2270 metastases in 488 patients is that the volume of the compartments of NSC regions was 2.23% relative to the whole brain, but the incidence of involvement of the NSC compartments was 1.1%, and the vast majority of NSC lesions were found in non-oligometastatic patients. We believe our data supports selective reduction of doses for these aforementioned structures, when treating oligometastatic patients with WBRT and locally advanced-stage small-cell lung cancer patients with PCI.

Adeno-associated virus type 2 vector-mediated glial cell line-derived neurotrophic factor gene transfer induces neuroprotection and neuroregeneration in a ubiquitin-proteasome system impairment animal model of Parkinson's disease

BACKGROUND

The impairment of the ubiquitin-proteasome system (UPS) is a cellular mechanism underlying the neurodegenerative process in Parkinson's disease (PD). A mouse model induced by the selective proteasome inhibitor lactacystin targeting on substantia nigra has been demonstrated to be valuable in investigating etiopathogenesis and neuroprotection for PD.

OBJECTIVE

In the present study, we used adeno-associated virus type 2 vector (AAV2) encoding glial cell line-derived neurotrophic factor (GDNF) injected into the striatum of this animal model to test the effectiveness and possible mechanisms of GDNF gene therapy.

RESULTS

Our results showed that AAV2-mediated GDNF gene therapy significantly attenuated lactacystin-induced loss of nigral dopamine (DA) neurons and striatal DA levels. Furthermore, we found that GDNF protein is mostly expressed in astrocytes in the subventricular zone (SVZ) and dentate gyrus (DG). AAV2-mediated GDNF therapy can induce neurogenesis in the SVZ and DG, and increase the number of nigral newborn DA neurons.

CONCLUSION

These data indicate that AAV2-mediated GDNF gene therapy can protect the nigral DA neurons from the UPS impairment-induced degeneration, which may partly result from the nigral DA neuron regeneration in the brain, and such experimental results may have implications for the treatment of PD.

Cognitive Sparing during the Administration of Whole Brain Radiotherapy and Prophylactic Cranial Irradiation: Current Concepts and Approaches

Whole brain radiotherapy (WBRT) for the palliation of metastases, or as prophylaxis to prevent intracranial metastases, can be associated with subacute and late decline in memory and other cognitive functions. Moreover, these changes are often increased in both frequency and severity when cranial irradiation is combined with the use of systemic or intrathecal chemotherapy. Approaches to preventing or reducing this toxicity include the use of stereotactic radiosurgery (SRS) instead of WBRT; dose reduction for PCI; exclusion of the limbic circuit, hippocampal formation, and/or neural stem cell regions of the brain during radiotherapy; avoidance of intrathecal and/or systemic chemotherapy during radiotherapy; the use of high-dose, systemic chemotherapy in lieu of WBRT. This review discusses these concepts in detail as well as providing both neuroanatomic and radiobiologic background relevant to these issues.

Biomaterials for neural-tissue engineering — Chitosan supports the survival, migration, and differentiation of adult-derived neural stem and progenitor cells

Neural precursor cells (NPCs or stem and progenitor cells) are promising in transplantation strategies to treat an injury to the central nervous system, such as a spinal cord injury (SCI), because of their ability to differentiate into neurons and glia. Transplantation studies to date have met with limited success for a number of reasons, including poor cell survival. One way to encourage cell survival in injured tissue is to provide the cells with a scaffold to enhance their survival, their integration, and potentially their differentiation into appropriate cell types. Towards this end, four amine-functionalized hydrogels were screened in vitro for adult murine NPC viability, migration, and differentiation: chitosan, poly(oligoethylene oxide dimethacrylate-co-2-amino ethyl methacrylate), blends of poly(oligoethylene oxide dimethacrylate-co-2-amino ethyl methacrylate), and poly(vinyl alcohol), and poly(glycerol dimethacrylate-co-2-amino ethyl methacrylate). The greatest cell viability was found on chitosan at all times examined, Chitosan had the greatest surface amine content and the lowest equilibrium water content, which likely contributed to the greater NPC viability observed over three weeks in culture. Only chitosan supported survival of multipotent stem cells and the differentiation of the progenitors into neurons, astrocytes, and oligodendrocytes. Plating intact NPC colonies revealed greater cell migration on chitosan relative to the other hydrogels. Importantly, long term cultures on chitosan showed no significant difference in total cell counts over time, suggesting no net cell growth. Together, these findings reveal chitosan as a promising material for the delivery of adult NPC cell-based therapies.

An organotypic culture model to study nigro-striatal degeneration

Functional and reliable in vitro models of Parkinson's disease (PD) are valuable for studying mechanisms of dopaminergic degeneration before proceeding to animal testing. At present, all in vitro models involve substitute cell types and thus their direct relevance to PD is questionable. Here, we describe an organotypic culture model which conserves the 3D architecture of the nigro-striatal pathway, together with the subventricular zone and cerebral cortex, and recapitulates a specific pattern of dopaminergic degeneration which is the principal hallmark of PD. The organotypic culture is kept in vitro for up to 12 days and dopaminergic degeneration is induced by the simple cutting of dopaminergic fibers. This organotypic model represents a rapid and useful method (30 min/pup for preparation and up to 12 days of cultivation) to investigate in vitro the mechanisms underlying neuronal death and protection, as well as neurogenesis and repair after nigro-striatal neurodegeneration.

How useful are stem cells in PD therapy?

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. The onset of PD is usually after the age of 50. Clinical symptoms of PD are not manifested until 60-80% of dopaminergic neurons in the midbrain have been affected. Cell replacement has been a promising approach for the treatment of PD. Fetal mesencephalic dopaminergic neurons seemed to improve the motor disability in patients in some early studies. However, the clinical application of this approach may be limited by ethical and logistic concerns, as well as by side effects. On the other hand, embryonic stem (ES) cells are promising candidates because of their ability to provide an unlimited supply of specific cell types, their accessibility to genetic modifications, and their broad developmental potentials. Transplants of undifferentiated ES cells were able to proliferate and fully differentiate into dopaminergic neurons in a rodent PD model. One of the concerns though is the risk of tumor formation. The tumorigenic potential of ES cells seems to be greatly reduced when cells are predifferentiated into dopaminergic neurons in vitro before implantation. Recent developments in the induction of pluripotent stem cells from somatic adult cells provide a tremendous opportunity for this field. Initial success has been reported in a rodent PD model using iPS cells (induced pluripotent stem cells). However, whether this initial result can be successfully translated into human clinical studies still needs to be determined.

Increase of intracellular Ca2+ by adenine and uracil nucleotides in human midbrain-derived neuronal progenitor cells

Nucleotides play an important role in brain development and may exert their action via ligand-gated cationic channels or G protein-coupled receptors. Patch-clamp measurements indicated that in contrast to AMPA, ATP did not induce membrane currents in human midbrain derived neuronal progenitor cells (hmNPCs). Various nucleotide agonists concentration-dependently increased [Ca(2+)](i) as measured by the Fura-2 method, with the rank order of potency ATP>ADP>UTP>UDP. A Ca(2+)-free external medium moderately decreased, whereas a depletion of the intracellular Ca(2+) storage sites by cyclopiazonic acid markedly depressed the [Ca(2+)](i) transients induced by either ATP or UTP. Further, the P2Y(1) receptor antagonistic PPADS and MRS 2179, as well as the nucleotide catalyzing enzyme apyrase, allmost abolished the effects of these two nucleotides. However, the P2Y(1,2,12) antagonistic suramin only slightly blocked the action of ATP, but strongly inhibited that of UTP. In agreement with this finding, UTP evoked the release of ATP from hmNPCs in a suramin-, but not PPADS-sensitive manner. Immunocytochemistry indicated the co-localization of P2Y(1,2,4)-immunoreactivities (IR) with nestin-IR at these cells. In conclusion, UTP may induce the release of ATP from hmNPCs via P2Y(2) receptor-activation and thereby causes [Ca(2+)](i) transients by stimulating a P2Y(1)-like receptor.

Basic mechanisms of rTMS: Implications in Parkinson's disease

BACKGROUND

Basic and clinical research suggests a potential role for repetitive transcranial magnetic stimulation (rTMS) in the treatment of Parkinson's disease. However, compared to the growing number of clinical studies on its putative therapeutic properties, the studies on the basic mechanisms of rTMS are surprisingly scarce.

RESULTS

Animal studies have broadened our understanding of how rTMS affects brain circuits and the causal chain in brain-behavior relationships. The observed changes are thought to be to neurotransmitter release, transsynaptic efficiency, signaling pathways and gene transcription. Furthermore, recent studies suggest that rTMS induces neurogenesis, neuronal viability and secretion of neuroprotective molecules.

CONCLUSION

The mechanisms underlying the disease-modifying effects of these and related rTMS in animals are the principle subject of the current review. The possible applications for treatment of Parkinson's disease are discussed.

Extremely low-frequency electromagnetic fields promote in vitro neurogenesis via upregulation of Ca(v)1-channel activity

We previously reported that exposure to extremely low-frequency electromagnetic fields (ELFEFs) increases the expression and function of voltage-gated Ca2+)channels and that Ca2+ influx through Ca(v)1 channels plays a key role in promoting the neuronal differentiation of neural stem/progenitor cells (NSCs). The present study was conducted to determine whether ELFEFs influence the neuronal differentiation of NSCs isolated from the brain cortices of newborn mice by modulating Ca(v)1-channel function. In cultures of differentiating NSCs exposed to ELFEFs (1 mT, 50 Hz), the percentage of cells displaying immunoreactivity for neuronal markers (beta-III-tubulin, MAP2) and for Ca(v)1.2 and Ca(v)1.3 channels was markedly increased. NSC-differentiated neurons in ELFEF-exposed cultures also exhibited significant increases in spontaneous firing, in the percentage of cells exhibiting Ca2+ transients in response to KCl stimulation, in the amplitude of these transients and of Ca2+ currents generated by the activation of Ca(v)1 channels. When the Ca(v)1-channel blocker nifedipine (5 microM) was added to the culture medium, the neuronal yield of NSC differentiation dropped significantly, and ELFEF exposure no longer produced significant increases in beta-III-tubulin- and MAP2-immunoreactivity rates. In contrast, the effects of ELFEFs were preserved when NSCs were cultured in the presence of either glutamate receptor antagonists or Ca(v)2.1- and Ca(v)2.2-channel blockers. ELFEF stimulation during the first 24 h of differentiation caused Ca(v)1-dependent increases in the number of cells displaying CREB phosphorylation. Our data suggest that ELFEF exposure promotes neuronal differentiation of NSCs by upregulating Ca(v)1-channel expression and function.

Bone-marrow-derived cell differentiation into microglia: A study in a progressive mouse model of Parkinson's disease

The migration of peripheral bone-marrow-derived cells (BMDCs) to the brain was studied in a chronic mouse model of Parkinson's disease (PD). BMDCs expressing the enhanced green fluorescent protein (GFP) were aseptically obtained from C57 BL/6-EGFP-Tg mice and intravenously injected into C57 BL/6j mice which had received a total body irradiation of 8 Gy to induce bone marrow ablation. Implanted GFP-BMDCs replenished the bone marrow of irradiated mice, and progressively crossed the blood-brain barrier (BBB), penetrating different mesencephalic and telencephalic brain regions in the following months. The progressive degeneration of dopamine (DA) cells with a small daily dose (4 mg/kg/day for 20 days) of 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP) increased the penetration of GFP-BMDCs into the brain, particularly into those regions with marked DA innervation and which showed the clearest DA cell loss. BMDC penetration increased before the DA cell loss was evident and persisted for a long time after MPTP withdrawal. Under these conditions, most BMDCs differentiated into microglia (CD68 expression was observed in 50% of GFP cells 60 days after MPTP administration). BMDC-derived microglia showed morphological characteristics of cell activation, with the glial cell line-derived neurotrophic factor only being expressed in 3% of the cells. No differentiation into neurons (NeuN expression), astrocites (GFAP), cytotoxic lymphocytes (CD8) and T-helper lymphocytes (CD4) was observed. Taken together, the present data suggest that a significant portion of microglial cells is of a peripheral origin. Bearing in mind that microglial reaction is a significant part of the degenerative process in PD, the increase of BMDC penetration into DA-rich areas during DA cell degeneration and their differentiation into microglia suggest that cells coming across the BBB may participate in the neurodegeneration process. The precise role of such a cell inflow into the brain requires further study. Nevertheless, this may represent an opportunity to develop neuroprotective therapeutic strategies for PD.