Exploratory drive, fear, and anxiety are dissociable and independent components in foraging mice

Behavioral manifestations and underlying mechanisms of amphetamine in constructing animal models of mania: a comprehensive review

Mania is a mind disorder with heightened emotions, etc. Amphetamine (AMPH), a drug with central nervous system excitatory effects, can disrupt neurotransmitter release and metabolism, causing mania. AMPH-induced animal models of mania show increased risk and reward-seeking behaviors and excessive locomotion like mania patients, verifiable by tests like Elevated Plus Maze (EPM). It also impacts neurotransmitter balance in different brain regions, aligning with the imbalance in mania patients. Multiple signaling pathways including extracellular regulated protein kinases and others are involved, and their altered activities link to mania symptoms. In the AMPH-induced mania model, regions like the frontal cortex have increased oxidative stress and inflammatory response. Moreover, AMPH changes neurotrophin levels, potentially causing neuronal damage and cognitive impairment. In summary, the AMPH-induced mania animal model is crucial for studying mania's pathogenesis. However, further in-depth studies on neurotransmitter regulation, signaling pathway intervention, and neurotrophic factors are needed to develop more effective and personalized treatment plans.

Minocycline treatment attenuates neurobehavioural abnormalities and neurostructural aberrations in the medial prefrontal cortex in mice fed a high-fat diet during adolescence

A preference for and overconsumption of a high-fat diet (HFD) are common among adolescents and are recognized as risk factors for multiple mental disorders. The protracted maturation of the medial prefrontal cortex (mPFC), a key brain structure that plays a critical role in mental functions that are essential for both developing and mature individuals (including emotional processing, decision making, risk assessment, and creative thinking), during adolescence renders it more vulnerable to the environmental insults experienced during this critical developmental window. However, the effects of HFD consumption during adolescence on mPFC-related behaviours and the underlying mechanisms need to be further investigated. In this study, we observed that mice fed a HFD throughout adolescence developed depressive- and anxiety-like behaviours and distinctively increased risk-avoidance behaviour, accompanied by morphological aberrations of both pyramidal neuron and microglia in the mPFC. The systemic administration of minocycline, a well-known broad-spectrum antibiotic, effectively attenuated the adverse effects of HFD consumption during adolescence on neurobehaviours and the morphology of pyramidal neurons in the mPFC. This study provides new insights into the psychological effects of long-term HFD consumption during adolescence and indicates the existence of a window during which microglial stabilization may be a promising strategy to protect against the HFD consumption-induced increase in the risk of psychiatric disorders.

The curious interpretation of novel object recognition tests

Novel object recognition tasks are commonly used to assess memory in rodents. These tests rely on an innate preference for exploring objects that are new or have been moved or changed. However, this preference, while normally seen in control conditions, is not immutable. Stressful experiences as well as lesions and genetic mutations can lead mice and rats to show clear preferences for exploring familiar objects and familiar locations. This opinion article discusses the evidence for changes in novelty preference, implications of this lability for assessing memory, and the significance of shifts in novelty preference as a readout of changes in curiosity with implications in approach-avoidance behavior and explore-exploit decision-making. Finally, we provide some recommendations for reporting and interpreting novelty preference task findings moving forward.

The gold standard control groups in physiological and pharmacological research are not that shiny: Intraperitoneal saline injection and needle pricking affect prepubescent mice's behavior in a sex-specific manner

Study design and experimental tools are crucial for good quality science, and an essential part of it is the choice of control groups to best test the hypothesis. Two of the standard control groups in physiological and pharmacological research are needle pricking without substance injection (Sham) and/or vehicle injection (Saline). However, both needle pricking and saline injection can act as stressors, potentially influencing the analyzed outcome. This raises the question of whether the dependent variable remains unaffected by the stress induced by these procedures. Despite the significance of this issue, very few studies have investigated the behavioral effects of a single intraperitoneal (I.P.) Sham and/or single I.P. Saline injection in mice, and those that have used mostly adult males. In this study, we investigated if a single I.P. Sham and/or I.P. Saline injection affects female and male prepubertal (4-weeks-old) mice behavior. After Sham or Saline injection, we examined exploratory/motor behavior (open field test - OFT), anxiety-like behavior (elevated plus-maze - EPM), and behavioral despair/depressive-like behavior (forced swimming test - FST). We observed that both Sham prepubertal females and males showed behavioral alterations in OFT and EPM, and Saline males showed behavioral alterations in OFT and FST. On the other hand, prepubertal Saline females showed an increase in exploratory behavior, risk assessment/anxiety-like behavior, and behavioral despair/depressive-like behavior. Thus, our findings indicate that control procedures commonly used in physiological and pharmacological experimental designs affect the behavior of prepubescent mice, with more pronounced effects in females than in males. This study suggests considering Naïve animals together with Sham and/or Vehicle for a better and more honest interpretation of the data.

Natural variations of adolescent neurogenesis and anxiety predict the hierarchical status of adult inbred mice

Hierarchy provides a survival advantage to social animals in challenging circumstances. In mice, social dominance is associated with trait anxiety which is regulated by adult hippocampal neurogenesis. Here, we test whether adolescent hippocampal neurogenesis may regulate social dominance behavior in adulthood. We observe that adolescent individuals with higher trait anxiety and lower levels of hippocampal neurogenesis prior to the formation of a new group become dominants, suggesting that baseline adolescent neurogenesis predicts hierarchical status. This phenotype persists beyond social hierarchy stabilization. Experimentally reducing neurogenesis prior to the stabilization of social hierarchy in group-housed adolescent males increases the probability of mice to become dominant and increases anxiety. Finally, when innate dominance is assessed in socially isolated and anxiety-matched animals, mice with impaired neurogenesis display a dominant status toward strangers. Together, these results indicate that adolescent neurogenesis predicts and regulates hierarchical and situational dominance behavior along with anxiety-related behavior. These results provide a framework to study the mechanisms underlying social hierarchy and the dysregulation of dominance behavior in psychiatric diseases related to anxiety.

Machine learning and confirmatory factor analysis show that buprenorphine alters motor and anxiety-like behaviors in male, female, and obese C57BL/6J mice

Buprenorphine is an opioid approved for medication-assisted treatment of opioid use disorder. Used off-label, buprenorphine has been reported to contribute to the clinical management of anxiety. Although human anxiety is a highly prevalent disorder, anxiety is a latent construct that cannot be directly measured. The present study combined machine learning techniques and artificial intelligence with confirmatory factor analysis to evaluate the hypothesis that buprenorphine alters motor and anxiety-like behavior in C57BL/6J (B6) mice (n = 30) as a function of dose, sex, and body mass. After administration of saline (control) or buprenorphine, mice were placed on an elevated zero maze (EZM) for 5 min. Digital video of mouse behavior was uploaded to the cloud, and mouse position on the maze was tracked and analyzed with supervised machine learning and artificial intelligence. ANOVA and post hoc test showed that buprenorphine significantly altered five motor behaviors. Confirmatory factor analysis revealed that the latent construct of anxiety-like behavior accounted for a statistically significant amount of variance in all five motor behaviors.NEW & NOTEWORTHY Machine learning and pose estimation using a convolutional neural network accurately detected and objectively scored buprenorphine-induced changes in locomotor behaviors of mice on an elevated zero maze (EZM). Confirmatory factor analysis supports the interpretation that the anxiety-like construct accounted for the buprenorphine-induced changes in motor behavior. The results have noteworthy implications for the relationship between Darwin's story model of mammalian emotions and computational models of anxiety-like behavior in mice.

Characterization of neuronal oscillations in the prelimbic cortex, nucleus accumbens and CA1 hippocampus during object retrieval task in rats predisposed to early life stress

BACKGROUND

Early life stress (ELS) during the stress hypo-responsive period (SHRP) alters the curiosity-like behavior later during adolescence. Previous studies have shown maternal separation (MS) stress-induced heightened curiosity and associated risk-taking behavior in the object retrieval task (ORT). However, the neural correlates of curiosity in adolescent rats predisposed to early life stress remain unexplored. Hence, the present study aimed to investigate the neural oscillatory patterns and network characteristics in the regions implicated in curiosity behavior, such as the Prelimbic cortex (PL), Nucleus Accumbens (NAc), and CA1 of the Hippocampus. The local field potentials data were analysed to understand the neural activity patterns in these areas during the risky zone crossing and object retrieval phase of the ORT in MS rats and compared with the normal control (NC) group.

RESULTS

In comparison to NC, MS rats showed a reduction in the theta power at 8-12 Hz, beta power at 12-20 Hz, and gamma power at 20-40 Hz range in the PL during risky zone crossing time. MS rats also showed reduced cross-correlation between PL-CA1 and reduced theta coherence between NAc-CA1 during risky zone crossing. During the object retrieval phase, the MS rats showed reduced peak cross-correlation between PL-CA1 and PL-NAc. Behaviourally, MS rats displayed an increased preference for the curiosity platform and retrieved more hidden objects, thus accounting for a higher curiosity index than controls.

CONCLUSION

In summary, a reduced synchronization between the PL, NAc, and CA1 during the object retrieval task indicates how early MS stress during a critical developmental period impacts the limbic circuit connectivity. This corresponded with enhanced curiosity index in adolescent MS rats, predicting an altered intrinsic motivation and hence a higher susceptibility to substance use disorders during adolescence.

Developmental Shifts in Amygdala Function

Mammals have evolved with strategies to optimize survival and thrive in their native environment. This includes both physical and behavioral adaptations, and extends to their social environment. However, within a social context, the roles of an animal change across development, and their behavior and biology must update to match these changes. The amygdala has a key role in social and emotional processing and expression, and displays developmental changes in early juvenile, adolescent, and adult transitions. Furthermore, the amygdala is highly sensitive to the social environment. This chapter will describe the primary amygdala developmental changes, how this maps onto major changes in social and emotional domains, and propose a framework where developmental stage of intra-amygdala circuits and its regulation by cortical inputs biases the animal toward developmentally appropriate social and emotional behavior. This developmental plasticity also presents an opportunity for retuning the developmental trajectory in the presence of ongoing challenges during maturation, such as constant threat or resource scarcity, so there can be realignment of behavior to match environmental demands.

Metabolomics Reveal Key Metabolic Pathway Responses to Anxiety State Regulated by Serotonin in Portunus trituberculatus

BACKGROUND

Anxiety refers to the pathological persistence and intensification of emotional responses to danger, affecting health from psychological and physical aspects. Serotonin is an important neurotransmitter involved in the onset of anxiety.

METHODS AND RESULTS

To explore the biological changes in the formation of anxiety in crustaceans under the regulation of serotonin, we applied the open field-like test method for assessing anxiety states of larval Portunus trituberculatus, a highly aggressive crustacean species with a more simple neural structure compared with rodents and mammals. Compared with the control group, serotonin treatment resulted in a significant decrease in the time spent by the larvae in the central zone, suggesting anxiety-like behavior. Clonazepam treatment reversed this result and provided further evidence that the behavior of larval P. trituberculatus displayed anxiety. Moreover, a non-targeted metabolomic analysis found a significant alteration in the metabolites involved in tryptophan metabolism pathways associated with anxiety, including L-kynurenine, N-acetyl serotonin, and serotonin. These metabolites are involved in the serotonin pathway, the kynurenine pathway, and other pathways that affect anxiety through tryptophan metabolism. There were no significant differences in tryptophan metabolism levels between the control and clonazepam treatment groups.

CONCLUSIONS

Our results demonstrate the possible existence of anxiety-like behavior in the larvae of P. trituberculatus from two perspectives. Being a species with a simpler neural structure than that of mammals, the larvae of P. trituberculatus offer a convenient model for studying the mechanisms of anxiety in crustaceans.

Neonatal limited bedding and nesting experience may lead to a sex-dependent increase in panic-like defensive behaviours in adult mice

In humans, adverse physical and/or psychological traumas in childhood may predispose to developing psychiatric disorders in adulthood, including panic disorder. To model early life adversity in mice, we subjected male and female C57BL/6 J mice to a limited bedding and nesting (LBN) protocol between postnatal days 2-9 and investigated its effect on responsiveness to panicogenic challenges in adulthood. Panic-like escape behaviour was assessed during exposure to a high concentration of CO2 (20%) or in the beetle mania task (BMT), used to model respiratory and non-respiratory-related types of panic respectively. Neonatal exposure to LBN increased panic-like jumping during the CO2 challenge in male but not female mice. In an initial pharmacological validation of the BMT as a panic-inducing paradigm, undirected jumping and horizontal escape behaviours were reduced significantly by the panicolytic alprazolam (0.05 and 0.1mg.kg-1 i.p.) whilst tolerance to the close proximity of the aversive robo-beetle increased. The anxiolytic diazepam (1 mg.kg-1 i.p.) reduced only the number of horizontal escape attempts. In both sexes, previous experience of LBN significantly enhanced the number of horizontal escape episodes, indicating a pro-panic phenotype. Directed escape to access a safe ledge on the wall of the test arena, which was seen only in males, was also reduced significantly following LBN. These findings indicate that early life adversity produced by fragmented and unpredictable maternal care promotes a sex-specific increase in susceptibility to panic-like behaviour in adulthood. Whilst non-respiratory-related panic-like behaviour was enhanced in both sexes, females were resilient to respiratory-related challenges.

Phasic Stimulation of Dopaminergic Neurons of the Lateral Substantia Nigra Increases Open Field Exploratory Behaviour and Reduces Habituation Over Time

Transient nigrostriatal dopaminergic signalling is well known for its role in reinforcement learning and increasingly so for its role in the initiation of voluntary movement. However, how transient bursts of dopamine modulate voluntary movement remains unclear, likely due to the heterogeneity of the nigrostriatal system, the focus of optogenetic studies on locomotion at sub-sec time intervals, and the overlapping roles of phasic dopamine in behaviour and novelty signalling. In this study we investigated how phasic activity in the lateral substantia nigra pars compacta (lateral SNc) over time affects voluntary behaviours during exploration. Using a transgenic mouse model of both sexes expressing channelrhodopsin (ChR2) in dopamine transporter-expressing cells, we stimulated the lateral SNc while mice explored an open field over two consecutive days. We found that phasic activation of the lateral SNc induced an increase in exploratory behaviours including horizontal movement activity, locomotion initiation, and rearing specifically on the first open field exposure, but not on the second day. In addition, stimulated animals did not habituate to the same extent as their ChR2-negative counterparts, as indicated by a lack of decrease in baseline activity. These findings suggest that rather than prompting voluntary movement in general, phasic nigrostriatal dopamine prompts context-appropriate behaviours. In addition, dopamine signalling that modulates movement acts over longer timescales than the transient signal, affecting behaviour even after the signal has ended.

A brainstem to hypothalamic arcuate nucleus GABAergic circuit drives feeding

The obesity epidemic is principally driven by the consumption of more calories than the body requires. It is therefore essential that the mechanisms underpinning feeding behavior are defined. Neurons within the brainstem dorsal vagal complex (DVC) receive direct information from the digestive system and project to second-order regions in the brain to regulate food intake. Although γ-aminobutyric acid is expressed in the DVC (GABADVC), its function in this region has not been defined. In order to discover the unique gene expression signature of GABADVC cells, we used single-nucleus RNA sequencing (Nuc-seq), and this revealed 19 separate clusters. We next probed the function of GABADVC cells and discovered that the selective activation of GABADVC neurons significantly controls food intake and body weight. Optogenetic interrogation of GABADVC circuitry identified GABADVC → hypothalamic arcuate nucleus (ARC) projections as appetite suppressive without creating aversion. Electrophysiological analysis revealed that GABADVC → ARC stimulation inhibits hunger-promoting neuropeptide Y (NPY) neurons via GABA release. Adopting an intersectional genetics strategy, we clarify that the GABADVC → ARC circuit curbs food intake. These data identify GABADVC as a new modulator of feeding behavior and body weight and a controller of orexigenic NPY neuron activity, thereby providing insight into the neural underpinnings of obesity.

HIV-1 Tat and morphine interactions dynamically shift striatal monoamine levels and exploratory behaviors over time

Despite the advent of combination anti-retroviral therapy (cART), nearly half of people infected with HIV treated with cART still exhibit HIV-associated neurocognitive disorders (HAND). HAND can be worsened by co-morbid opioid use disorder. The basal ganglia are particularly vulnerable to HIV-1 and exhibit higher viral loads and more severe pathology, which can be exacerbated by co-exposure to opioids. Evidence suggests that dopaminergic neurotransmission is disrupted by HIV exposure, however, little is known about whether co-exposure to opioids may alter neurotransmitter levels in the striatum and if this in turn influences behavior. Therefore, we assayed motor, anxiety-like, novelty-seeking, exploratory, and social behaviors, and levels of monoamines and their metabolites following 2 weeks and 2 months of Tat and/or morphine exposure in transgenic mice. Morphine decreased dopamine levels, but significantly elevated norepinephrine, the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the serotonin metabolite 5-hydroxyindoleacetic acid, which typically correlated with increased locomotor behavior. The combination of Tat and morphine altered dopamine, DOPAC, and HVA concentrations differently depending on the neurotransmitter/metabolite and duration of exposure but did not affect the numbers of tyrosine hydroxylase-positive neurons in the mesencephalon. Tat exposure increased the latency to interact with novel conspecifics, but not other novel objects, suggesting the viral protein inhibits exploratory behavior initiation in a context-dependent manner. By contrast, and consistent with prior findings that opioid misuse can increase novelty-seeking behavior, morphine exposure increased the time spent exploring a novel environment. Finally, Tat and morphine interacted to affect locomotor activity in a time-dependent manner, while grip strength and rotarod performance were unaffected. Together, our results provide novel insight into the unique effects of HIV-1 Tat and morphine on monoamine neurochemistry that may underlie their divergent effects on motor and exploratory behavior.

A neural signature for the subjective experience of threat anticipation under uncertainty

Uncertainty about potential future threats and the associated anxious anticipation represents a key feature of anxiety. However, the neural systems that underlie the subjective experience of threat anticipation under uncertainty remain unclear. Combining an uncertainty-variation threat anticipation paradigm that allows precise modulation of the level of momentary anxious arousal during functional magnetic resonance imaging (fMRI) with multivariate predictive modeling, we train a brain model that accurately predicts subjective anxious arousal intensity during anticipation and test it across 9 samples (total n = 572, both gender). Using publicly available datasets, we demonstrate that the whole-brain signature specifically predicts anxious anticipation and is not sensitive in predicting pain, general anticipation or unspecific emotional and autonomic arousal. The signature is also functionally and spatially distinguishable from representations of subjective fear or negative affect. We develop a sensitive, generalizable, and specific neuroimaging marker for the subjective experience of uncertain threat anticipation that can facilitate model development.

Lateral hypothalamic glutamatergic inputs to VTA glutamatergic neurons mediate prioritization of innate defensive behavior over feeding

The lateral hypothalamus (LH) is involved in feeding behavior and defense responses by interacting with different brain structures, including the Ventral Tegmental Area (VTA). Emerging evidence indicates that LH-glutamatergic neurons infrequently synapse on VTA-dopamine neurons but preferentially establish multiple synapses on VTA-glutamatergic neurons. Here, we demonstrated that LH-glutamatergic inputs to VTA promoted active avoidance, long-term aversion, and escape attempts. By testing feeding in the presence of a predator, we observed that ongoing feeding was decreased, and that this predator-induced decrease in feeding was abolished by photoinhibition of the LH-glutamatergic inputs to VTA. By VTA specific neuronal ablation, we established that predator-induced decreases in feeding were mediated by VTA-glutamatergic neurons but not by dopamine or GABA neurons. Thus, we provided evidence for an unanticipated neuronal circuitry between LH-glutamatergic inputs to VTA-glutamatergic neurons that plays a role in prioritizing escape, and in the switch from feeding to escape in mice.

Estimating foraging behavior in rodents using a modified paradigm measuring threat imminence dynamics

Animals need to respond to threats to avoid danger and approach rewards. In nature, these responses did not evolve alone but are always accompanied by motivational conflict. A semi-naturalistic threat imminence continuum model models the approach-avoidance conflict and is able to integrate multiple behaviors into a single paradigm. However, its comprehensive application is hampered by the lack of a detailed protocol and data about some fundamental factors including sex, age, and motivational level. Here, we modified a previously established paradigm measuring threat imminence continuum dynamics, involving modifications of training and testing protocols, and utilization of commercial materials combined with open science codes, making it easier to replicate. We demonstrate that foraging behavior is modulated by age, hunger level, and sex. This paradigm can be used to study foraging behaviors in animals in a more naturalistic manner with relevance to human approach-avoid conflicts and associated psychopathologies.

Diazepam effects on anxiety-related defensive behavior of male and female high and low open-field activity inbred mouse strains

Open-field activity is a commonly used measure of anxiety-related behavior in rodents. The inbred High and Low Activity strains of mice, selected for extreme differences in open-field activity, have been used as a genetic model of anxiety-related behaviors. These selected strains have been thoroughly studied through extensive behavioral testing, quantitative trait locus (QTL) mapping, whole-genome sequencing, and RNA sequencing, to uncover phenotypic and genotypic differences related to anxiety-related behavior. However, the effects of anxiolytic drugs on anxiety-related behavior in these strains have not been studied previously. This study allowed us to expand on previous findings to further characterize the anxiety-related behavior of these unique strains, using an anxiolytic drug. The goal of this study was to determine whether the treatment of adult male and female High Activity (low anxiety) and Low Activity (high anxiety) mice with diazepam, an agonist at the benzodiazepine allosteric site on the GABAA receptor and a drug commonly prescribed to treat anxiety disorders in humans, led to decreases in anxiety-like defensive behavioral responses as assessed in the open-field test (OFT) and elevated plus-maze (EPM). We tested the effects of three doses of diazepam (0, 0.5, 1.0, 3.0 mg/kg, i.p.), given 30 min before behavioral testing to one High Activity strain (H2) and two Low Activity strains (L1 and L2). There was an anxiolytic effect of diazepam observed in the High Activity strain, with more entries into the open arms of the elevated plus-maze, an effect similar to that seen in common mouse strains. However, the only anxiolytic effect of diazepam seen in the Low Activity strains was a reduction in stretch attend posture (SAP). Low Activity strains also displayed freezing behavior in both the OFT and EPM. The combination of the observed freezing behavior, that was not reduced by diazepam, and the reduction in SAP seen with diazepam, suggests a more complex phenotype that includes a component of innate fear in addition to anxiety-related risk assessment behaviors. Since fear and anxiety are distinguishable traits, and both contribute to human anxiety disorders, these results provide novel insight about interpretation of previous genetic and phenotypic differences observed between the High and Low Activity strains.

Understanding patch foraging strategies across development

Patch foraging is a near-ubiquitous behaviour across the animal kingdom and characterises many decision-making domains encountered by humans. We review how a disposition to explore in adolescence may reflect the evolutionary conditions under which hunter-gatherers foraged for resources. We propose that neurocomputational mechanisms responsible for reward processing, learning, and cognitive control facilitate the transition from exploratory strategies in adolescence to exploitative strategies in adulthood - where individuals capitalise on known resources. This developmental transition may be disrupted by psychopathology, as there is emerging evidence of biases in explore/exploit choices in mental health problems. Explore/exploit choices may be an informative marker for mental health across development and future research should consider this feature of decision-making as a target for clinical intervention.

Effect of apparatus characteristics on anxiety-like behavior in young adult and old mice of both sexes assessed by the elevated plus maze assay

Incidence of anxiety-like disorders in humans has been shown to decrease with aging; however, it is still under debate whether there are similarities in mice, which would support the use of mouse models in understanding the neuronal network changes that regulate anxiety-like behavior in aging. One of the most common tests used to assess anxiety-like behavior in laboratory animals is the elevated plus maze (EPM). Although several variables, such as room brightness and width of the maze arms, have been shown to influence the spontaneous animal behavior during the EPM test, none of these variables have ever been evaluated in aging to understand their possible differential effect on younger and older mice. We therefore decided to investigate the effect of apparatus construction on young adult and old mice of both sexes on EPM test performance. Our results show that distance traveled during the test is the variable that is most affected by apparatus characteristics independent of age and sex. We also found that apparatus construction was key in demonstrating that old mice spent more time and had relatively more entries in the open arms as compared to young mice, suggesting a decrease in anxiety-like behavior with age. Taken together, our data demonstrate that EPM apparatus characteristics dramatically affect test outcome with a wider arm apparatus being more effective in revealing age-dependent changes in anxiety-like behavior, thus, suggesting the use of a wider arm EPM when conducting aging studies in mice.

Sevoflurane Exposure in Neonates Perturbs the Expression Patterns of Specific Genes That May Underly the Observed Learning and Memory Deficits

Exposure to commonly used anesthetics leads to neurotoxic effects in animal models-ranging from cell death to learning and memory deficits. These neurotoxic effects invoke a variety of molecular pathways, exerting either immediate or long-term effects at the cellular and behavioural levels. However, little is known about the gene expression changes following early neonatal exposure to these anesthetic agents. We report here on the effects of sevoflurane, a commonly used inhalational anesthetic, on learning and memory and identify a key set of genes that may likely be involved in the observed behavioural deficits. Specifically, we demonstrate that sevoflurane exposure in postnatal day 7 (P7) rat pups results in subtle, but distinct, memory deficits in the adult animals that have not been reported previously. Interestingly, when given intraperitoneally, pre-treatment with dexmedetomidine (DEX) could only prevent sevoflurane-induced anxiety in open field testing. To identify genes that may have been altered in the neonatal rats after sevoflurane and DEX exposure, specifically those impacting cellular viability, learning, and memory, we conducted an extensive Nanostring study examining over 770 genes. We found differential changes in the gene expression levels after exposure to both agents. A number of the perturbed genes found in this study have previously been implicated in synaptic transmission, plasticity, neurogenesis, apoptosis, myelination, and learning and memory. Our data thus demonstrate that subtle, albeit long-term, changes observed in an adult animal's learning and memory after neonatal anesthetic exposure may likely involve perturbation of specific gene expression patterns.

Structural, functional and behavioral impact of allergic rhinitis on olfactory pathway and prefrontal cortex

BACKGROUND

Allergic rhinitis (AR) has been identified as a cause of olfactory dysfunction. Beyond the classic symptoms, AR has been associated with altered sleep patterns, a decline in cognitive performance and higher likelihood of depression and anxiety. The olfactory pathway has been postulated to be a possible link between nasal inflammation and central nervous system (CNS) modifications. Thus, we aimed to investigate the structural, functional and behavioral changes in the olfactory pathway and related areas in an animal model of AR.

METHODS

AR was induced in adult Wistar rats by ovalbumin sensitization and challenge. Following olfactory and behavioral tests we investigated the synaptic structure of the olfactory bulb (OB), anterior olfactory nuclei (AON), piriform cortex and prefrontal cortex (PFC), by immunofluorescence detection of synaptophysin (Syn) and glutamatergic, GABAergic and dopaminergic neuronal markers.

RESULTS

We detected a significant decrease in Syn in the glomerular layer (GL) of OB and in the PFC of the AR group. Additionally, the optical density of GAD67 and VGLUT2 was reduced in the OB, AON and PFC, compared to controls. The behavioral tests demonstrated olfactory dysfunction and reduced male aggressiveness in AR rats, but we did not find any difference in the cognition and anxiety-like behavior.

CONCLUSIONS

We confirmed olfactory dysfunction in a rat model of AR and we identified modifications in synaptic activity by reduction of Syn optical density in the GL of the OB and in the PFC. This was accompanied by structural changes in glutamatergic and GABAergic activity in essential components of the olfactory pathway and PFC.

Alteration of Lateral Habenula Function Prevents the Proper Exploration of a Novel Environment

The lateral habenula (LHb) is an epithalamic brain region viewed as a converging hub, integrating information from a large connectome and then projecting to few critical midbrain monoaminergic systems. Numerous studies have explored the roles of the LHb, notably in aversion and avoidance. An important recurring finding when manipulating the LHb is the induction of anxiety-related behaviours. However, its exact role in such behaviours remains poorly understood. In the present study, we used two pharmacological approaches altering LHb activity, intra-LHb infusion of either the GABA-A receptor agonist, Muscimol, or the glutamatergic AMPA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and exposed rats to three consecutive open field (OF) sessions. We found that both pharmacological treatments prevented rats to explore the centre of the OF, considered as the most anxiogenic part of the apparatus, across the three OF sessions. In addition, during the first, but not the two consecutive sessions, both treatments prevented a thorough exploration of the OF. Altogether, these results confirm the crucial role played by the LHb in anxiety-related behaviours and further suggest its implication in the exploration of new anxiogenic environments.

Modulation of foraging-like behaviors by cholesterol-FGF19 axis

BACKGROUND

Foraging for food precedes food consumption and is an important component of the overall metabolic programming that regulates feeding. Foraging is governed by central nervous system neuronal circuits but how it is influenced by diet and hormonal signals is still not well understood.

RESULTS

In this study, we show that dietary cholesterol exerted suppressive effects on locomotor activity and that these effects were partially mediated by the neuropeptide Agouti-related protein (AgRP). High dietary cholesterol stimulated intestinal expression of fibroblast growth factor 15 (Fgf15), an ortholog of the human fibroblast growth factor 19 (FGF19). Intracerebroventricular infusion of FGF19 peptide reduced exploratory activity in the open field test paradigm. On the other hand, the lack of dietary cholesterol enhanced exploratory activity in the open field test, but this effect was abolished by central administration of FGF19.

CONCLUSIONS

Experiments in this study show that dietary cholesterol suppresses locomotor activity and foraging-like behaviors, and this regulation is in part mediated by AgRP neurons. Dietary cholesterol or the central action of FGF19 suppresses exploratory behaviors, and the anxiogenic effects of dietary cholesterol may be mediated by the effect of FGF19 in the mouse brain. This study suggests that dietary cholesterol and intestinal hormone FGF15/19 signal a satiating state to the brain, thereby suppressing foraging-like behaviors.

Prolactin-Releasing Peptide Contributes to Stress-Related Mood Disorders and Inhibits Sleep/Mood Regulatory Melanin-Concentrating Hormone Neurons in Rats

Stress disorders impair sleep and quality of life; however, their pathomechanisms are unknown. Prolactin-releasing peptide (PrRP) is a stress mediator; we therefore hypothesized that PrRP may be involved in the development of stress disorders. PrRP is produced by the medullary A1/A2 noradrenaline (NA) cells, which transmit stress signals to forebrain centers, and by non-NA cells in the hypothalamic dorsomedial nucleus. We found in male rats that both PrRP and PrRP-NA cells innervate melanin-concentrating hormone (MCH) producing neurons in the dorsolateral hypothalamus (DLH). These cells serve as a key hub for regulating sleep and affective states. Ex vivo, PrRP hyperpolarized MCH neurons and further increased the hyperpolarization caused by NA. Following sleep deprivation, intracerebroventricular PrRP injection reduced the number of REM sleep-active MCH cells. PrRP expression in the dorsomedial nucleus was upregulated by sleep deprivation, while downregulated by REM sleep rebound. Both in learned helplessness paradigm and after peripheral inflammation, impaired coping with sustained stress was associated with (1) overactivation of PrRP cells, (2) PrRP protein and receptor depletion in the DLH, and (3) dysregulation of MCH expression. Exposure to stress in the PrRP-insensitive period led to increased passive coping with stress. Normal PrRP signaling, therefore, seems to protect animals against stress-related disorders. PrRP signaling in the DLH is an important component of the PrRP's action, which may be mediated by MCH neurons. Moreover, PrRP receptors were downregulated in the DLH of human suicidal victims. As stress-related mental disorders are the leading cause of suicide, our findings may have particular translational relevance.SIGNIFICANCE STATEMENT Treatment resistance to monoaminergic antidepressants is a major problem. Neuropeptides that modulate the central monoaminergic signaling are promising targets for developing alternative therapeutic strategies. We found that stress-responsive prolactin-releasing peptide (PrRP) cells innervated melanin-concentrating hormone (MCH) neurons that are crucial in the regulation of sleep and mood. PrRP inhibited MCH cell activity and enhanced the inhibitory effect evoked by noradrenaline, a classic monoamine, on MCH neurons. We observed that impaired PrRP signaling led to failure in coping with chronic/repeated stress and was associated with altered MCH expression. We found alterations of the PrRP system also in suicidal human subjects. PrRP dysfunction may underlie stress disorders, and fine-tuning MCH activity by PrRP may be an important part of the mechanism.

Anxiolytic-like effects of citral in the mouse elevated plus maze: involvement of GABAergic and serotonergic transmissions

Citral, a monoterpene which is a part of the essential oil of several medicinal plants, is generally regarded as safe for human and animal consumption. Studies have introduced citral as a functional component of some essential oils in anxiolytic and antidepressant therapies; however, the neuropharmacological characteristics of citral have not yet been reported. In the present study, we evaluated the anxiolytic activities of citral in comparison to two standard anxiolytics, diazepam and buspirone, in Swiss albino mice by intraperitoneal administration of 1, 2, 5, 10, and 20 mg/kg using elevated plus maze (EPM) and open-field test (OFT). Moreover, we also examined whether the GABA_A-benzodiazepine and 5-HT_1A receptor are involved in the anxiolytic-like effects of citral by pretreatment with flumazenil and WAY-100635, respectively. Citral dose-dependently decreased the number of border crossings and time spent in borders, and also the number of grooming and rearing in OFT without altering the exploratory behavior of mice. In the EPM, this monoterpene led to a significant increase in number of entries in open arms and time spent in open arms, as well as a decrease in time spent in closed arms. Pretreatment with flumazenil and WAY-100635 both could reverse the anxiolytic effects of the citral in the EPM. These results suggest that anxiolytic activity of citral occurs via the GABA_A and 5-HT_1A receptor modulation.

Dexmedetomidine Pre-Treatment of Neonatal Rats Prevents Sevoflurane-Induced Deficits in Learning and Memory in the Adult Animals

Anesthetics have been shown to cause cytotoxicity, cell death, affect neuronal growth and connectivity in animal models; however, their effects on learning and memory remain to be fully defined. Here, we examined the effects of the inhalation anesthetic sevoflurane (SEV)-both in vivo by examining learning and memory in freely behaving animals, and in vitro using cultured neurons to assess its impact on viability, mitochondrial structure, and function. We demonstrate here that neonatal exposure to sub-clinically used concentrations of SEV results in significant, albeit subtle and previously unreported, learning and memory deficits in adult animals. These deficits involve neuronal cell death, as observed in cell culture, and are likely mediated through perturbed mitochondrial structure and function. Parenthetically, both behavioural deficits and cell death were prevented when the animals and cultured neurons were pre-treated with the anesthetic adjuvant Dexmedetomidine (DEX). Taken together, our data provide direct evidence for sevoflurane-induced cytotoxic effects at the neuronal level while perturbing learning and memory at the behavioural level. In addition, our data underscore the importance of adjuvant agents such as DEX that could potentially counter the harmful effects of commonly used anesthetic agents for better clinical outcomes.

Multidimensional analysis of behavior predicts genotype with high accuracy in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a neurodevelopmental disorder caused by loss of expression of the maternal copy of the UBE3A gene. Individuals with AS have a multifaceted behavioral phenotype consisting of deficits in motor function, epilepsy, cognitive impairment, sleep abnormalities, as well as other comorbidities. Effectively modeling this behavioral profile and measuring behavioral improvement will be crucial for the success of ongoing and future clinical trials. Foundational studies have defined an array of behavioral phenotypes in the AS mouse model. However, no single behavioral test is able to fully capture the complex nature of AS-in mice, or in children. We performed multidimensional analysis (principal component analysis + k-means clustering) to quantify the performance of AS model mice (n = 148) and wild-type littermates (n = 138) across eight behavioral domains. This approach correctly predicted the genotype of mice based on their behavioral profile with ~95% accuracy, and remained effective with reasonable sample sizes (n = ~12-15). Multidimensional analysis was effective using different combinations of behavioral inputs and was able to detect behavioral improvement as a function of treatment in AS model mice. Overall, multidimensional behavioral analysis provides a tool for evaluating the effectiveness of preclinical treatments for AS. Multidimensional analysis of behavior may also be applied to rodent models of related neurodevelopmental disorders, and may be particularly valuable for disorders where individual behavioral tests are less reliable than in AS.

Investigation of Anxiety- and Depressive-like Symptoms in 4- and 8-Month-Old Male Triple Transgenic Mouse Models of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Approximately 50% of AD patients show anxiety and depressive symptoms, which may contribute to cognitive decline. We aimed to investigate whether the triple-transgenic mouse (3xTg-AD) is a good preclinical model of this co-morbidity. The characteristic histological hallmarks are known to appear around 6-month; thus, 4- and 8-month-old male mice were compared with age-matched controls. A behavioral test battery was used to examine anxiety- (open field (OF), elevated plus maze, light-dark box, novelty suppressed feeding, and social interaction (SI) tests), and depression-like symptoms (forced swim test, tail suspension test, sucrose preference test, splash test, and learned helplessness) as well as the cognitive decline (Morris water maze (MWM) and social discrimination (SD) tests). Acetylcholinesterase histochemistry visualized cholinergic fibers in the cortex. Dexamethasone-test evaluated the glucocorticoid non-suppression. In the MWM, the 3xTg-AD mice found the platform later than controls in the 8-month-old cohort. The SD abilities of the 3xTg-AD mice were missing at both ages. In OF, both age groups of 3xTg-AD mice moved significantly less than the controls. During SI, 8-month-old 3xTg-AD animals spent less time with friendly social behavior than the controls. In the splash test, 3xTg-AD mice groomed themselves significantly less than controls of both ages. Cortical fiber density was lower in 8-month-old 3xTg-AD mice compared to the control. Dexamethasone non-suppression was detectable in the 4-month-old group. All in all, some anxiety- and depressive-like symptoms were present in 3xTg-AD mice. Although this strain was not generally more anxious or depressed, some aspects of comorbidity might be studied in selected tests, which may help to develop new possible treatments.

Generation and Characterization of a Novel Angelman Syndrome Mouse Model with a Full Deletion of the Ube3a Gene

Angelman syndrome (AS) is a neurodevelopmental disorder caused by deficits in maternally inherited UBE3A. The disease is characterized by intellectual disability, impaired motor skills, and behavioral deficits, including increased anxiety and autism spectrum disorder features. The mouse models used so far in AS research recapitulate most of the cardinal AS characteristics. However, they do not mimic the situation found in the majority of AS patients who have a large deletion spanning 4–6 Mb. There is also a large variability in phenotypes reported in the available models, which altogether limits development of therapeutics. Therefore, we have generated a mouse model in which the Ube3a gene is deleted entirely from the 5′ UTR to the 3′ UTR of mouse Ube3a isoform 2, resulting in a deletion of 76 kb. To investigate its phenotypic suitability as a model for AS, we employed a battery of behavioral tests directed to reveal AS pathology and to find out whether this model better mirrors AS development compared to other available models. We found that the maternally inherited Ube3a-deficient line exhibits robust motor dysfunction, as seen in the rotarod and DigiGait tests, and displays abnormalities in additional behavioral paradigms, including reduced nest building and hypoactivity, although no apparent cognitive phenotype was observed in the Barnes maze and novel object recognition tests. The AS mice did, however, underperform in more complex cognition tasks, such as place reversal in the IntelliCage system, and exhibited a different circadian rhythm activity pattern. We show that the novel UBE3A-deficient model, based on a whole-gene deletion, is suitable for AS research, as it recapitulates important phenotypes characteristic of AS. This new mouse model provides complementary possibilities to study the Ube3a gene and its function in health and disease as well as possible therapeutic interventions to restore function.

Chronic allergic lung inflammation negatively influences neurobehavioral outcomes in mice

BACKGROUND

Asthma is a major public health problem worldwide. Emerging data from epidemiological studies show that allergies and allergic diseases may be linked to anxiety, depression and cognitive decline. However, little is known about the effect of asthma, an allergic lung inflammation, on cognitive decline/behavioral changes. Therefore, we investigated the hypothesis that allergic lung inflammation causes inflammation in the brain and leads to neurobehavioral changes in mice.

METHODS

Wild-type C57BL/6J female mice were sensitized with nasal house dust mite (HDM) antigen or control PBS for 6 weeks to induce chronic allergic lung inflammation. A series of neurocognitive tests for anxiety and/or depression were performed before and after the intranasal HDM administration. After the behavior tests, tissues were harvested to measure inflammation in the lungs and the brains.

RESULTS

HDM-treated mice exhibited significantly increased immobility times during tail suspension tests and significantly decreased sucrose preference compared with PBS controls, suggesting a more depressed and anhedonia phenotype. Spatial memory impairment was also observed in HDM-treated mice when assessed by the Y-maze novel arm tests. Development of lung inflammation after 6 weeks of HDM administration was confirmed by histology, bronchoalveolar lavage (BAL) cell count and lung cytokine measurements. Serum pro-inflammatory cytokines and Th2-related cytokines levels were elevated in HDM-sensitized mice. In the brain, the chemokine fractalkine was increased in the HDM group. The c-Fos protein, a marker for neuronal activity, Glial Fibrillary Acidic Protein (GFAP) and chymase, a serine protease from mast cells, were increased in the brains from mice in HDM group. Chymase expression in the brain was negatively correlated with the results of sucrose preference rate in individual mice.

CONCLUSIONS

6 weeks of intranasal HDM administration in mice to mimic the chronic status of lung inflammation in asthma, caused significant inflammatory histological changes in the lungs, and several behavioral changes consistent with depression and altered spatial memory. Chymase and c-Fos proteins were increased in the brain from HDM-treated mice, suggesting links between lung inflammation and brain mast cell activation, which could be responsible for depression-like behavior.

The role of hypoleptinemia in the psychological and behavioral adaptation to starvation: implications for anorexia nervosa

This narrative review aims to pinpoint mental and behavioral effects of starvation, which may be triggered by hypoleptinemia and as such may be amenable to treatment with leptin receptor agonists. The reduced leptin secretion results from the continuous loss of fat mass, thus initiating a graded triggering of diverse starvation related adaptive functions. In light of leptin receptors located in several peripheral tissues and many brain regions adaptations may extend beyond those of the hypothalamus-pituitary-end organ-axes. We focus on gastrointestinal tract and reward system as relevant examples of peripheral and central effects of leptin. Despite its association with extreme obesity, congenital leptin deficiency with its many parallels to a state of starvation allows the elucidation of mental symptoms amenable to treatment with exogenous leptin in both ob/ob mice and humans with this autosomal recessive disorder. For starvation induced behavioral changes with an intact leptin signaling we particularly focus on rodent models for which proof of concept has been provided for the causative role of hypoleptinemia. For humans, we highlight the major cognitive, emotional and behavioral findings of the Minnesota Starvation Experiment to contrast them with results obtained upon a lesser degree of caloric restriction. Evidence for hypoleptinemia induced mental changes also stems from findings obtained in lipodystrophies. In light of the recently reported beneficial cognitive, emotional and behavioral effects of metreleptin-administration in anorexia nervosa we discuss potential implications for the treatment of this eating disorder. We postulate that leptin has profound psychopharmacological effects in the state of starvation.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Using intra-brain drug infusion to investigate neural mechanisms underlying reward-seeking behavior in mice

Brain-region-specific drug infusion is a key way to investigate neural mechanisms underlying behavior and neurological diseases. Here, we present a detailed protocol for cannula implantation, intra-brain drug infusion, and two reward-seeking-related behavioral paradigms in mice: the light/dark box test and touchscreen version of progressive ratio test. In addition, we provide a user-friendly Python-based tool for behavioral data analysis. This protocol can be easily adapted to address various research questions related to behavioral pharmacology.

For complete details on the use and execution of this protocol, please refer to Peng et al. (2021).

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Intra-brain drug infusion for studying neural mechanisms underlying behavioral deficit

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Behavioral paradigms for testing reward-seeking behavior

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Python-based analysis tool for behavioral data processing

Effects of early life stress during stress hyporesponsive period (SHRP) on anxiety and curiosity in adolescent rats

Repeated exposure to adverse experiences in early life, termed Early Life Stress (ELS), can increase anxiety disorders later in life. Anxiety is directly associated with curiosity, a form of intrinsic drive state associated with increased novelty-seeking behaviour and risk taking for challenging opportunities and could probably modulate learning and memory. In humans, elevated curiosity during adolescence tends to elicit increased exploration, novelty seeking, high risk-taking behaviour and heightened emotionality. Such behaviours are beneficial in maintaining social skills and cognitive functions later in life. We investigated whether ELS-induced anxiety impacts curiosity-like behaviour at adolescence in an animal model. ELS was induced by subjecting Sprague Dawley rat pups to maternal separation and isolation (MS) stress during the stress hyporesponsive period (SHRP) from post-natal days (PND) 4-PND 14. This rat model was tested for anxiety, spontaneous exploratory behaviour and curiosity-like behaviour in a custom-designed arena during adolescence (PND 30-45). ELS-induced changes in the stress were confirmed by corticosterone, while, basal dopamine level was estimated to understand the neurochemical basis of MS stress-induced changes in curiosity. We observed an increase in the levels of anxiety and intrinsic drive state such as curiosity-like behaviour, which was associated with elevated plasma corticosterone and dopamine in MS animals during adolescence suggesting the impact of ELS during SHRP on adolescent behaviour.

Botulinum Neurotoxin Chimeras Suppress Stimulation by Capsaicin of Rat Trigeminal Sensory Neurons In Vivo and In Vitro

Chimeras of botulinum neurotoxin (BoNT) serotype A (/A) combined with /E protease might possess improved analgesic properties relative to either parent, due to inheriting the sensory neurotropism of the former with more extensive disabling of SNAP-25 from the latter. Hence, fusions of /E protease light chain (LC) to whole BoNT/A (LC/E-BoNT/A), and of the LC plus translocation domain (HN) of /E with the neuronal acceptor binding moiety (HC) of /A (BoNT/EA), created previously by gene recombination and expression in E. coli., were used. LC/E-BoNT/A (75 units/kg) injected into the whisker pad of rats seemed devoid of systemic toxicity, as reflected by an absence of weight loss, but inhibited the nocifensive behavior (grooming, freezing, and reduced mobility) induced by activating TRPV1 with capsaicin, injected at various days thereafter. No sex-related differences were observed. c-Fos expression was increased five-fold in the trigeminal nucleus caudalis ipsi-lateral to capsaicin injection, relative to the contra-lateral side and vehicle-treated controls, and this increase was virtually prevented by LC/E-BoNT/A. In vitro, LC/E-BoNT/A or /EA diminished CGRP exocytosis from rat neonate trigeminal ganglionic neurons stimulated with up to 1 µM capsaicin, whereas BoNT/A only substantially reduced the release in response to 0.1 µM or less of the stimulant, in accordance with the /E protease being known to prevent fusion of exocytotic vesicles.

Sex-Specific Behavioral Response to Early Adolescent Stress in the Genetically More Stress-Reactive Wistar Kyoto More Immobile, and Its Nearly Isogenic Wistar Kyoto Less Immobile Control Strain

Genetic predisposition and environmental stress are known etiologies of stress-related psychiatric disorders. Environmental stress during adolescence is assumed to be particularly detrimental for adult affective behaviors. To investigate how genetic stress-reactivity differences modify the effects of stress during adolescence on adult affective behaviors we employed two inbred strains with differing stress reactivity. The Wistar Kyoto More Immobile (WMI) rat strain show increased stress-reactivity and despair-like behaviors as well as passive coping compared to the nearly isogenic control strain, the Wistar Kyoto Less Immobile (WLI). Males and females of these strains were exposed to contextual fear conditioning (CFC) during early adolescence (EA), between 32 and 34 postnatal days (PND), and were tested for the consequences of this mild EA stress in adulthood. Early adolescent stress significantly decreased anxiety-like behavior, measured in the open field test (OFT) and increased social interaction and recognition in adult males of both strains compared to controls. In contrast, no significant effects of EA stress were observed in adult females in these behaviors. Both males and females of the genetically less stress-reactive WLI strain showed significantly increased immobility in the forced swim test (FST) after EA stress compared to controls. In contrast, immobility was significantly attenuated by EA stress in adult WMI females compared to controls. Transcriptomic changes of the glucocorticoid receptor (Nr3c1, GR) and the brain-derived neurotrophic factor (Bdnf) illuminate primarily strain and stress-dependent changes, respectively, in the prefrontal cortex and hippocampus of adults. These results suggest that contrary to expectations, limited adolescent stress is beneficial to males thru decreasing anxiety and enhancing social behaviors, and to the stress more-reactive WMI females by way of decreasing passive coping.

CB1 receptors in corticotropin-releasing factor neurons selectively control the acoustic startle response in male mice

The endocannabinoid system is an important regulator of the hormonal and behavioral stress responses, which critically involve corticotropin-releasing factor (CRF) and its receptors. While it has been shown that CRF and the cannabinoid type 1 (CB1) receptor are co-localized in several brain regions, the physiological relevance of this co-expression remains unclear. Using double in situ hybridization, we confirmed co-localization in the piriform cortex, the lateral hypothalamic area, the paraventricular nucleus, and the Barrington's nucleus, albeit at low levels. To study the behavioral and physiological implications of this co-expression, we generated a conditional knockout mouse line that selectively lacks the expression of CB1 receptors in CRF neurons. We found no effects on fear and anxiety-related behaviors under basal conditions nor after a traumatic experience. Additionally, plasma corticosterone levels were unaffected at baseline and after restraint stress. Only acoustic startle responses were significantly enhanced in male, but not female, knockout mice. Taken together, the consequences of depleting CB1 in CRF-positive neurons caused a confined hyperarousal phenotype in a sex-dependent manner. The current results suggest that the important interplay between the central endocannabinoid and CRF systems in regulating the organism's stress response is predominantly taking place at the level of CRF receptor-expressing neurons.

Let's get wild: A review of free-ranging rat assays as context-enriched supplements to traditional laboratory models

More than 24,000 rodent studies are published annually, with the vast majority of these studies focused on genetically undiverse animals in highly-controlled laboratory settings. However, findings from the laboratory have become increasingly unreliable for predicting outcomes in field and clinical settings, leading to a perceived crisis in translational research. One cause of this disparity might be that most human societies, in contrast to laboratory rodents, are genetically diverse and live in super-enriched environments. Methods for importing wild rats into the laboratory, and also exporting laboratory-style chambers into natural environments are not well-known outside their respective disciplines. Therefore, we have reviewed the current status of supplements to the laboratory rodent assay. We progress logically from highly-controlled experiments with natural breeding colonies to purely naturalistic approaches with free-ranging rats. We then highlight a number of approaches that allow genetically-diverse wild rats to be utilized in context-enriched paradigms. While considering the benefits and shortcomings of each available approach, we detail protocols for random sampling, remote-sensing, and deployment of laboratory chambers in the field. As supplements to standardized laboratory trials, some of these assays could offer key insights to help unify outcomes between laboratory and field studies. However, we note several outstanding questions that must be addressed such as: the trade-off between control and context, possible reductions in sample size, ramifications for the 'standardization fallacy', and ethical dilemmas of working with wild animals. Given these challenges, further innovation will be required before supplemental assays can be made broadly-accessible and thus, transferrable across disciplines.