Is rat an appropriate animal model to study the involvement of D-serine catabolism in schizophrenia? Insights from characterization of D-amino acid oxidase

D-Amino acid oxidase (DAAO; EC1.4.3.3) has been proposed to play a main role in the degradation of D-serine, an allosteric activator of the N-methyl-D-aspartate-type glutamate receptor in the human brain, and to be associated with the onset of schizophrenia. To prevent excessive D-serine degradation, novel drugs for schizophrenia treatment based on DAAO inhibition were designed and tested on rats. However, the properties of rat DAAO are unknown and various in vivo trials have demonstrated the effects of DAAO inhibitors on d-serine concentration in rats. In the present study, rat DAAO was efficiently expressed in Escherichia coli. The recombinant enzyme was purified as an active, 40 kDa monomeric flavoenzyme showing the basic properties of the dehydrogenase-oxidase class of flavoproteins. Rat DAAO differs significantly from the human counterpart because: (a) it possesses a different substrate specificity; (b) it shows a lower kinetic efficiency, mainly as a result of a low substrate affinity; (c) it differs in affinity for the binding of classical inhibitors; (d) it is a stable monomer in the absence of an active site ligand; and (e) it interacts with the mammalian protein modulator pLG72 yielding a ~100 kDa complex in addition to the ~200 kDa one, as formed by the human DAAO. Furthermore, the concentration of endogenous D-serine in U87 glioblastoma cells was not affected by transfection with rat DAAO, whereas it was significantly decreased when expressing the human homologue. These results raise doubt on the use of the rat as a model system for testing new drugs against schizophrenia and indicate a different physiological function of DAAO in rodents and humans.     

ECVAM: desperately needed or superfluous? An animal welfare perspective

Eurogroup for Animal Welfare is the umbrella organisation of the major animal welfare organisations in Europe. Whereas its long-term goal is the complete replacement of animal experiments by methods that do not involve pain, suffering or distress in animals, it is also committed to any reasonable effort to reduce and refine animal experiments, as long as these continue to be carried out. Eurogroup therefore supports the activities of ECVAM, and it acknowledges the contributions to animal protection in various areas of animal use for scientific purposes made by ECVAM to date. Eurogroup is not satisfied with the number of alternative methods accepted in the past, but it sees the main responsibility for the slow progress as being outside ECVAM. The insufficient involvement of ECVAM by the EU Commission in various issues that would require its competence is also a matter of concern to Eurogroup.     

An animal model for oroantral communications: a pilot study with Göttingen minipigs

A pilot study was performed to investigate whether the G?ttingen minipig is a suitable animal model for creating and closing oroantral communications (OACs) and to test whether these defects can be closed with a biodegradable polyurethane (PU) foam. In three adult minipigs, an OAC was created on both sides of the maxilla. The left side was closed by a standard surgical buccal flap procedure, the right side by applying a PU foam. The pigs were killed after two weeks, one month and three months, respectively. Postmortem and histological examination showed that an OAC was created in only one of six cases. In the remaining cases, the infraorbital canal was perforated instead of the floor of the maxillary sinus. It was concluded that the G?ttingen minipig is not a suitable animal model for OAC investigations. As a result, the closure of OACs with a biodegradable PU could not be evaluated.     

Is there an ideal animal model for SARS?

The outbreak of severe acute respiratory syndrome (SARS) in 2003 was controlled by public health measures at a time when specific interventions such as antiviral drugs, vaccines and immunotherapy were not available. Since then, several animal models have been developed for the study of SARS and, although no model replicates the human disease in all aspects, the use of animal models for SARS has led to the establishment of several important principles for vaccine and immunotherapy. Consistency and reproducibility of findings in a given model must be demonstrated to establish the superiority of one model over others. Here, we suggest aspects of an ideal animal model for studies of SARS pathogenesis and vaccine development and present our assessment of the strengths and limitations of the current animal models for SARS.     

Potential role of α-synuclein in neurodegeneration: studies in a rat animal model

Neuronal protein α-synuclein (α-syn) is an essential player in the development of neurodegenerative diseases called synucleinopathies. A spontaneous autosomal recessive rat model for neurodegeneration was developed in our laboratory. These rats demonstrate progressive increases in α-syn in the brain mesencephalon followed by loss of dopaminergic terminals in the basal ganglia (BG) and motor impairments. The severity of pathology is directly related to the overexpression of α-syn and parallel decrease in dopamine (DA) level in the striatum (ST) of affected rats. The neurodegeneration in this model is characterized by the presence of perikarya and neurites Lewis bodies (LB) and diffuse marked accumulation of perikaryal α-syn in the substantia nigra (SN), brain stem (BS), and striatum (ST) along with neuronal loss. Light and ultrastructural analyses revealed that the process of neuronal degeneration is a 'dying back' type. The disease process is accompanied by gliosis and release of inflammatory cytokines. This neurodegeneration is a multisystemic disease and implicate α-syn as a major factor in the pathogenesis of this inherited autosomal recessive animal model. Decrease dopamine (DA) and overexpression of α-syn in the brain mesencephalon may provide a naturally occurring animal model for Parkinson's disease (PD) and other synucleinopathies that reproduces significant pathological, neurochemical, and behavioral features of the human disease.     

TRP's: links to schizophrenia?

Schizophrenia is a chronic psychiatric disorder the cause of which is unknown. It is considered to be a neurodevelopmental disorder that results from an interaction of genetic and environmental factors. Direct evidence for links between schizophrenia and TRP channels is lacking. However, several aspects of the pathophysiology of the disorder point to a possible involvement of TRP channels. In this review evidence for links between TRP channels and schizophrenia with respect to neurodevelopment, dopaminergic and cannabinoid systems, thermoregulation, and sensory processes, is discussed. Investigation of these links holds the prospect of a new understanding of schizophrenia with resultant therapeutic advances.     

Construction of rat spinal cord injury model based on Allen’s animal model

The aim of this study is to explore the construction of rat spinal cord injury model guided by Allen's model. Methods: Male rats aged 4–5 weeks and weighing about 250 g are selected as subjects in the Animal Laboratory Center of XX Hospital. Rats are divided into two groups, which are experimental group 1 and experimental group 2, respectively, so as to construct spinal cord injury model in rats. The first group is given 300 g.cm hitting force of T10 spinal cord, and the second group is given 500 g.cm hitting force of T10 spinal cord. Within 25 days after spinal cord injury in Allen's rats, the survival, neurological function, diet, motor ability, tactile ability and auditory ability of the two groups are monitored and evaluated daily. Results: In terms of survival, the survival rate of rats in group 1 is 85%, while that of rats in group 2 is 21%, and there is a concentrated death phenomenon in group 2. In terms of neurological function recovery, experimental group 1 is stable and gets 7 points and experimental group 2 is stable and gets 3 points. In terms of diet, the experimental group 1 is stable and gets 5 points and the experimental group 2 is stable and gets 2 points. In terms of motor ability, the experimental group 1 is stable and gets 5 points and the experimental group 2 is stable and gets 2 points. In tactile sense, experimental group 1 is stable and gets 17 points and experimental group 2 is stable and gets 12 points. It can be seen that the post-operative recovery ability of the experimental group 1 is better than that of the experimental group 2. Conclusion: Under the guidance of Allen's model, compared with the group 2, the experimental group 1 of the rat spinal cord injury model has better recovery in each index. It can be seen that the smaller impact strength is more beneficial to the recovery of rats after spinal cord injury surgery.     

Where do animal alpha-amylases come from? An interkingdom trip

Alpha-amylases are widely found in eukaryotes and prokaryotes. Few amino acids are conserved among these organisms, but at an intra-kingdom level, conserved protein domains exist. In animals, numerous conserved stretches are considered as typical of animal alpha-amylases. Searching databases, we found no animal-type alpha-amylases outside the Bilateria. Instead, we found in the sponge Reniera sp. and in the sea anemone Nematostella vectensis, alpha-amylases whose most similar cognate was that of the amoeba Dictyostelium discoideum. We found that this "Dictyo-type" alpha-amylase was shared not only by these non-Bilaterian animals, but also by other Amoebozoa, Choanoflagellates, and Fungi. This suggested that the Dictyo-type alpha-amylase was present in the last common ancestor of Unikonts. The additional presence of the Dictyo-type in some Ciliates and Excavates, suggests that horizontal gene transfers may have occurred among Eukaryotes. We have also detected putative interkingdom transfers of amylase genes, which obscured the historical reconstitution. Several alternative scenarii are discussed.     

Microeukaryotes in animal and plant microbiomes: Ecologies of disease?

Studies of animal and plant microbiomes are burgeoning, but the majority of these focus on bacteria and rarely include microeukaryotes other than fungi. However, there is growing evidence that microeukaryotes living on and in larger organisms (e.g. plants, animals, macroalgae) are diverse and in many cases abundant. We present here a new combination of ‘anti-metazoan’ primers: 574*f–UNonMet_DB that amplify a wide diversity of microeukaryotes including some groups that are difficult to amplify using other primer combinations. While many groups of microeukaryotic parasites are recognised, myriad other microeukaryotes are associated with hosts as previously unknown parasites (often genetically divergent so difficult to amplify using standard PCR primers), opportunistic parasites, commensals, and other ecto- and endo-symbionts, across the ‘symbiotic continuum'. These fulfil a wide range of roles from pathogenesis to mutually beneficial symbioses, but mostly their roles are unknown and likely fall somewhere along this spectrum, with the potential to switch the nature of their interactions with the host under different conditions. The composition and dynamics of host-associated microbial communities are also increasingly recognised as important moderators of host health. This ‘pathobiome’ approach to understanding disease is beginning to supercede a one-pathogen-one-disease paradigm, which cannot sufficiently explain many disease scenarios.     

The evolution of early animal embryos: conservation or divergence?

There is a remarkable similarity in the appearance of groups of animal species during periods of their embryonic development. This classic observation has long been viewed as an emphatic realization of the principle of common descent. Despite the importance of embryonic conservation as a unifying concept, models seeking to predict and explain different patterns of conservation have remained in contention. Here, we focus on early embryonic development and discuss several lines of evidence, from recent molecular data, through developmental networks to life-history strategies, that indicate that early animal embryos are not highly conserved. Bringing this evidence together, we argue that the nature of early development often reflects adaptation to diverse ecological niches. Finally, we synthesize old and new ideas to propose a model that accounts for the evolutionary process by which embryos have come to be conserved.     

Evolution of Tandemly Repeated Sequences: What Happens at the End of an Array?

Tandemly repeated sequences are a major component of the eukaryotic genome. Although the general characteristics of tandem repeats have been well documented, the processes involved in their origin and maintenance remain unknown. In this study, a region on the paternal sex ratio (PSR) chromosome was analyzed to investigate the mechanisms of tandem repeat evolution. The region contains a junction between a tandem array of PSR2 repeats and a copy of the retrotransposon NATE, with other dispersed repeats (putative mobile elements) on the other side of the element. Little similarity was detected between the sequence of PSR2 and the region of NATE flanking the array, indicating that the PSR2 repeat did not originate from the underlying NATE sequence. However, a short region of sequence similarity (11/15 bp) and an inverted region of sequence identity (8 bp) are present on either side of the junction. These short sequences may have facilitated nonhomologous recombination between NATE and PSR2, resulting in the formation of the junction. Adjacent to the junction, the three most terminal repeats in the PSR2 array exhibited a higher sequence divergence relative to internal repeats, which is consistent with a theoretical prediction of the unequal exchange model for tandem repeat evolution. Other NATE insertion sites were characterized which show proximity to both tandem repeats and complex DNAs containing additional dispersed repeats. An ``accretion model' is proposed to account for this association by the accumulation of mobile elements at the ends of tandem arrays and into ``islands' within arrays. Mobile elements inserting into arrays will tend to migrate into islands and to array ends, due to the turnover in the number of intervening repeats. Received: 18 August 1997 / Accepted: 18 September 1998     

Immune dysregulation and self-reactivity in schizophrenia: do some cases of schizophrenia have an autoimmune basis?

Schizophrenia affects 1% of the world's population, but its cause remains obscure. Numerous theories have been proposed regarding the cause of schizophrenia, ranging from developmental or neurodegenerative processes or neurotransmitter abnormalities to infectious or autoimmune processes. In this review, findings suggestive of immune dysregulation and reactivity to self in patients with schizophrenia are examined with reference to criteria for defining whether or not a human disease is autoimmune in origin. Associations with other autoimmune diseases and particular MHC haplotypes, increased serum levels of autoantibodies, and in vivo and in vitro replication of some of the functional and ultrastructural abnormalities of schizophrenia by transfer of autoantibodies from the sera of patients with schizophrenia suggest that, in some patients at least, autoimmune mechanisms could play a role in the development of disease. Recent findings regarding specific autoimmune responses directed against neurotransmitter receptors in the brain in patients with schizophrenia will also be reviewed.     

Origin of glutaminyl-tRNA synthetase: An example of palimpsest?

Sequence data and evolutionary arguments suggest that a similarity may exist between the C-terminal end of glutaminyl-tRNA synthetase (GlnRS) and the catalytic domain of glutamine amidotransferases (GATs). If true, this would seem to imply that the amidation reaction of the Glu-tRNA^GIn complex was the evolutionary precursor of the direct tRNA^GIn aminoacylation pathway. Since the C-terminal end of GlnRS does not now have an important functional role, it can be concluded that this sequence contains vestiges that lead us to believe that it represents a palimpsest. This sequence still conserves the remains of the evolutionary transition: amidation reaction aminoacylation reaction. This may be important in deciding which mechanism gave origin to the genetic code organization. These observations, together with results obtained by Gatti and Tzagoloff [J. Mol. Biol. (1991) 218: 557–568], lead to the hypothesis that the class I aminoacyl-tRNA synthetases (ARSs) may be homologous to the GATs of the trpG subfamily, while the class Il ARSs may be homologous to the GATs of the purF subfamily. Overall, this seems to point to the existence of an intimate evolutionary link between the proteins involved in the primitive metabolism and aminoacyl-tRNA synthetases.     

Nematophagous fungi: prospective biological control agents of animal parasitic nematodes?

The rapidly escalating problem of anthelmintic resistance and the increasing concerns of chemical residues in livestock products and the environment pose serious threats to the future of chemotherapeutic control o f animal parasitic nematodes. One possible non-chemotherapeutic approach is biological control using nemotophagous fungi. Although Gr?nvold and colleagues recently described their experiments with two nematode-destroying fungi, Arthrobotrys and Duddingtonia, this alternate control option has received relatively little research attention. Here, Peter Waller broadens the discussion to consider the fundamental problems and prospects of this non-chemotheropeutic control strategy.