The translational study of apathy-an ecological approach

Mouse Model of Parkinson's Disease with Bilateral Dorsal Striatum Lesion with 6-Hydroxydopamine Exhibits Cognitive Apathy-like Behavior

Among the symptoms of Parkinson's disease (PD), apathy comprises a set of behavioral, affective, and cognitive features that can be classified into several subtypes. However, the pathophysiology and brain regions that are involved in these different apathy subtypes are still poorly characterized. We examined which subtype of apathy is elicited in a mouse model of PD with 6-hydroxydopamine (6-OHDA) lesions and the behavioral symptoms that are exhibited. Male C57/BL6J mice were allocated to sham (n = 8) and 6-OHDA (n = 13) groups and locally injected with saline or 4 µg 6-OHDA bilaterally in the dorsal striatum. We then conducted motor performance tests and apathy-related behavioral experiments. We then pathologically evaluated tyrosine hydroxylase (TH) immunostaining. The 6-OHDA group exhibited significant impairments in motor function. In the behavioral tests of apathy, significant differences were observed between the sham and 6-OHDA groups in the hole-board test and novelty-suppressed feeding test. The 6-OHDA group exhibited impairments in inanimate novel object preference, whereas social preference was maintained in the three-chamber test. The number of TH+ pixels in the caudate putamen and substantia nigra compacta was significantly reduced in the 6-OHDA group. The present mouse model of PD predominantly showed dorsal striatum dopaminergic neuronal loss and a decrease in novelty seeking as a symptom that is related to the cognitive apathy component.

Repetitive transcranial magnetic stimulation (rTMS) for depressive-like symptoms in rodent animal models

Repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive brain stimulation technique in the treatment of psychiatric disorders. Both preclinical and clinical studies as well as systematic reviews provide a heterogeneous picture, particularly concerning the stimulation protocols used in rTMS. Here, we present a review of rTMS effects in rodent models of depressive-like symptoms with the aim to identify the most relevant factors that lead to an increased therapeutic success. The influence of different factors, such as the stimulation parameters (stimulus frequency and intensity, duration of stimulation, shape and positioning of the coil), symptom severity and individual characteristics (age, species and genetic background of the rodents), on the therapeutic success are discussed. Accumulating evidence indicates that rTMS ameliorates a multitude of depressive-like symptoms in rodent models, most effectively at high stimulation frequencies (≥5 Hz) especially in adult rodents with a pronounced pathological phenotype. The therapeutic success of rTMS might be increased in the future by considering these factors and using more standardized stimulation protocols.

Behaviour Hallmarks in Alzheimer's Disease 5xFAD Mouse Model

The 5xFAD transgenic mouse model widely used in Alzheimer's disease (AD) research recapitulates many AD-related phenotypes with a relatively early onset and aggressive age-dependent progression. Besides developing amyloid peptide deposits alongside neuroinflammation by the age of 2 months, as well as exhibiting neuronal decline by the age of 4 months that intensifies by the age of 9 months, these mice manifest a broad spectrum of behavioural impairments. In this review, we present the extensive repertoire of behavioural dysfunctions in 5xFAD mice, organised into four categories: motor skills, sensory function, learning and memory abilities, and neuropsychiatric-like symptoms. The motor problems, associated with agility and reflex movements, as well as balance and coordination, and skeletal muscle function, typically arise by the time mice reach 9 months of age. The sensory function (such as taste, smell, hearing, and vision) starts to deteriorate when amyloid peptide buildups and neuroinflammation spread into related anatomical structures. The cognitive functions, encompassing learning and memory abilities, such as visual recognition, associative, spatial working, reference learning, and memory show signs of decline from 4 to 6 months of age. Concerning neuropsychiatric-like symptoms, comprising apathy, anxiety and depression, and the willingness for exploratory behaviour, it is believed that motivational changes emerge by approximately 6 months of age. Unfortunately, numerous studies from different laboratories are often contradictory on the conclusions drawn and the identification of onset age, making preclinical studies in rodent models not easily translatable to humans. This variability is likely due to a range of factors associated with animals themselves, housing and husbandry conditions, and experimental settings. In the forthcoming studies, greater clarity in experimental details when conducting behavioural testing in 5xFAD transgenic mice could minimise the inconsistencies and could ensure the reliability and the reproducibility of the results.

Environmental enrichment and the combined interventions of EE and metformin enhance hippocampal neuron survival and hippocampal-dependent memory in type 2 diabetic rats under stress through the BDNF-TrkB signaling pathways

BACKGROUND

Type 2 diabetes (T2D) with depression causes severe cognitive impairments. The devastating conditions will further compromise the overall quality of life. The overconsumption of high-fat and high-sucrose (HFS) diet is one of the modifiable risk factors for T2D, depression, and cognitive impairments. Thus, it is essential to identify effective therapeutic strategies to overcome the cognitive impairments in T2D with depression. We proposed environmental enrichment (EE) which encompasses social, cognitive, and physical components as the alternative treatment for such impairments. We also investigated the potential neuroprotective properties of the antidiabetic drug metformin. This study aimed to investigate the effects of EE and metformin interventions on hippocampal neuronal death, and hippocampal-dependent memory impairment in T2D rats under stress.

METHODS

Thirty-two male rats (200-250 g) were divided into four groups: C group (standard diet + conventional cage), DS group [HFS-induced T2D + restraint stress (RS)], DSE group [HFS-induced T2D + RS + EE] and DSEM group [HFS + RS + EE + metformin]. Serum corticosterone (CORT) was measured to evaluate stress levels. The serum Free Oxygen Radicals Testing (FORT) and Free Oxygen Radicals Defence Test (FORD) were measured to evaluate the systemic oxidative status (OS). Serum brain-derived neurotrophic factor (BDNF) and T-maze tasks were performed to evaluate cognitive functions. Rats were humanely sacrificed to collect brains for histological, morphometric, and hippocampal gene expression studies.

RESULTS

The CORT and the serum FORT levels in the DSE and DSEM groups were lower than in the DS group. Meanwhile, the serum BDNF, T-maze scores, histological, and morphometric analysis were improved in the DSE and DSEM groups than in the DS group. These findings supported that EE and the combined interventions of EE and metformin had neuroprotective properties. The hippocampal gene expression analysis revealed that the DSE and DSEM groups showed improved regulation of BDNF-TrkB signalling pathways, including the BDNF/TrkB binding, PI3K - Akt pathway, Ras-MAPK pathway, PLCγ-Ca2+ pathway, and CREB transcription.

CONCLUSION

EE and the combined interventions of EE and metformin improved hippocampal neuron survival and hippocampal-dependent memory in T2D rats under stress by enhancing gene expression regulation of neurogenesis and synaptic plasticity.

Maternal deprivation causes CaMKII downregulation and modulates glutamate, norepinephrine and serotonin in limbic brain areas in a rat model of single prolonged stress

BACKGROUND

Early life stress is a major risk factor for later development of psychiatric disorders, including post-traumatic stress disorder (PTSD). An intricate relationship exists between various neurotransmitters (such as glutamate, norepinephrine or serotonin), calcium/calmodulin-dependent protein kinase II (CaMKII), as an important regulator of glutamatergic synaptic function, and PTSD. Here, we developed a double-hit model to investigate the interaction of maternal deprivation (MD) as an early life stress model and single prolonged stress (SPS) as a PTSD model at the behavioral and molecular levels.

METHODS

Male Wistar rats exposed to these stress paradigms were subjected to a comprehensive behavioral analysis. In hippocampal synaptosomes we investigated neurotransmitter release and glutamate concentration. The expression of CaMKII and the content of monoamines were determined in selected brain regions. Brain-derived neurotrophic factor (BDNF) mRNA was quantified by radioactive in situ hybridization.

RESULTS

We report a distinct behavioral phenotype in the double-hit group. Double-hit and SPS groups had decreased hippocampal presynaptic glutamatergic function. In hippocampus, double-hit stress caused a decrease in autophosphorylation of CaMKII. In prefrontal cortex, both SPS and double-hit stress had a similar effect on CaMKII autophosphorylation. Double-hit stress, rather than SPS, affected the norepinephrine and serotonin levels in prefrontal cortex, and suppressed BDNF gene expression in prefrontal cortex and hippocampus.

LIMITATIONS

The study was conducted in male rats only. The affected brain regions cannot be restricted to hippocampus, prefrontal cortex and amygdala.

CONCLUSION

Double-hit stress caused more pronounced and distinct behavioral, molecular and functional changes, compared to MD or SPS alone.

The dangerous "West Coast Swing" by hyperglycaemia and chronic stress in the mouse hippocampus: Role of kynurenine catabolism

Growing epidemiological studies highlight a bi-directional relationship between depressive symptoms and diabetes mellitus. However, the detrimental impact of their co-existence on mental health suggests the need to treat this comorbidity as a separate entity rather than the two different pathologies. Herein, we characterized the peculiar mechanisms activated in mouse hippocampus from the concurrent development of hyperglycaemia, characterizing the different diabetes subtypes, and chronic stress, recognized as a possible factor predisposing to major depression. Our work demonstrates that kynurenine overproduction, leading to apoptosis in the hippocampus, is triggered in a different way depending on hyperglycaemia or chronic stress. Indeed, in the former, kynurenine appears produced by infiltered macrophages whereas, in the latter, peripheral kynurenine preferentially promotes resident microglia activation. In this scenario, QA, derived from kynurenine catabolism, appears a key mediator causing glutamatergic synapse dysfunction and apoptosis, thus contributing to brain atrophy. We demonstrated that the coexistence of hyperglycaemia and chronic stress worsened hippocampal damage through alternative mechanisms, such as GLUT-4 and BDNF down-expression, denoting mitochondrial dysfunction and apoptosis on one hand and evoking the compromission of neurogenesis on the other. Overall, in the degeneration of neurovascular unit, hyperglycaemia and chronic stress interacted each other as the partners of a "West Coast Swing" in which the leading role can be assumed alternatively by each partner of the dance. The comprehension of these mechanisms can open novel perspectives in the management of diabetic/depressed patients, but also in the understanding the pathogenesis of other neurodegenerative disease characterized by the compromission of hippocampal function.

Involvement of oxidative stress and pro-inflammatory cytokines in copper sulfate-induced depression-like disorders and abnormal neuronal morphology in mice

Epidemiological studies have implicated copper as one of the key environmental risk factors for the pathogenesis of depression. However, the precise mechanism by which copper contribute to the genesis of depression particularly the involvement of oxidative stress-driven neuroinflammation is yet to be fully investigated. Thus, this study was designed to evaluate the effects of copper sulfate (CuSO4) on depression-like behaviors and the role of oxidative stress and pro-inflammatory cytokines in mice. Forty male Swiss mice were distributed into control and three test groups (n = 10), and were treated orally with distilled water (10 mL/kg) or CuSO4 (25, 50 and 100 mg/kg) daily for 28 days. Afterwards, the tail suspension, forced swim, and sucrose splash tests were used for the detection of depression-like effects. The animals were then euthanized and the brains were processed for the estimation of biomarkers of oxidative stress and pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-6). The histomorphological features and neuronal viability of the prefrontal cortex, hippocampus and striatum were also determined. Mice exposed to CuSO4 displayed depression-like features when compared with controls. The brain concentrations of malondialdehyde, nitrite and pro-inflammatory cytokines were elevated in CuSO4-treated mice. Mice exposed to CuSO4 also had reduced brain antioxidant status (glutathione, glutathione-s-transferase, total thiols, superoxide-dismutase and catalase), as well as altered histomorphological features, and decreased population of viable neuronal cells. These findings suggest that CuSO4 increases oxidative stress and pro-inflammatory cytokines to elicit depression-like effects in mice.

Zoo Animal Welfare Assessment: Where Do We Stand?

Zoological institutions, such as zoos and aquariums, have made animal welfare a top priority, as it is not only a moral obligation but also crucial for fulfilling their roles in education and conservation. There is a need for science-based tools to assess and monitor animal welfare in these settings. However, assessing the welfare of zoo animals is challenging due to the diversity of species and lack of knowledge on their specific needs. This review aims to discuss the advantages and disadvantages of existing methodologies for assessing zoo animal welfare through: (1) A critical analysis of the main approaches to zoo animal welfare assessment; (2) A description of the most relevant animal-based welfare indicators for zoo animals with a particular focus on behavioural and physiological indicators; and (3) An identification of areas that require further research.

Emotional- and cognitive-like responses induced by social defeat stress in male mice are modulated by the BNST, amygdala, and hippocampus

Introduction

Chronic exposure to social defeat stress (SDS) has been used to investigate the neurobiology of depressive- and anxiety-like responses and mnemonic processes. We hypothesized that these affective, emotional, and cognitive consequences induced by SDS are regulated via glutamatergic neurons located in the bed nucleus of the stria terminalis (BNST), amygdaloid complex, and hippocampus in mice.

Methods

Here, we investigated the influence of chronic SDS on (i) the avoidance behavior assessed in the social interaction test, (ii) the anxiety-like behavior (e.g., elevated plus-maze, and open field tests) (iii) depressive-like behaviors (e.g., coat state, sucrose splash, nesting building, and novel object exploration tests), (iv) the short-term memory (object recognition test), (v) ΔFosB, CaMKII as well as ΔFosB + CaMKII labeling in neurons located in the BNST, amygdaloid complex, dorsal (dHPC) and the ventral (vHPC) hippocampus.

Results

The main results showed that the exposure of mice to SDS (a) increased defensive and anxiety-like behaviors and led to memory impairment without eliciting clear depressive-like or anhedonic effects; (b) increased ΔFosB + CaMKII labeling in BNST and amygdala, suggesting that both areas are strongly involved in the modulation of this type of stress; and produced opposite effects on neuronal activation in the vHPC and dHPC, i.e., increasing and decreasing, respectively, ΔFosB labeling. The effects of SDS on the hippocampus suggest that the vHPC is likely related to the increase of defensive- and anxiety-related behaviors, whereas the dHPC seems to modulate the memory impairment.

Discussion

Present findings add to a growing body of evidence indicating the involvement of glutamatergic neurotransmission in the circuits that modulate emotional and cognitive consequences induced by social defeat stress.

Introducing a depression-like syndrome for translational neuropsychiatry: a plea for taxonomical validity and improved comparability between humans and mice

Depressive disorders are the most burdensome psychiatric disorders worldwide. Although huge efforts have been made to advance treatment, outcomes remain unsatisfactory. Many factors contribute to this gridlock including suboptimal animal models. Especially limited study comparability and replicability due to imprecise terminology concerning depressive-like states are major problems. To overcome these issues, new approaches are needed. Here, we introduce a taxonomical concept for modelling depression in laboratory mice, which we call depression-like syndrome (DLS). It hinges on growing evidence suggesting that mice possess advanced socioemotional abilities and can display non-random symptom patterns indicative of an evolutionary conserved disorder-like phenotype. The DLS approach uses a combined heuristic method based on clinical depression criteria and the Research Domain Criteria to provide a biobehavioural reference syndrome for preclinical rodent models of depression. The DLS criteria are based on available, species-specific evidence and are as follows: (I) minimum duration of phenotype, (II) significant sociofunctional impairment, (III) core biological features, (IV) necessary depressive-like symptoms. To assess DLS presence and severity, we have designed an algorithm to ensure statistical and biological relevance of findings. The algorithm uses a minimum combined threshold for statistical significance and effect size (p value ≤ 0.05 plus moderate effect size) for each DLS criterion. Taken together, the DLS is a novel, biologically founded, and species-specific minimum threshold approach. Its long-term objective is to gradually develop into an inter-model validation standard and microframework to improve phenotyping methodology in translational research.

Apathy in depression: An arterial spin labeling perfusion MRI study

INTRODUCTION

Apathy, as defined as a deficit in goal-directed behaviors, is a critical clinical dimension in depression associated with chronic impairment. Little is known about its cerebral perfusion specificities in depression. To explore neurovascular mechanisms underpinning apathy in depression by pseudo-continuous arterial spin labeling (pCASL) magnetic resonance imaging (MRI).

METHODS

Perfusion imaging analysis was performed on 90 depressed patients included in a prospective study between November 2014 and February 2017. Imaging data included anatomical 3D T1-weighted and perfusion pCASL sequences. A multiple regression analysis relating the quantified cerebral blood flow (CBF) in different regions of interest defined from the FreeSurfer atlas, to the Apathy Evaluation Scale (AES) total score was conducted.

RESULTS

After confound adjustment (demographics, disease and clinical characteristics) and correction for multiple comparisons, we observed a strong negative relationship between the CBF in the left anterior cingulate cortex (ACC) and the AES score (standardized beta = -0.74, corrected p value = 0.0008).

CONCLUSION

Our results emphasized the left ACC as a key region involved in apathy severity in a population of depressed participants. Perfusion correlates of apathy in depression evidenced in this study may contribute to characterize different phenotypes of depression.

The importance of a multidimensional approach to the preclinical study of major depressive disorder and apathy

Both the neuropsychiatric syndrome of apathy and major depressive disorder comprise a heterogenous cluster of symptoms which span multiple behavioural domains. Despite this heterogeneity, there is a tendency in the preclinical literature to conclude a MDD or apathy-like phenotype from a single dimensional behavioural task used in isolation, which may lead to inaccurate phenotypic interpretation. This is significant, as apathy and major depressive disorder are clinically distinct with different underlying mechanisms and treatment approaches. At the clinical level, apathy and major depressive disorder can be dissociated in the negative valence (loss) domain of the Research Domain Criteria. Symptoms of MDD in the negative valence (loss) domain can include an exaggerated response to emotionally salient stimuli and low mood, while in contrast apathy is characterised by an emotionally blunted state. In this article, we highlight how using a single dimensional approach can limit psychiatric model interpretation. We discuss how integrating behavioural findings from both the positive and negative (loss) valence domains of the Research Domain Criteria can benefit interpretation of findings. We focus particularly on behaviours relating to the negative valence (loss) domain, which may be used to distinguish between apathy and major depressive disorder at the preclinical level. Finally, we consider how future approaches using home cage monitoring may offer a new opportunity to detect distinct behavioural profiles and benefit the overall translatability of findings.

Behavioural phenotypes of intrinsic motivation in schizophrenia determined by cluster analysis of objectively quantified real-world performance

Intrinsic motivation deficits are a prominent feature of schizophrenia that substantially impacts functional outcome. This study used cluster analysis of innate real-world behaviours captured during two open-field tasks to dimensionally examine heterogeneity in intrinsic motivation in schizophrenia patients (SZ) and healthy controls (HC). Wireless motion capture quantified participants' behaviours aligning with distinct aspects of intrinsic motivation: exploratory behaviour and effortful activity in the absence of external incentive. Cluster analysis of task-derived measures identified behaviourally differentiable subgroups, which were compared across standard clinical measures of general amotivation, cognition, and community functioning. Among 45 SZ and 47 HC participants, three clusters with characteristically different behavioural phenotypes emerged: low exploration (20 SZ, 19 HC), low activity (15 SZ, 8 HC), and high exploration/activity (10 SZ, 20 HC). Low performance in either dimension corresponded with similar increased amotivation. Within-cluster discrepancies emerged for amotivation (SZ > HC) within the low exploration and high performance clusters, and for functioning (SZ < HC) within all clusters, increasing from high performance to low activity to low exploration. Objective multidimensional characterization thus revealed divergent behavioural expression of intrinsic motivation deficits that may be conflated by summary clinical measures of motivation and overlooked by unidimensional evaluation. Deficits in either aspect may hinder general motivation and functioning particularly in SZ. Multidimensional phenotyping may help guide personalized remediation by discriminating between intrinsic motivation impairments that require amelioration versus unimpaired tendencies that may facilitate remediation.

Encore: Behavioural animal models of stress, depression and mood disorders

Animal studies over the past two decades have led to extensive advances in our understanding of pathogenesis of depressive and mood disorders. Among these, rodent behavioural models proved to be of highest informative value. Here, we present a comprehensive overview of the most popular behavioural models with respect to physiological, circuit, and molecular biological correlates. Behavioural stress paradigms and behavioural tests are assessed in terms of outcomes, strengths, weaknesses, and translational value, especially in the domain of pharmacological studies.

Oral carcinogenesis triggers a nociceptive behavior and c-Fos expression in rats' trigeminal pathway

OBJECTIVE

To recognize changes that occur along the trigeminal pathway in oral cancer in order to establish an effective approach to pain control.

METHODS

Wistar rats were divided into control and 4-NQO-groups for 8, 12, 16, or 20 weeks. 4-NQO suspension was administered on the animals` tongues. Mechanical hyperalgesia, assessment of facial expressions and an open field test were performed. After euthanasia, the animals' tongues were removed for macro and microscopic analysis. c-Fos expression was analyzed in the trigeminal pathway structures.

RESULTS

4-NQO induced time-dependent macroscopic lesions that were compatible with neoplastic tumors. Histopathological analysis confirmed oral squamous cell carcinoma in 50% of the animals on the 20th week. There was a significant nociceptive threshold reduction during the first two weeks, followed by a threshold return to the baseline levels, decreasing again from the 12th week. Facial nociceptive expression scores were observed on the 20th week, while increased grooming and exploratory activity were observed on the 8th week. Trigeminal ganglion showed an increased c-Fos immunoexpression on the 20th week and in the trigeminal subnucleus caudalis, it occurred on the 16th and 20th. The long-term carcinogenic exposure caused changes in the nociceptive behavior and c-Fos expression in the rats' trigeminal pathway.

Combined Administration of (R)-Ketamine and the mGlu2/3 Receptor Antagonist LY341495 Induces Rapid and Sustained Effects in the CUMS Model of Depression via a TrkB/BDNF-Dependent Mechanism

Ketamine is an effective, rapid-acting antidepressant drug (RAAD), but it induces side effects. To overcome these challenges, attempts have been made to use safer enantiomer ((R)-ketamine) or mGlu2/3 receptor antagonists, which induce ketamine-like effects and enhance its action. Here, we propose combining these two strategies to investigate the antidepressant-like effects of low doses of two ketamine enantiomers in combination with a low dose of the mGlu2/3 receptor antagonist LY341495. Rapid and sustained antidepressant-like effects were assessed in C57BL/6J mice using the tail suspension test (TST) and the chronic unpredictable mild stress (CUMS) model of depression in stress-naïve mice. ELISA was used to measure BDNF levels. In the TST, low doses of both (S)-ketamine and (R)-ketamine were potentiated by a subeffective dose of LY341495. However, in the CUMS model, only (R)-ketamine was able to induce long-lasting anti-apathetic and anti-anhedonic effects when coadministered with low-dose LY341495. The mechanism of this drug combination was dependent on BDNF and AMPA receptor activity. ELISA results suggest that the hippocampus might be the site of this action. MGlu2/3 receptor antagonists, in combination with (R)-ketamine, may serve as potential RAADs, with a high efficiency and low risk of side effects.

The effectiveness of (R)-ketamine and its mechanism of action differ from those of (S)-ketamine in a chronic unpredictable mild stress model of depression in C57BL/6J mice

(S)-ketamine has been approved as a rapid-acting antidepressant drug (RAAD). Although ketamine has an advantage over classic antidepressants (ADs) due to its rapid action, it remains a controversial drug due to its undesirable effects. Behavioral studies indicate that another enantiomer of ketamine, namely, (R)-ketamine, has been proposed as a safer but still effective RAAD. However, these conclusions have not been confirmed in any model of depression based on chronic environmental stress, which effectively reflects the core symptoms of this disease. Thus, we decided to compare the effects of (R)- and (S)-ketamine on chronic unpredictable mild stress (CUMS) in mice. Behavioral studies showed that (R)-ketamine induced anti-anhedonic and anti-apathetic efficacy up to seven days after administration, while the (S)-ketamine effect persisted up to 24 h or 3 days after injection. The behavioral effects of (R)-ketamine depended on the activation of TrkB receptors, while the (S)-ketamine effects did not. Western blot analyses showed that (S)-ketamine action might be related to both mTOR and ERK pathway activation and to the increased expression of GluA1 protein in the prefrontal cortex (PFC). In contrast, (R)-ketamine did not change ERK phosphorylation in the PFC, while it increased mTOR expression. (S)-Ketamine produced behavioral effects indicative of possible side effects in the dose range studied, while (R)-ketamine did not. This indicates that (R)-ketamine may be more effective, have a longer-lasting effect, and be safer to use than (S)-ketamine.

Mouse modeling for anxiety disorders in older adults

Anxiety disorders are common in older adults and are strongly associated with increased risk for numerous age-related conditions. Preclinical mechanistic data are needed to identify more specific therapeutic targets for treating and preventing these disorders. Mice serve as excellent preclinical models as they have been used extensively in aging studies, and behavioral tests have been developed. A panel of tests would capture the important clinical aspects of apathy, anxiety, and psychomotor behavior and allow longitudinal testing strategies in a rigorous and minimally stressful manner.

The group II mGlu receptor antagonist LY341495 induces a rapid antidepressant-like effect and enhances the effect of ketamine in the chronic unpredictable mild stress model of depression in C57BL/6J mice

Ketamine produces a rapid antidepressant effect, but its use can be associated with serious side effects. Hence, other therapeutic options that will allow us to obtain a quick and safe antidepressant effect by modulating glutamatergic transmission are needed. Antagonists of mGlu2/3 receptors, which share some mechanisms of action with ketamine, may be good candidates to obtain this effect. Here, we show that the metabotropic glutamate (mGlu) 2/3 receptor antagonist LY341495 induced a dose-dependent antidepressant-like effect in the chronic unpredictable mild stress (CUMS) model of depression in C57BL/6J mice after both single and subchronic (three-day) administration. Furthermore, a noneffective dose of LY341495 (0.3 mg/kg) given jointly with a noneffective dose of ketamine (3 mg/kg) reversed the CUMS-induced behavioral effects, indicating that coadministration of ketamine with an mGlu2/3 receptor antagonist might allow its therapeutically effective dose to be lowered. Western blot results indicate that mTOR pathway activation might be involved in the mechanism of action of this drug combination. Moreover, the combined doses of both substances did not produce undesirable behavioral effects characteristic of a higher dose of ketamine (10 mg/kg) commonly used in rodent studies to induce antidepressant effects. Coadministration of low doses of ketamine and LY341495 did not induce the hyperactivity typical of NMDA channel blockers, did not disturb short-term memory in the novel object recognition (NOR) test, and did not disturb motor coordination in the rotarod test. Our research not only confirmed the earlier data on the rapid antidepressant effect of mGlu2/3 receptor antagonists but also indicated that such compounds can safely lower the effective dose of ketamine.

Animal Models of Depression: What Can They Teach Us about the Human Disease?

Depression is apparently the most common psychiatric disease among the mood disorders affecting about 10% of the adult population. The etiology and pathogenesis of depression are still poorly understood. Hence, as for most human diseases, animal models can help us understand the pathogenesis of depression and, more importantly, may facilitate the search for therapy. In this review we first describe the more common tests used for the evaluation of depressive-like symptoms in rodents. Then we describe different models of depression and discuss their strengths and weaknesses. These models can be divided into several categories: genetic models, models induced by mental acute and chronic stressful situations caused by environmental manipulations (i.e., learned helplessness in rats/mice), models induced by changes in brain neuro-transmitters or by specific brain injuries and models induced by pharmacological tools. In spite of the fact that none of the models completely resembles human depression, most animal models are relevant since they mimic many of the features observed in the human situation and may serve as a powerful tool for the study of the etiology, pathogenesis and treatment of depression, especially since only few patients respond to acute treatment. Relevance increases by the fact that human depression also has different facets and many possible etiologies and therapies.

G-protein coupled receptor 88 knockdown in the associative striatum reduces psychiatric symptoms in a translational male rat model of Parkinson disease

BACKGROUND

In addition to motor disability, another characteristic feature of Parkinson disease is the early appearance of psychiatric symptoms, including apathy, depression, anxiety and cognitive deficits; treatments for these symptoms are limited by the development of adverse effects such as impulse-control disorders. In this context, we investigated the orphan G protein-coupled receptor 88 (GPR88) as a novel therapeutic target.

METHODS

We used lentiviral-mediated expression of specifically designed microRNA to knock down Gpr88 in a translational male rat model of early Parkinson disease obtained by dopamine loss in the dorsolateral striatum as a result of 6-hydroxydopamine lesions. We evaluated the impact of Gpr88 knockdown on the Parkinson disease model using behavioural, immunohistochemical and in situ hybridization studies.

RESULTS

Knockdown of Gpr88 in associative territories of the dorsal striatum efficiently reduced alterations in mood, motivation and cognition through modulation of the regulator of the G-protein signalling 4 and of the truncated splice variant of the FosB transcription factor. Knockdown of Gpr88 also reduced allostatic changes in striatal activity markers that may be related to patterns observed in patients and that provide support for an "overload" hypothesis for the etiology of the psychiatric symptoms of Parkinson disease.

LIMITATIONS

Behavioural tests assessing specific cognitive and motivational parameters are needed to further characterize the effects of the lesion and of Gpr88 knockdown in early-stage and advanced Parkinson disease models, presenting more extensive dopamine loss. Additional studies focusing on the direct and indirect striatal output pathways are also required, because little is known about the signalling pathways regulated by GPR88 in different striatal cell types.

CONCLUSION

GPR88 may constitute a highly relevant target for the treatment of the psychiatric symptoms of Parkinson disease.

Further evidence of anxiety- and depression-like behavior for total genetic ablation of cannabinoid receptor type 1

Cannabinoid receptor type 1 (CB1R) is the most abundant cannabinoid receptor in central nervous system. Clinical studies and animal models have shown that the attenuation of endocannabinoid system signaling correlates with the development of psychiatric disorders such as anxiety, depression and schizophrenia. In the present work, multiple behavioral tests were performed to evaluate behaviors related to anxiety and depression in CB1R^+/- and CB1R^-/-. CB1R^+/- mice had anxiety-related behavior similar to wild type (CB1R^+/+) mice, whereas CB1R^-/- mice displayed an anxious-like phenotype, which indicates that lower expression of CB1R is sufficient to maintain the neural circuits modulating anxiety. In addition, CB1R^-/- mice exhibited alterations in risk assessment and less exploration, locomotion, grooming, body weight and appetite. These phenotypic characteristics observed in CB1R^-/- mice could be associated with symptoms observed in human psychiatric disorders such as depression. A better knowledge of the neuromodulatory role of CB1R may contribute to understand scope and limitations of the development of medical treatments.

Treadmill Exercise Buffers Behavioral Alterations Related to Ethanol Binge-Drinking in Adolescent Mice

The binge-drinking pattern of EtOH consumption, which is frequently observed in adolescents, is known to induce several neurobehavioral alterations, but protection strategies against these impairments remain scarcely explored. We aimed to study the protective role of treadmill physical exercise on the deficits caused after repeated cycles of binge-like EtOH exposure in the cognition, motivation, exploration, and emotion of C57BL/6J mice from adolescence to adulthood. Animals were divided into four groups: control group, exercised group, EtOH group, and exercised + EtOH group (20% in tap water). The exercise was performed for 20 min, 5 days/week at 20 cm/s. Then, animals were submitted to several behavioral tasks. Compared to binge-drinking mice, the exercised + EtOH group exhibited diminished anxiolytic-related behaviors in the elevated plus-maze, enhanced exploratory activity in the open field, reduced preference for alcohol odor when another rewarding stimulus was present (social stimulus) and lower latency to start self-cleaning behaviors in the sucrose splash test. In contrast, other measurements such as habituation learning and working memory were not improved by exercise. Besides, exercise was not able to reduce alcohol consumption across the weeks. In conclusion, physical activity during adolescence and early adulthood could buffer certain neurobehavioral alterations associated with binge-drinking, despite not reducing the quantity of consumed alcohol.

Shared and dissociable features of apathy and reward system dysfunction in bipolar I disorder and schizophrenia

BACKGROUND

Bipolar disorder I (BD-I) is defined by episodes of mania, depression and euthymic states. These episodes are among other symptoms characterized by altered reward processing and negative symptoms (NS), in particular apathy. However, the neural correlates of these deficits are not well understood.

METHODS

We first assessed the severity of NS in 25 euthymic BD-I patients compared with 25 healthy controls (HC) and 27 patients with schizophrenia (SZ). Then, we investigated ventral (VS) and dorsal striatal (DS) activation during reward anticipation in a Monetary Incentive Delayed Task and its association with NS.

RESULTS

In BD-I patients NS were clearly present and the severity of apathy was comparable to SZ patients. Apathy scores in the BD-I group but not in the SZ group correlated with sub-syndromal depression scores. At the neural level, we found significant VS and DS activation in BD-I patients and no group differences with HC or SZ patients. In contrast to patients with SZ, apathy did not correlate with striatal activation during reward anticipation. Explorative whole-brain analyses revealed reduced extra-striatal activation in BD-I patients compared with HC and an association between reduced activation of the inferior frontal gyrus and apathy.

CONCLUSION

This study found that in BD-I patients apathy is present to an extent comparable to SZ, but is more strongly related to sub-syndromal depressive symptoms. The findings support the view of different pathophysiological mechanisms underlying apathy in the two disorders and suggest that extra-striatal dysfunction may contribute to impaired reward processing and apathy in BD-I.

Animal models of major depression: drawbacks and challenges

Major depression is a leading contributor to the global burden of disease. This situation is mainly related to the chronicity and/or recurrence of the disorder, and to poor response to antidepressant therapy. Progress in this area requires valid animal models. Current models are based either on manipulating the environment to which rodents are exposed (during the developmental period or adulthood) or biological underpinnings (i.e. gene deletion or overexpression of candidate genes, targeted lesions of brain areas, optogenetic control of specific neuronal populations, etc.). These manipulations can alter specific behavioural and biological outcomes that can be related to different symptomatic and pathophysiological dimensions of major depression. However, animal models of major depression display substantial shortcomings that contribute to the lack of innovative pharmacological approaches in recent decades and which hamper our capabilities to investigate treatment-resistant depression. Here, we discuss the validity of these models, review putative models of treatment-resistant depression, major depression subtypes and recurrent depression. Furthermore, we identify future challenges regarding new paradigms such as those proposing dimensional rather than categorical approaches to depression.

The Hyperactivity-Impulsivity-Irritiability-Disinhibition-Aggression-Agitation Domain in Alzheimer's Disease: Current Management and Future Directions

Behavioral and psychological symptoms of dementia (BPSD) afflict the vast majority of patients with dementia, especially those with Alzheimer's disease (AD). In clinical settings, patients with BPSD most often do not present with just one symptom. Rather, clusters of symptoms commonly co-occur and can, thus, be grouped into behavioral domains that may ultimately be the result of disruptions in overarching neural circuits. One major BPSD domain routinely identified across patients with AD is the hyperactivity-impulsivity-irritiability-disinhibition-aggression-agitation (HIDA) domain. The HIDA domain represents one of the most difficult sets of symptoms to manage in AD and accounts for much of the burden for caregivers and hospital staff. Although many studies recommend non-pharmacological treatments for HIDA domain symptoms as first-line, they demonstrate little consensus as to what these treatments should be and are often difficult to implement clinically. Certain symptoms within the HIDA domain also do not respond adequately to these treatments, putting patients at risk and necessitating adjunct pharmacological intervention. In this review, we summarize the current literature regarding non-pharmacological and pharmacological interventions for the HIDA domain and provide suggestions for improving treatment. As epigenetic changes due to both aging and AD cause dysfunction in drug-targeted receptors, we propose that HIDA domain treatments could be enhanced by adjunct strategies that modify these epigenetic alterations and, thus, increase efficacy and reduce side effects. To improve the implementation of non-pharmacological approaches in clinical settings, we suggest that issues regarding inadequate resources and guidance for implementation should be addressed. Finally, we propose that increased monitoring of symptom and treatment progression via novel sensor technology and the "DICE" (describe, investigate, create, and evaluate) approach may enhance both pharmacological and non-pharmacological interventions for the HIDA domain.

Self-awareness deficits associated with lower treatment motivation in cocaine addiction

BACKGROUND

Individuals with cocaine use disorder (CUD) often display behaviours that are paradoxically misaligned with their situation. Typical examples include poor treatment motivation and inconsistent self-reported craving. These behaviours may reflect impairments in the awareness of one's own behaviour.

OBJECTIVES

We examined whether impaired self-awareness of addiction-related frontostriatal dysfunction (i.e., symptoms of apathy, disinhibition, and executive dysfunction) was associated with treatment motivation and craving.

METHODS

Sixty-five outpatients with CUD (57 male) and their informants (those who knew the patient well) completed parallel self and informant versions of the Frontal Systems Behaviour Scale. Self-awareness was indexed through the discrepancy between self and informant scores in the three sub-scales; apathy, disinhibition and executive dysfunction. The University Rhode Island Change Assessment Scale assessed treatment motivation. Self-reported craving was assessed using a visual analogue scale. Multiple linear regression models examined associations between self-awareness and treatment motivation and craving, adjusting for sociodemographic factors and lifetime drug use.

RESULTS

We found an inverse relationship between self-awareness of symptoms of disinhibition and treatment motivation maintenance. Although impaired awareness of disinhibition was also correlated with craving, this association was not significant after adjusting for sociodemographic factors and drug use. The apathy and executive dysfunction awareness scores were not associated with treatment motivation or craving.

CONCLUSION

We show that people with lower insight into their disinhibition problems (e.g., impulsivity, mood instability) have more problems maintaining motivation when initiating treatment. Findings suggest that self-awareness interventions could be useful to prevent premature treatment dropout and improve addiction treatment outcomes.

Investigating the association of ventral and dorsal striatal dysfunction during reward anticipation with negative symptoms in patients with schizophrenia and healthy individuals

Background

Negative symptoms are a core feature of schizophrenia and also found in healthy individuals in subclinical forms. According to the current literature the two negative symptom domains, apathy and diminished expression may have different underlying neural mechanisms. Previous observations suggest that striatal dysfunction is associated with apathy in schizophrenia. However, it is unclear whether apathy is specifically related to ventral or dorsal striatal alterations. Here, we investigated striatal dysfunction during reward anticipation in patients with schizophrenia and a non-clinical population, to determine whether it is associated with apathy.

Methods

Chronic schizophrenia patients (n = 16) and healthy controls (n = 23) underwent an event- related functional MRI, while performing a variant of the Monetary Incentive Delay Task. The two negative symptom domains were assessed in both groups using the Brief Negative Symptoms Scale.

Results

In schizophrenia patients, we saw a strong negative correlation between apathy and ventral and dorsal striatal activation during reward anticipation. In contrast, there was no correlation with diminished expression. In healthy controls, apathy was not correlated with ventral or dorsal striatal activation during reward anticipation.

Conclusion

This study replicates our previous findings of a correlation between ventral striatal activity and apathy but not diminished expression in chronic schizophrenia patients. The association between apathy and reduced dorsal striatal activity during reward anticipation suggests that impaired action-outcome selection is involved in the pathophysiology of motivational deficits in schizophrenia.

Combining actigraphy, ecological momentary assessment and neuroimaging to study apathy in patients with schizophrenia

BACKGROUND

Apathy can be defined as a reduction of goal-directed behavior and is a strong predictor for poor functional outcome in schizophrenia. However, no objective measure of apathy has been identified and assessment is limited to retrospective interview-based ratings. Here we aimed to identify more precise objective readouts of apathy for translational research and clinical practice.

METHODS

We employed a combined approach including interview-based ratings of the two negative symptom factors apathy and diminished expression, actigraphy based measures of spontaneous motor activity and the evaluation of daily activities using ecological momentary assessment. Furthermore, a functional magnetic resonance imaging task for reward anticipation was applied to investigate shared and divergent neural correlates of interview-based and behaviorally measured apathy.

RESULTS

We found in 18 schizophrenia patients with high interview-based apathy levels that motor activity was negatively correlated with apathy but not with diminished expression. In contrast, measures of daily activities were not associated with apathy. Neural activation during reward anticipation revealed an association between hypoactivation of the ventral striatum and interview-based apathy as well as hypoactivation of the inferior frontal gyrus and motor activity level.

CONCLUSIONS

Spontaneous motor activity is an objective readout of apathy, which was specific and not present for diminished expression. On a neural level, interview-based and objective measures of apathy showed divergent neural correlates in the cortical-striatal network, which suggests dissociable neural processes. Finally, motor activity provides a promising readout for quantifying apathy in both translational research and clinical practice.

Objective assessment of exploratory behaviour in schizophrenia using wireless motion capture

Motivation deficits are a prominent feature of schizophrenia and have substantial consequences for functional outcome. The impact of amotivation on exploratory behaviour has not been extensively assessed by entirely objective means. This study evaluated deficits in exploratory behaviour in an open-field setting using wireless motion capture. Twenty-one stable adult outpatients with schizophrenia and twenty matched healthy controls completed the Novelty Exploration Task, in which participants explored a novel environment containing familiar and uncommon objects. Objective motion data were used to index participants' locomotor activity and tendency for visual and tactile object exploration. Clinical assessments of positive and negative symptoms, apathy, cognition, depression, medication side-effects, and community functioning were also administered. Relationships between task performance and clinical measures were evaluated using Spearman correlations, and group differences were evaluated using multivariate analysis of covariance tests. Although locomotor activity and tactile exploration were similar between the schizophrenia and healthy control groups, schizophrenia participants exhibited reduced visual object exploration (F(2,35)=3.40, p=0.045). Further, schizophrenia participants' geometric pattern of locomotion, visual exploration, and tactile exploration were correlated with overall negative symptoms (|ρ|=0.46-0.64, p<=0.039) and apathy (|ρ|=0.49-0.62, p<=0.028), and both visual and tactile exploration were also correlated with community functioning (|ρ|=0.46-0.48, p<=0.043). The Novelty Exploration Task may be a valuable tool to quantify exploratory behaviour beyond what is captured through standard clinical instruments and human observer ratings. Findings from this initial study suggest that locomotor activity and object interaction tendencies are impacted by motivation, and reveal deficits specifically in visual exploration in schizophrenia.

Fluoxetine induces paradoxical effects in C57BL6/J mice: comparison with BALB/c mice

The C57BL6/J mouse is the most commonly used strain in genetic investigations and behavioural tests. However, only a few studies have used C57BL6/J mice to assess the effects of antidepressant compounds. We carried out a study to compare the behavioural effects of fluoxetine (FLX) in a model of depression in two mice strains: C57BL6/J and BALB/c. We used an 8-week unpredictable chronic mild stress (UCMS) protocol during which FLX was administered (15 mg/kg, oral) from the third week to the end of the protocol. We found that UCMS induced degradation of the coat state in the two strains. Moreover, as expected, we observed that FLX elicited antidepressant-like effects in the BALB/c mice by reducing the coat state deterioration and the latency of grooming in splash test. However, in the C57BL6/J mice, it did not induce this action, but instead triggered an opposite effect: an increased sniffing latency in the novelty suppression of feeding test. We conclude that FLX exerts a paradoxical effect in the C57Bl6/J strain. This observation is consistent with some clinical features of hyper-reactivity to FLX observed in humans. Therefore, the UCMS protocol used in C57Bl6/J mice could be a good model to study the mechanisms of the paradoxical effects caused by selective serotonin reuptake inhibitors.