Abnormal Motor Activity and Thermoregulation in a Schizophrenia Rat Model for Translational Science

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

The 3-hit animal models of schizophrenia: Improving strategy to decipher and treat the disease?

Schizophrenia is a complex disease related to combination and interactions between genetic and environmental factors, with an epigenetic influence. After the development of the first mono-factorial animal models of schizophrenia (1-hit), that reproduced patterns of either positive, negative and/or cognitive symptoms, more complex models combining two factors (2-hit) have been developed to better fit with the multifactorial etiology of the disease. In the two past decades, a new way to design animal models of schizophrenia have emerged by adding a third hit (3-hit). This review aims to discuss the relevance of the risk factors chosen for the tuning of the 3-hit animal models, as well as the validities measurements and their contribution to schizophrenia understanding. We intended to establish a comprehensive overview to help in the choice of factors for the design of multiple-hit animal models of schizophrenia.

Assessing the effects of oxytocin in changes of core body temperature during LPS-induced endotoxemia: A novel approach using Extended Poincaré Plot Analysis

Oxytocin has shown cardioprotective effects during inflammation and may modify the core body temperature changes in LPS-induced endotoxemia. Notably, the time series analysis of core body temperature fluctuations may indicate thermoregulation alterations. This study aims to assess the effects of oxytocin on changes in the core body temperature by analyzing the fluctuations of the temperature time series of endotoxemic rats. Twelve hours of continuous core body temperature fluctuations time series were obtained from adult male Dark Agouti rats implanted with a telemetric transmitter under the following treatment: lipopolysaccharide (LPS); oxytocin (O); lipopolysaccharide + oxytocin (LPS + O), and vehicle or control (C). The temperature fluctuations time series were analyzed using the Extended Poincaré Plot Analysis (EPPA), a novel approach for measuring nonlinear features, to compute the autocorrelation by Pearson's correlation coefficient r, the standard deviation perpendicular to the line of identity (SD1), and the standard deviation parallel to the line of identity (SD2). The autocorrelation of the temperature fluctuations assessed by Pearson's coefficient was significantly higher in the LPS group compared to control rats (C). Likewise, the co-administration of oxytocin during endotoxemia (LPS + O) significantly reduced the autocorrelation and increased the short-term variability (SD1) of temperature fluctuations compared to those recorded with a single dose of LPS. Thus, we concluded that oxytocin may introduce thermoregulatory changes under LPS-induced endotoxemia. The EPPA is a simple and powerful approach to assess physiological variability that can provide valuable insights into changes in thermoregulation.

Neurobehavioral Profiles of Six Genetically-based Rat Models of Schizophrenia- related Symptoms

Schizophrenia is a chronic and severe mental disorder with high heterogeneity in its symptoms clusters. The effectiveness of drug treatments for the disorder is far from satisfactory. It is widely accepted that research with valid animal models is essential if we aim at understanding its genetic/ neurobiological mechanisms and finding more effective treatments. The present article presents an overview of six genetically-based (selectively-bred) rat models/strains, which exhibit neurobehavioral schizophrenia-relevant features, i.e., the Apomorphine-susceptible (APO-SUS) rats, the Low-prepulse inhibition rats, the Brattleboro (BRAT) rats, the Spontaneously Hypertensive rats (SHR), the Wisket rats and the Roman High-Avoidance (RHA) rats. Strikingly, all the strains display impairments in prepulse inhibition of the startle response (PPI), which remarkably, in most cases are associated with novelty-induced hyperlocomotion, deficits of social behavior, impairment of latent inhibition and cognitive flexibility, or signs of impaired prefrontal cortex (PFC) function. However, only three of the strains share PPI deficits and dopaminergic (DAergic) psychostimulant-induced hyperlocomotion (together with prefrontal cortex dysfunction in two models, the APO-SUS and RHA), which points out that alterations of the mesolimbic DAergic circuit are a schizophrenia-linked trait that not all models reproduce, but it characterizes some strains that can be valid models of schizophrenia-relevant features and drug-addiction vulnerability (and thus, dual diagnosis). We conclude by putting the research based on these genetically-selected rat models in the context of the Research Domain Criteria (RDoC) framework, suggesting that RDoC-oriented research programs using selectively-bred strains might help to accelerate progress in the various aspects of the schizophrenia-related research agenda.

Caffeine-Induced Acute and Delayed Responses in Cerebral Metabolism of Control and Schizophrenia-Like Wisket Rats

Recently, morphological impairments have been detected in the brain of a triple-hit rat schizophrenia model (Wisket), and delayed depressive effects of caffeine treatment in both control and Wisket animals have also been shown. The aims of this study were to determine the basal and caffeine-induced acute (30 min) and delayed (24 h) changes in the cerebral ¹⁸fluorodeoxyglucose (¹⁸F-FDG) uptake by positron emission tomography (PET) in control and Wisket rats. No significant differences were identified in the basal whole-brain metabolism between the two groups, and the metabolism was not modified acutely by a single intraperitoneal caffeine (20 mg/kg) injection in either group. However, one day after caffeine administration, significantly enhanced ¹⁸F-FDG uptake was detected in the whole brain and the investigated areas (hippocampus, striatum, thalamus, and hypothalamus) in the control group. Although the Wisket animals showed only moderate enhancements in the ¹⁸F-FDG uptake, significantly lower brain metabolism was observed in this group than in the caffeine-treated control group. This study highlights that the basal brain metabolism of Wisket animals was similar to control rats, and that was not influenced acutely by single caffeine treatment at the whole-brain level. Nevertheless, the distinct delayed responsiveness to this psychostimulant in Wisket model rats suggests impaired control of the cerebral metabolism.

Sleep-Wake Rhythm and Oscillatory Pattern Analysis in a Multiple Hit Schizophrenia Rat Model (Wisket)

Electroencephalography studies in schizophrenia reported impairments in circadian rhythm and oscillatory activity, which may reflect the deficits in cognitive and sensory processing. The current study evaluated the circadian rhythm and the state-dependent oscillatory pattern in control Wistar and a multiple hit schizophrenia rat model (Wisket) using custom-made software for identification of the artifacts and the classification of sleep-wake stages and the active and quiet awake substages. The Wisket animals have a clear light-dark cycle similar to controls, and their sleep-wake rhythm showed only a tendency to spend more time in non-rapid eye movement (NREM) and less in rapid eye movement (REM) stages. In spite of the weak diurnal variation in oscillation in both groups, the Wisket rats had higher power in the low-frequency delta, alpha, and beta bands and lower power in the high-frequency theta and gamma bands in most stages. Furthermore, the significant differences between the two groups were pronounced in the active waking substage. These data suggest that the special changes in the oscillatory pattern of this schizophrenia rat model may have a significant role in the impaired cognitive functions observed in previous studies.

Wisket rat model of schizophrenia: Impaired motivation and, altered brain structure, but no anhedonia

It is well-known that the poor cognition in schizophrenia is strongly linked to negative symptoms, including motivational deficit, which due to, at least partially, anhedonia. The goal of this study was to explore whether the schizophrenia-like Wisket animals with impaired motivation (obtained in the reward-based hole-board test), also show decreased hedonic behavior (investigated with the sucrose preference test). While neurochemical alterations of different neurotransmitter systems have been detected in the Wisket rats, no research has been performed on structural changes. Therefore, our additional aim was to reveal potential neuroanatomical and structural alterations in different brain regions in these rats. The rats showed decreased general motor activity (locomotion, rearing and exploration) and impaired task performance in the hole-board test compared to the controls, whereas no significant difference was observed in the sucrose preference test between the groups. The Wisket rats exhibited a significant decrease in the frontal cortical thickness and the hippocampal area, and moderate increases in the lateral ventricles and cell disarray in the CA3 subfield of hippocampus. To our knowledge, this is the first study to investigate the hedonic behavior and neuroanatomical alterations in a multi-hit animal model of schizophrenia. The results obtained in the sucrose preference test suggest that anhedonic behavior might not be involved in the impaired motivation obtained in the hole-board test. The neuropathological changes agree with findings obtained in patients with schizophrenia, which refine the high face validity of the Wisket model.

A Potential Interface between the Kynurenine Pathway and Autonomic Imbalance in Schizophrenia

Schizophrenia is a neuropsychiatric disorder characterized by various symptoms including autonomic imbalance. These disturbances involve almost all autonomic functions and might contribute to poor medication compliance, worsened quality of life and increased mortality. Therefore, it has a great importance to find a potential therapeutic solution to improve the autonomic disturbances. The altered level of kynurenines (e.g., kynurenic acid), as tryptophan metabolites, is almost the most consistently found biochemical abnormality in schizophrenia. Kynurenic acid influences different types of receptors, most of them involved in the pathophysiology of schizophrenia. Only few data suggest that kynurenines might have effects on multiple autonomic functions. Publications so far have discussed the implication of kynurenines and the alteration of the autonomic nervous system in schizophrenia independently from each other. Thus, the coupling between them has not yet been addressed in schizophrenia, although their direct common points, potential interfaces indicate the consideration of their interaction. The present review gathers autonomic disturbances, the impaired kynurenine pathway in schizophrenia, and the effects of kynurenine pathway on autonomic functions. In the last part of the review, the potential interaction between the two systems in schizophrenia, and the possible therapeutic options are discussed.

Caffeine - treat or trigger? Disparate behavioral and long-term dopaminergic changes in control and schizophrenia-like Wisket rats

The influence of caffeine on behavioral functions in both healthy and schizophrenic subjects is controversial. Here we aimed to reveal the effects of repeated caffeine pre- and post-training treatments on motor and exploratory activities and cognitive functions in a reward-based test (Ambitus) along with a brain region-specific dopamine D₂ receptor profile in control and schizophrenia-like WISKET model rats. In the control animals, pre-treatment caused temporary enhancement in motor activity, while permanent improvement in learning function was detected in the WISKET animals. Post-treatment produced significant impairments in both groups. Caffeine caused short-lasting hyperactivity followed by a rebound in the inactive phase determined in undisturbed circumstance. Caffeine treatment substantially enhanced the dopamine D₂ receptor mediated G-protein activation in the prefrontal cortex and olfactory bulb of both groups, while it increased in the dorsal striatum and cerebral cortex only in the WISKET animals. Caffeine enhanced the maximal binding capacity in the hippocampus and cerebral cortex of WISKET animals, but it decreased in the prefrontal cortex of the control animals. Regarding the dopamine D₂ receptor mRNA expression, caffeine treatment caused significant enhancement in the prefrontal cortex of WISKET animals, while it increased the hippocampal dopamine D₂ receptor protein amount in both groups. This study highlights the disparate effects of caffeine pre- versus post-training treatments on behavioral parameters in both control and schizophrenia-like animals and the prolonged changes in the dopaminergic system. It is supposed that the delayed depressive effects of caffeine might be compensated by frequent coffee intake, as observed in schizophrenic patients.

Aggravated mucosal and immune damage in a mouse model of ulcerative colitis with stress

The aim of the present study was to determine the influence of stress on the colonic mucosa and immune system and to further investigate the association between stress and development and pathogenesis of ulcerative colitis (UC). Mice were treated with 2,4,6-trinitrobenzenesulfonic acid to induce an animal model of UC, and stress was induced by water immersion and restraint. Subsequently, the disease activity index (DAI), secretory immunoglobulin A (sIgA), IgA, interleukin (IL)-6 and -8, tumor necrosis factor-α (TNF-α), complement component (C)3 and C4, and alterations in the colonic mucosa were observed. The DAI scores and the expression levels of IL-6, IL-8 and TNF-α significantly increased in the experimental UC mice compared with the control mice, while the expression levels of IgA and sIgA decreased (all P<0.01). DAI and colonic mucosa damage scores increased in the stress-treated mouse models of UC compared with the untreated mouse models of UC (P<0.05). Expression levels of IgA and sIgA decreased, while IL-6, IL-8 and TNF-α further increased in the stress-treated UC mice (P<0.05). The expression levels of C3 and C4 were not affected by stress or UC (P>0.05). These results indicated that UC may be associated with an immune disorder and that stress can aggravate colonic mucosa injury and alter the immune response. Furthermore, stress and immunity may serve roles in the pathogenesis of UC.

Comparative Analysis of Gene Expression Profiles Involved in Calcium Signaling Pathways Using the NLVH Animal Model of Schizophrenia

In this study, we evaluated the expression profile changes of genes that intervene in the calcium signaling pathway, in young and adult Wistar rats, using the animal model of neonatal lesion in ventral hippocampus (NLVH) (a recognized animal model for schizophrenia) and compared to the group of control animals (Sham). Through microarray technology, gene expression profiles were obtained from the three brain areas (nucleus accumbens, prefrontal cortex, and hippocampus) of young male Wistar rats (45 days) and adults (90 days) whether or not subjected to NLVH. The calcium signaling pathway reported a greater number of differentially expressed genes with z-score two values, > 2 (over-expression) and < - 2 (under-expression), in the three evaluated areas. The comparative analyses of this approach were performed in juvenile and adult rats with ventral hippocampal lesion in neonate rats (NLVH). NLVH influenced change expressions in various genes involved in Ca²⁺ homeostasis, including Cacna1d, Atp2a2, Adcy2, Ppp3cb, and Ptk2b. The expression of Adcy2, Ppp3cb, and Ptk2b genes changed in both age groups; therefore, the study of gene expression profiles between juvenile and adult rats may help to understand the molecular mechanisms of schizophrenia.

Decreased CB receptor binding and cannabinoid signaling in three brain regions of a rat model of schizophrenia

Schizophrenia is a serious mental health disorder characterized by several behavioral and biochemicel abnormalities. In a previous study we have shown that mu-opioid (MOP) receptor signaling is impaired in specific brain regions of our three-hit animal model of schizophrenia. Since the cannabinoid system is significantly influenced in schizophrenic patients, in the present work we investigated cannabinoid (CB) receptor binding and G-protein activation in cortical, subcortical and cerebellar regions of control and 'schizophrenic' rats. Cannabinoid agonist (WIN-55,212-2 mesylate) mediated G-protein activation was consistently decreased in all areas tested, and the difference was extremely significant in membranes prepared from the cerebellum. Interestingly, the cerebellar activity of WIN-55,212-2 stimulated G-proteins was substantially higher than those of cerebral cortex and subcortical region in control animals, indicating a primordial role of the cannabinoid system in the cerebellum. At the level of radioligand binding, the affinities of the CB receptors were also markedly decreased in the model animals. Capacity of the [³H]WIN-55,212-2 binding was only higher in the cerebellum of 'schizophrenic' model rats. Taken together, in all three brain areas of model rats both cannabinoid receptor binding and cannabinoid agonist-mediated G-protein activation were regularly decreased. Our results revealed that besides the opioids, the endocannabinoid - cannabis receptor system also shows impairment in our rat model, increasing its face validity and translational utility.

Mu-Opioid (MOP) receptor mediated G-protein signaling is impaired in specific brain regions in a rat model of schizophrenia

Schizophrenia is a complex mental health disorder. Clinical reports suggest that many patients with schizophrenia are less sensitive to pain than other individuals. Animal models do not interpret schizophrenia completely, but they can model a number of symptoms of the disease, including decreased pain sensitivities and increased pain thresholds of various modalities. Opioid receptors and endogenous opioid peptides have a substantial role in analgesia. In this biochemical study we investigated changes in the signaling properties of the mu-opioid (MOP) receptor in different brain regions, which are involved in the pain transmission, i.e., thalamus, olfactory bulb, prefrontal cortex and hippocampus. Our goal was to compare the transmembrane signaling mediated by MOP receptors in control rats and in a recently developed rat model of schizophrenia. Regulatory G-protein activation via MOP receptors were measured in [(35)S]GTPγS binding assays in the presence of a highly selective MOP receptor peptide agonist, DAMGO. It was found that the MOP receptor mediated activation of G-proteins was substantially lower in membranes prepared from the 'schizophrenic' model rats than in control animals. The potency of DAMGO to activate MOP receptor was also decreased in all brain regions studied. Taken together in our rat model of schizophrenia, MOP receptor mediated G-proteins have a reduced stimulatory activity compared to membrane preparations taken from control animals. The observed distinct changes of opioid receptor functions in different areas of the brain do not explain the augmented nociceptive threshold described in these animals.