Behavioral and molecular biomarkers in translational animal models for neuropsychiatric disorders

Chorioamnionitis in utero, schizophrenia in adulthood: limited current evidence-future research focus?

Background: Developmental adaptive processes during gestation that are known to be involved in permanent changes in physiology and metabolism or "early life programming" can adversely affect fetal brain development, impacting both brain structure and function.Data: Emerging evidence strongly supports the developmental origin of schizophrenia, which may potentially be a result of prenatal exposure to a diversity of factors, especially infections, in genetically predisposed subjects. Structural and functional brain changes during development of schizophrenia are determined by genetic components, altered expression of schizophrenia risk genes and epigenetic dysregulation. However, the precise mechanisms underlying these relationships remain unclear. Findings from human and animal studies suggest that inflammatory-immune responses and activation of oxidative stress pathways are crucial in mediating intrauterine infection-induced neurodevelopmental and neuropsychiatric diseases.Aim: Considering the high prevalence of intrauterine inflammation in the context of chorioamnionitis during human pregnancy and the paucity of knowledge on fetal programming of schizophrenia, this mini review aims to exclusively consolidate the current evidence supporting a potential association between chorioamnionitis and schizophrenia.

Ketogenic diet for schizophrenia: clinical implication

PURPOSE OF REVIEW

The aim of this article is to review recent findings on the efficacy of ketogenic diet in preclinical models and in patients with schizophrenia. This review will also highlight emerging evidence for compromised glucose and energy metabolism in schizophrenia, which provides a strong rationale and a potential mechanism of action for ketogenic diet.

RECENT FINDINGS

Recent transcriptomic, proteomic and metabolomic evidence from postmortem prefrontal cortical samples and in-vivo NMR spectroscopy results support the hypothesis that there is a bioenergetics dysfunction characterized by abnormal glucose handling and mitochondrial dysfunctions resulting in impaired synaptic communication in the brain of people with schizophrenia. Ketogenic diet, which provides alternative fuel to glucose for bioenergetic processes in the brain, normalizes schizophrenia-like behaviours in translationally relevant pharmacological and genetic mouse models. Furthermore, recent case studies demonstrate that ketogenic diet produces improvement in psychiatric symptoms as well as metabolic dysfunctions and body composition in patients with schizophrenia.

SUMMARY

These results support that ketogenic diet may present a novel therapeutic approach through restoring brain energy metabolism in schizophrenia. Randomized controlled clinical trials are needed to further show the efficacy of ketogenic diet as a co-treatment to manage both clinical symptoms and metabolic abnormalities inherent to the disease and resulted by antipsychotic treatment.

The Elevated Plus Maze Test for Measuring Anxiety-Like Behavior in Rodents

The elevated plus maze test is used to measure anxiety-like behavior in rodents. It can be used to gain insight into conditions such as posttraumatic stress disorder (PTSD) and other conditions marked by anxious behavior. It can also be used as a component in screening of novel compounds for anxiolytic properties. This model is based on aversion to open spaces, which is seen as the animal spending more time in the enclosed arms of the maze. This chapter describes the steps necessary for setting up and conducting the test, along with interpretation of the results.

Free Dyadic Social Interaction Test in Mice

Psychiatric disorders affect approximately one quarter of people worldwide at some point in their lifetime. This chapter provides a step-by-step guide to conduct behavioral tests in adult mice for investigations of social behavior, without the need for specific equipment. This test should allow the identification of key abnormalities in social interactions that can be followed up by targeted, more complex, behavioral analysis aimed at identification of new biomarkers and potential drug targets.

Object Burying Test for Assessment of Obsessive Compulsive Behaviors in Mice

Obsessive-compulsive disorder (OCD) can occur in several psychiatric illnesses such as autism spectrum disorders (ASD) and it is more prevalent in children. This condition is characterized by repeated and apparently meaningless behaviors such as frequent hand washing, counting, tapping, and rocking. This can disrupt normal socialization and in some cases lead to self-harm. Therefore there is interest in developing more effective therapies for individuals suffering from these conditions. This chapter describes how to conduct the mouse marble burying test as a sensitive measure of compulsive behaviors.

A review of the contributions of cross-discipline collaborative European IMI/EFPIA research projects to the development of Replacement, Reduction and Refinement strategies

The objective of this review is to report on whether, and if so, how, scientific research projects organised and managed within collaborative consortia across academia and industry are contributing to the Three Rs (i.e. reduction, replacement and refinement of the use of animals in research). A number of major technological developments have recently opened up possibilities for more direct, human-based approaches leading to a reassessment of the role and use of experimental animals in pharmacological research and biomedicine. This report reviews how projects funded by one of the research funding streams, the Innovative Medicines Initiative (IMI), are contributing to a better understanding of the challenges faced in using animal models. It also looks how the results from these various projects are impacting on the continued use of laboratory animals in research and development. From the progress identified, it is apparent that the approach of private-public partnership has demonstrated the value of multicentre studies, and how the spirit of collaboration and sharing of information can help address human health challenges. In so doing, this approach can reduce the dependence on animal use in areas where it has normally been viewed as necessary. The use of a collaborative platform enables the Three Rs to be addressed on multiple different levels, such that the selection of models to be tested, the protocols to be followed, and the interpretation of results generated, can all be optimised. This will, in turn, lead to an overall reduction in the use of laboratory animals.

Proteomic systems evaluation of the molecular validity of preclinical psychosis models compared to schizophrenia brain pathology

Pharmacological and genetic rodent models of schizophrenia play an important role in the drug discovery pipeline, but quantifying the molecular similarity of such models with the underlying human pathophysiology has proved difficult. We developed a novel systems biology methodology for the direct comparison of anterior prefrontal cortex tissue from four established glutamatergic rodent models and schizophrenia patients, enabling the evaluation of which model displays the greatest similarity to schizophrenia across different pathophysiological characteristics of the disease. Liquid chromatography coupled tandem mass spectrometry (LC-MS^E) proteomic profiling was applied comparing healthy and "disease state" in human post-mortem samples and rodent brain tissue samples derived from models based on acute and chronic phencyclidine (PCP) treatment, ketamine treatment or NMDA receptor knockdown. Protein-protein interaction networks were constructed from significant abundance changes and enrichment analyses enabled the identification of five functional domains of the disease such as "development and differentiation", which were represented across all four rodent models and were thus subsequently used for cross-species comparison. Kernel-based machine learning techniques quantified that the chronic PCP model represented schizophrenia brain changes most closely for four of these functional domains. This is the first study aiming to quantify which rodent model recapitulates the neuropathological features of schizophrenia most closely, providing an indication of face validity as well as potential guidance in the refinement of construct and predictive validity. The methodology and findings presented here support recent efforts to overcome translational hurdles of preclinical psychiatric research by associating functional dimensions of behaviour with distinct biological processes.

Prefrontal cortical activity associated with visual stimulus categorization in non-human primates measured with near-infrared spectroscopy

In biomedical research of brain dysfunction in psychiatric disorders, utilization of animal models is essential. However, translation of findings in animal models into the realm of human clinical conditions requires reliable biomarkers that are assessed with the methods mutually employed in animal models and human patients. Near-infrared spectroscopy (NIRS) is a functional neuroimaging technique that has now been widely utilized in human basic and clinical research. However, its application to animal models has been barely conducted. In this study, we developed the method to measure neural activity in the cortex of Japanese macaques using NIRS, and examined cortical responses to presentation of a set of visual stimuli that were categorized into four different groups (flower, monkey, snake, food). Prefrontal cortical (PFC) oxy- and deoxy-hemoglobin changes were found to reliably distinguish the categories of these visual stimuli. The results suggest that cortical activity measurement with NIRS in primates can be a valuable model for identifying biomarkers associated with psychiatric disorders.

Chronic stress affects the number of GABAergic neurons in the orbitofrontal cortex of rats

Cortical GABAergic dysfunctions have been documented by clinical studies in major depression. We used here an animal model for depression and investigated whether long-term stress exposure can affect the number of GABAergic neurons in the orbitofrontal cortex (OFC). Adult male rats were subjected to 7-weeks of daily stress exposure and behaviorally phenotyped as anhedonic or stress-resilient animals. GABAergic interneurons were identified by immunohistochemistry and systematically quantified. We analyzed calbindin-(CB), calretinin-(CR), cholecystokinin-(CCK), parvalbumin-(PV), neuropeptide Y-(NPY) and somatostatin-positive (SST+) neurons in the following specific subareas of the OFC: medial orbital (MO), ventral orbital (VO), lateral orbital (LO) and dorsolateral orbital (DLO) cortex. For comparison, we also analyzed the primary motor cortex (M1) as a non-limbic cortical area. Stress had a pronounced effect on CB+ neurons and reduced their densities by 40-50% in the MO, VO and DLO. Stress had no effect on CCK+, CR+, PV+, NPY+ and SST+ neurons in any cortical areas. None of the investigated GABAergic neurons were affected by stress in the primary motor cortex. Interestingly, in the stress-resilient animals, we observed a significantly increased density of CCK+ neurons in the VO. NPY+ neuron densities were also significantly different between the anhedonic and stress-resilient rats, but only in the LO. Our present data demonstrate that chronic stress can specifically reduce the density of calbindin-positive GABAergic neurons in the orbitofrontal cortex and suggest that NPY and CCK expression in the OFC may relate to the stress resilience of the animals.

Human dermal fibroblasts in psychiatry research

In order to decipher the disease etiology, progression and treatment of multifactorial human brain diseases we utilize a host of different experimental models. Recently, patient-derived human dermal fibroblast (HDF) cultures have re-emerged as promising in vitro functional system for examining various cellular, molecular, metabolic and (patho)physiological states and traits of psychiatric disorders. HDF studies serve as a powerful complement to postmortem and animal studies, and often appear to be informative about the altered homeostasis in neural tissue. Studies of HDFs from patients with schizophrenia (SZ), depression, bipolar disorder (BD), autism, attention deficit and hyperactivity disorder and other psychiatric disorders have significantly advanced our understanding of these devastating diseases. These reports unequivocally prove that signal transduction, redox homeostasis, circadian rhythms and gene*environment (G*E) interactions are all amenable for assessment by the HDF model. Furthermore, the reported findings suggest that this underutilized patient biomaterial, combined with modern molecular biology techniques, may have both diagnostic and prognostic value, including prediction of response to therapeutic agents.

Toward a Valid Animal Model of Bipolar Disorder: How the Research Domain Criteria Help Bridge the Clinical-Basic Science Divide

Bipolar disorder is a diagnostically heterogeneous disorder, although mania emerges as a distinct phenotype characterized by elevated mood and increased activity or energy. While bipolar disorder's cyclicity is difficult to represent in animals, models of mania have begun to decode its fundamental underlying neurobiology. When psychostimulants such as amphetamine or cocaine are administered to rodents, a resulting upsurge of motor activity is thought to share face and predictive validity with mania in humans. Studying black Swiss mice, which inherently exhibit proclivity for reward seeking and risk taking, also has yielded some insight. Further, translating the biology of bipolar disorder in humans into animal models has led to greater understanding of roles for candidate biological systems such as the GRIK2 and CLOCK genes, as well as the extracellular signal-related kinase pathway involved in the pathophysiology of the illness. The National Institute of Mental Health Research Domain Criteria initiative seeks to identify building blocks of complex illnesses like bipolar disorder in hopes of uncovering the neurobiology of each, as well as how each fits together to produce syndromes like bipolar disorder or why so many mental illnesses co-occur together. Research Domain Criteria-driven preclinical models of isolated behaviors and domains involved in mania and bipolar disorder will ultimately inform movement toward nosology supported by neurobiology.

Hippocampal Proteomic and Metabonomic Abnormalities in Neurotransmission, Oxidative Stress, and Apoptotic Pathways in a Chronic Phencyclidine Rat Model

Schizophrenia is a neuropsychiatric disorder affecting 1% of the world's population. Due to both a broad range of symptoms and disease heterogeneity, current therapeutic approaches to treat schizophrenia fail to address all symptomatic manifestations of the disease. Therefore, disease models that reproduce core pathological features of schizophrenia are needed for the elucidation of pathological disease mechanisms. Here, we employ a comprehensive global label-free liquid chromatography-mass spectrometry proteomic (LC-MS(E)) and metabonomic (LC-MS) profiling analysis combined with the targeted proteomics (selected reaction monitoring and multiplex immunoassay) of serum and brain tissues to investigate a chronic phencyclidine (PCP) rat model in which glutamatergic hypofunction is induced through noncompetitive NMDAR-receptor antagonism. Using a multiplex immunoassay, we identified alterations in the levels of several cytokines (IL-5, IL-2, and IL-1β) and fibroblast growth factor-2. Extensive proteomic and metabonomic brain tissue profiling revealed a more prominent effect of chronic PCP treatment on both the hippocampal proteome and metabonome compared to the effect on the frontal cortex. Bioinformatic pathway analysis confirmed prominent abnormalities in NMDA-receptor-associated pathways in both brain regions, as well as alterations in other neurotransmitter systems such as kainate, AMPA, and GABAergic signaling in the hippocampus and in proteins associated with neurodegeneration. We further identified abundance changes in the level of the superoxide dismutase enzyme (SODC) in both the frontal cortex and hippocampus, which indicates alterations in oxidative stress and substantiates the apoptotic pathway alterations. The present study could lead to an increased understanding of how perturbed glutamate receptor signaling affects other relevant biological pathways in schizophrenia and, therefore, support drug discovery efforts for the improved treatment of patients suffering from this debilitating psychiatric disorder.

Modeling heterogeneous patients with a clinical diagnosis of schizophrenia with induced pluripotent stem cells

Schizophrenia (SZ) is a devastating complex genetic mental condition that is heterogeneous in terms of clinical etiologies, symptoms, and outcomes. Despite decades of postmortem, neuroimaging, pharmacological, and genetic studies of patients, in addition to animal models, much of the biological mechanisms that underlie the pathology of SZ remain unknown. The ability to reprogram adult somatic cells into human induced pluripotent stem cells (hiPSCs) provides a new tool that supplies live human neurons for modeling complex genetic conditions such as SZ. The purpose of this review is to discuss the technical and clinical constraints currently limiting hiPSC-based studies. We posit that reducing the clinical heterogeneity of hiPSC-based studies, by selecting subjects with common clinical manifestations or rare genetic variants, will help our ability to draw meaningful insights from the necessarily small patient cohorts that can be studied at this time.

Modeling combined schizophrenia-related behavioral and metabolic phenotypes in rodents

Schizophrenia is a chronic, debilitating disorder with a complex behavioral and cognitive phenotype underlined by a similarly complex etiology involving an interaction between susceptibility genes and environmental factors during early development. Limited progress has been made in developing novel pharmacotherapy, partly due to a lack of valid animal models. The recent recognition of the potentially causal role of central and peripheral energy metabolism in the pathophysiology of schizophrenia raises the need of research on animal models that combine both behavioral and metabolic phenotypic domains, similar to what have been identified in humans. In this review we focus on selected genetic (DBA/2J mice, leptin receptor mutants, and PSD-93 knockout mice), early neurodevelopmental (maternal protein deprivation) and pharmacological (acute phencyclidine) animal models that capture the combined behavioral and metabolic abnormalities shown by schizophrenic patients. In reviewing behavioral phenotypes relevant to schizophrenia we apply the principles established by the Research Domain Criteria (RDoC) for better translation. We demonstrate that etiologically diverse manipulations such as specific breeding, deletion of genes that are primarily involved in metabolic regulation and in synaptic plasticity, as well as early metabolic deprivation and adult pharmacological challenge of the glutamate system can lead to schizophrenia-related behavioral and metabolic phenotypes, which suggest that these pathways might be interlinked. We propose that using animal models that combine different domains of schizophrenia can be used as a translationally valid approach to capture the system-level complex interplay between peripheral and central processes in the development of psychopathology.

Phenotype ontologies and cross-species analysis for translational research

The use of model organisms as tools for the investigation of human genetic variation has significantly and rapidly advanced our understanding of the aetiologies underlying hereditary traits. However, while equivalences in the DNA sequence of two species may be readily inferred through evolutionary models, the identification of equivalence in the phenotypic consequences resulting from comparable genetic variation is far from straightforward, limiting the value of the modelling paradigm. In this review, we provide an overview of the emerging statistical and computational approaches to objectively identify phenotypic equivalence between human and model organisms with examples from the vertebrate models, mouse and zebrafish. Firstly, we discuss enrichment approaches, which deem the most frequent phenotype among the orthologues of a set of genes associated with a common human phenotype as the orthologous phenotype, or phenolog, in the model species. Secondly, we introduce and discuss computational reasoning approaches to identify phenotypic equivalences made possible through the development of intra- and interspecies ontologies. Finally, we consider the particular challenges involved in modelling neuropsychiatric disorders, which illustrate many of the remaining difficulties in developing comprehensive and unequivocal interspecies phenotype mappings.

A combined metabonomic and proteomic approach identifies frontal cortex changes in a chronic phencyclidine rat model in relation to human schizophrenia brain pathology

Current schizophrenia (SCZ) treatments fail to treat the broad range of manifestations associated with this devastating disorder. Thus, new translational models that reproduce the core pathological features are urgently needed to facilitate novel drug discovery efforts. Here, we report findings from the first comprehensive label-free liquid-mass spectrometry proteomic- and proton nuclear magnetic resonance-based metabonomic profiling of the rat frontal cortex after chronic phencyclidine (PCP) intervention, which induces SCZ-like symptoms. The findings were compared with results from a proteomic profiling of post-mortem prefrontal cortex from SCZ patients and with relevant findings in the literature. Through this approach, we identified proteomic alterations in glutamate-mediated Ca(2+) signaling (Ca(2+)/calmodulin-dependent protein kinase II, PPP3CA, and VISL1), mitochondrial function (GOT2 and PKLR), and cytoskeletal remodeling (ARP3). Metabonomic profiling revealed changes in the levels of glutamate, glutamine, glycine, pyruvate, and the Ca(2+) regulator taurine. Effects on similar pathways were also identified in the prefrontal cortex tissue from human SCZ subjects. The discovery of similar but not identical proteomic and metabonomic alterations in the chronic PCP rat model and human brain indicates that this model recapitulates only some of the molecular alterations of the disease. This knowledge may be helpful in understanding mechanisms underlying psychosis, which, in turn, can facilitate improved therapy and drug discovery for SCZ and other psychiatric diseases. Most importantly, these molecular findings suggest that the combined use of multiple models may be required for more effective translation to studies of human SCZ.

Peripheral biomarkers in animal models of major depressive disorder

Investigations of preclinical biomarkers for major depressive disorder (MDD) encompass the quantification of proteins, peptides, mRNAs, or small molecules in blood or urine of animal models. Most studies aim at characterising the animal model by including the assessment of analytes or hormones affected in depressive patients. The ultimate objective is to validate the model to better understand the neurobiological basis of MDD. Stress hormones or inflammation-related analytes associated with MDD are frequently measured. In contrast, other investigators evaluate peripheral analytes in preclinical models to translate the results in clinical settings afterwards. Large-scale, hypothesis-free studies are performed in MDD models to identify candidate biomarkers. Other studies wish to propose new targets for drug discovery. Animal models endowed with predictive validity are investigated, and the assessment of peripheral analytes, such as stress hormones or immune molecules, is comprised to increase the confidence in the target. Finally, since the mechanism of action of antidepressants is incompletely understood, studies investigating molecular alterations associated with antidepressant treatment may include peripheral analyte levels. In conclusion, preclinical biomarker studies aid the identification of new candidate analytes to be tested in clinical trials. They also increase our understanding of MDD pathophysiology and help to identify new pharmacological targets.

Estudos traducionais de neuropsiquiatria e esquizofrenia: modelos animais genéticos e de neurodesenvolvimento

Sintomas psiquiátricos são subjetivos por natureza e tendem a se sobrepor entre diferentes desordens. Sendo assim, a criação de modelos de uma desordem neuropsiquiátrica encontra desafios pela falta de conhecimento dos fundamentos da fisiopatologia e diagnósticos precisos. Modelos animais são usados para testar hipóteses de etiologia e para representar a condição humana tão próximo quanto possível para aumentar nosso entendimento da doença e avaliar novos alvos para a descoberta de drogas. Nesta revisão, modelos animais genéticos e de neurodesenvolvimento de esquizofrenia são discutidos com respeito a achados comportamentais e neurofisiológicos e sua associação com a condição clínica. Somente modelos animais específicos de esquizofrenia podem, em último caso, levar a novas abordagens diagnósticas e descoberta de drogas. Argumentamos que biomarcadores moleculares são importantes para aumentar a tradução de animais a humanos, já que faltam a especificidade e a fidelidade necessárias às leituras comportamentais para avaliar sintomas psiquiátricos humanos.

Molecular validation of the acute phencyclidine rat model for schizophrenia: identification of translational changes in energy metabolism and neurotransmission

Administration of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine (PCP) to rodents is widely used as preclinical model for schizophrenia. Most studies on this model employ methods investigating behavior and brain abnormalities. However, little is known about the corresponding peripheral effects. In this study, we analyzed changes in brain and serum molecular profiles, together with alterations in behavior after acute PCP treatment of rats. Furthermore, abnormalities in peripheral protein expression of first and recent onset antipsychotic free schizophrenia patients were assessed for comparison with the preclinical model. PCP treatment induced hyperlocomotion and stereotypic behavior, which have been related to positive symptoms of schizophrenia. Multiplex immunoassay profiling of serum revealed molecular abnormalities similar to those seen in first and recent onset, antipsychotic free schizophrenia patients. Also, increased insulin levels were detected after administration of a glucose tolerance test (GTT), consistent with previous studies showing changes in insulin signaling in patients with schizophrenia. Finally, schizophrenia-relevant alterations in brain molecules were found in the hippocampus and to a lesser extent in the frontal cortex using liquid-chromatography mass spectrometry and (1)H nuclear magnetic resonance spectroscopy. In conclusion, this study identified behavioral and molecular alterations in the acute PCP rat model, which are also observed in human schizophrenia. We propose that the corresponding changes in serum in both animals and patients may have utility as surrogate markers in this model to facilitate discovery and development of novel drugs for treatment of certain pathological features of schizophrenia.

Animal models of eating disorders

Feeding is a fundamental process for basic survival and is influenced by genetics and environmental stressors. Recent advances in our understanding of behavioral genetics have provided a profound insight on several components regulating eating patterns. However, our understanding of eating disorders, such as anorexia nervosa, bulimia nervosa, and binge eating, is still poor. The animal model is an essential tool in the investigation of eating behaviors and their pathological forms, yet development of an appropriate animal model for eating disorders still remains challenging due to our limited knowledge and some of the more ambiguous clinical diagnostic measures. Therefore, this review will serve to focus on the basic clinical features of eating disorders and the current advances in animal models of eating disorders.