Comparison of methods for the estimation of the thickness of ultrathin tissue sections

A schizophrenia risk factor induces marked anatomical deficits at GABAergic-dopaminergic synapses in the rat ventral tegmental area: Essential evidence for new targeted therapies

To develop new therapies for schizophrenia, evidence accumulated over decades highlights the essential need to investigate the GABAergic synapses that presynaptically influence midbrain dopaminergic neurons. Since current technology restricts these studies to animals, and evidence accumulated in recent decades indicates a developmental origin of schizophrenia, we investigated synaptic changes in male rat offspring exposed to maternal immune activation (MIA), a schizophrenia risk factor. Using a novel combination of lentiviruses, peroxidase-immunogold double labeling, three-dimensional serial section transmission electron microscopy and stereology, we observed clear anatomical alterations in synaptic inputs on dopaminergic neurons in the midbrain posterior ventral tegmental area (pVTA). These changes relate directly to a characteristic feature of schizophrenia: increased dopamine release. In 3-month-old and 14-month-old MIA rats, we found a marked decrease in the volume of presynaptic GABAergic terminals from the rostromedial tegmental nucleus (RMTg) and in the length of the synapses they made, when innervating pVTA dopaminergic neurons. In MIA rats in the long-term, we also discovered a decrease in the volume of the postsynaptic density (PSD) and in the maximum thickness of the PSD at the same synapses. These marked deficits were evident in conventional GABA-dopamine synapses and in synaptic triads that we discovered involving asymmetric synapses that innervated RMTg GABAergic presynaptic terminals, which in turn innervated pVTA dopaminergic neurons. In triads, the PSD thickness of asymmetric synapses was significantly decreased in MIA rats in the long-term cohort. The extensive anatomical deficits provide a potential basis for new therapies targeted at synaptic inputs on midbrain pVTA dopaminergic neurons, in contrast to current striatum-targeted antipsychotic drugs.

Quantification of cell-surface expressed antigenic sites with 5-nm gold markers: Getting close to biologically relevant data

The T-derived subset of human peripheral blood normal lymphocytes has been selected as a model system to study the usefulness of 5 nm gold markers for quantification of single epitopes expressed on cell surfaces. The chosen epitopes are parts of the CD3 and CD5 molecules and can be specifically identified by hybridoma produced monoclonal antibodies (MoAbs; LEU-4 and LEU-1; Becton-Dick- inson, Mountain view, CA) . An indirect immunolabeling procedure, with goat anti-murine IgG adsorbed on the surface of 5 nm colloidal gold particles (GAM-G5, Janssen Pharmaceutica, Beerse, Belgium) has been used. Backscattered Electron Imaging (BEI) in a field emission scanning electronmicroscope (SEM) and transmission electron microscopy of thin sections of lymphocytes labeled before plastic embedding, were both used to identify and quantitate gold labeled cell surface sites, Estimating that the thickness of “silver” sections is approximately 60 nm and counting the number of gold particles on the entire cell perimeter, we calculated that, for LEU-4, the number of markers per um2 of cell surface is in the 140-160 range (Fig.l). Cell contour length measurements indicated that the surface of one lymphocyte is approximately 130-160 um2 that of a smooth sphere of identical diameter, reflecting the role of microvilli in expanding the surface area. The total number of gold labeled sites on the surface of one lymphocyte averages, therefore between 20,000 and 24,000 per cell.

Practicable methods for histological section thickness measurement in quantitative stereological analyses

The accuracy of quantitative stereological analysis tools such as the (physical) disector method substantially depends on the precise determination of the thickness of the analyzed histological sections. One conventional method for measurement of histological section thickness is to re-embed the section of interest vertically to its original section plane. The section thickness is then measured in a subsequently prepared histological section of this orthogonally re-embedded sample. However, the orthogonal re-embedding (ORE) technique is quite work- and time-intensive and may produce inaccurate section thickness measurement values due to unintentional slightly oblique (non-orthogonal) positioning of the re-embedded sample-section. Here, an improved ORE method is presented, allowing for determination of the factual section plane angle of the re-embedded section, and correction of measured section thickness values for oblique (non-orthogonal) sectioning. For this, the analyzed section is mounted flat on a foil of known thickness (calibration foil) and both the section and the calibration foil are then vertically (re-)embedded. The section angle of the re-embedded section is then calculated from the deviation of the measured section thickness of the calibration foil and its factual thickness, using basic geometry. To find a practicable, fast, and accurate alternative to ORE, the suitability of spectral reflectance (SR) measurement for determination of plastic section thicknesses was evaluated. Using a commercially available optical reflectometer (F20, Filmetrics^®, USA), the thicknesses of 0.5 μm thick semi-thin Epon (glycid ether)-sections and of 1–3 μm thick plastic sections (glycolmethacrylate/ methylmethacrylate, GMA/MMA), as regularly used in physical disector analyses, could precisely be measured within few seconds. Compared to the measured section thicknesses determined by ORE, SR measures displayed less than 1% deviation. Our results prove the applicability of SR to efficiently provide accurate section thickness measurements as a prerequisite for reliable estimates of dependent quantitative stereological parameters.

Image-based correction of continuous and discontinuous non-planar axial distortion in serial section microscopy

Motivation

Serial section microscopy is an established method for detailed anatomy reconstruction of biological specimen. During the last decade, high resolution electron microscopy (EM) of serial sections has become the de-facto standard for reconstruction of neural connectivity at ever increasing scales (EM connectomics). In serial section microscopy, the axial dimension of the volume is sampled by physically removing thin sections from the embedded specimen and subsequently imaging either the block-face or the section series. This process has limited precision leading to inhomogeneous non-planar sampling of the axial dimension of the volume which, in turn, results in distorted image volumes. This includes that section series may be collected and imaged in unknown order.

Results

We developed methods to identify and correct these distortions through image-based signal analysis without any additional physical apparatus or measurements. We demonstrate the efficacy of our methods in proof of principle experiments and application to real world problems.

Availability and Implementation

We made our work available as libraries for the ImageJ distribution Fiji and for deployment in a high performance parallel computing environment. Our sources are open and available at http://github.com/saalfeldlab/section-sort, http://github.com/saalfeldlab/z-spacing and http://github.com/saalfeldlab/z-spacing-spark.

Supplementary information

Supplementary data are available at Bioinformatics online

Multimodal Probes: Superresolution and Transmission Electron Microscopy Imaging of Mitochondria, and Oxygen Mapping of Cells, Using Small-Molecule Ir(III) Luminescent Complexes

We describe an Ir(III)-based small-molecule, multimodal probe for use in both light and electron microscopy. The direct correlation of data between light- and electron-microscopy-based imaging to investigate cellular processes at the ultrastructure level is a current challenge, requiring both dyes that must be brightly emissive for luminescence imaging and scatter electrons to give contrast for electron microscopy, at a single working concentration suitable for both methods. Here we describe the use of Ir(III) complexes as probes that provide excellent image contrast and quality for both luminescence and electron microscopy imaging, at the same working concentration. Significant contrast enhancement of cellular mitochondria was observed in transmission electron microscopy imaging, with and without the use of typical contrast agents. The specificity for cellular mitochondria was also confirmed with MitoTracker using confocal and 3D-structured illumination microscopy. These phosphorescent dyes are part of a very exclusive group of transition-metal complexes that enable imaging beyond the diffraction limit. Triplet excited-state phosphorescence was also utilized to probe the O₂ concentration at the mitochondria in vitro, using lifetime mapping techniques.

Impact of prenatal nicotine on the structure of midbrain dopamine regions in the rat

In utero exposure of rats to nicotine (NIC) provides a useful animal model for studying the impact of smoking during pregnancy on human offspring. Certain sequelae of prenatal NIC exposure suggest an impact on the development of the midbrain dopamine (DA) system, which receives a robust cholinergic innervation from the mesopontine tegmentum. We therefore investigated whether prenatal NIC induced structural changes in cells and synapses within the midbrain that persisted into adulthood. Osmotic minipumps delivering either sodium bitartrate (vehicle; VEH) or NIC bitartrate at 2 mg/kg/day were implanted into nine timed-pregnant dams at E4. At birth, rat pups were culled to litters of six males each, and the litters were cross-fostered. Plasma levels of NIC and cotinine from killed pups provided evidence of NIC exposure in utero. Pups separated from dams at weaning showed a trend toward reduced locomotor activity at this time point but not when tested again in adulthood. Adult rats were killed for anatomical studies. Estimates of brain size and volume did not vary with NIC treatment. Midbrain sections stained for Nissl or by immunoperoxidase for tyrosine hydroxylase and analyzed using unbiased stereology revealed no changes in volume or cell number in the substantia nigra compacta or ventral tegmental area as a result of NIC exposure. Within the ventral tegmental area, electron microscopic physical disector analysis showed no significant differences in the number of axon terminals or the number of asymmetric (putative excitatory) or symmetric (putative inhibitory) synapses. Although too infrequent to estimate by unbiased stereology, no obvious difference in the proportion of cholinergic axons was noted in NIC- versus VEH-treated animals. These data suggest that activation of nicotinic receptors during prenatal development induces no significant modifications in the structure of cells in the ventral midbrain when assessed in adulthood.

Effects of context-drug learning on synaptic connectivity in the basolateral nucleus of the amygdala in rats

Context-drug learning produces structural and functional synaptic changes in the circuitry of the basolateral nucleus of the amygdala (BLA). However, how the synaptic changes translated to the neuronal targets was not established. Thus, in the present study, immunohistochemistry with a cell-specific marker and the stereological quantification of synapses was used to determine if context-drug learning increases the number of excitatory and inhibitory/modulatory synapses contacting the gamma-aminobutyric acid (GABA) interneurons and/or the pyramidal neurons in the BLA circuitry. Amphetamine-conditioned place preference increased the number of asymmetric (excitatory) synapses contacting the spines and dendrites of pyramidal neurons and the number of multisynaptic boutons contacting pyramidal neurons and GABA interneurons. Context-drug learning increased asymmetric (excitatory) synapses onto dendrites of GABA interneurons and increased symmetric (inhibitory or modulatory) synapses onto dendrites but not perikarya of these same interneurons. The formation of context-drug associations alters the synaptic connectivity in the BLA circuitry, findings that have important implications for drug-seeking behavior.

Serial block-face imaging and its potential for reconstructing diminutive cell systems: a case study from arthropods

Until recently, three-dimensional reconstruction on an ultrastructural level was only possible using serial section transmission electron microscopy (ssTEM). However, ssTEM is highly challenging and prone to artifacts as, e.g., section loss and image distortions. New methods, such as serial block-face scanning electron microscopy (SBFSEM) overcome these limitations and promise a high lateral resolution. However, little is known about the usability of SBFSEM in diminutive, but highly complex cellular systems. We used spider sperm (~3 µm in diameter), which fulfills these conditions, to analyze the potential of SBFSEM compared with ssTEM. Our data suggest that the resolution obtained by SBFSEM allows depicting structures on a cellular level and is sufficient to discriminate subcellular components, but is highly dependent on previous staining procedures and electron density of the target structures.

An improved procedure for subcellular spatial alignment during live-cell CLEM

Live-cell correlative light and electron microscopy (CLEM) offers unique insights into the ultrastructure of dynamic cellular processes. A critical and technically challenging part of CLEM is the 3-dimensional relocation of the intracellular region of interest during sample processing. We have developed a simple CLEM procedure that uses toner particles from a laser printer as orientation marks. This facilitates easy tracking of a region of interest even by eye throughout the whole procedure. Combined with subcellular fluorescence markers for the plasma membrane and nucleus, the toner particles allow for precise subcellular spatial alignment of the optical and electron microscopy data sets. The toner-based reference grid is printed and transferred onto a polymer film using a standard office printer and laminator. We have also designed a polymer film holder that is compatible with most inverted microscopes, and have validated our strategy by following the ultrastructure of mitochondria that were selectively photo-irradiated during live-cell microscopy. In summary, our inexpensive and robust CLEM procedure simplifies optical imaging, without limiting the choice of optical microscope.

Aberrant restoration of spines and their synapses in L-DOPA-induced dyskinesia: involvement of corticostriatal but not thalamostriatal synapses

We examined the structural plasticity of excitatory synapses from corticostriatal and thalamostriatal pathways and their postsynaptic targets in adult Sprague-Dawley rats to understand how these striatal circuits change in l-DOPA-induced dyskinesias (LIDs). We present here detailed electron and light microscopic analyses that provide new insight into the nature of the structural and synaptic remodeling of medium spiny neurons in response to LIDs. Numerous studies have implicated enhanced glutamate signaling and persistent long-term potentiation as central to the behavioral sensitization phenomenon of LIDs. Moreover, experience-dependent alterations in behavior are thought to involve structural modifications, specifically alterations in patterns of synaptic connectivity. Thus, we hypothesized that in the striatum of rats with LIDs, one of two major glutamatergic pathways would form new or altered contacts, especially onto the spines of medium spiny neuron (MSNs). Our data provide compelling evidence for a dramatic rewiring of the striatum of dyskinetic rats and that this rewiring involves corticostriatal but not thalamostriatal contacts onto MSNs. There is a dramatic increase in corticostriatal contacts onto spines and dendrites that appear to be directly linked to dyskinetic behaviors, since they were not seen in the striatum of animals that did not develop dyskinesia. There is also an aberrant increase in spines receiving more than one excitatory contact(i.e., multisynaptic spines) in the dyskinetic animals compared with the 6-hydroxydopamine-treated and control rats. Such alterations could substantially impair the ability of striatal neurons to gate cortically driven signals and contribute to the loss of bidirectional synaptic plasticity.

Counting and measuring ultrastructural features of biological samples

Ultrastructural features of cells can be fractions of a micrometer in diameter, and electron microscopy is needed to resolve them to a degree that is compatible with stereological techniques. Because the focal depth of transmission electron microscopy (TEM) images is thousands of times greater than the thickness of the sections used with TEM, virtual sectioning of sections suitable for TEM is not possible, as it is with light microscopy and the optical disector probe. With features the size of neuronal synapses, for example, this necessitates the use of physical sections and physical disectors. Regardless of how the imaging is performed, the design of stereological studies for quantifying ultrastructural features will be essentially the same as that used in the example described here, which uses physically separated ultrathin sections viewed with conventional TEM to estimate the number and size of synapses in a particular brain region.

Retrieval of contextual memories increases activity-regulated cytoskeleton-associated protein in the amygdala and hippocampus

Activity-regulated cytoskeleton-associated protein (Arc) integrates information from multiple intracellular signaling cascades and, in turn, regulates cytoskeletal proteins involved in structural synaptic modifications. The purposes of the present study were: (1) to determine if the retrieval of contextual memories would induce Arc in hippocampal and amygdalar neurons; (2) use unbiased stereology at the ultrastructural level to quantify synapses contacting Arc-labeled (Arc+) and unlabeled (Arc-) postsynaptic structures in brain regions in which the amount of Arc integrated density (ID) correlated strongly with the degree of amphetamine conditioned place preference (AMPH CPP). The retrieval of contextual memories increased the Arc ID in the dentate gyrus, cornu ammonis (CA)1, and CA3 fields of the hippocampus and the basolateral, lateral, and central nuclei of the amygdala but not the primary auditory cortex, a control region. Stereological quantification of Arc+ and Arc- synapses in the basolateral nucleus of the amygdala (BLA) was undertaken because the strongest relationship between the amount of Arc ID and AMPH CPP was observed in the BLA. The retrieval of contextual memories increased the number and density of asymmetric (presumed excitatory) synapses contacting Arc+ spines and dendrites of BLA neurons, symmetric (presumed inhibitory or modulatory) synapses contacting Arc+ dendrites of BLA neurons, and multisynaptic boutons contacting Arc+ postsynaptic structures. Thus, the retrieval of contextual memories increases Arc in the amygdala and hippocampus, an effect that could be important for approach behavior to a drug-associated context.

Efferent synapses return to inner hair cells in the aging cochlea

Efferent innervation of the cochlea undergoes extensive modification early in development, but it is unclear if efferent synapses are modified by age, hearing loss, or both. Structural alterations in the cochlea affecting information transfer from the auditory periphery to the brain may contribute to age-related hearing deficits. We investigated changes to efferent innervation in the vicinity of inner hair cells (IHCs) in young and old C57BL/6 mice using transmission electron microscopy to reveal increased efferent innervation of IHCs in older animals. Efferent contacts on IHCs contained focal presynaptic accumulations of small vesicles. Synaptic vesicle size and shape were heterogeneous. Postsynaptic cisterns were occasionally observed. Increased IHC efferent innervation was associated with a smaller number of afferent synapses per IHC, increased outer hair cell loss, and elevated auditory brainstem response thresholds. Efferent axons also formed synapses on afferent dendrites but with a reduced prevalence in older animals. Age-related reduction of afferent activity may engage signaling pathways that support the return to an immature state of efferent innervation of the cochlea.

Further development of the NCTC 2544 IL-18 assay to identify in vitro contact allergens

Several European Union legislations request the use of in vitro methods for toxicological evaluations, including sensitization, in order to increase consumer safety but also to reduce the use of animals. The EU project SENS-IT-IV addresses the need of developing predictive in vitro tests to assess contact and respiratory hypersensitivity reactions. In this context, we have recently reported the possibility to use IL-18 production in the human keratinocyte cell line NCTC 2544 to discriminate contact sensitizer from irritants and low molecular weight respiratory allergens. The aims of the present study were to further develop this assay in order to optimize experimental conditions; to develop a 96-well plate format to establish a high throughput assay; to test the performance of other available keratinocyte cell lines, and to understand the signal transduction pathway involved in p-phenylenediamine (PPD)-induced IL-18 production. If cells reach confluence at the moment of treatment, the ability to identify contact allergens is lost; therefore a careful check for the optimal cell density using PPD as reference contact allergen is critical. In our hands, a cell density of 1-2.5 × 10(5)cells/ml gave optimal stimulation. In order to develop a high throughput test, cells seeded in 96-well plate were exposed to contact allergens (2,4-dinitrochlorobenzene, p-phenylenediamine, isoeugenol, cinnamaldehyde, tetramethylthiuram disulfite, resorcinol, cinnamic alcohol and eugenol), irritants (phenol, sodium laurel sulphate, lactic acid and salicylic acid) and respiratory allergens (hexachloroplatinate, diphenylmethane diisocyanate, trimellitic anhydride). A selective increase in total (intracellular plus released) IL-18 was observed 24h later in cells treated with contact allergens, whereas no changes were observed following treatment with respiratory allergens and irritants, confirming previous results obtained in a 24-well format assay. A selective induction of IL-18 was also obtained testing with PPD other keratinocyte cell lines, namely HPKII and HaCaT, with the HPKII showing the highest stimulation index. Regarding the signal transduction pathway, we could demonstrate using selective inhibitors a role for oxidative stress, NF-κB and p38 MAPK activation in PPD-induced IL-18 production. In conclusion, results obtained suggest that the production of IL-18 represents a promising endpoint for the screening of potential contact allergens. The assay can be performed in a 96-well plate format, different keratinocyte cell lines can be used, and a role for oxidative stress in contact allergen-induced IL-18 was demonstrated.

Amphetamine-associated contextual learning is accompanied by structural and functional plasticity in the basolateral amygdala

Drug seeking and the vulnerability to relapse occur when individuals are exposed to an environment with sensory cues in which drug taking has occurred. Memory formation is thought to require plasticity in synaptic circuits, and so we examined whether the memory for a drug-paired environment correlates with changes in the synaptic circuits of the basolateral amygdala (BLA), in which emotional learning is a recognized phenomenon. We used amphetamine (AMPH) as the unconditioned stimulus in the conditioned place preference (CPP) paradigm. Rats were conditioned with 1.0 mg/kg AMPH and tested, drug free, 72 h after the last conditioning session. Controls included a saline-conditioned group and a home cage AMPH injection group, whose exposure to the CPP apparatus was delayed by 4 h, long enough to clear the AMPH from the brain. We counted excitatory synapses in the BLA using the electron microscope and the physical disector design (stereology). Rats that expressed AMPH CPP had an increase in excitatory synapses compared with controls. Excitatory synaptic activity was measured using in vivo intracellular recordings from the BLA in anesthetized rats. We found that AMPH CPP, but not drug alone, increased measures of synaptic drive, including the frequency of synaptic events, and the paired-pulse ratio of synaptic inputs to BLA pyramidal neurons. The in vivo findings suggest that the increase in BLA neuronal excitatory drive reflects the change in excitatory synapse number. Thus, context-drug associations are accompanied by structural and functional plasticity in the BLA, findings that have important implications for drug-seeking behavior.

Important factors for the three-dimensional reconstruction of neuronal structures from serial ultrathin sections

Quantitative analysis of anatomical synaptic connectivity in microcircuits depends upon accurate three-dimensional (3D) reconstructions of synaptic ultrastructure using electron microscopy of serial ultrathin sections. Here we address two pitfalls in current methodology that lead to inaccurate reconstructions and compromise conclusions drawn from the data. The first pitfall is inaccurate determination of ultrathin section thickness, which negatively affects the 3D shape of reconstructions and therefore impairs quantitative measurement of synaptic structures. Secondly, current methodology significantly underestimates the number of synaptic junctions, with only two-thirds or less of genuine synaptic contacts being identified in dendrites that radiate within the plane of section. Here we propose a new methodology utilizing precise optical measurements of section thickness and successive observations of synaptic elements across serial ultrathin sections that corrects for these limitations to allow accurate 3D reconstruction of synaptic ultrastructure. We use this methodology to reveal that parvalbumin-expressing cortical interneurons have a much higher synaptic density than previously shown. This result suggests that this technique will be useful for re-examining synaptic connectivity of other cell types.

The use of dual beam ESEM FIB to reveal the internal ultrastructure of hydroxyapatite nanoparticle-sugar-glass composites

Microparticles (MP) spray dried from hydroxyapatite (HA) nanoparticle (NP) sugar suspensions are currently under development as a prolonged release vaccine vehicle. Those with a significant sugar component cannot be sectioned by ultramicrotomy as resins are excluded by the sugar. Focused ion beam (FIB) milling is the only method to prepare thin sections that enables the inspection of the MPs ultrastructure by transmission electron microscopy (TEM). Several methods have been explored and we have found it is simplest to encapsulate MPs in silver dag, sandwiched between gold foils for FIB-milling to enable multiple MPs to be sectioned simultaneously. Spray dried MPs containing 80% sugar have an inter-nanoparticle separation that is comparable with NP size (approximately 50 nm). MPs spray dried with 50% sugar or no sugar are more tightly packed. Nano-porosity in the order of 10 nm exists between NPs. MPs spray dried in the absence of sugar and sectioned by ultramicrotomy or by FIB-milling have comparable nanoscale morphologies. Selected area electron diffraction (SAED) demonstrates that the HA remains (substantially) crystalline following FIB-milling.

Synaptic contact number and size in stratum radiatum CA1 of APP/PS1DeltaE9 transgenic mice

Synaptic changes occur early in the course of Alzheimer's disease and are key to understanding the initial events in associated neurodegenerative processes. The quantitative analysis of synaptic morphology in transgenic mouse models of Alzheimer's disease can provide important insights into these processes. To this end, the total number and the distribution of the diameters of synaptic contacts in the stratum radiatum of the CA1 region of the hippocampus of 12-month-old APP/PS1DeltaE9 transgenic mice and wild type littermates have been evaluated by applying design-based stereological methods to material prepared for electron microscopy. Although there were no differences in the size of the synaptic contacts, the total number of synaptic contacts was significantly larger in the transgenic mice, suggesting that the transgenic effect at this age is synaptotrophic and that the presence of amyloid plaques and an elevated Abeta42/40 ratio are not necessarily detrimental to populations of synapses. The potential of this type of data in evaluating synaptic changes related to Alzheimer's disease is discussed and the methodology described in detail.

Is adolescence a sensitive period for depression? Behavioral and neuroanatomical findings from a social stress model

OBJECTIVES

Sex differences in depressive symptoms emerge during adolescence, with females more at risk than males. However, adverse life events during development have greater impact on males. An animal model that incorporates behavioral and anatomical changes following adolescent stress is needed.

EXPERIMENTAL DESIGN

Sprague-Dawley rats were exposed to social stress (SS; isolation housing during P30-35) or remained group-housed (GRP) and tested in the forced swim test (FST), the triadic learned helplessness model (LH), and the elevated plus maze. Western immunoblots of myelin basic protein (MBP) and synaptophysin (SVP) and spinophillin indexed synaptic and dendritic plasticity, respectively.

PRINCIPAL OBSERVATIONS

At P36, SS increased climbing behavior in both sexes, and decreased the latency to immobility in females following a 15 min inescapable swim in the FST. Depressive-like behaviors were differentially elevated in both sexes 24 h later. GRP females exhibited higher levels of depression-related behaviors than GRP males in both FST and LH paradigms. SS significantly increased depressive behaviors in the FST in males, and impaired their ability to escape shock previously conditioned to be controllable. SS decreased open arm time in females only. The greatest reductions in synaptic plasticity proteins were observed in the prefrontal cortex: spinophillin (19.1%), SVP (7.9%), and MBP (48.7%, males only). Smaller reductions in spinophillin were observed in the hippocampus and amygdala.

CONCLUSIONS

Adolescent separation produces both behavioral and neural changes associated with stress-related depression and anxiety. Additional work is needed to improve our understanding of stress as it relates to depression during this vulnerable period of development.

Orexin axons in the rat ventral tegmental area synapse infrequently onto dopamine and gamma-aminobutyric acid neurons

Cells in the ventral tegmental area (VTA) facilitate motivated behaviors, and the activity of VTA neurons is regulated by dense projections from the lateral hypothalamic area (LHA). Orexin (Orx) neurons in the lateral and perifornical hypothalamus play important roles in arousal, feeding, and energy metabolism. Orx cells contribute substantially to the LHA projection to the rat midbrain. However, the morphological features of Orx fibers in the VTA and whether they synapse onto dopamine (DA) or gamma-aminobutyric acid (GABA) neurons have not yet been investigated. We utilized immunoperoxidase and immunogold-silver staining to examine the morphological features and synaptic incidence of Orx-labeled axons in the VTA. We then combined immunoperoxidase labeling for Orx with immunogold-silver labeling for GABA or for tyrosine hydroxylase (TH) in DA neurons. Electron microscopic analysis revealed that most Orx-labeled axons in the VTA were passing fibers. The less common Orx varicosities were occasionally apposed to TH- or GABA-labeled dendrites without synapsing. Only a small proportion of Orx-positive axons synapsed onto dendrites or soma. The synapses included both asymmetric and symmetric types and targeted TH- and GABA-labeled profiles with equal frequency. These findings suggest that most Orx fibers in the VTA are axons passing to caudal brainstem structures. However, Orx does mediate some direct synaptic influence on VTA DA and GABA neurons. Additional nonsynaptic effects are suggested by the presence of numerous dense-cored vesicles. These studies have important implications for understanding the mechanisms whereby Orx can alter behavior through regulating VTA DA and GABA cell activity.

Serial sectioning and electron microscopy of large tissue volumes for 3D analysis and reconstruction: a case study of the calyx of Held

Serial section electron microscopy is typically applied to investigation of small tissue volumes encompassing subcellular structures. However, in neurobiology, the need to relate subcellular structure to organization of neural circuits can require investigation of large tissue volumes at ultrastructural resolution. Analysis of ultrastructure and three-dimensional reconstruction of even one to a few cells is time consuming, and still does not generate the necessary numbers of observations to form well-grounded insights into biological principles. We describe an assemblage of existing computer-based methods and strategies for graphical analysis of large photographic montages to accomplish the study of multiple neurons through large tissue volumes. Sample preparation, data collection and subsequent analyses can be completed within 3-4 months. These methods generate extremely large data sets that can be mined in future studies of nervous system organization.

Synaptic alterations at inner hair cells precede spiral ganglion cell loss in aging C57BL/6J mice

Hearing deficits have often been associated with loss of or damage to receptor hair cells and/or degeneration of spiral ganglion cells. There are, however, some physiological abnormalities that are not reliably attributed to loss of these cells. The afferent synapse between radial fibers of spiral ganglion neurons and inner hair cells (IHCs) emerges as another site that could be involved in transmission abnormalities. We tested the hypothesis that the structure of these afferent terminals would differ between young animals and older animals with significant hearing loss. Afferent endings and their synapses were examined by transmission electron microscopy at approximately 45% distance from the basal end of the cochlea in 2-3 month-old and 8-12 month-old C57BL/6J mice. The number of terminals in older animals was reduced by half compared to younger animals. In contrast, there was no difference in the density of SGCs between the age groups. Older animals featured enlarged terminals and mitochondria and enlarged postsynaptic densities and presynaptic bodies. These morphological changes may be a combination of pathologic, adaptive and compensatory responses to sensory dysfunction. Improved knowledge of these processes is necessary to understand the role of afferent connectivity in dysfunction of the aging cochlea.

Chronic restraint stress induces changes in synapse morphology in stratum lacunosum-moleculare CA1 rat hippocampus: a stereological and three-dimensional ultrastructural study

Chronic restraint stress is known to affect the morphology and synaptic organization of the hippocampus, predominantly within CA3 but also in CA1 and dentate gyrus. In this study, we provide the first evidence for specific ultrastructural alterations affecting asymmetric axo-spinous synapses in CA1 stratum lacunosum-moleculare following chronic restraint stress (6 h/day, 21 days) in the rat. The structure of asymmetric axo-spinous post-synaptic densities was investigated using serial section three-dimensional reconstruction procedures in control (n=4) and chronic restraint stress (n=3) animals. Dendritic spine profiles (spine head+neck) associated with the sampled synaptic contacts (30 per animal) were also reconstructed in three-dimensions. Morphometric analyses revealed a significant increase in post-synaptic density surface area (+36%; P=0.03) and a highly significant increase in post-synaptic density volume (+79%; P=0.003) in the chronic restraint stress group. These changes were directly associated with 'non-macular' (perforated, complex and segmented) post-synaptic densities. A highly significant overall increase in the 'post-synaptic density surface area/spine surface area' ratio was also detected in the chronic restraint stress group (+27%; P=0.002). In contrast, no quantitative changes in spine parameters were found between groups. The Cavalieri method was used to assess the effects of chronic restraint stress exposure upon CA1 hippocampal volume. The mean volume of total dorsal anterior CA1 hippocampus was significantly lower in the chronic restraint stress group (-16%; P=0.036). However, when corrected for volume changes, no significant alteration in a relative estimate of the mean number of asymmetric axo-spinous synapses was detected in CA1 stratum lacunosum-moleculare between control and chronic restraint stress groups. The data indicate a structural remodeling of excitatory axo-spinous synaptic connectivity in rat CA1 stratum lacunosum-moleculare as a result of chronic restraint stress.

Passive avoidance training decreases synapse density in the hippocampus of the domestic chick

The bird hippocampus (Hp), although lacking the cellular lamination of the mammalian Hp, possesses comparable roles in spatial orientation and is implicated in passive avoidance learning. As in rodents it can be divided into dorsal and ventral regions based on immunocytochemical, tracing and electrophysiological studies. To study the effects of passive avoidance learning on synapse morphometry in the Hp, spine and shaft synapse densities of 1-day-old domestic chicks were determined in dorsal and ventral Hp of each hemisphere by electron microscopy, 6 and 24 h following training to avoid pecking at a bead coated with a bitter-tasting substance, methyl anthranilate (MeA). The density of asymmetric spine and shaft synapses in MeA-trained birds at 6 h post-training was significantly lower in the dorsal and ventral Hp of the right hemisphere relative to control (untrained) chicks, but by 24 h this difference was absent. A hemispheric asymmetry was apparent in the ventral Hp where the water-trained group showed enhanced shaft and spine synapse density in the left hemisphere, whilst in the MeA-trained group only asymmetric shaft synapses follow the same pattern in relation to the right hemisphere. There were no differences in asymmetric shaft synapses in the dorsal Hp at 6 h post-training, but at 24 h post-training there was a reduction in the density of shaft synapses in the right hemisphere in MeA compared with control birds. These data are discussed in relation to the pruning effects of stress and learning on synapse density in chick Hp.

Efficient quantification of afferent cochlear ultrastructure using design-based stereology

The afferent synapse between the auditory nerve fiber and the inner hair cell (IHC) represents a critical junction for hearing. Elucidation of the structure at this site will help establish the substrate for normal sound encoding as well as pathologic processes associated with hearing dysfunction. Previous applications of unbiased (design-based) stereological principles have expanded our knowledge of neuro-morphological changes evident with the light microscope. Applying these principles at the level of the synapse is a promising morphometric approach for the efficient sampling of large reference spaces with electron microscopy. This study tests the accuracy of using ultra-thin sections at a fixed interval, known as disector pairs, to quantify afferent innervation density. We analyzed the total numbers of afferent terminals, synaptic thickenings, and synaptic bodies associated with each IHC in the C57BL/6J mouse cochlea, and confirmed the accuracy of the stereological approach in comparison to three-dimensional reconstructions of serial alternate sections. The higher sampling efficiency of the disector pair method rapidly increases precision while also reducing the largest source of variability, inter-animal differences. We conclude that ultrastructural quantification of afferent innervation can be accomplished in the cochlea using efficient design-based stereology.

Spontaneous electrical activity and dendritic spine size in mature cerebellar Purkinje cells

Previous experiments have shown that in the mature cerebellum both blocking of spontaneous electrical activity and destruction of the climbing fibres by a lesion of the inferior olive have a similar profound effect on the spine distribution on the proximal dendrites of the Purkinje cells. Many new spines develop that are largely innervated by parallel fibers. Here we show that blocking electrical activity leads to a significant decrease in size of the spines on the branchlets. We have also compared the size of the spines of the proximal dendritic domain that appear during activity block and after an inferior olive lesion. In this region also, the spines in the absence of activity are significantly smaller. In the proximal dendritic domain, the new spines that develop in the absence of activity are innervated by parallel fibers and are not significantly different in size from those of the branchlets, although they are shorter. Thus, the spontaneous activity of the cerebellar cortex is necessary not only to maintain the physiological spine distribution profile in the Purkinje cell dendritic tree, but also acts as a signal that prevents spines from shrinking.

The relation between resolution measurements and numbers of retinal ganglion cells in the same human subjects

Limiting factors of resolution have previously only been investigated by using resolution data and retinal ganglion cell spacing data from different individuals. We report on our unique opportunity to study the intra-individual relationship in three human subjects between retinal ganglion cell separations and resolution thresholds, measured with high-pass resolution perimetry. Our data show that resolution is directly proportional to half the midget population, in accordance with the hypothesis that a dichotomous midget ON/OFF population mediates resolution.

Two types of afferent terminals innervate cochlear inner hair cells in C57BL/6J mice

Afferent synapses on inner hair cells (IHC) transfer auditory information to the central nervous system (CNS). Despite the importance of these synapses for normal hearing, their response to cochlear disease and dysfunction is not well understood. The C57BL/6J mouse is a model for presbycusis and noise-induced hearing loss because of its age-related hearing loss and susceptibility to acoustic over-exposure. In this context, we sought to establish normal synaptic structure in order to better evaluate synaptic changes due to presbycusis and noise exposure. Ultrastructural analysis of IHCs and afferent terminals was performed in a normal hearing 3-month-old C57BL/6J mouse at cochlear sites corresponding to 8, 16 and 32 kHz using semi-serial sections. A stereologic survey of random sections was conducted of IHCs in 11 additional mice. Two morphologically distinct groups of afferent terminals were identified at all 3 frequency locations in 11 out of 12 animals. "Simple" endings demonstrated classic features of bouton terminals, whereas "folded" endings were larger in size and exhibited a novel morphologic feature that consisted of a fully internalized double membrane that partially divided the terminal into two compartments. In many cases, the double membrane was continuous with the outer terminal membrane as if produced by an invagination. We still must determine the generality of these observations with respect to other mouse strains.

Ultrastructural and behavioural changes precede amyloid deposition in a transgenic model of Alzheimer’s disease

We describe the thorough characterisation of a new transgenic mouse line overexpressing the 695-amino acid isoform of human amyloid precursor protein harbouring the Swedish double familial Alzheimer's disease mutation. This line, referred to as TAS10, exhibits neuropathological features and cognitive deficits that are closely correlated to the accumulation of Abeta in their brain and that are reminiscent of those observed in AD. Data on the TAS10 line are presented at five time points: 2, 6, 12, 18 and 24 months in a longitudinal study. The TAS10 line is characterised by the following changes: i) significant age-related increases in the levels of total and individual species (1-40, 1-42) of beta-amyloid in the brains of transgenics compared with non-transgenic littermates; ii) transgenic mice showed pronounced spatial learning deficits in the Morris water maze at 6 months and working memory deficits by 12 months; iii) amyloid plaque and associated pathologies were observed by the 12-month time point and the burden increased substantially, particularly in the cortex, by 18 months; iv) electron microscopy of the hippocampus of transgenic mice showed evidence of abnormal ultrastructural features such as dystrophic neurites and lipid deposits that developed from 6 months and increased in number and severity with age. Morphometric studies demonstrate that the synapse to neuron ratio is higher in transgenics than in control mice at 12 months, but this ratio decreases as they age and synapse size increases. Thus, this mouse model exhibits a close correlation of amyloid burden with behavioural deficits and ultrastructural abnormalities and so represents an ideal system to study the mechanisms underlying the impact of amyloid pathology on CNS function.

Morphological changes in hippocampal dentate gyrus synapses following spatial learning in rats are transient

The hippocampus is believed to play a crucial role in the formation of memory for spatial tasks. In the present study quantitative electron microscopy was used to investigate morphological changes in the hippocampal dentate gyrus of 3-month-old male rats at 3, 9 and 24 h after training to find a hidden platform in a Morris water maze. Average escape latency (time taken to reach the platform) in all trained groups decreased progressively with increased training but data from a probe trial (quadrant analysis test) at the end of training indicated that only animals in the 9- and 24-h groups, not the 3-h group, displayed significant retention of platform location. Unbiased stereological methods were used to estimate synapse and neuronal density at each time point after training. The majority of synapses had unperforated postsynaptic densities, were localized on small dendritic spines and were classed as axo-spinous. In comparison to age-matched untrained rats, significant but transient increases were observed in axo-spinous synapse density and synapse-to-neuron ratio 9 h after the start of training, but not at earlier (3 h) or later (24 h) times. These changes at 9 h post-training were accompanied by transient decreases in both mean synaptic height and area of postsynaptic density. No such changes were observed in an exercise-matched control group of rats, indicating that the transient synaptic changes in the dentate gyrus are most likely to be specifically related to processes involved in memory formation for the spatial learning task.

Therapeutic effects of complex motor training on motor performance deficits induced by neonatal binge-like alcohol exposure in rats: II. A quantitative stereological study of synaptic plasticity in female rat cerebellum

Twenty days of complex motor skill training in adult rats was previously demonstrated to rehabilitate motor performance deficits induced by binge alcohol exposure in neonatal rats. This follow-up study evaluated morphological plasticity in the paramedian lobule of the cerebellum (PML) using the same treatment and training regimens. On postnatal days (PD) 4-9, female Long-Evans rats were given either alcohol (Alcohol Exposure - AE, 4.5 g/kg/day via artificial rearing), exposure to gastrostomy control (GC) artificial rearing procedures, or reared normally as suckle controls (SC). After weaning, all rats were housed two to three per cage. At 180 days old, rats were randomly assigned either to a rehabilitation condition (RC: given 20 days of complex motor skill training), or to an inactive condition (IC: remained in their home cage). The AE rats were delayed in acquiring the training, but there were no group differences in performance over the last 2 weeks of training. Unbiased stereological techniques were used to evaluate PML volume, Purkinje cell and parallel fiber synapse density. Although total volume of PML was significantly reduced in the AE rats, complex motor skill training resulted in a significant increase in the PML molecular layer in all three postnatal treatment groups. The RC animals from the SC and AE groups had more parallel fiber synapses per Purkinje cell than corresponding IC animals. These data support the hypothesis that 'rehabilitative' motor training stimulates synaptogenesis in the PML, and that Purkinje neurons that survive the early postnatal alcohol insult are capable of substantial experience-induced plasticity.

Effects of age and insulin-like growth factor-1 on neuron and synapse numbers in area CA3 of hippocampus

Age-related effects associated with the hippocampus include declines in numbers of neurons and synapses in the dentate gyrus and area CA1, and decreased cognitive ability as assessed with the Morris water maze. The present study quantified both neuron and synapse number in the same tissue block of area CA3 of the hippocampus. No investigations of both density of neurons and synapses together in area CA3 of hippocampus have been performed previously, despite its importance as the terminal field of dentate gyrus mossy fibers, the second synapse in the trisynaptic circuit in the hippocampus. Numerical density of neurons and synapses were assessed in 4-, 18-, and 29-month-old rats receiving infusions of saline into the lateral ventricle and in 29-month-old rats receiving infusions of insulin-like growth factor-1 (IGF-1). Numerical density of neurons of the stratum pyramidale of CA3 of hippocampus remained constant across the life span as did the numerical density of synapses in stratum lucidum of area CA3. Despite the reported role of IGF-1 in synaptogenesis and improvements in behavior with age, ventricular infusion of this growth factor did not affect the numerical density of neurons or synapses in 29-month-old rats when compared to saline-infused old rats. Further, reported effects of IGF-1 on adult neurogenesis in the dentate gyrus are not reflected in an IGF-1-related increase in synapse density in this region.

Re-structuring of synapses 24 hours after induction of long-term potentiation in the dentate gyrus of the rat hippocampus in vivo

In male rats, long-term potentiation was induced unilaterally in the dentate gyrus, either by high frequency (200Hz) or theta rhythm stimulation. Structural synaptic changes were examined 24h after induction using quantitative electron microscopy. A disector technique was employed in order to estimate the density of synapses (using 70-80-nm sections) and of granule cell nuclei (using 2-microm sections) in the middle, and inner molecular layer in both hemispheres. Synaptic height and total lateral areas of synaptic active zones per unit tissue volume were assessed via assumption-free stereological techniques coupled with image analysis. The results obtained indicated that both synaptic density and number (corrected per neuron) of axo-spinous, but not axo-dendritic, synapses were approximately 40% higher in the middle, but not inner molecular layer of the potentiated hemisphere compared to the contralateral (control hemisphere). No significant inter-hemispheric difference was found in the volume densities of lateral areas of active zones. These data suggest that 24h after long-term potentiation induction, active zones of existing axo-spinous synapses either split forming separate contacts, or decrease in size while new synapses are formed.

Extending unbiased stereology of brain ultrastructure to three-dimensional volumes

OBJECTIVE

Analysis of brain ultrastructure is needed to reveal how neurons communicate with one another via synapses and how disease processes alter this communication. In the past, such analyses have usually been based on single or paired sections obtained by electron microscopy. Reconstruction from multiple serial sections provides a much needed, richer representation of the three-dimensional organization of the brain. This paper introduces a new reconstruction system and new methods for analyzing in three dimensions the location and ultrastructure of neuronal components, such as synapses, which are distributed non-randomly throughout the brain.

DESIGN AND MEASUREMENTS

Volumes are reconstructed by defining transformations that align the entire area of adjacent sections. Whole-field alignment requires rotation, translation, skew, scaling, and second-order nonlinear deformations. Such transformations are implemented by a linear combination of bivariate polynomials. Computer software for generating transformations based on user input is described. Stereological techniques for assessing structural distributions in reconstructed volumes are the unbiased bricking, disector, unbiased ratio, and per-length counting techniques. A new general method, the fractional counter, is also described. This unbiased technique relies on the counting of fractions of objects contained in a test volume. A volume of brain tissue from stratum radiatum of hippocampal area CA1 is reconstructed and analyzed for synaptic density to demonstrate and compare the techniques.

RESULTS AND CONCLUSIONS

Reconstruction makes practicable volume-oriented analysis of ultrastructure using such techniques as the unbiased bricking and fractional counter methods. These analysis methods are less sensitive to the section-to-section variations in counts and section thickness, factors that contribute to the inaccuracy of other stereological methods. In addition, volume reconstruction facilitates visualization and modeling of structures and analysis of three-dimensional relationships such as synaptic connectivity.

Termination of the geniculocortical projection in the striate cortex of macaque monkey: a quantitative immunoelectron microscopic study

The goal of this present study was to derive a new estimate of the synaptic contribution of the dorsal lateral geniculate nucleus (dLGN) to the subdivisions of its main recipient layer, layer 4C, of striate cortex of macaque monkey. The projection from the dLGN and its terminal boutons within layer 4C were visualized by immunodetection of the calcium binding protein, parvalbumin (PV), which is expressed in relay cells of the dLGN. The proportion of asymmetric synapses formed by PV-positive boutons within the alpha and beta sublayers of 4C was estimated by using a nonbiased stereological counting method. The proportion of asymmetric synapses contributed by the PV-positive boutons to layer 4Calpha is 8.7%; to 4Cbeta is 6.9%. Assuming all the PV-positive asymmetric synapses derive from the dLGN relay cells, this gives a ratio of dLGN synapses per neuron of 192 in layer 4Calpha and 128 in layer 4Cbeta. Thus, the recurrent excitatory input from neighboring cortical neurons must play an important part in responses of the neurons lying at the input stage of the cortical circuit.

Ultrastructural changes of human cardiac atrial nerve endings in diabetes mellitus

BACKGROUND

Autonomic neuropathy resulting from long-term diabetes mellitus may affect heart innervation. However, so far diabetes induced morphological changes of cardiac nerves are not well-known. In this study human cardiac atrial tissue from diabetic patients was analysed by electron microscopy for structural alterations as a result of diabetic neuropathy.

METHODS

In coronary bypass surgery, an edge of the right auricle was routinely resected for reason of extracorporal circulation. Thin cardiac tissue sections of 100 nm were studied by electron microscopy. Atrial tissue samples were collected from 5 patients with long-standing diabetes (for at least 8 years) and compared to atrial tissue samples from 5 patients without diabetes, equally undergoing coronary bypass surgery.

RESULTS

In all atria-free nerve endings with unmyelinized, axons were observed. Cross sections of 479 axons from diabetic patients were compared to 419 axons of nondiabetic patients. The number of altered axons was significantly higher in cardiac tissue of diabetic patients (32%) in comparison to normal subjects (17%). In diabetic patients, 20% of the intra-axonal mitochondria were condensed or hydropic, whereas in nondiabetic patients only 4% of the mitochondria were altered. Membrane fragments were present in 21% of the axons in atria of diabetic patients compared to 10% in nondiabetic subjects. Only in cardiac axons from diabetic patients there were lamellar bodies, dissolved axoplasma and junctions between neighbouring axons in a minor number. Few vacuoles were present in axons of both groups.

CONCLUSION

In myocardial atrial-free nerve fibre bundles of diabetic patients, the amount of degenerative changes was higher in comparison to atrial cardiac tissue from nondiabetic subjects. These morphological alterations may indicate manifestation of diabetic neuropathy and might contribute to the impairment of autonomic neural control affecting the heart in long-standing diabetes mellitus.

Effects of chronic ethanol consumption on SER of Purkinje neurons in old F344 rats

The purpose of this study was to determine whether the observed swelling of smooth endoplasmic reticulum (SER) profiles in Purkinje dendrites in our old ethanol-fed F344 rats: (1) represented measurable dilatation, (2) was present in dendritic shafts and spines, and (3) was reversed following recovery from ethanol. Of the 45 rats in 3 treatment groups (chow-fed, pair-fed, and ethanol-fed), 30 rats were euthanized after 40 weeks, and 15 were maintained on rat chow for an additional 20-week recovery period. Electron microscopy of cerebellar preparations was used to analyze morphological alterations in SER profile size within the dendritic shafts and spines of Purkinje neurons. Results showed significant SER dilatation following 40 weeks of ethanol consumption, which disappeared after ethanol withdrawal.

Synapses in hippocampus occupy only 1-2% of cell membranes and are spaced less than half-micron apart: a quantitative ultrastructural analysis with discussion of physiological implications

Relatively little information exists regarding the spatial structure of synaptic neuropil in the brain. The present electron microscopic study employs unbiased stereological techniques and Monte Carlo simulations to characterise quantitatively the spatial organisation of synaptic circuitry in the dentate gyrus of the hippocampus, an area of particular importance in mechanisms of learning and the subject of a number of experimental neurobiological models of synaptic plasticity such as long-term potentiation. Firstly, tissue shrinkage/expansion resulting from embedding was assessed by imaging 300-microm thick hippocampal slices in the course of the entire embedding protocol, giving a value of 94.3 +/- 1.1% for distance measures and 84.3 +/- 2.8% for volumetric measures. Secondly, numeric synaptic density, Nv, was estimated using the disector. Thirdly, accumulated area of post-synaptic densities (PSDs) per tissue volume, Sv, and the overall cell membrane area per tissue volume, Sv*, were assessed using unbiased stereological rules coupled with image analysis of single sections. Finally, the mean area of individual PSDs was derived as a ratio Sv/Nv giving: 0.0394 microm2 for axo-spinous PSDs (thus representing approximately 1.3% of total cell membranes) and 0.0769 microm2 for dendritic shaft PSDs (approximately 0.25% of total cell membranes). From these data, the mean nearest neighbour distance between synapses was estimated using Monte Carlo simulations of a random 3D arrangement of synapses constrained by PSD sizes (a truncated Poisson process), giving a value of 0.48-0.51 microm. The physiological importance of the morphometric data obtained is discussed in terms of assessing (i) the role of synaptic environment in modifying synaptic efficacy and (ii) the plausibility of cross talk between synapses in relation to extrasynaptic neurotransmitter diffusion and transient depletion of extracellular Ca2+.

Ultrastructural synaptic correlates of spatial learning in rat hippocampus

Memory formation is believed to alter neural circuitry at the synaptic level. Although the hippocampus is known to play an important role in spatial learning, no experimental data exist on the synaptic correlates of this process at the ultrastructural level. Here, we have employed quantitative electron microscopy in order to compare the density, size and spatial arrangement of synapses in the dentate gyrus, and in area CA1, of spatially trained (water maze, invisible platform) versus control (visible platform) rats. No training-associated changes of hippocampal volume were found using a stereological estimaion (disector) of the volume density of dentate granule, or CA1 pyramidal cells. Nor were changes found in either density, or sizes of synapses (spinous or dendritic), in CA1 or dentate gyrus. However, analysis of synaptic spatial distribution showed a training-associated increase in the frequency of shorter distances (i.e. clustering) between synaptic active zones in CA1, but not dentate, thus indicating alterations in local neural circuitry. This finding indicates subtle changes in synaptic organization in area CA1 of the hippocampus following a learning experience, suggesting that spatial memory formation in mammalian hippocampus may involve topographical changes in local circuitry without synapse formation de novo.

How to count synapses unbiasedly and efficiently at the ultrastructural level: proposal for a standard sampling and counting protocol

After almost 40 years, there is still no consensus on criteria for identifying different types of synapse seen in electron microscopical thin sections or on methods for counting them unbiasedly in 3D. This review proposes a procedure which meets these aims and could be adopted as a standard best-practice sampling and counting convention. It deals exclusively with unbiased stereological methods for counting particles in 3D space because these are efficient and applicable to arbitrary particles regardless of their size, shape and orientation. Methods based on individual sections are excluded because arbitrary particles cannot be counted unbiasedly with such sections. Model-based methods (e.g. treating synaptic membrane densities as circular disks) are excluded because they are not unbiased in general and now have limited (mainly historical) interest only. For unbiased counting, the absolute minimum requirement is a pair of parallel sections (dissector). The following protocol is recommended for future studies on synapse number: (1) use para(membrane) densities as synaptic counting units, (2) do not qualify definition of the counting unit by reference to a minimum number of synaptic vesicle profiles, (3) sample and count synapses unbiasedly using the dissector, and (4) in preference convert number per volume into absolute number or, in this is not possible, estimate a synapse-to-neuron ratio.

Unbiased stereological estimation of the total number of synapses in a brain region

Modern stereological methods have been used to make unbiased estimates of the total number of synapses in the striatum radiatum of the hippocampal CA1 region of five rabbits. The approach used involved a two stage analysis and is generally applicable to all parts of the nervous system. During the first stage of the analysis, the reference volume was estimated by point counting, at the light microscope level, according to the Cavalieri principle. During the second stage, the numerical density of synapses was estimated with dissectors at the electron microscopic level. The total number of synapses was calculated as the product of the numerical density and the volume of the region. The sampling with points and dissectors was carried out in all three dimensions of the entire CA1 region in a manner that ensured that all parts of the region and all synapses within it had equal probabilities of being sampled. An analysis of the precision of the estimate of total synapse number has been performed in terms of the variances of volume and synaptic numerical density at different levels of sampling, i.e. at the level of points, sections, individual animals and group of animals. Detailed descriptions of the procedures used to estimate the total number of synapses, evaluate the precision of the estimates, and optimize the sampling scheme are provided.

Reduction in numerical synapse density in chick (Gallus domesticus) dorsal hippocampus following transient cerebral ischaemia

Transient forebrain ischaemia was induced by a two-vessel occlusion method in the domestic chick. One week post-surgery, hippocampal tissue was processed for electron microscopy and synapse density assessed using the disector technique. Hippocampal volume was estimated using image analysis of serial coronal cryostat sections. The density of asymmetric synapses was significantly reduced (27%; P < 0.005) in ischaemic chicks. This appears to be a real reduction as hippocampal volume was not significantly decreased.

Morphometric applications in anatomic pathology

The components of the cell and tissue changes in many diseases are variable and can therefore be quantified. Characterization of these quantitative changes provides data that is useful not only for making a definitive, cell- and tissue-based diagnosis of disease, but also for predicting the course of disease. The spectrum of changes found in malignant tumors, ie, cell grade, architecture, cellularity, extent of invasion, nature and extent of inflammatory reaction, exemplify this range of quantifiable features. The diagnosis and prognosis of nonneoplastic diseases, ie, myopathy and metabolic bone disease, can also be determined by quantitating tissue changes. Morphometry is the quantification of changes in the "objects" of tissues, ie, cells and organelles, and their organization, using quantitative evaluation tools. The principles of morphometry have been known for a century. With the increasing availability of affordable, powerful computer systems and increasingly flexible and user-friendly software has come easier ability to measure these changes. This article discusses the principles of morphometry with illustrations of types of analysis (ie, area fraction, object counting, shape and size analyses, and mutliparametric analyses) using examples of these applications with discussions of error sources and limitations of morphometry.

Reduction in numerical synapse density in chick (Gallus domesticus) dorsal hippocampus following transient cerebral ischaemia

Transient forebrain ischaemia was induced by a two-vessel occlusion method in the domestic chick. One week post-surgery, hippocampal tissue was processed for electron microscopy and synapse density assessed using the disector technique. Hippocampal volume was estimated using image analysis of serial coronal cryostat sections. The density of asymmetric synapses was significantly reduced (27%; P < 0.005) in ischaemic chicks. This appears to be a real reduction as hippocampal volume was not significantly decreased.

Effects of light hatching on synapse number and size in the intermediate and medial part of the hyperstriatum ventrale of the domestic chick

The effects of pre-hatch light exposure on synaptic development in the intermediate and medial part of the hyperstriatum ventrale (IMHV) of the chick brain were investigated. Quantitative electron microscopical techniques were used to determine the size and numerical density of synapses and it was seen that in light hatched chicks there was a significant increase in the density of synapses in the left IMHV but that the size of synapses in these birds was decreased. These results provide a link between synaptic development and plasticity.