Weeks Of Postnatal Development Research Articles

Chronic silencing of subsets of cortical layer 5 pyramidal neurons has a long-term influence on the laminar distribution of parvalbumin interneurons and the perineuronal nets.

Neural networks are established throughout cortical development, which require the right ratios of glutamatergic and GABAergic neurons. Developmental disturbances in pyramidal neuron number and function can impede the development of GABAergic neurons, which can have long-lasting consequences on inhibitory networks. However, the role of deep-layer pyramidal neurons in instructing the development and distribution of GABAergic neurons is still unclear. To unravel the role of deep-layer pyramidal neuron activity in orchestrating the spatial and laminar distribution of parvalbumin neurons, we selectively manipulated subsets of layer 5 projection neurons. By deleting Snap25 selectively from Rbp4-Cre + pyramidal neurons, we abolished regulated vesicle release from subsets of cortical layer 5 projection neurons. Our findings revealed that chronically silencing subsets of layer 5 projection neurons did not change the number and distribution of parvalbumin neurons in the developing brain. However, it did have a long-term impact on the laminar distribution of parvalbumin neurons and their perineuronal nets in the adult primary motor and somatosensory cortices. The laminar positioning of parvalbumin neurons was altered in layer 4 of the primary somatosensory cortex in the adult Snap25 cKO mice. We discovered that the absence of layer 5 activity only had a transient effect on the soma morphology of striatal PV neurons during the third week of postnatal development. We also showed that the relationship between parvalbumin neurons and the perineuronal nets varied across different cortical layers and regions; therefore, their relationship is far more complex than previously described. The current study will help us better understand the bidirectional interaction between deep-layer pyramidal cells and GABAergic neurons, as well as the long-term impact of interrupting pyramidal neuron activity on inhibitory network formation.

Quantitative label-free digital holographic imaging of cardiomyocyte optical volume, nucleation, and cell division

Cardiac regeneration in newborn rodents depends on the ability of pre-existing cardiomyocytes to proliferate and divide. This capacity is lost within the first week of postnatal development when these cells rapidly switch from hyperplasia to hypertrophy, withdraw from the cell cycle, become binucleated, and increase in size. How these dynamic changes in cell size and nucleation impact cardiomyocyte proliferative potential is not well understood. In this study, we innovate the application of a commercially available digital holographic imaging microscope, the Holomonitor M4, to evaluate the proliferative responses of mononucleated and binucleated cardiomyocytes after CHIR99021 treatment, a model proliferative stimulus. This system enables long-term label-free quantitative tracking of primary cardiomyocyte dynamics in real-time with single-cell resolution. Our results confirm that chemical inhibition of glycogen synthase kinase 3 with CHIR99021 promotes complete cell division of both mononucleated and binucleated cardiomyocytes with high frequency. Quantitative tracking of cardiomyocyte volume dynamics during these proliferative events revealed that both mononucleated and binucleated cardiomyocytes reach a similar size-increase threshold prior to attempted cell division. Binucleated cardiomyocytes attempt to divide with lower frequency than mononucleated cardiomyocytes, which may be associated with inadequate increases in cell size. By defining the interrelationship between cardiomyocyte size, nucleation, and cell cycle control, we may better understand the cellular mechanisms that drive the loss of mammalian cardiac regenerative capacity after birth.

Retinal Input Is Required for the Maintenance of Neuronal Laminae in the Ventrolateral Geniculate Nucleus.

Retinal ganglion cell (RGC) axons provide direct input into several brain regions, including the dorsal lateral geniculate nucleus (dLGN), which is important for image-forming vision, and the ventrolateral geniculate nucleus (vLGN), which is associated with nonimage-forming vision. Through both activity- and morphogen-dependent mechanisms, retinal inputs play important roles in the development of dLGN, including the refinement of retinal projections, morphological development of thalamocortical relay cells (TRCs), timing of corticogeniculate innervation, and recruitment and distribution of inhibitory interneurons. In contrast, little is known about the role of retinal inputs in the development of vLGN. Grossly, vLGN is divided into two domains, the retinorecipient external vLGN (vLGNe) and nonretinorecipient internal vLGN (vLGNi). Studies previously found that vLGNe consists of transcriptionally distinct GABAergic subtypes distributed into at least four adjacent laminae. At present, it remains unclear whether retinal inputs influence the development of these cell-type-specific neuronal laminae in vLGNe. Here, we elucidated the developmental timeline for these laminae in the mouse vLGNe, and results indicate that these laminae are specified at or before birth. We observed that mutant mice without retinal inputs have a normal laminar distribution of GABAergic cells at birth; however, after the first week of postnatal development, these mutants exhibited a dramatic disruption in the laminar organization of inhibitory neurons and clear boundaries between vLGNe and vLGNi. Overall, our results show that while the formation of cell-type-specific layers in mouse vLGNe does not depend on RGC inputs, retinal signals are critical for their maintenance.

Somatostatin interneurons control the timing of developmental desynchronization in cortical networks

Synchronous neuronal activity is a hallmark of the developing brain. In the mouse cerebral cortex, activity decorrelates during the second week of postnatal development, progressively acquiring the characteristic sparse pattern underlying the integration of sensory information. The maturation of inhibition seems critical for this process, but the interneurons involved in this crucial transition of network activity in the developing cortex remain unknown. Using invivo longitudinal two-photon calcium imaging during the period that precedes the change from highly synchronous to decorrelated activity, we identify somatostatin-expressing (SST+) interneurons as critical modulators of this switch in mice. Modulation of the activity of SST+ cells accelerates or delays the decorrelation of cortical network activity, a process that involves regulating the maturation of parvalbumin-expressing (PV+) interneurons. SST+ cells critically link sensory inputs with local circuits, controlling the neural dynamics in the developing cortex while modulating the integration of other interneurons into nascent cortical circuits.

Serotonin modulates excitatory synapse maturation in the developing prefrontal cortex

Serotonin (5-HT) imbalances in the developing prefrontal cortex (PFC) are linked to long-term behavioral deficits. However, the synaptic mechanisms underlying 5-HT-mediated PFC development are unknown. We found that chemogenetic suppression and enhancement of 5-HT release in the PFC during the first two postnatal weeks decreased and increased the density and strength of excitatory spine synapses, respectively, on prefrontal layer 2/3 pyramidal neurons in mice. 5-HT release on single spines induced structural and functional long-term potentiation (LTP), requiring both 5-HT2A and 5-HT7 receptor signals, in a glutamatergic activity-independent manner. Notably, LTP-inducing 5-HT stimuli increased the long-term survival of newly formed spines ( ≥ 6 h) via 5-HT7 Gαs activation. Chronic treatment of mice with fluoxetine, a selective serotonin-reuptake inhibitor, during the first two weeks, but not the third week of postnatal development, increased the density and strength of excitatory synapses. The effect of fluoxetine on PFC synaptic alterations in vivo was abolished by 5-HT2A and 5-HT7 receptor antagonists. Our data describe a molecular basis of 5-HT-dependent excitatory synaptic plasticity at the level of single spines in the PFC during early postnatal development.

Localization of cadherins in the postnatal cochlear epithelium and their relation to space formation.

The sensory epithelium of the cochlea, the organ of Corti, has complex cytoarchitecture consisting of mechanosensory hair cells intercalated by epithelial support cells. The support cells provide important trophic and structural support to the hair cells. Thus, the support cells must be stiff yet compliant enough to withstand and modulate vibrations to the hair cells. Once the sensory cells are properly patterned, the support cells undergo significant remodeling from a simple epithelium into a structurally rigid epithelium with fluid-filled spaces in the murine cochlea. Cell adhesion molecules such as cadherins are necessary for sorting and connecting cells in an intact epithelium. To create the fluid-filled spaces, cell adhesion properties of adjoining cell membranes between cells must change to allow the formation of spaces within an epithelium. However, the dynamic localization of cadherins has not been properly analyzed as these spaces are formed. There are three cadherins that are reported to be expressed during the first postnatal week of development when the tunnel of Corti forms in the cochlea. In this study, we characterize the dynamic localization of cadherins that are associated with cytoskeletal remodeling at the contacting membranes of the inner and outer pillar cells flanking the tunnel of Corti.

Dopamine modulates the retinal clock through melanopsin-dependent regulation of cholinergic waves during development

BackgroundThe mammalian retina contains an autonomous circadian clock that controls various aspects of retinal physiology and function, including dopamine (DA) release by amacrine cells. This neurotransmitter plays a critical role in retina development, visual signalling, and phase resetting of the retinal clock in adulthood. Interestingly, bidirectional regulation between dopaminergic cells and melanopsin-expressing retinal ganglion cells has been demonstrated in the adult and during development. Additionally, the adult melanopsin knockout mouse (Opn4−/−) exhibits a shortening of the endogenous period of the retinal clock. However, whether DA and / or melanopsin influence the retinal clock mechanism during its maturation is still unknown.ResultsUsing wild-type Per2Luc and melanopsin knockout (Opn4−/−::Per2Luc) mice at different postnatal stages, we found that the retina generates self-sustained circadian rhythms from postnatal day 5 in both genotypes and that the ability to express these rhythms emerges in the absence of external time cues. Intriguingly, only in wild-type explants, DA supplementation lengthened the endogenous period of the clock during the first week of postnatal development through both D1- and D2-like dopaminergic receptors. Furthermore, the blockade of spontaneous cholinergic retinal waves, which drive DA release in the early developmental stages, shortened the period and reduced the light-induced phase shift of the retinal clock only in wild-type retinas.ConclusionsThese data suggest that DA modulates the molecular core of the clock through melanopsin-dependent regulation of acetylcholine retinal waves, thus offering an unprecedented role of DA and melanopsin in the endogenous functioning and the light response of the retinal clock during development.

Prenatal nicotine exposure alters gene expression profiles of neurons in the sub-regions of the VTA during early postnatal development

Brain growth occurs during the first 2 weeks of postnatal development in rats. This developmental period is equivalent to the third trimester of human gestation. Dendritic arborization, axonal growth, and gliogenesis are observed along with a strong maturation of neurotransmission during this critical development period. Furthermore, nicotine exposure during early development causes deficiencies in sensory and cognitive processing in adults. In this study, we further investigated the gene expression of neuron groups and the influence of perinatal nicotine exposure on gene expressions of neurons within the sub-regions of the ventral tegmental area (VTA) in 1 week, 2 week and 3-week-old rat pups. We exposed pregnant rats to nicotine perinatally on gestational day 7 through postnatal day 14. Pups are exposed to nicotine during pregnancy and through breastfeeding to investigate its effect in rat pups during early neuronal development. Real time PCR was used to find the relative expressions of gamma-aminobutyric acid (GABA), dopamine, and glutamate neuron markers within the three sub-regions of the VTA including the parabrachial pigmented nucleus (PBP), parainterfascicular (PIF), and paranigral nucleus (PN). Our results indicated that during early maturation, the dopamine marker tyrosine hydroxylase (TH) showed a consistently increased significance in PN sub-region compared to PIF and PBP. These results suggest that following perinatal nicotine exposure, VTA dopamine neurons, especially within the PN sub-region, are significantly excited starting from birth.

Development of the B-Cell Progenitor Niche Is Dependent on Cells Derived from the Migratory Neural Crest

INTRODUCTION: The earliest stages of B-cell production occur in the bone marrow (BM), where hematopoietic stem cells (HSCs) differentiate into common lymphoid and myeloid progenitors. Common lymphoid progenitors then undergo progressive differentiation as B cell progenitors (BCPs) prior to exiting the BM and completing their maturation in the spleen and lymph nodes. BCP development is regulated by lymphotrophic cytokines produced by BM mesenchymal stromal cells (MSCs) and osteoprogenitors (OPs). While the factors that regulate the formation and activity of the BCP niche in the BM are unknown, other laboratories have determined that signals from the peripheral nervous system (PNS) direct the formation and activity of the HSC BM niche. In this study, we hypothesized that the PNS also coordinates the formation and activity of the BCP BM niche. METHODS: To test this hypothesis, we targeted Schwann cells (SCs), which are required for peripheral nerve function, via a well-described mouse model of global peripheral nerve dysfunction (MP0-Cre+/-; Lamc1fl/fl, hereafter referred to as mutant). MP0 is expressed in the migratory neural crest from which SCs are derived, and the Lamc1 gene encodes an extracellular matrix protein (laminin-gamma-1) required for perinatal SC morphogenesis and differentiation. In mutant mice, SC development arrests at the 'immature' stage. Mutant SCs do not form myelinating or nonmyelinating SCs, which in mice takes place during the initial three weeks of postnatal development. Mutant mice die between 4-5 weeks of age; therefore 3-3.5 week old mice were used for all studies detailed below. RESULTS: In comparison to controls, mutant mice were lymphopenic. There were no differences in number of red cells, neutrophils or platelets between control and mutant mice. In the bone marrow, Pre-B-cell but not myeloid colony formation was significantly reduced in mutant mice, as were the number of both Pre and Pro B cells. Insulin Like Growth Factor Type 1 (IGF-1), an osteoprogenitor-derived lymphopoietic cytokine required for BCP maturation, was reduced by 60% in mutant bone marrow supernatant. IGF-1 transcript was also reduced in osteoprogenitor/osteoblast cells (CD45-Tert119-CD31-Sca1-CD51+) from mutant BM. Control and mutant femurs were examined by µCT, which identified significant impairment in mutant cortical and trabecular bone structure and density. A fluorescent reporter transgene (ROSAmT/eGFP) was employed to facilitate isolation and characterization of those BM niche cells genetically targeted by MP0-Cre. Using flow cytometry, we determined that less than four percent of osteoprogenitor/osteoblast cells expressed eGFP and were thus derived from the migratory neural crest. None of the MSCs (Tert119-CD31-Sca1+CD51+) expressed eGFP. The relative contribution of the migratory neural crest to each niche cell fraction did not vary between control and mutant BM. Lamc1 transcript from mutant eGFP+ cells was nearly undetectable and significantly less than from control eGFP+cells. Transcripts typically enriched in juvenile and nonmyelinating SCs (Erbb3, Sox10, GFAP, and s-100b) were enriched in eGFP+ but not eGFP- BM niche cells from both control (MP0-Cre+/-; Lamc1fl/+; ROSAmT/eGFP) and mutant (MP0-Cre+/-; Lamc1fl/fl) mice. There was no quantitative difference in IGF1 transcription between control and mutant eGFP+ cells. CONCLUSIONS: From these data, we conclude that postnatal maturation of the migratory neural crest is required for establishment of the BCP niche. While the migratory neural crest cells found within the bone marrow are enriched with SC-transcripts, they also contribute a small fraction of BM stromal cells and potentially some neurons (sympathetic and parasympathetic). Since mutant mice are paretic, it is also possible that weight bearing-induced mechanical forces contribute to osteogenic BCP niche formation. Our work to date does not differentiate between these possibilities, but does provide significant preliminary evidence to support our hypothesis that 'neuronal' development contributes to formation and activity of the BCP niche within the BM.

MGluR5 Is Substitutable for mGluR1 in Cerebellar Purkinje Cells for Motor Coordination, Developmental Synapse Elimination, and Motor Learning.

Group I metabotropic glutamate receptors (mGluRs) include mGluR1 and mGluR5, which are coupled to the Gq family of heterotrimeric G-proteins and readily activated by their selective agonist 3,5-dihydroxyphenilglycine (DHPG). mGluR1 and mGluR5 exhibit nearly complementary distributions spatially or temporally in the central nervous system (CNS). In adult cerebellar Purkinje cells (PCs), mGluR1 is a dominant group I mGluR and mGluR5 is undetectable. mGluR1 expression increases substantially during the first three weeks of postnatal development and remains high throughout adulthood. On the other hand, mGluR5 expression is observed during the first two postnatal weeks and then decreases. However, functional differences between mGluR1 and mGluR5 in the CNS remains to be elucidated. To address this issue, we generated “mGluR5-rescue” mice in which mGluR5 is specifically expressed in PCs in global mGluR1-knockout (KO) mice. mGluR5-rescue mice exhibited apparently normal motor coordination, developmental elimination of redundant climbing fiber (CF)-PC synapses, and delay eyeblink conditioning, which were severely impaired in mGluR1-KO mice. We concluded that mGluR5 is functionally comparable with mGluR1 in cerebellar PCs.

Analysis of the Expression and Subcellular Distribution of eEF1A1 and eEF1A2 mRNAs during Neurodevelopment.

Neurodevelopment is accompanied by a precise change in the expression of the translation elongation factor 1A variants from eEF1A1 to eEF1A2. These are paralogue genes that encode 92% identical proteins in mammals. The switch in the expression of eEF1A variants has been well studied in mouse motor neurons, which solely express eEF1A2 by four weeks of postnatal development. However, changes in the subcellular localization of eEF1A variants during neurodevelopment have not been studied in detail in other neuronal types because antibodies lack perfect specificity, and immunofluorescence has a low sensitivity. In hippocampal neurons, eEF1A is related to synaptic plasticity and memory consolidation, and decreased eEF1A expression is observed in the hippocampus of Alzheimer’s patients. However, the specific variant involved in these functions is unknown. To distinguish eEF1A1 from eEF1A2 expression, we have designed single-molecule fluorescence in-situ hybridization probes to detect either eEF1A1 or eEF1A2 mRNAs in cultured primary hippocampal neurons and brain tissues. We have developed a computational framework, ARLIN (analysis of RNA localization in neurons), to analyze and compare the subcellular distribution of eEF1A1 and eEF1A2 mRNAs at specific developmental stages and in mature neurons. We found that eEF1A1 and eEF1A2 mRNAs differ in expression and subcellular localization over neurodevelopment, and eEF1A1 mRNAs localize in dendrites and synapses during dendritogenesis and synaptogenesis. Interestingly, mature hippocampal neurons coexpress both variant mRNAs, and eEF1A1 remains the predominant variant in dendrites.

Transcriptional regulation of PEBP1 expression by androgen receptor in mouse testes

ABSTRACT Androgen and AR are essential for maintaining spermatogenesis and male fertility. Previous studies have shown that the phosphatidyl ethanolamine binding protein 1 (Pebp1) gene is down-regulated in the selective ablation of the AR in the Sertoli cells of mouse testes compared with wild-type mice, indicating that Pebp1 is a candidate target of AR. The ChIP-PCR data and ChIP-sequencing results of this study verified that Pebp1 is a target gene regulated by AR. Real-time PCR, Western blot analysis, and immunofluorescence data showed that Pebp1 is expressed at all stages of testicular development, with an increasing trend from 1 to 8 weeks of postnatal development. PEBP1 was principally located in the cytoplasm, and high-intensity fluorescence revealed PEBP in the lumen of the testicular tubules. Bioinformatics analysis indicated effective androgen-responsive elements (AREs) located in the promotor of Pepb1 gene. Dual fluorescence assay data showed that androgens and AR could bind to the AREs of Pebp1 and induce an increase of gene expression. These data suggest that Pepb1 is a newfound target gene regulated by androgens and AR in mouse Sertoli cells. However, the detailed molecular mechanism of their role in spermatogenesis still needs to be further studied. Abbreviations: AR: androgen receptor; Pebp1: phosphatidyl ethanolamine binding protein 1; ARKO: androgen receptor knockout; WT: wild type; SCARKO: Sertoli cell-selective androgen receptor knockout; ChIP: chromatin immunoprecipitation; RKIP: Raf kinase inhibitory protein; MAPK: mitogen-activated protein kinase; NF-κB: nuclear factor kappa-light-chain-enhancer of activated B cells; GSK-3: glycogen synthase kinase-3; RT-PCR: reverse transcriptase polymerase chain reaction; SEM: standard error of the mean

The Role of Metabolism in Heart Failure and Regeneration.

Heart failure is the leading cause of death worldwide. The inability of the adult mammalian heart to regenerate following injury results in the development of systolic heart failure. Thus, identifying novel approaches toward regenerating the adult heart has enormous therapeutic potential for adult heart failure. Mitochondrial metabolism is an essential homeostatic process for maintaining growth and survival. The emerging role of mitochondrial metabolism in controlling cell fate and function is beginning to be appreciated. Recent evidence suggests that metabolism controls biological processes including cell proliferation and differentiation, which has profound implications during development and regeneration. The regenerative potential of the mammalian heart is lost by the first week of postnatal development when cardiomyocytes exit the cell cycle and become terminally differentiated. This inability to regenerate following injury is correlated with the metabolic shift from glycolysis to fatty acid oxidation that occurs during heart maturation in the postnatal heart. Thus, understanding the mechanisms that regulate cardiac metabolism is key to unlocking metabolic interventions during development, disease, and regeneration. In this review, we will focus on the emerging role of metabolism in cardiac development and regeneration and discuss the potential of targeting metabolism for treatment of heart failure.

Ventral root evoked entrainment of disinhibited bursts across early postnatal development in mice

Early in the postnatal period, motoneuron axon stimulation can excite motor networks in the spinal cord. Here we tested if these excitatory effects changed across early postnatal development up to postnatal day (P) 24 by when mice are capable of weight-bearing locomotion and locomotor networks are considered functionally mature. This was accomplished in the isolated spinal cord preparation using ventral root evoked entrainment of disinhibited bursts. Ventral root evoked entrainment was defined and characterized over the first 2 weeks of postnatal development, and was found to decline over this period, but entrainment could still be detected in mice as old as P24. Disinhibited bursting could be elicited, and dorsal root evoked entrainment could be recorded as late as P39 and remained unchanged in effectiveness, suggesting that poor tissue viability may not be the cause of the decline in ventral root evoked entrainment. Pharmacological experiments performed on younger animals established that dopamine D2 receptor antagonists and mGluR1 agonists both enhanced ventral root evoked entrainment. In conclusion, the motoneuronal inputs to spinal motor networks via the excitatory pathway is modulated by dopamine and metabotropic glutamate receptors and may be under powerful inhibitory control, which may explain why there is a developmental decline in entrainment.

Developmental Phase Transitions in Spatial Organization of Spontaneous Activity in Postnatal Barrel Cortex Layer 4.

Spatially-organized spontaneous activity is a characteristic feature of developing mammalian sensory systems. However, the transitions of spontaneous-activity spatial organization during development and related mechanisms remain largely unknown. We reported previously that layer 4 (L4) glutamatergic neurons in the mouse barrel cortex exhibit spontaneous activity with a patchwork-type pattern at postnatal day (P)5, which is during barrel formation. In the current work, we revealed that spontaneous activity in mouse barrel-cortex L4 glutamatergic neurons exhibits at least three phases during the first two weeks of postnatal development. Phase I activity has a patchwork-type pattern and is observed not only at P5, but also P1, before barrel formation. Phase II is found at P9, by which time barrel formation is completed, and exhibits broadly synchronized activity across barrel borders. Phase III emerges around P11 when L4-neuron activity is desynchronized. The Phase I activity, but not Phase II or III activity, is blocked by thalamic inhibition, demonstrating that the Phase I to II transition is associated with loss of thalamic dependency. Dominant-negative (DN)-Rac1 expression in L4 neurons hampers the Phase II to III transition. It also suppresses developmental increases in spine density and excitatory synapses of L4 neurons in the second postnatal week, suggesting that Rac1-mediated synapse maturation could underlie the Phase II to III transition. Our findings revealed the presence of distinct mechanisms for Phase I to II and Phase II to III transition. They also highlighted the role of a small GTPase in the developmental desynchronization of cortical spontaneous activity.SIGNIFICANCE STATEMENT Developing neocortex exhibits spatially-organized spontaneous activity, which plays a critical role in cortical circuit development. The features of spontaneous-activity spatial organization and the mechanisms underlying its changes during development remain largely unknown. In the present study, using two-photon in vivo imaging, we revealed three phases (Phases I, II, and III) of spontaneous activity in barrel-cortex layer 4 (L4) glutamatergic neurons during the first two postnatal weeks. We also demonstrated the presence of distinct mechanisms underlying phase transitions. Phase I to II shift arose from the switch in the L4-neuron driving source, and Phase II to III transition relied on L4-neuron Rac1 activity. These results provide new insights into the principles of developmental transitions of neocortical spontaneous-activity spatial patterns.

Recombinant adiponectin protects the newborn rat lung from lipopolysaccharide-induced inflammatory injury.

Preterm infants are at high risk for developing bronchopulmonary dysplasia and pulmonary hypertension from inflammatory lung injury. In adult models, adiponectin (APN)—an adipocyte‐derived hormone—protects the lung from inflammatory injury and pulmonary vascular remodeling. Cord blood APN levels in premature infants born < 26 weeks gestation are 5% of the level in infants born at term. We previously reported the expression profile of APN and its receptors in neonatal rat lung homogenates during the first 3 weeks of postnatal development. Here, we characterize the expression profile of APN and its receptors in specific lung cells and the effects of exogenous recombinant APN (rAPN) on lipopolysaccharide‐(LPS)‐induced cytokine and chemokine production in total lung homogenates and specific lung cells. In vitro, rAPN added to primary cultures of pulmonary artery smooth muscle cells attenuated the expression of LPS‐induced pro‐inflammatory cytokines while increasing the expression of anti‐inflammatory cytokines. In vivo, intraperitoneal rAPN (2 mg/kg), given 4 hr prior to intrapharyngeal administration of LPS (5 mg/kg) to newborn rats at postnatal day 4, significantly reduced gene and protein expression of the pro‐inflammatory cytokine IL‐1ß and reduced protein expression of the chemokines monocyte chemoattractant protein (MCP‐1) and macrophage inflammatory protein‐1 alpha (MIP‐1α) in the lung. LPS‐induced histopathological changes in the lung were also decreased. Moreover, rAPN given 20 hr after intrapharyngeal LPS had a similar effect on lung inflammation. These findings suggest a role for APN in protecting the lung from inflammation during early stages of lung development.

A Developmental Analysis of Juxtavascular Microglia Dynamics and Interactions with the Vasculature.

Microglia, a resident CNS macrophage, are dynamic cells, constantly extending and retracting their processes as they contact and functionally regulate neurons and other glial cells. There is far less known about microglia-vascular interactions, particularly under healthy steady-state conditions. Here, we use the male and female mouse cerebral cortex to show that a higher percentage of microglia associate with the vasculature during the first week of postnatal development compared with older ages and that the timing of these associations is dependent on the fractalkine receptor (CX3CR1). Similar developmental microglia-vascular associations were detected in the human brain. Using live imaging in mice, we found that juxtavascular microglia migrated when microglia are actively colonizing the cortex and became stationary by adulthood to occupy the same vascular space for nearly 2 months. Further, juxtavascular microglia at all ages associate with vascular areas void of astrocyte endfeet, and the developmental shift in microglial migratory behavior along vessels corresponded to when astrocyte endfeet more fully ensheath vessels. Together, our data provide a comprehensive assessment of microglia-vascular interactions. They support a mechanism by which microglia use the vasculature to migrate within the developing brain parenchyma. This migration becomes restricted on the arrival of astrocyte endfeet such that juxtavascular microglia become highly stationary and stable in the mature cortex.SIGNIFICANCE STATEMENT We report the first extensive analysis of juxtavascular microglia in the healthy, developing, and adult brain. Live imaging revealed that juxtavascular microglia within the cortex are highly motile and migrate along vessels as they are colonizing cortical regions. Using confocal, expansion, super-resolution, and electron microscopy, we determined that microglia associate with the vasculature at all ages in areas lacking full astrocyte endfoot coverage and motility of juxtavascular microglia ceases as astrocyte endfeet more fully ensheath the vasculature. Our data lay the fundamental groundwork to investigate microglia-astrocyte cross talk and juxtavascular microglial function in the healthy and diseased brain. They further provide a potential mechanism by which vascular interactions facilitate microglial colonization of the brain to later regulate neural circuit development.

Changes in the Expression of GAT1 (GABA transporter) in the Ventrolateral Part of the Solitary Tract Nucleus in Prenatal Serotonin Deficiency in Rats

Objectives. To study the expression of GAT1 (GABA transporter) at the early periods of postnatal development in the ventrolateral part of the solitary tract nucleus in prenatal serotonin deficiency in rats. Materials and methods. The endogenous serotonin level in the embryonic period was decreased by inhibition of tryptophan hydroxylase with para-chlorophenylalanine (PCPA) (Sigma, USA). GAT-1 transporter was detected using primary rabbit polyclonal antibodies (anti-GABA transporter 1, GAT1) (AbCam, UK). Results. From the early neonatal period to the beginning of juvenile age, the neuropil and the processes, terminals, and synaptic structures of the lateral and ventral parts of the solitary tract nucleus of control rats showed a gradual increase in GAT1 expression in experimental animals. The level of expression of GAT1 transporter was significantly greater in the lateral and ventral parts during postnatal weeks 1 and 2 than in controls, though by the end of week 3, i.e., by the beginning of juvenile age, it decreased to become significantly lower than in controls. Conclusions. The respiratory areas of the solitary tract nucleus in control rats in the first three weeks of postnatal development showed a gradual increase in GAT1 expression. Serotonin deficiency during the prenatal period led to impaired expression of GAT1 in the early postnatal period. These changes can lead to changes in GABA transmission, which may in turn be the cause of imbalance between inhibitory and excitatory effects in the respiratory center in the early postnatal period and, thus, may be the basis of the development of respiratory dysfunctions at early age.

MT1-MMP deficiency leads to defective ependymal cell maturation, impaired ciliogenesis, and hydrocephalus.

Hydrocephalus is characterized by abnormal accumulation of cerebrospinal fluid (CSF) in the ventricular cavity. The circulation of CSF in brain ventricles is controlled by the coordinated beating of motile cilia at the surface of ependymal cells (ECs). Here, we show that MT1-MMP is highly expressed in olfactory bulb, rostral migratory stream, and the ventricular system. Mice deficient for membrane-type 1-MMP (MT1-MMP) developed typical phenotypes observed in hydrocephalus, such as dome-shaped skulls, dilated ventricles, corpus callosum agenesis, and astrocyte hypertrophy, during the first 2 weeks of postnatal development. MT1-MMP-deficient mice exhibited reduced and disorganized motile cilia with the impaired maturation of ECs, leading to abnormal CSF flow. Consistent with the defects in motile cilia morphogenesis, the expression of promulticiliogenic genes was significantly decreased, with a concomitant hyperactivation of Notch signaling in the walls of lateral ventricles in Mmp14-/- brains. Inhibition of Notch signaling by γ-secretase inhibitor restored ciliogenesis in Mmp14-/- ECs. Taken together, these data suggest that MT1-MMP is required for ciliogenesis and EC maturation through suppression of Notch signaling during early brain development. Our findings indicate that MT1-MMP is critical for early brain development and loss of MT1-MMP activity gives rise to hydrocephalus.

Defects in syntabulin-mediated synaptic cargo transport associate with autism-like synaptic dysfunction and social behavioral traits.

The formation and maintenance of synapses require long-distance delivery of newly synthesized synaptic proteins from the soma to distal synapses, raising the fundamental question of whether impaired transport is associated with neurodevelopmental disorders such as autism. We previously revealed that syntabulin acts as a motor adaptor linking kinesin-1 motor and presynaptic cargos. Here, we report that defects in syntabulin-mediated transport and thus reduced formation and maturation of synapses are one of core synaptic mechanisms underlying autism-like synaptic dysfunction and social behavioral abnormalities. Syntabulin expression in the mouse brain peaks during the first two weeks of postnatal development and progressively declines during brain maturation. Neurons from conditional syntabulin−/− mice (stb cKO) display impaired transport of presynaptic cargos, reduced synapse density and active zones, and altered synaptic transmission and long-term plasticity. Intriguingly, stb cKO mice exhibit core autism-like traits, including defective social recognition and communication, increased stereotypic behavior, and impaired spatial learning and memory. These phenotypes establish a new mechanistic link between reduced transport of synaptic cargos and impaired maintenance of synaptic transmission and plasticity, contributing to autism-associated behavioral abnormalities. This notion is further confirmed by the human missense variant STB-R178Q, which is found in an autism patient and loses its adaptor capacity for binding kinesin-1 motors. Expressing STB-R178Q fails to rescue reduced synapse formation and impaired synaptic transmission and plasticity in stb cKO neurons. Altogether, our study suggests that defects in syntabulin-mediated transport mechanisms underlie the synaptic dysfunction and behavioral abnormalities that bear similarities to autism.