Behavioral methods to study anxiety in rodents

Behavioral and transcriptomic effects of a novel cannabinoid on a rat valproic acid model of autism

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by impaired social communication, restricted interests, repetitive behavior and irritability. Exposure to valproic acid (VPA) during pregnancy has been shown to increase the risk of autism in children and has led to the development of the in-utero VPA rat model that elicits neurodevelopmental autistic-like features. Offspring exhibit behavioral and neurobiological alterations modelling ASD symptoms. We performed a behavioral and molecular assessment in a rat in-utero VPA model treated with a novel botanical cannabinoid, JZP541. Male offspring from dams treated with VPA were tested acutely and sub-chronically with JZP541 (10, 30, or 100 mg/kg, intraperitoneally). A behavioral testing battery was performed, and brain frontal cortex and hippocampus used for RNA sequencing. In utero exposure to VPA resulted in progeny showing behavioral phenotypes characteristic of ASD. JZP541 attenuated these deficits in social, stereotypic, hyperactivity and irritability behavior in a dose-dependent fashion. VPA exposure was associated with a substantial transcriptional dysregulation impacting multiple key biological processes in a tissue-dependent manner. The expression profiles were integrated with publicly available datasets of autism-associated genes to support the validity of the model used and to focus on the effects of treatment on known autism-relevant transcriptional targets. This approach indicated a strong and dose-dependent reduction of the autism-associated gene expression signature in brain samples from animals dosed with JZP541. Our findings demonstrate JZP541 was able to ameliorate ASD associated behavioral deficits, and this was supported by improvements in putative transcriptional biomarkers of ASD.

Species differences in comorbid alcohol use disorder and major depressive disorder: A narrative review

Alcohol use disorder (AUD) and major depressive disorder (MDD) are often comorbid, and it is estimated that between 15 % to 33% of people dependent on alcohol have an MDD diagnosis. Mood-related symptoms are also common in humans during acute withdrawal, but by most accounts, symptoms abate after 2-4 weeks of alcohol abstinence. Preclinical studies, important for understanding the etiology and finding treatments for this comorbidity, also find depression-like and anxiety-like phenotypes in early abstinence along with protracted negative affect detectable past 2 weeks postcessation. In this narrative review, we focus on the translational divergence of AUD and MDD comorbidity with a focus on the time line mismatch between species in concurrent AUD + MDD and MDD following AUD. We also highlight the preclinical success and clinical failure of classic antidepressants for AUD and the relative absence of withdrawal and negative affect in high-drinking selected lines of mice and rats. We suggest sources of these discrepancies, including discussion of relief/reward-driven drinking subpopulations and future directions for the field.

Behavioral comorbidities of early-life seizures: Insights from developmental studies in rats

Childhood epilepsy is frequently associated with neurobehavioral comorbidities such as depression, anxiety, cognitive impairments, and social dysfunction, as revealed by both clinical and experimental studies. Despite extensive neurophysiological research, behavioral studies in developing animals remain limited and underreported. Here, we review the behavioral impact of early-life seizures (ELSs) in commonly used rat models in developmental studies. We outline suitable tests and provide guidance on how traditional tests should be adapted and interpreted in this context. Finally, we examine factors influencing behavioral analysis in developmental studies, exploring confounding variables and offering strategies to minimize their impact.

Teucrium Polium ameliorates amyloid β-induced brain network disorders in rats: electrophysiological and behavioral studies

Synaptic failure in specific cholinergic networks in rat brains has been implicated in amyloid β-induced neurodegeneration. Teucrium polium is a promising candidate for drug development against Alzheimer's disease (AD) and similar disorders. However, the protective effect of Teucrium polium against amyloid β-induced impairment of short-term synaptic plasticity is still poorly understood. In this study, we used in vivo extracellular single-unit recordings to investigate the preventive efficacy of Teucrium polium on Aβ(25-35)-induced aberrant neuronal activity in the hippocampus and basolateral amygdala of rats, in response to high-frequency stimulation of the cholinergic nucleus basalis magnocellularis (NBM). After 12 weeks of intracerebroventricular administration of Aβ(25-35), alterations such as decreased excitatory responses and increased inhibitory synaptic activity were observed in the NBM-hippocampus and NBM-basolateral amygdala cholinergic circuits. Treatment with Teucrium polium improved the balance of excitatory and inhibitory responses by modulating synaptic transmission strength and restoring short-term plasticity. Acute injection of a therapeutic dose of Teucrium temporarily inhibited spiking activity in single NBM neurons. Open field tests revealed that amyloid-injected rats displayed anxiety and reduced exploratory drive. Treatment with Teucrium polium improved these behaviors, reducing anxiety and increasing exploration. Teucrium polium mitigated amyloid β-induced alterations in cholinergic circuits by enhancing the adaptive capacity of short-term synaptic plasticity. These findings suggest that Teucrium polium could serve as a preventive strategy to delay the progression of cholinergic neurodegeneration.

Astrocytes in Rodent Anxiety-Related Behavior: Role of Calcium and Beyond

Anxiety is a physiological, emotional response that anticipates distal threats. When kept under control, anxiety is a beneficial response, helping animals to maintain heightened attention in environments with potential dangers. However, an overestimation of potential threats can lead to an excessive expression of anxiety that, in humans, may evolve into anxiety disorders. Pharmacological treatments show variable efficacy among patients, highlighting the need for more efforts to better understand the pathogenesis of anxiety disorders. Mounting evidence suggests that astrocytes, a type of glial cells, are active partners of neurons in brain circuits and in the regulation of behaviors under both physiological and pathological conditions. In this review, I summarize the current literature on the role of astrocytes from different brain regions in modulating anxious states, with the goal of exploring novel cerebral mechanisms to identify potential innovative therapeutic targets for the treatment of anxiety disorders.

Safety in treatment: Classical pharmacotherapeutics and new avenues for addressing maternal depression and anxiety during pregnancy

We aimed to review clinical research on the safety profiles of antidepressant drugs and associations with maternal depression and neonatal outcomes. We focused on neuroendocrine changes during pregnancy and their effects on antidepressant pharmacokinetics. Pregnancy-induced alterations in drug disposition and metabolism impacting mothers and their fetuses are discussed. We considered evidence for the risks of antidepressant use during pregnancy. Teratogenicity associated with ongoing treatment, new prescriptions during pregnancy, or pausing medication while pregnant was examined. The Food and Drug Administration advises caution regarding prenatal exposure to most drugs, including antidepressants, largely owing to a dearth of safety studies caused by the common exclusion of pregnant individuals in clinical trials. We contrasted findings on antidepressant use with the lack of treatment where detrimental effects to mothers and children are well researched. Overall, drug classes such as selective serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors appear to have limited adverse effects on fetal health and child development. In the face of an increasing prevalence of major mood and anxiety disorders, we assert that individuals should be counseled before and during pregnancy about the risks and benefits of antidepressant treatment given that withholding treatment has possible negative outcomes. Moreover, newer therapeutics, such as ketamine and κ-opioid receptor antagonists, warrant further investigation for use during pregnancy. SIGNIFICANCE STATEMENT: The safety of antidepressant use during pregnancy remains controversial owing to an incomplete understanding of how drug exposure affects fetal development, brain maturation, and behavior in offspring. This leaves pregnant people especially vulnerable, as pregnancy can be a highly stressful experience for many individuals, with stress being the biggest known risk factor for developing a mood or anxiety disorder. This review focuses on perinatal pharmacotherapy for treating mood and anxiety disorders, highlighting the current knowledge and gaps in our understanding of consequences of treatment.

Chronic unpredictable stress during adolescence exerts sex-specific effects on depressive-like behavior and neural activation triggered by tail suspension test

During adolescence, acute stress can modify neuronal excitability in various brain regions, leading to negative behavioral outcomes. However, the impact of chronic stress during adolescence on neuronal responses to acute stimuli remains unclear. To address this, we subjected adolescent mice to 12 days of chronic unpredictable stress (CUS). Anxiety and depressive behaviors were evaluated, along with changes in c-Fos expression, which is one of the most widely used markers of neuronal activation. By comparing c-Fos immunoreactivity between the CUS and control groups both before and after the tail suspension test (TST), we found that adolescent CUS induced depressive behaviors in male mice, but not in female mice. Adolescent CUS primarily affected the excitability of neurons in the infralimbic cortex (IL), the dorsomedial and dorsolateral area of the bed nucleus of the stria terminalis (BNST), and the ventral hippocampus CA3. TST exerted a significant main effect on the density of c-Fos+ neurons in the prelimbic cortex (PL), infralimbic cortex (IL), cingulate areas 1 and 2 (Cg1, Cg2), the lateral septum (LS), BNST, and lateral habenular (LHb). Furthermore, the excitability of neurons in the paraventricular thalamic nucleus (PVT) was impacted by sex. These data suggest that adolescent CUS elicits region- and sex-specific modifications in TST-induced c-Fos expression, establishing a theoretical basis for understanding the pathophysiological alterations in mood disorders following adolescent stress.

Maze-Based Scalable Wireless Power Transmission Experimental Arena for Freely Moving Small Animals Applications

This paper presents an innovative T/Y-maze-based wireless power transmission (WPT) system designed to monitor spatial reference memory and learning behavior in freely moving rats. The system facilitates uninterrupted optical/electrical stimulation and neural recording experiments through the integration of wireless headstages or implants in T/Y maze setups. Utilizing an array of resonators covering the entire underneath of the mazes, the wireless platform ensures scalability with various configurations. The array is designed to ensure a natural localization mechanism to localize the Tx power toward the location of the Rx coil. The system is analyzed and modeled using ANSYS HFSS software to optimize design. The primary goal was to achieve uniform wireless power delivery throughout the mazes through a comparative study of different transmitter (Tx) array configurations, such as float, series, and parallel resonators. The calculated Specific Absorption Rate (SAR) in rat tissue model equals 1.7 W/kg at the power carrier frequency of 13.56 MHz. A prototype of the proposed maze-based WPT design, featuring 8 Tx resonators, a Tx coil and power amplifier, and a headstage power harvesting unit, is successfully implemented and its performance characterized for all three resonator configurations. The implemented T-maze-based WPT system has a total length of 128 cm. In the overlapping Tx resonators configuration, a homogeneity of 94% is achieved for the measured power transfer efficiency at over 30%, while continuously delivering over 60 mW for series configuration.

Distinguishing classes of neuroactive drugs based on computational physicochemical properties and experimental phenotypic profiling in planarians

Mental illnesses put a tremendous burden on afflicted individuals and society. Identification of novel drugs to treat such conditions is intrinsically challenging due to the complexity of neuropsychiatric diseases and the need for a systems-level understanding that goes beyond single molecule-target interactions. Thus far, drug discovery approaches focused on target-based in silico or in vitro high-throughput screening (HTS) have had limited success because they cannot capture pathway interactions or predict how a compound will affect the whole organism. Organismal behavioral testing is needed to fill the gap, but mammalian studies are too time-consuming and cost-prohibitive for the early stages of drug discovery. Behavioral medium-throughput screening (MTS) in small organisms promises to address this need and complement in silico and in vitro HTS to improve the discovery of novel neuroactive compounds. Here, we used cheminformatics and MTS in the freshwater planarian Dugesia japonica-an invertebrate system used for neurotoxicant testing-to evaluate the extent to which complementary insight could be gained from the two data streams. In this pilot study, our goal was to classify 19 neuroactive compounds into their functional categories: antipsychotics, anxiolytics, and antidepressants. Drug classification was performed with the same computational methods, using either physicochemical descriptors or planarian behavioral profiling. As it was not obvious a priori which classification method was most suited to this task, we compared the performance of four classification approaches. We used principal coordinate analysis or uniform manifold approximation and projection, each coupled with linear discriminant analysis, and two types of machine learning models-artificial neural net ensembles and support vector machines. Classification based on physicochemical properties had comparable accuracy to classification based on planarian profiling, especially with the machine learning models that all had accuracies of 90-100%. Planarian behavioral MTS correctly identified drugs with multiple therapeutic uses, thus yielding additional information compared to cheminformatics. Given that planarian behavioral MTS is an inexpensive true 3R (refine, reduce, replace) alternative to vertebrate testing and requires zero a priori knowledge about a chemical, it is a promising experimental system to complement in silico cheminformatics to identify new drug candidates.

A Neural Circuit For Bergamot Essential Oil-Induced Anxiolytic Effects

Aromatic essential oils have been shown to relieve anxiety and enhance relaxation, although the neural circuits underlying these effects have remained unknown. Here, it is found that treatment with 1.0% bergamot essential oil (BEO) exerts anxiolytic-like effects through a neural circuit projecting from the anterior olfactory nucleus (AON) to the anterior cingulate cortex (ACC) in acute restraint stress model mice. Collectively, in vivo two-photon calcium imaging, viral tracing, and whole-cell patch clamp recordings show that inhalation exposure to 1.0% BEO can activate glutamatergic projections from the AON to GABAergic neurons in the ACC, which drives inhibition of local glutamatergic neurons (AONGlu→ACCGABA→Glu). Optogenetic or chemogenetic manipulation of this pathway can recapitulate or abolish the BEO-induced anxiolytic-like behavioral effects in mice with ARS. Beyond depicting a previously unrecognized pathway involved in stress response, this study provides a circuit mechanism for the effects of BEO and suggests a potential target for anxiety treatment.

Behavioral changes and transcriptional regulation of mesolimbic dopaminergic genes in a mouse model of binge eating disorder by diet intermittent access

Binge Eating Disorder (BED) is among the most prevalent eating disorders worldwide. It is characterized by recurrent episodes of excessive consumption of palatable foods in short periods, accompanied by a sense of loss of control and distress around the episode, which tends to worsen over time. The mesolimbic dopaminergic system influences on reinforcement and reward-seeking behaviors is implicated in the disorder's pathogenesis. Animal models that replicate the clinical conditions observed in humans, including the disorder progression, are essential for understanding the underlying physiological mechanisms of BED. This study aimed to evaluate binge eating behavior induced by intermittent High Sugar and Butter (HSB) diet access in mice, their phenotypes, transcriptional regulation of mesolimbic dopaminergic system genes, and behavior. Thus, mice were subdivided into three groups: CHOW (maintenance diet only), HSB-i (maintenance diet with thrice-weekly access to HSB), and HSB (continuous access to HSB). Animals were subjected to marble-burying and light-dark box behavioral tests, and transcriptional regulation was evaluated by RT-qPCR. The results indicated that the HSB-i group established a feeding pattern of significantly more kilocalories on days when HSB was available and reduced intake on non-HSB days similar to human binge eating. Over time, binge episodes intensified, potentially indicating a tolerance effect. Additionally, these animals behave differently towards preferring the HSB diet and exhibited altered transcriptional regulation of the Drd1, Slc6a3, and Lrrk2 genes. Our study provides a mouse model that reflects human BED, showing a progression in binge episodes and mesolimbic dopamine pathway involvement, suggesting targets for future therapeutic interventions.

Impact of Omega-3 on Endocannabinoid System Expression and Function, Enhancing Cognition and Behavior in Male Mice

Background/Objectives: Omega-3 long-chain polyunsaturated fatty acids (PUFAs) support brain cell membrane integrity and help mitigate synaptic plasticity deficits. The endocannabinoid system (ECS) is integral to synaptic plasticity and regulates various brain functions. While PUFAs influence the ECS, the effects of omega-3 on the ECS, cognition, and behavior in a healthy brain remain unclear. Methods and Results: Here, we demonstrate that hippocampal synaptosomes from male mice fed an omega-3-rich diet exhibit increased levels of cannabinoid CB1 receptors (~30%), phospholipase C β1 (PLCβ1, ~30%), monoacylglycerol lipase (MAGL, ~30%), and cannabinoid receptor-interacting protein 1a (Crip1a, ~60%). Conversely, these synaptosomes show decreased levels of diacylglycerol lipase α (DAGLα, ~40%), synaptosomal-associated protein 25kDa (SNAP-25, ~30%), and postsynaptic density protein 95 (PSD-95, ~40%). Omega-3 intake also reduces Gαo and Gαi3 levels, though receptor-stimulated [35S]GTPγS binding remains unaffected. Stimulation of the medial perforant path (MPP) induced long-term potentiation (LTP) in omega-3-fed mice. This LTP was dependent on group I metabotropic glutamate receptors (mGluR), 2 arachidonoylglycerol (2-AG), CB1 receptors, N-type Ca2+ channels, and actin filaments. Behaviorally, omega-3-fed mice displayed reduced exploratory behavior and significantly improved object discrimination in the novel object recognition test (NORT). They also spent more time in open arms and exhibited reduced freezing time in the elevated plus maze (EPM), indicative of reduced anxiety-like behavior. Conclusions: Our findings suggest that omega-3 leverages the ECS to enhance brain function under normal conditions.

Sex Differences in Mouse Models of Voluntary Alcohol Drinking and Abstinence-Induced Negative Emotion

Alcohol Use Disorder (AUD) is a growing problem worldwide, causing an incredible burden on health and the economy. Though AUD impacts people of all backgrounds and demographics, increasing evidence has suggested robust sex differences in alcohol drinking patterns and AUD-induced negative emotionality or hyperkatifeia. Rates of problematic drinking have significantly risen among women, and women face more severe negative emotional consequences in abstinence such as increased risk of comorbidity with an anxiety or mood disorder and more severe symptoms of depression. As such, a bevy of preclinical literature using contingent methods of alcohol (ethanol) consumption has amassed in recent years to better understand sex as a biological variable in alcohol drinking and abstinence-induced negative emotionality. Mice are widely used to model alcohol drinking, as they are conducive to genetic manipulation strategies, and many strains will voluntarily consume alcohol. Sex-specific results from these mouse studies, however, have been inconsistent. Therefore, this review aims to summarize the current knowledge on sex differences in AUD-related contingent ethanol drinking and abstinence-induced negative emotionality in mice. Various contingent mouse drinking models and negative emotional-based behavioral paradigms are introduced and subsequently discussed in the context of sex differences to show increasing indications of sex specificity in mouse preclinical studies of AUD. With this review, we hope to inform future research on potential sex differences in preclinical mouse models of AUD and provide mounting evidence supporting the need for more widespread inclusion of preclinical female subjects in future studies.

General anesthesia activates a central anxiolytic center in the BNST

Low doses of general anesthetics like ketamine and dexmedetomidine have anxiolytic properties independent of their sedative effects, but the underlying mechanisms remain unclear. We discovered a population of GABAergic neurons in the oval division of the bed nucleus of the stria terminalis that are activated by multiple anesthetics and the anxiolytic drug diazepam (ovBNSTGA). The majority of ovBNSTGA neurons express neurotensin receptor 1 (Ntsr1) and form circuits with brain regions known to regulate anxiety and stress responses. Optogenetic activation of ovBNSTGA or ovBNSTNtsr1 neurons significantly attenuated anxiety-like behaviors in both naive animals and mice with inflammatory pain, while inhibition of these cells elevated anxiety. Activation of these neurons decreased heart rate and increased heart rate variability, suggesting that they reduce anxiety by modulating autonomic responses. Our study identifies ovBNSTGA/ovBNSTNtsr1 neurons as a common neural substrate mediating the anxiolytic effect of low-dose anesthetics and a potential therapeutic target for treating anxiety-related disorders.

The Impact of Early Life Experiences on Stress Neurobiology and the Development of Anxiety

We examine the association between stress exposure during early development (i.e., the prenatal period through the first two postnatal years) and variation in brain structure and function relevant to anxiety. Evidence of stress-related effects occurring in regions essential for emotional processing and regulation may increase susceptibility to anxiety.

Orbitofrontal and Prelimbic Cortices Serve Complementary Roles in Adapting Reward Seeking to Learned Anxiety

BACKGROUND

Anxiety is a common symptom of several mental health disorders and adversely affects motivated behaviors. Anxiety can emerge from associating risk of future harm while engaged in goal-guided actions. Using a recently developed behavioral paradigm to model this aspect of anxiety, we investigated the role of 2 cortical subregions, the prelimbic medial frontal cortex (PL) and lateral orbitofrontal cortex (lOFC), which have been implicated in anxiety and outcome expectation, in flexible representation of actions associated with harm risk.

METHODS

A seek-take reward-guided instrumental task design was used to train animals (N = 8) to associate the seek action with a variable risk of punishment. After learning, animals underwent extinction training for this association. Fiber photometry was used to measure and compare neuronal activity in the PL and lOFC during learning and extinction.

RESULTS

Animals increased action suppression in response to punishment contingencies. This increase dissipated after extinction training. These behavioral changes were associated with region-specific changes in neuronal activity. PL neuronal activity preferentially adapted to the threat of punishment, whereas lOFC activity adapted to safe aspects of the task. Moreover, correlated activity between these regions was suppressed during actions associated with harm risk, suggesting that these regions may guide behavior independently under anxiety.

CONCLUSIONS

These findings suggest that the PL and lOFC serve distinct but complementary roles in the representation of learned anxiety. This dissociation may provide a mechanism to explain how overlapping cortical systems are implicated in reward-guided action execution during anxiety.

Enduring memory consequences of early-life stress / adversity: Structural, synaptic, molecular and epigenetic mechanisms

Adverse early life experiences are strongly associated with reduced cognitive function throughout life. The link is strong in many human studies, but these do not enable assigning causality, and the limited access to the live human brain can impede establishing the mechanisms by which early-life adversity (ELA) may induce cognitive problems. In experimental models, artificially imposed chronic ELA/stress results in deficits in hippocampus dependent memory as well as increased vulnerability to the deleterious effects of adult stress on memory. This causal relation of ELA and life-long memory impairments provides a framework to probe the mechanisms by which ELA may lead to human cognitive problems. Here we focus on the consequences of a one-week exposure to adversity during early postnatal life in the rodent, the spectrum of the ensuing memory deficits, and the mechanisms responsible. We highlight molecular, cellular and circuit mechanisms using convergent trans-disciplinary approaches aiming to enable translation of the discoveries in experimental models to the clinic.

Methodology for Studying Hypothalamic Regulation of Feeding Behaviors

Continuous advances in neurological research techniques are enabling researchers to further understand the neural mechanisms that regulate energy balance. In this review, we specifically highlight key tools and techniques and explore how they have been applied to study the role of the hypothalamic arcuate nucleus in feeding behaviors. Additionally, we provide a detailed discussion of the advantages and limitations associated with each methodology.

Preexisting risk-avoidance and enhanced alcohol relief are driven by imbalance of the striatal dopamine receptors in mice

Alcohol use disorder (AUD) is frequently comorbid with anxiety disorders, yet whether alcohol abuse precedes or follows the expression of anxiety remains unclear. Rodents offer control over the first drink, an advantage when testing the causal link between anxiety and AUD. Here, we utilized a risk-avoidance task to determine anxiety-like behaviors before and after alcohol exposure. We found that alcohol's anxiolytic efficacy varied among inbred mice and mice with high risk-avoidance showed heightened alcohol relief. While dopamine D1 receptors in the striatum are required for alcohol's relief, their levels alone were not correlated with relief. Rather, the ratio between striatal D1 and D2 receptors was a determinant factor for risk-avoidance and alcohol relief. We show that increasing striatal D1 to D2 receptor ratio was sufficient to promote risk-avoidance and enhance alcohol relief, even at initial exposure. Mice with high D1 to D2 receptor ratio were more prone to continue drinking despite adverse effects, a hallmark of AUD. These findings suggest that an anxiety phenotype may be a predisposing factor for AUD.

Examining Brain Activity Responses during Rat Ultrasonic Vocalization Playback: Insights from a Novel fMRI Translational Paradigm

Despite decades of preclinical investigation, there remains limited understanding of the etiology and biological underpinnings of anxiety disorders. Sensitivity to potential threat is characteristic of anxiety-like behavior in humans and rodents, but traditional rodent behavioral tasks aimed to assess threat responsiveness lack translational value, especially with regard to emotionally valenced stimuli. Therefore, development of novel preclinical approaches to serve as analogues to patient assessments is needed. In humans, the fearful face task is widely used to test responsiveness to socially communicated threat signals. In rats, ultrasonic vocalizations (USVs) are analogous social cues associated with positive or negative affective states that can elicit behavioral changes in the receiver. It is therefore likely that when rats hear aversive alarm call USVs (22 kHz), they evoke translatable changes in brain activity comparable with the fearful face task. We used functional magnetic resonance imaging in male and female rats to assess changes in BOLD activity induced by exposure to aversive 22 kHz alarm calls emitted in response to threatening stimuli, prosocial (55 kHz) USVs emitted in response to appetitive stimuli, or a computer-generated 22 kHz tone. Results show patterns of regional activation that are specific to each USV stimulus. Notably, limbic regions clinically relevant to psychiatric disorders (e.g., amygdala, bed nucleus of the stria terminalis) are preferentially activated by either aversive 22 kHz or appetitive 55 kHz USVs. These results support the use of USV playback as a promising translational tool to investigate affective processing under conditions of distal threat in preclinical rat models.

Involvement of basolateral amygdala-rostral anterior cingulate cortex in mechanical allodynia and anxiety-like behaviors and potential mechanisms of electroacupuncture

AIMS

Chronic pain is highly associated with anxiety. Electroacupuncture (EA) is effective in relieving pain and anxiety. Currently, little is known about the neural mechanisms underlying the comorbidity of chronic pain and anxiety and the EA mechanism. This study investigated a potential neural circuit underlying the comorbid and EA mechanisms.

METHODS

Spared nerve injury (SNI) surgery established the chronic neuropathic pain mouse model. The neural circuit was activated or inhibited using the chemogenetic method to explore the relationship between the neural circuit and mechanical allodynia and anxiety-like behaviors. EA combined with the chemogenetic method was used to explore whether the effects of EA were related to this neural circuit.

RESULTS

EA attenuated mechanical allodynia and anxiety-like behaviors in SNI mice, which may be associated with the activity of CaMKII neurons in the basolateral amygdala (BLA). Inhibition of BLACaMKII-rACC induced mechanical allodynia and anxiety-like behaviors in sham mice. Activation of the BLACaMKII-rACC alleviated neuropathic pain and anxiety-like behaviors in SNI mice. The analgesic and anxiolytic effects of 2 Hz EA were antagonized by the inhibition of the BLACaMKII-rACC.

CONCLUSION

BLACaMKII-rACC mediates mechanical allodynia and anxiety-like behaviors. The analgesic and anxiolytic effects of 2 Hz EA may be associated with the BLACaMKII-rACC.

Threat-dependent scaling of prelimbic dynamics to enhance fear representation

Promptly identifying threatening stimuli is crucial for survival. Freezing is a natural behavior displayed by rodents toward potential or actual threats. Although it is known that the prelimbic cortex (PL) is involved in both risk evaluation and in fear and anxiety-like behavior expression, here we explored whether PL neuronal activity can dynamically represent different internal states of the same behavioral output (i.e., freezing). We found that freezing can always be decoded from PL activity at a population level. However, the sudden presentation of a fearful stimulus quickly reshaped the PL to a new neuronal activity state, an effect not observed in other cortical or subcortical regions examined. This shift changed PL freezing representation and is necessary for fear memory expression. Our data reveal the unique role of the PL in detecting threats and internally adjusting to distinguish between different freezing-related states in both unconditioned and conditioned fear representations.

Emotional vocalizations alter behaviors and neurochemical release into the amygdala

The basolateral amygdala (BLA), a brain center of emotional expression, contributes to acoustic communication by first interpreting the meaning of social sounds in the context of the listener's internal state, then organizing the appropriate behavioral responses. We propose that modulatory neurochemicals such as acetylcholine (ACh) and dopamine (DA) provide internal-state signals to the BLA while an animal listens to social vocalizations. We tested this in a vocal playback experiment utilizing highly affective vocal sequences associated with either mating or restraint, then sampled and analyzed fluids within the BLA for a broad range of neurochemicals and observed behavioral responses of adult male and female mice. In male mice, playback of restraint vocalizations increased ACh release and usually decreased DA release, while playback of mating sequences evoked the opposite neurochemical release patterns. In non-estrus female mice, patterns of ACh and DA release with mating playback were similar to males. Estrus females, however, showed increased ACh, associated with vigilance, as well as increased DA, associated with reward-seeking. Experimental groups that showed increased ACh release also showed the largest increases in an aversive behavior. These neurochemical release patterns and several behavioral responses depended on a single prior experience with the mating and restraint behaviors. Our results support a model in which ACh and DA provide contextual information to sound analyzing BLA neurons that modulate their output to downstream brain regions controlling behavioral responses to social vocalizations.

Role of electrophysiological activity and interactions of lateral habenula in the development of depression-like behavior in a chronic restraint stress model

Closed-loop deep brain stimulation (DBS) system offers a promising approach for treatment-resistant depression, but identifying universally accepted electrophysiological biomarkers for closed-loop DBS systems targeting depression is challenging. There is growing evidence suggesting a strong association between the lateral habenula (LHb) and depression. Here, we took LHb as a key target, utilizing multi-site local field potentials (LFPs) to study the acute and chronic changes in electrophysiology, functional connectivity, and brain network characteristics during the formation of a chronic restraint stress (CRS) model. Furthermore, our model combining the electrophysiological changes of LHb and interactions between LHb and other potential targets of depression can effectively distinguish depressive states, offering a new way for developing effective closed-loop DBS strategies.

Effect of high fat diet on maternal behavior, brain-derived neurotrophic factor and neural stem cell proliferation in mice expressing human placental lactogen during pregnancy

Maternal obesity is a serious health concern because it increases risks of neurological disorders, including anxiety and peripartum depression. In mice, a high fat diet (HFD) in pregnancy can negatively affect placental structure and function as well as maternal behavior reflected by impaired nest building and pup-retrieval. In humans, maternal obesity in pregnancy is associated with reduced placental lactogen (PL) gene expression, which has been linked to a higher risk of depression. PL acting predominantly through the prolactin receptor maintains energy homeostasis and is a marker of placenta villous trophoblast differentiation during pregnancy. Impaired neurogenesis and low serum levels of brain-derived neurotrophic factor (BDNF) have also been implicated in depression. Augmented neurogenesis in brain during pregnancy was reported in the subventricular zone (SVZ) of mice at gestation day 7 and linked to increased prolactin receptor signaling. Here, we used transgenic CD-1 mice that express human (h) PL during pregnancy to investigate whether the negative effects of diet on maternal behavior are mitigated in these (CD-1[hGH/PL]) mice. Specifically, we examined the effect of a HFD on nest building prepartum and pup retrieval postpartum, as well as on brain BDNF levels and neurogenesis. In contrast to wild-type CD-1[WT]mice, CD-1[hGH/PL] mice displayed significantly less anxiety-like behavior, and showed no impairment in prepartum nest building or postpartum pup-retrieval when fed a HFD. Furthermore, the HFD decreased prepartum and increased postpartum BDNF levels in CD-1[WT] but not CD-1[hGH/PL] mice. Finally, neurogenesis in the SVZ as well as phosphorylated mitogen-activated protein kinase, indicative of lactogenic signaling, appeared unaffected by pregnancy and diet at gestation day 7 in CD-1[hGH/PL] mice. These observations indicate that CD-1[hGH/PL] mice are resistant to the negative effects of HFD reported for CD-1[WT] mice, including effects on maternal behaviors and BDNF levels, and potentially, neurogenesis. This difference probably reflects a direct or indirect effect of the products of the hGH/PL transgene.

Mild exercise plus levothyroxine ameliorate deficits of spatial navigation, anxiety profile, and hippocampal BDNF in hypothyroid male offspring rats

PURPOSE

Levothyroxine (LEV) monotherapy cannot completely improve cognitive and behavioral impairments induced by hypothyroidism, whereas a combination therapy of exercise and LEV may ameliorate these deficits. This study aimed to determine the effects of mild-intensity forced exercise and LEV treatment on the anxiety profile and cognitive functions in male offspring of hypothyroid dams.

METHOD

Twenty-four female rats (mothers) were randomly divided into sham (healthy) and hypothyroidism groups and then placed with male rats to mate. The presence of vaginal plaque confirmed pregnancy (gestational day, GD 0). 6-propyl-2-thiouracil (PTU, 100 ppm) was added to the drinking water of the hypothyroidism group from GD 6 to the 21st postnatal day (PND). The sham group received tap water. On PND 21, serum T4 levels of mothers, and 10 pups were measured to confirm hypothyroidism. Sixty-four male pups were left undisturbed for 30 days and then were divided into eight groups that received saline or LEV (50 μg/kg, i.p.) with or without forced mild-intensity exercise. After 14 days of interventions, anxiety-like behaviors, spatial learning and memory, and hippocampal brain-derived neurotrophic factor (BDNF) levels were evaluated.

FINDING

A pre and postnatal PTU-induced model of hypothyroidism increased anxiety-like behaviors, impaired spatial learning and memory, and decreased hippocampal BDNF levels in male offspring rats. LEV alone increased BDNF levels and improved spatial learning. Exercise alone increased BDNF levels, improved spatial learning and memory, and decreased anxiety-like behaviors. Exercise plus LEV more effectively improved anxiety-like behaviors and spatial learning than exercise or LEV alone.

CONCLUSION

Practically, these pre-clinical findings highlight the importance of the combination of exercise and LEV regimen in treating patients with hyperthyroidism.

Animal models to study cognitive impairment of chronic kidney disease

Mild cognitive impairment (MCI) is common in people with chronic kidney disease (CKD), and its prevalence increases with progressive loss of kidney function. MCI is characterized by a decline in cognitive performance greater than expected for an individual age and education level but with minimal impairment of instrumental activities of daily living. Deterioration can affect one or several cognitive domains (attention, memory, executive functions, language, and perceptual motor or social cognition). Given the increasing prevalence of kidney disease, more and more people with CKD will also develop MCI causing an enormous disease burden for these individuals, their relatives, and society. However, the underlying pathomechanisms are poorly understood, and current therapies mostly aim at supporting patients in their daily lives. This illustrates the urgent need to elucidate the pathogenesis and potential therapeutic targets and test novel therapies in appropriate preclinical models. Here, we will outline the necessary criteria for experimental modeling of cognitive disorders in CKD. We discuss the use of mice, rats, and zebrafish as model systems and present valuable techniques through which kidney function and cognitive impairment can be assessed in this setting. Our objective is to enable researchers to overcome hurdles and accelerate preclinical research aimed at improving the therapy of people with CKD and MCI.

Spared nerve injury decreases motivation in long-access homecage-based operant tasks in mice

ABSTRACT

Neuropathic pain causes both sensory and emotional maladaptation. Preclinical animal studies of neuropathic pain-induced negative affect could result in novel insights into the mechanisms of chronic pain. Modeling pain-induced negative affect, however, is variable across research groups and conditions. The same injury may or may not produce robust negative affective behavioral responses across different species, strains, and laboratories. Here, we sought to identify negative affective consequences of the spared nerve injury model on C57BL/6J male and female mice. We found no significant effect of spared nerve injury across a variety of approach-avoidance conflict, hedonic choice, and coping strategy assays. We hypothesized these inconsistencies may stem in part from the short test duration of these assays. To test this hypothesis, we used the homecage-based Feeding Experimentation Device version 3 to conduct 12-hour, overnight progressive ratio testing to determine whether mice with chronic spared nerve injury had decreased motivation to earn palatable food rewards. Our data demonstrate that despite equivalent task learning, spared nerve injury mice are less motivated to work for a sugar pellet than sham controls. Furthermore, when we normalized behavioral responses across all the behavioral assays we tested, we found that a combined normalized behavioral score is predictive of injury state and significantly correlates with mechanical thresholds. Together, these results suggest that homecage-based operant behaviors provide a useful platform for modeling nerve injury-induced negative affect and that valuable pain-related information can arise from agglomerative data analyses across behavioral assays-even when individual inferential statistics do not demonstrate significant mean differences.

PINK1 knockout rats show premotor cognitive deficits measured through a complex maze

Cognitive decline in Parkinson's disease (PD) is a critical premotor sign that may occur in approximately 40% of PD patients up to 10 years prior to clinical recognition and diagnosis. Delineating the mechanisms and specific behavioral signs of cognitive decline associated with PD prior to motor impairment is a critical unmet need. Rodent PD models that have an impairment in a cognitive phenotype for a time period sufficiently long enough prior to motor decline can be useful to establish viable candidate mechanisms. Arguably, the methods used to evaluate cognitive decline in rodent models should emulate methods used in the assessment of humans to optimize translation. Premotor cognitive decline in human PD can potentially be examined in the genetically altered PINK1-/- rat model, which exhibits a protracted onset of motor decline in most studies. To increase translation to cognitive assessment in human PD, we used a modified non-water multiple T-maze, which assesses attention, cognitive flexibility, and working memory similarly to the Trail Making Test (TMT) in humans. Similar to the deficiencies revealed in TMT test outcomes in human PD, 4-month-old PINK1-/- rats made more errors and took longer to complete the maze, despite a hyperkinetic phenotype, compared to wild-type rats. Thus, we have identified a potential methodological tool with cross-species translation to evaluate executive functioning in an established PD rat model.

Differential Effects of Neonatal Ventral Hippocampus Lesion on Behavior and Corticolimbic Plasticity in Wistar-Kyoto and Spontaneously Hypertensive Rats

Dysfunction of the corticolimbic system, particularly at the dendritic spine level, is a recognized core mechanism in neurodevelopmental disorders such as schizophrenia. Neonatal ventral hippocampus lesion (NVHL) in Sprague-Dawley rats induces both a schizophrenia-related behavioral phenotype and dendritic spine pathology (reduced total number and mature spines) in corticolimbic areas, which is mitigated by antipsychotics. However, there is limited information on the impact of rat strain on NVHL outcomes and antipsychotic effects. We compared the behavioral performance in the open field, novel object recognition (NORT), and social interaction tests, as well as structural neuroplasticity with the Golgi-Cox stain in Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) male rats with and without NVHL. Additionally, we explored the effect of the atypical antipsychotic risperidone (RISP). WKY rats with NVHL displayed motor hyperactivity without impairments in memory and social behavior, accompanied by dendritic spine pathology in the neurons of the prefrontal cortex (PFC) layer 3 and basolateral amygdala. RISP treatment reduced motor activity and had subtle and selective effects on the neuroplasticity alterations. In SH rats, NVHL increased the time spent in the border area during the open field test, impaired the short-term performance in NORT, and reduced social interaction time, deficits that were corrected after RISP administration. The NVHL caused dendritic spine pathology in the PFC layers 3 and 5 of SH rats, which RISP treatment ameliorated. Our results support the utility of the NVHL model for exploring neuroplasticity mechanisms in schizophrenia and understanding pharmacotherapy.

Influence of maternal high-fat diet on offspring's locomotor activity during anxiety-related behavioral tests: A systematic review

The aim of this review was to summarize and discuss the impact of a maternal high-fat diet on the locomotor activity of offspring during anxiety-related behavioral tests. A search was performed in the LILACS, Web of Science, SCOPUS and PUMBED databases, using the following inclusion criteria: studies in which rodent dams were submitted to a high-fat diet during gestation and/or lactation and in which the locomotor activity parameters of offspring were evaluated during an anxiety-related test. Twenty-three articles met these criteria and were included. Most studies, 14 out of 23, found that a maternal high-fat diet did not alter offspring locomotor activity. Six articles found that a maternal high-fat diet increased the locomotor activity of offspring, while three found decreased locomotion. This effect may be associated with the initial response to the test and the fact that it was the first day of exposure to the apparatus.

Creative Commons 4.0 Exploring the complex interplay between anxiety, aging, and behavior in CB6F1 and C57BL/6 mice: implications for cognitive function

Anxiety is a pervasive emotional response that can profoundly impact well-being and cognitive function in both humans and animals. The relationship between anxiety and aging remains complex and multifaceted. To explore this relationship in more detail, an open-field photobeam system was used to quantify anxiety-related behaviors in aging CB6F1 and C57BL/6 male mice and to determine associations with aging phenotypes, including short- and long-term memory, grip strength, rotarod performance, and self-motivated wheel running. Results indicated a heightened anxiety in novel environments with increasing age as evidenced by a preference for peripheral areas during the open-field test. Elevated anxiety levels were not associated with decreased cognitive performance, suggesting that anxiety and cognition operate somewhat independently of each other. A negative correlation was observed between anxiety levels and distance run in the voluntary wheel running assessment, while no associations were seen with grip strength or rotarod performance. These observations contribute to a better understanding of anxiety and its consequences in aging mice, providing insights into potential therapeutic interventions aimed at delaying aging through anxiety management.

P2X7 receptor inhibition alleviates mania-like behavior independently of interleukin-1β

Purinergic dysfunctions are associated with mania and depression pathogenesis. P2X7 receptor (P2X7R) mediates the IL-1β maturation via NLRP3 inflammasome activation. We tested in a mouse model of the subchronic amphetamine (AMPH)-induced hyperactivity whether P2X7R inhibition alleviated mania-like behavior through IL-1β. Treatment with JNJ-47965567, a P2X7R antagonist, abolished AMPH-induced hyperlocomotion in wild-type and IL-1α/β-knockout male mice. The NLRP3 inhibitor MCC950 failed to reduce AMPH-induced locomotion in WT mice, whereas the IL-1 receptor antagonist anakinra slightly increased it. AMPH increased IL-10, TNF-α, and TBARS levels, but did not influence BDNF levels, serotonin, dopamine, and noradrenaline content in brain tissues in either genotypes. JNJ-47965567 and P2rx7-gene deficiency, but not IL-1α/β-gene deficiency, attenuated AMPH-induced [3H]dopamine release from striatal slices. In wild-type and IL-1α/β-knockout female mice, JNJ-47965567 was also effective in attenuating AMPH-induced hyperlocomotion. This study suggests that AMPH-induced hyperactivity is modulated by P2X7Rs, but not through IL-1β.

Perinatal exposure to bisphenol A or S: Effects on anxiety-related behaviors and serotonergic system

Bisphenols, synthetic organic compounds used in the production of plastics, are an extremely abundant class of Endocrine Disrupting Chemicals, i.e., exogenous chemicals or mixtures of chemicals that can interfere with any aspect of hormone action. Exposure to BPs can lead to a wide range of effects, and it is especially dangerous if it occurs during specific critical periods of life. Focusing on the perinatal exposure to BPA or its largely used substitute BPS, we investigated the effects on anxiety-related behaviors and the serotonergic system, which is highly involved in controlling these behaviors, in adult mice. We treated C57BL/6J dams orally with a dose of 4 μg/kg body weight/day (i.e., EFSA TDI) of BPA or BPS dissolved in corn oil or with vehicle alone, at the onset of mating and continued treatment until the offspring were weaned. Adult offspring of both sexes performed the elevated plus maze and the open field tests. Then, we analyzed the serotonergic system in dorsal (DR) and median (MnR) raphe nuclei by immunohistochemical techniques. Behavioral tests highlighted alterations in BPA- and BPS-treated mice, suggesting different effects of the bisphenols exposure on anxiety-related behavior in males (anxiolytic) and females (anxiogenic). The analysis of the serotonergic system highlighted a sex dimorphism in the DR only, with control females showing higher values of serotonin immunoreactivity (5-HT-ir) than control males. BPA-treated males displayed a significant increase of 5-HT-ir in all analyzed nuclei, whereas BPS-treated males showed an increase in ventral DR only. In females, both bisphenols-treated groups showed a significant increase of 5-HT-ir in dorsal DR compared to the controls, and BPA-treated females also showed a significant increase in MnR.These results provide evidence that exposure during the early phases of life to BPA or BPS alters anxiety and the raphe serotonergic neurons in a sex-dependent manner.

Adolescent food insecurity in female rodents and susceptibility to diet-induced obesity

Food insecurity is defined as having limited or uncertain access to nutritious foods, and adolescent food insecurity is associated with obesity and disordered eating behaviors in humans. We developed a rodent model of adolescent food insecurity to determine whether adolescent food insecurity per se promotes increased susceptibility to diet-induced obesity and altered eating behaviors during adulthood. Female juvenile Wistar rats were singly housed and assigned to three experimental diets: food-secure with standard chow (CHOW), food-secure with a high-fat/sugar Western diet (WD), and food-insecure with WD (WD-FI). Food-secure rats (CHOW and WD) received meals at fixed feeding times (9:00, 13:00, and 16:00). WD-FI rats received meals at unpredictable intervals of the above-mentioned feeding times but had isocaloric amounts of food to WD. We investigated the impact of adolescent food insecurity on motivation for sucrose (Progressive Ratio), approach-avoidance behavior for palatable high-fat food (Approach-Avoidance task), and susceptibility to weight gain and hyperphagia when given an obesogenic choice diet. Secondary outcomes were the effects of food insecurity during development on anxiety-like behaviors (Open Field and Elevated Plus Maze) and learning and memory function (Novel Location Recognition task). Rodents with adolescent food insecurity showed a greater trend of weight gain and significantly increased fat mass and liver fat accumulation on an obesogenic diet in adulthood, despite no increases in motivation for sucrose or high-fat food. These data suggest that adolescent unpredictable food access increases susceptibility to diet-induced fat gain without impacting food motivation or food intake in female rodents. These findings are among a small group of recent studies modeling food insecurity in rodents and suggest that adolescent food insecurity in females may have long-term implications for metabolic physiology later in life.

Treatment with a new barbituric acid derivative suppresses diet-induced metabolic dysfunction and non-alcoholic fatty liver disease in mice

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, often accompanied by obesity, diabetes, and increased risks of depression and anxiety. Currently, there are no FDA-approved drugs to treat NAFLD and its related systemic symptoms. Previously, we identified a new barbituric acid derivative (BA-5) that expressed effectiveness against fibrosis and drug-resistant hepatocellular carcinoma.

AIMS

This study investigated the potential of BA-5 against high-fat diet (HFD)-induced NAFLD and mood disorders in mice.

MAIN METHODS

Six-weeks-old male C57BL/6 mice were fed with a 45 % HFD for 8 weeks to induce NAFLD and associated metabolic disorders. Mice were treated with a BA-5 and the therapeutic effects and the underlying molecular mechanisms were investigated.

KEY FINDINGS

Administration of BA-5 significantly reduced serum levels of alanine aminotransferase (ALT), low-density lipoprotein (LDL), fatty acids (FA), and triglycerides (TG) in HFD-fed mice. BA-5 treatment decreased expressions of hepatic lipogenesis-related markers (acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), and ATP-citrate lyase (ACLY)), increased fatty acid oxidation markers (carnitine palmitoyltransferase 1A (CPT1A) and acyl-CoA oxidase 1 (ACOX1)), and attenuated hepatic fat accumulation in HFD-fed mice. Moreover, HFD-induced adipocyte size enlargement and activation of lipolysis markers such as phosphorylated (p)-hormone-sensitive lipase (HSL) 565, p-HSL 660, and perilipin were inhibited in BA-5-treated mice. Notably, HFD-induced anxiety- and depression-like behaviors significantly improved in the BA-5 treated group through enhanced anti-inflammatory responses in the hippocampus.

SIGNIFICANCE

This study provides new insights into clinical therapeutic strategies of barbituric acid derivatives for HFD-induced NAFLD and associated mood disturbances.

Selenium alleviates modafinil-induced neurobehavioral toxicity in rat via PI3K/Akt/mTOR/GSK3B signaling pathway and suppression of oxidative stress and apoptosis: in vivo and in silico study

Nonmedical use of modafinil (MOD) led to increased rates of overdose toxicity, road accidents, addiction, withdrawal, suicide, and mental illnesses. The current study aims to determine the probable MOD brain toxicity and elucidate the possible role of selenium (Se) in ameliorating the neurotoxicity in rat models. Fifty-four male Albino rats were randomly assigned into nine groups. The groups were G1 (control negative), G2 (Se0.1), G3 (Se0.2), G4 (MOD300), G5 (MOD600), G6 (Se0.1 + MOD300), G7 (Se0.2 + MOD300), G8 (Se0.1 + MOD600), and G9 (Se0.2 + MOD600). After finishing the experiment, blood and brain tissue were harvested for biochemical and histological investigation. Neurobehavior parameters were assessed. Tissue neurotransmitter levels and oxidative stress markers were assessed. Gene expression of PI3K/Akt/mTOR-GSK3B, orexin, and orexin receptor2 was measured by qRT-PCR. Histological and immunohistochemistry assessments, as well as molecular docking, were carried out. MOD-induced neurobehavioral toxicity exhibited by behavioral and cognitive function impairments, which are associated with decreased antioxidant activities, increased MDA levels, and decreases in neurotransmitter levels. Brain levels of mRNA expression of PI3K, Akt, and mTOR were decreased, while GS3K, orexin, and orexin receptors were significantly elevated. These disturbances were confirmed by histopathological brain changes with increased silver and Bax immunostaining and decreased crystal violet levels. MOD induced neurotoxic effects in a dose-dependent manner. Compared with the MOD groups, SE coadministration significantly attenuates MOD-induced toxic changes. Docking study shows the protective role of Se as an apoptosis inhibitor and inflammation inhibitor. In conclusion, Se could be used as a biologically effective antioxidant compound to protect from MOD neurobehavioral toxicity in Wistar rats by reversing behavioral alterations, inflammation, apoptosis, and oxidative injury.

Cilostazol pretreatment prevents PTSD-related anxiety behavior through reduction of hippocampal neuroinflammation

Current pharmacological treatments against post-traumatic stress disorder (PTSD) lack adequate efficacy. As a result, intense research has focused on identifying other molecular pathways mediating the pathogenesis of this condition. One such pathway is neuroinflammation, which has demonstrated a role in PTSD pathogenesis by causing synaptic dysfunction, neuronal death, and functional impairment in the hippocampus. Phosphodiesterase (PDE) inhibitors (PDEIs) have emerged as promising therapeutic agents against neuroinflammation in other neurological conditions. Furthermore, PDEIs have shown some promise in animal models of PTSD. However, the current model of PTSD pathogenesis, which is based on dysregulated fear learning, implies that PDE inhibition in neurons should enhance the acquisition of fear memory from the traumatic event. As a result, we hypothesized that PDEIs may improve PTSD symptoms through inhibiting neuroinflammation rather than long-term potentiation-related mechanisms. To this end, we tested the therapeutic efficacy of cilostazol, a selective inhibitor of PDE3, on PTSD-related anxiety symptoms in the underwater trauma model of PTSD. PDE3 is expressed much more richly in microglia and astrocytes compared to neurons in the murine brain. Furthermore, we used hippocampal indolamine 2,3-dioxygenase 1 (IDO) expression and interleukin 1 beta (IL-1β) concentration as indicators of neuroinflammation. We observed that cilostazol pretreatment prevented the development of anxiety symptoms and the increase in hippocampal IDO and IL-1β following PTSD induction. As a result, PDE3 inhibition ameliorated the neuroinflammatory processes involved in the development of PTSD symptoms. Therefore, cilostazol and other PDEIs may be promising candidates for further investigation as pharmacological therapies against PTSD.

General Anesthesia Activates a Central Anxiolytic Center in the BNST

Low doses of general anesthetics like ketamine and dexmedetomidine have anxiolytic properties independent of their sedative effects. How these different drugs exert these anxiolytic effects is not well understood. We discovered a population of GABAergic neurons in the oval division of the bed nucleus of the stria terminalis that is activated by multiple anesthetics and the anxiolytic drug diazepam (ovBNST GA ). A majority of ovBNST GA neurons express neurotensin receptor 1 (Ntsr1) and innervate brain regions known to regulate anxiety and stress responses. Optogenetic activation ovBNST GA or ovBNST Ntsr1 neurons significantly attenuated anxiety-like behaviors in both naïve animals and mice with inflammatory pain, while inhibition of these cells increased anxiety. Notably, activation of these neurons decreased heart rate and increased heart rate variability, suggesting that they reduce anxiety through modulation of the autonomic nervous system. Our study identifies ovBNST GA /ovBNST Ntsr1 neurons as one of the brain's endogenous anxiolytic centers and a potential therapeutic target for treating anxiety-related disorders.

HIGHLIGHTS

General anesthetics and anxiolytics activate a population of neurons in the ovBNSTAnesthesia-activated ovBNST neurons bidirectionally modulate anxiety-like behaviorMost anesthesia-activated ovBNST neurons express neurotensin receptor 1 ovBNST Ntsr1 neuron activation shifts autonomic responses to an anxiolytic state.

Differential Roles of Oxytocin Receptors in the Prefrontal Cortex and Nucleus Accumbens on Cocaine Self-Administration and Reinstatement of Cued Cocaine Seeking in Male Rats

BACKGROUND

Little is known about the specific roles of cortical and accumbal oxytocin receptors in drug use disorders. To better understand the importance of the endogenous oxytocin system in cocaine relapse behavior, we developed an adeno-associated viral vector-expressing short hairpin (sh) RNAs to selectively degrade the rat oxytocin receptor (OxyR) mRNA in vivo.

METHODS

Male (Sprague-Dawley) rats received bilateral infusions of the shRNA for the oxytocin receptor (shOxyR) or an shRNA control virus into the prefrontal cortex (PFC) or the nucleus accumbens core (NAc). Rats self-administered cocaine on an escalating FR ratio for 14 days, lever responding was extinguished, and rats were tested for cued and cocaine-primed reinstatement of drug seeking.

RESULTS

OxyR knockdown in the PFC delayed the acquisition of lever pressing on an fixed ratio 1 schedule of reinforcement. All rats eventually acquired the same level of lever pressing and discrimination, and there were no differences in extinction. OxyR knockdown in the NAc had no effect during acquisition. In both the PFC and NAc, the shOxyR decreased cued reinstatement relative to shRNA control virus but was without effect during drug-primed reinstatement. OxyR knockdown in the PFC increased chamber activity during a social interaction task.

CONCLUSIONS

This study provides critical new information about how endogenous OxyRs function to affect drug seeking in response to different precipitators of relapse. The tool developed to knockdown OxyRs in rat could provide important new insights that aid development of oxytocin-based therapeutics to reduce return-to-use episodes in people with substance use disorder and other neuropsychiatric disorders.

Emotion in action: When emotions meet motor circuits

The brain is a remarkably complex organ responsible for a wide range of functions, including the modulation of emotional states and movement. Neuronal circuits are believed to play a crucial role in integrating sensory, cognitive, and emotional information to ultimately guide motor behavior. Over the years, numerous studies employing diverse techniques such as electrophysiology, imaging, and optogenetics have revealed a complex network of neural circuits involved in the regulation of emotional or motor processes. Emotions can exert a substantial influence on motor performance, encompassing both everyday activities and pathological conditions. The aim of this review is to explore how emotional states can shape movements by connecting the neural circuits for emotional processing to motor neural circuits. We first provide a comprehensive overview of the impact of different emotional states on motor control in humans and rodents. In line with behavioral studies, we set out to identify emotion-related structures capable of modulating motor output, behaviorally and anatomically. Neuronal circuits involved in emotional processing are extensively connected to the motor system. These circuits can drive emotional behavior, essential for survival, but can also continuously shape ongoing movement. In summary, the investigation of the intricate relationship between emotion and movement offers valuable insights into human behavior, including opportunities to enhance performance, and holds promise for improving mental and physical health. This review integrates findings from multiple scientific approaches, including anatomical tracing, circuit-based dissection, and behavioral studies, conducted in both animal and human subjects. By incorporating these different methodologies, we aim to present a comprehensive overview of the current understanding of the emotional modulation of movement in both physiological and pathological conditions.

Differential effects of acute stress on spatial learning and memory in the open-field tower maze across the female estrous cycle

The purpose of the present investigation was to test how acute stress and levels of circulating estrogens together influence acquisition and retention of spatial learning, as well as explorative behaviors in female rats. We used the hippocampus-dependent Open-field Tower Maze (OFTM) task to assess acquisition followed by a retention test (reacquisition) that was given 48 h later. Immediately prior to acquisition, experimental rats were exposed to an acute restraint stress and were trained under bright lights. Female rats' estrous cycles were tracked throughout training and testing. Exposure to stress did not affect learning when levels of estrogens were low (i.e., during estrus and metestrus). However, acute stress exposure significantly lowered spatial acquisition of the female rats in the phases with rising levels of estrogens (i.e., during diestrus and proestrus). Furthermore, this stress-induced diminishment during acquisition was evident at the beginning of the retention without any presentation of stress. The present findings provide insight about the interactive relationship between stress and sex hormones on cognitive functions.

Effects of Dietary Methionine Restriction on Cognition in Mice

Dietary restriction of the essential amino acid, methionine, has been shown to induce unique metabolic protection. The peripheral benefits of methionine restriction (MR) are well established and include improvements in metabolic, energy, inflammatory, and lifespan parameters in preclinical models. These benefits all occur despite MR increasing energy intake, making MR an attractive dietary intervention for the prevention or reversal of many metabolic and chronic conditions. New and emerging evidence suggests that MR also benefits the brain and promotes cognitive health. Despite widespread interest in MR over the past few decades, many findings are limited in scope, and gaps remain in our understanding of its comprehensive effects on the brain and cognition. This review details the current literature investigating the impact of MR on cognition in various mouse models, highlights some of the key mechanisms responsible for its cognitive benefits, and identifies gaps that should be addressed in MR research moving forward. Overall findings indicate that in animal models, MR is associated with protection against obesity-, age-, and Alzheimer's disease-induced impairments in learning and memory that depend on different brain regions, including the prefrontal cortex, amygdala, and hippocampus. These benefits are likely mediated by increases in fibroblast growth factor 21, alterations in methionine metabolism pathways, reductions in neuroinflammation and central oxidative stress, and potentially alterations in the gut microbiome, mitochondrial function, and synaptic plasticity.

A conserved role for frizzled in sleep architecture

Previous studies of natural variants in Drosophila melanogaster implicated the Wnt signaling receptor frizzled in sleep. Given that the Wnt signaling pathway is highly conserved across species, we hypothesized that frizzled class receptor 1 (Fzd1), the murine homolog of frizzled, would also have a role in sleep. Using a CRISPR transgenic approach, we removed most of the Fzd1 coding region from C57BL/6N mice. We used a video assay to measure sleep characteristics in Fzd1-deficient mice. As Wnt signaling is known to affect visuospatial memory, we also examined the impact of the deletion on learning and memory using the novel object recognition (NOR) paradigm. Fzd1-deficient mice had altered sleep compared to littermate controls. The mice did not respond differently to the NOR paradigm compared to controls but did display anxiety-like behavior. Our strategy demonstrates that the study of natural variation in Drosophila sleep translates into candidate genes for sleep in vertebrate species such as the mouse.

Endothelin Modulates Rhythm Disturbances and Autonomic Responses to Acute Emotional Stress in Rats

The ubiquitous peptide endothelin is currently under investigation as a modulatory factor of autonomic responses to acute emotional stress. Baseline plasma levels of endothelin alter blood pressure responses, but it remains unclear whether autonomic activity and arrhythmogenesis (i.e., brady- or tachyarrhythmias) are affected. We recorded sympathetic and vagal indices (derived from heart rate variability analysis), rhythm disturbances, voluntary motion, and systolic blood pressure after acute emotional stress in conscious rats with implanted telemetry devices. Two strains were compared, namely wild-type and ETB-deficient rats, the latter displaying elevated plasma endothelin. No differences in heart rate or blood pressure were evident, but sympathetic responses were blunted in ETB-deficient rats, contrasting prompt activation in wild-type rats. Vagal withdrawal was observed in both strains at the onset of stress, but vagal activity was subsequently restored in ETB-deficient rats, accompanied by low voluntary motion during recovery. Reflecting such distinct autonomic patterns, frequent premature ventricular contractions were recorded in wild-type rats, as opposed to sinus pauses in ETB-deficient rats. Thus, chronically elevated plasma endothelin levels blunt autonomic responses to acute emotional stress, resulting in vagal dominance and bradyarrhythmias. Our study provides further insights into the pathophysiology of stress-induced tachyarrhythmias and syncope.

Pharmacological modulation of conditioned fear in the fear-potentiated startle test: a systematic review and meta-analysis of animal studies

RATIONALE AND OBJECTIVES

Fear conditioning is an important aspect in the pathophysiology of anxiety disorders. The fear-potentiated startle test is based on classical fear conditioning and over the years, a broad range of drugs have been tested in this test. Synthesis of the available data may further our understanding of the neurotransmitter systems that are involved in the expression of conditioned fear.

METHODS

Following a comprehensive search in Medline and Embase, we included 68 research articles that reported on 103 drugs, covering 56 different drug classes. The systematic review was limited to studies using acute, systemic drug administration in naive animals.

RESULTS

Qualitative data synthesis showed that most clinically active anxiolytics, but not serotonin-reuptake inhibitors, reduced cued fear. Anxiogenic drugs increased fear potentiation in 35% of the experiments, reduced fear potentiation in 29% of the experiments, and were without effect in 29% of the experiments. Meta-analyses could be performed for five drug classes and showed that benzodiazepines, buspirone, 5-HT1A agonists, 5-HT1A antagonists, and mGluR2,3 agonists reduced cued conditioned fear. The non-cued baseline startle response, which may reflect contextual anxiety, was only significantly reduced by benzodiazepines and 5-HT1A antagonists. No associations were found between drug effects and methodological characteristics, except for strain.

CONCLUSIONS

The fear-potentiated startle test appears to have moderate to high predictive validity and may serve as a valuable tool for the development of novel anxiolytics. Given the limited available data, the generally low study quality and high heterogeneity additional studies are warranted to corroborate the findings of this review.

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.

Dose-Dependent Beneficial Effect of Ketone Supplement-Evoked Ketosis on Anxiety Level in Female WAG/Rij Rats: Sometimes Less Is More

While one-third of the population can be affected by anxiety disorders during their lifetime, our knowledge of the pathophysiology of these disorders is far from complete. Previously, it has been demonstrated in male animals that exogenous ketone supplement-evoked ketosis can decrease anxiety levels in preclinical rodent models, such as Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. Thus, in this study, we investigated whether intragastric gavage of the exogenous ketone supplement KEMCT (mix of 1,3-butanediol-acetoacetate diester/ketone ester/KE and medium-chain triglyceride/MCT oil in 1:1 ratio) for 7 days can alter the anxiety levels of female WAG/Rij rats using the light-dark box (LDB) test. We demonstrated that a lower dose of KEMCT (3 g/kg/day) increased blood R-βHB (R-β-hydroxybutyrate) levels and significantly decreased anxiety levels (e.g., increased the time spent in the light compartment) in female WAG/Rij rats on the seventh day of administration. Although the higher KEMCT dose (5 g/kg/day) increased blood R-βHB levels more effectively, compared with the lower KEMCT dose, anxiety levels did not improve significantly. We conclude that ketone supplementation might be an effective strategy to induce anxiolytic effects not only in male but also in female WAG/Rij rats. However, these results suggest that the optimal level may be moderately, not highly, elevated blood R-βHB levels when the goal is to alleviate symptoms of anxiety. More studies are needed to understand the exact mechanism of action of ketone supplementation on anxiety levels and to investigate their use in other animal models and humans for the treatment of anxiety disorders and other mental health conditions.

Playback of rat 22-kHz ultrasonic vocalizations as a translational assay of negative affective states: An analysis of evoked behavior and brain activity

The subjective nature of human emotions makes them uniquely challenging to investigate in preclinical models. While behavioral assays in rodents aim to evaluate affect (i.e., anxiety, hypervigilance), they often lack ethological validity. Playback of negatively valenced 22-kHz ultrasonic vocalizations (USVs) in rats shows promise as a translational tool to investigate affective processing. Much like how human facial expressions can communicate internal states, rats emit 22-kHz USVs that similarly convey negative affective states to conspecifics indicating possible threat. 22-kHz USV playback elicits avoidance and hypervigilant behaviors, and recruit brain regions comparable to those seen in human brains evoked by viewing fearful faces. Indeed, 22-kHz playback alters neural activity in brain regions associated with negative valence systems (i.e., amygdala, bed nucleus of the stria terminalis, periaqueductal gray) alongside increases in behaviors typically associated with anxiety. Here, we present evidence from the literature that supports leveraging 22-kHz USV playback in rat preclinical models to obtain clinically relevant and translational findings to identify the neural underpinnings of affective processing and neuropathological dysfunction.