Mechanopathology of biofilm-like Mycobacterium tuberculosis cords

Mycobacterium tuberculosis (Mtb) cultured axenically without detergent forms biofilm-like cords, a clinical identifier of virulence. In lung-on-chip (LoC) and mouse models, cords in alveolar cells contribute to suppression of innate immune signaling via nuclear compression. Thereafter, extracellular cords cause contact-dependent phagocyte death but grow intercellularly between epithelial cells. The absence of these mechanopathological mechanisms explains the greater proportion of alveolar lesions with increased immune infiltration and dissemination defects in cording-deficient Mtb infections. Compression of Mtb lipid monolayers induces a phase transition that enables mechanical energy storage. Agent-based simulations demonstrate that the increased energy storage capacity is sufficient for the formation of cords that maintain structural integrity despite mechanical perturbation. Bacteria in cords remain translationally active despite antibiotic exposure and regrow rapidly upon cessation of treatment. This study provides a conceptual framework for the biophysics and function in tuberculosis infection and therapy of cord architectures independent of mechanisms ascribed to single bacteria.

ADAMTS18+ villus tip telocytes maintain a polarized VEGFA signaling domain and fenestrations in nutrient-absorbing intestinal blood vessels

The small intestinal villus tip is the first point of contact for lumen-derived substances including nutrients and microbial products. Electron microscopy studies from the early 1970s uncovered unusual spatial organization of small intestinal villus tip blood vessels: their exterior, epithelial-facing side is fenestrated, while the side facing the villus stroma is non-fenestrated, covered by pericytes and harbors endothelial nuclei. Such organization optimizes the absorption process, however the molecular mechanisms maintaining this highly specialized structure remain unclear. Here we report that perivascular LGR5⁺ villus tip telocytes (VTTs) are necessary for maintenance of villus tip endothelial cell polarization and fenestration by sequestering VEGFA signaling. Mechanistically, unique VTT expression of the protease ADAMTS18 is necessary for VEGFA signaling sequestration through limiting fibronectin accumulation. Therefore, we propose a model in which LGR5⁺ ADAMTS18⁺ telocytes are necessary to maintain a “just-right” level and location of VEGFA signaling in intestinal villus blood vasculature to ensure on one hand the presence of sufficient endothelial fenestrae, while avoiding excessive leakiness of the vessels and destabilization of villus tip epithelial structures.

The molecular mechanisms ensuring the specialized structure of small intestinal villus tip blood vessels are incompletely understood. Here the authors show that ADAMTS18⁺ telocytes maintain a “just-right” level and location of VEGFA signaling on intestinal villus blood vessels, thereby ensuring the presence of endothelial fenestrae for nutrient absorption, while avoiding excessive leakiness and destabilization of villus tip epithelial structures.

Early invasion of the bladder wall by solitary bacteria protects UPEC from antibiotics and neutrophil swarms in an organoid model

Recurrence of uropathogenic Escherichia coli (UPEC) infections has been attributed to reactivation of quiescent intracellular reservoirs (QIRs) in deep layers of the bladder wall. QIRs are thought to arise late during infection following dispersal of bacteria from intracellular bacterial communities (IBCs) in superficial umbrella cells. Here, we track the formation of QIR-like bacteria in a bladder organoid model that recapitulates the stratified uroepithelium within a volume suitable for high-resolution live-cell imaging. Bacteria injected into the organoid lumen enter umbrella-like cells and proliferate to form IBC-like bodies. In parallel, single bacteria penetrate deeper layers of the organoid wall, where they localize within or between uroepithelial cells. These "solitary" bacteria evade killing by antibiotics and neutrophils and are morphologically distinct from bacteria in IBCs. We conclude that bacteria with QIR-like properties may arise at early stages of infection, independent of IBC formation and rupture.

Dynamic persistence of UPEC intracellular bacterial communities in a human bladder-chip model of urinary tract infection

Uropathogenic Escherichia coli (UPEC) proliferate within superficial bladder umbrella cells to form intracellular bacterial communities (IBCs) during early stages of urinary tract infections. However, the dynamic responses of IBCs to host stresses and antibiotic therapy are difficult to assess in situ. We develop a human bladder-chip model wherein umbrella cells and bladder microvascular endothelial cells are co-cultured under flow in urine and nutritive media respectively, and bladder filling and voiding mimicked mechanically by application and release of linear strain. Using time-lapse microscopy, we show that rapid recruitment of neutrophils from the vascular channel to sites of infection leads to swarm and neutrophil extracellular trap formation but does not prevent IBC formation. Subsequently, we tracked bacterial growth dynamics in individual IBCs through two cycles of antibiotic administration interspersed with recovery periods which revealed that the elimination of bacteria within IBCs by the antibiotic was delayed, and in some instances, did not occur at all. During the recovery period, rapid proliferation in a significant fraction of IBCs reseeded new foci of infection through bacterial shedding and host cell exfoliation. These insights reinforce a dynamic role for IBCs as harbors of bacterial persistence, with significant consequences for non-compliance with antibiotic regimens.

Urinary tract infections are one of the most common reasons people need antibiotics. These bacterial infections are typically caused by uropathogenic Escherichia coli (also known as UPEC), which either float freely in the urine and wash away when the bladder empties, or form communities inside cells that the bladder struggles to clear. It is possible that the bacteria living within cells are also more protected from the immune system and antibiotics. But this is hard to study in animal models.

To overcome this, Sharma et al. built a ‘bladder-chip’ which mimics the interface between the blood vessels and the tissue layers of the human bladder. Similar chip devices have also been made for other organs. However, until now, no such model had been developed for the bladder.

On the chip created by Sharma et al. is a layer of bladder cells which sit at the bottom of a channel filled with diluted human urine. These cells were infected with UPEC, and then imaged over time to see how the bacteria moved, interacted with the bladder cells, and aggregated together. Immune cells from human blood were then added to a vascular channel underneath the bladder tissue, which is coated with endothelial cells that normally line blood vessels. The immune cells rapidly crossed the endothelial barrier and entered the bladder tissue, and swarmed around sites of infection. In some instances, they released the contents of their cells to form net-like traps to catch the bacteria. But these traps failed to remove the bacteria living inside bladder cells.

Antibiotics were then added to the urine flowing over the bladder cells as well as the vascular channel, similar to how drugs would be delivered in live human tissue. Sharma et al. discovered that the antibiotics killed bacteria residing in bladder cells slower than bacteria floating freely in the urine. Furthermore, they found that bacteria living in tightly packed communities within bladder cells were more likely to survive treatment and go on to re-infect other parts of the tissue.

Antibiotic resistance is a pressing global challenge, and recurrent urinary tract infections are a significant contributor. The bladder-chip presented here could further our understanding of how these bacterial infections develop in vivo and how good antibiotics are at removing them. This could help researchers identify the best dosing and treatment strategies, as well as provide a platform for rapidly testing new antibiotic drugs and other therapies.

Ultrastructural comparison of dendritic spine morphology preserved with cryo and chemical fixation

Previously, we showed that cryo fixation of adult mouse brain tissue gave a truer representation of brain ultrastructure in comparison with a standard chemical fixation method (Korogod et al., 2015). Extracellular space matched physiological measurements, there were larger numbers of docked vesicles and less glial coverage of synapses and blood capillaries. Here, using the same preservation approaches, we compared the morphology of dendritic spines. We show that the length of the spine and the volume of its head is unchanged; however, the spine neck width is thinner by more than 30% after cryo fixation. In addition, the weak correlation between spine neck width and head volume seen after chemical fixation was not present in cryo-fixed spines. Our data suggest that spine neck geometry is independent of the spine head volume, with cryo fixation showing enhanced spine head compartmentalization and a higher predicted electrical resistance between spine head and parent dendrite.

The process of Lewy body formation, rather than simply α-synuclein fibrillization, is one of the major drivers of neurodegeneration

Parkinson's disease (PD) is characterized by the accumulation of misfolded and aggregated α-synuclein (α-syn) into intraneuronal inclusions named Lewy bodies (LBs). Although it is widely believed that α-syn plays a central role in the pathogenesis of PD, the processes that govern α-syn fibrillization and LB formation remain poorly understood. In this work, we sought to dissect the spatiotemporal events involved in the biogenesis of the LBs at the genetic, molecular, biochemical, structural, and cellular levels. Toward this goal, we further developed a seeding-based model of α-syn fibrillization to generate a neuronal model that reproduces the key events leading to LB formation, including seeding, fibrillization, and the formation of inclusions that recapitulate many of the biochemical, structural, and organizational features of bona fide LBs. Using an integrative omics, biochemical and imaging approach, we dissected the molecular events associated with the different stages of LB formation and their contribution to neuronal dysfunction and degeneration. In addition, we demonstrate that LB formation involves a complex interplay between α-syn fibrillization, posttranslational modifications, and interactions between α-syn aggregates and membranous organelles, including mitochondria, the autophagosome, and endolysosome. Finally, we show that the process of LB formation, rather than simply fibril formation, is one of the major drivers of neurodegeneration through disruption of cellular functions and inducing mitochondria damage and deficits, and synaptic dysfunctions. We believe that this model represents a powerful platform to further investigate the mechanisms of LB formation and clearance and to screen and evaluate therapeutics targeting α-syn aggregation and LB formation.

Publisher Correction: Gas cluster ion beam SEM for imaging of large tissue samples with 10 nm isotropic resolution

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Gas cluster ion beam SEM for imaging of large tissue samples with 10 nm isotropic resolution

We demonstrate gas cluster ion beam scanning electron microscopy (SEM), in which wide-area ion milling is performed on a series of thick tissue sections. This three-dimensional electron microscopy technique acquires datasets with <10 nm isotropic resolution of each section, and these can then be stitched together to span the sectioned volume. Incorporating gas cluster ion beam SEM into existing single-beam and multibeam SEM workflows should be straightforward, increasing reliability while improving z resolution by a factor of three or more.

Cellular Uptake and Intracellular Trafficking of Poly( N-(2-Hydroxypropyl) Methacrylamide)

Cellular uptake and intracellular trafficking of polymer conjugates or polymer nanoparticles is typically monitored using fluorescence-based techniques such as confocal microscopy. While these methods have provided a wealth of insight into the internalization and trafficking of polymers and polymer nanoparticles, they require fluorescent labeling of the polymer or polymer nanoparticle. Because in biological media fluorescent dyes may degrade, be cleaved from the polymer or particle, or even change uptake and trafficking pathways, there is an interest in fluorescent label-free methods to study the interactions between cells and polymer nanomedicines. This article presents a first proof-of-concept that demonstrates the feasibility of NanoSIMS to monitor the intracellular localization of polymer conjugates. For the experiments reported here, poly( N-(2-hydroxypropyl) methacrylamide)) (PHPMA) was selected as a prototypical polymer-drug conjugate. This PHPMA polymer contained a ¹⁹F-label at the α-terminus, which was introduced in order to allow NanoSIMS analysis. Prior to the NanoSIMS experiments, the uptake and intracellular trafficking of the polymer was established using confocal microscopy and flow cytometry. These experiments not only provided detailed insight into the kinetics of these processes but were also important to select time points for the NanoSIMS analysis. For the NanoSIMS experiments, HeLa cells were investigated that had been exposed to the PHPMA polymer for a period of 4 or 15 h, which was known to lead to predominant lysosomal accumulation of the polymer. NanoSIMS analysis of resin-embedded and microtomed samples of the cells revealed a punctuated fluorine signal, which was found to colocalize with the sulfur signal that was attributed to the lysosomal compartments. The localization of the polymer in the endolysosomal compartments was confirmed by TEM analysis on the same cell samples. The results of this study illustrate the potential of NanoSIMS to study the uptake and intracellular trafficking of polymer nanomedicines.

Locally coordinated synaptic plasticity of visual cortex neurons in vivo

Plasticity of cortical responses in vivo involves activity-dependent changes at synapses, but the manner in which different forms of synaptic plasticity act together to create functional changes in neurons remains unknown. We found that spike timing-induced receptive field plasticity of visual cortex neurons in mice is anchored by increases in the synaptic strength of identified spines. This is accompanied by a decrease in the strength of adjacent spines on a slower time scale. The locally coordinated potentiation and depression of spines involves prominent AMPA receptor redistribution via targeted expression of the immediate early gene product Arc. Hebbian strengthening of activated synapses and heterosynaptic weakening of adjacent synapses thus cooperatively orchestrate cell-wide plasticity of functional neuronal responses.

Neuron Segmentation With High-Level Biological Priors

We present a novel approach to the problem of neuron segmentation in image volumes acquired by an electron microscopy. Existing methods, such as agglomerative or correlation clustering, rely solely on boundary evidence and have problems where such an evidence is lacking (e.g., incomplete staining) or ambiguous (e.g., co-located cell and mitochondria membranes). We investigate if these difficulties can be overcome by means of sparse region appearance cues that differentiate between pre- and postsynaptic neuron segments in mammalian neural tissue. We combine these cues with the traditional boundary evidence in the asymmetric multiway cut (AMWC) model, which simultaneously solves the partitioning and the semantic region labeling problems. We show that AMWC problems over superpixel graphs can be solved to global optimality with a cutting plane approach, and that the introduction of semantic class priors leads to significantly better segmentations.

Differences in cisplatin distribution in sensitive and resistant ovarian cancer cells: a TEM/NanoSIMS study

Cisplatin is a widely used anti-cancer drug, but its effect is often limited by acquired resistance to the compound during treatment. Here, we use a combination of transmission electron microscopy (TEM) and nanoscale-secondary ion mass spectrometry (NanoSIMS) to reveal differences between cisplatin uptake in human ovarian cancers cells, which are known to be susceptible to acquired resistance to cisplatin. Both cisplatin sensitive and resistant cell lines were studied, revealing markedly less cisplatin in the resistant cell line. In cisplatin sensitive cells, Pt was seen to distribute diffusely in the cells with hotspots in the nucleolus, mitochondria, and autophagosomes. Inductively coupled plasma mass spectrometry (ICP-MS) was used to validate the NanoSIMS results.

Motifs in the tau protein that control binding to microtubules and aggregation determine pathological effects

Tau pathology is associated with cognitive decline in Alzheimer’s disease, and missense tau mutations cause frontotemporal dementia. Hyperphosphorylation and misfolding of tau are considered critical steps leading to tauopathies. Here, we determine how motifs controlling conformational changes in the microtubule-binding domain determine tau pathology in vivo. Human tau was overexpressed in the adult mouse forebrain to compare variants carrying residues that modulate tau propensity to acquire a β-sheet conformation. The P301S mutation linked to frontotemporal dementia causes tau aggregation and rapidly progressing motor deficits. By comparison, wild-type tau becomes heavily hyperphosphorylated, and induces behavioral impairments that do not progress over time. However, the behavioral defects caused by wild-type tau can be suppressed when β-sheet breaking proline residues are introduced in the microtubule-binding domain of tau. This modification facilitates tau interaction with microtubules, as shown by lower levels of phosphorylation, and by the enhanced protective effects of mutated tau against the severing of the cytoskeleton in neurons exposed to vinblastine. Altogether, motifs that are critical for tau conformation determine interaction with microtubules and subsequent pathological modifications, including phosphorylation and aggregation.

The Differential Distribution of RAPTA-T in Non-Invasive and Invasive Breast Cancer Cells Correlates with Its Anti-Invasive and Anti-Metastatic Effects

Nanoscale secondary ion mass spectrometry (NanoSIMS) combined with transmission electron microscopy (TEM) can be a powerful approach to visualize the exact distribution of drugs at the sub-cellular level. In this work, we exploit this approach to identify the distribution and localisation of the organometallic ruthenium(II)-arene drug Ru(η⁶-C₆H₅Me)(pta)Cl₂, termed RAPTA-T, in MDA-MB-231 and MCF-7 human breast cancer cells. These cell lines have been chosen because the former cell lines are highly invasive and resistant to most chemotherapeutic agents and the latter ones are very sensitive to hormonal-based therapies. In the MDA-MB-231 cells, RAPTA-T was found to predominantly localise on the cell membrane and to a lesser extent in the nucleolus. These findings are consistent with the previously reported anti-metastatic properties of RAPTA-T and the observation that once internalized RAPTA-T is associated with chromatin. RAPTA-T shows a lack of membrane accumulation on the non-invasive MCF-7 cells, which correlates well with its selective anti-metastatic properties on invasive cell lines.

Identification of aminopyrimidine-sulfonamides as potent modulators of Wag31-mediated cell elongation in mycobacteria

There is an urgent need to discover new anti-tubercular agents with novel mechanisms of action in order to tackle the scourge of drug-resistant tuberculosis. Here, we report the identification of such a molecule - an AminoPYrimidine-Sulfonamide (APYS1) that has potent, bactericidal activity against M. tuberculosis. Mutations in APYS1-resistant M. tuberculosis mapped exclusively to wag31, a gene that encodes a scaffolding protein thought to orchestrate cell elongation. Recombineering confirmed that a Gln201Arg mutation in Wag31 was sufficient to cause resistance to APYS1, however, neither overexpression nor conditional depletion of wag31 impacted M. tuberculosis susceptibility to this compound. In contrast, expression of the wildtype allele of wag31 in APYS1-resistant M. tuberculosis was dominant and restored susceptibility to APYS1 to wildtype levels. Time-lapse imaging and scanning electron microscopy revealed that APYS1 caused gross malformation of the old pole of M. tuberculosis, with eventual lysis. These effects resembled the morphological changes observed following transcriptional silencing of wag31 in M. tuberculosis. These data show that Wag31 is likely not the direct target of APYS1, but the striking phenotypic similarity between APYS1 exposure and genetic depletion of Wag31 in M. tuberculosis suggests that APYS1 might indirectly affect Wag31 through an as yet unknown mechanism.

NanoSIMS analysis of an isotopically labelled organometallic ruthenium(II) drug to probe its distribution and state in vitro

The in vitro inter- and intra-cellular distribution of an isotopically labelled ruthenium(II)-arene (RAPTA) anti-metastatic compound in human ovarian cancer cells was imaged using nano-scale secondary ion mass spectrometry (NanoSIMS). Ultra-high resolution isotopic images of (13)C, (15)N, and Ru indicate that the phosphine ligand remains coordinated to the ruthenium(II) ion whereas the arene detaches. The complex localizes mainly on the membrane or at the interface between cells which correlates with its anti-metastatic effects.

Ultrastructural analysis of adult mouse neocortex comparing aldehyde perfusion with cryo fixation

Analysis of brain ultrastructure using electron microscopy typically relies on chemical fixation. However, this is known to cause significant tissue distortion including a reduction in the extracellular space. Cryo fixation is thought to give a truer representation of biological structures, and here we use rapid, high-pressure freezing on adult mouse neocortex to quantify the extent to which these two fixation methods differ in terms of their preservation of the different cellular compartments, and the arrangement of membranes at the synapse and around blood vessels. As well as preserving a physiological extracellular space, cryo fixation reveals larger numbers of docked synaptic vesicles, a smaller glial volume, and a less intimate glial coverage of synapses and blood vessels compared to chemical fixation. The ultrastructure of mouse neocortex therefore differs significantly comparing cryo and chemical fixation conditions.

Modeling brain circuitry over a wide range of scales

If we are ever to unravel the mysteries of brain function at its most fundamental level, we will need a precise understanding of how its component neurons connect to each other. Electron Microscopes (EM) can now provide the nanometer resolution that is needed to image synapses, and therefore connections, while Light Microscopes (LM) see at the micrometer resolution required to model the 3D structure of the dendritic network. Since both the topology and the connection strength are integral parts of the brain's wiring diagram, being able to combine these two modalities is critically important. In fact, these microscopes now routinely produce high-resolution imagery in such large quantities that the bottleneck becomes automated processing and interpretation, which is needed for such data to be exploited to its full potential. In this paper, we briefly review the Computer Vision techniques we have developed at EPFL to address this need. They include delineating dendritic arbors from LM imagery, segmenting organelles from EM, and combining the two into a consistent representation.

Ultrastructurally smooth thick partitioning and volume stitching for large-scale connectomics

Focused-ion-beam scanning electron microscopy (FIB-SEM) has become an essential tool for studying neural tissue at resolutions below 10 nm × 10 nm × 10 nm, producing data sets optimized for automatic connectome tracing. We present a technical advance, ultrathick sectioning, which reliably subdivides embedded tissue samples into chunks (20 μm thick) optimally sized and mounted for efficient, parallel FIB-SEM imaging. These chunks are imaged separately and then 'volume stitched' back together, producing a final three-dimensional data set suitable for connectome tracing.

PGC-1α activity in nigral dopamine neurons determines vulnerability to α-synuclein

Introduction

Mitochondrial dysfunction and oxidative stress are critical factors in the pathogenesis of age-dependent neurodegenerative diseases. PGC-1α, a master regulator of mitochondrial biogenesis and cellular antioxidant defense, has emerged as a possible therapeutic target for Parkinson’s disease, with important roles in the function and survival of dopaminergic neurons in the substantia nigra. The objective of this study is to determine if the loss of PGC-1α activity contributes to α-synuclein-induced degeneration.

Results

We explore the vulnerability of PGC-1α null mice to the accumulation of human α-synuclein in nigral neurons, and assess the neuroprotective effect of AAV-mediated PGC-1α expression in this experimental model. Using neuronal cultures derived from these mice, mitochondrial respiration and production of reactive oxygen species are assessed in conditions of human α-synuclein overexpression. We find ultrastructural evidence for abnormal mitochondria and fragmented endoplasmic reticulum in the nigral dopaminergic neurons of PGC-1α null mice. Furthermore, PGC-1α null nigral neurons are more prone to degenerate following overexpression of human α-synuclein, an effect more apparent in male mice. PGC-1α overexpression restores mitochondrial morphology, oxidative stress detoxification and basal respiration, which is consistent with the observed neuroprotection against α-synuclein toxicity in male PGC-1α null mice.

Conclusions

Altogether, our results highlight an important role for PGC-1α in controlling the mitochondrial function of nigral neurons accumulating α-synuclein, which may be critical for gender-dependent vulnerability to Parkinson’s disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0200-8) contains supplementary material, which is available to authorized users.

Correction: NanoSIMS analysis of an isotopically labelled organometallic ruthenium(ii) drug to probe its distribution and state in vitro

Correction for ‘NanoSIMS analysis of an isotopically labelled organometallic ruthenium(ii) drug to probe its distribution and state in vitro’ by Ronald F. S. Lee et al., Chem. Commun., 2015, DOI: 10.1039/c5cc06983a.

Conditional expression of Parkinson's disease-related R1441C LRRK2 in midbrain dopaminergic neurons of mice causes nuclear abnormalities without neurodegeneration

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause late-onset, autosomal dominant Parkinson's disease (PD). The clinical and neurochemical features of LRRK2-linked PD are similar to idiopathic disease although neuropathology is somewhat heterogeneous. Dominant mutations in LRRK2 precipitate neurodegeneration through a toxic gain-of-function mechanism which can be modeled in transgenic mice overexpressing human LRRK2 variants. A number of LRRK2 transgenic mouse models have been developed that display abnormalities in dopaminergic neurotransmission and alterations in tau metabolism yet without consistently inducing dopaminergic neurodegeneration. To directly explore the impact of mutant LRRK2 on the nigrostriatal dopaminergic pathway, we developed conditional transgenic mice that selectively express human R1441C LRRK2 in dopaminergic neurons from the endogenous murine ROSA26 promoter. The expression of R1441C LRRK2 does not induce the degeneration of substantia nigra dopaminergic neurons or striatal dopamine deficits in mice up to 2years of age, and fails to precipitate abnormal protein inclusions containing alpha-synuclein, tau, ubiquitin or autophagy markers (LC3 and p62). Furthermore, mice expressing R1441C LRRK2 exhibit normal motor activity and olfactory function with increasing age. Intriguingly, the expression of R1441C LRRK2 induces age-dependent abnormalities of the nuclear envelope in nigral dopaminergic neurons including reduced nuclear circularity and increased invaginations of the nuclear envelope. In addition, R1441C LRRK2 mice display increased neurite complexity of cultured midbrain dopaminergic neurons. Collectively, these novel R1441C LRRK2 conditional transgenic mice reveal altered dopaminergic neuronal morphology with advancing age, and provide a useful tool for exploring the pathogenic mechanisms underlying the R1441C LRRK2 mutation in PD.

Semiautomated correlative 3D electron microscopy of in vivo-imaged axons and dendrites

This protocol describes how in vivo-imaged dendrites and axons in adult mouse brains can subsequently be prepared and imaged with focused ion beam scanning electron microscopy (FIBSEM). The procedure starts after in vivo imaging with chemical fixation, followed by the identification of the fluorescent structures of interest. Their position is then highlighted in the fixed tissue by burning fiducial marks with the two-photon laser. Once the section has been stained and resin-embedded, a small block is trimmed close to these marks. Serially aligned EM images are acquired through this region, using FIBSEM, and the neurites of interest are then reconstructed semiautomatically by using the ilastik software (http://ilastik.org/). This reliable imaging and reconstruction technique avoids the use of specific labels to identify the structures of interest in the electron microscope, enabling optimal chemical fixation techniques to be applied and providing the best possible structural preservation for 3D analysis. The entire protocol takes ∼4 d.

Correlative in vivo 2-photon imaging and focused ion beam scanning electron microscopy: 3D analysis of neuronal ultrastructure

This protocol describes how dendrites and axons, imaged in vivo, can subsequently be analyzed in 3D using focused ion beam scanning electron microscopy (FIBSEM). The fluorescent structures are identified after chemical fixation and their position highlighted using the 2-photon laser to burn fiducial marks around the region. Once the section has been stained and resin embedded, a small block is trimmed close to these marks. Serially aligned EM images are acquired through this region, using FIBSEM, and the neurites of interest then reconstructed semi-automatically using the Ilastik software (ilastik.org). This fast and reliable imaging and reconstruction technique avoids the use of specific labels to identify the features of interest in the electron microscope and optimizes their preservation for high-quality imaging and 3D analysis.

FOXO3 determines the accumulation of α-synuclein and controls the fate of dopaminergic neurons in the substantia nigra

Parkinson's disease (PD) is characterized by the selective degeneration of neuronal populations presumably due to pathogenic interactions between aging and predisposing factors such as increased levels of α-synuclein. Here, we genetically modulate the activity of the transcription factor Forkhead box protein O3 (FOXO3) in adult nigral dopaminergic neurons using viral vectors and explore how this determinant of longevity impacts on neuronal fate in normal and diseased conditions. We find that dopaminergic neurons are particularly vulnerable to changes in FOXO3 activity in the substantia nigra. While constitutive activation has proapoptotic effects leading to neuronal loss, inhibition of FOXO-mediated transcription by a dominant-negative competitor causes oxidative damage and is detrimental at high vector dose. To address the role of FOXO3 in PD, we modulate its activity in dopaminergic neurons overexpressing human α-synuclein. In this pathogenic condition, we find that FOXO inhibition has protective effects, suggesting that this transcription factor ultimately contributes to neuronal cell death. Nevertheless, mild FOXO3 activity also protects nigral neurons against the accumulation of human α-synuclein, albeit to a lesser extent. FOXO3 reduces the amount of α-synuclein present in the soluble protein fraction and promotes the coalescence of dense proteinase K-resistant aggregates, with an accumulation of autophagic vacuoles containing lipofuscin. Consistent with these in vivo observations, we find that FOXO3 controls autophagic flux in neuronal cells. Altogether, these results point to FOXO3 as an important determinant of neuronal survival in the substantia nigra, which may oppose α-synuclein accumulation and proteotoxicity.

Imaging green fluorescent protein-labeled neurons using light and electron microscopy

The ability to observe axons and dendrites with transmission electron microscopy (EM) after they have been previously imaged live with laser-scanning microscopy is a useful technique to study their synaptic connectivity. This protocol provides a detailed method by which neurons that were imaged in a live brain or slice culture can be reimaged using EM. First, brain tissue expressing green fluorescent protein (GFP) is chemically fixed. Then, an immunocytochemistry process is used to render the fluorescent protein electron dense so that it can first be located using light microscopy and then serial thin-sectioned for EM so that the ultrastructure of specific parts of neurites can be analyzed in three dimensions. Patterns of blood vessels observed in the live brain are used to locate the previously imaged neurons. The method described here allows for a complete three-dimensional (3D) reconstruction to be made of the imaged structures from serial electron micrographs.

Correlative in vivo 2 photon and focused ion beam scanning electron microscopy of cortical neurons

Correlating in vivo imaging of neurons and their synaptic connections with electron microscopy combines dynamic and ultrastructural information. Here we describe a semi-automated technique whereby volumes of brain tissue containing axons and dendrites, previously studied in vivo, are subsequently imaged in three dimensions with focused ion beam scanning electron microcopy. These neurites are then identified and reconstructed automatically from the image series using the latest segmentation algorithms. The fast and reliable imaging and reconstruction technique avoids any specific labeling to identify the features of interest in the electron microscope, and optimises their preservation and staining for 3D analysis.

Pansynaptic enlargement at adult cortical connections strengthened by experience

Behavioral experience alters the strength of neuronal connections in adult neocortex. These changes in synaptic strength are thought to be central to experience-dependent plasticity, learning, and memory. However, it is not known how changes in synaptic transmission between neurons become persistent, thereby enabling the storage of previous experience. A long-standing hypothesis is that altered synaptic strength is maintained by structural modifications to synapses. However, the extent of synaptic modifications and the changes in neurotransmission that the modifications support remain unclear. To address these questions, we recorded from pairs of synaptically connected layer 2/3 pyramidal neurons in the barrel cortex and imaged their contacts with high-resolution confocal microscopy after altering sensory experience by whisker trimming. Excitatory connections strengthened by experience exhibited larger axonal varicosities, dendritic spines, and interposed contact zones. Electron microscopy showed that contact zone size was strongly correlated with postsynaptic density area. Therefore, our findings indicate that whole synapses are larger at strengthened connections. Synaptic transmission was both stronger and more reliable following experience-dependent synapse enlargement. Hence, sensory experience modified both presynaptic and postsynaptic function. Our findings suggest that the enlargement of synaptic contacts is an integral part of long-lasting strengthening of cortical connections and, hence, of information storage in the neocortex.

Plasticity of astrocytic coverage and glutamate transporter expression in adult mouse cortex

Astrocytes play a major role in the removal of glutamate from the extracellular compartment. This clearance limits the glutamate receptor activation and affects the synaptic response. This function of the astrocyte is dependent on its positioning around the synapse, as well as on the level of expression of its high-affinity glutamate transporters, GLT1 and GLAST. Using Western blot analysis and serial section electron microscopy, we studied how a change in sensory activity affected these parameters in the adult cortex. Using mice, we found that 24 h of whisker stimulation elicited a 2-fold increase in the expression of GLT1 and GLAST in the corresponding cortical column of the barrel cortex. This returns to basal levels 4 d after the stimulation was stopped, whereas the expression of the neuronal glutamate transporter EAAC1 remained unaltered throughout. Ultrastructural analysis from the same region showed that sensory stimulation also causes a significant increase in the astrocytic envelopment of excitatory synapses on dendritic spines. We conclude that a period of modified neuronal activity and synaptic release of glutamate leads to an increased astrocytic coverage of the bouton-spine interface and an increase in glutamate transporter expression in astrocytic processes.

Spine growth precedes synapse formation in the adult neocortex in vivo

Dendritic spines appear and disappear in an experience-dependent manner. Although some new spines have been shown to contain synapses, little is known about the relationship between spine addition and synapse formation, the relative time course of these events, or whether they are coupled to de novo growth of axonal boutons. We imaged dendrites in barrel cortex of adult mice over 1 month, tracking gains and losses of spines. Using serial section electron microscopy, we analyzed the ultrastructure of spines and associated boutons. Spines reconstructed shortly after they appeared often lacked synapses, whereas spines that persisted for 4 d or more always had synapses. New spines had a large surface-to-volume ratio and preferentially contacted boutons with other synapses. In some instances, two new spines contacted the same axon. Our data show that spine growth precedes synapse formation and that new synapses form preferentially onto existing boutons.

Ciliary neurotrophic factor activates astrocytes, redistributes their glutamate transporters GLAST and GLT-1 to raft microdomains, and improves glutamate handling in vivo

To study the functional role of activated astrocytes in glutamate homeostasis in vivo, we used a model of sustained astrocytic activation in the rat striatum through lentiviral-mediated gene delivery of ciliary neurotrophic factor (CNTF). CNTF-activated astrocytes were hypertrophic, expressed immature intermediate filament proteins and highly glycosylated forms of their glutamate transporters GLAST and GLT-1. CNTF overexpression produced a redistribution of GLAST and GLT-1 into raft functional membrane microdomains, which are important for glutamate uptake. In contrast, CNTF had no detectable effect on the expression of a number of neuronal proteins and on the spontaneous glutamatergic transmission recorded from striatal medium spiny neurons. These results were replicated in vitro by application of recombinant CNTF on a mixed neuron/astrocyte striatal culture. Using microdialysis in the rat striatum, we found that the accumulation of extracellular glutamate induced by quinolinate (QA) was reduced threefold with CNTF. In line with this result, CNTF significantly increased QA-induced [(18)F]-fluoro-2-deoxyglucose uptake, an indirect index of glutamate uptake by astrocytes. Together, these data demonstrate that CNTF activation of astrocytes in vivo is associated with marked phenotypic and molecular changes leading to a better handling of increased levels of extracellular glutamate. Activated astrocytes may therefore be important prosurvival agents in pathological conditions involving defects in glutamate homeostasis.

Experience-dependent and cell-type-specific spine growth in the neocortex

Functional circuits in the adult neocortex adjust to novel sensory experience, but the underlying synaptic mechanisms remain unknown. Growth and retraction of dendritic spines with synapse formation and elimination could change brain circuits. In the apical tufts of layer 5B (L5B) pyramidal neurons in the mouse barrel cortex, a subset of dendritic spines appear and disappear over days, whereas most spines are persistent for months. Under baseline conditions, new spines are mostly transient and rarely survive for more than a week. Transient spines tend to be small, whereas persistent spines are usually large. Because most excitatory synapses in the cortex occur on spines, and because synapse size and the number of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are proportional to spine volume, the excitation of pyramidal neurons is probably driven through synapses on persistent spines. Here we test whether the generation and loss of persistent spines are enhanced by novel sensory experience. We repeatedly imaged dendritic spines for one month after trimming alternate whiskers, a paradigm that induces adaptive functional changes in neocortical circuits. Whisker trimming stabilized new spines and destabilized previously persistent spines. New-persistent spines always formed synapses. They were preferentially added on L5B neurons with complex apical tufts rather than simple tufts. Our data indicate that novel sensory experience drives the stabilization of new spines on subclasses of cortical neurons. These synaptic changes probably underlie experience-dependent remodelling of specific neocortical circuits.

Primary sensory afferent innervation of the developing superficial dorsal horn in the South American opossum Monodelphis domestica

The development of the primary sensory innervation of the superficial dorsal horn (SDH) was studied in postnatal opossums Monodelphis domestica by using DiI labelling of primary afferents and with GSA-IB(4) lectin binding and calcitonin gene-related peptide (CGRP) immunoreactivity to label primary afferent subpopulations. We also compared the timing of SDH innervation in the cervical and lumbar regions of the spinal cord. The first primary afferent projections to SDH emerge from the most lateral part of the dorsal root entry zone at postnatal day 5 and project around the lateral edge of the SDH toward lamina V. Innervation of the SDH occurs slowly over the second and third postnatal weeks, with the most dorsal aspect becoming populated by mediolaterally oriented varicose fibers before the rest of the dorsoventral thickness of the SDH becomes innervated by fine branching varicose fibers. Labelling with GSA-IB(4) lectin also labelled fibers at the lateral edge of the dorsal horn and SDH at P5, indicating that the GSA-IB(4) is expressed on SDH/lamina V primary afferents at the time when they are making their projections into the spinal cord. In contrast, CGRP-immunoreactive afferents were not evident until postnatal day 7, when a few short projections into the lateral dorsal horn were observed. These afferents then followed a pattern similar to the development of GSA-IB(4) projects but with a latency of several days. The adult pattern of labelling by GSA-IB(4) is achieved by about postnatal day 20, whereas the adult pattern of CGRP labelling was not seen until postnatal day 30. Electron microscopy revealed a few immature synapses in the region of the developing SDH at postnatal day 10, and processes considered to be precursors of glomerular synapses (and thus of primary afferent origin) were first seen at postnatal day 16 and adopted their definitive appearance between postnatal days 28 and 55. Although structural and functional development of forelimbs of neonatal Monodelphis is more advanced than the hindlimbs, we found little evidence of a significant delay in the invasion of the spinal cord by primary afferents in cervical and lumbar regions. These observations, together with the broadly similar maturational appearance of histological sections of rostral and caudal spinal cord, suggest that, unlike the limbs they innervate, the spinal regions do not exhibit a large rostrocaudal gradient in their maturation.

Experience and activity-dependent maturation of perisomatic GABAergic innervation in primary visual cortex during a postnatal critical period

The neocortical GABAergic network consists of diverse interneuron cell types that display distinct physiological properties and target their innervations to subcellular compartments of principal neurons. Inhibition directed toward the soma and proximal dendrites is crucial in regulating the output of pyramidal neurons, but the development of perisomatic innervation is poorly understood because of the lack of specific synaptic markers. In the primary visual cortex, for example, it is unknown whether, and to what extent, the formation and maturation of perisomatic synapses are intrinsic to cortical circuits or are regulated by sensory experience. Using bacterial artificial chromosome transgenic mice that label a defined class of perisomatic synapses with green fluorescent protein, here we show that perisomatic innervation developed during a protracted postnatal period after eye opening. Maturation of perisomatic innervation was significantly retarded by visual deprivation during the third, but not the fifth, postnatal week, implicating an important role for sensory input. To examine the role of cortical intrinsic mechanisms, we developed a method to visualize perisomatic synapses from single basket interneurons in cortical organotypic cultures. Characteristic perisomatic synapses formed through a stereotyped process, involving the extension of distinct terminal branches and proliferation of perisomatic boutons. Neuronal spiking in organotypic cultures was necessary for the proliferation of boutons and the extension, but not the maintenance, of terminal branches. Together, our results suggest that although the formation of perisomatic synapses is intrinsic to the cortex, visual experience can influence the maturation and pattern of perisomatic innervation during a postnatal critical period by modulating the level of neural activity within cortical circuits.

Transient and persistent dendritic spines in the neocortex in vivo

Dendritic spines were imaged over days to months in the apical tufts of neocortical pyramidal neurons (layers 5 and 2/3) in vivo. A fraction of thin spines appeared and disappeared over a few days, while most thick spines persisted for months. In the somatosensory cortex, from postnatal day (PND) 16 to PND 25 spine retractions exceeded additions, resulting in a net loss of spines. The fraction of persistent spines (lifetime > or = 8 days) grew gradually during development and into adulthood (PND 16-25, 35%; PND 35-80, 54%; PND 80-120, 66%; PND 175-225, 73%), providing evidence that synaptic circuits continue to stabilize even in the adult brain, long after the closure of known critical periods. In 6-month-old mice, spines turn over more slowly in visual compared to somatosensory cortex, possibly reflecting differences in the capacity for experience-dependent plasticity in these brain regions.

Altered synapse formation in the adult somatosensory cortex of brain-derived neurotrophic factor heterozygote mice

Increased sensory stimulation in the adult whisker-to-barrel pathway induces the expression of BDNF as well as synapse formation in cortical layer IV. Here, we investigated whether BDNF plays a role in the alterations of connectivity between neurons by analyzing the ultrastructure of the BDNF heterozygote mouse, characterized by a reduced level of BDNF expression. Using serial section electron microscopy, we measured synapse density, spine morphology, and synaptic vesicle distribution to show that mice with a reduced level of BDNF have a barrel neuropil that is indistinguishable from wild-type controls. After 24 hr of whisker stimulation, however, there is no indication of synapse formation in the heterozygous mouse. Whereas the balance between excitatory and inhibitory synapses is modified in the controls, it remains constant in the heterozygotes. The distribution of synaptic vesicles in excitatory synapses is the same in heterozygous and wild-type mice and is not influenced by the stimulation paradigm. Spine volume, however, is unchanged by stimulation in the wild-type animals, but does increase significantly in the heterozygous animal. These results provide evidence that, in vivo, BDNF plays an important role in the structural rearrangement of adult cortical circuitry as a consequence of an increased sensory input.

Morphological and molecular heterogeneity in release sites of single neurons

We have previously shown that labelling intensities for synaptic proteins vary strongly among synaptic boutons. Here we addressed the questions as to whether there are heterogeneous levels of integral membrane synaptic vesicle proteins at distinct active release sites of single neurons and if these sites possess the ultrastructural features of synapses. By double-immunostaining with specific antibodies against synaptophysin, synaptotagmin I, VAMP1 and VAMP2, we identified different relative levels of these integral membrane proteins of synaptic vesicles in comparison to boutons of the same rat cortical neuron. This heterogeneity could also be observed between the two isoforms VAMP1 and VAMP2. By studying pairs of these proteins implicated in neurotransmitter release, including both VAMP isoforms, we also show that the sites that contained predominantly one protein were nevertheless functional, as they internalized and released FM1-43 upon potassium stimulation. Using electron microscopy, we show that these active sites could have either synaptic specializations, or the features of vesicle-containing varicosities without a postsynaptic target. Different varicosities of the same neuron showed different intensities for synaptic vesicle proteins; some varicosities were capable of internalizing and releasing FM1-43, while others were silent. These results show that integral membrane synaptic vesicle proteins are differentially distributed among functional release sites of the same neuron.

Long-term in vivo imaging of experience-dependent synaptic plasticity in adult cortex

Do new synapses form in the adult cortex to support experience-dependent plasticity? To address this question, we repeatedly imaged individual pyramidal neurons in the mouse barrel cortex over periods of weeks. We found that, although dendritic structure is stable, some spines appear and disappear. Spine lifetimes vary greatly: stable spines, about 50% of the population, persist for at least a month, whereas the remainder are present for a few days or less. Serial-section electron microscopy of imaged dendritic segments revealed retrospectively that spine sprouting and retraction are associated with synapse formation and elimination. Experience-dependent plasticity of cortical receptive fields was accompanied by increased synapse turnover. Our measurements suggest that sensory experience drives the formation and elimination of synapses and that these changes might underlie adaptive remodelling of neural circuits.

Formation of dendritic spines with GABAergic synapses induced by whisker stimulation in adult mice

During development, alterations in sensory experience modify the structure of cortical neurons, particularly at the level of the dendritic spine. Are similar adaptations involved in plasticity of the adult cortex? Here we show that a 24 hr period of single whisker stimulation in freely moving adult mice increases, by 36%, the total synaptic density in the corresponding cortical barrel. This is due to an increase in both excitatory and inhibitory synapses found on spines. Four days after stimulation, the inhibitory inputs to the spines remain despite total synaptic density returning to pre-stimulation levels. Functional analysis of layer IV cells demonstrated altered response properties, immediately after stimulation, as well as four days later. These results indicate activity-dependent alterations in synaptic circuitry in adulthood, modifying the flow of sensory information into the cerebral cortex.

The nature and composition of the internal environment of the developing brain

1. The fetal brain develops within its own environment, which is protected from free exchange of most molecules among its extracellular fluid, blood plasma, and cerebrospinal fluid (CSF) by a set of mechanisms described collectively as "brain barriers." 2. There are high concentrations of proteins in fetal CSF, which are due not to immaturity of the blood-CSF barrier (tight junctions between the epithelial cells of the choroid plexus), but to a specialized transcellular mechanism that specifically transfers some proteins across choroid plexus epithelial cells in the immature brain. 3. The proteins in CSF are excluded from the extracellular fluid of the immature brain by the presence of barriers at the CSF-brain interfaces on the inner and outer surfaces. These barriers are not present in the adult. 4. Some plasma proteins are present within the cells of the developing brain. Their presence may be explained by a combination of specific uptake from the CSF and synthesis in situ. 5. Information about the composition of the CSF (electrolytes as well as proteins) in the developing brain is of importance for the culture conditions used for experiments with fetal brain tissue in vitro, as neurons in the developing brain are exposed to relatively high concentrations of proteins only when they have cell surface membrane contact with CSF. 6. The developmental importance of high protein concentrations in CSF of the immature brain is not understood but may be involved in providing the physical force (colloid osmotic pressure) for expansion of the cerebral ventricles during brain development, as well as possibly having nutritive and specific cell development functions.

Barriers in the immature brain

1. The term "blood-brain barrier" describes a range of mechanisms that control the exchange of molecules between the internal environment of the brain and the rest of the body. 2. The underlying morphological feature of these barriers is the presence of tight junctions which are present between cerebral endothelial cells and between choroid plexus epithelial cells. These junctions are present in blood vessels in fetal brain and are effective in restricting entry of proteins from blood into brain and cerebrospinal fluid. However, some features of the junctions appear to mature during brain development. 3. Although proteins do not penetrate into the extracellular space of the immature brain, they do penetrate into cerebrospinal fluid by a mechanism that is considered in the accompanying review (Dziegielewska et al., 2000). 4. In the immature brain there are additional morphological barriers at the interface between cerebrospinal fluid and brain tissue: strap junctions at the inner neuroependymal surface and these and other intercellular membrane specializations at the outer (piaarachnoid) surface. These barriers disappear later in development and are absent in the adult. 5. There is a decline in permeability to low molecular weight lipid-insoluble compounds during brain development which appears to be due mainly to a decrease in the intrinsic permeability of the blood-brain and blood-cerebrospinal fluid interfaces.

Development of motoneurons and primary sensory afferents in the thoracic and lumbar spinal cord of the South American opossum Monodelphis domestica

The postnatal development of the primary sensory afferent projection to the thoracic (T4) and lumbar (L4) spinal cord of the marsupial species Monodelphis domestica was studied by using anterograde and retrograde neuronal tracers. Large numbers of primary afferents and motoneurons were labelled by application of the carbocyanine dye DiI into individual dorsal root ganglia (DRG) afferents in short-term organ cultures. Dorsal root axons had entered the cord at birth, but most primary afferent innervation of the grey matter and the establishment of cytoarchitectural lamination occurs postnatally. In addition to ipsilateral projections, some primary afferents that projected to the dorsal horn extended across the midline into the equivalent contralateral regions of the grey matter. Similarly, motoneuron dendrites occasionally extended across midline and into the contralateral grey matter. The first fibres innervating the spinal cord project to the ventral horn and formed increasingly complex terminal arbours in the motor columns between P1 and P7. After P5 many afferents were seen projecting to the dorsal horn, with the superficial dorsal horn being the last region of the spinal grey to be innervated. Histochemical labelling with the lectin Griffonia simplicifolia indicated that C fibre primary afferents had arborised in the superficial dorsal horn by P14. The sequence of primary afferent innervation is thus similar to that described in the rat, but this sequence occurs over a period of several weeks in Monodelphis, compared with several days in the rat.

Development of thalamocortical projections in the South American gray short-tailed opossum (Monodelphis domestica)

We determined the time-course and general pattern of thalamocortical development of Monodelphis domestica by tracing projections with carbocyanine dye in fixed postnatal brains between postnatal day 2 (P2) and P30. By P2, the first neurons have migrated to form the preplate of the lateral cortex and have sent out axons into the intermediate zone. By P3, fibers from the preplate of more dorsal cortex have entered the intermediate zone, and, by P5, they reach the primitive internal capsule. Crystal placements in the dorsal thalamus at P2-P3 reveal thalamic axons extending down through the diencephalon and growing out through the internal capsule among groups of back-labelled cells that already project into the thalamus. Thalamic axons arrive at the cortex after the arrival of cells of the true cortical plate has split the preplate into marginal zone and subplate. Axons from the ventral part of the dorsal thalamus reach the lateral cortex by P5: Dorsal thalamic fibers arrive at the extreme dorsal cortex by P9. The deeper layers of the cortex appear to mature relatively earlier in Monodelphis than in eutherian mammals, and the subplate becomes less distinct. Thalamic fibers and their side branches proceed into the cortex without an obvious period of waiting in the subplate, but they do not penetrate the dense cortical plate itself. Monodelphis could provide an excellent model species, because the development of its thalamocortical connections is entirely an extrauterine process: The period P0-P15 corresponds to that of E12-P0 in the rat.

Permeability of the developing and mature blood-brain barriers to theophylline in rats

1. In the present study, the uptake of theophylline and L-glucose into the adult and neonatal rat brain has been investigated. Steady state cerebrospinal fluid (CSF) and brain concentrations of theophylline were reached within 1 h following a single intraperitoneal (i.p.) injection, whereas steady state CSF and brain concentrations of L-glucose were not approached until after 5 h. 2. Steady state brain:plasma and CSF:plasma concentration ratios for theophylline and L-glucose in neonatal rats were significantly higher than ratios in adult rats. Erythrocyte:plasma ratios for theophylline in neonatal rats were also significantly higher than ratios in adult rats. Steady state ratios for theophylline were significantly higher than those for L-glucose in both neonatal and adult rats. 3. Respiratory acidosis (pH 6.9-7.0) did not affect steady state CSF:plasma or brain:plasma ratios for theophylline in neonatal or adult rats. In contrast, steady state CSF:plasma and brain:plasma ratios for L-glucose were increased by respiratory acidosis. 4. The lower steady state CSF:plasma, brain:plasma and erythrocyte:plasma ratios for theophylline in adult rats are likely to be due to a higher concentration of plasma proteins in adult blood compared with neonates, with a greater retention of protein-bound (non-exchangeable) theophylline in adult blood, and are unlikely to be due to p-glycoprotein-mediated efflux of theophylline at the adult blood-brain barrier.

Development of walking, swimming and neuronal connections after complete spinal cord transection in the neonatal opossum, Monodelphis domestica

Development of coordinated movements was quantitatively assessed in adult opossums (Monodelphis domestica) with thoracic spinal cords transected by (1) crushing 7-8 d after birth [postnatal days 7-8 (P7-P8)]; at 2-3 years of age, systematic behavioral tests (e.g., climbing, footprint analysis, and swimming) showed only minor differences between control (n = 5) and operated (n = 10) animals; and (2) cutting on P4-P6; at 1 month these opossums exhibited coordinated walking movements but were unable to right themselves from a supine position, unlike controls (n = 6). When tested at 2 or 6 months, they could right themselves and showed remarkable coordination, albeit with more differences from controls than after a crush. No animals with spinal cords that were crushed at P14-18 survived because of cannibalism by the mother. Morphological studies (n = 10) 3 months-3 years after crush at 1 week showed restoration of structural continuity and normal appearance at the lesion site. Animals with cut rather than crushed cords showed continuity but greater morphological deficits. That lesions were complete was demonstrated by examining morphology and nerve impulse conduction immediately after crushing or cutting the spinal cord in controls. After lumbar spinal cord injection of 10 kDa dextran amine, retrogradely labeled cells were found rostral to the lesion in hindbrain and midbrain nuclei. Conduction was restored across the site of the lesion. Thus complete spinal cord transection in neonatal Monodelphis was followed by development of coordinated movements and repair of the spinal cord, a process that included development of functional connections by axons that crossed the lesion.

TGF-beta receptor type II and fetuin in the developing sheep neocortex

Fetuin shows a characteristic pattern of distribution in the developing neocortex in many mammalian species. Its expression is confined to early-appearing cortical-plate and later subplate neurons. A short 19 amino-acid sequence of fetuin shows a degree of homology to an 18 amino-acid sequence of the TGF-beta type II receptor (TbetaR-II) and in vitro fetuin binds to members of the TGF-beta family of cytokines. It has been suggested that fetuin is the biologically significant antagonist of these cytokines. We have compared, using immunocytochemistry, the distribution pattern of TbetaR-II and fetuin in the developing neocortex of foetal sheep. TbetaR-II immunoreactivity first appears at around 40 days of gestation in the fetal sheep (E40, term in sheep is 150 days from conception), localised in two discreet bands: one just outside the cortical plate in the inner part of the marginal zone and one deep in the cortical plate in what becomes the transient subplate zone. By E70-E80, TbetaR-II is prominent in a population of subplate cells, whereas, by E120 only small patches of TbetaR-II-positive cells are visible, principally in pyramidal cells in layer VI. The developmental sequence of the staining pattern for TbetaR-II in the neocortex is complementary to that for fetuin, rather than overlapping with it. Double-labelling of fetuin and TbetaR-II shows some cellular co-localisation, especially at E60, but most fetuin-positive cells are not immunoreactive for TbetaR-II. Thus, fetuin's proposed role as an antagonist of TGF-beta cytokines and mimic of TbetaR-II is not consistent with the observed distribution of these two molecules in the developing neocortex of the foetal sheep.

Fetuin expression in the dorsal root ganglia and trigeminal ganglia of perinatal rats

Fetuin, a fetal plasma glycoprotein, has been shown previously to be present in sub-populations of neurons in the developing central and peripheral nervous system. To gain a more complete description of the time course of the appearance of fetuin during neurogenesis we have examined fetuin immunoreactivity, and the presence of fetuin mRNA, in the developing rat trigeminal and dorsal root ganglia. Fetuin immunoreactivity and its mRNA were first seen at embryonic day 15 in the trigeminal ganglia, and at embryonic day 16 in dorsal root ganglia. In both trigeminal and dorsal root ganglion, fetuin appeared to be present up until around the time of birth, and then again between postnatal days 3 and 16. The results suggest that fetuin first appears at around the time that ganglion cell axons reach their central targets, which is also approximately when the cell-death period begins. The proportion of ganglion neurons that were fetuin immunoreactive at different ages was inversely related to the amount of cell death that is known to occur in these populations, thus it seems that fetuin is more likely to be associated not with dying cells, but with those that survive the cell-death period.