Neurotrophins regulate dendritic growth in developing visual cortex

Dendritic growth and synaptic organization from activity-independent cues and local activity-dependent plasticity

Dendritic branching and synaptic organization shape single-neuron and network computations. How they emerge simultaneously during brain development as neurons become integrated into functional networks is still not mechanistically understood. Here, we propose a mechanistic model in which dendrite growth and the organization of synapses arise from the interaction of activity-independent cues from potential synaptic partners and local activity-dependent synaptic plasticity. Consistent with experiments, three phases of dendritic growth - overshoot, pruning, and stabilization - emerge naturally in the model. The model generates stellate-like dendritic morphologies that capture several morphological features of biological neurons under normal and perturbed learning rules, reflecting biological variability. Model-generated dendrites have approximately optimal wiring length consistent with experimental measurements. In addition to establishing dendritic morphologies, activity-dependent plasticity rules organize synapses into spatial clusters according to the correlated activity they experience. We demonstrate that a trade-off between activity-dependent and -independent factors influences dendritic growth and synaptic location throughout development, suggesting that early developmental variability can affect mature morphology and synaptic function. Therefore, a single mechanistic model can capture dendritic growth and account for the synaptic organization of correlated inputs during development. Our work suggests concrete mechanistic components underlying the emergence of dendritic morphologies and synaptic formation and removal in function and dysfunction, and provides experimentally testable predictions for the role of individual components.

Fetal growth restriction adversely impacts trajectory of hippocampal neurodevelopment and function

The last pregnancy trimester is critical for fetal brain development but is a vulnerable period if the pregnancy is compromised by fetal growth restriction (FGR). The impact of FGR on the maturational development of neuronal morphology is not known, however, studies in fetal sheep allow longitudinal analysis in a long gestation species. Here we compared hippocampal neuron dendritogenesis in FGR and control fetal sheep at three timepoints equivalent to the third trimester of pregnancy, complemented by magnetic resonance image for brain volume, and electrophysiology for synaptic function. We hypothesized that the trajectory of hippocampal neuronal dendrite outgrowth would be decreased in the growth-restricted fetus, with implications for hippocampal volume, connectivity, and function. In control animals, total dendrite length increased with advancing gestation, but not in FGR, resulting in a significantly reduced trajectory of dendrite outgrowth in FGR fetuses for total length, branching, and complexity. Ex vivo electrophysiology analysis shows that paired-pulse facilitation was reduced in FGR compared to controls for cornu ammonis 1 hippocampal outputs, reflecting synaptic dysfunction. Hippocampal brain-derived neurotrophic factor density decreased over late gestation in FGR fetuses but not in controls. This study reveals that FGR is associated with a significant deviation in the trajectory of dendrite outgrowth of hippocampal neurons. Where dendrite length significantly increased over the third trimester of pregnancy in control brains, there was no corresponding increase over time in FGR brains, and the trajectory of dendrite outgrowth in FGR offspring was significantly reduced compared to controls. Reduced hippocampal dendritogenesis in FGR offspring has severe implications for the development of hippocampal connectivity and long-term function.

BDNF Differentially Affects Low- and High-Frequency Neurons in a Primary Nucleus of the Chicken Auditory Brainstem

Neurotrophins are proteins that mediate neuronal development using spatiotemporal signaling gradients. The chicken nucleus magnocellularis (NM), an analogous structure to the mammalian anteroventral cochlear nucleus, provides a model system in which signaling between the brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB) is temporally regulated. In the NM, TrkB expression is high early in development (embryonic [E] day 9) and is downregulated until maturity (E18-21). It is currently unknown how BDNF-TrkB signaling affects neuronal properties throughout development and across a spatial (i.e., frequency) axis. To investigate this, we exogenously applied BDNF onto NM neurons ex vivo and studied intrinsic properties using whole-cell patch clamp electrophysiology. Early in development (E13), when TrkB expression is detectable with immunohistochemistry, BDNF application slowed the firing of high-frequency NM neurons, resembling an immature phenotype. Current measurements and biophysical modeling revealed that this was mediated by a decreased conductance of the voltage-dependent potassium channels. Interestingly, this effect was seen only in high-frequency neurons and not in low-frequency neurons. BDNF-TrkB signaling induced minimal changes in late-developing NM neurons (E20-21) of high and low frequencies. Our results indicate that normal developmental downregulation of BDNF-TrkB signaling promotes neuronal maturation tonotopically in the auditory brainstem, encouraging the appropriate development of neuronal properties.

Photobiomodulation as a Potential Treatment for Alzheimer's Disease: A Review Paper

BACKGROUND

Alzheimer's disease (AD), the most prevalent form of dementia, is a leading neurodegenerative disorder currently affecting approximately 55 million individuals globally, a number projected to escalate to 139 million by 2050. Despite extensive research spanning several decades, the cure for AD remains at a developing stage. The only existing therapeutic options are limited to symptom management, and are often accompanied by adverse side effects. The pathological features of AD, including the accumulation of beta-amyloid plaques and tau protein tangles, result in progressive neuronal death, synaptic loss, and brain atrophy, leading to significant cognitive decline and a marked reduction in quality of life.

OBJECTIVE

In light of the shortcomings of existing pharmacological interventions, this review explores the potential of photobiomodulation (PBM) as a non-invasive therapeutic option for AD. PBM employs infrared light to facilitate cellular repair and regeneration, focusing on addressing the disease's underlying biomechanical mechanisms.

METHOD

This paper presents a comprehensive introduction to the mechanisms of PBM and an analysis of preclinical studies evaluating its impact on cellular health, cognitive function, and disease progression in AD.The review provides a comprehensive overview of the various wavelengths and application methods, evaluating their efficacy in mitigating AD-related symptoms.

CONCLUSIONS

The findings underscore the significant potential of PBM as a safe and effective alternative treatment for Alzheimer's disease, emphasizing the necessity for further research and clinical trials to establish its therapeutic efficacy conclusively.

Acupuncture may play a key role in anti-depression through various mechanisms in depression

Depression has emerged as a significant global health concern, exerting a profound impact on individuals, as evidenced by its high prevalence and associated suicide rates. Considering its pervasive nature, the absence of optimal treatment modalities remains a challenge. Acupuncture has garnered substantial clinical and experimental validation for its efficacy in addressing diverse forms of depression, including postpartum, post-stroke, and adolescent depression. This article endeavors to elucidate the distinctive attributes and underlying mechanisms of acupuncture in the contemporary treatment of depression. Research has demonstrated that acupuncture exerts diverse physiological effects in animal models of depression, encompassing modulation of the brain, serum, and brain-gut axis. These effects are attributed to various mechanisms, including anti-inflammatory and anti-oxidative actions, promotion of neuronal plasticity, neuroprotection, neurotrophic effects, modulation of neurotransmitters, regulation of endocrine and immune functions, and modulation of cell signal pathways. Currently, the therapeutic mechanism of acupuncture involves the engagement of multiple targets, pathways, and bidirectional regulation. Hence, acupuncture emerges as a promising alternative medical modality, exhibiting substantial research prospects and meriting comprehensive worth further study and dissemination.

VEGFD signaling balances stability and activity-dependent structural plasticity of dendrites

Mature neurons have stable dendritic architecture, which is essential for the nervous system to operate correctly. The ability to undergo structural plasticity, required to support adaptive processes like memory formation, is still present in mature neurons. It is unclear what molecular and cellular processes control this delicate balance between dendritic structural plasticity and stabilization. Failures in the preservation of optimal dendrite structure due to atrophy or maladaptive plasticity result in abnormal connectivity and are associated with various neurological diseases. Vascular endothelial growth factor D (VEGFD) is critical for the maintenance of mature dendritic trees. Here, we describe how VEGFD affects the neuronal cytoskeleton and demonstrate that VEGFD exerts its effects on dendrite stabilization by influencing the actin cortex and reducing microtubule dynamics. Further, we found that during synaptic activity-induced structural plasticity VEGFD is downregulated. Our findings revealed that VEGFD, acting on its cognate receptor VEGFR3, opposes structural changes by negatively regulating dendrite growth in cultured hippocampal neurons and in vivo in the adult mouse hippocampus with consequences on memory formation. A phosphoproteomic screening identified several regulatory proteins of the cytoskeleton modulated by VEGFD. Among the actin cortex-associated proteins, we found that VEGFD induces dephosphorylation of ezrin at tyrosine 478 via activation of the striatal-enriched protein tyrosine phosphatase (STEP). Activity-triggered structural plasticity of dendrites was impaired by expression of a phospho-deficient mutant ezrin in vitro and in vivo. Thus, VEGFD governs the equilibrium between stabilization and plasticity of dendrites by acting as a molecular brake of structural remodeling.

Acupuncture influences multiple diseases by regulating gut microbiota

Acupuncture, an important green and side effect-free therapy in traditional Chinese medicine, is widely use both domestically and internationally. Acupuncture can interact with the gut microbiota and influence various diseases, including metabolic diseases, gastrointestinal diseases, mental disorders, nervous system diseases, and other diseases. This review presents a thorough analysis of these interactions and their impacts and examines the alterations in the gut microbiota and the potential clinical outcomes following acupuncture intervention to establish a basis for the future utilization of acupuncture in clinical treatments.

Stochastic growth and selective stabilization generate stereotyped dendritic arbors

Stereotyped dendritic arbors are shaped by dynamic and stochastic growth during neuronal development. It remains unclear how guidance receptors and ligands coordinate branch dynamic growth, retraction, and stabilization to specify dendritic arbors. We previously showed that extracellular ligand SAX-7/LICAM dictates the shape of the PVD sensory neuron via binding to the dendritic guidance receptor DMA-1, a single transmembrane adhesion molecule. Here, we perform structure-function analyses of DMA-1 and unexpectedly find that robust, stochastic dendritic growth does not require ligand-binding. Instead, ligand-binding inhibits growth, prevents retraction, and specifies arbor shape. Furthermore, we demonstrate that dendritic growth requires a pool of ligand-free DMA-1, which is maintained by receptor endocytosis and reinsertion to the plasma membrane via recycling endosomes. Mutants defective of DMA-1 endocytosis show severely truncated dendritic arbors. We present a model in which ligand-free guidance receptor mediates intrinsic, stochastic dendritic growth, while extracellular ligands instruct dendrite shape by inhibiting growth.

Studying the social mind: An updated summary of findings from the Vietnam Head Injury Study

Lesion mapping studies allow us to evaluate the potential causal contribution of specific brain areas to human cognition and complement other cognitive neuroscience methods, as several authors have recently pointed out. Here, we present an updated summary of the findings from the Vietnam Head Injury Study (VHIS) focusing on the studies conducted over the last decade, that examined the social mind and its intricate neural and cognitive underpinnings. The VHIS is a prospective, long-term follow-up study of Vietnam veterans with penetrating traumatic brain injury (pTBI) and healthy controls (HC). The scope of the work is to present the studies from the latest phases (3 and 4) of the VHIS, 70 studies since 2011, when the Raymont et al. paper was published (Raymont et al., 2011). These studies have contributed to our understanding of human social cognition, including political and religious beliefs, theory of mind, but also executive functions, intelligence, and personality. This work finally discusses the usefulness of lesion mapping as an approach to understanding the functions of the human brain from basic science and clinical perspectives.

Postnatal survival of phrenic motor neurons is promoted by BDNF/TrkB.FL signaling

The number of motor neurons (MNs) declines precipitously during the final trimester before birth. Thereafter, the number of MNs remains relatively stable, with their connections to skeletal muscle dependent on neurotrophins, including brain-derived neurotrophic factor (BDNF) signaling through its high-affinity full-length tropomyosin-related kinase receptor subtype B (TrkB.FL) receptor. As a genetic knockout of BDNF leads to extensive MN loss and postnatal death within 1-2 days after birth, we tested the hypothesis that postnatal inhibition of BDNF/TrkB.FL signaling is important for postnatal phrenic MN (PhMN) survival. In the present study, we used a 1NMPP1-sensitive TrkBF616A mutant mouse to evaluate the effects of inhibition of TrkB kinase activity on phrenic MN (PhMN) numbers and diaphragm muscle (DIAm) fiber cross-sectional area (CSA). Pups were exposed to 1NMPP1 or vehicle (DMSO) from birth to 21 days old (weaning) via the mother's ingestion in the drinking water. Following weaning, the right phrenic nerve was exposed in the neck and the proximal end dipped in a rhodamine solution to retrogradely label PhMNs. After 24 h, the cervical spinal cord and DIAm were excised. Labeled PhMNs were imaged using confocal microscopy, whereas DIAm strips were frozen at ∼1.5× resting length, cryosectioned, and stained with hematoxylin and eosin to assess CSA. We observed an ∼34% reduction in PhMN numbers and increased primary dendrite numbers in 1NMPP1-treated TrkBF616A mice. The distribution of PhMN size (somal surface area) DIAm fiber cross-sectional areas did not differ. We conclude that survival of PhMNs during early postnatal development is sensitive to BDNF/TrkB.FL signaling.NEW & NOTEWORTHY During early postnatal development, BDNF/TrkB signaling promotes PhMN survival. Inhibition of BDNF/TrkB signaling in early postnatal development does not impact PhMN size. Inhibition of BDNF/TrkB signaling in early postnatal development does not impact the number or CSA of DIAm fibers.

Distinct roles of Bdnf I and Bdnf IV transcript variant expression in hippocampal neurons

Brain-derived neurotrophic factor (Bdnf) plays a critical role in brain development, dendritic growth, synaptic plasticity, as well as learning and memory. The rodent Bdnf gene contains nine 5' non-coding exons (I-IXa), which are spliced to a common 3' coding exon (IX). Transcription of individual Bdnf variants, which all encode the same BDNF protein, is initiated at unique promoters upstream of each non-coding exon, enabling precise spatiotemporal and activity-dependent regulation of Bdnf expression. Although prior evidence suggests that Bdnf transcripts containing exon I (Bdnf I) or exon IV (Bdnf IV) are uniquely regulated by neuronal activity, the functional significance of different Bdnf transcript variants remains unclear. To investigate functional roles of activity-dependent Bdnf I and IV transcripts, we used a CRISPR activation system in which catalytically dead Cas9 fused to a transcriptional activator (VPR) is targeted to individual Bdnf promoters with single guide RNAs, resulting in transcript-specific Bdnf upregulation. Bdnf I upregulation is associated with gene expression changes linked to dendritic growth, while Bdnf IV upregulation is associated with genes that regulate protein catabolism. Upregulation of Bdnf I, but not Bdnf IV, increased mushroom spine density, volume, length, and head diameter, and also produced more complex dendritic arbors in cultured rat hippocampal neurons. In contrast, upregulation of Bdnf IV, but not Bdnf I, in the rat hippocampus attenuated contextual fear expression. Our data suggest that while Bdnf I and IV are both activity-dependent, BDNF produced from these promoters may serve unique cellular, synaptic, and behavioral functions.

Brain-derived neurotrophic factor scales presynaptic calcium transients to modulate excitatory neurotransmission

Brain-derived neurotrophic factor (BDNF) plays a critical role in synaptic physiology, as well as mechanisms underlying various neuropsychiatric diseases and their treatment. Despite its clear physiological role and disease relevance, BDNF's function at the presynaptic terminal, a fundamental unit of neurotransmission, remains poorly understood. In this study, we evaluated single synapse dynamics using optical imaging techniques in hippocampal cell cultures. We find that exogenous BDNF selectively increases evoked excitatory neurotransmission without affecting spontaneous neurotransmission. However, acutely blocking endogenous BDNF has no effect on evoked or spontaneous release, demonstrating that different approaches to studying BDNF may yield different results. When we suppressed BDNF-Tropomyosin receptor kinase B (TrkB) activity chronically over a period of days to weeks using a mouse line enabling conditional knockout of TrkB, we found that evoked glutamate release was significantly decreased while spontaneous release remained unchanged. Moreover, chronic blockade of BDNF-TrkB activity selectively downscales evoked calcium transients without affecting spontaneous calcium events. Via pharmacological blockade by voltage-gated calcium channel (VGCC) selective blockers, we found that the changes in evoked calcium transients are mediated by the P/Q subtype of VGCCs. These results suggest that BDNF-TrkB activity increases presynaptic VGCC activity to selectively increase evoked glutamate release.

Relationship between physical activity and cerebral white matter hyperintensity volumes in older adults with depressive symptoms and mild memory impairment: a cross-sectional study

Introduction

Cerebral white matter hyperintensities (WMHs) are commonly found in the aging brain and have been implicated in the initiation and severity of many central nervous system diseases. Furthermore, an increased WMH volume indicates reduced brain health in older adults. This study investigated the association between WMH volume and physical activity in older adults with depressive symptoms (DS) and mild memory impairment (MMI). Factors associated with the WMH volume were also investigated.

Methods

A total of 57 individuals aged over 65 years with DS and MMI were included in this study. The participants underwent magnetic resonance imaging to quantify WMH volumes. After WMH volume was accumulated, normalized to the total intracranial volume (TIV), the percentage of WMH volume was calculated. In addition, all participants wore a triaxial accelerometer for 2 weeks, and the average daily physical activity and number of steps were measured. The levels of blood biomarkers including cortisol, interleukin-6 (IL-6), brain-derived insulin-like growth factor-1, and brain-derived neurotrophic factor were measured. Motor and cognitive functions were also assessed.

Results

Faster maximum walking speed and longer time spent engaged in moderate physical activity were associated with a smaller percent of WMH volume, whereas higher serum IL-6 levels were associated with a larger percent of WMH volume. The number of steps per day, time spent engaged in low levels of physical activity, cognitive function, and all other measured biomarkers were not significantly associated with percent of WMH volume.

Discussion

Higher blood inflammatory cytokine levels, shorter duration of moderate physical activity, and lower maximum walking speed were associated with a higher percent of WMH volume. Our results provide useful information for maintaining brain health in older adults at a high risk of developing dementia and may contribute to the development of preventive medicine for brain health.

Immunohistochemical phenotype of sensory neurons associated with sympathetic plexuses in the trigeminal ganglia of adult nerve growth factor transgenic mice

Following peripheral nerve injury, postganglionic sympathetic axons sprout into the affected sensory ganglia and form perineuronal sympathetic plexuses with somata of sensory neurons. This sympathosensory coupling contributes to the onset and persistence of injury-induced chronic pain. We have documented the presence of similar sympathetic plexuses in the trigeminal ganglia of adult mice that ectopically overexpress nerve growth factor (NGF), in the absence of nerve injury. In this study, we sought to further define the phenotype(s) of these trigeminal sensory neurons having sympathetic plexuses in our transgenic mice. Using quantitative immunofluorescence staining analyses, we show that the invading sympathetic axons specifically target sensory somata immunopositive for several biomarkers: NGF high-affinity receptor tyrosine kinase A (trkA), calcitonin gene-related peptide (CGRP), neurofilament heavy chain (NFH), and P2X purinoceptor 3 (P2X3). Based on these phenotypic characteristics, the majority of the sensory somata surrounded by sympathetic plexuses are likely to be NGF-responsive nociceptors (i.e., trkA expressing) that are peptidergic (i.e., CGRP expressing), myelinated (i.e., NFH expressing), and ATP sensitive (i.e., P2X3 expressing). Our data also show that very few sympathetic plexuses surround sensory somata expressing other nociceptive (pain) biomarkers, including substance P and acid-sensing ion channel 3. No sympathetic plexuses are associated with sensory somata that display isolectin B4 binding. Though the cellular mechanisms that trigger the formation of sympathetic plexus (with and without nerve injury) remain unknown, our new observations yield an unexpected specificity with which invading sympathetic axons appear to target a precise subtype of nociceptors. This selectivity likely contributes to pain development and maintenance associated with sympathosensory coupling.

Neurotrophin NT-4/5 Promotes Structural Changes in Neurons of the Developing Visual Cortex

Current hypotheses on the mechanisms underlying the development and plasticity of the ocular dominance system through competitive interactions between pathways serving the two eyes strongly suggest the involvement of neurotrophins and their high affinity receptors. In the cat, infusion of the tyrosine kinase B ligand (trkB), neurotrophin-4/5 (NT-4/5), abolishes ocular dominance plasticity that follows monocular deprivation (Gillespie et al., 2000), while tyrosine kinase A and C ligands (trkA and trkC) do not have this effect. One interpretation of this finding is that NT-4/5 causes overgrowth and sprouting of thalamocortical and/or corticocortical terminals, leading to promiscuous neuronal connections which override the experience-dependent fine tuning of connections based on correlated activity. The present study tested whether neurons in cortical regions infused with NT-4/5 showed anatomical changes compatible with this hypothesis. Cats at the peak of the critical period received chronic infusion NT-4/5 into visual cortical areas 17/18 via an osmotic minipump. Visual cortical neurons were labeled in fixed slices using the DiOlistics methods (Gan et al., 2000) and analyzed in confocal microscopy. Infusion of NT-4/5 induced a significant increase of spine-like processes on primary dendrites and a distinctive sprouting of protuberances from neuronal somata in all layers. The increase of neuronal membrane was paralleled by an increase in density of the presynaptic marker synaptophysin in infused areas, suggesting an increase in the numbers of synapses. A contingent of these newly formed synapses may feed into inhibitory circuits, as suggested by an increase of GAD-65 immunostaining in NT-4/5 affected areas. These anatomical changes are consistent with the physiological changes in such animals, suggesting that excess trkB neurotrophin can stimulate the formation of promiscuous connections during the critical period.

Extracellular molecular signals shaping dendrite architecture during brain development

Proper growth and branching of dendrites are crucial for adequate central nervous system (CNS) functioning. The neuronal dendritic geometry determines the mode and quality of information processing. Any defects in dendrite development will disrupt neuronal circuit formation, affecting brain function. Besides cell-intrinsic programmes, extrinsic factors regulate various aspects of dendritic development. Among these extrinsic factors are extracellular molecular signals which can shape the dendrite architecture during early development. This review will focus on extrinsic factors regulating dendritic growth during early neuronal development, including neurotransmitters, neurotrophins, extracellular matrix proteins, contact-mediated ligands, and secreted and diffusible cues. How these extracellular molecular signals contribute to dendritic growth has been investigated in developing nervous systems using different species, different areas within the CNS, and different neuronal types. The response of the dendritic tree to these extracellular molecular signals can result in growth-promoting or growth-limiting effects, and it depends on the receptor subtype, receptor quantity, receptor efficiency, the animal model used, the developmental time windows, and finally, the targeted signal cascade. This article reviews our current understanding of the role of various extracellular signals in the establishment of the architecture of the dendrites.

Early tactile stimulation influences the development of Alzheimer's disease in gestationally stressed APP NL-G-F adult offspring NL-G-F/NL-G-F mice

Alzheimer's disease (AD) is associated with cerebral plaques and tangles, reduced synapse number, and shrinkage in several brain areas and these morphological effects are associated with the onset of compromised cognitive, motor, and anxiety-like behaviours. The appearance of both anatomical and behavioural symptoms is worsened by stress. The focus of this study was to examine the effect of neonatal tactile stimulation on AD-like behavioural and neurological symptoms on APP NL-G-F/NL-G-F mice, a mouse model of AD, who have been gestationally stressed. Our findings indicate that neonatal tactile stimulation improves cognition, motor skills, and anxiety-like symptoms in both gestationally stressed and non-stressed adult APP mice and that these alterations are associated with reduced Aβ plaque formation. Thus, tactile stimulation appears to be a promising non-invasive preventative strategy for slowing the onset of dementia in aging animals.

Reduction of restricted repetitive behavior by environmental enrichment: Potential neurobiological mechanisms

Restricted repetitive behaviors (RRB) are one of two diagnostic criteria for autism spectrum disorder and common in other neurodevelopmental and psychiatric disorders. The term restricted repetitive behavior refers to a wide variety of inflexible patterns of behavior including stereotypy, self-injury, restricted interests, insistence on sameness, and ritualistic and compulsive behavior. However, despite their prevalence in clinical populations, their underlying causes remain poorly understood hampering the development of effective treatments. Intriguingly, numerous animal studies have demonstrated that these behaviors are reduced by rearing in enriched environments (EE). Understanding the processes responsible for the attenuation of repetitive behaviors by EE should offer insights into potential therapeutic approaches, as well as shed light on the underlying neurobiology of repetitive behaviors. This review summarizes the current knowledge of the relationship between EE and RRB and discusses potential mechanisms for EE's attenuation of RRB based on the broader EE literature. Existing gaps in the literature and future directions are also discussed.

Speech- and language-linked FOXP2 mutation targets protein motors in striatal neurons

Human speech and language are among the most complex motor and cognitive abilities. The discovery of a mutation in the transcription factor FOXP2 in KE family members with speech disturbances has been a landmark example of the genetic control of vocal communication in humans. Cellular mechanisms underlying this control have remained unclear. By leveraging FOXP2 mutation/deletion mouse models, we found that the KE family FOXP2R553H mutation directly disables intracellular dynein-dynactin 'protein motors' in the striatum by induction of a disruptive high level of dynactin1 that impairs TrkB endosome trafficking, microtubule dynamics, dendritic outgrowth and electrophysiological activity in striatal neurons alongside vocalization deficits. Dynactin1 knockdown in mice carrying FOXP2R553H mutations rescued these cellular abnormalities and improved vocalization. We suggest that FOXP2 controls vocal circuit formation by regulating protein motor homeostasis in striatal neurons, and that its disruption could contribute to the pathophysiology of FOXP2 mutation/deletion-associated speech disorders.

Neurotrophin-4 promotes the specification of trophectoderm lineage after parthenogenetic activation and enhances porcine early embryonic development

Neurotrophin-4 (NT-4), a neurotrophic factor, appears to affect early embryonic development because it is secreted not only by neurons but also by oviductal and uterine epithelial cells. However, no studies have characterized the effects of NT-4 on early embryonic development in pigs. In this study, we applied the experimental model of parthenogenetic-activation (PA)-derived embryos. Herein, we investigated the effect of NT-4 supplementation during the in vitro culture (IVC) of embryos, analyzed the transcription levels of specific genes, and outlined the first cell lineage specification for porcine PA-derived blastocysts. We confirmed that NT-4 and its receptor proteins were localized in both the inner cell mass (ICM) and trophectoderm (TE) in porcine blastocysts. Across different concentrations (0, 1, 10, and 100 ng/mL) of NT-4 supplementation, the optimal concentration of NT-4 to improve the developmental competence of porcine parthenotes was 10 ng/mL. NT-4 supplementation during porcine IVC significantly (p < 0.05) increased the proportion of TE cells by inducing the transcription of TE lineage markers (CDX2, PPAG3, and GATA3 transcripts). NT-4 also reduced blastocyst apoptosis by regulating the transcription of apoptosis-related genes (BAX and BCL2L1 transcripts) and improved blastocyst quality via the interaction of neurotrophin-, Hippo-yes-associated protein (Hippo-YAP) and mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) pathway. Additionally, NT-4 supplementation during IVC significantly (p < 0.05) increased YAP1 transcript levels and significantly (p < 0.01) decreased LATS2 transcript levels, respectively, in the porcine PA-derived blastocysts. We also confirmed through fluorescence intensity that the YAP1 protein was significantly (p < 0.001) increased in the NT-4-treated blastocysts compared with that in the control. NT-4 also promoted differentiation into the TE lineage rather than into the ICM lineage during porcine early embryonic development. In conclusion, 10 ng/mL NT-4 supplementation enhanced blastocyst quality by regulating the apoptosis- and TE lineage specification-related genes and interacting with neurotrophin-, Hippo-YAP-, and MAPK/ERK signaling pathway during porcine in vitro embryo development.

Maternal diabetes decreases the expression of GABAAα1, GABAB1, and mGlu2 receptors in the visual cortex of male rat neonates

AIMS

This study examines the impact of maternal diabetes on the expression of GABAB1, GABAAα1, and mGlu2 receptors in the primary visual cortex layers of male rat newborns.

MAIN METHODS

In diabetic group (Dia), diabetes was induced in adult female rats using an intraperitoneal dose of Streptozotocin (STZ) 65 (mg/kg). Diabetes was managed by daily subcutaneous injection of NPH insulin in insulin-treated diabetic group (Ins). Control group (Con) received normal saline intraperitoneally rather than STZ. Male offspring born to each group of female rats were euthanized via CO2 inhalation at P0, P7, and P14 days after delivery and the expression of GABAB1, GABAAα1, and mGlu2 receptors in their primary visual cortex was determined using immunohistochemistry (IHC).

KEY FINDINGS

The expression of GABAB1, GABAAα1, and mGlu2 receptors increased gradually with age in the male offspring born to Con group while the highest expression was detected in layer IV of the primary visual cortex. In Dia group newborns, the expression of these receptors was significantly reduced in all layers of the primary visual cortex at every three days. Insulin treatment in diabetic mothers restored the expression of these receptors to normal levels in their newborns.

SIGNIFICANCE

The study indicates that diabetes reduces the expression of GABAB1, GABAAα1, and mGlu2 receptors in the primary visual cortex of male offspring born to diabetic rats at P0, P7, and P14. However, insulin treatment can counteract these effects.

Neurotrophin signalling in the human nervous system

This review focuses on neurotrophins and their tyrosine kinase receptors, with an emphasis on their relevance to the function and dysfunction in the human nervous system. It also deals with measurements of BDNF levels and highlights recent findings from our laboratory on TrkB and TrkC signalling in human neurons. These include ligand selectivity and Trk activation by neurotrophins and non-neurotrophin ligands. The ligand-induced down-regulation and re-activation of Trk receptors is also discussed.

Distinct roles of Bdnf I and Bdnf IV transcript variant expression in hippocampal neurons

Brain-derived neurotrophic factor (Bdnf) plays a critical role in brain development, dendritic growth, synaptic plasticity, as well as learning and memory. The rodent Bdnf gene contains nine 5' non-coding exons (I-IXa), which are spliced to a common 3' coding exon (IX). Transcription of individual Bdnf variants, which all encode the same BDNF protein, is initiated at unique promoters upstream of each non-coding exon, enabling precise spatiotemporal and activity-dependent regulation of Bdnf expression. Although prior evidence suggests that Bdnf transcripts containing exon I (Bdnf I) or exon IV (Bdnf IV) are uniquely regulated by neuronal activity, the functional significance of different Bdnf transcript variants remains unclear. To investigate functional roles of activity-dependent Bdnf I and IV transcripts, we used a CRISPR activation (CRISPRa) system in which catalytically-dead Cas9 (dCas9) fused to a transcriptional activator (VPR) is targeted to individual Bdnf promoters with single guide RNAs (sgRNAs), resulting in transcript-specific Bdnf upregulation. Bdnf I upregulation is associated with gene expression changes linked to dendritic growth, while Bdnf IV upregulation is associated with genes that regulate protein catabolism. Upregulation of Bdnf I, but not Bdnf IV, increased mushroom spine density, volume, length, and head diameter, and also produced more complex dendritic arbors in cultured rat hippocampal neurons. In contrast, upregulation of Bdnf IV, but not Bdnf I, in the rat hippocampus attenuated contextual fear expression. Our data suggest that while Bdnf I and IV are both activity-dependent, BDNF produced from these promoters may serve unique cellular, synaptic, and behavioral functions.

Delayed Outgrowth in Response to the BDNF and Altered Synaptic Proteins in Neurons From SHR Rats

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by inattention, hyperactivity, and impulsivity symptoms. Neuroimaging studies have revealed a delayed cortical and subcortical development pattern in children diagnosed with ADHD. This study followed up on the development in vitro of frontal cortical neurons from Spontaneously hypertensive rats (SHR), an ADHD rat model, and Wistar-Kyoto rats (WKY), control strain, over their time in culture, and in response to BDNF treatment at two different days in vitro (DIV). These neurons were also evaluated for synaptic proteins, brain-derived neurotrophic factor (BDNF), and related protein levels. Frontal cortical neurons from the ADHD rat model exhibited shorter dendrites and less dendritic branching over their time in culture. While pro- and mature BDNF levels were not altered, the cAMP-response element-binding (CREB) decreased at 1 DIV and SNAP-25 decreased at 5 DIV. Different from control cultures, exogenous BDNF promoted less dendritic branching in neurons from the ADHD model. Our data revealed that neurons from the ADHD model showed decreased levels of an important transcription factor at the beginning of their development, and their delayed outgrowth and maturation had consequences in the levels of SNAP-25 and may be associated with less response to BDNF. These findings provide an alternative tool for studies on synaptic dysfunctions in ADHD. They may also offer a valuable tool for investigating drug effects and new treatment opportunities.

Peripheral brain-derived neurotrophic factor (BDNF) in insomnia: A systematic review and meta-analysis

The brain-derived neurotrophic factor (BDNF) is associated with emotional and cognitive functioning, and it is considered a transdiagnostic biomarker for mental disorders. Literature on insomnia related BDNF changes yielded contrasting results and it has never been synthetized using meta-analysis. To fill this gap, we conducted a systematic review and meta-analysis of case-control studies examining the levels of peripheric BDNF in individuals with insomnia and healthy controls using the PRISMA guidelines. PubMed, Scopus, Medline, PsycINFO and CINAHL were searched up to Nov 2022. Nine studies met the inclusion criteria and were assessed using the Newcastle-Ottawa Scale. Eight studies reported sufficient data for meta-analysis. Random-effects models showed lower BDNF in subjects with insomnia (n = 446) than in controls (n = 706) (Hedge's g = -0.86, 95% CI: -1.39 to -0.32, p = .002). Leave-one-out sensitivity analysis confirmed that the pooled effect size was robust and not driven by any single study. However, given the small sample size, the cross-sectional nature of the measurement, and the high heterogeneity of included data, the results should be cautiously interpreted. Progress in the study of BDNF in insomnia is clinically relevant to better understand the mechanisms that may explain the relationship between disturbed sleep and mental disorders.

EMG Testing throughout behavioral recovery after rat sciatic nerve crush injury results in exuberant motoneuron dendritic hypertrophy

Background

Peripheral nerve injury (PNI) is the most common type of nerve trauma yet, while injured motoneurons exhibit a robust capacity for regeneration, behavioral recovery is protracted and typically poor. Neurotherapeutic approaches to PNI and repair have primarily focused on the enhancement of axonal regeneration, in terms of rate, axonal sprouting, and reconnection connectivity. Both electrical stimulation (ES) and treatment with androgens [e.g., testosterone propionate (TP)] have been demonstrated to enhance axonal sprouting, regeneration rate and functional recovery following PNI. To date, very little work has been done to examine the effects of ES and/or TP on dendritic morphology and organization within the spinal cord after PNI.

Objective

The objective of the current study was to examine the impact of treatment with TP and ES, alone or in combination, on the dendritic arbor of spinal motoneurons after target disconnection via sciatic nerve crush injury in the rat.

Methods

Rats received a crush injury to the sciatic nerve. Following injury, some animals received either (1) no further treatment beyond implantation with empty Silastic capsules, (2) electrical nerve stimulation immediately after injury, (3) implantation with Silastic capsules filled with TP, or (4) electrical nerve stimulation immediately after injury as well as implantation with TP. All of these groups of axotomized animals also received bi-weekly electromyography (EMG) testing. Additional groups of intact untreated animals as well as a group of injured animals who received no further treatment or EMG testing were also included. Eight weeks after injury, motoneurons innervating the anterior tibialis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions.

Results

After nerve crush and ES and/or TP treatment, motoneurons innervating the anterior tibialis underwent marked dendritic hypertrophy. Surprisingly, this dendritic hypertrophy occurred in all animals receiving repeated bi-weekly EMG testing, regardless of treatment. When the EMG testing was eliminated, the dendritic arbor extent and distribution after nerve crush in the treated groups did not significantly differ from intact untreated animals.

Conclusions

The ability of repeated EMG testing to so dramatically affect central plasticity following a peripheral nerve injury was unexpected. It was also unexpected that gonadal steroid hormones and/or ES, two neurotherapeutic approaches with demonstrated molecular/behavioral changes consistent with peripheral improvements in axonal repair and target reconnection, do not appear to impact central plasticity in a similar manner. The significance of peripheral EMG testing and resulting central plasticity reorganization remains to be determined.

A novel intergenic enhancer that regulates Bdnf expression in developing cortical neurons

Brain-derived neurotrophic factor (BDNF) promotes neuronal differentiation and survival and is implicated in the pathogenesis of many neurological disorders. Here, we identified a novel intergenic enhancer located 170 kb from the Bdnf gene, which promotes the expression of Bdnf transcript variants during mouse neuronal differentiation and activity. Following Bdnf activation, enhancer-promoter contacts increase, and the region moves away from the repressive nuclear periphery. Bdnf enhancer activity is necessary for neuronal clustering and dendritogenesis in vitro, and for cortical development in vivo. Our findings provide the first evidence of a regulatory mechanism whereby the activation of a distal enhancer promotes Bdnf expression during brain development.

Automated algorithm development to assess survival of human neurons using longitudinal single-cell tracking: Application to synucleinopathy

The development of phenotypic assays with appropriate analyses is an important step in the drug discovery process. Assays using induced pluripotent stem cell (iPSC)-derived human neurons are emerging as powerful tools for drug discovery in neurological disease. We have previously shown that longitudinal single cell tracking enabled the quantification of survival and death of neurons after overexpression of α-synuclein with a familial Parkinson's disease mutation (A53T). The reliance of this method on manual counting, however, rendered the process labor intensive, time consuming and error prone. To overcome these hurdles, we have developed automated detection algorithms for neurons using the BioStation CT live imaging system and CL-Quant software. In the current study, we use these algorithms to successfully measure the risk of neuronal death caused by overexpression of α-synuclein (A53T) with similar accuracy and improved consistency as compared to manual counting. This novel method also provides additional key readouts of neuronal fitness including total neurite length and the number of neurite nodes projecting from the cell body. Finally, the algorithm reveals the neuroprotective effects of brain-derived neurotrophic factor (BDNF) treatment in neurons overexpressing α-synuclein (A53T). These data show that an automated algorithm improves the consistency and considerably shortens the analysis time of assessing neuronal health, making this method advantageous for small molecule screening for inhibitors of synucleinopathy and other neurodegenerative diseases.

Differential impact of two paradigms of early-life adversity on behavioural responses to social defeat in young adult rats and morphology of CA3 pyramidal neurons

Early life stress (ELS) is an important factor in programing the brain for future response to stress, and resilience or vulnerability to stress-induced emotional disorders. The hippocampal formation, with essential roles in both regulating the stress circuitry and emotionality, contributes to this adaptive programing. Here, we examined the effects of early handling (EH) and maternal deprivation (MD) as mild and intense postnatal stressors, respectively, on the behavioural responses to social defeat stress in young adulthood. We also evaluated the interaction of mild and intense ELS with later social defeat (SD) stress on the morphology and dendritic spine density of Golgi-cox-stained CA3 hippocampal neurons. SD stress in adult rats, as expected, increased anxiety and depressive-like behaviours in the open field, elevated plus-maze and forced swimming test. These effects were associated with reduction of dendritic spines and soma size of CA3 neurons. Both behavioural and structural alterations were significantly ameliorated in socially defeated rats that experienced early handling (EH-SD). Basal dendrites of CA3 neurons in EH-SD rats also showed longer dendrites and more intersections with Sholl circles in the distal portion, compared to both control and SD rats. On the other hand, in socially defeated rats with maternal deprivation experience (MD-SD) the stress-induced behavioural and structural alterations were generally intensified compared to SD rats. In MD-SD rats, apical dendrites of CA3 neurons demonstrated remarkable retraction; an effect that was not detected in SD rats. The reduction of dendritic spines density on the apical dendrites of CA3 neurons was also more pronounced in MD-SD rats compared to SD rats. Dendritic arbors and spines comprise the major neuronal substrate for the circuit connectivity, and cell region-specific alterations of dendrites and spines in CA3 neurons reveal plausible mechanisms that can underlie the impact of different ELSs on risk for affective disorders in response to social stress in adulthood.

Blue-Light-Blocking Lenses Ameliorate Structural Alterations in the Rodent Hippocampus

Evidence suggests that prolonged blue-light exposure can impact vision; however, less is known about its impact on non-visual higher-order functions in the brain, such as learning and memory. Blue-light-blocking lenses (BBLs) claim to reduce these potential impacts. Hence, we assessed structural and functional hippocampal alterations following blue-light exposure and the protective efficacy of BBLs. Male Wistar rats were divided into (n = 6 in each group) normal control (NC), blue-light exposure (LE), and blue-light with BBLs (Crizal Prevencia, CP and DuraVision Blue, DB) groups. After 28 days of light exposure (12:12 light: dark cycle), rats were trained for the Morris water maze memory retention test, and brain tissues were sectioned for hippocampal neuronal analysis using Golgi and Cresyl violet stains. The memory retention test was significantly delayed (p < 0.05) in LE compared with DB groups on day 1 of training. Comparison of Golgi-stained neurons showed significant structural alterations, particularly in the basal dendrites of hippocampal neurons in the LE group, with BBLs significantly mitigating these structural changes (p < 0.05). Comparison of Cresyl-violet-stained neurons revealed significantly (p < 0.001) increased degenerated hippocampal neurons in LE rats, with fewer degenerated neurons in the CP lens group for CA1 neurons (p < 0.05), and for both CP and DB groups (p < 0.05) for CA3 neurons. Thus, in addition to documented effects on visual centers, high-level blue-light exposure also results in degeneration in hippocampal neurons with associated behavioral deficits. These changes can be partially ameliorated with blue-light-blocking lenses.

The Role of Neurotrophin Signaling in Age-Related Cognitive Decline and Cognitive Diseases

Neurotrophins are a family of secreted proteins expressed in the peripheral nervous system and the central nervous system that support neuronal survival, synaptic plasticity, and neurogenesis. Brain-derived neurotrophic factor (BDNF) and its high affinity receptor TrkB are highly expressed in the cortical and hippocampal areas and play an essential role in learning and memory. The decline of cognitive function with aging is a major risk factor for cognitive diseases such as Alzheimer’s disease. Therefore, an alteration of BDNF/TrkB signaling with aging and/or pathological conditions has been indicated as a potential mechanism of cognitive decline. In this review, we summarize the cellular function of neurotrophin signaling and review the current evidence indicating a pathological role of neurotrophin signaling, especially of BDNF/TrkB signaling, in the cognitive decline in aging and age-related cognitive diseases. We also review the therapeutic approach for cognitive decline by the upregulation of the endogenous BDNF/TrkB-system.

Actions of the TrkB Agonist Antibody ZEB85 in Regulating the Architecture and Synaptic Plasticity in Hippocampal Neurons

Signaling of BDNF via its TrkB receptor is crucial in regulating several critical aspects of the architecture and function of neurons both during development and in the adult central nervous system. Indeed, several neurological conditions, such as neurodevelopmental and neurodegenerative disorders are associated with alterations both in the expression levels of BDNF and TrkB, and in their intracellular signaling. Thus, the possibility of promoting BDNF/TrkB signaling has become relevant as a potential therapeutic intervention for neurological disorders. However, the clinical potential of BDNF itself has been limited due to its restricted diffusion rate in biological tissue, poor bioavailability and pharmacological properties, as well as the potential for unwanted side effects due to its ability to also signal via the p75NTR pathway. Several small molecule and biologic drug candidate TrkB agonists have been developed and are reported to have effects in rescuing both the pathological alterations and disease related symptoms in mouse models of several neurological diseases. However, recent side-by-side comparative studies failed to show their specificity for activating TrkB signaling cascades, suggesting the need for the generation and validation of improved candidates. In the present study, we examine the ability of the novel, fully human TrkB agonist antibody ZEB85 to modulate the architecture, activity and synaptic plasticity of hippocampal murine neurons under physiological conditions. Moreover, we show here that ZEB85 prevents β-amyloid toxicity in cultured hippocampal neurons, in a manner which is comparable to BDNF.

Antillatoxin-Stimulated Neurite Outgrowth Involves the Brain-Derived Neurotrophic Factor (BDNF) - Tropomyosin Related Kinase B (TrkB) Signaling Pathway

Voltage-gated sodium channel (VGSC) activators promote neurite outgrowth by augmenting intracellular Na⁺ concentration ([Na⁺]_i) and upregulating N-methyl-d-aspartate receptor (NMDAR) function. NMDAR activation stimulates calcium (Ca²⁺) influx and increases brain-derived neurotrophic factor (BDNF) release and activation of tropomyosin receptor kinase B (TrkB) signaling. The BDNF-TrkB pathway has been implicated in activity-dependent neuronal development. We have previously shown that antillatoxin (ATX), a novel lipopeptide isolated from the cyanobacterium Moorea producens, is a VGSC activator that produces an elevation of [Na⁺]_i. Here we address the effect of ATX on the synthesis and release of BDNF and determine the signaling mechanisms by which ATX enhances neurite outgrowth in immature cerebrocortical neurons. ATX treatment produced a concentration-dependent release of BDNF. Acute treatment with ATX also resulted in increased synthesis of BDNF. ATX stimulation of neurite outgrowth was prevented by pretreatment with a TrkB inhibitor or transfection with a dominant-negative Trk-B. The ATX activation of TrkB and Akt was blocked by both a NMDAR antagonist (MK-801) and a VGSC blocker (tetrodotoxin). These results suggest that VGSC activators such as the structurally novel ATX may represent a new pharmacological strategy to promote neuronal plasticity through a NMDAR-BDNF-TrkB-dependent mechanism.

Ultrasound Used for Diagnostic Imaging Facilitates Dendritic Branching of Developing Neurons in the Mouse Cortex

Neuronal differentiation and synaptogenesis are regulated by precise orchestration of intrinsic and extrinsic chemical and mechanical factors throughout all developmental steps critical for the assembly of neurons into functional circuits. While ultrasound is known to alter neuronal migration and activity acutely, its chronic effect on neuronal behavior or morphology is not well characterized. Furthermore, higher-frequency (3–5 MHz) ultrasound (HFU) is extensively used in gynecological practice for imaging, and while it has not been shown harmful for the developing brain, it might be associated with mild alterations that may have functional consequences. To shed light on the neurobiological effects of HFU on the developing brain, we examined cortical pyramidal cell morphology in a transgenic mouse model, following a single and short dose of high-frequency ultrasound. Layer V neurons in the retrosplenial cortex of mouse embryos were labeled with green and red fluorescent proteins by in utero electroporation at the time of their appearance (E14.5). At the time of their presumptive arrival to layer V (E18.5), HFU stimulation was performed with parameters matched to those used in human prenatal examinations. On the third postnatal day (P3), basic morphometric analyses were performed on labeled neurons reconstructed with Neurolucida. Low-intensity HFU-treated cells showed significantly increased dendritic branching compared to control (non-stimulated) neurons and showed elevated c-fos immunoreactivity. Labeled neurons were immunopositive for the mechanosensitive receptor TRPC4 at E18.5, suggesting the role of this receptor and the associated signaling pathways in the effects of HFU stimulation.

Huntingtin gene intermediate alleles influence the progression from Subjective Cognitive Decline to Mild Cognitive Impairment: a 14-year follow-up study

BACKGROUND

Huntingtin (HTT) is a gene containing a key region of CAG repeats. HTT alleles containing from 27 to 35 CAG repeats are termed as intermediate alleles (IAs). We aim to assess the effect of IAs on progression of cognitive impairment in patients with subjective cognitive decline (SCD).

METHODS

We included 106 patients with SCD. All the patients underwent neuropsychological assessments and blood sample collections at baseline. Patients were followed-up for a median time of 13.75 (IQR=8.17) years. We genotyped APOE and HTT at the end of the follow-up.

RESULTS

Eleven out of 106 patients (10.38% [95%C.I.=4.57-16.18]) were carriers of IA (IA⁺ ). During the follow-up, 44 patients (41.51% [95%C.I.=32.13-50.89]) progressed to MCI (p-SCD), while 62 patients (58.49% [95% C.I.=49.11-67.87]) did not (np-SCD). Rate of progression to MCI was associated with IAs, age at baseline, and APOE ɛ4. We dichotomized age at baseline (<60 = younger patients [YP], >60 = older patients [OP]) and classified patients into four groups: YP/IAs^- , YP/IAs⁺ , OP/IAs^-  and OP/IAs⁺ . OP/IAs⁺  had a higher proportion of progression from SCD to MCI (85.71% [95%C.I.=59.79-100]) as compared to YP/IAs^-  (28.57% [95%C.I.=13.60-43.54], χ² =15.25, p<0.001) and OP/IAs^-  (45.00% [95%C.I.=32.41-57.59], χ² =7.903, p=0.005). We classified patients according to APOE and IA as: ɛ4^- /IA^- , ɛ4^- /IA⁺ , ɛ4⁺ /IA^- , ɛ4⁺ /IA⁺ . Proportion of progression in ɛ4⁺ /IA⁺  group (100%) was higher as compared to ɛ4^- /IA^-  (33.33% [95%C.I.=21.96-44.71], χ² =14.43, p <0.001) and ɛ4⁺ /IA^-  (55.56% [95%C.I.=36.81-74.30], χ² =4.60, p=0.032).

CONCLUSIONS

IAs interact with age and APOE ɛ4 increasing the risk of progression to MCI in SCD patients.

Pathway-specific TNF-mediated metaplasticity in hippocampal area CA1

Long-term potentiation (LTP) is regulated in part by metaplasticity, the activity-dependent alterations in neural state that coordinate the direction, amplitude, and persistence of future synaptic plasticity. Previously, we documented a heterodendritic metaplasticity effect whereby high-frequency priming stimulation in stratum oriens (SO) of hippocampal CA1 suppressed subsequent LTP in the stratum radiatum (SR). The cytokine tumor necrosis factor (TNF) mediated this heterodendritic metaplasticity in wild-type rodents and in a mouse model of Alzheimer’s disease. Here, we investigated whether LTP at other afferent synapses to CA1 pyramidal cells were similarly affected by priming stimulation. We found that priming stimulation in SO inhibited LTP only in SR and not in a second independent pathway in SO, nor in stratum lacunosum moleculare (SLM). Synapses in SR were also more sensitive than SO or SLM to the LTP-inhibiting effects of pharmacological TNF priming. Neither form of priming was sex-specific, while the metaplasticity effects were absent in TNFR1 knock-out mice. Our findings demonstrate an unexpected pathway specificity for the heterodendritic metaplasticity in CA1. That Schaffer collateral/commissural synapses in SR are particularly susceptible to such metaplasticity may reflect an important control of information processing in this pathway in addition to its sensitivity to neuroinflammation under disease conditions.

BDNF signaling in context: From synaptic regulation to psychiatric disorders

Brain-derived neurotrophic factor (BDNF) is a neuropeptide that plays numerous important roles in synaptic development and plasticity. While its importance in fundamental physiology is well established, studies of BDNF often produce conflicting and unclear results, and the scope of existing research makes the prospect of setting future directions daunting. In this review, we examine the importance of spatial and temporal factors on BDNF activity, particularly in processes such as synaptogenesis, Hebbian plasticity, homeostatic plasticity, and the treatment of psychiatric disorders. Understanding the fundamental physiology of when, where, and how BDNF acts and new approaches to control BDNF signaling in time and space can contribute to improved therapeutics and patient outcomes.

CAG Repeats Within the Non-pathological Range in the HTT Gene Influence Personality Traits in Patients With Subjective Cognitive Decline: A 13-Year Follow-Up Study

OBJECTIVE

HTT is a gene containing a key region of CAG repeats. When expanded beyond 39 repeats, Huntington disease (HD) develops. HTT genes with <35 repeats are not associated with HD. The biological function of CAG repeat expansion below the non-pathological threshold is not well understood. In fact higher number of repeats in HTT confer advantageous changes in brain structure and general intelligence, but several studies focused on establishing the association between CAG expansions and susceptibility to psychiatric disturbances and to other neurodegenerative disease than HD. We hypothesized that HTT CAG repeat length below the pathological threshold might influence mood and personality traits in a longitudinal sample of individuals with Subjective Cognitive Decline.

METHODS

We included 54 patients with SCD. All patients underwent an extensive neuropsychological battery at baseline, APOE genotyping and analysis of HTT alleles. We used the Big Five Factors Questionnaire (BFFQ) and Hamilton Depression Rating Scale (HDRS), respectively, to assess personality traits of patients and depression at baseline. Patients who did not progress to Mild Cognitive Impairment (MCI) had at least 5-year follow-up time.

RESULTS

In the whole sample, CAG repeat number in the shorter HTT allele was inversely correlated with conscientiousness (Pearson = -0.364, p = 0.007). There was no correlation between HDRS and CAG repeats. During the follow-up, 14 patients [25.93% (95% C.I. = 14.24-37.61)] progressed to MCI (MCI⁺) and 40 [74.07% (95% C.I. = 62.39-85.76)] did not (MCI^-). When we performed the same analysis in the MCI⁺ group we found that: CAG repeat length on the shorter allele was inversely correlated with energy (Pearson = 0.639, p = 0.014) and conscientiousness (Pearson = -0.695, p = 0.006). CAG repeat length on the longer allele was inversely correlated with conscientiousness (Pearson = -0.901, p < 0.001) and directly correlated with emotional stability (Pearson = 0.639, p = 0.014). These associations were confirmed also by multivariate analysis. We found no correlations between BFFQ parameters and CAG repeats in the MCI^- group.

DISCUSSION

Personality traits and CAG repeat length in the intermediate range have been associated with progression of cognitive decline and neuropathological findings consistent with AD. We showed that CAG repeat lengths in the HTT gene within the non-pathological range influence personality traits.

IRS1 expression in hippocampus is age-dependent and is required for mature spine maintenance and neuritogenesis

Insulin and insulin-like growth factor type I (IGF-1) play prominent roles in brain activity throughout the lifespan. Insulin/IGF1 signaling starts with the activation of the intracellular insulin receptor substrates (IRS). In this work, we performed a comparative study of IRS1 and IRS2, together with the IGF1 (IGF1R) and insulin (IR) receptor expression in the hippocampus and prefrontal cortex during development. We found that IRS1 and IRS2 expression is prominent during development and declines in the aged hippocampus, contrary to IR, which increases in adulthood and aging. In contrast, IGF1R expression is unaffected by age. Expression patterns are similar in the prefrontal cortex. Neurite development occurs postnatally in the rodent hippocampus and cortex, and it declines in the mature and aged brain and is influenced by trophic factors. In our previous work, we demonstrated that knockdown of IRS1 by shRNA impairs learning and reduces synaptic plasticity in a rat model, as measured by synaptophysin puncta in axons. In this study, we report that shIRS1 alters spine maturation in adult hilar hippocampal neurons. Lastly, to understand the role of IRS1 in neuronal neurite tree, we transfect shIRS1 into primary neuronal cultures and observed that shIRS1 reduced neurite branching and neurite length. Our results demonstrate that IRS1/2 and insulin/IGF1 receptors display different age-dependent expression profiles and that IRS1 is required for spine maturation, demonstrating a novel role for IRS1 in synaptic plasticity.

Altered trajectory of neurodevelopment associated with fetal growth restriction

Fetal growth restriction (FGR) is principally caused by suboptimal placental function. Poor placental function causes an under supply of nutrients and oxygen to the developing fetus, restricting development of individual organs and overall growth. Estimated fetal weight below the 10th or 3rd percentile with uteroplacental dysfunction, and knowledge regarding the onset of growth restriction (early or late), provide diagnostic criteria for fetuses at greatest risk for adverse outcome. Brain development and function is altered with FGR, with ongoing clinical and preclinical studies elucidating neuropathological etiology. During the third trimester of pregnancy, from ~28 weeks gestation, neurogenesis is complete and neuronal complexity is expanding, through axonal and dendritic outgrowth, dendritic branching and synaptogenesis, accompanied by myelin production. Fetal compromise over this period, as occurs in FGR, has detrimental effects on these processes. Total brain volume and grey matter volume is reduced in infants with FGR, first evident in utero, with cortical volume particularly vulnerable. Imaging studies show that cerebral morphology is disturbed in FGR, with altered cerebral cortex, volume and organization of brain networks, and reduced connectivity of long- and short-range circuits. Thus, FGR induces a deviation in brain development trajectory affecting both grey and white matter, however grey matter volume is preferentially reduced, contributed by cell loss, and reduced neurite outgrowth of surviving neurons. In turn, cell-to-cell local networks are adversely affected in FGR, and whole brain left and right intrahemispheric connections and interhemispheric connections are altered. Importantly, disruptions to region-specific brain networks are linked to cognitive and behavioral impairments.

Chronic Stress Weakens Connectivity in the Prefrontal Cortex: Architectural and Molecular Changes

Chronic exposure to uncontrollable stress causes loss of spines and dendrites in the prefrontal cortex (PFC), a recently evolved brain region that provides top-down regulation of thought, action, and emotion. PFC neurons generate top-down goals through recurrent excitatory connections on spines. This persistent firing is the foundation for higher cognition, including working memory, and abstract thought. However, exposure to acute uncontrollable stress drives high levels of catecholamine release in the PFC, which activates feedforward calcium-cAMP signaling pathways to open nearby potassium channels, rapidly weakening synaptic connectivity to reduce persistent firing. Chronic stress exposures can further exacerbate these signaling events leading to loss of spines and resulting in marked cognitive impairment. In this review, we discuss how stress signaling mechanisms can lead to spine loss, including changes to BDNF-mTORC1 signaling, calcium homeostasis, actin dynamics, and mitochondrial actions that engage glial removal of spines through inflammatory signaling. Stress signaling events may be amplified in PFC spines due to cAMP magnification of internal calcium release. As PFC dendritic spine loss is a feature of many cognitive disorders, understanding how stress affects the structure and function of the PFC will help to inform strategies for treatment and prevention.

Connecting the Neurobiology of Developmental Brain Injury: Neuronal Arborisation as a Regulator of Dysfunction and Potential Therapeutic Target

Neurodevelopmental disorders can derive from a complex combination of genetic variation and environmental pressures on key developmental processes. Despite this complex aetiology, and the equally complex array of syndromes and conditions diagnosed under the heading of neurodevelopmental disorder, there are parallels in the neuropathology of these conditions that suggest overlapping mechanisms of cellular injury and dysfunction. Neuronal arborisation is a process of dendrite and axon extension that is essential for the connectivity between neurons that underlies normal brain function. Disrupted arborisation and synapse formation are commonly reported in neurodevelopmental disorders. Here, we summarise the evidence for disrupted neuronal arborisation in these conditions, focusing primarily on the cortex and hippocampus. In addition, we explore the developmentally specific mechanisms by which neuronal arborisation is regulated. Finally, we discuss key regulators of neuronal arborisation that could link to neurodevelopmental disease and the potential for pharmacological modification of arborisation and the formation of synaptic connections that may provide therapeutic benefit in the future.

Low-intensity pulsed ultrasound for regenerating peripheral nerves: potential for penile nerve

Peripheral nerve damage, such as that found after surgery or trauma, is a substantial clinical challenge. Much research continues in attempts to improve outcomes after peripheral nerve damage and to promote nerve repair after injury. In recent years, low-intensity pulsed ultrasound (LIPUS) has been studied as a potential method of stimulating peripheral nerve regeneration. In this review, the physiology of peripheral nerve regeneration is reviewed, and the experiments employing LIPUS to improve peripheral nerve regeneration are discussed. Application of LIPUS following nerve surgery may promote nerve regeneration and improve functional outcomes through a variety of proposed mechanisms. These include an increase of neurotrophic factors, Schwann cell (SC) activation, cellular signaling activations, and induction of mitosis. We searched PubMed for articles related to these topics in both in vitro and in vivo animal research models. We found numerous studies, suggesting that LIPUS following nerve surgery promotes nerve regeneration and improves functional outcomes. Based on these findings, LIPUS could be a novel and valuable treatment for nerve injury-induced erectile dysfunction.

The Effect of CAG Repeats within the Non-Pathological Range in the HTT Gene on Cognitive Functions in Patients with Subjective Cognitive Decline and Mild Cognitive Impairment

The Huntingtin gene (HTT) is within a class of genes containing a key region of CAG repeats. When expanded beyond 39 repeats, Huntington disease (HD) develops. Individuals with less than 35 repeats are not associated with HD. Increasing evidence has suggested that CAG repeats play a role in modulating brain development and brain function. However, very few studies have investigated the effect of CAG repeats in the non-pathological range on cognitive performances in non-demented individuals. In this study, we aimed to test how CAG repeats' length influences neuropsychological scores in patients with subjective cognitive decline (SCD) and mild cognitive impairment (MCI). We included 75 patients (46 SCD and 29 MCI). All patients underwent an extensive neuropsychological battery and analysis of HTT alleles to quantify the number of CAG repeats. Results: CAG repeat number was positively correlated with scores of tests assessing for executive function, visual-spatial ability, and memory in SCD patients, while in MCI patients, it was inversely correlated with scores of visual-spatial ability and premorbid intelligence. When we performed a multiple regression analysis, we found that these relationships still remained, also when adjusting for possible confounding factors. Interestingly, logarithmic models better described the associations between CAG repeats and neuropsychological scores. CAG repeats in the HTT gene within the non-pathological range influenced neuropsychological performances depending on global cognitive status. The logarithmic model suggested that the positive effect of CAG repeats in SCD patients decreases as the number of repeats grows.

Current Methodological Pitfalls and Caveats in the Assessment of Exercise-Induced Changes in Peripheral Brain-Derived Neurotrophic Factor: How Result Reproducibility Can Be Improved

Neural mechanisms, such as enhanced neuroplasticity within the motor system, underpin exercise-induced motor improvements. Being a key mediator of motor plasticity, brain-derived neurotrophic factor (BDNF) is likely to play an important role in mediating exercise positive effects on motor function. Difficulties in assessing brain BDNF levels in humans have drawn attention to quantification of blood BDNF and raise the question of whether peripheral BDNF contributes to exercise-related motor improvements. Methodological and non-methodological factors influence measurements of blood BDNF introducing a substantial variability that complicates result interpretation and leads to inconsistencies among studies. Here, we discuss methodology-related issues and approaches emerging from current findings to reduce variability and increase result reproducibility.

Acupuncture Can Play an Antidepressant Role by Regulating the Intestinal Microbes and Neurotransmitters in a Rat Model of Depression

BACKGROUND Acupuncture, which has many good effects and few adverse effects, is widely recognized as an alternative therapy for depression in clinical practice. This study aimed to explore the mechanism of acupuncture in antidepressant treatment. MATERIAL AND METHODS In this experiment, Sprague-Dawley rats were randomly divided into 4 groups: control, chronic unpredictable mild stress (CUMS), acupuncture, and fluoxetine groups. The CUMS, acupuncture, and fluoxetine groups were orphaned and subjected to chronic unpredictable stress for 6 weeks, and the acupuncture and fluoxetine groups were treated with their respective intervention in weeks 4-6. The body weight of rats was monitored weekly. After behavioral tests were completed, serum, feces, and hippocampal tissue of rats were collected. RESULTS The results showed that the acupuncture and fluoxetine treatments could alleviate the behavioral changes caused by CUMS. The treatments increased the total distance of rat crossing in the open-field test, prolonged the activity time of the open cross maze in the open arm, and improved the rate of sucrose consumption in the sucrose preference test. In addition, both the decreased level of dopamine (DA) and 5-hydroxytryptamine (5-HT) in serum and hippocampus caused by CUMS were improved after the treatments with acupuncture and fluoxetine, and the decreased expression of brain-derived neurotrophic factor signaling and the astrocytes in the hippocampus caused by CUMS were increased after the treatments with acupuncture and fluoxetine. Acupuncture and fluoxetine also decreased the ß isoform of calmodulin-dependent protein kinase II in the hippocampus, which was increased by CUMS. Furthermore, acupuncture regulated intestinal microbial disorders caused by CUMS, which reduced the relative abundance ratio of Bacteroidetes/Firmicutes in rats. CONCLUSIONS Our experimental results indicate that acupuncture can alleviate depression-like performance in CUMS rats by regulating intestinal microbes and neurotransmitters.

Glial cells modulate retinal cell survival in rotenone-induced neural degeneration

Administration of the mitochondrial complex I inhibitor rotenone provides an excellent model to study the pathomechanism of oxidative stress-related neural degeneration diseases. In this study, we examined the glial roles in retinal cell survival and degeneration under the rotenone-induced oxidative stress condition. Mouse-derived Müller, microglial (BV-2), and dissociated retinal cells were used for in vitro experiments. Gene expression levels and cell viability were determined using quantitative reverse transcription-polymerase chain reaction and the alamarBlue assay, respectively. Conditioned media were prepared by stimulating glial cells with rotenone. Retinal ganglion cells (RGCs) and inner nuclear layer (INL) were visualized on rat retinal sections by immunohistochemistry and eosin/hematoxylin, respectively. Rotenone dose-dependently induced glial cell death. Treatment with rotenone or rotenone-stimulated glial cell-conditioned media altered gene expression of growth factors and inflammatory cytokines in glial cells. The viability of dissociated retinal cells significantly increased upon culturing in media conditioned with rotenone-stimulated or Müller cell-conditioned media-stimulated BV-2 cells. Furthermore, intravitreal neurotrophin-5 administration prevented the rotenone-induced reduction of RGC number and INL thickness in rats. Thus, glial cells exerted both positive and negative effects on retinal cell survival in rotenone-induced neural degeneration via altered expression of growth factors, especially upregulation of microglia-derived Ntf5, and proinflammatory cytokines.

Absence of Thyroid Hormone Induced Delayed Dendritic Arborization in Mouse Primary Hippocampal Neurons Through Insufficient Expression of Brain-Derived Neurotrophic Factor

Thyroid hormone (TH) plays important roles in the developing brain. TH deficiency in early life leads to severe developmental impairment in the hippocampus. However, the mechanisms of TH action in the developing hippocampus are still largely unknown. In this study, we generated 3,5,3'-tri-iodo-l-thyronine (T3)-free neuronal supplement, based on the composition of neuronal supplement 21 (NS21), to examine the effect of TH in the developing hippocampus using primary cultured neurons. Effects of TH on neurons were compared between cultures in this T3-free culture medium (-T3 group) and a medium in which T3 was added (+T3 group). Morphometric analysis and RT-qPCR were performed on 7, 10, and 14 days in vitro (DIV). On 10 DIV, a decreased dendrite arborization in -T3 group was observed. Such difference was not observed on 7 and 14 DIV. Brain-derived neurotrophic factor (Bdnf) mRNA levels also decreased significantly in -T3 group on 10 DIV. We then confirmed protein levels of phosphorylated neurotrophic tyrosine kinase type 2 (NTRK2, TRKB), which is a receptor for BDNF, on 10 DIV by immunocytochemistry and Western blot analysis. Phosphorylated NTRK2 levels significantly decreased in -T3 group compared to +T3 group on 10 DIV. Considering the role of BDNF on neurodevelopment, we examined its involvement by adding BDNF on 8 and 9 DIV. Addition of 10 ng/ml BDNF recovered the suppressed dendrite arborization induced by T3 deficiency on 10 DIV. We show that the lack of TH induces a developmental delay in primary hippocampal neurons, likely caused through a decreased Bdnf expression. Thus, BDNF may play a role in TH-regulated dendritogenesis.

Molecular mechanisms that mediate dendrite morphogenesis

Neurons develop dendritic morphologies that bear cell type-specific features in dendritic field size and geometry, branch placement and density, and the types and distributions of synaptic contacts. Dendritic patterns influence the types and numbers of inputs a neuron receives, and the ways in which neural information is processed and transmitted in the circuitry. Even subtle alterations in dendritic structures can have profound consequences on neuronal function and are implicated in neurodevelopmental disorders. In this chapter, I review how growing dendrites acquire their exquisite patterns by drawing examples from diverse neuronal cell types in vertebrate and invertebrate model systems. Dendrite morphogenesis is shaped by intrinsic and extrinsic factors such as transcriptional regulators, guidance and adhesion molecules, neighboring cells and synaptic partners. I discuss molecular mechanisms that regulate dendrite morphogenesis with a focus on five aspects of dendrite patterning: (1) Dendritic cytoskeleton and cellular machineries that build the arbor; (2) Gene regulatory mechanisms; (3) Afferent cues that regulate dendritic arbor growth; (4) Space-filling strategies that optimize dendritic coverage; and (5) Molecular cues that specify dendrite wiring. Cell type-specific implementation of these patterning mechanisms produces the diversity of dendrite morphologies that wire the nervous system.

Kinase Signaling in Dendritic Development and Disease

Dendrites undergo extensive growth and remodeling during their lifetime. Specification of neurites into dendrites is followed by their arborization, maturation, and functional integration into synaptic networks. Each of these distinct developmental processes is spatially and temporally controlled in an exquisite fashion. Protein kinases through their highly specific substrate phosphorylation regulate dendritic growth and plasticity. Perturbation of kinase function results in aberrant dendritic growth and synaptic function. Not surprisingly, kinase dysfunction is strongly associated with neurodevelopmental and psychiatric disorders. Herein, we review, (a) key kinase pathways that regulate dendrite structure, function and plasticity, (b) how aberrant kinase signaling contributes to dendritic dysfunction in neurological disorders and (c) emergent technologies that can be applied to dissect the role of protein kinases in dendritic structure and function.