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

Excitatory and inhibitory imbalances in the trisynaptic pathway in the hippocampus in schizophrenia: a postmortem ultrastructural study

BACKGROUND

A preponderance of evidence suggests that the hippocampus is a key region of dysfunction in schizophrenia. Neuroimaging and other studies indicate a relationship between hippocampal dysfunction and the degree of psychosis. Clinical data indicate hyperactivity in the hippocampus that precedes the onset of psychosis, and is correlated with symptom severity. In this study, we sought to identify circuitry at the electron microscopic level that could contribute to region-specific imbalances in excitation and inhibition in the hippocampus in schizophrenia. We used postmortem tissue from the anterior hippocampus from patients with schizophrenia and matched controls. Using stereological techniques, we counted and measured synapses, postsynaptic densities (PSDs), and evaluated size, number and optical density of mitochondria and parvalbumin-containing interneurons in key nodes of the trisynaptic pathway. Compared to controls, the schizophrenia group had decreased numbers of inhibitory synapses in CA3 and increased numbers of excitatory synapses in CA1; together, this indicates deficits in inhibition and an increase in excitation. The thickness of the PSD was larger in excitatory synapses in CA1, suggesting greater synaptic strength. In the schizophrenia group, there were fewer mitochondria in the dentate gyrus and a decrease in the optical density, a measure of functional integrity, in CA1. The number and optical density of parvalbumin interneurons were lower in CA3. The results suggest region-specific increases in excitatory circuitry, decreases in inhibitory neurotransmission and fewer or damaged mitochondria. These results are consistent with the hyperactivity observed in the hippocampus in schizophrenia in previous studies.

Evidence for upregulation of excitatory synaptic transmission in the substantia nigra in Schizophrenia: a postmortem ultrastructural study

The dopamine hypothesis of schizophrenia suggests that psychotic symptoms originate from dysregulation of dopaminergic activity, which may be controlled by upstream innervation. We hypothesized that we would find anatomical evidence for the hyperexcitability seen in the SN. We examined and quantified synaptic morphology, which correlates with function, in the postmortem substantia nigra (SN) from 15 schizophrenia and 12 normal subjects. Synapses were counted using stereological techniques and classified based on the morphology of the post-synaptic density (PSD) and the presence or absence of a presynaptic density. The density and proportion of excitatory synapses was higher in the schizophrenia group than in controls, while the proportion (but not density) of inhibitory synapses was lower. We also detected in the schizophrenia group an increase in density of synapses with a PSD of intermediate thickness, which may represent excitatory synapses. The density of synapses with presynaptic densities was similar in both groups. The density of synapses with mixed morphologies was higher in the schizophrenia group than in controls. The human SN contains atypical synaptic morphology. We found an excess amount and proportion of excitatory synapses in the SN in schizophrenia that could result in hyperactivity and drive the psychotic symptoms of schizophrenia. The sources of afferent excitatory inputs to the SN arise from the subthalamic nucleus, the pedunculopontine nucleus, and the ventral tegmental area (VTA), areas that could be the source of excess excitation. Synapses with mixed morphologies may represent inputs from the VTA, which release multiple transmitters.

Ultrastructural evidence for glutamatergic dysregulation in schizophrenia

The aim of this paper is to summarize ultrastructural evidence for glutamatergic dysregulation in several linked regions in postmortem schizophrenia brain. Following a brief summary of glutamate circuitry and how synapses are identified at the electron microscopic (EM) level, we will review EM pathology in the cortex and basal ganglia. We will include the effects of antipsychotic drugs and the relation of treatment response. We will discuss how these findings support or confirm other postmortem findings as well as imaging results. Briefly, synaptic and mitochondrial density in anterior cingulate cortex was decreased in schizophrenia, versus normal controls (NCs), in a selective layer specific pattern. In dorsal striatum, increases in excitatory synaptic density were detected in caudate matrix, a compartment associated with cognitive and motor function, and in the putamen patches, a region associated with limbic function and in the core of the nucleus accumbens. Patients who were treatment resistant or untreated had significantly elevated numbers of excitatory synapses in limbic striatal areas in comparison to NCs and responders. Protein levels of vGLUT2, found in subcortical glutamatergic neurons, were increased in the nucleus accumbens in schizophrenia. At the EM level, schizophrenia subjects had an increase in density of excitatory synapses in several areas of the basal ganglia. In the substantia nigra, the protein levels of vGLUT2 were elevated in untreated patients compared to NCs. The density of inhibitory synapses was decreased in schizophrenia versus NCs. In schizophrenia, glutamatergic synapses are differentially affected depending on the brain region, treatment status, and treatment response.

Synaptic environment and extrasynaptic glutamate signals: The quest continues

Behaviour of a mammal relies on the brain's excitatory circuits equipped with glutamatergic synapses. In most cases, glutamate escaping from the synaptic cleft is rapidly buffered and taken up by high-affinity transporters expressed by nearby perisynaptic astroglial processes (PAPs). The spatial relationship between glutamatergic synapses and PAPs thus plays a crucial role in understanding glutamate signalling actions, yet its intricate features can only be fully appreciated using methods that operate beyond the diffraction limit of light. Here, we examine principal aspects pertaining to the receptor actions of glutamate, inside and outside the synaptic cleft in the brain, where the organisation of synaptic micro-physiology and micro-environment play a critical part. In what conditions and how far glutamate can escape the synaptic cleft activating its target receptors outside the immediate synapse has long been the subject of debate. Evidence is also emerging that neuronal activity- and astroglia-dependent glutamate spillover actions could be important across the spectrum of cognitive functions This article is part of the special issue on 'Glutamate Receptors - The Glutamatergic Synapse'.

Basic quantitative morphological methods applied to the central nervous system

Generating numbers has become an almost inevitable task associated with studies of the morphology of the nervous system. Numbers serve a desire for clarity and objectivity in the presentation of results and are a prerequisite for the statistical evaluation of experimental outcomes. Clarity, objectivity, and statistics make demands on the quality of the numbers that are not met by many methods. This review provides a refresher of problems associated with generating numbers that describe the nervous system in terms of the volumes, surfaces, lengths, and numbers of its components. An important aim is to provide comprehensible descriptions of the methods that address these problems. Collectively known as design-based stereology, these methods share two features critical to their application. First, they are firmly based in mathematics and its proofs. Second and critically underemphasized, an understanding of their mathematical background is not necessary for their informed and productive application. Understanding and applying estimators of volume, surface, length or number does not require more of an organizational mastermind than an immunohistochemical protocol. And when it comes to calculations, square roots are the gravest challenges to overcome. Sampling strategies that are combined with stereological probes are efficient and allow a rational assessment if the numbers that have been generated are "good enough." Much may be unfamiliar, but very little is difficult. These methods can no longer be scapegoats for discrepant results but faithfully produce numbers on the material that is assessed. They also faithfully reflect problems that associated with the histological material and the anatomically informed decisions needed to generate numbers that are not only valid in theory. It is within reach to generate practically useful numbers that must integrate with qualitative knowledge to understand the function of neural systems.

Cognitive aging is associated with redistribution of synaptic weights in the hippocampus

Behaviors that rely on the hippocampus are particularly susceptible to chronological aging, with many aged animals (including humans) maintaining cognition at a young adult-like level, but many others the same age showing marked impairments. It is unclear whether the ability to maintain cognition over time is attributable to brain maintenance, sufficient cognitive reserve, compensatory changes in network function, or some combination thereof. While network dysfunction within the hippocampal circuit of aged, learning-impaired animals is well-documented, its neurobiological substrates remain elusive. Here we show that the synaptic architecture of hippocampal regions CA1 and CA3 is maintained in a young adult-like state in aged rats that performed comparably to their young adult counterparts in both trace eyeblink conditioning and Morris water maze learning. In contrast, among learning-impaired, but equally aged rats, we found that a redistribution of synaptic weights amplifies the influence of autoassociational connections among CA3 pyramidal neurons, yet reduces the synaptic input onto these same neurons from the dentate gyrus. Notably, synapses within hippocampal region CA1 showed no group differences regardless of cognitive ability. Taking the data together, we find the imbalanced synaptic weights within hippocampal CA3 provide a substrate that can explain the abnormal firing characteristics of both CA3 and CA1 pyramidal neurons in aged, learning-impaired rats. Furthermore, our work provides some clarity with regard to how some animals cognitively age successfully, while others' lifespans outlast their "mindspans."

Quantitative and Qualitative Evaluation of Photoreceptor Synapses in Developing, Degenerating and Regenerating Retinas

Quantitative and qualitative evaluation of synapses is crucial to understand neural connectivity. This is particularly relevant now, in view of the recent advances in regenerative biology and medicine. There is an urgent need to evaluate synapses to access the extent and functionality of reconstructed neural network. Most of the currently used synapse evaluation methods provide only all-or-none assessments. However, very often synapses appear in a wide spectrum of transient states such as during synaptogenesis or neural degeneration. Robust evaluation of synapse quantity and quality is therefore highly sought after. In this paper we introduce QUANTOS, a new method that can evaluate the number, likelihood, and maturity of photoreceptor ribbon synapses based on graphical properties of immunohistochemistry images. QUANTOS is composed of ImageJ Fiji macros, and R scripts which are both open-source and free software. We used QUANTOS to evaluate synaptogenesis in developing and degenerating retinas, as well as de novo synaptogenesis of mouse iPSC-retinas after transplantation to a retinal degeneration mouse model. Our analysis shows that while mouse iPSC-retinas are largely incapable of forming synapses in vitro, they can form extensive synapses following transplantation. The de novo synapses detected after transplantation seem to be in an intermediate state between mature and immature compared to wildtype retina. Furthermore, using QUANTOS we tested whether environmental light can affect photoreceptor synaptogenesis. We found that the onset of synaptogenesis was earlier under cyclic light (LD) condition when compared to constant dark (DD), resulting in more synapses at earlier developmental stages. The effect of light was also supported by micro electroretinography showing larger responses under LD condition. The number of synapses was also increased after transplantation of mouse iPSC-retinas to rd1 mice under LD condition. Our new probabilistic assessment of synapses may prove to be a valuable tool to gain critical insights into neural-network reconstruction and help develop treatments for neurodegenerative disorders.

Conditional deletion of Neurog1 in the cerebellum of postnatal mice delays inhibitory interneuron maturation

The transcriptional programs that drive the generation of diverse GABAergic neuron populations from their common progenitor pools in the developing cerebellum remain unclear. Neurog1 is a pro-neural basic helix-loop-helix transcription factor expressed in GABAergic progenitor cells in the ventricular zone (VZ) of embryos and subsequently in the presumptive white matter (pWM) tracts of developing postnatal mice. Genetic inducible fate-mapping labels Purkinje cells and all inhibitory interneuron cell types of the cerebellar cortex. As conventional Neurog1^Neo knockout (KO) mice are neonatal lethal, we generated Neurog1^loxP mutant mice to examine the effects of conditional Neurog1 deletion on the postnatal development of the cerebellum. Targeted Neurog1 loss-of-function in the developing cerebellum does not result in significant differences in cerebellar morphology or in the number of GABAergic neurons in the cerebellar cortex of mice at postnatal day 21 (P21). To determine the effects of Neurog1 deletion on GABAergic progenitors, we quantified rates of cell proliferation and cell cycle progression or re-entry in embryonic Neurog1^Neo and postnatal Neurog1^loxP mutants. The data revealed no significant effect of Neurog1 loss-of-function on embryonic day 12.5 (E12.5) VZ progenitors or on P5 and P6 progenitors in the pWM at P7. However, 4-5 day pulse-labeling of P5 and P6 progenitors revealed reductions in inhibitory interneuron dispersal from the pWM to the cerebellar cortex in P10 conditional Neurog1^loxP/loxP KO mice. Thus, our conditional Neurog1 KO approach reveals a requirement for Neurog1 activity in inhibitory interneuron cell dispersal from pWM tracts in the developing cerebellum of postnatal mice.

Total Number Is Important: Using the Disector Method in Design-Based Stereology to Understand the Structure of the Rodent Brain

The advantages of using design-based stereology in the collection of quantitative data, have been highlighted, in numerous publications, since the description of the disector method by Sterio (1984). This review article discusses the importance of total number derived with the disector method, as a key variable that must continue to be used to understand the rodent brain and that such data can be used to develop quantitative networks of the brain. The review article will highlight the huge impact total number has had on our understanding of the rodent brain and it will suggest that neuroscientists need to be aware of the increasing number of studies where density, not total number, is the quantitative measure used. It will emphasize that density can result in data that is misleading, most often in an unknown direction, and that we run the risk of this type of data being accepted into the collective neuroscience knowledge database. It will also suggest that design-based stereology using the disector method, can be used alongside recent developments in electron microscopy, such as serial block-face scanning electron microscopy (SEM), to obtain total number data very efficiently at the ultrastructural level. Throughout the article total number is discussed as a key parameter in understanding the micro-networks of the rodent brain as they can be represented as both anatomical and quantitative networks.

Coordinated Plasticity of Synapses and Astrocytes Underlies Practice-Driven Functional Vicariation in Peri-Infarct Motor Cortex

Motor rehabilitative training after stroke can improve motor function and promote topographical reorganization of remaining motor cortical movement representations, but this reorganization follows behavioral improvements. A more detailed understanding of the neural bases of rehabilitation efficacy is needed to inform therapeutic efforts to improve it. Using a rat model of upper extremity impairments after ischemic stroke, we examined effects of motor rehabilitative training at the ultrastructural level in peri-infarct motor cortex. Extensive training in a skilled reaching task promoted improved performance and recovery of more normal movements. This was linked with greater axodendritic synapse density and ultrastructural characteristics of enhanced synaptic efficacy that were coordinated with changes in perisynaptic astrocytic processes in the border region between head and forelimb areas of peri-infarct motor cortex. Disrupting synapses and motor maps by infusions of anisomycin (ANI) into anatomically reorganized motor, but not posterior parietal, cortex eliminated behavioral gains from rehabilitative training. In contrast, ANI infusion in the equivalent cortical region of intact animals had no effect on reaching skills. These results suggest that rehabilitative training efficacy for improving manual skills is mediated by synaptic plasticity in a region of motor cortex that, before lesions, is not essential for manual skills, but becomes so as a result of the training. These findings support that experience-driven synaptic structural reorganization underlies functional vicariation in residual motor cortex after motor cortical infarcts.SIGNIFICANCE STATEMENT Stroke is a leading cause of long-term disability. Motor rehabilitation, the main treatment for physical disability, is of variable efficacy. A better understanding of neural mechanisms underlying effective motor rehabilitation would inform strategies for improving it. Here, we reveal synaptic underpinnings of effective motor rehabilitation. Rehabilitative training improved manual skill in the paretic forelimb and induced the formation of special synapse subtypes in coordination with structural changes in astrocytes, a glial cell that influences neural communication. These changes were found in a region that is nonessential for manual skill in intact animals, but came to mediate this skill due to training after stroke. Therefore, motor rehabilitation efficacy depends on synaptic changes that enable remaining brain regions to assume new functions.

Comparative ultrastructural features of excitatory synapses in the visual and frontal cortices of the adult mouse and monkey

The excitatory glutamatergic synapse is the principal site of communication between cortical pyramidal neurons and their targets, a key locus of action of many drugs, and highly vulnerable to dysfunction and loss in neurodegenerative disease. A detailed knowledge of the structure of these synapses in distinct cortical areas and across species is a prerequisite for understanding the anatomical underpinnings of cortical specialization and, potentially, selective vulnerability in neurological disorders. We used serial electron microscopy to assess the ultrastructural features of excitatory (asymmetric) synapses in the layers 2-3 (L2-3) neuropil of visual (V1) and frontal (FC) cortices of the adult mouse and compared findings to those in the rhesus monkey (V1 and lateral prefrontal cortex [LPFC]). Analyses of multiple ultrastructural variables revealed four organizational features. First, the density of asymmetric synapses does not differ between frontal and visual cortices in either species, but is significantly higher in mouse than in monkey. Second, the structural properties of asymmetric synapses in mouse V1 and FC are nearly identical, by stark contrast to the significant differences seen between monkey V1 and LPFC. Third, while the structural features of postsynaptic entities in mouse and monkey V1 do not differ, the size of presynaptic boutons are significantly larger in monkey V1. Fourth, both presynaptic and postsynaptic entities are significantly smaller in the mouse FC than in the monkey LPFC. The diversity of synaptic ultrastructural features demonstrated here have broad implications for the nature and efficacy of glutamatergic signaling in distinct cortical areas within and across species.

Mammillary Bodies in Alzheimer's Disease: A Golgi and Electron Microscope Study

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by irreversible memory decline, concerning no rarely spatial memory and orientation, alterations of the mood and personality, gradual loss of motor skills, and substantial loss of capacities obtained by previous long education. We attempted to describe the morphological findings of the mammillary bodies in early cases of AD. Samples were processed for electron microscopy and silver impregnation techniques. The nuclei of the mammillary bodies demonstrated a substantial decrease in the neuronal population and marked abbreviation of dendritic arbors. Decrease in spine density and morphological abnormalities of dendritic spines was also seen. Synaptic alterations were prominent. Alzheimer's pathology, such as deposits of amyloid-β peptide and neurofibrillary degeneration, was minimal. Electron microscopy revealed mitochondrial alterations and fragmentation of Golgi apparatus, associated frequently with synaptic pathology.

Microcirculation of the brain: morphological assessment in degenerative diseases and restoration processes

Brain microcirculation plays an important role in the pathogenesis of various brain diseases. Several specific features of the circulation in the brain and its functions deserve special attention. The brain is extremely sensitive to hypoxia, and brain edema is more dangerous than edema in other tissues. Brain vessels are part of the blood-brain barrier, which prevents the penetration of some of the substances in the blood into the brain tissue. Herein, we review the processes of angiogenesis and the changes that occur in the brain microcirculation in the most prevalent neurodegenerative diseases. There are no uniform vascular changes in the neurodegenerative diseases. In some cases, the vascular changes are secondary consequences of the pathological process, but they could also be involved in the pathogenesis of the primary disease and contribute to the degeneration of neurons, based on their quantitative characteristics. Additionally, we described the stereological methods that are most commonly used for generating qualitative and quantitative data to assess changes in the microvascular bed of the brain.

Decreased synaptic and mitochondrial density in the postmortem anterior cingulate cortex in schizophrenia

Schizophrenia (SZ) is a mental illness characterized by psychosis, negative symptoms, and cognitive deficits. The anterior cingulate cortex (ACC), a structurally and functionally diverse region, is one of several brain regions that is abnormal in SZ. The present study compared synaptic organization and mitochondrial number and morphology in postmortem ACC in SZ versus normal control (NC). Total synaptic density in the combined ACC was decreased in SZ, to 72% of normal controls (NCs), due to selective decreases in axospinous synapses, both asymmetric (excitatory) and symmetric (inhibitory). These changes were present in layers 3 and 5/6. The density of mitochondria in all axon terminals combined in SZ was decreased to 64% of NC. In layer 3, mitochondrial density was decreased only in terminals forming asymmetric synapses with spines, while in layers 5/6 mitochondrial density was decreased in terminals forming symmetric synapses with spines and dendrites. The proportion of terminals making symmetric synapses that contained mitochondria was significantly lower in SZ than in NCs, especially for symmetric axospinous synapses. The number of mitochondria per neuronal somata was decreased in the ACC in SZ compared to NCs; this finding was present in layers 5-6. The size of mitochondria in neuronal somata and throughout the neuropil was similar in SZ and NCs. Our results, though preliminary, are well supported by the literature, and support an anatomical substrate for some of the altered executive functions found in SZ.

Post-mortem brain analyses of the Lothian Birth Cohort 1936: extending lifetime cognitive and brain phenotyping to the level of the synapse

INTRODUCTION

Non-pathological, age-related cognitive decline varies markedly between individuals andplaces significant financial and emotional strain on people, their families and society as a whole.Understanding the differential age-related decline in brain function is critical not only for the development oftherapeutics to prolong cognitive health into old age, but also to gain insight into pathological ageing suchas Alzheimer's disease. The Lothian Birth Cohort of 1936 (LBC1936) comprises a rare group of people forwhom there are childhood cognitive test scores and longitudinal cognitive data during older age, detailedstructural brain MRI, genome-wide genotyping, and a multitude of other biological, psycho-social, andepidemiological data. Synaptic integrity is a strong indicator of cognitive health in the human brain;however, until recently, it was prohibitively difficult to perform detailed analyses of synaptic and axonalstructure in human tissue sections. We have adapted a novel method of tissue preparation at autopsy toallow the study of human synapses from the LBC1936 cohort in unprecedented morphological andmolecular detail, using the high-resolution imaging techniques of array tomography and electronmicroscopy. This allows us to analyze the brain at sub-micron resolution to assess density, proteincomposition and health of synapses. Here we present data from the first donated LBC1936 brain andcompare our findings to Alzheimer's diseased tissue to highlight the differences between healthy andpathological brain ageing.

RESULTS

Our data indicates that compared to an Alzheimer's disease patient, the cognitively normalLBC1936 participant had a remarkable degree of preservation of synaptic structures. However,morphological and molecular markers of degeneration in areas of the brain associated with cognition(prefrontal cortex, anterior cingulate cortex, and superior temporal gyrus) were observed.

CONCLUSIONS

Our novel post-mortem protocol facilitates high-resolution neuropathological analysis of the well-characterized LBC1936 cohort, extending phenotyping beyond cognition and in vivo imaging to nowinclude neuropathological changes, at the level of single synapses. This approach offers an unprecedentedopportunity to study synaptic and axonal integrity during ageing and how it contributes to differences in agerelatedcognitive change.

Repeated dose of ketamine effect to the rat hippocampus tissue

AIM

We aimed to determine the neurotoxic effect of repeated ketamine administration on brain tissue and if neurotoxic effect was present, whether this effect continued 16 days later using histological stereological method, a quantitative and objective method.

MATERIALS AND METHODS

Female rats were divided into three groups, each containing five rats. Rats in Group I were given 0.9% saline solution 4 times a day for 5 days. The rats in Groups II and III were given ketamine as intraperitoneal injections. Rats in Groups I and II were sacrificed on 5(th) day while the ones in Group III on 21(st) day. Cornu ammonis (CA) and gyrus dentatus (GD) regions in hippocampus tissue of rats were studied using optic fractionation method.

FINDINGS

There were significantly less number of cells in hippocampal CA and GD regions of rats from Groups II and III compared to the ones from Group I. Difference in cell number was also significantly higher in Group III than in Group II, but this difference was not as pronounced as the one between Groups III and I.

CONCLUSION

Repeated ketamine doses caused neurotoxicity in rat hippocampus.

The hypothalamus in Alzheimer's disease: a Golgi and electron microscope study

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by irreversible decline of mental faculties, emotional and behavioral changes, loss of motor skills, and dysfunction of autonomic nervous system and disruption of circadian rhythms (CRs). We attempted to describe the morphological findings of the hypothalamus in early cases of AD, focusing our study mostly on the suprachiasmatic nucleus (SCN), the supraoptic nucleus (SON), and the paraventricular nucleus (PVN). Samples were processed for electron microscopy and silver impregnation techniques. The hypothalamic nuclei demonstrated a substantial decrease in the neuronal population, which was particularly prominent in the SCN. Marked abbreviation of dendritic arborization, in association with spinal pathology, was also seen. The SON and PVN demonstrated a substantial number of dystrophic axons and abnormal spines. Alzheimer's pathology, such as deposits of amyloid-β peptide and neurofibrillary degeneration, was minimal. Electron microscopy revealed mitochondrial alterations in the cell body and the dendritic branches. The morphological alterations of the hypothalamic nuclei in early cases of AD may be related to the gradual alteration of CRs and the instability of autonomic regulation.

Functional and structural deficits at accumbens synapses in a mouse model of Fragile X

Fragile X is the most common cause of inherited intellectual disability and a leading cause of autism. The disease is caused by mutation of a single X-linked gene called fmr1 that codes for the Fragile X mental retardation protein (FMRP), a 71 kDa protein, which acts mainly as a translation inhibitor. Fragile X patients suffer from cognitive and emotional deficits that coincide with abnormalities in dendritic spines. Changes in spine morphology are often associated with altered excitatory transmission and long-term plasticity, the most prominent deficit in fmr1-/y mice. The nucleus accumbens, a central part of the mesocortico-limbic reward pathway, is now considered as a core structure in the control of social behaviors. Although the socio-affective impairments observed in Fragile X suggest dysfunctions in the accumbens, the impact of the lack of FMRP on accumbal synapses has scarcely been studied. Here we report for the first time a new spike timing-dependent plasticity paradigm that reliably triggers NMDAR-dependent long-term potentiation (LTP) of excitatory afferent inputs of medium spiny neurons (MSN) in the nucleus accumbens core region. Notably, we discovered that this LTP was completely absent in fmr1-/y mice. In the fmr1-/y accumbens intrinsic membrane properties of MSNs and basal excitatory neurotransmission remained intact in the fmr1-/y accumbens but the deficit in LTP was accompanied by an increase in evoked AMPA/NMDA ratio and a concomitant reduction of spontaneous NMDAR-mediated currents. In agreement with these physiological findings, we found significantly more filopodial spines in fmr1-/y mice by using an ultrastructural electron microscopic analysis of accumbens core medium spiny neuron spines. Surprisingly, spine elongation was specifically due to the longer longitudinal axis and larger area of spine necks, whereas spine head morphology and postsynaptic density size on spine heads remained unaffected in the fmr1-/y accumbens. These findings together reveal new structural and functional synaptic deficits in Fragile X.

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.

Blockade of excitatory synaptogenesis with proximal dendrites of dentate granule cells following rapamycin treatment in a mouse model of temporal lobe epilepsy

Inhibiting the mammalian target of rapamycin (mTOR) signaling pathway with rapamycin blocks granule cell axon (mossy fiber) sprouting after epileptogenic injuries, including pilocarpine-induced status epilepticus. However, it remains unclear whether axons from other types of neurons sprout into the inner molecular layer and synapse with granule cell dendrites despite rapamycin treatment. If so, other aberrant positive-feedback networks might develop. To test this possibility stereological electron microscopy was used to estimate the numbers of excitatory synapses in the inner molecular layer per hippocampus in pilocarpine-treated control mice, in mice 5 days after pilocarpine-induced status epilepticus, and after status epilepticus and daily treatment beginning 24 hours later with rapamycin or vehicle for 2 months. The optical fractionator method was used to estimate numbers of granule cells in Nissl-stained sections so that numbers of excitatory synapses in the inner molecular layer per granule cell could be calculated. Control mice had an average of 2,280 asymmetric synapses in the inner molecular layer per granule cell, which was reduced to 63% of controls 5 days after status epilepticus, recovered to 93% of controls in vehicle-treated mice 2 months after status epilepticus, but remained at only 63% of controls in rapamycin-treated mice. These findings reveal that rapamycin prevented excitatory axons from synapsing with proximal dendrites of granule cells and raise questions about the recurrent excitation hypothesis of temporal lobe epilepsy.

Clift MJ, Blank F, Petri-Fink A, Rothen-Rutishauser B. Quantification of nanoparticles at the single-cell level: an overview about state-of-the-art techniques and their limitations

With the increasing production and use of engineered nanoparticles it is crucial that their interaction with biological systems is understood. Due to the small size of nanoparticles, their identification and localization within single cells is extremely challenging. Therefore, various cutting-edge techniques are required to detect and to quantify metals, metal oxides, magnetic, fluorescent, as well as electron-dense nanoparticles. Several techniques will be discussed in detail, such as inductively coupled plasma atomic emission spectroscopy, flow cytometry, laser scanning microscopy combined with digital image restoration, as well as quantitative analysis by means of stereology on transmission electron microscopy images. An overview will be given regarding the advantages of those visualization/quantification systems, including a thorough discussion about limitations and pitfalls.

Evidence for Alzheimer's disease-linked synapse loss and compensation in mouse and human hippocampal CA1 pyramidal neurons

Alzheimer's disease (AD) is associated with alterations in the distribution, number, and size of inputs to hippocampal neurons. Some of these changes are thought to be neurodegenerative, whereas others are conceptualized as compensatory, plasticity-like responses, wherein the remaining inputs reactively innervate vulnerable dendritic regions. Here, we provide evidence that the axospinous synapses of human AD cases and mice harboring AD-linked genetic mutations (the 5XFAD line) exhibit both, in the form of synapse loss and compensatory changes in the synapses that remain. Using array tomography, quantitative conventional electron microscopy, immunogold electron microscopy for AMPARs, and whole-cell patch-clamp physiology, we find that hippocampal CA1 pyramidal neurons in transgenic mice are host to an age-related synapse loss in their distal dendrites, and that the remaining synapses express more AMPA-type glutamate receptors. Moreover, the number of axonal boutons that synapse with multiple spines is significantly reduced in the transgenic mice. Through serial section electron microscopic analyses of human hippocampal tissue, we further show that putative compensatory changes in synapse strength are also detectable in axospinous synapses of proximal and distal dendrites in human AD cases, and that their multiple synapse boutons may be more powerful than those in non-cognitively impaired human cases. Such findings are consistent with the notion that the pathophysiology of AD is a multivariate product of both neurodegenerative and neuroplastic processes, which may produce adaptive and/or maladaptive responses in hippocampal synaptic strength and plasticity.

Ultrastructural localization of tyrosine hydroxylase in tree shrew nucleus accumbens core and shell

Many behavioral, physiological, and anatomical studies utilize animal models to investigate human striatal pathologies. Although commonly used, rodent striatum may not present the optimal animal model for certain studies due to a lesser morphological complexity than that of non-human primates, which are increasingly restricted in research. As an alternative, the tree shrew could provide a beneficial animal model for studies of the striatum. The gross morphology of the tree shrew striatum resembles that of primates, with separation of the caudate and putamen by the internal capsule. The neurochemical anatomy of the ventral striatum, specifically the nucleus accumbens, has never been examined. This major region of the limbic system plays a role in normal physiological functioning and is also an area of interest for human striatal disorders. The current study uses immunohistochemistry of calbindin and tyrosine hydroxylase (TH) to determine the ultrastructural organization of the nucleus accumbens core and shell of the tree shrew (Tupaia glis belangeri). Stereology was used to quantify the ultrastructural localization of TH, which displays weaker immunoreactivity in the core and denser immunoreactivity in the shell. In both regions, synapses with TH-immunoreactive axon terminals were primarily symmetric and showed no preference for targeting dendrites versus dendritic spines. The results were compared to previous ultrastructural studies of TH and dopamine in rat and monkey nucleus accumbens. Tree shrews and monkeys show no preference for the postsynaptic target in the shell, in contrast to rats which show a preference for synapsing with dendrites. Tree shrews have a ratio of asymmetric to symmetric synapses formed by TH-immunoreactive terminals that is intermediate between rats and monkeys. The findings from this study support the tree shrew as an alternative model for studies of human striatal pathologies.

N-cadherin regulates molecular organization of excitatory and inhibitory synaptic circuits in adult hippocampus in vivo

N-Cadherin and β-catenin form a transsynaptic adhesion complex required for spine and synapse development. In adulthood, N-cadherin mediates persistent synaptic plasticity, but whether the role of N-cadherin at mature synapses is similar to that at developing synapses is unclear. To address this, we conditionally ablated N-cadherin from excitatory forebrain synapses in mice starting in late postnatal life and examined hippocampal structure and function in adulthood. In the absence of N-cadherin, β-catenin levels were reduced, but numbers of excitatory synapses were unchanged, and there was no impact on number or shape of dendrites or spines. However, the composition of synaptic molecules was altered. Levels of GluA1 and its scaffolding protein PSD95 were diminished and the density of immunolabeled puncta was decreased, without effects on other glutamate receptors and their scaffolding proteins. Additionally, loss of N-cadherin at excitatory synapses triggered increases in the density of markers for inhibitory synapses and decreased severity of hippocampal seizures. Finally, adult mutant mice were profoundly impaired in hippocampal-dependent memory for spatial episodes. These results demonstrate a novel function for the N-cadherin/β-catenin complex in regulating ionotropic receptor composition of excitatory synapses, an appropriate balance of excitatory and inhibitory synaptic proteins and the maintenance of neural circuitry necessary to generate flexible yet persistent cognitive and synaptic function.

Gonadectomy increases neurogenesis in the male adolescent rhesus macaque hippocampus

New neurons are continuously produced in the subgranular zone of the adult hippocampus and can modulate hippocampal plasticity across life. Adolescence is characterized by dramatic changes in sex hormone levels, and social and emotional behaviors. It is also an age for increased risk of psychiatric disorders, including schizophrenia, which may involve altered hippocampal neurogenesis. The extent to which testosterone and other testicular hormones modulate hippocampal neurogenesis and adolescent behavioral development is unclear. This study aimed to determine if removal of testicular hormones during adolescence alters neurogenesis in the male rhesus macaque hippocampus. We used stereology to examine levels of cell proliferation, cell survival and neuronal differentiation in late adolescent male rhesus macaques (4.6-yrs old) that had previously been gonadectomized or sham operated prior to puberty (2.4-yrs old). While the absence of adolescent testicular hormones had no effect on cell proliferation, cell survival was increased by 65% and indices of immature neuronal differentiation were increased by 56% in gonadectomized monkeys compared to intact monkeys. We show for the first time that presence of circulating testicular hormones, including testosterone, may decrease neuronal survival in the primate hippocampus during adolescence. Our findings are in contrast to existing studies in adults where testosterone tends to be a pro-survival factor and demonstrate that testicular hormones may reduce hippocampal neurogenesis during the age typical of schizophrenia onset.

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.

Fine structural organization of the hemiellipsoid body of the land hermit crab, Coenobita clypeatus

Electron microscopical observations of the hemiellipsoid bodies of the land hermit crab Coenobita clypeatus resolve microglomerular synaptic complexes that are comparable to those observed in the calyces of insect mushroom bodies and which characterize olfactory inputs onto intrinsic neurons. In an adult hermit crab, intrinsic neurons and one class of efferent neurons originate from neuronal somata of globuli cells covering the hemiellipsoid bodies. Counts of their nucleoli show that about 120,000 globuli cells supply each hemiellipsoid body in an adult hermit crab. This number is comparable to the number of globuli cells supplying mushroom bodies of certain insects, such as honey bees and cockroaches. Counts of axons in tracts leading from the olfactory lobes to the hemiellipsoid bodies resolve 20,000 afferent axons, however, an order of magnitude greater than known for any insect. These afferent axons provide numerous swollen varicosities, each presynaptic to many small profiles, and thus comparable to the microglomeruli that characterize insect mushroom body calyces. Also, common to mushroom bodies and hemiellipsoid bodies are arrangements of intrinsic neurons, afferent neurons containing dense core vesicles, and systems of serial synaptic complexes that relate to postsynaptic profiles of efferent neurons. Together, the ultrastructural organization of the hemiellipsoid bodies of C. clypeatus supports the proposition that this center may share a common origin with the insect mushroom body despite obvious divergent evolution of overall shape.

TrakEM2 software for neural circuit reconstruction

A key challenge in neuroscience is the expeditious reconstruction of neuronal circuits. For model systems such as Drosophila and C. elegans, the limiting step is no longer the acquisition of imagery but the extraction of the circuit from images. For this purpose, we designed a software application, TrakEM2, that addresses the systematic reconstruction of neuronal circuits from large electron microscopical and optical image volumes. We address the challenges of image volume composition from individual, deformed images; of the reconstruction of neuronal arbors and annotation of synapses with fast manual and semi-automatic methods; and the management of large collections of both images and annotations. The output is a neural circuit of 3d arbors and synapses, encoded in NeuroML and other formats, ready for analysis.

Effects of electromagnetic radiation on spatial memory and synapses in rat hippocampal CA1

In this study, we investigated the effects of mobile phone radiation on spatial learning, reference memory, and morphology in related brain regions. After the near-field radiation (0.52-1.08 W/kg) was delivered to 8-week-old Wistar rats 2 hours per day for 1 month, behavioral changes were examined using the Morris water maze. Compared with the sham-irradiated rats, the irradiated rats exhibited impaired performance. Morphological changes were investigated by examining synaptic ultrastructural changes in the hippocampus. Using the physical dissector technique, the number of pyramidal neurons, the synaptic profiles, and the length of postsynaptic densities in the CA1 region were quantified stereologically. The morphological changes included mitochondrial degenerations, fewer synapses, and shorter postsynaptic densities in the radiated rats. These findings indicate that mobile phone radiation can significantly impair spatial learning and reference memory and induce morphological changes in the hippocampal CA1 region.

Parecoxib mitigates spatial memory impairment induced by sevoflurane anesthesia in aged rats

BACKGROUND

Inflammation in brain plays a critical role in the pathogenesis of cognitive impairment. Anti-inflammatory therapy may thus constitute a novel approach for associated cognitive dysfunction. The present study investigated the effects of parecoxib in the prevention of cognitive impairments induced by sevoflurane in aged rats.

METHODS

Sixty-six aged rats were divided randomly into three groups: control group (n = 22, sham anesthesia), sevoflurane group (n = 22, received 2% sevoflurane for 5 h) and parecoxib group (n = 22, received intraperitoneal injections of 10 mg/kg parecoxib and then exposed to 2% sevoflurane for 5 h). Spatial learning performance was tested by Morris water maze. The expression of cyclooxygenase-2 protein and ultrastructure of synapse in hippocampus were measured.

RESULTS

Sevoflurane anesthesia impaired the spatial learning and memory in aged rats. Compared with sevoflurane group, parecoxib group showed shorter escape latency and more number of crossings over the previous platform area. Furthermore, parecoxib treatment also significantly prevented the synaptic changes induced by sevoflurane.

CONCLUSION

Parecoxib mitigates spatial memory impairment induced by sevoflurane anesthesia in aged rats. The synaptic morphometry change may be one of the mechanisms involved in learning and memory deficit.

Reorganization of synaptic inputs to the hypothalamic paraventricular nucleus during chronic psychogenic stress in rats

BACKGROUND

Chronic stress in humans precipitates hyper-reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis and triggers symptoms associated with certain forms of depression. Reorganization of neuronal networks has been implicated in development of depression, however it remained unknown how chronic exposure to psychogenic challenges affects excitatory and inhibitory inputs to corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus that govern neuroendocrine stress response.

METHODS

Rats (n = 32) were exposed for 21 days to chronic variable stress and their behavioral (sucrose preference) and hormonal (corticosterone) responses were followed together with electron microscopic stereologic analysis of excitatory and gamma-aminobutyric acid (GABA)-containing, inhibitory synapses on the CRH synthesizing neurons.

RESULTS

Chronic stress in rats resulted in weight loss, anhedonia, and hyperactivity of hypothalamic-pituitary-adrenocortical axis. Following 3 weeks' exposure to variable psychologic stressors the number of synapses has been doubled in the paraventricular nucleus. Asymmetrical excitatory as well as GABAergic inhibitory synaptic contacts were increased on CRH neurons; however, the excitatory/inhibitory input ratio remained constant. In response to chronic stress, we found rearrangement of inhibitory GABA-containing inputs with the increase of contacts on dendrites and decrease at the soma region of CRH neurons.

CONCLUSIONS

Significant remodeling of synaptic contacts was found on CRH neurons in response to chronic stress. This morphologic plasticity might be related to the hyperactivity of the HPA axis and to development of stress-related psychopathologies such as depression.

Immunohistochemical localization of enkephalin in the human striatum: a postmortem ultrastructural study

Within the basal ganglia, the functionally defined region referred to as the striatum contains a subset of GABAergic medium spiny neurons expressing the neuropeptide enkephalin. Although the major features of ultrastructural enkephalin localization in striatum have been characterized among various species, its ultrastructural organization has never been studied in the human brain. Human striatal tissue was obtained from the Maryland and Alabama Brain Collections from eight normal controls. The brains were received and fixed within 8 h of death allowing for excellent preservation suitable for electron microscopy. Tissue from the dorsal striatum was processed for enkephalin immunoreactivity and prepared for electron microscopy. General morphology of the dorsal striatum was consistent with light microscopy in human. The majority of neurons labeled with enkephalin was medium-sized and had a large nonindented nucleus with a moderate amount of cytoplasm, characteristic of medium spiny neurons. Of the spines receiving synapses in dorsal striatum, 39% were labeled for enkephalin and were of varied morphologies. Small percentages (2%) of synapses were formed by labeled axon terminals. Most (82%) labeled terminals formed symmetric synapses. Enkephalin-labeled terminals showed no preference toward spines or dendrites for postsynaptic targets, whereas in rat and monkey, the vast majority of synapses in the neuropil are formed with dendritic shafts. Thus, there is an increase in the prevalence of axospinous synapses formed by enkephalin-labeled axon terminals in human compared with other species. Quantitative differences in synaptic features were also seen between the caudate nucleus and the putamen in the human tissue.

Automated detection and segmentation of synaptic contacts in nearly isotropic serial electron microscopy images

We describe a protocol for fully automated detection and segmentation of asymmetric, presumed excitatory, synapses in serial electron microscopy images of the adult mammalian cerebral cortex, taken with the focused ion beam, scanning electron microscope (FIB/SEM). The procedure is based on interactive machine learning and only requires a few labeled synapses for training. The statistical learning is performed on geometrical features of 3D neighborhoods of each voxel and can fully exploit the high z-resolution of the data. On a quantitative validation dataset of 111 synapses in 409 images of 1948×1342 pixels with manual annotations by three independent experts the error rate of the algorithm was found to be comparable to that of the experts (0.92 recall at 0.89 precision). Our software offers a convenient interface for labeling the training data and the possibility to visualize and proofread the results in 3D. The source code, the test dataset and the ground truth annotation are freely available on the website http://www.ilastik.org/synapse-detection.

Striatal mitochondria in subjects with chronic undifferentiated vs. chronic paranoid schizophrenia

Schizophrenia (SZ) is a heterogeneous disease with a spectrum of symptoms, risk factors, and etiology. Abnormalities in mitochondria, the energy-producing organelles of the cell, have been observed in mixed cohorts of subjects with SZ. The purpose of the present study was to determine if striatal mitochondria were differentially affected in two different DSM-IV subgroups of SZ. Postmortem striatal tissue was examined from normal controls (NC), chronic paranoid SZs (SZP), and chronic undifferentiated SZs (SZU). Tissue was processed for calbindin immunohistochemistry to identify striosomal compartments, prepared for electron microscopy and analyzed using stereological methods. In both caudate and putamen, the density of mitochondria in the neuropil was decreased in SZP compared to both NCs and SZU. In the putamen, both the SZP and the SZU subgroups had fewer mitochondria per synapse than did NCs. When examining patch matrix compartments, striatal compartments associated with different circuitry and function, only the matrix exhibited changes. In the caudate matrix, the SZP subgroup had fewer mitochondria in the neuropil than did the SZU and NCs. In the putamen matrix, the SZP had fewer mitochondria in the neuropil as compared to NCs, but not the SZU. The numbers of mitochondria per synapse in both the SZP and the SZU groups were similar to each other and fewer than that of NCs. A decrease in mitochondrial density in the neuropil distinguishes the SZP from the SZU subgroup, which could be associated with the symptoms of paranoia and/or could represent a protective mechanism against some of the symptoms that are less pronounced in this subtype than in the SZU subgroup such as cognitive and emotional deficits.

Mitochondria in the striatum of subjects with schizophrenia: relationship to treatment response

Schizophrenia (SZ) is a severe mental illness with neuropathology in many regions, including the striatum. The typical symptoms of this disease are psychosis (such as hallucinations and delusions), cognitive impairments, and the deficit syndrome. Not all patients respond to treatment and, in those who do, only psychotic symptoms are improved. Imaging studies support a biological distinction between treatment response and resistance, but postmortem examinations of this issue are rare. This study tests the hypotheses that abnormalities in mitochondria, the energy producing organelles in the cell, may correlate with treatment response. Postmortem striatal tissue was obtained from the Maryland Brain Collection. The density of mitochondria (in various neuropil compartments) and the number of mitochondria per synapse (all types of synapses combined) were tallied using electron microscopy and stereology in striatum from SZ subjects (rated treatment responsive or not) and normal controls. The number of mitochondria per synapse was significantly different among groups for both the caudate nucleus (P < 0.025) and putamen (P < 0.002). Compared to controls, treatment-responsive SZ subjects had a 37-43% decrease in the number of mitochondria per synapse in the caudate nucleus and putamen. In the putamen, treatment-responsive subjects also had decreases in this measure compared to treatment-resistant subjects (34%). Our results provide further support for a biological distinction between treatment response and treatment resistance in SZ. Because treatment responders have fewer mitochondria per synapse than controls, although the treatment-resistant subjects have similar results to that of controls, fewer mitochondria per synapse may be related to treatment response.

IκB kinase regulates social defeat stress-induced synaptic and behavioral plasticity

The neurobiological underpinnings of mood and anxiety disorders have been linked to the nucleus accumbens (NAc), a region important in processing the rewarding and emotional salience of stimuli. Using chronic social defeat stress, an animal model of mood and anxiety disorders, we investigated whether alterations in synaptic plasticity are responsible for the long-lasting behavioral symptoms induced by this form of stress. We hypothesized that chronic social defeat stress alters synaptic strength or connectivity of medium spiny neurons (MSNs) in the NAc to induce social avoidance. To test this, we analyzed the synaptic profile of MSNs via confocal imaging of Lucifer-yellow-filled cells, ultrastructural analysis of the postsynaptic density, and electrophysiological recordings of miniature EPSCs (mEPSCs) in mice after social defeat. We found that NAc MSNs have more stubby spine structures with smaller postsynaptic densities and an increase in the frequency of mEPSCs after social defeat. In parallel to these structural changes, we observed significant increases in IκB kinase (IKK) in the NAc after social defeat, a molecular pathway that has been shown to regulate neuronal morphology. Indeed, we find using viral-mediated gene transfer of dominant-negative and constitutively active IKK mutants that activation of IKK signaling pathways during social defeat is both necessary and sufficient to induce synaptic alterations and behavioral effects of the stress. These studies establish a causal role for IKK in regulating stress-induced adaptive plasticity and may present a novel target for drug development in the treatment of mood and anxiety disorders in humans.

Mitochondria in the striatum of subjects with schizophrenia

OBJECTIVES

Schizophrenia is a severe mental illness that manifests pathology in many brain regions, including the striatum. Among the abnormalities in schizophrenia are those related to mitochondria. The present study sought to determine whether the number of mitochondria was affected at the level of the synapse.

METHODS

Human postmortem striatum from schizophrenia subjects and controls was examined at the ultrastructural level. The density of mitochondria and synapses were tabulated using stereology.

RESULTS

There were similar overall numbers of mitochondria in the caudate nucleus and putamen of schizophrenia subjects vs. controls, but a differential distribution of existing mitochondria. Schizophrenia subjects had 26?30% fewer mitochondria per synapse compared to controls. This may contribute to the pathophysiology of the illness, may be a medication effect, or an adaptive response to normalize the high number of striatal synapses we have previously found. The higher density of mitochondria in dendrites in the caudate nucleus in certain subgroups of schizophrenia vs. controls (>34%) may be related to more synaptic inputs.

CONCLUSIONS

The role of mitochondria in the various symptoms of schizophrenia is still unclear. A comparison of schizophrenia subjects with differing symptoms or treatment response might shed light on whether differences in mitochondrial density are abnormal or adaptive.

As-rigid-as-possible mosaicking and serial section registration of large ssTEM datasets

Motivation: Tiled serial section Transmission Electron Microscopy (ssTEM) is increasingly used to describe high-resolution anatomy of large biological specimens. In particular in neurobiology, TEM is indispensable for analysis of synaptic connectivity in the brain. Registration of ssTEM image mosaics has to recover the 3D continuity and geometrical properties of the specimen in presence of various distortions that are applied to the tissue during sectioning, staining and imaging. These include staining artifacts, mechanical deformation, missing sections and the fact that structures may appear dissimilar in consecutive sections.

Results: We developed a fully automatic, non-rigid but as-rigid-as-possible registration method for large tiled serial section microscopy stacks. We use the Scale Invariant Feature Transform (SIFT) to identify corresponding landmarks within and across sections and globally optimize the pose of all tiles in terms of least square displacement of these landmark correspondences. We evaluate the precision of the approach using an artificially generated dataset designed to mimic the properties of TEM data. We demonstrate the performance of our method by registering an ssTEM dataset of the first instar larval brain of Drosophila melanogaster consisting of 6885 images.

Availability: This method is implemented as part of the open source software TrakEM2 (http://www.ini.uzh.ch/∼acardona/trakem2.html) and distributed through the Fiji project (http://pacific.mpi-cbg.de).

Contact:tomancak@mpi-cbg.de

Region-specific genetic alterations in the aging hippocampus: implications for cognitive aging

Aging is associated with cognitive decline in both humans and animals and of all brain regions, the hippocampus appears to be particularly vulnerable to senescence. Age-related spatial learning deficits result from alterations in hippocampal connectivity and plasticity. These changes are differentially expressed in each of the hippocampal fields known as cornu ammonis 1 (CA1), cornu ammonis 3 (CA3), and the dentate gyrus. Each sub-region displays varying degrees of susceptibility to aging. For example, the CA1 region is particularly susceptible in Alzheimer's disease while the CA3 region shows vulnerability to stress and glucocorticoids. Further, in animals, aging is the main factor associated with the decline in adult neurogenesis in the dentate gyrus. This review discusses the relationship between region-specific hippocampal connectivity, morphology, and gene expression alterations and the cognitive deficits associated with senescence. In particular, data are reviewed that illustrate how the molecular changes observed in the CA1, CA3, and dentate regions are associated with age-related learning deficits. This topic is of importance because increased understanding of how gene expression patterns reflect individual differences in cognitive performance is critical to the process of identifying new and clinically useful biomarkers for cognitive aging.

Cocaine- and morphine-induced synaptic plasticity in the nucleus accumbens

The critical brain areas and molecular mechanisms involved in drug abuse and dependence have been extensively studied. Drug-induced persistent behaviors such as sensitization, tolerance, or relapse, however, far outlast any previously reported mechanisms. A challenge in the field of addiction, therefore, has been to identify drug-induced changes in brain circuitry that may subserve long-lasting changes in behavior. This study examined behavioral changes and electron microscopic evidence of altered synaptic connectivity within the nucleus accumbens (NAc) following repeated administration of cocaine or morphine. The unbiased quantitative stereological physical disector method was used to estimate the number of synapses per neuron. Increases in the synapse-to-neuron ratio were found in the NAc shell of cocaine-treated (49.1%) and morphine-treated (55.1%) rats and in the NAc core of cocaine-treated animals (49.1%). This study provides direct ultrastructural evidence of drug-induced synaptic plasticity and identifies synaptic remodeling as a potential neural substrate underlying drug-induced behavioral sensitization.

Identifying neuronal lineages of Drosophila by sequence analysis of axon tracts

The Drosophila brain is formed by an invariant set of lineages, each of which is derived from a unique neural stem cell (neuroblast) and forms a genetic and structural unit of the brain. The task of reconstructing brain circuitry at the level of individual neurons can be made significantly easier by assigning neurons to their respective lineages. In this article we address the automation of neuron and lineage identification. We focused on the Drosophila brain lineages at the larval stage when they form easily recognizable secondary axon tracts (SATs) that were previously partially characterized. We now generated an annotated digital database containing all lineage tracts reconstructed from five registered wild-type brains, at higher resolution and including some that were previously not characterized. We developed a method for SAT structural comparisons based on a dynamic programming approach akin to nucleotide sequence alignment and a machine learning classifier trained on the annotated database of reference SATs. We quantified the stereotypy of SATs by measuring the residual variability of aligned wild-type SATs. Next, we used our method for the identification of SATs within wild-type larval brains, and found it highly accurate (93-99%). The method proved highly robust for the identification of lineages in mutant brains and in brains that differed in developmental time or labeling. We describe for the first time an algorithm that quantifies neuronal projection stereotypy in the Drosophila brain and use the algorithm for automatic neuron and lineage recognition.

Altered neurotransmission in the mesolimbic reward system of Girk mice

Mice lacking the Girk2 subunit of G protein-gated inwardly rectifying K+ (Girk) channels exhibit dopamine-dependent hyperactivity and elevated responses to drugs that stimulate dopamine neurotransmission. The dopamine-dependent phenotypes seen in Girk2(-/-) mice could reflect increased intrinsic excitability of or diminished inhibitory feedback to midbrain dopamine neurons, or secondary adaptations triggered by Girk2 ablation. We addressed these possibilities by evaluating Girk(-/-) mice in behavioral, electrophysiological, and cell biological assays centered on the mesolimbic dopamine system. Despite differences in the contribution of Girk1 and Girk2 subunits to Girk signaling in midbrain dopamine neurons, Girk1(-/-) and Girk2(-/-) mice exhibited comparable baseline hyperactivities and enhanced responses to cocaine. Girk ablation also correlated with altered afferent input to dopamine neurons in the ventral tegmental area. Dopamine neurons from Girk1(-/-) and Girk2(-/-) mice exhibited elevated glutamatergic neurotransmission, paralleled by increased synaptic levels of alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate glutamate receptors. In addition, synapse density, alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor levels, and glutamatergic neurotransmission were elevated in medium spiny neurons of the nucleus accumbens from Girk1(-/-) and Girk2(-/-) mice. We conclude that dopamine-dependent phenotypes in Girk2(-/-) mice are not solely attributable to a loss of Girk signaling in dopamine neurons, and likely involve secondary adaptations facilitating glutamatergic signaling in the mesolimbic reward system.

Initial loss but later excess of GABAergic synapses with dentate granule cells in a rat model of temporal lobe epilepsy

Many patients with temporal lobe epilepsy display neuron loss in the dentate gyrus. One potential epileptogenic mechanism is loss of GABAergic interneurons and inhibitory synapses with granule cells. Stereological techniques were used to estimate numbers of gephyrin-positive punctae in the dentate gyrus, which were reduced short-term (5 days after pilocarpine-induced status epilepticus) but later rebounded beyond controls in epileptic rats. Stereological techniques were used to estimate numbers of synapses in electron micrographs of serial sections processed for postembedding GABA-immunoreactivity. Adjacent sections were used to estimate numbers of granule cells and glutamic acid decarboxylase-positive neurons per dentate gyrus. GABAergic neurons were reduced to 70% of control levels short-term, where they remained in epileptic rats. Integrating synapse and cell counts yielded average numbers of GABAergic synapses per granule cell, which decreased short-term and rebounded in epileptic animals beyond control levels. Axo-shaft and axo-spinous GABAergic synapse numbers in the outer molecular layer changed most. These findings suggest interneuron loss initially reduces numbers of GABAergic synapses with granule cells, but later, synaptogenesis by surviving interneurons overshoots control levels. In contrast, the average number of excitatory synapses per granule cell decreased short-term but recovered only toward control levels, although in epileptic rats excitatory synapses in the inner molecular layer were larger than in controls. These findings reveal a relative excess of GABAergic synapses and suggest that reports of reduced functional inhibitory synaptic input to granule cells in epilepsy might be attributable not to fewer but instead to abundant but dysfunctional GABAergic synapses.

Counting Synapses Using FIB/SEM Microscopy: A True Revolution for Ultrastructural Volume Reconstruction

The advent of transmission electron microscopy (TEM) in the 1950s represented a fundamental step in the study of neuronal circuits. The application of this technique soon led to the realization that the number of synapses changes during the course of normal life, as well as under certain pathological or experimental circumstances. Since then, one of the main goals in neurosciences has been to define simple and accurate methods to estimate the magnitude of these changes. Contrary to analysing single sections, TEM reconstructions are extremely time-consuming and difficult. Therefore, most quantitative studies use stereological methods to define the three-dimensional characteristics of synaptic junctions that are studied in two dimensions. Here, to count the exact number of synapses per unit of volume we have applied a new three-dimensional reconstruction method that involves the combination of focused ion beam milling and scanning electron microscopy (FIB/SEM). We show that the images obtained with FIB/SEM are similar to those obtained with TEM, but with the advantage that FIB/SEM permits serial reconstructions of large volumes of tissue to be generated rapidly and automatically. Furthermore, we compared the estimates of the number of synapses obtained with stereological methods with the values obtained by FIB/SEM reconstructions. We concluded that FIB/SEM not only provides the actual number of synapses per volume but it is also much easier and faster to use than other currently available TEM methods. More importantly, it also avoids most of the errors introduced by stereological methods and overcomes the difficulties associated with these techniques.

Dopaminergic synapses in the caudate of subjects with schizophrenia: relationship to treatment response

The typical symptoms of schizophrenia (SZ) are psychotic symptoms (hallucinations, delusions, disorders of thought or speech, grossly disorganized behavior) as well as cognitive impairments and negative symptoms. Not all patients respond to treatment and in those who do, only psychotic symptoms are usually improved. Imaging studies have shown that SZ subjects with high striatal dopamine release are far more responsive to antipsychotic drugs than those patients who have dopamine levels lower than or comparable to that of normal controls. In the present study we hypothesized that there was a link between psychosis and the number of dopaminergic synapses in the caudate nucleus in SZ. We examined dopaminergic synapses at the electron microscopic level in postmortem caudate from cases obtained from the Maryland Brain Collection. SZs were subdivided based on treatment response or resistance. The tissue was processed for the immunocytochemical localization of tyrosine hydroxylase (TH), the synthesizing enzyme for dopamine, and prepared for electron microscopy. The density of all TH labeled synapses was 43% greater in treatment responders than in controls and 62% greater in than in treatment resistant SZ. Axodendritic, but not axospinous, TH-labeled synapses showed this increase. TH-labeled axodendritic synapses in treatment responders were elevated in density (1.95 +/- 0.093/10 microm(3)) compared to treatment resistant SZ (0.04 +/- 0.017/10 microm(3)) and controls (0.11 +/- 0.044/10 microm(3)). The results of the present study suggest that one anatomical underpinning of good treatment response may be a higher density of dopaminergic synapses and support a biological basis to treatment response and resistance. Moreover, these data have important implications for linking specific neuropathology with particular symptoms.

A systematic random sampling scheme optimized to detect the proportion of rare synapses in the neuropil

Synapses can only be morphologically identified by electron microscopy and this is often a very labor-intensive and time-consuming task. When quantitative estimates are required for pathways that contribute a small proportion of synapses to the neuropil, the problems of accurate sampling are particularly severe and the total time required may become prohibitive. Here we present a sampling method devised to count the percentage of rarely occurring synapses in the neuropil using a large sample (approximately 1000 sampling sites), with the strong constraint of doing it in reasonable time. The strategy, which uses the unbiased physical disector technique, resembles that used in particle physics to detect rare events. We validated our method in the primary visual cortex of the cat, where we used biotinylated dextran amine to label thalamic afferents and measured the density of their synapses using the physical disector method. Our results show that we could obtain accurate counts of the labeled synapses, even when they represented only 0.2% of all the synapses in the neuropil.

Increased synapses in the medial prefrontal cortex are associated with repeated amphetamine administration

Psychostimulant drug experience leads not only to long-lasting changes in behavior but also modifications in the activity and morphology of pyramidal neurons in the medial prefrontal cortex (mPFC). The objective of this study was to establish whether repeated treatment of rats with amphetamine (AMPH) is accompanied by changes in the pattern or types of synapses in the mPFC and, specifically, onto neurons that project to the lateral hypothalamus, where our earlier work has shown increased markers of neuronal activity after repeated AMPH treatment (Morshedi and Meredith [2008] Psychopharmacology (Berl) 197:179-189). Rats were treated with a behaviorally sensitizing regimen of AMPH, following which synapses in the infralimbic and prelimbic cortices of the mPFC, were analyzed with unbiased stereology (physical disector and electron microscopy). All synapses were counted and their targets were identified by standard methodological criteria. Repeated AMPH administration was associated with a significant increase in the number of asymmetric axospinous synapses, no change in axodendritic or axosomatic contacts, and no change in the total number of synapses on corticolateral hypothalamic pyramidal neurons compared to vehicle-treated rats. Therefore, behavioral sensitization as a result of repeated exposure to AMPH is accompanied by the increased formation of spine, but not dendritic, synapses onto pyramidal neurons in the mPFC.

Axospinous synaptic subtype-specific differences in structure, size, ionotropic receptor expression, and connectivity in apical dendritic regions of rat hippocampal CA1 pyramidal neurons

The morphology of axospinous synapses and their parent spines varies widely. Additionally, many of these synapses are contacted by multiple synapse boutons (MSBs) and show substantial variability in receptor expression. The two major axospinous synaptic subtypes are perforated and nonperforated, but there are several subcategories within these two classes. The present study used serial section electron microscopy to determine whether perforated and nonperforated synaptic subtypes differed with regard to their distribution, size, receptor expression, and connectivity to MSBs in three apical dendritic regions of rat hippocampal area CA1: the proximal and distal thirds of stratum radiatum, and the stratum lacunosum-moleculare. All synaptic subtypes were present throughout the apical dendritic regions, but there were several subclass-specific differences. First, segmented, completely partitioned synapses changed in number, proportion, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor expression with distance from the soma beyond that found within other perforated synaptic subtypes. Second, atypically large, nonperforated synapses showed N-methyl-D-aspartate (NMDA) receptor immunoreactivity identical to that of perforated synapses, levels of AMPA receptor expression intermediate to that of nonperforated and perforated synapses, and perforated synapse-like changes in structure with distance from the soma. Finally, MSB connectivity was highest in the proximal stratum radiatum, but only for those MSBs composed of nonperforated synapses. The immunogold data suggest that most MSBs would not generate simultaneous depolarizations in multiple neurons or spines, however, because the vast majority of MSBs are comprised of two synapses with abnormally low levels of receptor expression, or involve one synapse with a high level of receptor expression and another with only a low level.

Dopaminergic denervation and spine loss in the striatum of MPTP-treated monkeys

Striatal spine loss is a key pathological feature of human Parkinson's disease (PD) that can be induced after complete degeneration of the nigrostriatal dopaminergic system in rodent models of parkinsonism. In line with these observations, our findings reveal a significant (30-50%) reduction in spine density in both the caudate nucleus and putamen of severely DA-depleted striata of MPTP-treated monkeys; the sensorimotor post-commissural putamen being the most severely affected region for both dopamine depletion and spine loss. Using MPTP-treated monkeys with complete or partial striatal dopamine (DA) denervation, we also demonstrate that striatal spine loss is an early pathological feature of parkinsonism, which progresses along a positive rostrocaudal and mediolateral gradient in parallel with the extent of striatal dopamine denervation. Quantitative electron microscopy immunocytochemistry for D1 dopamine receptor (D1) in the striatum of control and severely DA-depleted animals revealed that both D1-immunoreactive and immunonegative spines are lost in the putamen of MPTP-treated monkeys. These data demonstrate that striatal spine loss in MPTP-treated monkeys is an early pathological event of parkinsonism, tightly correlated with the degree of nigrostriatal dopamine denervation that likely affects both direct and indirect striatofugal pathways.