Lesion-induced neurogenesis in the hypothalamus is involved in behavioral recovery in adult ring doves

Although neurogenesis in the brain of adult vertebrates is region dependent, lesion induces generation of new neurons in non-neurogenic brain regions. These findings raise the question of the role of new neurons in brain repair and functional recovery. We addressed this question by applying previous observations that electrolytic lesion induced neurogenesis in the ventromedial nucleus (VMN) of the hypothalamus in adult ring doves. Such lesions disrupted the male's courtship behavior, which could be reinstated after rehabilitation with a female. We investigated whether lesion-induced newborn neurons in the VMN facilitate the recovery of courtship behavior in the lesioned birds. We conducted systematic observations of cytological, morphological, and neuroanatomical changes in the lesioned VMN, and concurrently we monitored behavioral changes. Using a multitude of specific cell markers, we found a well-circumscribed cellular zone that proliferated actively. This highly proliferative zone initially appeared along the periphery of the lesion site, where cells had high levels of expression of neuronal, glial, and neurovascular markers. As newborn neurons matured at the lesion site, the necrosis gradually decreased, whereas a downsized proliferative zone relocated to a region ventral to the VMN. Some of the mature neurons were found to project to the midbrain vocal nuclei. Restoration of these projection neurons coincided with the recovery of courtship vocalization. Finally, we found that a social factor, that is, when the male doves were cohoused with a mate, facilitated neurogenesis and behavioral recovery. These results suggest that lesion-induced neurogenesis contributes to behavioral recovery in adult animals.     

损毁成体鸽下丘脑腹内侧核对神经元增生的影响

本实验应用（＾３Ｈ）放射自显影和免疫组织化学方法首次报道了高等脊椎动物成体鸟脑损伤引起神经元增生的观察结果。电损毁非鸣禽成体环鸽下丘脑腹内侧核后能引起端脑外侧室带区中（＾３Ｈ）标记细胞的大量增生和在端脑尾部ＬＶＺ中的特异性分布。     

The studies on neurogenesis induced by brain injury in adult ring dove

INTRODUCTIONItisacommonstatementthatillhighervertebratestheCNScompletesneuronaldevelopmentduringthepre--andprenatalperiods.Preliminaryworkshowedthatneurogenesisconfinuedinthebrainofsongbirdduringadulthood.Manynewbornneuronsareincorporatedintothevocal-cont…     

Newborn GnRH neurons in the adult forebrain of the ring dove

The preoptic area of the hypothalamus is a key area that produces gonadotrophin-releasing hormone (GnRH). In birds, the chicken GnRH-I-form neurons are responsible for the hypothalamus-pituitary-gonadal system, which controls reproduction. In the ring dove, electrolytic lesion in the adult hypothalamus induces neurogenesis. In this study, we determined whether adult neurogenesis is involved in repairing GnRH neurons, specifically by generating newborn cells exhibiting GnRH-I immunoreactive properties. We selectively applied electrolytic lesions to three different regions of the diencephalon, including the preoptic area, which contains GnRH-I neurons, and identified new cells (BrdU-positive cells) that co-labeled with GnRH-I-immunoreactive cells. The BrdU⁺/GnRH⁺ double labeled cells were then confirmed with confocal laser analysis. In brains of both male and female ring doves we found new neurons at the lesion site of the preoptic region that were GnRH-I immunoreactive. However, the total number of GnRH neurons in the lesioned brains was less than that of sham-lesioned brains. When two other regions of the diencephalon that contain GnRH-I neurons were damaged, no recruitment of new GnRH-I neurons was detected. The rate of neurogenesis depends on the bird's reproductive phase when the lesion was applied. We found BrdU⁺/GnRH⁺ double-labeled cells almost exclusively during the pre-laying phase when birds are engaged in active courtship that leads to egg laying. Our observations suggest that recruitment of GnRH immunoreactive new neurons is restricted to the hypothalamic region and is sensitive to the reproductive stage of the birds.     

Functional restoration of acoustic units and adult‐generated neurons after hypothalamic lesion

The hypothalamus of the adult ring dove contains acoustic units that respond to species‐specific coo vocalization. Loss of nest coo leads to unsuccessful breeding. However, the recovery of nest coo in some doves suggests that these units are capable of self‐renewal. We have previously shown that lesioning the hypothalamus generates the addition of new neurons at the lesioned area. In this study, we sought to determine whether lesion‐induced new neurons are involved in the recovery of coo‐responsive units. We systematically recorded electrical activity in the ventromedial nucleus (VMN) of the hypothalamus, before and after lesion, for varying periods up to 3 months. Recordings were made when the birds were at rest (spontaneous discharge) and when the birds were exposed to acoustic stimulations (evoked discharge). Concurrently, the lesioned area was monitored for changes in cell types by using bromodeoxyuridine (BrdU) to label newly divided cells and NeuN to identify mature neurons. For 1 month after lesion, there was no sign of electrical activity, and only BrdU‐labeled cells were present. When the first electrical activity occurred, it displayed abnormal spontaneous bursting patterns. The mature discharge patterns (both spontaneous and evoked) occurred after detection of BrdU⁺/NeuN⁺ double‐labeled cells 2–3 months postlesion and were similar to those found in intact and sham‐lesioned birds. Double‐labeled cells bore morphologic characteristics of a neuron and were confirmed with z‐stack analysis using confocal laser scanning microscopy. Moreover, double‐labeled cells were not stained for glial fibrillary acidic protein (GFAP), suggesting that they were neurons. The number of coo‐responsive units was significantly correlated with that of BrdU⁺/NeuN⁺ cells. Furthermore, the marker for recording sites revealed that coo‐responsive units were colocalized with BrdU⁺/NeuN⁺ cells. Taken together, the evidence strongly suggests that lesion‐induced addition of new neurons promotes the functional recovery of the adult hypothalamus. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 197–213, 2004     

Ischemia-induced neurogenesis is preserved but reduced in the aged rodent brain

The adult mammalian brain retains the capacity for neurogenesis, by which new neurons may be generated to replace those lost through physiological or pathological processes. However, neurogenesis diminishes with aging, and this casts doubt on its feasibility as a therapeutic target for cell replacement therapy in stroke and neurodegenerative disorders, which disproportionately affect the aged brain. In previous studies, neurogenesis was stimulated by cerebral ischemia in young rodents, and the neurogenesis response of the aged rodent brain to physiological stimuli, such as hormonal manipulation and growth factors, was preserved. To investigate the effect of aging on ischemia-induced neurogenesis, transient (60 min) middle cerebral artery occlusion was induced in young adult (3-month) and aged (24-month) rats, who were also given bromodeoxyuridine to label newborn cells. As found in prior studies, basal neurogenesis in control, nonischemic rats was reduced with aging. Ischemia failed to stimulate neurogenesis in the dentate gyrus (DG) subgranular zone (SGZ), in contrast to results obtained previously after more prolonged (90-120 min) middle cerebral artery occlusion, but increased the number of BrdU-labeled cells in the forebrain subventricular zone (SVZ). This effect was less prominent in aged than in young adult rats, with fold-stimulation of BrdU incorporation reduced by approximately 20% and the total number of cells generated diminished by approximately 50%. BrdU-labeled cells in SVZ coexpressed neuronal lineage markers, consistent with newborn neurons. We conclude that ischemia-induced neurogenesis occurs in the aged brain, and that measures designed to augment this phenomenon might have therapeutic applications.     

Functional restoration of acoustic units and adult-generated neurons after hypothalamic lesion

The hypothalamus of the adult ring dove contains acoustic units that respond to species-specific coo vocalization. Loss of nest coo leads to unsuccessful breeding. However, the recovery of nest coo in some doves suggests that these units are capable of self-renewal. We have previously shown that lesioning the hypothalamus generates the addition of new neurons at the lesioned area. In this study, we sought to determine whether lesion-induced new neurons are involved in the recovery of coo-responsive units. We systematically recorded electrical activity in the ventromedial nucleus (VMN) of the hypothalamus, before and after lesion, for varying periods up to 3 months. Recordings were made when the birds were at rest (spontaneous discharge) and when the birds were exposed to acoustic stimulations (evoked discharge). Concurrently, the lesioned area was monitored for changes in cell types by using bromodeoxyuridine (BrdU) to label newly divided cells and NeuN to identify mature neurons. For 1 month after lesion, there was no sign of electrical activity, and only BrdU-labeled cells were present. When the first electrical activity occurred, it displayed abnormal spontaneous bursting patterns. The mature discharge patterns (both spontaneous and evoked) occurred after detection of BrdU+/NeuN+ double-labeled cells 2-3 months postlesion and were similar to those found in intact and sham-lesioned birds. Double-labeled cells bore morphologic characteristics of a neuron and were confirmed with z-stack analysis using confocal laser scanning microscopy. Moreover, double-labeled cells were not stained for glial fibrillary acidic protein (GFAP), suggesting that they were neurons. The number of coo-responsive units was significantly correlated with that of BrdU+/NeuN+ cells. Furthermore, the marker for recording sites revealed that coo-responsive units were colocalized with BrdU+/NeuN+ cells. Taken together, the evidence strongly suggests that lesion-induced addition of new neurons promotes the functional recovery of the adult hypothalamus.     

成体神经干(前体)细胞在中枢神经系统退行性病变中的修复作用

尽管传统概念长期认为成体哺乳动物中枢神经系统缺乏再生增殖能力,但近年来发现,在成体若干脑区内确实存在具有再生与分化能力的神经干或神经前体细胞。这些干细胞在正常倩况下仅表现较低的再生分化活动。不过,在神经退行性病变中,病灶区内的干细胞可被动员、激活,并以较高的速率分裂分化以及取代坏死的神经元或胶质细胞,达到自身原位修复的作用。许多神经生长和营养因子具有增强或抑制干细胞分裂秋或分化的能力,在神经退行性病变中,病灶区内外成熟或新生细胞即可通过表达这些因子,有效调节干细胞的活动和干细胞主导的修复过程。总之,成体神经干细胞可以积极参与急性或慢性神经组织损伤的修复,通过再生来提供新的神经元以及其他必需的细胞,以促进功能的恢复。     

Mitogen‐ and stress‐activated kinases regulate progenitor cell proliferation and neuron development in the adult dentate gyrus

The neurogenic niche within the subgranular zone (SGZ) of the dentate gyrus is a source of new neurons throughout life. Interestingly, SGZ proliferative capacity is regulated by both physiological and pathophysiological conditions. One outstanding question involves the molecular mechanisms that regulate both basal and inducible adult neurogenesis. Here, we examined the role of the MAPK‐regulated kinases, mitogen‐ and stress‐activated kinase (MSK)1 and MSK2. as regulators of dentate gyrus SGZ progenitor cell proliferation and neurogenesis. Under basal conditions, MSK1/2 null mice exhibited significantly reduced progenitor cell proliferation capacity and a corollary reduction in the number of doublecortin (DCX)‐positive immature neurons. Strikingly, seizure‐induced progenitor proliferation was totally blocked in MSK1/2 null mice. This blunting of cell proliferation in MSK1/2 null mice was partially reversed by forskolin infusion, indicating that the inducible proliferative capacity of the progenitor cell population was intact. Furthermore, in MSK1/2 null mice, DCX‐positive immature neurons exhibited reduced neurite arborization. Together, these data reveal a critical role for MSK1/2 as regulators of both basal and activity‐dependent progenitor cell proliferation and morphological maturation in the SGZ.     

Locating and labeling neural stem cells in the brain

The phenomenon of adult neurogenesis has been demonstrated in most mammals including humans. At least two regions of the adult brain maintain stem cells throughout life; the subgranular zone (SGZ) of the hippocampal dentate gyrus, and the subventricular zone (SVZ) of the lateral ventricle wall. Both regions continuously produce neurons that mature and become integrated into functional networks that are involved in learning and memory and odor discrimination, respectively. Apart from these well‐studied regions neurogenesis has been reported in a number of other brain regions, such as amygdala and cortex. However, these studies have been contested and there is currently no well‐postulated function for non‐SVZ/SGZ neurogenesis. The studies of the regional localization of neurogenesis in the brain have been made possible due to several methods for detecting adult neurogenesis including; bromodeoxyuridine labeling (BrdU) together with markers of mature neurons, genetic labeling, by mouse transgenesis, or with the use of viral vectors. These techniques are already put to creative use and will be essential for the discovery of the nature of the adult neural stem cells. In this mini‐review, we will discuss the localization of neural stem/progenitor cells in the brain and their implications as well as discussing the pro's and con's of stem cell labeling techniques. J. Cell. Physiol. 226: 1–7, 2010. © 2010 Wiley‐Liss, Inc.     

Adult neurogenesis in the mammalian brain: significant answers and significant questions

Adult neurogenesis, a process of generating functional neurons from adult neural precursors, occurs throughout life in restricted brain regions in mammals. The past decade has witnessed tremendous progress in addressing questions related to almost every aspect of adult neurogenesis in the mammalian brain. Here we review major advances in our understanding of adult mammalian neurogenesis in the dentate gyrus of the hippocampus and from the subventricular zone of the lateral ventricle, the rostral migratory stream to the olfactory bulb. We highlight emerging principles that have significant implications for stem cell biology, developmental neurobiology, neural plasticity, and disease mechanisms. We also discuss remaining questions related to adult neural stem cells and their niches, underlying regulatory mechanisms, and potential functions of newborn neurons in the adult brain. Building upon the recent progress and aided by new technologies, the adult neurogenesis field is poised to leap forward in the next decade.     

室管膜下区神经干细胞与神经发生的研究进展

室管膜下区(subventricular zone,SVZ)存在着神经干细胞(nueral stem cells,NSCs),是成年哺乳动物脑内重要的神经发生区域。神经发生过程极为复杂,包括一系列的生物学事件。在病理状态下,SVZ区的细胞增殖,新生的神经细胞迁移到病灶处,取代或修复受损的细胞,起到保护脑组织的作用。该文就SVZ区的神经干细胞、神经发生过程及病理状态下神经发生的相关研究做一综述。     

The microtubule destabilizing protein stathmin controls the transition from dividing neuronal precursors to postmitotic neurons during adult hippocampal neurogenesis

The hippocampus is one of the two areas in the mammalian brain where adult neurogenesis occurs. Adult neurogenesis is well known to be involved in hippocampal physiological functions as well as pathophysiological conditions. Microtubules (MTs), providing intracellular transport, stability, and transmitting force, are indispensable for neurogenesis by facilitating cell division, migration, growth, and differentiation. Although there are several examples of MT‐stabilizing proteins regulating different aspects of adult neurogenesis, relatively little is known about the function of MT‐destabilizing proteins. Stathmin is such a MT‐destabilizing protein largely restricted to the CNS, and in contrast to its developmental family members, stathmin is also expressed at significant levels in the adult brain, notably in areas involved in adult neurogenesis. Here, we show an important role for stathmin during adult neurogenesis in the subgranular zone of the mouse hippocampus. After carefully mapping stathmin expression in the adult dentate gyrus (DG), we investigated its role in hippocampal neurogenesis making use of stathmin knockout mice. Although hippocampus development appears normal in these animals, different aspects of adult neurogenesis are affected. First, the number of proliferating Ki‐67+ cells is decreased in stathmin knockout mice, as well as the expression of the immature markers Nestin and PSA‐NCAM. However, newborn cells that do survive express more frequently the adult marker NeuN and have a more mature morphology. Furthermore, our data suggest that migration in the DG might be affected. We propose a model in which stathmin controls the transition from neuronal precursors to early postmitotic neurons. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 74: 1226–1242, 2014     

Glycogen Synthase Kinase-3β Regulates Equilibrium Between Neurogenesis and Gliogenesis in Rat Model of Parkinson’s Disease: a Crosstalk with Wnt and Notch Signaling

Neurogenesis involves generation of functional newborn neurons from neural stem cells (NSCs). Insufficient formation or accelerated degeneration of newborn neurons may contribute to the severity of motor/nonmotor symptoms of Parkinson’s disease (PD). However, the functional role of adult neurogenesis in PD is yet not explored and whether glycogen synthase kinase-3β (GSK-3β) affects multiple steps of adult neurogenesis in PD is still unknown. We investigated the possible underlying molecular mechanism of impaired adult neurogenesis associated with PD. Herein, we show that single intra-medial forebrain bundle (MFB) injection of 6-hydroxydopamine (6-OHDA) efficiently induced long-term activation of GSK-3β and reduced NSC self-renewal, proliferation, neuronal migration, and neuronal differentiation accompanied with increased astrogenesis in subventricular zone (SVZ) and hippocampal dentate gyrus (DG). Indeed, 6-OHDA also delayed maturation of neuroblasts in the DG as witnessed by their reduced dendritic length and arborization. Using a pharmacological approach to inhibit GSK-3β activation by specific inhibitor SB216763, we show that GSK-3β inhibition enhances radial glial cells, NSC proliferation, self-renewal in the SVZ, and the subgranular zone (SGZ) in the rat PD model. Pharmacological inhibition of GSK-3β activity enhances neuroblast population in SVZ and SGZ and promotes migration of neuroblasts towards the rostral migratory stream and lesioned striatum from dorsal SVZ and lateral SVZ, respectively, in PD model. GSK-3β inhibition enhances dendritic arborization and survival of granular neurons and stimulates NSC differentiation towards the neuronal phenotype in DG of PD model. The aforementioned effects of GSK-3β involve a crosstalk between Wnt/β-catenin and Notch signaling pathways that are known to regulate NSC dynamics.     

Newborn cells in the adult crayfish brain differentiate into distinct neuronal types

Mitotically active regions persist in the brains of decapod crustaceans throughout their lifetimes, as they do in many vertebrates. The most well-studied of these regions in decapods occurs within a soma cluster, known as cluster 10, located in the deutocerebrum. Cluster 10 in crayfish and lobsters is composed of the somata of two anatomically and functionally distinct classes of projection neurons: olfactory lobe (OL) projection neurons and accessory lobe (AL) projection neurons. While adult-generated cells in cluster 10 survive for at least a year, their final phenotypes remain unknown. To address this question, we combined BrdU labeling of proliferating cells with specific neuronal and glial markers and tracers to examine the differentiation of newborn cells in cluster 10 of the crayfish, Cherax destructor. Our results show that large numbers of adult-generated cells in cluster 10 differentiate into neurons expressing the neuropeptide crustacean-SIFamide. No evidence was obtained suggesting that cells differentiate into glia. The functional phenotypes of newborn neurons in cluster 10 were examined by combining BrdU immunocytochemistry with the application of dextran dyes to different brain neuropils. These studies showed that while the majority of cells born during the early postembryonic development of C. destructor differentiate in AL projection neurons, neurogenesis in adult crayfish is characterized by the addition of both OL and AL projection neurons. In addition to our examination of neurogenesis in the olfactory pathway, we provide the first evidence that adult neurogenesis is also a characteristic feature of the optic neuropils of decapod crustaceans.     

Olfactory bulb neurogenesis and its neurological impact

Contrary to the long-held dogma according to which the adult mammalian brain does not produce neurons anymore, neuronal turnover has been reported in two discrete areas of the adult brain: the hippocampus and the olfactory bulb. Adult-generated neurons are produced from neural stem cells located in the hippocampal subgranular zone and the subventricular zone of the lateral ventricles. Recently, number of genetic and epigenetic factors that modulate proliferation of stem cells, migration, differentiation and survival of newborn neurons have been characterized. We know that neurogenesis increases in the diseased brain, after stroke or after traumatic brain injury. Importantly, progenitors from the subventricular zone, but not from the subgranular zone, are incorporated at the sites of injury, where they replace some of the degenerated neurons. Thus, the central nervous system has the capacity to regenerate itself after injury and, today, researchers develop strategies aimed at promoting neurogenesis in diseased areas. This basic research is attracting a lot of attention because of the hope that it will lead to regeneration and reconstruction therapy for the damaged brain. In this review, we discuss major findings concerning the organization of the neurogenic niche located in the subventricular zone and examine both intrinsic and extrinsic factors that regulate adult neurogenesis. Then, we present evidences for the intrinsic capability of the adult brain for cell replacement, and shed light on recent works demonstrating that one can greatly enhance appropriate brain cell replacement by using molecular cues known to endogenously control proliferation, migration, differentiation and/or survival of subventricular zone progenitors. Finally, we review some of the advantages and limits of strategies aimed at using endogenous progenitors and their relevance to human clinics.     

Migration and differentiation of neural precursors derived from human embryonic stem cells in the rat brain

Human embryonic stem (hES) cells provide a potentially unlimited cell source for regenerative medicine. Recently, differentiation strategies were developed to direct hES cells towards neural fates in vitro. However, the interaction of hES cell progeny with the adult brain environment remains unexplored. Here we report that hES cell-derived neural precursors differentiate into neurons, astrocytes and oligodendrocytes in the normal and lesioned brain of young adult rats and migrate extensively along white matter tracts. The differentiation and migration behavior of hES cell progeny was region specific. The hES cell-derived neural precursors integrated into the endogenous precursor pool in the subventricular zone, a site of persistent neurogenesis. Like adult neural stem cells, hES cell-derived precursors traveled along the rostral migratory stream to the olfactory bulb, where they contributed to neurogenesis. We found no evidence of cell fusion, suggesting that hES cell progeny are capable of responding appropriately to host cues in the subventricular zone.     

神经元再生:抑郁症治疗的新策略

成年哺乳动物一生中,海马等脑区神经元是可以再生的,而海马脑区神经元再生的减少和增多分别是抑郁症发生和恢复的重要因素。如果神经元再生过程被抑制,在抑郁症的动物模型上抗抑郁剂将会失去其行为学效应。长期给予不同种类的抗抑郁剂可以显著地促进动物海马神经元再生。随着对神经元再生调节机制研究的不断深入,为进一步探讨抑郁症的发生机制,以及发展新型抗抑郁治疗药物提供了新的思路与视角。     

Endogenous neurogenesis after intracerebral hemorrhage

Currently, it is accepted that brain injury promotes endogenous neurogenesis in mammals, primarily in the subventricular zone (SVZ), and newborn cells can migrate to the injured area. We examined the pattern of endogenous neurogenesis in adult rats after intracerebral hemorrhage (ICH) that was caused by intrastrial administration of collagenase type IV. Our results showed that ICH induced strong endogenous neurogenesis between 72 hours and 7 days after injury, but that the majority of newborn cells did not survive longer than 3 weeks due to apoptosis-mediated cell death. Furthermore, endogenous neurogenesis remained into a small extent at least 1 year after ICH. Because of the growing interest in new strategies for brain regeneration, these data suggest endogenous neurogenesis and inhibiting apoptosis of newborn neuroblasts as potential strategies to improve the consequences of hemorrhagic stroke in humans.     

Prenatal Stress Inhibits Hippocampal Neurogenesis but Spares Olfactory Bulb Neurogenesis

The dentate gyrus (DG) and the olfactory bulb (OB) are two regions of the adult brain in which new neurons are integrated daily in the existing networks. It is clearly established that these newborn neurons are implicated in specific functions sustained by these regions and that different factors can influence neurogenesis in both structures. Among these, life events, particularly occurring during early life, were shown to profoundly affect adult hippocampal neurogenesis and its associated functions like spatial learning, but data regarding their impact on adult bulbar neurogenesis are lacking. We hypothesized that prenatal stress could interfere with the development of the olfactory system, which takes place during the prenatal period, leading to alterations in adult bulbar neurogenesis and in olfactory capacities. To test this hypothesis we exposed pregnant C57Bl/6J mice to gestational restraint stress and evaluated behavioral and anatomic consequences in adult male offspring.We report that prenatal stress has no impact on adult bulbar neurogenesis, and does not alter olfactory functions in adult male mice. However, it decreases cell proliferation and neurogenesis in the DG of the hippocampus, thus confirming previous reports on rats. Altogether our data support a selective and cross-species long-term impact of prenatal stress on neurogenesis.