Assessment of calcium-binding proteins (Parvalbumin and Calbindin D-28K) and perineuronal nets in normal and scrapie-affected adult sheep brains

Histological and Immunohistochemical Investigation of the Cerebellum in Porcupine and Guinea Pig

The present study was designed to investigate the cerebellum histology and immunohistochemistry in porcupine (Hystrix cristata) and guinea pig (Cavia porcellus). Two adult porcupines and two adult guinea pigs were used. For general histology, crystal violet and Luxol fast blue stains were applied. For immunohistochemistry, myelin-associated glycoprotein (MAG), neurofilament 200 (NF200), calbindin D-28K, and glial fibrillary-associated protein (GFAP) were investigated. The cerebellar cortex in both species was composed of three cellular layers: molecular, granular, and Purkinje cell (PC) layers. Purkinje cells in the porcupine showed a purple-colored and dark blue-colored cytoplasm in reaction to the crystal violet and Luxol fast blue staining, respectively. In the guinea pig, PC has a uniform reaction to the Luxol fast blue with dark-blue-colored cytoplasm. However, in response to the crystal violet, some PC with dark-purple cytoplasm showed stronger reaction than other PC which showed light-purple cytoplasm. The PC layer in some folia of the porcupine cerebellum was composed of 2-3 layers. The expression rates of calbindin D-28K, MAG, GFAP, and NF200 in the porcupine cerebellum were determined to be 19%, 42.5%, 62%, and 30%, respectively. These values were determined to be 27%, 34%, 43.5%, and 31.5%, respectively, in the guinea pig cerebellum.

An Extracellular Perspective on CNS Maturation: Perineuronal Nets and the Control of Plasticity

During restricted time windows of postnatal life, called critical periods, neural circuits are highly plastic and are shaped by environmental stimuli. In several mammalian brain areas, from the cerebral cortex to the hippocampus and amygdala, the closure of the critical period is dependent on the formation of perineuronal nets. Perineuronal nets are a condensed form of an extracellular matrix, which surrounds the soma and proximal dendrites of subsets of neurons, enwrapping synaptic terminals. Experimentally disrupting perineuronal nets in adult animals induces the reactivation of critical period plasticity, pointing to a role of the perineuronal net as a molecular brake on plasticity as the critical period closes. Interestingly, in the adult brain, the expression of perineuronal nets is remarkably dynamic, changing its plasticity-associated conditions, including memory processes. In this review, we aimed to address how perineuronal nets contribute to the maturation of brain circuits and the regulation of adult brain plasticity and memory processes in physiological and pathological conditions.

Chronic fluoxetine treatment impairs motivation and reward learning by affecting neuronal plasticity in the central amygdala

BACKGROUND AND PURPOSE

The therapeutic effects of fluoxetine are believed to be due to increasing neuronal plasticity and reversing some learning deficits. Nevertheless, a growing amount of evidence shows adverse effects of this drug on cognition and some forms of neuronal plasticity.

EXPERIMENTAL APPROACH

To study the effects of chronic fluoxetine treatment, we combine an automated assessment of motivation and learning in mice with an investigation of neuronal plasticity in the central amygdala and basolateral amygdala. We use immunohistochemistry to visualize neuronal types and perineuronal nets, along with DI staining to assess dendritic spine morphology. Gel zymography is used to test fluoxetine's impact on matrix metalloproteinase-9, an enzyme involved in synaptic plasticity.

KEY RESULTS

We show that chronic fluoxetine treatment in non-stressed mice increases perineuronal nets-dependent plasticity in the basolateral amygdala, while impairing MMP-9-dependent plasticity in the central amygdala. Further, we illustrate how the latter contributes to anhedonia and deficits of reward learning. Behavioural impairments are accompanied by alterations in morphology of dendritic spines in the central amygdala towards an immature state, most likely reflecting animals' inability to adapt. We strengthen the link between the adverse effects of fluoxetine and its influence on MMP-9 by showing that behaviour of MMP-9 knockout animals remains unaffected by the drug.

CONCLUSION AND IMPLICATIONS

Chronic fluoxetine treatment differentially affects various forms of neuronal plasticity, possibly explaining its opposing effects on brain and behaviour. These findings are of immediate clinical relevance since reported side effects of fluoxetine pose a potential threat to patients.

An updated investigation on the dromedary camel cerebellum (Camelus dromedarius) with special insight into the distribution of calcium-binding proteins

Studying the cerebella of different animals is important to expand the knowledge about the cerebellum. Studying the camel cerebellum was neglected even though the recent research in the middle east and Asia. Therefore, the present study was designed to achieve a detailed description of the morphology and the cellular organization of the camel cerebellum. Because of the high importance of the calcium ions as a necessary moderator the current work also aimed to investigate the distribution of calcium binding proteins (CaBP) such as calbindin D-28K (CB), parvalbumin (PV) and calretinin (CR) in different cerebellar cells including the non-traditional neurons. The architecture of camel cerebellum, as different mammals, consists of the medulla and three layered-cortex. According to our observation the cells in the granular layer were not crowded and many spaces were observed. CB expression was the highest by Purkinje cells including their dendritic arborization. In addition to its expression by the inhibitory interneurons (basket, stellate and Golgi neurons), it is also expressed by the excitatory granule cells. PV was expressed by Purkinje cells, including their primary arborization, and by the molecular layer cells. CR immunoreactivity (-ir) was obvious in almost all cell layers with varying degrees, however a weak or any expression by the Purkinje cells. The molecular layer cells and the Golgi and the non traditional large neurons of the granular layer showed the strongest CR-ir. Granule neurons showed moderate immunoreactivity for CB and CR. In conclusion, the results of the current study achieved a complete map for the neurochemical organization of CaBP expression and distribution by different cells in the camel cerebellum.

Loss of interneurons and disruption of perineuronal nets in the cerebral cortex following hypoxia-ischaemia in near-term fetal sheep

Hypoxia-ischaemia (HI) in term infants is a common cause of brain injury and neurodevelopmental impairment. Development of gamma-aminobutyric acid (GABA)ergic circuitry in the cerebral cortex is a critical event in perinatal brain development. Perineuronal nets (PNNs) are specialised extracellular matrix structures that surround GABAergic interneurons, and are important for their function. Herein, we hypothesised that HI would reduce survival of cortical interneurons and disrupt PNNs in a near-term fetal sheep model of global cerebral ischaemia. Fetal sheep (0.85 gestation) received sham occlusion (n = 5) or 30 min of reversible cerebral ischaemia (HI group; n = 5), and were recovered for 7 days. Expression of interneurons (glutamate decarboxylase [GAD]⁺; parvalbumin [PV]⁺) and PNNs (Wisteria floribunda agglutinin, WFA) was assessed in the parasagittal cortex by immunohistochemistry. HI was associated with marked loss of both GAD⁺ and PV⁺ cortical interneurons (all layers of the parasagittal cortex and layer 6) and PNNs (layer 6). The expression and integrity of PNNs was also reduced on surviving GAD⁺ interneurons. There was a trend towards a linear correlation of the proportion of GAD⁺ neurons that were WFA⁺ with seizure burden (r² = 0.76, p = 0.0534). Overall, these data indicate that HI may cause deficits in the cortical GABAergic system involving loss of interneurons and disruption of PNNs, which may contribute to the range of adverse neurological outcomes following perinatal brain injury.

Abolished perineuronal nets and altered parvalbumin-immunoreactivity in the nucleus reticularis thalami of wildtype and 3xTg mice after experimental stroke

Treatment strategies for ischemic stroke are still limited, since numerous attempts were successful only in preclinical research but failed under clinical condition. To overcome this translational roadblock, clinical relevant stroke models should consider co-morbidities, age-related effects and the complex neurovascular unit (NVU) concept. The NVU includes neurons, vessels and glial cells with astrocytic endfeet in close relation to the extracellular matrix (ECM). However, the role of the ECM after stroke-related tissue damage is poorly understood and mostly neglected for treatment strategies. This study is focused on alterations of perineuronal nets (PNs) as ECM constituents and parvalbumin-containing GABAergic neurons in mice with emphasis on the nucleus reticularis thalami (NRT) in close proximity to the ischemic lesion as induced by a filament-based stroke model. One day after ischemia onset, immunofluorescence-based quantitative analyses revealed drastically declined PNs in the ischemia-affected NRT from 3- and 12-month-old wildtype and co-morbid triple-transgenic (3xTg) mice with Alzheimer-like alterations. Parvalbumin-positive cells decreased numerically in the ischemia-affected NRT, while staining intensity did not differ between the affected and non-affected hemisphere. Additional qualitative analyses demonstrated ischemia-induced loss of PNs and allocated neuropil ECM immunoreactive for aggrecan and neurocan, and impaired immunoreactivity for calbindin, the potassium channel subunit Kv3.1b and the glutamate decarboxylase isoforms GAD65 and GAD67 in the NRT. In conclusion, these data confirm PNs as highly sensitive constituents of the ECM along with impaired neuronal integrity of GABAergic neurons. Therefore, specific targeting of ECM components might appear as a promising strategy for future treatment strategies in stroke.

Calbindin D28k distribution in neurons and reactive gliosis in cerebellar cortex of natural Rabies virus-infected cattle

Rabies has been an enigmatic disease because microscopic findings in central nervous system tissues do not always correlate well with the severity of the clinical illness. Immunohistochemical staining of the calcium-binding protein calbindin (specifically CbD28k) seems to be the technique most used to identify Purkinje neurons under normal and pathological conditions. In the present work, we evaluated CbD28k immunoreactivity in the cerebellar cortex of normal and natural Rabies virus (RABV)-infected cattle. We examined brains from 3 normal cows and from 6 crossbreed cattle with a histologic diagnosis of rabies. Samples were taken from the cerebral cortex, cerebellum, hippocampus, and brainstem. Immunohistochemistry was carried out using the following primary antibodies: anti-RABV, anti-GFAP, and anti-CbD28k. In the cerebellar cortex, RABV infection caused the loss of CbD28k immunostaining in Purkinje cells; some large interneurons in the granular layer maintained their positive CbD28k immunoreaction. The identification of this loss of CbD28k reactivity in cerebellar Purkinje cells of RABV-infected cattle presents a potentially valuable tool to explore the impairment of Ca(2+) homeostasis. In addition, this may become a useful method to identify specific molecular alterations associated with the higher prevalence of Negri bodies in Purkinje cells of cattle. Furthermore, we detected the presence of rabies viral antigens in different regions of the central nervous system, accompanied by microglial proliferation and mild reactive astrogliosis.

Protective Properties of Neural Extracellular Matrix

The extracellular matrix (ECM) of the central nervous system (CNS) occupies a large part of the neural tissue. It serves a variety of functions ranging from support of cell migration and regulating synaptic transmission and plasticity to the active modulation of the neural tissue after injury. In addition, evidence for neuroprotective properties of ECM components has accumulated more recently. In contrast to other connective tissues, the central nervous ECM is mainly composed of glycosaminoglycans, which can be present unbound in the form of hyaluronan or bound to proteins, thus forming proteoglycans. A subtype of this molecular family are the chondroitin sulphate proteoglycans (CSPGs), which are composed of a core protein that carries at least one covalently bound glycosaminoglycan side chain with a certain degree of sulphation. Several studies could show neuroprotective features of CSPGs against excitotoxicity, amyloid-ß toxicity, or oxidative stress. Recently, we could provide evidence for a neuroprotective function of a specialized form of ECM, the so-called perineuronal net ensheathing a subtype of neurons. Here, we will give an overview on recently emerging aspects of neuroprotective properties of CSPGs and perineuronal nets that might be relevant for our understanding on the distribution and progression of brain pathology and future perspectives toward modifying neurodegenerative diseases.

ECM in brain aging and dementia

An essential component of the brain extracellular space is the extracellular matrix contributing to the spatial assembly of cells by binding cell-surface adhesion molecules, supporting cell migration, differentiation, and tissue development. The most interesting and complex functions of the central nervous system are the abilities to encode new information (learning) and to store this information (memory). The creation of perineuronal nets, consisting mostly of chondroitin sulfate proteoglycans, stabilizes the synapses and memory trails and forms protective shields against neurodegenerative processes but terminates plasticity and the potential for recovery of the tissue. Age-related changes in the extracellular matrix composition and the extracellular space volume and permissivity are major determinants of the onset and development of the most common neurodegenerative disorder, Alzheimer's disease. In this regard, heparan sulfate proteoglycans, involved in amyloid clearance from the brain, play an important role in Alzheimer's disease and other types of neurodegeneration. Additional key players in the modification of the extracellular matrix are matrix metalloproteinases. Recent studies show that the extracellular matrix and matrix metalloproteinases are important regulators of plasticity, learning, and memory and might be involved in different neurological disorders like epilepsy, schizophrenia, addiction, and dementia. The identification of molecules and mechanisms that modulate these processes is crucial for the understanding of brain function and dysfunction and for the design of new therapeutic approaches targeting the molecular mechanism underlying these neurological disorders.

Neurochemical mapping of the human hippocampus reveals perisynaptic matrix around functional synapses in Alzheimer's disease

Perineuronal matrix is an extracellular protein scaffold to shape neuronal responsiveness and survival. Whilst perineuronal nets engulf the somatodendritic axis of neurons, axonal coats are focal extracellular protein aggregates surrounding individual synapses. Here, we addressed the chemical identity and subcellular localization of both perineuronal and perisynaptic matrices in the human hippocampus, whose neuronal circuitry is progressively compromised in Alzheimer's disease. We hypothesized that (1) the cellular expression sites of chondroitin sulphate proteoglycan-containing extracellular matrix associate with specific neuronal identities, reflecting network dynamics, and (2) the regional distribution and molecular composition of axonal coats must withstand Alzheimer's disease-related modifications to protect functional synapses. We show by epitope-specific antibodies that the perineuronal protomap of the human hippocampus is distinct from other mammals since pyramidal cells but not calretinin(+) and calbindin(+) interneurons, neurochemically classified as novel neuronal subtypes, lack perineuronal nets. We find that cartilage link protein-1 and brevican-containing matrices form isolated perisynaptic coats, engulfing both inhibitory and excitatory terminals in the dentate gyrus and entorhinal cortex. Ultrastructural analysis revealed that presynaptic neurons contribute components of perisynaptic coats via axonal transport. We demonstrate, by combining biochemical profiling and neuroanatomy in Alzheimer's patients and transgenic (APdE9) mice, the preserved turnover and distribution of axonal coats around functional synapses along dendrite segments containing hyperphosphorylated tau and in amyloid-β-laden hippocampal microdomains. We conclude that the presynapse-driven formation of axonal coats is a candidate mechanism to maintain synapse integrity under neurodegenerative conditions.

Medulla oblongata transcriptome changes during presymptomatic natural scrapie and their association with prion-related lesions

BACKGROUND

The pathogenesis of natural scrapie and other prion diseases is still poorly understood. Determining the variations in the transcriptome in the early phases of the disease might clarify some of the molecular mechanisms of the prion-induced pathology and allow for the development of new biomarkers for diagnosis and therapy. This study is the first to focus on the identification of genes regulated during the preclinical phases of natural scrapie in the ovine medulla oblongata (MO) and the association of these genes with prion deposition, astrocytosis and spongiosis.

RESULTS

A custom microarray platform revealed that 86 significant probes had expression changes greater than 2-fold. From these probes, we identified 32 genes with known function; the highest number of regulated genes was included in the phosphoprotein-encoding group. Genes encoding extracellular marker proteins and those involved in the immune response and apoptosis were also differentially expressed. In addition, we investigated the relationship between the gene expression profiles and the appearance of the main scrapie-associated brain lesions. Quantitative Real-time PCR was used to validate the expression of some of the regulated genes, thus showing the reliability of the microarray hybridization technology.

CONCLUSIONS

Genes involved in protein and metal binding and oxidoreductase activity were associated with prion deposition. The expression of glial fibrillary acidic protein (GFAP) was associated with changes in the expression of genes encoding proteins with oxidoreductase and phosphatase activity, and the expression of spongiosis was related to genes encoding extracellular matrix components or transmembrane transporters. This is the first genome-wide expression study performed in naturally infected sheep with preclinical scrapie. As in previous studies, our findings confirm the close relationship between scrapie and other neurodegenerative diseases.

Neuropathological changes correlate temporally but not spatially with selected neuromodulatory responses in natural scrapie

AIM

Neuropathological changes classically associated with sheep scrapie do not always correlate with clinical disease. We aimed to determine if selected neuromodulatory responses were altered during the course of the infection as it has been described in Creutzfeldt-Jakob disease and experimental bovine spongiform encephalopathy.

METHODS

Hemi-brains from healthy sheep and natural scrapie cases at two stages of infection were examined for biochemical alterations related to the expression of type I metabotropic glutamatergic receptors (mGluR(1) ) and type I adenosine receptors I (A(1) R), and of selected downstream intermediate signalling targets. Immunohistochemistry for different scrapie-related neuropathological changes was performed in the contralateral hemi-brains.

RESULTS

PrP(d) deposition, spongiform change, astrocytosis and parvalbumin expression were significantly altered in brains from clinically affected sheep compared with preclinical cases and negative controls; the latter also showed significantly higher immunoreactivity for synaptophysin than clinical cases. Between clinically affected and healthy sheep, no differences were found in the protein levels of mGluR(1) , while phospholipase Cβ1 expression in terminally ill sheep was increased in some brain areas but decreased in others. Adenyl cyclase 1 and A(1) R levels were significantly lower in various brain areas of affected sheep. No abnormal biochemical expression levels of these markers were found in preclinically infected sheep.

CONCLUSIONS

These findings point towards an involvement of mGluR(1) and A(1) R downstream pathways in natural scrapie. While classical prion disease lesions and neuromodulatory responses converge in some affected regions, they do not do so in others suggesting that there are independent regulatory factors for distinct degenerative and neuroprotective responses.

Gene expression profiling and association with prion-related lesions in the medulla oblongata of symptomatic natural scrapie animals

The pathogenesis of natural scrapie and other prion diseases remains unclear. Examining transcriptome variations in infected versus control animals may highlight new genes potentially involved in some of the molecular mechanisms of prion-induced pathology. The aim of this work was to identify disease-associated alterations in the gene expression profiles of the caudal medulla oblongata (MO) in sheep presenting the symptomatic phase of natural scrapie. The gene expression patterns in the MO from 7 sheep that had been naturally infected with scrapie were compared with 6 controls using a Central Veterinary Institute (CVI) custom designed 4×44K microarray. The microarray consisted of a probe set on the previously sequenced ovine tissue library by CVI and was supplemented with all of the Ovis aries transcripts that are currently publicly available. Over 350 probe sets displayed greater than 2-fold changes in expression. We identified 148 genes from these probes, many of which encode proteins that are involved in the immune response, ion transport, cell adhesion, and transcription. Our results confirm previously published gene expression changes that were observed in murine models with induced scrapie. Moreover, we have identified new genes that exhibit differential expression in scrapie and could be involved in prion neuropathology. Finally, we have investigated the relationship between gene expression profiles and the appearance of the main scrapie-related lesions, including prion protein deposition, gliosis and spongiosis. In this context, the potential impacts of these gene expression changes in the MO on scrapie development are discussed.

Changes in HSP gene and protein expression in natural scrapie with brain damage

Heat shock proteins (Hsp) perform cytoprotective functions such as apoptosis regulation and inflammatory response control. These proteins can also be secreted to the extracellular medium, acting as inflammatory mediators, and their chaperone activity permits correct folding of proteins and avoids the aggregation of anomalous isoforms. Several studies have proposed the implication of Hsp in prion diseases. We analysed the gene expression and protein distribution of different members of the Hsp27, Hsp70, and Hsp90 families in the central nervous system of sheep naturally infected with scrapie. Different expression profiles were observed in the areas analysed. Whereas changes in transcript levels were not observed in the cerebellum or medulla oblongata, a significant decrease in HSP27 and HSP90 was detected in the prefrontal cortex. In contrast, HSP73 was over-expressed in diencephalons of scrapie animals. Western blotting did not reveal significant differences in Hsp90 and Hsp70 protein expression between scrapie and control animals. Expression rates identified by real-time RT-PCR and western blotting were compared with the extent of classical scrapie lesions using stepwise regression. Changes in Hsp gene and protein expression were associated with prion protein deposition, gliosis and spongiosis rather than with apoptosis. Finally, immunohistochemistry revealed intense Hsp70 and Hsp90 immunolabelling in Purkinje cells of scrapie sheep. In contrast, controls displayed little or no staining in these cells. The observed differences in gene expression and protein distribution suggest that the heat shock proteins analysed play a role in the natural form of the disease.

Consequences of dietary manganese and copper imbalance on neuronal apoptosis in a murine model of scrapie

AIMS

Copper and manganese levels are altered in mice both lacking PrPc and prion-infected brains. The aim of this study was to analyse the effects of manganese and copper imbalance on neuronal apoptosis in a scrapie-infected Tga20 mouse model.

METHODS

Immunoreactivities for the apoptotic proteins Bax and active caspase-3 were evaluated in nine regions of the brain of scrapie-infected and control Tga20 mice treated with one of several diets: depleted cooper (-Cu), loaded manganese (+Mn), depleted copper/loaded manganese (-Cu+Mn) and regular diet. Immunohistochemical determination of NeuN was used to detect possible neuronal loss.

RESULTS

Intracellular Bax detection was significantly decreased in animals fed with modified diets, particularly in those treated with copper-depleted diets. A decrease in active caspase-3 was primarily observed in animals fed with enhanced manganese diets. Our results show that the -Cu, -Cu+Mn and +Mn diets protected against apoptosis in scrapie-infected mice. However, NeuN immunolabelling quantification revealed that no diet was sufficient to arrest neuronal death.

CONCLUSIONS

With regard to apoptosis induction, the response of Tga20 mice to prion infection was similar to that reported for other mice models. Our results demonstrate the neuroprotective effects of -Cu, -Cu+Mn and +Mn diets in a murine model of scrapie. However, neuronal death induced by infection with prions seems to be independent of apoptosis marker signalling. Moreover, copper-modified diets were neuroprotective against the possible toxicity of the prion transgene in Tga20 control and infected mice even though manganese supplementation could not counteract this toxicity.

Immunohistochemical characterisation of classical scrapie neuropathology in sheep

Neuroinflammation elicited by PrP(res) (resistant prion protein [PrP]) deposits in the central nervous system (CNS) has been shown to involve cellular and oxidative stress responses in bovine spongiform encephalopathy (BSE) as well as in several murine models of transmissible spongiform encephalopathy (TSE). Additionally, deregulation of water homeostasis has been suggested to be a further component of the spongiform changes observed in TSEs. The aim of the present study was to characterize the pathogenic events occurring in the CNS of sheep with spontaneously arising classical scrapie. Brains from seven affected animals and two controls were subject to immunohistochemical and histochemical examinations. Semi-quantitative evaluation of PrP(res) deposits and spongiform changes throughout the encephalon confirmed that PrP(res) deposition elicits significant astroglial and microglial reactions, as evidenced by an increase in the number of glial cells and changes in glial cell morphology involving increased expression of vimentin. The altered expression of metallothionein and heat shock protein 25 (HSP25) suggested that this neuroinflammatory reaction entails cellular and oxidative stress responses. In contrast, there was no change in expression of the membrane-associated water channel aquaporin 1 when PrP(res) accumulated in the brain.

Structural and functional analysis of the ovine laminin receptor gene (RPSA): Possible involvement of the LRP/LR protein in scrapie response

Scrapie is a prion disease affecting sheep and goats. Susceptibility to this neurodegenerative disease shows polygenic variance. The involvement of the laminin receptor (LRP/LR) in the metabolism and propagation of prions has previously been demonstrated. In the present work, the ovine laminin receptor gene (RPSA) was isolated, characterized, and mapped to ovine chromosome OAR19q13. Real-time RT-PCR revealed a significant decrease in RPSA mRNA in cerebellum after scrapie infection. Conversely, no differences were detected in other brain regions such as diencephalon and medulla oblongata. Association analysis showed that a polymorphism reflecting the presence of a RPSA pseudogene was overrepresented in a group of sheep resistant to scrapie infection. No amino acid change in the LRP/LR protein was found in the 126 sheep analyzed. However, interesting amino acid positions (241, 272, and 290), which could participate in the species barrier to scrapie and maybe to other transmissible spongiform encephalopathies, were identified by comparing LRP/LR sequences from various mammals with variable levels of resistance to scrapie.