Preclinical screening for antidepressant activity - shifting focus away from the Forced Swim Test to the use of translational biomarkers

Depression is the world's predominant mental health problem and a leading cause of disability. Neuropharmacological research has not yet advanced treatments to sufficiently meet clinical need, largely due to the failure of animal models to predict clinical efficacy. The forced swim test (FST) has been extensively used in the field of antidepressant research but has been under scrutiny due to its perceived severity to animals. Any use of animals in experiments and testing must have a scientific or regulatory purpose and researchers need to ensure that there is no scientifically valid alternative. However, regulatory requirements have been incorrectly cited as a reason to support the use of the FST. More research is required on tests that do not involve stressing animals as replacements for the FST. Non-behavioural neurochemical measures might provide a means to advance neuropharmacological developments while reducing animal suffering. For example, brain-derived neurotrophic factor (BDNF) may be promising.

Requirements for Animal Experiments: Problems and Challenges

In vivo models remain a principle screening tool in the drug discovery pipeline. Here, the challenges associated with the need for animal experiments, as well as their impact on research, individual/societal, and economic contexts are discussed. A number of alternatives that, with further development, optimization, and investment, may replace animal experiments are also revised.

Advances in Central Nervous System Organoids: A Focus on Organoid-Based Models for Motor Neuron Disease

Despite their large societal burden, the development of therapeutic treatments for neurodegenerative diseases (NDDs) has been relatively unsuccessful. This is, in part, due to a lack of representative experimental models that reveal fundamental aspects of human brain pathology. Recently, assays for in vitro modeling of the human central nervous system (CNS) have significantly improved with the development of brain and spinal cord organoids. Coupled with induced-pluripotent stem cell and genome editing technologies, CNS organoids are a promising tool for studying neurodegeneration in a patient-specific manner. An extensive array of protocols for the generation of organoids for different brain regions has been developed and used for studying neurodegenerative and other brain diseases. However, their application in the field of motor neuron disease (MND) has been limited due to a lack of adequate organoid models. The development of protocols to derive spinal cord and trunk organoids and progress in the field of assembloids are providing new opportunities for modeling MND. In this study here we review recent advances in the development of CNS organoid models, their application in NDDs, and technical limitations. Finally, we discuss future perspectives for the development of organoid-based systems for MND and provide a framework for their development. Impact statement Animal models and two-dimensional cultures are currently the main platforms for studying neurodegenerative diseases (NDDs). However, central nervous system (CNS) organoid technology offers novel possibilities for studying these diseases. Organoid modeling in combination with emerging organ-on-a-chip approaches, induced-pluripotent stem cell technology, and genome editing render in vitro modeling of NDDs more robust and physiologically relevant. In this study, we review the principles underlying CNS organoid generation, their use in NDD research, and future perspectives in organoid technology. Finally, we discuss how advances in different fields could be combined to generate a multisystem organoid-on-a-chip model to investigate a specific class of NDDs, motor neuron diseases.

Cardiovascular disease models: A game changing paradigm in drug discovery and screening

Cardiovascular disease is the leading cause of death worldwide. Although investment in drug discovery and development has been sky-rocketing, the number of approved drugs has been declining. Cardiovascular toxicity due to therapeutic drug use claims the highest incidence and severity of adverse drug reactions in late-stage clinical development. Therefore, to address this issue, new, additional, replacement and combinatorial approaches are needed to fill the gap in effective drug discovery and screening. The motivation for developing accurate, predictive models is twofold: first, to study and discover new treatments for cardiac pathologies which are leading in worldwide morbidity and mortality rates; and second, to screen for adverse drug reactions on the heart, a primary risk in drug development. In addition to in vivo animal models, in vitro and in silico models have been recently proposed to mimic the physiological conditions of heart and vasculature. Here, we describe current in vitro, in vivo, and in silico platforms for modelling healthy and pathological cardiac tissues and their advantages and disadvantages for drug screening and discovery applications. We review the pathophysiology and the underlying pathways of different cardiac diseases, as well as the new tools being developed to facilitate their study. We finally suggest a roadmap for employing these non-animal platforms in assessing drug cardiotoxicity and safety.

Cholinergic Mechanisms of Target Oddball Stimuli Detection: The Late "P300-Like" Event-Related Potential in Rats

Event-related potentials (ERPs) and oscillations (EROs) provide powerful tools for studying the brain's synaptic function underlying information processing. The P300 component of ERPs indexing attention and working memory shows abnormal amplitude and latency in neurological and psychiatric diseases that are sensitive to pharmacological agents. In the active auditory oddball discriminant paradigm, behavior and auditory-evoked potentials (AEPs) were simultaneously recorded in awake rats to investigate whether P300-like potentials generated in rats responding to rare target oddball tones are sensitive to subcutaneous modulation of the cholinergic tone by donepezil (1 mg/kg) and scopolamine (0.64 mg/kg). After operant training, rats consistently discriminate rare target auditory stimuli from frequent irrelevant nontarget auditory stimuli by a higher level of correct lever presses (i.e., accuracy) in target trials associated with a food reward. Donepezil attenuated the disruptive effect of scopolamine on the level of accuracy and premature responses in target trials. Larger P300-like peaks with early and late components were revealed in correct rare target stimuli trials as compared to frequent tones. Donepezil enhanced the peak amplitude of the P300-like component to target stimuli and evoked slow theta and gamma oscillations, whereas scopolamine altered the amplitude of the P300-like component and EROs to target stimuli. Pretreatment with donepezil attenuated effects of scopolamine on the peak amplitude of the P300-like component and on EROs. This study provides evidence that AEP P300-like responses can be elicited by rats engaged in attentive and memory processing of target stimuli and outline the relevance of the cholinergic system in stimulus discrimination processing. The findings highlight the sensitivity of this translational index for investigating brain circuits and/or novel pharmacological agents, which modulate cholinergic transmission associated with increased allocation of attentional resources.

Effects of anterior cingulate cortex lesions on a continuous performance task for mice

Important tools in the study of prefrontal cortical-dependent executive functions are cross-species behavioural tasks with translational validity. A widely used test of executive function and attention in humans is the continuous performance task (CPT). Optimal performance in variations of this task is associated with activity along the medial wall of the prefrontal cortex, including the anterior cingulate cortex (ACC), for its essential components such as response control, target detection and processing of false alarm errors. We assess the validity of a recently developed rodent touchscreen continuous performance task (rCPT) that is analogous to typical human CPT procedures. Here we evaluate the performance of mice with quinolinic acid-induced lesions centred on the ACC in the rCPT following a range of task parameter manipulations designed to challenge attention and impulse control. Lesioned mice showed a disinhibited response profile expressed as a decreased response criterion and increased false alarm rates. ACC lesions also resulted in a milder increase in inter-trial interval responses ('ITI touches') and hit rate. Lesions did not affect discriminative sensitivity d'. The disinhibited behaviour of ACC lesioned animals was stable and not affected by the manipulation of variable task parameter manipulations designed to increase task difficulty. The results are in general agreement with human studies implicating the ACC in the processing of inappropriate responses. We conclude that the rCPT may be useful for studying prefrontal cortex function in mice and has the capability of providing meaningful links between animal and human cognitive tasks.

Introducing Therioepistemology: the study of how knowledge is gained from animal research

This focus issue of Lab Animal coincides with a tipping point in biomedical research. For the first time, the scale of the reproducibility and translatability crisis is widely understood beyond the small cadre of researchers who have been studying it and the pharmaceutical and biotech companies who have been living it. Here we argue that an emerging literature, including the papers in this focus issue, has begun to congeal around a set of recurring themes, which themselves represent a paradigm shift. This paradigm shift can be characterized at the micro level as a shift from asking "what have we controlled for in this model?" to asking "what have we chosen to ignore in this model, and at what cost?" At the macro level, it is a shift from viewing animals as tools (the furry test tube), to viewing them as patients in an equivalent human medical study. We feel that we are witnessing the birth of a new discipline, which we term Therioepistemology, or the study of how knowledge is gained from animal research. In this paper, we outline six questions that serve as a heuristic for critically evaluating animal-based biomedical research from a therioepistemological perspective. These six questions sketch out the broad reaches of this new discipline, though they may change or be added to as this field evolves. Ultimately, by formalizing therioepistemology as a discipline, we can begin to discuss best practices that will improve the reproducibility and translatability of animal-based research, with concomitant benefits in terms of human health and animal well-being.

Methodological Considerations for Optimizing and Validating Behavioral Assays

Preclinical animal models are indispensable tools for translational research for which behavioral characterization and phenotyping are essential to testing hypotheses and for evaluating the potential of novel therapeutic agents to treat diseases. The methods employed for comprehensive behavioral phenotyping and pharmacological experiments are complex and should be conducted exclusively by trained technicians with demonstrated proficiency. The ultimate goal is to identify disease-relevant and translational behavioral endpoints that are robust, reliable, and reproducible, and that can be employed to evaluate potential of novel therapeutic agents to treat disease. The intent of the present article is to provide a pragmatic outline for establishing and optimizing behavioral assays and phenotyping batteries, ensuring that the assays and the data are reliable such that they can be reproduced within and across technicians and laboratories and, more importantly, that the data is translatable to the clinic. © 2016 by John Wiley & Sons, Inc.

Stratified medicine for mental disorders

There is recognition that biomedical research into the causes of mental disorders and their treatment needs to adopt new approaches to research. Novel biomedical techniques have advanced our understanding of how the brain develops and is shaped by behaviour and environment. This has led to the advent of stratified medicine, which translates advances in basic research by targeting aetiological mechanisms underlying mental disorder. The resulting increase in diagnostic precision and targeted treatments may provide a window of opportunity to address the large public health burden, and individual suffering associated with mental disorders. While mental health and mental disorders have significant representation in the "health, demographic change and wellbeing" challenge identified in Horizon 2020, the framework programme for research and innovation of the European Commission (2014-2020), and in national funding agencies, clear advice on a potential strategy for mental health research investment is needed. The development of such a strategy is supported by the EC-funded "Roadmap for Mental Health Research" (ROAMER) which will provide recommendations for a European mental health research strategy integrating the areas of biomedicine, psychology, public health well being, research integration and structuring, and stakeholder participation. Leading experts on biomedical research on mental disorders have provided an assessment of the state of the art in core psychopathological domains, including arousal and stress regulation, affect, cognition social processes, comorbidity and pharmacotherapy. They have identified major advances and promising methods and pointed out gaps to be addressed in order to achieve the promise of a stratified medicine for mental disorders.