A systematic scoping review of rodent models of catatonia: Clinical correlations, translation and future approaches.

Catatonia is a psychiatric disorder, which subsumes a plethora of affective, motor and behavioral symptoms. In the last two decades, the number of behavioral and neuroimaging studies on catatonia has steadily increased. The majority of behavioral and neuroimaging studies in psychiatric patients suggested aberrant higher-order frontoparietal networks which, on the biochemical level, are insufficiently modulated by gamma-aminobutyric acid (GABA)-ergic and glutamatergic transmission. However, the pathomechanisms of catatonic symptoms have rarely been studied using rodent models. Here, we performed a scoping review of literature available on PubMed for studies on rodent models of catatonia. We sought to identify what we could learn from pre-clinical animal models of catatonia-like symptoms, their underlying neuronal correlates, and the complex molecular (i.e. genes and neurotransmitter) mechanisms by which its modulation exerts its effects. What becomes evident is that although many transgenic models present catatonia-like symptoms, they have not been used to better understand the pathophysiological mechanisms underlying catatonia so far. However, the identified neuronal correlates of catatonia-like symptoms correlate to a great extent with findings from neuroscience research in psychiatric patients. This points us towards fundamental cortical-striatal-thalamocortical and associated networks modulated by white matter inflammation as well as aberrant dopaminergic, GABAergic, and glutamatergic neurotransmission that is involved in catatonia. Therefore, this scoping review opens up the possibility of finally using transgenic models to help with identifying novel target mechanisms for the development of new drugs for the treatment of catatonia.

Evidence-based severity assessment of the forced swim test in the rat.

The forced swim test (FST) is a traditional assay, which has been used for more than 40 years to assess antidepressant effects of novel drug candidates. In recent years, a debate about the test has focused on the assumption that the FST is highly aversive and burdening for the animals because of the earlier anthropomorphic interpretation and designation as a "behavioral despair test". The Directive 2010/63/EU and the German Animal Welfare law require a prospective severity classification of the planned experimental procedures. Still, an objective examination of the animals' burden in this test has not been performed yet. To fill this gap, we conducted an evidence-based severity assessment of the forced swim test in rats according to a 'standard protocol' with a water temperature of 25°C. We examined parameters representing the physiological and the affective state, and natural as well as locomotion-associated behaviors in three separate experiments to reflect as many dimensions as possible of the animal's condition in the test. Hypothermia was the only effect observed in all animals exposed to the FST when using this standard protocol. Additional adverse effects on body weight, food consumption, and fecal corticosterone metabolite concentrations occurred in response to administration of the antidepressant imipramine, which is frequently used as positive control when testing for antidepressant effects of new substances. We conclude that this version of the FST itself is less severe for the animals than assumed, and we suggest a severity classification of 'moderate' because of the acute and short-lasting effects of hypothermia. To refine the FST according to the 3Rs, we encourage confirming the predictive validity in warmer water temperatures to allow the rats to maintain physiological body temperature.

A systematic mapping review of the evolution of the rat Forced Swim Test: Protocols and outcome parameters.

As depression is projected to become the leading mental disease burden globally by 2030, understanding the underlying pathology, as well as screening potential anti-depressants with a higher efficacy, faster onset of action, and/or fewer side-effects is essential. A commonly used test for screening novel antidepressants and studying depression-linked aspects in rodents is the Porsolt Forced Swim Test. The present systematic mappping review gives a comprehensive overview of the evolution and of the most prevalently used set-ups of this test in rats, including the choice of animals (strain, sex, and age), technical aspects of protocol and environment, as well as reported outcome measures. Additionally, we provide an accessible list of all existing publications, to support informed decision-making for procedural and technical aspects of the test, to thereby enhance reproducibility and comparability. This should further contribute to reducing the number of unnecessarily replicated experiments, and consequently, reduce the number of animals used in future.

Dopamine transporter silencing in the rat: systems-level alterations in striato-cerebellar and prefrontal-midbrain circuits.

Silencing of dopamine transporter (DAT), a main controlling factor of dopaminergic signaling, results in biochemical and behavioral features characteristic for neuropsychiatric diseases with presumed hyperdopaminergia including schizophrenia, attention deficit hyperactivity disorder (ADHD), bipolar disorder, and obsessive-compulsive disorder (OCD). Investigation of DAT silencing thus provides a transdiagnostic approach towards a systems-level understanding of common underlying pathways. Using a high-field multimodal imaging approach and a highly sensitive cryogenic coil, we integrated structural, functional and metabolic investigations in tandem with behavioral assessments on a newly developed preclinical rat model, comparing DAT homozygous knockout (DAT-KO, N = 14), heterozygous knockout (N = 8) and wild-type male rats (N = 14). We identified spatially distributed structural and functional brain alterations encompassing motor, limbic and associative loops that demonstrated strong behavioral relevance and were highly consistent across imaging modalities. DAT-KO rats manifested pronounced volume loss in the dorsal striatum, negatively correlating with cerebellar volume increase. These alterations were associated with hyperlocomotion, repetitive behavior and loss of efficient functional small-world organization. Further, prefrontal and midbrain regions manifested opposite changes in functional connectivity and local network topology. These prefrontal disturbances were corroborated by elevated myo-inositol levels and increased volume. To conclude, our imaging genetics approach provides multimodal evidence for prefrontal-midbrain decoupling and striato-cerebellar neuroplastic compensation as two key features of constitutive DAT blockade, proposing them as transdiagnostic mechanisms of hyperdopaminergia. Thus, our study connects developmental DAT blockade to systems-level brain changes, underlying impaired action inhibition control and resulting in motor hyperactivity and compulsive-like features relevant for ADHD, schizophrenia and OCD.

Cre-Activation in ErbB4-Positive Neurons of Floxed Grin1/NMDA Receptor Mice Is Not Associated With Major Behavioral Impairment.

Extensive evidence suggests a dysfunction of the glutamate NMDA receptor (NMDAR) in schizophrenia, a severe psychiatric disorder with putative early neurodevelopmental origins, but clinical onset mainly during late adolescence. On the other hand, pharmacological models using NMDAR antagonists and the clinical manifestation of anti-NMDAR encephalitis indicate that NMDAR blockade/hypofunction can trigger psychosis also at adult stages, without any early developmental dysfunction. Previous genetic models of NMDAR hypofunction restricted to parvalbumin-positive interneurons indicate the necessity of an early postnatal impairment to trigger schizophrenia-like abnormalities, whereas the cellular substrates of NMDAR-mediated psychosis at adolescent/adult stages are unknown. Neuregulin 1 (NRG1) and its receptor ErbB4 represent schizophrenia-associated susceptibility factors that closely interact with NMDAR. To determine the neuronal populations implicated in "late" NMDAR-driven psychosis, we analyzed the effect of the inducible ablation of NMDARs in ErbB4-expressing cells in mice during late adolescence using a pharmacogenetic approach. Interestingly, the tamoxifen-inducible NMDAR deletion during this late developmental stage did not induce behavioral alterations resembling depression, schizophrenia or anxiety. Our data indicate that post-adolescent NMDAR deletion, even in a wider cell population than parvalbumin-positive interneurons, is also not sufficient to generate behavioral abnormalities resembling psychiatric disorders. Other neuronal substrates that have to be revealed by future studies, may underlie post-adolescent NMDAR-driven psychosis.

The continued need for animals to advance brain research.

Policymakers aim to move toward animal-free alternatives for scientific research and have introduced very strict regulations for animal research. We argue that, for neuroscience research, until viable and translational alternatives become available and the value of these alternatives has been proven, the use of animals should not be compromised.

Systematic analysis of severity in a widely used cognitive depression model for mice.

Animal models in psychiatric research are indispensable for insights into mechanisms of behaviour and mental disorders. Distress is an important aetiological factor in psychiatric diseases, especially depression, and is often used to mimic the human condition. Modern bioethics requires balancing scientific progress with animal welfare concerns. Therefore, scientifically based severity assessment of procedures is a prerequisite for choosing the least compromising paradigm according to the 3Rs principle. Evidence-based severity assessment in psychiatric animal models is scarce, particularly in depression research. Here, we assessed severity in a cognitive depression model by analysing indicators of stress and well-being, including physiological (body weight and corticosterone metabolite concentrations) and behavioural (nesting and burrowing behaviour) parameters. Additionally, a novel approach for objective individualised severity grading was employed using clustering of voluntary wheel running (VWR) behaviour. Exposure to the paradigm evoked a transient elevation of corticosterone, but neither affected body weight, nesting or burrowing behaviour. However, the performance in VWR was impaired after recurrent stress exposure, and the individual severity level increased, indicating that this method is more sensitive in detecting compromised welfare. Interestingly, the direct comparison to a somatic, chemically induced colitis model indicates less distress in the depression model. Further objective severity assessment studies are needed to classify the severity of psychiatric animal models in order to balance validity and welfare, reduce the stress load and thus promote refinement.

Effects of Soy in Laboratory Rodent Diets on the Basal, Affective, and Cognitive Behavior of C57BL/6 Mice.

Soy is one of the most common sources of protein in many commercial formulas for laboratory rodent diets. Soy contains isoflavones, which are estrogenic. Therefore, soy-containing animal diets might influence estrogen-regulated systems, including basal behavioral domains, as well as affective behavior and cognition. Furthermore, the isoflavone content of soy varies, potentially unpredictably confounding behavioral results. Therefore researchers are increasingly considering completely avoiding dietary soy to circumvent this problem. Several animal studies have investigated the effects of soy free diets but produced inconsistent results. In addition, most of these previous studies were performed in outbred rat or mouse strains. In the current study, we assessed whether a soy-free diet altered locomotion, exploration, nesting, anxiety-related behaviors, learning, and memory in C57BL/6 mice, the most common inbred strain used in biomedical research. The parameters evaluated address measures of basic health, natural behavior, and affective state that also are landmarks for animal welfare. We found minor differences between feeding groups but no indications of altered welfare. We therefore suggest that a soy-free diet can be used as a standard diet to prevent undesirable side effects of isoflavones and to further optimize diet standardization, quality assurance, and ultimately increase the reproducibility of experiments.

Altered prepulse inhibition of the acoustic startle response in BDNF-deficient mice in a model of early postnatal hypoxia: implications for schizophrenia.

The brain-derived neurotrophic factor (BDNF) is a major proliferative agent in the nervous system. Both BDNF-deficiency and perinatal hypoxia represent genetic/environmental risk factors for schizophrenia. Moreover, a decreased BDNF response to birth hypoxia was associated with the disease. BDNF expression is influenced by neuronal activity and environmental conditions such as hypoxia. Thus, it may partake in neuroprotective and reparative mechanisms in acute or chronic neuronal insults. However, the interaction of hypoxia and BDNF is insufficiently understood and the behavioral outcome unknown. Therefore, we conducted a battery of behavioral tests in a classical model of chronic early postnatal mild hypoxia (10% O2), known to significantly impair brain development, in BDNF-deficient mice. We found selective deficits in measures associated with sensorimotor gating, namely enhanced acoustic startle response (ASR) and reduced prepulse inhibition (PPI) of ASR in BDNF-deficient mice. Unexpectedly, the alterations of sensorimotor gating were caused only by BDNF-deficiency alone, whereas hypoxia failed to evoke severe deficits and even leads to a milder phenotype in BDNF-deficient mice. As deficits in sensorimotor gating are present in schizophrenia and animal models of the disease, our results are of relevance regarding the involvement of BDNF in its pathogenesis. On the other hand, they suggest that the effect of perinatal hypoxia on long-term brain abnormalities is complex, ranging from protective to deleterious actions, and may critically depend on the degree of hypoxia. Therefore, future studies may refine existing hypoxia protocols to better understand neurodevelopmental consequences associated with schizophrenia.

Molecular and cellular dissection of NMDA receptor subtypes as antidepressant targets.

A growing body of evidence supports the idea that drugs targeting the glutamate system may represent a valuable therapeutic alternative in major depressive disorders (MDD). The rapid and prolonged mood elevating effect of the NMDA receptor (NMDAR) antagonist ketamine has been studied intensely. However, its clinical use is hampered by deleterious side-effects, such as psychosis. Therefore, a better understanding of the mechanisms of the psychotropic effects after NMDAR blockade is necessary to develop glutamatergic antidepressants with improved therapeutic profile. Here we review recent experimental data that addressed molecular/cellular determinants of the antidepressant effect mediated by inactivating NMDAR subtypes. We refer to results obtained both in pharmacological and genetic animal models, ranging from global to conditional NMDAR manipulation. Our main focus is on the contribution of different NMDAR subtypes to the psychoactive effects induced by NMDAR ablation/blockade. We review data analyzing the effect of NMDAR subtype deletions limited to specific neuronal populations/brain areas in the regulation of mood. Altogether, these studies suggest effective and putative specific NMDAR drug targets for MDD treatment.

MicroRNA Profiling in the Medial and Lateral Habenula of Rats Exposed to the Learned Helplessness Paradigm: Candidate Biomarkers for Susceptibility and Resilience to Inescapable Shock.

Depression is a highly heterogeneous disorder presumably caused by a combination of several factors ultimately causing the pathological condition. The genetic liability model of depression is likely to be of polygenic heterogeneity. miRNAs can regulate multiple genes simultaneously and therefore are candidates that align with this model. The habenula has been linked to depression in both clinical and animal studies, shifting interest towards this region as a neural substrate in depression. The goal of the present study was to search for alterations in miRNA expression levels in the medial and lateral habenula of rats exposed to the learned helplessness (LH) rat model of depression. Ten miRNAs showed significant alterations associating with their response to the LH paradigm. Of these, six and four miRNAs were significantly regulated in the MHb and LHb, respectively. In the MHb we identified miR-490, miR-291a-3p, MiR-467a, miR-216a, miR-18b, and miR-302a. In the LHb miR-543, miR-367, miR-467c, and miR-760-5p were significantly regulated. A target gene analysis showed that several of the target genes are involved in MAPK signaling, neutrophin signaling, and ErbB signaling, indicating that neurotransmission is affected in the habenula as a consequence of exposure to the LH paradigm.