Neuroblast migration along cellular substrates in the developing porcine brain

In the past decade it has become evident that neuroblasts continue to supply the human cortex with interneurons via unique migratory streams shortly following birth. Owing to the size of the human brain, these newborn neurons must migrate long distances through complex cellular landscapes to reach their final locations. This process is poorly understood, largely because of technical difficulties in acquiring and studying neurotypical postmortem human samples along with diverging developmental features of well-studied mouse models. We reasoned that migratory streams of neuroblasts utilize cellular substrates, such as blood vessels, to guide their trek from the subventricular zone to distant cortical targets. Here, we evaluate the association between young interneuronal migratory streams and their preferred cellular substrates in gyrencephalic piglets during the developmental equivalent of human birth, infancy, and toddlerhood.

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Migratory streams of neuroblasts are preserved through postnatal swine development

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Evidence of young neocortical interneurons within migratory streams

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Neuroblasts are tightly associated with vascular and astrocytic cellular substrates

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Harm to migratory interneurons or their substrates may have lifelong consequences

Pleiotropic effects of BDNF on the cerebellum and hippocampus: Implications for neurodevelopmental disorders

Brain-derived neurotrophic factor (BDNF) is one of the most studied neurotrophins in the mammalian brain, essential not only to the development of the central nervous system but also to synaptic plasticity. BDNF is present in various brain areas, but highest levels of expression are seen in the cerebellum and hippocampus. After birth, BDNF acts in the cerebellum as a mitogenic and chemotactic factor, stimulating the cerebellar granule cell precursors to proliferate, migrate and maturate, while in the hippocampus BDNF plays a fundamental role in synaptic transmission and plasticity, representing a key regulator for the long-term potentiation, learning and memory. Furthermore, the expression of BDNF is highly regulated and changes of its expression are associated with both physiological and pathological conditions. The purpose of this review is to provide an overview of the current state of knowledge on the BDNF biology and its neurotrophic role in the proper development and functioning of neurons and synapses in two important brain areas of postnatal neurogenesis, the cerebellum and hippocampus. Dysregulation of BDNF expression and signaling, resulting in alterations in neuronal maturation and plasticity in both systems, is a common hallmark of several neurodevelopmental diseases, such as autism spectrum disorder, suggesting that neuronal malfunction present in these disorders is the result of excessive or reduced of BDNF support. We believe that the more the relevance of the pathophysiological actions of BDNF, and its downstream signals, in early postnatal development will be highlighted, the more likely it is that new neuroprotective therapeutic strategies will be identified in the treatment of various neurodevelopmental disorders.

Postnatal Neurogenesis Beyond Rodents: the Groundbreaking Research of Joseph Altman and Gopal Das

An integral component of neural ontogeny and plasticity is the ongoing generation of new neurons from precursor cells throughout the lifespan in virtually all animals with a nervous system. In mammals, postnatal neurogenesis has been documented in the cerebellum, olfactory bulb, hippocampus, striatum, substantia nigra, hypothalamus, and amygdala. Germinal centers of new neuron production in the adult brain have been identified in the neuroepithelium of the subventricular zone and the dentate gyrus. One of the earliest lines of evidence gathered came from studies on the production of cerebellar microneurons in the external germinal layer of rodents and carnivores in the 1960s and 1970s. The undeniable pioneer of that research was the insightful developmental neurobiologist Joseph Altman (1925-2016). This Cerebellar Classic is devoted to the groundbreaking work of Altman and his graduate student and, subsequently, fellow faculty member, Gopal Das (1933-1991), on postnatal neurogenesis using tritiated thymidine autoradiography to tag newly formed neurons in the cerebellum of cats. Perseverant to their ideas and patiently working in West Lafayette (Indiana), they were the founders of two fields that brought about paradigm shifts and led to an explosive growth in brain research: adult neurogenesis and neural tissue transplantation.

Adult stem cell niches for tissue homeostasis

Adult stem cells are fundamental to maintain tissue homeostasis, growth, and regeneration. They reside in specialized environments called niches. Following activating signals, they proliferate and differentiate into functional cells that are able to preserve tissue physiology, either to guarantee normal turnover or to counteract tissue damage caused by injury or disease. Multiple interactions occur within the niche between stem cell‐intrinsic factors, supporting cells, the extracellular matrix, and signaling pathways. Altogether, these interactions govern cell fate, preserving the stem cell pool, and regulating stem cell proliferation and differentiation. Based on their response to body needs, tissues can be largely classified into three main categories: tissues that even in normal conditions are characterized by an impressive turnover to replace rapidly exhausting cells (blood, epidermis, or intestinal epithelium); tissues that normally require only a basal cell replacement, though able to efficiently respond to increased tissue needs, injury, or disease (skeletal muscle); tissues that are equipped with less powerful stem cell niches, whose repairing ability is not able to overcome severe damage (heart or nervous tissue). The purpose of this review is to describe the main characteristics of stem cell niches in these different tissues, highlighting the various components influencing stem cell activity. Although much has been done, more work is needed to further increase our knowledge of niche interactions. This would be important not only to shed light on this fundamental chapter of human physiology but also to help the development of cell‐based strategies for clinical therapeutic applications, especially when other approaches fail.

Voluntary wheel running improves outcomes in an early life stress-induced model of urologic chronic pelvic pain syndrome in male mice

ABSTRACT

Patients with a history of early life stress (ELS) exposure have an increased risk of developing chronic pain and mood disorders later in life. The severity of ELS in patients with urologic chronic pelvic pain syndrome (UCPPS) is directly correlated with symptom severity and increased comorbidity, and is inversely related to likelihood of improvement. Voluntary exercise improves chronic pain symptoms, and our group and others have shown that voluntary wheel running can improve outcomes in stress-induced UCPPS models, suggesting that exercise may negate some of the outcomes associated with ELS. Here, we provide further evidence that voluntary wheel running can attenuate increased perigenital mechanical sensitivity, bladder output, and mast cell degranulation in the bladder and prostate in male mice that underwent neonatal maternal separation (NMS). Sedentary male NMS mice had reduced serum corticosterone, which was not impacted by voluntary wheel running, although stress-related regulatory gene expression in the hypothalamus and hippocampus was significantly increased after exercise. Neurogenesis in the dentate gyrus of the hippocampus was diminished in sedentary NMS mice and significantly increased in both exercised naïve and NMS mice. Sucrose consumption increased in exercised naïve but not NMS mice, and anxiety behaviors measured on an elevated plus maze were increased after exercise. Together these data suggest that voluntary wheel running is sufficient to normalize many of the UCPPS-related outcomes resulting from NMS. Exercise also increased hippocampal neurogenesis and stress-related gene expression within the hypothalamic-pituitary-adrenal axis, further supporting exercise as a nonpharmacological intervention for attenuating outcomes related to ELS exposure.

Podoplanin Gene Disruption in Mice Promotes in vivo Neural Progenitor Cells Proliferation, Selectively Impairs Dentate Gyrus Synaptic Depression and Induces Anxiety-Like Behaviors

Podoplanin (Pdpn), a brain-tumor-related glycoprotein identified in humans and animals, is endogenously expressed in several organs critical for life support such as kidney, lung, heart and brain. In the brain, Pdpn has been identified in proliferative nestin-positive adult neural progenitor cells and in neurons of the neurogenic hippocampal dentate gyrus (DG), a structure associated to anxiety, critical for learning and memory functions and severely damaged in people with Alzheimer's Disease (AD). The in vivo role of Pdpn in adult neurogenesis and anxiety-like behavior remained however unexplored. Using mice with disrupted Pdpn gene as a model organism and applying combined behavioral, molecular biological and electrophysiological assays, we here show that the absence of Pdpn selectively impairs long-term synaptic depression in the neurogenic DG without affecting the CA3-Schaffer's collateral-CA1 synapses. Pdpn deletion also enhanced the proliferative capacity of DG neural progenitor cells and diminished survival of differentiated neuronal cells in vitro. In addition, mice with podoplanin gene disruption showed increased anxiety-like behaviors in experimentally validated behavioral tests as compared to wild type littermate controls. Together, these findings broaden our knowledge on the molecular mechanisms influencing hippocampal synaptic plasticity and neurogenesis in vivo and reveal Pdpn as a novel molecular target for future studies addressing general anxiety disorder and synaptic depression-related memory dysfunctions.

Neonatal exposure to propofol affects interneuron development in the piriform cortex and causes neurobehavioral deficits in adult mice

RATIONALE

Animal studies have shown that early postnatal propofol administration is involved in neurobehavioral alterations in adults. However, the underlying mechanism is not clear.

METHODS

We used c-Fos immunohistochemistry to identify activated neurons in brain regions of neonatal mice under propofol exposure and performed behavioral tests to observe the long-term consequences.

RESULTS

Exposure to propofol (30g or 60 mg/kg) on P7 produced significant c-Fos expression in the deep layers of the piriform cortex on P8. Double immunofluorescence of c-Fos with interneuron markers in the piriform cortex revealed that c-Fos was specifically induced in calbindin (CB)-positive interneurons. Repeated propofol exposure from P7 to P9 induced behavioral deficits in adult mice, such as olfactory function deficit in a buried food test, decreased sociability in a three-chambered choice task, and impaired recognitive ability of learning and memory in novel object recognition tests. However, locomotor activity in the open-field test was not generally affected. Propofol treatment also significantly decreased the number of CB-positive interneurons in the piriform cortex of mice on P21 and adulthood.

CONCLUSIONS

These results suggest that CB-positive interneurons in the piriform cortex are vulnerable to propofol exposure during the neonatal period, and these neurons are involved in the damage effects of propofol on behavior changes. These data provide a new target of propofol neurotoxicity and may elucidate the mechanism of neurobehavioral deficits in adulthood.

JNK Isoforms Are Involved in the Control of Adult Hippocampal Neurogenesis in Mice, Both in Physiological Conditions and in an Experimental Model of Temporal Lobe Epilepsy

Neurogenesis in the adult dentate gyrus (DG) of the hippocampus allows the continuous generation of new neurons. This cellular process can be disturbed under specific environmental conditions, such as epileptic seizures; however, the underlying mechanisms responsible for their control remain largely unknown. Although different studies have linked the JNK (c-Jun-N-terminal-kinase) activity with the regulation of cell proliferation and differentiation, the specific function of JNK in controlling adult hippocampal neurogenesis is not well known. The purpose of this study was to analyze the role of JNK isoforms (JNK1/JNK2/JNK3) in adult-hippocampal neurogenesis. To achieve this goal, we used JNK-knockout mice (Jnk1^-/-, Jnk2^-/-, and Jnk3^-/-), untreated and treated with intraperitoneal injections of kainic acid (KA), as an experimental model of epilepsy. In each condition, we identified cell subpopulations at different stages of neuronal maturation by immunohistochemical specific markers. In physiological conditions, we evidenced that JNK1 and JNK3 control the levels of one subtype of early progenitor cells (GFAP⁺/Sox2⁺) but not the GFAP⁺/Nestin⁺ cell subtype. Moreover, the absence of JNK1 induces an increase of immature neurons (Doublecortin⁺; PSA-NCAM⁺ cells) compared with wild-type (WT). On the other hand, Jnk1^-/- and Jnk3^-/- mice showed an increased capacity to maintain hippocampal homeostasis, since calbindin immunoreactivity is higher than in WT. An important fact is that, after KA injection, Jnk1^-/- and Jnk3^-/- mice show no increase in the different neurogenic cell subpopulation analyzed, in contrast to what occurs in WT and Jnk2^-/- mice. All these data support that JNK isoforms are involved in the adult neurogenesis control.

Environmental Forces that Shape Early Development: What We Know and Still Need to Know

Understanding health requires more than knowledge of the genome. Environmental factors regulate gene function through epigenetics. Collectively, environmental exposures have been called the "exposome." Caregivers are instrumental in shaping exposures in a child's initial years. Maternal dietary patterns, physical activity, degree of weight gain, and body composition while pregnant will influence not only fetal growth, but also the infant's metabolic response to nutrients and energy. Maternal over- or underweight, excess caloric intake, nutrient imbalances, glucose dysregulation, and presence of chronic inflammatory states have been shown to establish risk for many later chronic diseases. During the period from birth to age 3 y, when the infant's metabolic rate is high and synaptogenesis and myelination of the brain are occurring extremely rapidly, the infant is especially prone to damaging effects from nutrient imbalances. During this period, the infant changes from a purely milk-based diet to one including a wide variety of foods. The process, timing, quality, and ultimate dietary pattern acquired are a direct outcome of the caregiver-infant feeding relationship, with potentially lifelong consequences. More research on how meal time interactions shape food acceptance is needed to avoid eating patterns that augment existing disease risk. Traditional clinical trials in nutrition, meant to isolate single factors for study, are inadequate to study the highly interconnected realm of environment-gene interactions in early life. Novel technologies are being used to gather broad exposure data on disparate populations, employing pioneering statistical approaches and correlations applied specifically to the individual, based on their genetic make-up and unique environmental experiences.

The role of neuro-epithelial-like and radial-glial stem and progenitor cells in development, plasticity, and repair

Neural stem and progenitor cells (NSPCs) are the primary source of new neurons in the brain and serve critical roles in tissue homeostasis and plasticity throughout life. Within the vertebrate brain, NSPCs are located within distinct neurogenic niches differing in their location, cellular composition, and proliferative behaviour. Heterogeneity in the NSPC population is hypothesized to reflect varying capacities for neurogenesis, plasticity and repair between different neurogenic zones. Since the discovery of adult neurogenesis, studies have predominantly focused on the behaviour and biological significance of adult NSPCs (aNSPCs) in rodents. However, compared to rodents, who show lifelong neurogenesis in only two restricted neurogenic niches, zebrafish exhibit constitutive neurogenesis across multiple stem cell niches that provide new neurons to every major brain division. Accordingly, zebrafish are a powerful model to probe the unique cellular and molecular profiles of NSPCs and investigate how these profiles govern tissue homeostasis and regenerative plasticity within distinct stem cell populations over time. Amongst the NSPC populations residing in the zebrafish central nervous system (CNS), proliferating radial-glia, quiescent radial-glia and neuro-epithelial-like cells comprise the majority. Here, we provide insight into the extent to which these distinct NSPC populations function and mature during development, respond to experience, and contribute to successful CNS regeneration in teleost fish. Together, our review brings to light the dynamic biological roles of these individual NSPC populations and showcases their diverse regenerative modes to achieve vertebrate brain repair later in life.

Multifaceted Roles of Connexin 43 in Stem Cell Niches

Purpose of Review

Considerable progress has been made in the field of stem cell research; nonetheless, the use of stem cells for regenerative medicine therapies, for either endogenous tissue repair or cellular grafts post injury, remains a challenge. To better understand how to maintain stem cell potential in vivo and promote differentiation ex vivo, it is fundamentally important to elucidate the interactions between stem cells and their surrounding partners within their distinct niches.

Recent Findings

Among the vast array of proteins depicted as mediators for cell-to-cell interactions, connexin-comprised gap junctions play pivotal roles in the regulation of stem cell fate both in vivo and in vitro.

Summary

This review summarizes and illustrates the current knowledge regarding the multifaceted roles of Cx43, specifically, in various stem cell niches.

Home sweet home: the neural stem cell niche throughout development and after injury

Neural stem cells and their progeny reside in two distinct neurogenic niches within the mammalian brain: the subventricular zone and the dentate gyrus. The interplay between the neural stem cells and the niche in which they reside can have significant effects on cell kinetics and neurogenesis. A comprehensive understanding of the changes to the niche that occur through postnatal development and aging, as well as following injury, is relevant for developing therapeutics and interventions to promote neural repair. We discuss changes that occur within the neural stem and progenitor cell populations, the vasculature, extracellular matrix, microglia, and secreted proteins through aging which impact cell behavior within the neurogenic niches. We examine neural precursor cell and niche responses to injury in neonatal hypoxia-ischemia, juvenile cranial irradiation, and adult stroke. This review examines the interplay between the niche and stem cell behavior through aging and following injury as a means to understand intrinsic and extrinsic factors that regulate neurogenesis in vivo.

Early depletion of CA1 neurons and late neurodegeneration in a mouse tauopathy model

Alzheimer's disease (AD) and tauopathies, such as frontotemporal dementia (FTD), are characterized by formation of neurofibrillary tangles consisting of hyperphosphorylated tau. Further neuropathological characteristics include synaptic loss, neurodegeneration and brain atrophy. Here, we explored the association between hyperphosphorylated tau species, brain atrophy, synaptic and neuronal loss in a mouse model (rTg4510) carrying the human tau (hTau) P301L mutation found in a familiar form of FTD. We established that hTau expression during the first 6 postnatal weeks was important for the progression of tauopathy in rTg4510 mice. Short term suppression of postnatal hTau expression delayed the onset of tau pathology by approximately 6months in this model. Early postnatal hTau expression was detrimental to CA1 neurons of the hippocampus and reduced neuronal numbers in 6-10weeks young rTg4510 mice prior to the appearance of hyperphosphorylated hTau species in the hippocampus. Hyperphosphorylated hTau species emerged from 10 to 24weeks of age and were associated with increased ubiquitin levels, gliosis, and brain atrophy and preceded the synaptic loss and CA1 neurodegeneration that occurred at 48weeks of age. We present two consequences of hTau expression in CA1 in rTg4510 mice: an early decrease in neuron number already established prior to the presence of hyperphosphorylated tau species and a later neurodegeneration dependent on hyperphosphorylated tau. Neurodegeneration and synaptic protein loss were completely prevented when hTau expression was suppressed prior to the appearance of hyperphosphorylated tau species. Suppression of hTau expression after the onset of tau hyperphosphorylation and tangle pathology initiated at 16weeks partially rescued neuronal loss at 48weeks of age, while a reduction of neurodegeneration was no longer possible when hTau suppression was introduced as late as at 24weeks of age. Our results in rTg4510 mice argue that it is promising to lower hyperphosphorylated tau species at early stages of tau pathology to protect from neurodegeneration.

Seasonal variations in auditory processing in the inferior colliculus of Eptesicus fuscus

Eptesicus fuscus is typical of temperate zone bats in that both sexes undergo marked seasonal changes in behavior, endocrine status, and reproductive status. Acoustic communication plays a key role in many seasonal behaviors. For example, males emit specialized vocalizations during mating in the fall, and females use different specialized vocalizations to communicate with infants in late spring. Bats of both sexes use echolocation for foraging during times of activity, but engage in little sound-directed behavior during torpor and hibernation in winter. Auditory processing might be expected to reflect these marked seasonal changes. To explore the possibility that seasonal changes in hormonal status could drive functional plasticity in the central auditory system, we examined responses of single neurons in the inferior colliculus throughout the year. The average first spike latency in females varied seasonally, almost doubling in spring compared to other times of year. First spike latencies in males remained relatively stable throughout the year. Latency jitter for both sexes was higher in winter and spring than in summer or fall. Females had more burst responders than other discharge patterns throughout the year whereas males had more transient responders at all times of year except fall, when burst responses were the predominant type. The percentage of simple discharge patterns (sustained and transient) was higher in males than females in the spring and higher in females than males in the fall. In females, the percentage of shortpass duration-tuned neurons doubled in summer and remained elevated through fall and early winter. In males, the percentage of shortpass duration-tuned cells increased in spring and the percentage of bandpass duration-tuned cells doubled in the fall. These findings suggest that there are clear seasonal changes in basic response characteristics of midbrain auditory neurons in Eptesicus, especially in temporal response properties and duration sensitivity. Moreover, the pattern of changes is different in males and females, suggesting that hormone-driven plasticity adjusts central auditory processing to fit the characteristics of vocalizations specific to seasonal behavioral patterns.

Annual Research Review: Enduring neurobiological effects of childhood abuse and neglect

BACKGROUND

Childhood maltreatment is the most important preventable cause of psychopathology accounting for about 45% of the population attributable risk for childhood onset psychiatric disorders. A key breakthrough has been the discovery that maltreatment alters trajectories of brain development.

METHODS

This review aims to synthesize neuroimaging findings in children who experienced caregiver neglect as well as from studies in children, adolescents and adults who experienced physical, sexual and emotional abuse. In doing so, we provide preliminary answers to questions regarding the importance of type and timing of exposure, gender differences, reversibility and the relationship between brain changes and psychopathology. We also discuss whether these changes represent adaptive modifications or stress-induced damage.

RESULTS

Parental verbal abuse, witnessing domestic violence and sexual abuse appear to specifically target brain regions (auditory, visual and somatosensory cortex) and pathways that process and convey the aversive experience. Maltreatment is associated with reliable morphological alterations in anterior cingulate, dorsal lateral prefrontal and orbitofrontal cortex, corpus callosum and adult hippocampus, and with enhanced amygdala response to emotional faces and diminished striatal response to anticipated rewards. Evidence is emerging that these regions and interconnecting pathways have sensitive exposure periods when they are most vulnerable.

CONCLUSIONS

Early deprivation and later abuse may have opposite effects on amygdala volume. Structural and functional abnormalities initially attributed to psychiatric illness may be a more direct consequence of abuse. Childhood maltreatment exerts a prepotent influence on brain development and has been an unrecognized confound in almost all psychiatric neuroimaging studies. These brain changes may be best understood as adaptive responses to facilitate survival and reproduction in the face of adversity. Their relationship to psychopathology is complex as they are discernible in both susceptible and resilient individuals with maltreatment histories. Mechanisms fostering resilience will need to be a primary focus of future studies.

Expression of Dbn1 during mouse brain development and neural stem cell differentiation

Dbn1 is a newly discovered gene in the drebrin gene family of mice. Previous studies have reported that Dbn1 is specifically expressed in the mouse brain suggesting its potential role in brain development. However, a detailed analysis of Dbn1 expression during mouse brain development has not been demonstrated. Here, we describe the expression pattern of Dbn1 and the coexpression of Dbn1 and actin during the development of the mouse brain from embryonic day 14 (E14) to adulthood and during the differentiation of neural stem cells (NSCs), as determined using immunohistochemistry, double-labeling immunofluorescence, and quantitative real-time polymerase chain reaction. During mouse brain development, Dbn1 expression level was high at E14, attenuated postnatally, reached its highest point at postnatal day 7 (P7), and showed a very low level at adulthood. Imaging data showed that Dbn1 was mainly expressed in the hippocampus, ventricular zone, and cortex, where NSCs are densely distributed, and that the intracellular distribution of Dbn1 was predominantly located in the cytoplasm edges and neurites. Moreover, the signal for colocalization of Dbn1 with actin was intense at E14, P0, and P7, but it was weak at adulthood. During NSC differentiation, Dbn1 mRNA expression increased after the onset of differentiation and reached its highest point at 3days, followed by a decrease in expression. The imaging data showed that Dbn1 was increasingly expressed in the extending neurites in accordance with the cell morphological changes that occur during differentiation. Furthermore, obvious colocalization signals of Dbn1 with actin were found in the neurites and dendritic spines. Collectively, these results suggest that Dbn1 may play a key role in mouse brain development and may regulate NSC differentiation by filamentous actin.

The cockayne syndrome B protein is essential for neuronal differentiation and neuritogenesis

Cockayne syndrome (CS) is a progressive developmental and neurodegenerative disorder resulting in premature death at childhood and cells derived from CS patients display DNA repair and transcriptional defects. CS is caused by mutations in csa and csb genes, and patients with csb mutation are more prevalent. A hallmark feature of CSB patients is neurodegeneration but the precise molecular cause for this defect remains enigmatic. Further, it is not clear whether the neurodegenerative condition is due to loss of CSB-mediated functions in adult neurogenesis. In this study, we examined the role of CSB in neurogenesis by using the human neural progenitor cells that have self-renewal and differentiation capabilities. In this model system, stable CSB knockdown dramatically reduced the differentiation potential of human neural progenitor cells revealing a key role for CSB in neurogenesis. Neurite outgrowth, a characteristic feature of differentiated neurons, was also greatly abolished in CSB-suppressed cells. In corroboration with this, expression of MAP2 (microtubule-associated protein 2), a crucial player in neuritogenesis, was also impaired in CSB-suppressed cells. Consistent with reduced MAP2 expression in CSB-depleted neural cells, tandem affinity purification and chromatin immunoprecipitation studies revealed a potential role for CSB in the assembly of transcription complex on MAP2 promoter. Altogether, our data led us to conclude that CSB has a crucial role in coordinated regulation of transcription and chromatin remodeling activities that are required during neurogenesis.