Stress, depression, and anhedonia: caveats concerning animal models

The neuropathology of Self-Injurious Behavior: Studies using animal models

Self-injurious behavior is a debilitating characteristic that is highly prevalent in autism and other neurodevelopmental disorders. In these populations, self-injury has typically been interpreted in relation to behavioral reinforcement and/or sensory stimulation. However, self-injury is also commonly exhibited by people with a variety of neuropsychiatric disorders, where it is typically described in relation to emotional regulation and the presence or absence of suicidal ideation. Interestingly, self-injury has also been documented in many non-human animal species, especially when exposed to early environmental deprivation, isolation, and distress. Despite the propensity of animals to self-injure under adverse conditions, animal models of self-injury have not been the focus of much research, and translation of the data from these models has largely been limited to autism and neurodevelopmental disorders. This review summarizes evidence that common biological and environmental mechanisms may contribute to vulnerability for self-injury in neurodevelopmental disorders, psychiatric disorders, and distressed animals, and that investigations using animal models may be highly beneficial when considering self-injury as a behavioral phenotype that exists across diagnostic categories. Investigations using animal models have revealed that individual differences in stress responses and anxiety-related behavior contribute to vulnerability for self-injury. Animal models have implicated dysregulation of monoaminergic, glutamatergic, and other neurotransmitter systems in expression of self-injury, and these models have suggested neural targets for pharmacotherapy that have potential relevance for diverse clinical populations.

Psychosocial and neurobiological aspects of the worldwide refugee crisis: From vulnerability to resilience

Anisman, H., Doubad, D., Asokumar, A. & Matheson, K. Psychosocial and neurobiological aspects of the worldwide refugee crisis: From vulnerability to resilience. NEUROSCI BIOBEHAV REV, XXXX. Immigration occurs between countries either to obtain employment, for family reunification or to escape violence and other life-threatening conditions. Refugees and asylum seekers are often obligated to overcome a uniquely challenging set of circumstances prior to and during migration. Settlement following immigration may pose yet another set of stressors related to acculturation to the host country, as well as financial insecurity, discrimination, language barriers, and social isolation. Here we discuss the multiple consequences of immigration experiences, focusing on the health disturbances that frequently develop in adults and children. Aside from the psychosocial influences, immigration-related challenges may cause hormonal, inflammatory immune, and microbiota changes that favor psychological and physical illnesses. Some biological alterations are subject to modification by epigenetic changes, which have implications for intergenerational trauma transmission, as might disruptions in parenting behaviors and family dysfunction. Despite the hardships experienced, many immigrants and their families exhibit positive psychological adjustment after resettlement. We provide information to diminish the impacts associated with immigration and offer strength-based approaches that may foster resilience.

Combined effects of physical activity and life events on depression and PTSD in Chinese students aged 16-24 years

Background

Life events are important risk factors for depression and post-traumatic stress disorder (PTSD). Physical activity is a beneficial behavior to physiological and psychological health. While it has not been reported at present the combined effect of physical activity and life events on individual depression and PTSD, and whether it can alleviate the psychological risks induced by life events.

Objective

To comprehensively investigate the current status of life events experiences in Chinese students aged 16-24 years and analyze the combined effects of physical activity and life events on their depression and PTSD.

Methods

An online cross-sectional survey was conducted on physical activity levels, life events experiences, depression and PTSD of 1,552 Chinese students aged 16-24 using short version of International Physical Activity Questionnaire (IPAQ-S), adolescent self-rating life events checklist (ASLEC), PTSD Check List-Civilian Version (PCL-C) and Patient Health Questionnaire Depression Scale. Then, logistic regression equation and stratified analysis were used to explore the combined effects of physical activity and life events on depression and PTSD.

Results

Regression analysis showed that, except for female, <8 h of sleep, smoking, single parent/reorganized families and poor family economic status, experiencing medium-intensity and high-intensity life events were both risk factors for depression. Compared with those who experienced low-intensity life events, those who experienced medium- and high-intensity life events had a 27 and 131% increased risk of depression, respectively. In contrast, medium- and high-level physical activity could reduce the risk of depression by 49 and 53%, respectively. Similar results were obtained with PTSD as a dependent variable. Combined correlation analysis showed that, compared with those with high-level physical activity and low-intensity life events, those with low-level physical activity and high-intensity life events had a 209 and 121% increased risk of depression and PTSD, respectively. Stratified analysis showed that the threshold for life events induced depression and PTSD rose with the increase in the level of physical activity.

Conclusion

Lack of physical activity and experience of high-intensity life events are independent risk factors for depression and PTSD, and strengthening physical activity can compensate for the harm of depression and PTSD caused by life events to some extent.

Effects of heat stress on the feeding preference of yellow-feathered broilers and its possible mechanism

Heat stress is the most critical factor affecting animal feeding in summer. This experiment was conducted to investigate the effects of heat stress on the feeding preference of yellow-feathered broilers and its possible mechanism. As a result, the preference of yellow-feathered broilers for Tenebrio molitor was significantly decreased, and the fear response and serum corticosterone of broilers were significantly increased when the ambient temperatures are 35 °C (P < 0.05). In the central nervous system, consistent with the change in feeding preference, decreased dopamine in the nucleus accumbens (NAc) and increased mRNA levels of MAO-B in the ventral tegmental area (VTA) and NAc were found in yellow-feathered broilers (P < 0.05). In addition, we found significantly increased mRNA levels of corticotropin-releasing hormone receptor 1, corticotropin-releasing hormone receptor 2 and glucocorticoid receptor in the VTA and NAc of female broilers (P < 0.05). However, no similar change was found in male broilers. On the other hand, the serum levels of insulin and glucagon-like peptide-1 were increased only in male broilers (P < 0.05). Accordingly, the mRNA levels of insulin receptor and glucagon-like peptide-1 receptor in the VTA and the phosphorylation of mTOR and PI3K were increased only in male broilers (P < 0.05). In summary, the preference of yellow-feathered broilers for Tenebrio molitor feed decreased under heat stress conditions, and hedonic feeding behavior was significantly inhibited. However, the mechanism by which heat stress affects hedonic feeding behavior may contain gender differences. The insulin signaling pathway may participate in the regulation of heat stress on the male broiler reward system, while stress hormone-related receptors in the midbrain may play an important role in the effect of heat stress on the reward system of female broilers.

Noradrenergic Regulation of the Medial Prefrontal Cortex Mediates Stress Coping in Postpartum Female Mice

The prevalence of depression in women increases during the postpartum period. We previously reported that subchronic exposure to social stress decreased passive coping in postpartum female mice. This study aimed to investigate whether noradrenaline regulation might regulate coping styles in mice. We first determined whether a different type of stress, subchronic physical stress, decreases passive coping in postpartum females. Postpartum female, virgin female, and male mice were exposed to subchronic restraint stress (restraint stress for 4 h for 5 consecutive days). Subchronic restraint stress decreased passive coping in postpartum females but not in virgin females and males in the forced swim and tail suspension tests. We next examined the neuronal mechanism by which subchronic stress decreases passive coping in postpartum female mice. Neuronal activity and expression of noradrenergic receptors in the medial prefrontal cortex (mPFC) were analyzed using immunohistochemistry and reverse transcription-quantitative polymerase chain reaction, respectively. The mPFC was manipulated using chemogenetics, knockdown, or an α2A adrenergic receptor (AR) antagonist. Immunohistochemistry revealed that subchronic restraint stress increased glutamatergic neuron activation in the mPFC via forced swim stress and decreased α2A AR expression in postpartum females. Chemogenetic activation of glutamatergic neurons in the mPFC, knockdown of α2AAR in the mPFC, and the α2A AR receptor antagonist atipamezole treatment decreased passive coping in postpartum females. Subchronic restraint stress decreased passive coping in postpartum females by increasing glutamatergic neuron activity in the mPFC through α2A AR attenuation. The noradrenergic regulation of the mPFC may be a new target for treating postpartum depression.

Childhood unpredictability is associated with increased risk for long- and short-term depression and anhedonia symptoms following combat deployment

High unpredictability has emerged as a dimension of early-life adversity that may contribute to a host of deleterious consequences later in life. Early-life unpredictability affects development of limbic and reward circuits in both rodents and humans, with a potential to increase sensitivity to stressors and mood symptoms later in life. Here, we examined the extent to which unpredictability during childhood was associated with changes in mood symptoms (anhedonia and general depression) after two adult life stressors, combat deployment and civilian reintegration, which were assessed ten years apart. We also examined how perceived stress and social support mediated and /or moderated links between childhood unpredictability and mood symptoms. To test these hypotheses, we leveraged the Marine Resiliency Study, a prospective longitudinal study of the effects of combat deployment on mental health in Active-Duty Marines and Navy Corpsman. Participants (N = 273) were assessed for depression and anhedonia before (pre-deployment) and 3-6 months after (acute post-deployment) a combat deployment. Additional assessment of depression and childhood unpredictability were collected 10 years post-deployment (chronic post-deployment). Higher childhood unpredictability was associated with higher anhedonia and general depression at both acute and chronic post-deployment timepoints (βs ≥ 0.16, ps ≤.007). The relationship between childhood unpredictability and subsequent depression at acute post-deployment was partially mediated by lower social support (b = 0.07, 95% CI [0.03, 0.15]) while depression at chronic post-deployment was fully mediated by a combination of lower social support (b = 0.14, 95% CI [0.07, 0.23]) and higher perceived stress (b = 0.09, 95% CI [0.05, 0.15]). These findings implicate childhood unpredictability as a potential risk factor for depression in adulthood and suggest that increasing the structure and predictability of childhood routines and developing social support interventions after life stressors could be helpful for preventing adult depression.

Do cows with stereotypic tongue-rolling behaviour cope better with their environment?

Introduction

Stereotypic behaviours, especially oral stereotypic behaviours, are frequently expressed in farm animals. Tongue-rolling is the most common oral stereotypic behaviour in dairy cows (Bos taurus). If animals frequently display stereotypic behaviours, this is an indication of poor welfare. It has been suggested that animals express stereotypic behaviours as a way of coping with stress. As a result, animals with stereotypic behaviours may have lower levels of stress hormones than animals without stereotypic behaviours.

Methods

In this study, 916 Holstein cows in the first lactation were subjected to scan sampling behavioural observations 200 times for 10 days. All cows were assigned to either a stereotypic behaviours group (SB) or a control group (CON). The SB group was further subdivided into a tongue-rolling group (TR) and an other-stereotypic behaviours group (OS). The TR group was also split into an only tongue-rolling group (OTR) and a mixed tongue-rolling and other stereotypic behaviours group (TROS). Some cows in the TR group belonged to an extreme tongue-rolling group (ETR). Hair and saliva samples were collected from 601 cows to test cortisol concentrations and dairy herd improvement (DHI) data were collected from a total of 762 cows.

Results

There were no differences in hair or saliva cortisol concentrations between the groups (p>0.05), and the frequencies of tongue-rolling were not associated with cortisol concentrations (p>0.05). For DHI in cows, the milk protein percentage (p = 0.028), milk true protein percentage (p = 0.021) and milk crude protein percentage (p = 0.023) of cows in the ETR group were significantly lower than those in the CON group. For cows in ETR group, as the frequencies of tongue-rolling increased, the milk protein percentage (p = 0.034, r = 0.365), milk true protein percentage (p = 0.022, r = 0.393) and milk crude protein percentage (p = 0.035, r = 0.363) increased.

Discussion

We investigated the relationship between stereotypic behaviours and stress by using a non-invasive sampling method to minimise harm to the cows. We suggest that tongue-rolling may not be a way for cows to cope with stress, at least in terms of cortisol concentrations.

Comparative analysis of the nucleus accumbens transcriptional features in multiple depressive animal models

Chronic stress is deemed a significant clinical contributor to depression. The use of animal models of chronic stress can fully reveal the complex pathological mechanisms and their changing trends in the pathogenesis of depression, which is crucial for both disease prevention and therapy. It is also unknown how various forms of stress differ in their impact on animal physiology and behavior. The nucleus accumbens (NAc), an essential brain area for the pathophysiology of depression, and its underlying neural mechanisms remain unclear. Here, we systematically compared transcriptional signatures in the NAc of four chronic stress models in rats: chronic unpredictable mild stress (CUMS), chronic social defeat stress (CSDS), learned helplessness (LH), chronic restraint stress (CRS). The majority of differentially expressed genes (DEGs) were unique to a single depression model, while the rank-rank hypergeometric overlap analysis showed that the CSDS and CRS models had the greatest overlap, and the CRS and CUMS models had the least. Then, we performed pathway analysis of the differential genes and found that the neuroactive ligand-receptor interaction pathway was significantly enriched not only in the LH, CRS and CSDS stress models, but also significantly enriched in stress genes that were also altered in at least two stress models. Finally, we found three hub genes (Dcx, Tnc and Wdfy4) by constructing co-expression networks for stress genes. In summary, our research has the potential to offer fresh insights into the molecular mechanisms underlying depression induced by different types of stress, highlighting both their similarities and differences. It may provide valuable clues for understanding the pathogenesis of depression.

Effects of different chronic restraint stress periods on anxiety- and depression-like behaviors and tryptophan-kynurenine metabolism along the brain-gut axis in C57BL/6N mice

Chronic restraint stress (CRS) is a widely used stimulus to induce anxiety- and depression-like behaviors, linked to alterations in tryptophan-kynurenine (TRP-KYN) metabolism in animals. This study assessed the effects of different CRS periods on anxiety- or depression-like behaviors and TRP-KYN metabolism along brain-gut axis in C57BL/6N mice. Results showed that one-week CRS decreased the open arm entries of mice in elevated plus maze and delayed latency of feeding in novelty suppressed feeding test. Four-week CRS reduced sucrose preference, increases forced swimming immobility time, and also induced anxiety-like behaviors of mice. UPLC-MS/MS analysis revealed decreased levels of the neurotoxic 3-hydroxykynurenine (3-HK) and quinolinic acid (QA), and an increase in the neuroprotective kynurenic acid (KA) in the hippocampus of one-week CRS mice; meanwhile, four-week CRS mice displayed a reduction in KA and increases in 3-HK and QA. In the colon, both one-week and four-week CRS mice exhibited significant reductions in 3-HK and QA, with a marked increase of KA exclusively in four-week CRS mice. Briefly, one-week CRS only induced anxiety-like behaviors with hippocampal neuroprotection in TRP-KYN metabolism, whereas four-week CRS caused anxiety- and depression-like behaviors with neurotoxicity. In the colon, during both CRS periods, KYN was metabolized in the direction of NAD+ production. However, four-week CRS triggered intestinal inflammation risk with increased KA. Summarily, slightly short-term stress has beneficial effects on mice, while prolonged chronic stress can lead to pathological changes. This study offers valuable insights into stress-induced emotional disturbances.

Neuropsychological Effects of Antidepressants: Translational Studies

Pharmacological treatments that improve mood were first identified serendipitously, but more than half a century later, how these drugs induce their antidepressant effects remains largely unknown. With the help of animal models, a detailed understanding of their pharmacological targets and acute and chronic effects on brain chemistry and neuronal function has been achieved, but it remains to be elucidated how these effects translate to clinical efficacy. Whilst the field has been dominated by the monoamine and neurotrophic hypotheses, the idea that the maladaptive cognitive process plays a critical role in the development and perpetuation of mood disorders has been discussed since the 1950s. Recently, studies using objective methods to quantify changes in emotional processing found acute effects with conventional antidepressants in both healthy volunteers and patients. These positive effects on emotional processing and cognition occur without a change in the subjective ratings of mood. Building from these studies, behavioural methods for animals that quantify similar cognitive affective processes have been developed. Integrating these behavioural approaches with pharmacology and targeted brain manipulations, a picture is beginning to emerge of the underlying mechanisms that may link the pharmacology of antidepressants, these neuropsychological constructs and clinical efficacy. In this chapter, we discuss findings from animal studies, experimental medicine and patients investigating the neuropsychological effects of antidepressant drugs. We discuss the possible neural circuits that contribute to these effects and discuss whether a neuropsychological model of antidepressant effects could explain the temporal differences in clinical benefits observed with conventional delayed-onset antidepressants versus rapid-acting antidepressants.

Engeletin alleviates depression-like phenotype by increasing synaptic plasticity via the BDNF-TrkB-mTORC1 signalling pathway

Major depressive disorder (MDD) is a severe mental disorder associated with high rates of morbidity and mortality. Current first-line pharmacotherapies for MDD are based on enhancement of monoaminergic neurotransmission, but these antidepressants are still insufficient and produce significant side-effects. Consequently, the development of novel antidepressants and therapeutic targets is desired. Engeletin, a natural Smilax glabra rhizomilax derivative, is a compound with proven efficacy in treating ischemic stroke, yet its therapeutic effects and mechanisms for depression remain unexplored. The effects of engeletin were assessed in the forced swimming test (FST) and tail suspension test (TST) in mice. Engeletin was also investigated in the chronic restraint stress (CRS) mouse model of depression with fluoxetine (FLX) as the positive control. Changes in prefrontal cortex (PFC) spine density, synaptic plasticity-linked protein expressions and the brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB)- mammalian target of rapamycin complex 1 (mTORC1) signalling pathway after chronic stress and engeletin treatment were then investigated. The TrkB and mTORC1 selective inhibitors, ANA-12 and rapamycin, respectively, were utilized to assess the engeletin's antidepressive mechanisms. Our data shows that engeletin exhibited antidepressant-like activity in the FST and TST in mice without affecting locomotor activity. Furthermore, it exhibited efficiency against the depression of CRS model. Moreover, it enhanced the BDNF-TrkB-mTORC1 pathway in the PFC during CRS and altered the reduction in dendritic spine density and levels of synaptic plasticity-linked protein induced by CRS. In conclusion, engeletin has antidepressant activity via activation of the BDNF-TrkB-mTORC1 signalling pathway and upregulation of PFC synaptic plasticity.

Evaluation of Holstein cows with different tongue-rolling frequencies: stress immunity, rumen environment and general behavioural activity

BACKGROUND

The tongue-rolling behaviour of cows is regarded as an outward sign of stressed animals in a low welfare status. The primary aim of this observational study was to evaluate the association between the frequency of tongue-rolling behaviour and its physiological function. The secondary aim was to explore the relationship between general activities and the frequency of tongue-rolling behaviour of cows. A total of 126 scan sampling behavioural observations were collected over 7 d on 348 Holstein cows with the same lactation stage in the same barn. The tongue-rolling frequency was defined as the number of tongue-rolling observations as a percentage to the total observations per individual cow. According to their tongue-rolling frequency, the cows were grouped into the CON (no tongue-rolling), LT (frequency 1%), MT (frequency 5%), and HT (frequency 10%) groups. Six cows from each group were randomly selected for sampling. Serum samples, rumen fluid, milk yield, and background information were collected. The general behaviour data during 72 continuous hours of dairy cows, including eating time, rumination time, food time (eating time + rumination time), and lying time, were recorded by the collar sensor.

RESULTS

Cortisol (P = 0.012), γ-hydroxybutyric acid (P = 0.008), epinephrine (P = 0.030), and dopamine (P = 0.047) levels were significantly higher in tongue-rolling groups than in the CON group. Cortisol levels and tongue-rolling frequency had a moderate positive correlation (linearly r = 0.363). With the increase in tongue-rolling frequency, the rumen pH decreased first and then increased (P = 0.013), comparing to the CON group. HT cows had significantly less food time than CON cows (P = 0.035). The frequency of tongue-rolling had a moderate negative relationship with rumination time (r = -0.384) and food time (r = -0.492).

CONCLUSIONS

The tongue-rolling behaviour is considered as a passive coping mechanism, as the stress response in cows with high tongue-rolling frequency increased. Food intake and rumination activities were all closely related to the occurrence of tongue-rolling behaviour.

Effect of chronic unpredictable stress in female Wistar-Kyoto rats subjected to progesterone withdrawal: Relevance for Premenstrual Dysphoric Disorder neurobiology

Premenstrual Dysphoric Disorder (PMDD) is related to an abrupt drop in progesterone and impairments in the HPA axis that cause anxiety. Suffering persons report higher daily-life stress and anxiety proneness that may contribute to developing PMDD, considered a chronic stress-related disorder. Here, we explored the effect of chronic unpredictable stress (CUS) in rats subjected to progesterone withdrawal (PW) and evaluated gene expression of HPA axis activation in the stress-vulnerable Wistar-Kyoto (WKY) rat strain that is prone to anxiety. Ovariectomized WKY rats were randomly assigned to CUS or Standard-housed conditions (SHC) for 30 days. To induce PW, animals received 2 mg/kg of progesterone on day 25th for 5 days; 24 h later, they were tested using the anxiety-like burying behavior test (BBT). After behavioral completion, rats were euthanized, and brains were extracted to measure Crh (PVN) and Nr3c1 (hippocampus) mRNA. Blood corticosterone and vasopressin levels were determined. Results showed that PW exacerbated anxiety-like behaviors through passive coping in CUS-WKY. PW decreased Crh-PVN mRNA and the Nr3c1-hippocampal mRNA expression in SHC. CUS decreased Crh-PVN mRNA compared to SHC, and no further changes were observed by PW or BBT exposure. CUS reduced Nr3c1-hippocampal gene expression compared to SHC animals, and lower Nr3c1 mRNA was detected due to BBT. The PW increased corticosterone in SHC and CUS rats; however, CUS blunted corticosterone when combined with PW+BBT and similarly occurred in vasopressin concentrations. Chronic stress blunts the response of components of the HPA axis regulation when PW and BBT (systemic and psychogenic stressors, respectively) are presented. This response may facilitate less adaptive behaviors through passive coping in stress-vulnerable subjects in a preclinical model of premenstrual anxiety.

Connecting Dots between Mitochondrial Dysfunction and Depression

Mitochondria are the prime source of cellular energy, and are also responsible for important processes such as oxidative stress, apoptosis and Ca2+ homeostasis. Depression is a psychiatric disease characterized by alteration in the metabolism, neurotransmission and neuroplasticity. In this manuscript, we summarize the recent evidence linking mitochondrial dysfunction to the pathophysiology of depression. Impaired expression of mitochondria-related genes, damage to mitochondrial membrane proteins and lipids, disruption of the electron transport chain, higher oxidative stress, neuroinflammation and apoptosis are all observed in preclinical models of depression and most of these parameters can be altered in the brain of patients with depression. A deeper knowledge of the depression pathophysiology and the identification of phenotypes and biomarkers with respect to mitochondrial dysfunction are needed to help early diagnosis and the development of new treatment strategies for this devastating disorder.

Impact of ketamine administration on chronic unpredictable stress-induced rat model of depression during extremely low-frequency electromagnetic field exposure: Behavioral, histological and molecular study

OBJECTIVES

In the study, we examined the effects of ketamine and extremely low-frequency electromagnetic fields (ELF-EMF) on depression-like behavior, learning and memory, expression of GFAP, caspase-3, p53, BDNF, and NMDA receptor in animals subjected to chronic unpredictable stress (CUS).

METHODS

After applying 21 days of chronic unpredictable stress, male rats received intraperitoneal (IP) of ketamine (5 mg/kg) and then were exposed to ELF-EMF (10-Hz, 10-mT exposure conditions) for 3 days (3 h per day) and behavioral assessments were performed 24 h after the treatments. Instantly after the last behavioral test, the brain was extracted for Nissl staining, immunohistochemistry, and real-time PCR analyses. Immunohistochemistry (IHC) was conducted to assess the effect of ketamine and ELF-EMF on the expression of astrocyte marker (glial fibrillary acidic protein, GFAP) in the CA1 area of the hippocampus and medial prefrontal cortex (mPFC). Also, real-time PCR analyses were used to investigate the impacts of the combination of ketamine and ELF-EMF on the expression of caspase3, p53, BDNF, and NMDA receptors in the hippocampus in rats submitted to the CUS procedure. Results were considered statistically significant when p < .05.

RESULTS

Our results revealed that the combination of ketamine and ELF-EMF increased depression-like behavior, increased degenerated neurons and decreased the number of GFAP (+) cells in the CA1 area and mPFC, incremented the expression of caspase-3, and reduced the expression of BDNF in the hippocampus but showed no effect on the expression of p53 and NMDA-R.

CONCLUSIONS

These results reveal that combining ketamine and ELF-EMF has adverse effects on animals under chronic unpredictable stress (CUS).

Stress in adolescence as a first hit in stress-related disease development: Timing and context are crucial

The two-hit stress model predicts that exposure to stress at two different time-points in life may increase or decrease the risk of developing stress-related disorders later in life. Most studies based on the two-hit stress model have investigated early postnatal stress as the first hit with adult stress as the second hit. Adolescence, however, represents another highly sensitive developmental window during which exposure to stressful events may affect programming outcomes following exposure to stress in adulthood. Here, we discuss the programming effects of different types of stressors (social and nonsocial) occurring during adolescence (first hit) and how such stressors affect the responsiveness toward an additional stressor occurring during adulthood (second hit) in rodents. We then provide a comprehensive overview of the potential mechanisms underlying interindividual and sex differences in the resilience/susceptibility to developing stress-related disorders later in life when stress is experienced in two different life stages.

Potential of Capric Acid in Neurological Disorders: An Overview

To solve the restrictions of a classical ketogenic diet, a modified medium-chain triglyceride diet was introduced which required only around 60% of dietary energy. Capric acid (CA), a small molecule, is one of the main components because its metabolic profile offers itself as an alternate source of energy to the brain in the form of ketone bodies. This is possible with the combined capability of CA to cross the blood-brain barrier and achieve a concentration of 50% concentration in the brain more than any other fatty acid in plasma. Natural sources of CA include vegetable oils such as palm oil and coconut oil, mammalian milk and some seeds. Several studies have shown that CA has varied action on targets that include AMPA receptors, PPAR-γ, inflammatory/oxidative stress pathways and gut dysbiosis. Based on these lines of evidence, CA has proved to be effective in the amelioration of neurological diseases such as epilepsy, affective disorders and Alzheimer's disease. But these studies still warrant more pre-clinical and clinical studies that would further prove its efficacy. Hence, to understand the potential of CA in brain disease and associated comorbid conditions, an advance and rigorous molecular mechanistic study, apart from the reported in-vitro/in-vivo studies, is urgently required for the development of this compound through clinical setups.

Agarwood essential oil inhalation exerts antianxiety and antidepressant effects via the regulation of Glu/GABA system homeostasis

Depression and anxiety are common diseases that endanger the physical and mental health of individuals. Agarwood incense inhalation has been used as a traditional Chinese medicine for relaxation and to improve sleep for centuries. In a previous study by the authors it was demonstrated that agarwood essential oil (AEO) injection exerted anxiolytic and antidepressant effects. Therefore the present study further investigated the anxiolytic and antidepressant effects of AEO inhalation on anxiolytic mice induced by M-chlorophenylpiperazine and depressive mice induced by chronic unpredictable mild stress. The results demonstrated that AEO exerted a significant anxiolytic effect, whereby autonomous movements were inhibited during the light dark exploration test and open field test. Furthermore, the tail suspension test and the forced swimming test demonstrated that AEO also exerted an antidepressant effect, whereby the immobility times were decreased. Moreover, AEO was determined to increase the levels of 5-hydroxytryptamine, γ-aminobutyric acid (GABA) A receptor (GABA_A) and glutamate (Glu) in anxiolytic mice and inhibit the levels of GABA_A and Glu in depressive mice. Further investigations into how AEO affected the Glu/GABA system demonstrated that AEO markedly increased the protein expression levels of GABA transaminase (GABAT), glutamate metabotropic receptor 5 (GRM5), glutamate ionotropic receptor AMPA type subunit 1 (GluR1) and vesicular glutamate transporter 1 (VGluT1). Furthermore, AEO reduced the expression levels of GABAT, glutamate ionotropic receptor NMDA type subunit 2B and GRM5, and enhanced the expression levels of GluR1 and VGluT1. These results demonstrated that AEO potentially possesses antianxiety and antidepressant properties. The present study determined that the mechanism was related to the regulation of Glu/GABA neurotransmitter system homeostasis.

Evaluating accurate and efficient sampling strategies designed to measure social behavior and brush use in drylot housed cattle

Efficient sampling strategies expedite behavioral data collection. While multiple studies have evaluated sampling strategies for core behaviors in cattle, few have focused on social interactions. To identify sampling strategies that accurately captured cattle social behaviors and brush use feedlot steers (n = 3 pens; 9 steers/pen) were observed from 8:00 to 17:00. Average bout duration (sec), total duration per day (sec), and bout frequency were recorded for allogrooming, bar licking, tongue rolling, and brush utilization. Frequency was recorded for headbutting and mounting. Data was extracted from continuous observation datasets using eight different sampling strategies and the results subsequently compared. Differences among sampling strategies were evaluated using a non-parametric One-Way ANOVA Kruskal-Wallis Test. Pearson correlation evaluated the strength of association between a specific sampling strategy and continuous observations. Bout duration for allogrooming (P > 0.65), bar licking (P > 0.60), tongue rolling (P > 0.99), brush use (P > 0.99), and mounting frequency (P > 0.70) did not differ from continuous observations. Tongue rolling (r2 > 0.95, P <0.0001) and brush use (r2 > 0.70, P < 0.0003) were best captured when cattle were observed from 08:00 to 14:00. When cattle were continuously observed from 08:00 to 14:00 or for 15 minutes every 30 minutes, allogrooming (P > 0.2) (frequency, duration), bar licking (P > 0.95) (frequency, duration), brush use (P > 0.1) (frequency, duration), heat butt (P > 0.30) (frequency), or tongue rolling (P > 0.30) (frequency, duration) did not differ from continuous observations. Observing cattle for 15 minutes every 30 minutes yielded the highest accuracy for all behavioral metrics and was considered the most effective strategy for comprehensively evaluating cattle social behavior (r2 > 75; P < 0.05). These results provide insight into accurate and efficient sampling strategies that expedite social behavior data collection in cattle and will facilitate efficient generation of new knowledge regarding cattle social behaviors.

18β-Glycyrrhetinic Acid Ameliorates Neuroinflammation Linked Depressive Behavior Instigated by Chronic Unpredictable Mild Stress via Triggering BDNF/TrkB Signaling Pathway in Rats

Evidence shows that inflammatory responses may encompass the onset of severe depressive illness. Traditionally used licorice contains 18β-glycyrrhetinic acid (18βGA), which has been demonstrated to reduce inflammation and oxidative stress. This study investigates the antidepressant effects of 18βGA and the underlying mechanism in rats exposed to chronic unpredictable mild stress (CUMS). Wistar rats were exposed to CUMS for 36 consecutive days to establish depression. 18βGA (10, 20, and 50 mg/kg) or fluoxetine was given once daily (from day 30 to day 36). Thereafter, behavior parameters (sucrose preference test, forced-swimming test, open-field test, body weight), pro-inflammatory cytokines, neurotransmitters, adrenocorticotropic hormone (ACTH), corticosterone (CORT), and liver biomarkers were studied. Immunohistochemistry and western blot analyses were conducted to investigate the protein's expression. 18βGA (20 and 50 mg/kg) treatment increased sucrose intake, locomotion in the open-field test, decreased immobility time in the forced swim test, and improved body weight in CUMS-exposed rats. The therapy of 18βGA dramatically declined cytokines, ACTH and CORT and improved 5HT and norepinephrine in CUMS rats. Furthermore, BDNF and TrkB proteins were down-regulated in CUMS group, which was increased to varying degrees by 18βGA at doses of 20 and 50 mg/kg. Therefore, 18βGA ameliorates depressive-like behavior persuaded by chronic unpredictable mild stress, decreases neuroinflammation, liver biomarkers, stress hormones, and improves body weight, brain neurotransmitter concentration via activating on BDNF/TrkB signaling pathway in both PFC and hippocampus in rats.

Handling method affects measures of anxiety, but not chronic stress in mice

Studies in mice have shown that less aversive handling methods (e.g. tunnel or cup handling) can reduce behavioural measures of anxiety in comparison to picking mice up by their tail. Despite such evidence, tail handling continues to be used routinely. Besides resistance to change accustomed procedures, this may also be due to the fact that current evidence in support of less aversive handling is mostly restricted to effects of extensive daily handling, which may not apply to routine husbandry practices. The aim of our study was to assess whether, and to what extent, different handling methods during routine husbandry induce differences in behavioural and physiological measures of stress in laboratory mice. To put the effects of handling method in perspective with chronic stress, we compared handling methods to a validated paradigm of unpredictable chronic mild stress (UCMS). We housed mice of two strains (Balb/c and C57BL/6) and both sexes either under standard laboratory conditions (CTRL) or under UCMS. Half of the animals from each housing condition were tail handled and half were tunnel handled twice per week, once during a cage change and once for a routine health check. We found strain dependent effects of handling method on behavioural measures of anxiety: tunnel handled Balb/c mice interacted with the handler more than tail handled conspecifics, and tunnel handled CTRL mice showed increased open arm exploration in the elevated plus-maze. Mice undergoing UCMS showed increased plasma corticosterone levels and reduced sucrose preference. However, we found no effect of handling method on these stress-associated measures. Our results therefore indicate that routine tail handling can affect behavioural measures of anxiety, but may not be a significant source of chronic husbandry stress. Our results also highlight strain dependent responses to handling methods.

The effect of chronic stress and its preconditioning on spatial memory as well as hippocampal LRP1 and RAGE expression in a streptozotocin-induced rat model of Alzheimer's disease

According to available evidence, prolonged or chronic exposure to stress is detrimental to various brain structures, including the hippocampus. The current study examined the expression of two critical blood-brain barrier receptors required for amyloid-beta clearance to understand better the mechanism by which chronic stress impairs learning and memory in patients with Alzheimer's disease (AD). Rats were randomly assigned to one of two groups in this study: experiment 1 and experiment 2. Each main group was then divided into four subgroups. Rats were bilaterally injected with streptozotocin (STZ, 3 mg/kg, twice) using the intracerebroventricular (ICV) technique to induce the Alzheimer's model. Additionally, they were subjected to foot shock (1 mA, 1 Hz) for 10 s every 60 s (1 h/day) for ten consecutive days prior to and following STZ injection. The Morris Water Maze (MWM) test was used to assess spatial learning and memory. Real-time PCR was used to determine Low-density lipoprotein receptor-related protein-1 (LRP1) and receptor for advanced glycation end-products (RAGE) mRNA levels in the hippocampus. Moreover, the animals' body weights were determined as physiological parameters in all groups. The results indicated that 10-day chronic electric foot shock stress reduced body weight, impaired spatial learning and memory, decreased hippocampal LRP1 mRNA expression, and increased hippocampal RAGE mRNA expression in a rat AD model. It can be concluded that chronic stress in conjunction with AD alters the expression of LRP1 and RAGE in the hippocampus. The findings pave the way for scientists to develop novel treatment strategies for AD.

Adolescent chronic unpredictable stress leads to increased anxiety and attention deficit/hyperactivity-like symptoms in adulthood

BACKGROUND

Early-life adversities during development (e.g., child abuse and neglect) are linked to multiple behavioral and cognitive dysfunctions, such as attention deficit/hyperactivity disorder (ADHD) and anxiety disorders, which have high comorbidity. However, the impact of adversities during adolescence, a crucial period in early life for these disorders, is understudied. Using a chronic unpredictable stress (CUS) model in rats, we investigated whether adversities in adolescence could lead to increased anxiety and ADHD-like symptoms in adulthood.

METHODS

Mid- to late-adolescent (5-7-week-old) male and female Sprague-Dawley rats underwent a mild CUS procedure for 2 weeks. Various stressors were applied in an unpredictable way. Rats of both sexes were then trained with a 2-choice reaction time (2-CRT) task during adulthood, which are designed to detect ADHD-like symptoms, including increased impulsivity and lapse of attention. In addition, an open field test was conducted to examine if CUS resulted in a persistent increase in anxiety-like behavior during adulthood.

RESULTS

Both male and female rats with CUS exposure travelled shorter distances in the open field and spent less time in the center zone, indicating increased anxiety. In the 2-CRT task, rats of both sexes with CUS exposure showed increased impulsivity. Augmented lapses of attention were observed in female but not male rats.

CONCLUSION

Chronic unpredictable stress during adolescence increases anxiety and leads to ADHD-like symptoms in both male and female rats in adulthood. The deficits are more severe in females than in males. These observations support that adversities during adolescence persistently increase anxiety, which is comorbid with attention deficits.

The Relationship between Social Anhedonia and Perceived Pleasure from Food-An Exploratory Investigation on a Consumer Segment with Depression and Anxiety

Anhedonia, the diminished ability to experience pleasure, is a key symptom of a range of mental and neurobiological disorders and is associated with altered eating behavior. This research study investigated the concept of anhedonia in relation to mental disorders and the perception of pleasure from food to better understand the link between anhedonia and eating behavior. A consumer survey (n = 1051), including the Food Pleasure Scale, the Chapman Revised Social Anhedonia Scale, the Patient Health Questionnaire, and the Generalized Anxiety Disorder scale, was conducted to explore the perception of pleasure from food among people with anhedonic traits. Comparative analyses were performed between people with symptoms of depression and/or anxiety and people with no symptoms of these conditions. A segmentation analysis was furthermore performed based on three levels of anhedonia: Low, Intermediate and High anhedonia. Thus, insights into how food choice and eating habits may be affected by different levels of anhedonia are provided for the first time. Our findings showed that the 'Low anhedonia' segment found pleasure in all aspects of food pleasure, except for the aspect 'eating alone'. 'Eating alone' was, however, appreciated by the 'Intermediate anhedonia' and 'High anhedonia' segments. Both the 'Intermediate anhedonia' and 'High anhedonia' segments proved that their perceptions of food pleasure in general were affected by anhedonia, wherein the more complex aspects in particular, such as 'product information' and 'physical sensation', proved to be unrelated to food pleasure. For the 'High anhedonia' segment, the sensory modalities of food were also negatively associated with food pleasure, indicating that at this level of anhedonia the food itself is causing aversive sensations and expectations. Thus, valuable insights into the food pleasure profiles of people with different levels of anhedonia have been found for future research in the fields of mental illness, (food) anhedonia, and consumer behaviors.

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Cytokine database of stress and metabolic disorders (CdoSM): a connecting link between stress and cardiovascular disease, hypertension, diabetes and obesity

The risk of metabolic diseases is greatly increased by both chronic and acute stress. Irrespective of the cause, chronic or acute stress has the capacity to alter an individual's cytokine profile. For instance, it has been observed that stress significantly increased concentrations of IL 1 beta, IL 6 and TNF alpha. Alteration in cytokine profiles increase the likelihood of dysregulated metabolism, which subsequently acts as a driving force in the development of disorders, such as cardiovascular disease (CVD), hypertension, diabetes and obesity. Considering the dynamic and versatile role of cytokines in health and disease, an in-depth computational analysis (qualitative and quantitative) was performed to study the role of cytokines as an immuno-molecular link between rising stress levels and an increase in CVD, hypertension, diabetes and obesity. Upon a qualitative comparative analysis of cytokine profiles, a total of 14 cytokines (IL-6, TNF-alpha, IFN-gamma, IL-10, etc.) were observed to be commonly involved in stress and aforementioned four metabolic disorders. Further analysis of quantitative studies has revealed that the cytokine profile for coronary artery disease (CAD) showed remarkable increase in a couple of cytokines. IL 9 registered an increase of 67 percent to reach a concentration of 75 pg/mL. IL 3, on the other hand, was absent in control candidates but reached 56 ± 14 pg/mL in CAD patients. In case of diabetes, IFN-gamma showed an increase of 290 pg/mL. For obesity it was observed that both MCP-1 and IL-1 beta fell by 12.2 pg/mL to reach 44.4 pg/mL in obese patients. A fall of approximately 50 pg/mL was observed in the concentration of VEGF in obese patients. Similarly, hypertension was marked by reduction in concentration of several cytokines - MCP-1 and VEGF being a couple of them. Apart from performing an analysis of cytokine profiles, an innovative database [Cytokine database of Stress and Metabolic disorders (CdoSM)-https://www.akbi-nsut.co.in/] has also been created comprising cytokines involved in stress and the aforementioned metabolic disorders. Upon accessing the database, a user can find the list cytokines associated with a particular condition along with information on cytokine receptor/s; related research articles; cytokine concentration in control v/s diseased candidates for some specific cytokines and the Uniprot ID for the respective cytokine. Database can be accessed by the link-https://www.akbi-nsut.co.in/.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03375-0.

Neutral CB1 Receptor Antagonists as Pharmacotherapies for Substance Use Disorders: Rationale, Evidence, and Challenge

Cannabinoid receptor 1 (CB1R) has been one of the major targets in medication development for treating substance use disorders (SUDs). Early studies indicated that rimonabant, a selective CB1R antagonist with an inverse agonist profile, was highly promising as a therapeutic for SUDs. However, its adverse side effects, such as depression and suicidality, led to its withdrawal from clinical trials worldwide in 2008. Consequently, much research interest shifted to developing neutral CB1R antagonists based on the recognition that rimonabant’s side effects may be related to its inverse agonist profile. In this article, we first review rimonabant’s research background as a potential pharmacotherapy for SUDs. Then, we discuss the possible mechanisms underlying its therapeutic anti-addictive effects versus its adverse effects. Lastly, we discuss the rationale for developing neutral CB1R antagonists as potential treatments for SUDs, the supporting evidence in recent research, and the challenges of this strategy. We conclude that developing neutral CB1R antagonists without inverse agonist profile may represent attractive strategies for the treatment of SUDs.

A Moderate Duration of Stress Promotes Behavioral Adaptation and Spatial Memory in Young C57BL/6J Mice

Stress may serve multiple roles in cerebral functioning, ranging from a highly appropriate behavioral adaptation to a critical risk factor for susceptibility to mood disorder and cognitive impairment. It is well known that E/I (excitation/inhibition) balance is essential for maintaining brain homeostasis. However, it remains largely unknown how GABAergic and Glutamatergic neurons respond to different stressful stimuli and whether the GABAergic-Glutamatergic neuron balance is related to the transition between adaptive and maladaptive behaviors. Here, we subjected 3-month-old mice to chronic mild stress (CMS) for a period of one, two, and four weeks, respectively. The results showed that the two-week CMS procedure produced adaptive effects on behaviors and cognitive performance, with a higher number of GABAergic neuron and VGluT1-positive neurons, increasing the expressions of p-GluN2B, Reelin, and syn-PSD-95 protein in the hippocampus. In contrast, the prolonged behavioral challenge (4 week) imposes a passive coping behavioral strategy and cognitive impairment, decreased the number of GABAergic neuron, hyperactivity of VGluT1-positive neuron, increased the ratio of p-GluN2B, and decreased the expression of Reelin, syn-PSD-95 in the hippocampus. These findings suggest that a moderate duration of stress probably promotes behavioral adaptation and spatial memory by maintaining a GABAergic-Glutamatergic neuron balance and promoting the expression of synaptic plasticity-related proteins in the brain.

Anxiety-like Behavior and GABAAR/BDZ Binding Site Response to Progesterone Withdrawal in a Stress-Vulnerable Strain, the Wistar Kyoto Rats

Stress susceptibility could play a role in developing premenstrual anxiety due to abnormalities in the hypothalamus–pituitary–adrenal (HPA) axis and impairments in the GABAA receptors’ benzodiazepine (BDZ) site. Hence, we studied the stress-vulnerable Wistar Kyoto rat strain (WKY) to evaluate progesterone withdrawal (PW) effects on anxiety, HPA axis response, and to explore indicators of GABAA functionality in the BDZ site. For five days, ovariectomized WKY rats were administered 2.0 mg/kg of progesterone. Twenty-four hours after the last administration, rats were tested in the anxiety-like burying behavior test (BBT) or elevated plus maze test (EPM), and corticosterone was determined. [3H]Flunitrazepam binding autoradiography served as the BDZ binding site index of the GABAA receptor in amygdala nuclei and hippocampus’s dentate gyrus (DG). Finally, different doses of diazepam in PW-WKY rats were tested in the BBT. PW induced anxiety-like behaviors in both BBT and EPM compared with No-PW rats. PW increased corticosterone, but was blunted when combined with PW and BBT. PW increased [3H]Flunitrazepam binding in the DG and central amygdala compared with No-PW rats. Diazepam at a low dose induced an anxiogenic-like response in PW rats, suggesting a paradoxical response to benzodiazepines. Overall, PW induced anxiety-like behavior, a blunted HPA axis response, and higher GABAAR/BZD binding site sensitivity in a stress-vulnerable rat strain. These findings demonstrate the role of stress-susceptibility in GABAAR functionality in a preclinical approximation of PMDD.

Comprehensive Preclinical Assessment of Sensory, Functional, Motivational-Affective, and Neurochemical Outcomes in Neuropathic Pain: The Case of the Sigma-1 Receptor

Chronic pain remains a major health problem and is currently facing slow drug innovation. New drug treatments should address not only the sensory-discriminative but also functional and motivational-affective components of chronic pain. In a mouse model of neuropathic pain induced by partial sciatic nerve ligation (PSNL), we analyzed sensory and functional-like outcomes by hindpaw mechanical stimulation and automated gait analysis (CatWalk). We characterized over time a reward-seeking task based on diminished motivation for natural reinforcers (anhedonic-like behavior). To differentiate the appetitive ("wanting") and consummatory ("liking") aspects of motivational behavior, we quantified the latency and number of approaches to eat white chocolate, as well as the eating duration and amount consumed. We explored a putative chronic pain-induced dysregulation of monoamine function by measuring monoamine levels in the nucleus accumbens (NAc), a well-known brain reward area. Finally, we investigated the role of sigma-1 receptor (σ₁R) modulation, a nonopioid target, in these multiple dimensions by genetic deletion and pharmacological dose-response studies. After 6 weeks, PSNL increased the approach latency and reduced the consumption of white chocolate in 20-25% of the mice, while around 50-60% had one or the other parameter affected independently. After 10 weeks, sham-operated mice also displayed anhedonic-like behavior. PSNL was associated with reduced extracellular baseline dopamine and increased norepinephrine in the NAc and with a suppression of increased dopamine and serotonin efflux in response to the rewarding stimulus. Genetic and pharmacological blockade of σ₁R relieved these multiple alterations in nerve-injured mice. We comprehensively describe sensory, functional, and depression-like impairment of key components of motivated behavior associated with nerve injury. We provide a neurochemical substrate for the depressed mesocorticolimbic reward processing in chronic pain, with a potentially increased translational value. Our results also highlight σ₁R for the therapeutic intervention of neuropathic pain.

Prophylactic (R,S)-Ketamine Is Effective Against Stress-Induced Behaviors in Adolescent but Not Aged Mice

BACKGROUND

(R,S)-ketamine, an N-methyl-D-aspartate receptor antagonist, is frequently used as an anesthetic and as a rapid-acting antidepressant. We and others have reported that (R,S)-ketamine is prophylactic against stress in adult mice but have yet to test its efficacy in adolescent or aged populations.

METHODS

Here, we administered saline or (R,S)-ketamine as a prophylactic at varying doses to adolescent (5-week-old) and aged (24-month-old) 129S6/SvEv mice of both sexes 1 week before a 3-shock contextual fear-conditioning (CFC) stressor. Following CFC, we assessed behavioral despair, avoidance, perseverative behavior, locomotion, and contextual fear discrimination. To assess whether the prophylactic effect could persist into adulthood, adolescent mice were injected with saline or varying doses of (R,S)-ketamine and administered a 3-shock CFC as a stressor 1 month later. Mice were then re-exposed to the aversive context 5 days later and administered behavioral tests as aforementioned. Brains were also processed to quantify Cyclooxygenase 2 expression as a proxy for inflammation to determine whether the prophylactic effects of (R,S)-ketamine were partially due to changes in brain inflammation.

RESULTS

Our data indicate that (R,S)-ketamine is prophylactic at sex-specific doses in adolescent but not aged mice. (R,S)-ketamine attenuated learned fear and perseverative behavior in females, reduced behavioral despair in males, and facilitated contextual fear discrimination in both sexes. (R,S)-ketamine reduced Cyclooxygenase 2 expression specifically in ventral Cornu Ammonis region 3 of male mice.

CONCLUSIONS

These findings demonstrate that prophylactic (R,S)-ketamine efficacy is sex, dose, and age dependent and will inform future studies investigating (R,S)-ketamine efficacy across the lifespan.

New Horizons for Phenotyping Behavior in Rodents: The Example of Depressive-Like Behavior

The evolution of the field of behavioral neuroscience is significantly dependent on innovative disruption triggered by our ability to model and phenotype animal models of neuropsychiatric disorders. The ability to adequately elicit and measure behavioral parameters are the fundaments on which the behavioral neuroscience community establishes the pathophysiological mechanisms of neuropsychiatric disorders as well as contributes to the development of treatment strategies for those conditions. Herein, we review how mood disorders, in particular depression, are currently modeled in rodents, focusing on the limitations of these models and particularly on the analyses of the data obtained with different behavioral tests. Finally, we propose the use of new paradigms to study behavior using multidimensional strategies that better encompasses the complexity of psychiatric conditions, namely depression; these paradigms provide holistic phenotyping that is applicable to other conditions, thus promoting the emergence of novel findings that will leverage this field.

Short Juvenile Stress Has No Long-Lasting Effects on Anxiety-Like Behavior, Object Recognition Memory, or Gross Brain Morphology but Affects Dendritic Spines in the Hippocampus in Male Rats

PURPOSE

During the juvenile stage, such areas as the hippocampus and corpus callosum (CC) are still immature and sensitive to stress exposure. The present study investigated whether two different types of stressors in the juvenile stage of life have a long-lasting impact on behavior and biological outcomes in adult rats.

METHODS

Male juvenile rats were exposed to restraint or predator stress on postnatal day 25 (P25) for 3 days. Thirty-two days later (P60-74), behavioral and biological analyses were conducted. The behavioral analysis included measures of anxiety-like behavior and recognition memory. The biological analysis investigated gross cerebral morphology, based on volume analysis of the CC and hippocampus, perirhinal cortex thickness, and dendritic spine density.

RESULTS

Neither restraint stress nor predator stress affected anxiety-like behavior or object recognition memory in adulthood. Body weight and adrenal gland weight were unaffected by both types of stress. Overall, volumetric measures of the CC and hippocampus were not significant, with no changes in perirhinal cortex thickness. Spine density in the medial prefrontal cortex also was unaffected, but a decrease in dendritic spine density was found in the hippocampus in response to restraint stress and an increase to predator stress.

CONCLUSION

Short-term and daily restraint and predator stress during the juvenile stage had no long-lasting effects on anxiety-like behavior, object memory, volume of the CC or hippocampus, or perirhinal cortex thickness, but a decrease in dendritic spine density was found in the hippocampus. These findings suggest that different types of stressors have different impacts on microstructures in the brain without affecting behavior or the gross morphology of stress-sensitive brain areas.

Deep brain stimulation of the "medial forebrain bundle": a strategy to modulate the reward system and manage treatment-resistant depression

The medial forebrain bundle-a white matter pathway projecting from the ventral tegmental area-is a structure that has been under a lot of scrutinies recently due to its implications in the modulation of certain affective disorders such as major depression. In the following, we will discuss major depression in the context of being a disorder dependent on multiple relevant networks, the pathological performance of which is responsible for the manifestation of various symptoms of the disease which extend into emotional, motivational, physiological, and also cognitive domains of daily living. We will focus on the reward system, an evolutionarily conserved pathway whose underperformance leads to anhedonia and lack of motivation, which are key traits in depression. In the field of deep brain stimulation (DBS), different "hypothesis-driven" targets have been chosen as the subject of clinical trials on efficacy in the treatment-resistant depressed patient. The "medial forebrain bundle" is one such target for DBS, and has had remarkably rapid success in alleviating depressive symptoms, improving anhedonia and motivation. We will review what we have learned from pre-clinical animal studies on defining this white matter tract, its connectivity, and the complex molecular (i.e., neurotransmitter) mechanisms by which its modulation exerts its effects. Imaging studies in the form of tractographic depictions have elucidated its presence in the human brain. Such has led to ongoing clinical trials of DBS targeting this pathway to assess efficacy, which is promising yet still lack in sufficient numbers. Ultimately, one must confirm the mechanism of action and validate proof of antidepressant effect in order to have such treatment become mainstream, to promote widespread improvement in the quality of life of suffering patients.

Chronic mild stress paradigm as a rat model of depression: facts, artifacts, and future perspectives

RATIONALE

The chronic mild stress (CMS) paradigm was first described almost 40 years ago and has become a widely used model in the search for antidepressant drugs for major depression disorder (MDD). It has resulted in the publication of almost 1700 studies in rats alone. Under the original CMS procedure, the expression of an anhedonic response, a key symptom of depression, was seen as an essential feature of both the model and a depressive state. The prolonged exposure of rodents to unpredictable/uncontrollable mild stressors leads to a reduction in the intake of palatable liquids, behavioral despair, locomotor inhibition, anxiety-like changes, and vegetative (somatic) abnormalities. Many of the CMS studies do not report these patterns of behaviors, and they often fail to include consistent molecular, neuroanatomical, and physiological phenotypes of CMS-exposed animals.

OBJECTIVES

To critically review the CMS studies in rats so that conceptual and methodological flaws can be avoided in future studies.

RESULTS

Analysis of the literature supports the validity of the CMS model and its impact on the field. However, further improvements could be achieved by (i) the stratification of animals into 'resilient' and 'susceptible' cohorts within the CMS animals, (ii) the use of more refined protocols in the sucrose test to mitigate physiological and physical artifacts, and (iii) the systematic evaluation of the non-specific effects of CMS and implementation of appropriate adjustments within the behavioral tests.

CONCLUSIONS

We propose methodological revisions and the use of more advanced behavioral tests to refine the rat CMS paradigm, which offers a valuable tool for developing new antidepressant medications.

Towards Modeling Anhedonia and Its Treatment in Zebrafish

Mood disorders, especially depression, are a major cause of human disability. The loss of pleasure (anhedonia) is a common, severely debilitating symptom of clinical depression. Experimental animal models are widely used to better understand depression pathogenesis and to develop novel antidepressant therapies. In rodents, various experimental models of anhedonia have already been developed and extensively validated. Complementing rodent studies, the zebrafish (Danio rerio) is emerging as a powerful model organism to assess pathobiological mechanisms of affective disorders, including depression. Here, we critically discuss the potential of zebrafish for modeling anhedonia and studying its molecular mechanisms and translational implications.

Environmental certainty influences the neural systems regulating responses to threat and stress

Flexible calibration of threat responding in accordance with the environment is an adaptive process that allows an animal to avoid harm while also maintaining engagement of other goal-directed actions. This calibration process, referred to as threat response regulation, requires an animal to calculate the probability that a given encounter will result in a threat so they can respond accordingly. Here we review the neural correlates of two highly studied forms of threat response suppression: extinction and safety conditioning. We focus on how relative levels of certainty or uncertainty in the surrounding environment alter the acquisition and application of these processes. We also discuss evidence indicating altered threat response regulation following stress exposure, including enhanced fear conditioning, and disrupted extinction and safety conditioning. To conclude, we discuss research using an animal model of coping that examines the impact of stressor controllability on threat responding, highlighting the potential for previous experiences with control, or other forms of coping, to protect against the effects of future adversity.

Suppression of pyramidal neuron G protein-gated inwardly rectifying K+ channel signaling impairs prelimbic cortical function and underlies stress-induced deficits in cognitive flexibility in male, but not female, mice

Imbalance in prefrontal cortical (PFC) pyramidal neuron excitation:inhibition is thought to underlie symptomologies shared across stress-related disorders and neuropsychiatric disease, including dysregulation of emotion and cognitive function. G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels mediate excitability of medial PFC pyramidal neurons, however, the functional role of these channels in mPFC-dependent regulation of affect, cognition, and cortical dynamics is unknown. We used a viral-cre approach in male and female mice harboring a "floxed" version of the kcnj3 (Girk1) gene, to disrupt GIRK1-containing channel expression in pyramidal neurons within the prelimbic cortex (PrL). In males, loss of pyramidal GIRK1-dependent signaling differentially impacted measures of affect and impaired working memory and cognitive flexibility. Unexpectedly, ablation of PrL GIRK1-dependent signaling did not impact affect or cognition in female mice. Additional studies used a model of chronic unpredictable stress (CUS) to determine the impact on PrL GIRK-dependent signaling and cognitive function. CUS exposure in male mice produced deficits in cognition that paralleled a reduction in PrL pyramidal GIRK-dependent signaling akin to viral approaches whereas CUS exposure in female mice did not alter cognitive flexibility performance. Stress-induced behavioral deficits in male mice were rescued by systemic injection of a novel, GIRK1-selective agonist, ML297. In conclusion, GIRK1-dependent signaling in male mice, but not females, is critical for maintaining optimal PrL function and behavioral control. Disruption of this inhibition may underlie stress-related dysfunction of the PrL and represent a therapeutic target for treating stress-induced deficits in affect regulation and impaired cognition that reduce quality of life.

Dopaminergic signaling in prefrontal cortex contributes to the antidepressant effect of electroacupuncture: An iTRAQ-based proteomics analysis in a rat model of CUMS

Electroacupuncture (EA) is used as an adjunctive treatment for depression. This study was conducted to evaluate the efficacy and mechanisms of EA in the depressive rat model induced by chronic unpredictable mild stress (CUMS) in male adult Wistar rats. The underlying mechanisms were explored by using isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analysis of the proteins in the prefrontal cortex (PFC), and observing the number of the PFC neurons stained with hematoxylin and eosin (H&E) and synaptic morphological changes under transmission electron microscopy (TEM). The results showed that EA plus paroxetine (EA + Par) for 1 week significantly relieved depression-like anhedonia symptoms and improved anxiety-like behavior, accompanied by the improvements in synaptic morphology and a significant increase of PFC neurons. Moreover, EA or paroxetine alone significantly alleviated anhedonia symptoms after 2 weeks of intervention. Additionally, iTRAQ analysis showed that dopaminergic signaling was significantly altered in CUMS rats after 1 week of EA treatment. As the critical enzyme of this pathway, aromatic-l-amino-acid decarboxylase (DDC) was significantly upregulated after the treatment with EA + Par for 1 week. These findings suggested that the dopaminergic signaling pathway in PFC may be involved in the antidepressant mechanisms of EA.

The olfactory bulbectomy disease model: A Re-evaluation

The olfactory bulbectomized rodent has long been one of the preferred animal models of depression and certain other neuropsychiatric diseases. In fact, it is considered unparalleled, by some, in the search for antidepressant medication and the literature generated about the model is prodigious. We have revisited the "syndrome" of behavioral sequela following bulbectomy choosing ecologically valid tests likely to be underpinned with evolutionarily preserved neural circuits. Our test battery included measurements of activity, intermale aggression, pleasure seeking, stress/fear and non-spatial memory. The emphasis was on the timetable of syndrome emergence, since this has been understudied and bears on the widely held belief that non-olfactory effects dominate. Our results largely agree with previous reports describing the behavioral syndrome in that we document bulbectomized mice as hyperactive, non-aggressive and fearless. However, we did not find deficits in memory as have frequently been reported in previous studies. Notably, our results revealed that some syndrome behaviors-including the hallmark of hyperactivity-appear immediately or soon after surgery. This rapid appearance casts doubt on the widely held view that compensatory reorganization of limbic and prefrontal cortical areas following bulbectomy underlies the syndrome. Rather, hyperactivity, non-aggressiveness, reduced fear and diminished sucrose preference in the olfactory bulbectomized mouse find ready explanations in the loss of smell that is the immediate and irreversible outcome of bulbectomy. Finally, after a critical consideration of the literature and our results, we conclude that the olfactory bulbectomy model lacks the validity and simplicity previously credited to it. Indeed, we deem this lesion unsuitable as a model of most neuropsychiatric diseases since its effects are at least as complex and misunderstood as the disorders it is purported to model.

Temporal discounting when outcomes are experienced in the moment: Validation of a novel paradigm and comparison with a classic hypothetical intertemporal choice task

When faced with intertemporal choices, people typically devalue rewards available in the future compared to rewards more immediately available, a phenomenon known as temporal discounting. Decisions involving intertemporal choices arise daily, with critical impact on health and financial wellbeing. Although many such decisions are "experiential" in that they involve delays and rewards that are experienced in real-time and can inform subsequent choices, most studies have focused on intertemporal choices with hypothetical outcomes (or outcomes delivered after all decisions are made). The present study focused on experiential intertemporal choices. First, a novel intertemporal choice task was developed and validated, using delays experienced in real time and artistic photographs as consumable perceptual rewards. Second, performance on the experiential task was compared to performance on a classic intertemporal choice task with hypothetical outcomes. Involvement of distinct processes across tasks was probed by examining differential relations to state and trait anxiety. A two-parameter logistic function framework was proposed to fit indifference point data. This approach accounts for individual variability not only in the delay at which an individual switches from choosing the delayed to more immediate option, but also in the slope of that switch. Fit results indicated that the experiential task elicited temporal discounting, with effective trade-off between delay and perceptual reward. Comparison with the hypothetical intertemporal choice task suggested distinct mechanisms: first, temporal discounting across the two tasks was not correlated; and second, state and trait anxiety both were associated with choice behavior in the experiential task, albeit in distinct ways, whereas neither was significantly associated with choice behavior in the hypothetical task. The engagement of different processes in the experiential compared to hypothetical task may align with neural evidence for the recruitment of the hippocampus in animal but not in classic human intertemporal choice studies.

[Anhedonia in depression: neurobiological and genetic aspects]

Anhedonia is indeed a pathogenetically important clinical phenotype and a promising endophenotype for depressive symptoms with a very high contribution of biological and genetic factors. Neurobiological mechanisms of anhedonia are impaired functioning of the reward system of the brain, which is confirmed by many neuroimaging, genetic and experimental studies. Anhedonia has a trans-diagnoctic character and should be understood as a complex phenomenon, and it is important to correctly evaluate it within the framework of a particular research paradigm. It seems optimal to form several complementary research strategies that evaluate the most important «facets» of anhedonia, regardless of the nosological form of the disease, within the framework of one study using various methods to search for adequate biomarkers of anhedonia severity (genetic, neuroimaging, biochemical). Given the high-quality organization of such comprehensive studies based on the correct methodology of evidence-based medicine, it is likely that significant biomarker systems will be available in the near future, which, if replicated in independent samples, can be used to personalize the diagnosis and treatment of depression.

Do different types of stress differentially alter behavioural and neurobiological outcomes associated with depression in rodent models? A systematic review

Cataloguing the effects of different types of stress on behaviour and physiology in rodent models has not been comprehensively attempted. Here, we systematically review whether chronic exposure to physical stress, psychosocial stress, or both types of stress can induce different behavioural and neurobiological outcomes in male and female rodents. We found that physical stress consistently increased depressive-like behaviour, impaired social interaction and decreased body weight, while psychosocial stress consistently increased both anxiety- and depressive-like behaviour, impaired social interaction and learning and memory, increased HPA axis activity, peripheral inflammation and microglial activation, and decreased hippocampal neurogenesis in male rodents. Moreover, we found that the combined effect of both stress types resulted in a more severe pathological state defined by increased anxiety- and depressive-like behaviour, impaired social interaction and learning and memory, increased HPA axis activity and central inflammation, and reduced hippocampal neurogenesis and neural plasticity in male rodents. Phenotypes for females were less consistent, irrespective of the type of stress exposure, on account of the limited number of studies using females. This review highlights that the type of stress may indeed matter and will help animal researchers to more appropriately choose a stress/depression model that fits their research purposes.

The Relationship between Anxiety and Depression Levels with Perceived Stress and Coping Strategies in Health Care Workers during the COVID-19 Pandemic

Objectives:

Coronavirus disease (COVID-19) has spread rapidly, locally and internationally after it started in Hubei province of China in December 2019. During the spread of this infectious disease in the world, health care workers are taking place as the main people in the screening and treatment of the disease. The present study aims to evaluate the relationship between anxiety and depression levels with perceived stress and coping strategies in health care workers during the COVID-19 pandemic.

Methods:

In this study, 200 participants were included. Beck Anxiety Inventory (BDI), Beck Depression Inventory (BDI), Perceived Stress Scale-10 (PSS-10) and COPE (Coping Orientation to Problems Experienced) were applied.

Results:

Mean scores for BDI and BAI were 9.2±8.9 and 8.2±9.2, respectively. BDI scores of 33 (16.5%) of 200 participants were ≥17. 62% of the participants had minimal depression, 21.5% of the participants had mild depression, 13.5 % of the participants had moderate depression, and 3% of the participants had severe depression according to BDI scores. 60.5% of the participants had minimal anxiety, 25.5% of the participants had mild anxiety, 8.5% of the participants had moderate anxiety and 5.5% of the participants had severe anxiety according to BAI scores. BAI and BDI scores of the female participants were statistically higher than the male participants. A statistically significant positive correlation was found between BAI and BDI scores and PSS-10 scores. A statistically significant difference was found in the averages of BAI and BDI, PSS-10 COPE 3 (Focus on and venting of emotions), 7 (Religious coping) and 13 (Acceptance) subscales levels in occupational groups. A statistically significant difference was found in BDI levels in the clinical units during the pandemic.

Conclusion:

This study indicated that different coping strategies can be used in health care workers regarding anxiety, depression and stress levels during the COVID-19 pandemic. While problem-solving and emotion-focused adaptive coping mechanisms help reduce symptoms, maladaptive and negative coping mechanisms can cause symptoms to exacerbate. Thus, training should be given to developing attitudes of health care workers to cope with stress.

Effects of CRMP2 DNA Methylation in the Hippocampus on Depressive-Like Behaviors and Cytoskeletal Proteins in Rats

Chronic stress appears to alter DNA methylation and DNA methyltransferases (DNMTs) in brain regions related to emotion. Collapsin response mediator protein-2 (CRMP2) mediates the development of depression by regulating microtubule dynamics. In this study, rats were subjected to chronic unpredictable mild stress (CUMS). At the end of the CUMS procedure, normal saline or fluoxetine was administered to the rats. Moreover, normal saline or the 5-aza-2’-deoxycytidine (5-aza) was administered to the hippocampal CA1 region of the rats. Behavioral tests were performed to evaluate the depressive-like phenotypes. The CRMP2 DNA methylation levels and cytoskeletal microtubular system-related biomarkers were detected by several molecular biology techniques. The results showed that the rat model of depression was successfully established by exposure to CUMS, and fluoxetine treatment exerted an antidepressant-like effect. We observed the upregulation of DNMT1 and DNMT3a in the hippocampus of stressed rats. CUMS induced a decrease in CRMP2 expression and an increase in phosphorylated CRMP2 (pCRMP2) expression in the hippocampus of rats. The rate of DNA methylation in the CpG island of the CRMP2 promoter region in the hippocampus of stressed rats was significantly higher than that in control rats. Moreover, CUMS significantly decreased the interaction between CRMP2 and α-tubulin and decreased the microtubule dynamics. Chronic fluoxetine treatment reversed these changes. Also, hypomethylation induced by 5-aza injection into the hippocampal CA1 region caused antidepressant-like effects and increased CRMP2 expression and microtubule dynamics. These results suggested that CRMP2 DNA methylation may be involved in regulating the cytoskeletal microtubular system and mediating depressive-like behaviors.

Sexual dimorphism in pre-clinical studies of depression

Although there is a sex bias in the pathological mechanisms exhibited by brain disorders, investigation of the female brain in biomedical science has long been neglected. Use of the male model has generally been the preferred option as the female animal model exhibits both biological variability and hormonal fluctuations. Existing studies that compare behavioral and/or molecular alterations in animal models of brain diseases are generally underrepresented, and most utilize the male model. Nevertheless, in recent years there has been a trend toward the increased inclusion of females in brain studies. However, current knowledge regarding sex-based differences in depression and stress-related disorders is limited. This can be improved by reviewing preclinical studies that highlight sex differences in depression. This paper therefore presents a review of sex-based preclinical studies of depression. These shed light on the discrepancies between males and females regarding the biological mechanisms that underpin mechanistic alterations in the diseased brain. This review also highlights the conclusions drawn by preclinical studies to advance our understanding of mood disorders, encouraging researchers to promote ways of investigating and managing sexually dimorphic disorders.