Integration of adult generated neurons during epileptogenesis

Effects of minocycline on dendrites, dendritic spines, and microglia in immature mouse brains after kainic acid-induced status epilepticus

PURPOSE

This study aimed to investigate whether minocycline could influence alterations of microglial subtypes, the morphology of dendrites and dendritic spines, the microstructures of synapses and synaptic proteins, or even cognition outcomes in immature male mice following status epilepticus (SE) induced by kainic acid.

METHODS

Golgi staining was performed to visualize the dendrites and dendritic spines of neurons of the hippocampus. The microstructures of synapses and synaptic proteins were observed using transmission electron microscopy and western blotting analysis, respectively. Microglial reactivation and their markers were evaluated using flow cytometry. The Morris water maze (MWM) test was used to analyze spatial learning and memory ability.

RESULTS

Significant partial spines increase (predominate in thin spines) was observed in the dendrites of neurons after acute SE and partial loss (mainly in thin spines) was presented by days 14 and 28 post-SE. The postsynaptic ultrastructure was impaired on the 7th and 14th days after SE. The proportion of M1 microglia increased significantly only after acute SE Similarly, the proportion of M2 microglia increased in the acute stage with high expression levels of all surface markers. In contrast, a decrease in M2 microglia and their markers was noted by day 14 post-SE. Minocycline could reverse the changes in dendrites and synaptic proteins caused by SE, and increase the levels of synaptic proteins. Meanwhile, minocycline could inhibit the reactivation of M1 microglia and the expression of their markers, except for promoting CD200R. In addition, treatment with minocycline could regulate the expression of M2 microglia and their surface markers, as well as ameliorating the impaired spatial learning and memory on the 28th day after SE.

CONCLUSIONS

Dendritic spines and microglia are dynamically changed after SE. Minocycline could ameliorate the impaired cognition in the kainic acid-induced mouse model by decreasing the damage to dendrites and altering microglial reactivation.

A Modified Mediterranean Ketogenic Diet mitigates modifiable risk factors of Alzheimer's Disease: a serum and CSF-based metabolic analysis

Alzheimer's disease (AD) is influenced by a variety of modifiable risk factors, including a person's dietary habits. While the ketogenic diet (KD) holds promise in reducing metabolic risks and potentially affecting AD progression, only a few studies have explored KD's metabolic impact, especially on blood and cerebrospinal fluid (CSF). Our study involved participants at risk for AD, either cognitively normal or with mild cognitive impairment. The participants consumed both a modified Mediterranean-ketogenic diet (MMKD) and the American Heart Association diet (AHAD) for 6 weeks each, separated by a 6-week washout period. We employed nuclear magnetic resonance (NMR)-based metabolomics to profile serum and CSF and metagenomics profiling on fecal samples. While the AHAD induced no notable metabolic changes, MMKD led to significant alterations in both serum and CSF. These changes included improved modifiable risk factors, like increased HDL-C and reduced BMI, reversed serum metabolic disturbances linked to AD such as a microbiome-mediated increase in valine levels, and a reduction in systemic inflammation. Additionally, the MMKD was linked to increased amino acid levels in the CSF, a breakdown of branched-chain amino acids (BCAAs), and decreased valine levels. Importantly, we observed a strong correlation between metabolic changes in the CSF and serum, suggesting a systemic regulation of metabolism. Our findings highlight that MMKD can improve AD-related risk factors, reverse some metabolic disturbances associated with AD, and align metabolic changes across the blood-CSF barrier.

Disrupted in Schizophrenia 1 Reverse Ectopic Migration of Neural Precursors in Mouse Hilus After Pilocarpine-Induced Status Epilepticus

Neural precursors in the subgranular zone (SGZ) can be stimulated by status epilepticus (SE) and ectopically migrate to the hilus. These mislocated cells serve as "potential pacemakers" of spontaneous recurrent seizures, and targeting them could potentially reverse the seizure process. Disrupted-in-Schizophrenia 1 (DISC1) regulates hippocampal neurogenesis after seizures both in vitro and in vivo. Our previous study found that DISC1 was colocalized with neural precursors in the hilus after SE. However, its molecular mechanism and pathways contribute to the ectopic migration of neural precursors to the hilus induced by SE awaits exploration. Here, we showed that both Reelin-ApoER2/EphB2 and Reelin-Integrin β1/Integrin α5 axes may participate in the modulation of neurogenesis after SE. Especially, DISC1, as a protective role, might partly reversed the ectopic progenitor migration via EphB2 pathway. Our findings demonstrated that DISC1 played a protective role in the ectopic migration of neural precursors induced by SE insults and DISC1 could be an attractive new target for the treatment of epilepsy.

Pharmacological Modulation of Neurite Outgrowth in Human Neural Progenitor Cells by Inhibiting Non-muscle Myosin II

Studies on neural development and neuronal regeneration after injury are mainly based on animal models. The establishment of pluripotent stem cell (PSC) technology, however, opened new perspectives for better understanding these processes in human models by providing unlimited cell source for hard-to-obtain human tissues. Here, we aimed at identifying the molecular factors that confine and modulate an early step of neural regeneration, the formation of neurites in human neural progenitor cells (NPCs). Enhanced green fluorescent protein (eGFP) was stably expressed in NPCs differentiated from human embryonic and induced PSC lines, and the neurite outgrowth was investigated under normal and injury-related conditions using a high-content screening system. We found that inhibitors of the non-muscle myosin II (NMII), blebbistatin and its novel, non-toxic derivatives, initiated extensive neurite outgrowth in human NPCs. The extracellular matrix components strongly influenced the rate of neurite formation but NMII inhibitors were able to override the inhibitory effect of a restrictive environment. Non-additive stimulatory effect on neurite generation was also detected by the inhibition of Rho-associated, coiled-coil-containing protein kinase 1 (ROCK1), the upstream regulator of NMII. In contrast, inhibition of c-Jun N-terminal kinases (JNKs) had only a negligible effect, suggesting that the ROCK1 signal is dominantly manifested by actomyosin activity. In addition to providing a reliable cell-based in vitro model for identifying intrinsic mechanisms and environmental factors responsible for impeded axonal regeneration in humans, our results demonstrate that NMII and ROCK1 are important pharmacological targets for the augmentation of neural regeneration at the progenitor level. These studies may open novel perspectives for development of more effective pharmacological treatments and cell therapies for various neurodegenerative disorders.

Microglial activation and adult neurogenesis after brain stroke

The discovery that new neurons are produced in some regions of the adult mammalian brain is a paradigm-shift in neuroscience research. These new-born cells are produced from neuroprogenitors mainly in the subventricular zone at the margin of the lateral ventricle, subgranular zone in the hippocampal dentate gyrus and in the striatum, a component of the basal ganglia, even in humans. In the human hippocampus, neuroblasts are produced even in elderlies. The regulation of adult neurogenesis is a complex phenomenon involving a multitude of molecules, neurotransmitters and soluble factors released by different sources including glial cells. Microglia, the resident macrophages of the central nervous system, are considered to play an important role on the regulation of adult neurogenesis both in physiological and pathological conditions. Following stroke and other acute neural disorders, there is an increase in the numbers of neuroblast production in the neurogenic niches. Microglial activation is believed to display both beneficial and detrimental role on adult neurogenesis after stroke, depending on the activation level and brain location. In this article, we review the scientific evidence addressing the role of microglial activation on adult neurogenesis after ischemia. A comprehensive understanding of the microglial role after stroke and other neural disorders it is an important step for development of future therapies based on manipulation of adult neurogenesis.

Glycyrrhizin Blocks the Detrimental Effects of HMGB1 on Cortical Neurogenesis After Traumatic Neuronal Injury

Despite medical advances, neurological recovery after severe traumatic brain injury (TBI) remains poor. Elevated levels of high mobility group box protein-1 (HMGB1) are associated with poor outcomes; likely via interaction with receptors for advanced-glycation-end-products (RAGE). We examined the hypothesis that HMGB1 post-TBI is anti-neurogenic and whether this is pharmacologically reversible. Post-natal rat cortical mixed neuro-glial cell cultures were subjected to needle-scratch injury and examined for HMGB1-activation/neuroinflammation. HMGB1-related genes/networks were examined using genome-wide RNA-seq studies in cortical perilesional tissue samples from adult mice. Post-natal rat cortical neural stem/progenitor cell cultures were generated to quantify effects of injury-condition medium (ICM) on neurogenesis with/without RAGE antagonist glycyrrhizin. Needle-injury upregulated TNF-α/NOS-2 mRNA-expressions at 6 h, increased proportions of activated microglia, and caused neuronal loss at 24 h. Transcriptome analysis revealed activation of HMGB1 pathway genes/canonical pathways in vivo at 24 h. A 50% increase in HMGB1 protein expression, and nuclear-to-cytoplasmic translocation of HMGB1 in neurons and microglia at 24 h post-injury was demonstrated in vitro. ICM reduced total numbers/proportions of neuronal cells, but reversed by 0.5 μM glycyrrhizin. HMGB1 is activated following in vivo post mechanical injury, and glycyrrhizin alleviates detrimental effects of ICM on cortical neurogenesis. Our findings highlight glycyrrhizin as a potential therapeutic agent post-TBI.

Adult neurogenesis in the mammalian dentate gyrus

Earlier observations in neuroscience suggested that no new neurons form in the mature central nervous system. Evidence now indicates that new neurons do form in the adult mammalian brain. Two regions of the mature mammalian brain generate new neurons: (a) the border of the lateral ventricles of the brain (subventricular zone) and (b) the subgranular zone (SGZ) of the dentate gyrus of the hippocampus. This review focuses only on new neuron formation in the dentate gyrus of the hippocampus. During normal prenatal and early postnatal development, neural stem cells (NSCs) give rise to differentiated neurons. NSCs persist in the dentate gyrus SGZ, undergoing cell division, with some daughter cells differentiating into functional neurons that participate in learning and memory and general cognition through integration into pre-existing neural networks. Axons, which emanate from neurons in the entorhinal cortex, synapse with dendrites of the granule cells (small neurons) of the dentate gyrus. Axons from granule cells synapse with pyramidal cells in the hippocampal CA3 region, which send axons to synapse with CA1 hippocampal pyramidal cells that send their axons out of the hippocampus proper. Adult neurogenesis includes proliferation, differentiation, migration, the death of some newly formed cells and final integration of surviving cells into neural networks. We summarise these processes in adult mammalian hippocampal neurogenesis and discuss the roles of major signalling molecules that influence neurogenesis, including neurotransmitters and some hormones. The recent controversy raised concerning whether or not adult neurogenesis occurs in humans also is discussed.

Wnt/β-catenin signaling as a potential target for novel epilepsy therapies

Epilepsy is one of the most common neurological disorders, and yet many afflicted individuals are resistant to all available therapeutic treatments. Existing pharmaceutical treatments function primarily to reduce hyperexcitability and prevent seizures, but fail to influence the underlying pathophysiology of the disorder. Recently, research efforts have focused on identifying alternative mechanistic targets for anti-epileptogenic therapies that can prevent the development of chronic epilepsy. The Wnt/β-catenin pathway, one possible target, has been demonstrated to be disrupted in both acute and chronic phases of epilepsy. Wnt/β-catenin signaling can regulate many seizure-induced changes in the brain, including neurogenesis and neuronal death, as well as can influence seizure susceptibility and potentially the development of chronic epilepsy. Several genome-wide studies and in vivo knockout animal models have provided evidence for an association between disrupted Wnt/β-catenin signaling and epilepsy. Furthermore, approved pharmaceutical drugs and other small molecule compounds that target components of the β-catenin destruction complex or antagonize endogenous inhibitors of the pathway have shown to be protective following seizures. However, additional studies are needed to determine the optimal time period in which modulation of the pathway may be most beneficial. Overall, disrupted molecular networks such as Wnt/β-catenin signaling, could be a promising anti-epileptogenic target for future epilepsy therapies.

Increased gyrification and aberrant adult neurogenesis of the dentate gyrus in adult rats

A remarkable example of maladaptive plasticity is the development of epilepsy after a brain insult or injury to a normal animal or human. A structure that is considered central to the development of this type of epilepsy is the dentate gyrus (DG), because it is normally a relatively inhibited structure and its quiescence is thought to reduce hippocampal seizure activity. This characteristic of the DG is also considered to be important for normal hippocampal-dependent cognitive functions. It has been suggested that the brain insults which cause epilepsy do so because they cause the DG to be more easily activated. One type of brain insult that is commonly used is induction of severe seizures (status epilepticus; SE) by systemic injection of a convulsant drug. Here we describe an alteration in the DG after this type of experimental SE that may contribute to chronic seizures that has not been described before: large folds or gyri that develop in the DG by 1 month after SE. Large gyri appeared to increase network excitability because epileptiform discharges recorded in hippocampal slices after SE were longer in duration when recorded inside gyri relative to locations outside gyri. Large gyri may also increase excitability because immature adult-born neurons accumulated at the base of gyri with time after SE, and previous studies have suggested that abnormalities in adult-born DG neurons promote seizures after SE. In summary, large gyri after SE are a common finding in adult rats, show increased excitability, and are associated with the development of an abnormal spatial distribution of adult-born neurons. Together these alterations may contribute to chronic seizures and associated cognitive comorbidities after SE.

Neuroanatomical Distribution of DEK Protein in Corticolimbic Circuits Associated with Learning and Memory in Adult Male and Female Mice

DEK, a chromatin-remodeling gene expressed in most human tissues, is known for its role in cancer biology and autoimmune diseases. DEK depletion in vitro reduces cellular proliferation, induces DNA damage subsequently leading to apoptosis, and down-regulates canonical Wnt/β-catenin signaling, a molecular pathway essential for learning and memory. Despite a recognized role in cancer (non-neuronal) cells, DEK expression and function is not well characterized in the central nervous system. We conducted a gene ontology analysis (ToppGene), using a cancer database to identify genes associated with DEK deficiency, which pinpointed several genes associated with cognitive-related diseases (i.e., Alzheimer's disease, presenile dementia). Based on this information, we examined DEK expression in corticolimbic structures associated with learning and memory in adult male and female mice using immunohistochemistry. DEK was expressed throughout the brain in both sexes, including the medial prefrontal cortex (prelimbic, infralimbic and dorsal peduncular). DEK was also abundant in all amygdalar subdivisions (basolateral, central and medial) and in the hippocampus including the CA1, CA2, CA3, dentate gyrus (DG), ventral subiculum and entorhinal cortex. Of note, compared to males, females had significantly higher DEK immunoreactivity in the CA1, indicating a sex difference in this region. DEK was co-expressed with neuronal and microglial markers in the CA1 and DG, whereas only a small percentage of DEK cells were in apposition to astrocytes in these areas. Given the reported inverse cellular and molecular profiles (e.g., cell survival, Wnt pathway) between cancer and Alzheimer's disease, these findings suggest a potentially important role of DEK in cognition.

Cellular responses to recurrent pentylenetetrazole-induced seizures in the adult zebrafish brain

A seizure is a sustained increase in brain electrical activity that can result in loss of consciousness and injury. Understanding how the brain responds to seizures is important for development of new treatment strategies for epilepsy, a neurological condition characterized by recurrent and unprovoked seizures. Pharmacological induction of seizures in rodent models results in a myriad of cellular alterations, including inflammation, angiogenesis, and adult neurogenesis. The purpose of this study is to investigate the cellular responses to recurrent pentylenetetrazole seizures in the adult zebrafish brain. We subjected zebrafish to five once-daily pentylenetetrazole-induced seizures and characterized the cellular consequences of these seizures. In response to recurrent seizures, we found histologic evidence of vasodilatation, perivascular leukocyte egress and leukocyte proliferation suggesting seizure-induced acute CNS inflammation. We also found evidence of increased proliferation, neurogenesis, and reactive gliosis following pentylenetetrazole-induced seizures. Collectively, our results suggest that the cellular responses to seizures in the adult zebrafish brain are similar to those observed in mammalian brains.

The maternal brain under stress: Consequences for adaptive peripartum plasticity and its potential functional implications

The peripartum period represents a time during which all mammalian species undergo substantial physiological and behavioural changes, which prepare the female for the demands of motherhood. In addition to behavioural and physiological alterations, numerous brain regions, such as the medial prefrontal cortex, olfactory bulb, medial amygdala and hippocampus are subject to substantial peripartum-associated neuronal, dendritic and synaptic plasticity. These changes, which are temporally- and spatially-distinct, are strongly influenced by gonadal and adrenal hormones, such as estrogen and cortisol/corticosterone, which undergo dramatic fluctuations across this period. In this review, we describe our current knowledge regarding these plasticity changes and describe how stress affects such normal adaptations. Finally, we discuss the mechanisms potentially underlying these neuronal, dendritic and synaptic changes and their functional relevance for the mother and her offspring.

The Role of Wnt/β-Catenin Signaling Pathway in Disrupted Hippocampal Neurogenesis of Temporal Lobe Epilepsy: A Potential Therapeutic Target?

Temporal lobe epilepsy is one of the most common clinical neurological disorders. One of the major pathological findings in temporal lobe epilepsy is hippocampal sclerosis, characterized by massive neuronal loss and severe gliosis. The epileptogenesis process of temporal lobe epilepsy usually starts with initial precipitating insults, followed by neurodegeneration, abnormal hippocampus circuitry reorganization, and the formation of hypersynchronicity. Experimental and clinical evidence strongly suggests that dysfunctional neurogenesis is involved in the epileptogenesis. Recent data demonstrate that neurogenesis is induced by acute seizures or precipitating insults, whereas the capacity of neuronal recruitment and proliferation substantially decreases in the chronic phase of epilepsy. Participation of the Wnt/β-catenin signaling pathway in neurogenesis reveals its importance in epileptogenesis; its dysfunction contributes to the structural and functional abnormality of temporal lobe epilepsy, while rescuing this pathway exerts neuroprotective effects. Here, we summarize data supporting the involvement of Wnt/β-catenin signaling in the epileptogenesis of temporal lobe epilepsy. We also propose that the Wnt/β-catenin signaling pathway may serve as a promising therapeutic target for temporal lobe epilepsy treatment.

Cortical neurogenesis in adult rats after ischemic brain injury: most new neurons fail to mature

The present study examines the hypothesis that endogenous neural progenitor cells isolated from the neocortex of ischemic brain can differentiate into neurons or glial cells and contribute to neural regeneration. We performed middle cerebral artery occlusion to establish a model of cerebral ischemia/reperfusion injury in adult rats. Immunohistochemical staining of the cortex 1, 3, 7, 14 or 28 days after injury revealed that neural progenitor cells double-positive for nestin and sox-2 appeared in the injured cortex 1 and 3 days post-injury, and were also positive for glial fibrillary acidic protein. New neurons were labeled using bromodeoxyuridine and different stages of maturity were identified using doublecortin, microtubule-associated protein 2 and neuronal nuclei antigen immunohistochemistry. Immature new neurons coexpressing doublecortin and bromodeoxyuridine were observed in the cortex at 3 and 7 days post-injury, and semi-mature and mature new neurons double-positive for microtubule-associated protein 2 and bromodeoxyuridine were found at 14 days post-injury. A few mature new neurons coexpressing neuronal nuclei antigen and bromodeoxyuridine were observed in the injured cortex 28 days post-injury. Glial fibrillary acidic protein/bromodeoxyuridine double-positive astrocytes were also found in the injured cortex. Our findings suggest that neural progenitor cells are present in the damaged cortex of adult rats with cerebral ischemic brain injury, and that they differentiate into astrocytes and immature neurons, but most neurons fail to reach the mature stage.

Identification of a sustained neurogenic zone at the dorsal surface of the adult mouse hippocampus and its regulation by the chemokine SDF-1

We identified a previously unknown neurogenic region at the dorsal surface of the hippocampus; (the "subhippocampal zone," SHZ) in the adult brain. Using a reporter mouse in which SHZ cells and their progeny could be traced through the expression of EGFP under the control of the CXCR4 chemokine receptor promoter we observed the presence of a pool of EGFP expressing cells migrating in direction of the dentate gyrus (DG), which is maintained throughout adulthood. This population appeared to originate from the SHZ where cells entered a caudal migratory stream (aCMS) that included the fimbria, the meninges and the DG. Deletion of CXCR4 from neural stem cells (NSCs) or neuroinflammation resulted in the appearance of neurons in the DG, which were the result of migration of NSCs from the SHZ. Some of these neurons were ectopically placed. Our observations indicate that the SHZ is a neurogenic zone in the adult brain through migration of NSCs in the aCMS. Regulation of CXCR4 signaling in these cells may be involved in repair of the DG and may also give rise to ectopic granule cells in the DG in the context of neuropathology.

Dual-transmitter neurons: functional implications of co-release and co-transmission

Co-transmission, the ability of a neuron to release multiple transmitters, has long been recognized in selected circuits. However, the release of multiple primary neurotransmitters from a single neuron is only beginning to be appreciated. Here we consider recent examples of co-transmission as well as co-release-the packaging of multiple neurotransmitters into a single vesicle. The properties associated with each mode of release greatly enhance the possible action of such neurons within circuits. The functional importance of dual- (or multi-) transmitter neurons extends beyond actions on postsynaptic receptors, due in part to differential spatial and temporal profiles of each neurotransmitter. Recent evidence also suggests that the dual-transmitter phenotype can be dynamically regulated during development and following injury or disease.

Neuroligin-1 knockdown reduces survival of adult-generated newborn hippocampal neurons

Survival of adult-born hippocampal granule cells is modulated by neural activity, and thought to be enhanced by excitatory synaptic signaling. Here, we report that a reduction in the synaptogenic protein neuroligin-1 in adult-born neurons in vivo decreased their survival, but surprisingly, this effect was independent of changes in excitatory synaptic function. Instead, the decreased survival was associated with unexpected changes in dendrite and spine morphology during granule cell maturation, suggesting a link between cell growth and survival.

The Caenorhabditis elegans microtubule minus-end binding homolog PTRN-1 stabilizes synapses and neurites

Microtubule dynamics facilitate neurite growth and establish morphology, but the role of minus-end binding proteins in these processes is largely unexplored. CAMSAP homologs associate with microtubule minus-ends, and are important for the stability of epithelial cell adhesions. In this study, we report morphological defects in neurons and neuromuscular defects in mutants of the C. elegans CAMSAP, ptrn-1. Mechanosensory neurons initially extend wild-type neurites, and subsequently remodel by overextending neurites and retracting synaptic branches and presynaptic varicosities. This neuronal remodeling can be activated by mutations known to alter microtubules, and depends on a functioning DLK-1 MAP kinase pathway. We found that PTRN-1 localizes to both neurites and synapses, and our results suggest that alterations of microtubule structures caused by loss of PTRN-1 function activates a remodeling program leading to changes in neurite morphology. We propose a model whereby minus-end microtubule stabilization mediated by a functional PTRN-1 is necessary for morphological maintenance of neurons. DOI: http://dx.doi.org/10.7554/eLife.01637.001.

Caspase 3 involves in neuroplasticity, microglial activation and neurogenesis in the mice hippocampus after intracerebral injection of kainic acid

BACKGROUND

The roles of caspase 3 on the kainic acid-mediated neurodegeneration, dendritic plasticity alteration, neurogenesis, microglial activation and gliosis are not fully understood. Here, we investigate hippocampal changes using a mouse model that receive a single kainic acid-intracerebral ventricle injection. The effects of caspase 3 inhibition on these changes were detected during a period of 1 to 7 days post kainic acid injection.

RESULT

Neurodegeneration was assessed by Fluoro-Jade B staining and neuronal nuclei protein (NeuN) immunostaining. Neurogenesis, gliosis, neuritic plasticity alteration and caspase 3 activation were examined using immunohistochemistry. Dendritic plasticity, cleavvage-dependent activation of calcineurin A and glial fibrillary acidic protein cleavage were analyzed by immunoblotting. We found that kainic acid not only induced neurodegeneration but also arouse several caspase 3-mediated molecular and cellular changes including dendritic plasticity, neurogenesis, and gliosis. The acute caspase 3 activation occurred in pyramidal neurons as well as in hilar interneurons. The delayed caspase 3 activation occurred in astrocytes. The co-injection of caspase 3 inhibitor did not rescue kainic acid-mediated neurodegeneration but seriously and reversibly disturb the structural integrity of axon and dendrite. The kainic acid-induced events include microglia activation, the proliferation of radial glial cells, neurogenesis, and calcineurin A cleavage were significantly inhibited by the co-injection of caspase 3 inhibitor, suggesting the direct involvement of caspase 3 in these events. Alternatively, the kainic acid-mediated astrogliosis is not caspase 3-dependent, although caspase 3 cleavage of glial fibrillary acidic protein occurred.

CONCLUSIONS

Our results provide the first direct evidence of a causal role of caspase 3 activation in the cellular changes during kainic acid-mediated excitotoxicity. These findings may highlight novel pharmacological strategies to arrest disease progression and control seizures that are refractory to classical anticonvulsant treatment.

Cortical endogenic neural regeneration of adult rat after traumatic brain injury

Focal and diffuse neuronal loss happened after traumatic brain injury (TBI). With little in the way of effective repair, recent interest has focused on endogenic neural progenitor cells (NPCs) as a potential method for regeneration. Whether endogenic neural regeneration happened in the cortex of adult rat after TBI remains to be determined. In this study, rats were divided into a sham group and a TBI group, and the rat model of medium TBI was induced by controlled cortical impact. Rats were injected with BrdU at 1 to 7 days post-injury (dpi) to allow identification of differentiated cells and sacrificed at 1, 3, 7, 14 and 28 dpi for immunofluorescence. Results showed nestin(+)/sox-2(+) NPCs and GFAP(+)/sox-2(+) radial glial (RG)-like cells emerged in peri-injured cortex at 1, 3, 7, 14 dpi and peaked at 3 dpi. The number of GFAP(+)/sox-2(+) cells was less than that of nestin(+)/sox-2(+) cells. Nestin(+)/sox-2(+) cells from posterior periventricle (pPV) immigrated into peri-injured cortex through corpus callosum (CC) were found. DCX(+)/BrdU(+) newborn immature neurons in peri-injured cortex were found only at 3, 7, 14 dpi. A few MAP-2(+)/BrdU(+) newborn neurons in peri-injured cortex were found only at 7 and 14 dpi. NeuN(+)/BrdU(+) mature neurons were not found in peri-injured cortex at 1, 3, 7, 14 and 28 dpi. While GFAP(+)/BrdU(+) astrocytes emerged in peri-injured cortex at 1, 3, 7, 14, 28 dpi and peaked at 7 dpi then kept in a stable state. In the corresponding time point, the percentage of GFAP(+)/BrdU(+) astrocytes in BrdU(+) cells was more than that of NPCs or newborn neurons. No CNP(+)/BrdU(+) oligodendrocytes were found in peri-injured cortex. These findings suggest that NPCs from pPV and reactive RG-like cells emerge in peri-injured cortex of adult rats after TBI. It can differentiate into immature neurons and astrocytes, but the former fail to grow up to mature neurons.

Adult neural stem cells: an endogenous tool to repair brain injury?

Research on stem cells has developed as one of the most promising areas of neurobiology. In the beginning of the 1990s, neurogenesis in the adult brain was indisputably accepted, eliciting great research efforts. Neural stem cells in the adult mammalian brain are located in the 'neurogenic' areas of the subventricular and subgranular zones. Nevertheless, many reports indicate that they subsist in other regions of the adult brain. Adult neural stem cells have arisen considerable interest as these studies can be useful to develop new methods to replace damaged neurons and treat severe neurological diseases such as neurodegeneration, stroke or spinal cord lesions. In particular, a promising field is aimed at stimulating or trigger a self-repair system in the diseased brain driven by its own stem cell population. Here, we will revise the latest findings on the characterization of active and quiescent adult neural stem cells in the main regions of neurogenesis and the factors necessary to maintain their active and resting states, stimulate migration and homing in diseased areas, hoping to outline the emerging knowledge for the promotion of regeneration in the brain based on endogenous stem cells.

Neuroligin-1 overexpression in newborn granule cells in vivo

Adult-born dentate granule cells integrate into the hippocampal network, extend neurites and form synapses in otherwise mature tissue. Excitatory and inhibitory inputs innervate these new granule cells in a stereotyped, temporally segregated manner, which presents a unique opportunity to study synapse development in the adult brain. To examine the role of neuroligins as synapse-inducing molecules in vivo, we infected dividing neural precursors in adult mice with a retroviral construct that increased neuroligin-1 levels during granule cell differentiation. By 21 days post-mitosis, exogenous neuroligin-1 was expressed at the tips of dendritic spines and increased the number of dendritic spines. Neuroligin-1-overexpressing cells showed a selective increase in functional excitatory synapses and connection multiplicity by single afferent fibers, as well as an increase in the synaptic AMPA/NMDA receptor ratio. In contrast to its synapse-inducing ability in vitro, neuroligin-1 overexpression did not induce precocious synapse formation in adult-born neurons. However, the dendrites of neuroligin-1-overexpressing cells did have more thin protrusions during an early period of dendritic outgrowth, suggesting enhanced filopodium formation or stabilization. Our results indicate that neuroligin-1 expression selectively increases the degree, but not the onset, of excitatory synapse formation in adult-born neurons.

G-protein-coupled receptors in adult neurogenesis

The importance of adult neurogenesis has only recently been accepted, resulting in a completely new field of investigation within stem cell biology. The regulation and functional significance of adult neurogenesis is currently an area of highly active research. G-protein-coupled receptors (GPCRs) have emerged as potential modulators of adult neurogenesis. GPCRs represent a class of proteins with significant clinical importance, because approximately 30% of all modern therapeutic treatments target these receptors. GPCRs bind to a large class of neurotransmitters and neuromodulators such as norepinephrine, dopamine, and serotonin. Besides their typical role in cellular communication, GPCRs are expressed on adult neural stem cells and their progenitors that relay specific signals to regulate the neurogenic process. This review summarizes the field of adult neurogenesis and its methods and specifies the roles of various GPCRs and their signal transduction pathways that are involved in the regulation of adult neural stem cells and their progenitors. Current evidence supporting adult neurogenesis as a model for self-repair in neuropathologic conditions, adult neural stem cell therapeutic strategies, and potential avenues for GPCR-based therapeutics are also discussed.

The duration of sustained convulsive seizures determines the pattern of hippocampal neurogenesis and the development of spontaneous epilepsy in rats

The duration of sustained seizures (SS) plays a crucial role in the occurrence of spontaneous recurrent seizures (SRS) in experimental animals. We tested whether rats with varying durations of initial convulsive SS exhibited differential neurogenesis patterns in the hippocampal dentate gyrus that may be related to subsequent epileptogenesis. Sprague-Dawley rats with pilocarpine-induced convulsive SS were divided into short SS (30 min) and long SS (2 h) groups. Their behavior was monitored to identify convulsive SRS. From 1 to 28 days post-SS, cell proliferation was evaluated by 5'-bromo-2'-deoxyuridine (BrdU) labeling and immature neuroblasts in the dentate gyrus were identified by doublecortin immunohistochemistry. Convulsive SRS was detected in 8 out of the 9 long SS rats, but not in the 9 short SS rats. During day 1-3, proliferative cells were diffusely localized throughout the hippocampus in the long SS rats but were primarily confined within the subgranular zone in the short SS rats. Within the subgranular zone, a significant increase in the number of BrdU-positive cells was found at days 3 and 7 after the long SS and on day 1 after the short SS. Notably, abnormal dendritic outgrowth and hilar-ectopic localization of doublecortin-positive cells were present in the long SS rats. In conclusion, aberrant hippocampal neurogenesis following long SS may contribute to the development of SRS.

miR-132 mediates the integration of newborn neurons into the adult dentate gyrus

Neuronal activity enhances the elaboration of newborn neurons as they integrate into the synaptic circuitry of the adult brain. The role microRNAs play in the transduction of neuronal activity into growth and synapse formation is largely unknown. MicroRNAs can influence the expression of hundreds of genes and thus could regulate gene assemblies during processes like activity-dependent integration. Here, we developed viral-based methods for the in vivo detection and manipulation of the activity-dependent microRNA, miR-132, in the mouse hippocampus. We find, using lentiviral and retroviral reporters of miR-132 activity, that miR-132 is expressed at the right place and right time to influence the integration of newborn neurons. Retroviral knockdown of miR-132 using a specific ‘sponge’ containing multiple target sequences impaired the integration of newborn neurons into the excitatory synaptic circuitry of the adult brain. To assess potential miR-132 targets, we used a whole-genome microarray in PC12 cells, which have been used as a model of neuronal differentiation. miR-132 knockdown in PC12 cells resulted in the increased expression of hundreds of genes. Functional grouping indicated that genes involved in inflammatory/immune signaling were the most enriched class of genes induced by miR-132 knockdown. The correlation of miR-132 knockdown to increased proinflammatory molecular expression may indicate a mechanistic link whereby miR-132 functions as an endogenous mediator of activity-dependent integration in vivo.

Enhanced integration of newborn neurons after neonatal insults

The production and integration of adult-generated neurons in the dentate gyrus is dramatically perturbed by a variety of pathological insults, including repetitive seizures and hypoxia/ischemia. Less is known about how insults affect early postnatal neurogenesis, during the developmental period when the majority of dentate neurons are produced. Here we tested how single episodes of hypoxia or chemically induced seizure activity in postnatal day 10 mice alter granule cell production and integration. Although neither insult was sufficient to alter the number of newborn neurons nor the population of proliferating cells, both treatments increased the dendritic complexity of newborn granule cells that were born around the time of the insult. Surprisingly, only the dendritic enhancement caused by hypoxia was associated with increased synaptic integration. These results suggest that alterations in dendritic integration can be dissociated from altered neural production and that integration appears to have a lower threshold for perturbation. Furthermore, newborn neurons in adult mice that experienced neonatal hypoxia had reduced dendritic length while having no alterations in number. Together these results suggest that single insults during the neonatal period can have both long- and short-term consequences for neuronal maturation.

Effect of corticosterone and paroxetine on masculine mating behavior: possible involvement of neurogenesis

INTRODUCTION

Corticosterone inhibits male rodent sexual behavior while the mechanism remains obscured. Recent studies have disclosed that neurogenesis in the subventricular zone (SVZ) can be increased by pheromone exposure from the opposite sex, and neurogenesis is essential for normal mating behavior of female mice. Together with the neurogenesis-inhibiting effect of corticosterone, we hypothesize that cell proliferation in the olfactory system is essential for male rodent sexual functioning.

AIM

The current study explored the relationship between cell proliferation in the olfactory system and male sexual behavior.

MAIN OUTCOME MEASURES

Sexual behavior performance, proliferative cell counts, and c-fos-expressing cell counts.

METHODS

Adult male rats were treated with corticosterone and/or paroxetine, an antidepressant, for 2 weeks. These two drugs were shown to suppress and enhance hippocampus and SVZ cell proliferation, respectively. Mating behavior was assessed after the treatment, and proliferation of new cells and c-fos-expressing cells, activated neurons in the mating-related regions in the brain, were analyzed. To further confirm the necessity of cell proliferation in mating, inhibition of cell proliferation was performed by intracerebroventricular infusion of cytostatic cytosine arabinose (Ara-c).

RESULTS

Corticosterone treatment, which inhibited cell proliferation in both the SVZ and olfactory epithelium, led to inhibited male sexual performance. In contrast, paroxetine increased cell proliferation and improved the performance in corticosterone-treated animals. When cell proliferation in the brain was inhibited by Ara-c, a suppressed sexual performance was found. However, cell proliferation in olfactory epithelium was not inhibited by Ara-c and thus the sexual inhibition is unlikely to be linked to this region. Furthermore, a decrease in c-fos expression in the mating-related regions upon female pheromone stimulation was found.

CONCLUSIONS

These results suggest that cell proliferation in the SVZ and hippocampus may be involved in the reproduction of the male rodents, and pharmacological treatments may affect sexual functioning through alteration of neurogenesis.

The effect of amygdala kindling on hippocampal neurogenesis coincides with decreased reelin and DISC1 expression in the adult dentate gyrus

Temporal lobe seizures can induce the proliferation and abnormal migration of newly generated dentate granule cells, but little is known about the molecular mechanisms that govern these pathological events. Reelin and DISC1 (disrupted-in-schizophrenia 1) are proteins that play a regulatory role in the maturation and integration of new neurons in the developing and adult brain. In this study, we examined whether amygdala kindling results in aberrant neurogenesis and altered expression of reelin and DISC1 in the adult dentate gyrus. Using doublecortin immunohistochemistry, we found that short-term kindling (i.e., 30 electrical stimulations) significantly increased the number of immature neurons in the dentate subgranular zone (SGZ), whereas long-term kindling (i.e., 99 electrical stimulations) did not. However, doublecortin-labeled neurons in long-term kindled rats showed greater dendritic complexity than they did in short-term kindled or control rats. We also found that long-term kindling decreased the number of reelin-positive cells and decreased DISC1 expression in the dentate granule cell layer and subgranular zone. Interestingly, kindling-induced changes in reelin and DISC1 expression coincided with the appearance of ectopically located Prox1-labeled granule cells in the hilus. These effects occurred independently of alterations in granule cell layer length, dentate volume, or the number of hilar neurons. Taken together, these findings suggest a novel role for DISC1 in the pathophysiology of temporal lobe epilepsy and further suggest that changes in reelin and DISC1 expression may contribute to aberrant neurogenesis in the kindling model.

Modulation of neurogenesis by targeted hippocampal irradiation fails to affect kindling progression

Changes in the rate of dentate granule cell neurogenesis and in the fate of newborn granule cells have been implicated in the development and progression of epilepsies. Strategies to normalize neurogenesis in chronic epilepsy models are thought to increase our understanding of the functional consequences of aberrant neurogenesis in the epileptic brain. Therefore, we modulated neurogenesis in an amygdala kindling paradigm in rats by targeted irradiation of the hippocampus using a medical linear accelerator device. Selective irradiation normalized the hippocampal cell proliferation rate in kindled animals. Both, in kindled and nonkindled rats the number of BrdU/NeuN-labeled newborn neurons was reduced in response to irradiation. Whereas kindling resulted in a pronounced increase in the number of neuroblasts identified based on doublecortin-labeling, irradiation prevented the expansion of the neuroblast population. Moreover, irradiation counteracted the kindling-associated increase in hilar basal dendrites, and kept the fraction of cells with basal dendrites at control levels. Despite the efficacious modulation of neurogenesis, irradiation did not affect the rate of kindling progression. Both, the number of stimulations as well as the cumulative afterdischarge duration to reach respective seizure stages were comparable in animals with and without irradiation. In addition, pre- and postkindling thresholds as well as seizure parameters recorded at threshold stimulation remained unaffected by irradiation. In conclusion, the fact that the efficacious modulation of neurogenesis by irradiation did not exert any effects on kindling acquisition and kindled seizures suggests that newborn neurons do not critically contribute to the hyperexcitable state in the chronic epilepsy model used.

Partial kindling induces neurogenesis, activates astrocytes and alters synaptic morphology in the dentate gyrus of freely moving adult rats

A partial kindling procedure was used to investigate the correlation between focal seizure development and changes in dendritic spine morphology, ongoing neurogenesis and reactive astrogliosis in the adult rat dentate gyrus (DG). The processes of neurogenesis and astrogliosis were investigated using markers for doublecortin (DCX), 5-bromo-2-deoxyuridine (BrdU) and glial fibrillary acidic protein (GFAP). Our data demonstrate that mild focal seizures induce a complex series of cellular events in the DG one day after cessation of partial rapid kindling stimulation consisting (in comparison to control animals that were electrode implanted but unkindled), firstly, of an increase in the number of postmitotic BrdU labeled cells, and secondly, an increase in the number of DCX labeled cells, mainly in subgranular zone. Ultrastructural changes were examined using qualitative electron microscope analysis and 3-D reconstructions of both dendritic spines and postsynaptic densities. Typical features of kindling in comparison to control tissue included translocation of mitochondria to the base of the dendritic spine stalks; a migration of multivesicular bodies into mushroom dendritic spines, and most notably formation of "giant" spinules originating from the head of the spines of DG neurons. These morphological alterations arise at seizure stages 2-3 (focal seizures) in the absence of signs of the severe generalized seizures that are generally recognized as potentially harmful for neuronal cells. We suggest that an increase in ongoing neurogenesis, reactive astrogliosis and dendritic spine reorganization in the DG is the crucial step in the chain of events leading to the progressive development of seizure susceptibility in hippocampal circuits.

Cellular immortality in brain tumours: an integration of the cancer stem cell paradigm

Brain tumours are a diverse group of neoplasms that continue to present a formidable challenge in our attempt to achieve curable intervention. Our conceptual framework of human brain cancer has been redrawn in the current decade. There is a gathering acceptance that brain tumour formation is a phenotypic outcome of dysregulated neurogenesis, with tumours viewed as abnormally differentiated neural tissue. In relation, there is accumulating evidence that brain tumours, similar to leukaemia and many solid tumours, are organized as a developmental hierarchy which is maintained by a small fraction of cells endowed with many shared properties of tissue stem cells. Proof that neurogenesis persists throughout adult life, compliments this concept. Although the cancer cell of origin is unclear, the proliferative zones that harbour stem cells in the embryonic, post-natal and adult brain are attractive candidates within which tumour-initiation may ensue. Dysregulated, unlimited proliferation and an ability to bypass senescence are acquired capabilities of cancerous cells. These abilities in part require the establishment of a telomere maintenance mechanism for counteracting the shortening of chromosomal termini. A strategy based upon the synthesis of telomeric repeat sequences by the ribonucleoprotein telomerase, is prevalent in approximately 90% of human tumours studied, including the majority of brain tumours. This review will provide a developmental perspective with respect to normal (neurogenesis) and aberrant (tumourigenesis) cellular turnover, differentiation and function. Within this context our current knowledge of brain tumour telomere/telomerase biology will be discussed with respect to both its developmental and therapeutic relevance to the hierarchical model of brain tumourigenesis presented by the cancer stem cell paradigm.

Adult neurogenesis, mental health, and mental illness: hope or hype?

Psychiatric and neurologic disorders take an enormous toll on society. Alleviating the devastating symptoms and consequences of neuropsychiatric disorders such as addiction, depression, epilepsy, and schizophrenia is a main force driving clinical and basic researchers alike. By elucidating these disease neuromechanisms, researchers hope to better define treatments and preventive therapies. Research suggests that regulation of adult hippocampal neurogenesis represents a promising approach to treating and perhaps preventing mental illness. Here we appraise the role of adult hippocampal neurogenesis in major psychiatric and neurologic disorders within the essential framework of recent progress made in understanding "normal" adult neurogenesis. Topics addressed include the following: the life cycle of an adult hippocampal stem cell and the implications for aging; links between learning and hippocampal neurogenesis; the reciprocal relationship between cocaine self-administration and adult hippocampal neurogenesis; the role of adult neurogenesis in an animal model of depression and response to antidepressant exposure; the impact of neonatal seizures on dentate gyrus neurogenesis; and the contribution of a schizophrenia-susceptibility gene to adult hippocampal neurogenesis. These topics are discussed in light of the regulation of adult neurogenesis, the relationship to normal neurogenesis in adulthood and aging, and, importantly, the manipulation of neurogenesis to promote mental health and treat mental illness.

Hippocampal neurogenesis and neural stem cells in temporal lobe epilepsy

Virtually all mammals, including humans, exhibit neurogenesis throughout life in the hippocampus, a learning and memory center in the brain. Numerous studies in animal models imply that hippocampal neurogenesis is important for functions such as learning, memory, and mood. Interestingly, hippocampal neurogenesis is very sensitive to physiological and pathological stimuli. Certain pathological stimuli such as seizures alter both the amount and the pattern of neurogenesis, though the overall effect depends on the type of seizures. Acute seizures are classically associated with augmentation of neurogenesis and migration of newly born neurons into ectopic regions such as the hilus and the molecular layer of the dentate gyrus. Additional studies suggest that abnormally migrated newly born neurons play a role in the occurrence of epileptogenic hippocampal circuitry characteristically seen after acute seizures, status epilepticus, or head injury. Recurrent spontaneous seizures such as those typically observed in chronic temporal lobe epilepsy are associated with substantially reduced neurogenesis, which, interestingly, coexists with learning and memory impairments and depression. In this review, we discuss both the extent and the potential implications of abnormal hippocampal neurogenesis induced by acute seizures as well as recurrent spontaneous seizures. We also discuss the consequences of chronic spontaneous seizures on differentiation of neural stem cell progeny in the hippocampus and strategies that are potentially useful for normalizing neurogenesis in chronic temporal lobe epilepsy.

Potential consequences of altered neurogenesis on learning and memory in the epileptic brain

Studies of epilepsy and memory are tied by their common dependence on the hippocampal formation and the adjacent brain structures in the temporal lobe. With the discovery of adult neurogenesis and the consequent revisions of our understanding of how the hippocampus works, the role of neurogenesis in epilepsy needs to be addressed. In this article, we outline two theories describing how neurogenesis contributes to the hippocampus-dependent learning. We speculate that any drastic changes in neurogenesis will negatively impact the hippocampal memory processing.