A combined marble burying–locomotor activity test in mice: A practical screening test with sensitivity to different classes of anxiolytics and antidepressants

Advances in animal models of prenatal opioid exposure

Neonatal opioid withdrawal syndrome (NOWS) is a growing public health concern. The complexity of in utero opioid exposure in clinical studies makes it difficult to investigate underlying mechanisms that could ultimately inform early diagnosis and treatments. Clinical studies are unable to dissociate the influence of maternal polypharmacy or the environment from direct effects of in utero opioid exposure, highlighting the need for effective animal models. Early animal models of prenatal opioid exposure primarily used the prototypical opioid, morphine, and opioid exposure that was often limited to a narrow period during gestation. In recent years, the number of preclinical studies has grown rapidly. Newer models utilize both prescription and nonprescription opioids and vary the onset and duration of opioid exposure. In this review, we summarize novel prenatal opioid exposure models developed in recent years and attempt to reconcile results between studies while critically identifying gaps within the current literature.

Neuroinflammation drives sex-dependent effects on pain and negative affect in a murine model of repeated mild traumatic brain injury

ABSTRACT

The Center for Disease Control and Prevention estimates that 75% of reported cases of traumatic brain injury (TBI) are mild, where chronic pain and depression are 2 of the most common symptoms. In this study, we used a murine model of repeated mild TBI to characterize the associated pain hypersensitivity and affective-like behavior and to what extent microglial reactivity contributes to these behavioral phenotypes. Male and female C57BL/6J mice underwent sham or repeated mild traumatic brain injury (rmTBI) and were tested for up to 9 weeks postinjury, where an anti-inflammatory/neuroprotective drug (minocycline) was introduced at 5 weeks postinjury in the drinking water. Repeated mild traumatic brain injury mice developed cold nociceptive hypersensitivity and negative affective states, as well as increased locomotor activity and risk-taking behavior. Minocycline reversed negative affect and pain hypersensitivities in male but not female mice. Repeated mild traumatic brain injury also produced an increase in microglial and brain-derived neurotropic factor mRNA transcripts in limbic structures known to be involved in nociception and affect, but many of these changes were sex dependent. Finally, we show that the antiepileptic drug, gabapentin, produced negative reinforcement in male rmTBI mice that was prevented by minocycline treatment, whereas rmTBI female mice showed a place aversion to gabapentin. Collectively, pain hypersensitivity, increased tonic-aversive pain components, and negative affective states were evident in both male and female rmTBI mice, but suppression of microglial reactivity was only sufficient to reverse behavioral changes in male mice. Neuroinflammation in limbic structures seems to be a contributing factor in behavioral changes resulting from rmTBI.

Exploring the Roles of Vitamins C and D and Etifoxine in Combination with Citalopram in Depression/Anxiety Model: A Focus on ICAM-1, SIRT1 and Nitric Oxide

The study of intercellular adhesion molecule-1 (ICAM-1) and SIRT1, a member of the sirtuin family with nitric oxide (NO), is emerging in depression and anxiety. As with all antidepressants, the efficacy is delayed and inconsistent. Ascorbic acid (AA) and vitamin D (D) showed antidepressant properties, while etifoxine (Etx), a GABAA agonist, alleviates anxiety symptoms. The present study aimed to investigate the potential augmentation of citalopram using AA, D and Etx and related the antidepressant effect to brain and serum ICAM-1, SIRT1 and NO in an animal model. BALB/c mice were divided into naive, control, citalopram, citalopram + etx, citalopram + AA, citalopram + D and citalopram + etx + AA + D for 7 days. On the 8th day, the mice were restrained for 8 h, followed by a forced swim test and marble burying test before scarification. Whole-brain and serum expression of ICAM-1, Sirt1 and NO were determined. Citalopram's antidepressant and sedative effects were potentiated by ascorbic acid, vitamin D and etifoxine alone and in combination (p < 0.05), as shown by the decreased floating time and rearing frequency. Brain NO increased significantly (p < 0.05) in depression and anxiety and was associated with an ICAM-1 increase versus naive (p < 0.05) and a Sirt1 decrease (p < 0.05) versus naive. Both ICAM-1 and Sirt1 were modulated by antidepressants through a non-NO-dependent pathway. Serum NO expression was unrelated to serum ICAM-1 and Sirt1. Brain ICAM-1, Sirt1 and NO are implicated in depression and are modulated by antidepressants.

Neuropharmacological Evidence Implicating Drug-Induced Glutamate Receptor Dysfunction in Affective and Cognitive Sequelae of Subchronic Methamphetamine Self-Administration in Mice

Methamphetamine (MA) is a highly addictive drug, and MA use disorder is often comorbid with anxiety and cognitive impairment. These comorbid conditions are theorized to reflect glutamate-related neurotoxicity within the frontal cortical regions. However, our prior studies of MA-sensitized mice indicate that subchronic, behaviorally non-contingent MA treatment is sufficient to dysregulate glutamate transmission in mouse brain. Here, we extend this prior work to a mouse model of high-dose oral MA self-administration (0.8, 1.6, or 3.2 g/L; 1 h sessions × 7 days) and show that while female C57BL/6J mice consumed more MA than males, MA-experienced mice of both sexes exhibited some signs of anxiety-like behavior in a behavioral test battery, although not all effects were concentration-dependent. No MA effects were detected for our measures of visually cued spatial navigation, spatial learning, or memory in the Morris water maze; however, females with a history of 3.2 g/L MA exhibited reversal-learning deficits in this task, and mice with a history of 1.6 g/L MA committed more working-memory incorrect errors and relied upon a non-spatial navigation strategy during the radial-arm maze testing. Relative to naïve controls, MA-experienced mice exhibited several changes in the expression of certain glutamate receptor-related proteins and their downstream effectors within the ventral and dorsal areas of the prefrontal cortex, the hippocampus, and the amygdala, many of which were sex-selective. Systemic pretreatment with the mGlu1-negative allosteric modulator JNJ 162596858 reversed the anxiety-like behavior expressed by MA-experienced mice in the marble-burying test, while systemic pretreatment with NMDA or the NMDA antagonist MK-801 bi-directionally affected the MA-induced reversal-learning deficit. Taken together, these data indicate that a relatively brief history of oral MA is sufficient to induce some signs of anxiety-like behavior and cognitive dysfunction during early withdrawal that reflect, at least in part, MA-induced changes in the corticolimbic expression of certain glutamate receptor subtypes of potential relevance to treating symptoms of MA use disorder.

Novel Psilocin Prodrugs with Altered Pharmacological Properties as Candidate Therapies for Treatment-Resistant Anxiety Disorders

The psychedelic prodrug psilocybin has shown therapeutic benefits for the treatment of numerous psychiatric conditions. Despite positive clinical end points targeting depression and anxiety, concerns regarding the duration of the psychedelic experience produced by psilocybin, associated with enduring systemic exposure to the active metabolite psilocin, pose a barrier to its therapeutic application. Our objective was to create a novel prodrug of psilocin with similar therapeutic benefits but a reduced duration of psychedelic effects compared with psilocybin. Here, we report the synthesis and functional screening of 28 new chemical entities. Our strategy was to introduce a diversity of cleavable groups at the 4-hydroxy position of the core indole moiety to modulate metabolic processing. We identified several novel prodrugs of psilocin with altered pharmacokinetic profiles and reduced pharmacological exposure compared with psilocybin. These candidate prodrugs have the potential to maintain the long-term benefits of psilocybin therapy while attenuating the duration of psychedelic effects.

Methodological approach: using a within-subjects design in the marble burying assay

In 2016, the National Institutes of Health mandated the use of both male and female mice in funded research. The use of both sexes is an important variable to consider; however, it comes with negative consequences such as increased animal expenses. One way to combat these negatives is to explore the option of using a within-subjects design (repeated measures) in behavioral assays that historically use a between-subjects design. Our study aimed to determine if a within-subjects design can be utilized in the marble burying assay. The marble burying assay is used as a tool for screening putative anxiolytic compounds as the assay is thought to measure obsessive-compulsive disorder- or anxiety-like behaviors. First, we compared the effects of sex and digging medium (corn cob or Sani Chip) on the number of marbles buried using CD-1 mice. Second, we determined if mice would continue to bury marbles after repeated exposures to the test arena. Lastly, we tested three positive controls (buspirone, ketamine, and fluoxetine). We found that mice buried significantly more marbles within Sani Chip digging medium, and no sex differences were observed. Next, the number of marbles buried and locomotor activity remained consistent across four test sessions. The positive controls buspirone (3.2-10 mg/kg) ketamine (32 mg/kg), and fluoxetine (10 mg/kg) decreased the number of marbles buried using the within-subjects design. These data suggest that a within-subjects design is optimal for the marble burying assay as it will reduce the number of animals and increase statistical power.

EPD1504: a novel μ-opioid receptor partial agonist attenuates obsessive-compulsive disorder (OCD)-like behaviors

Low doses of μ-opioid receptor (MOR) agonists rapidly ameliorate symptoms in treatment-resistant obsessive-compulsive disorder (OCD) patients (10-50% of OCD patients). However, the utility of MOR agonists is limited by their safety liabilities. We developed a novel MOR partial agonist (EPD1540) that has an improved respiratory safety profile when compared to buprenorphine. Buprenorphine is a MOR partial agonist primarily used in the treatment of opiate-use disorder, which in investigator-led trials, has been shown to rapidly ameliorate symptoms in treatment-resistant OCD patients. In this study, we show that doses of EPD1504 and buprenorphine that occupy small fractions of MORs in the CNS (approximately 20%) are as effective as fluoxetine at ameliorating OCD-like behaviors in two different rat models (an operant probabilistic reversal task and marble burying). Importantly, effective doses of EPD1504 did not impair either locomotor activity, or respiration under normoxic or hypercapnic conditions. Additionally, EPD1504 had effects comparable to buprenorphine in the conditioned place preference assay. These results indicate that EPD1504 may provide a safer alternative to buprenorphine for the treatment of OCD patients.

Bifidobacterium breve Bif11 supplementation improves depression-related neurobehavioural and neuroinflammatory changes in the mouse

Gut dysbiosis has been closely linked to the onset and progression of several brain-related disorders such as depression. The administration of microbiota-based formulations such as probiotics helps restore healthy gut flora and plays a role in preventing and treating depression-like behavior. Therefore, we evaluated the efficacy of probiotic supplementation using our recently isolated putative probiotic Bifidobacterium breve Bif11 in ameliorating lipopolysaccharide (LPS)-induced depression-like behavior in male Swiss albino mice. Mice were fed orally with B. breve Bif11 (1 × 10¹⁰ CFU and 2 × 10¹⁰ CFU) for 21 days before being challenged with a single intraperitoneal LPS injection (0.83 mg/kg). Behavioral, biochemical, histological and molecular analysis were done with an emphasis on inflammatory pathways linked to depression-like behavior. Daily supplementation with B. breve Bif11 for 21 days prevented the onset of depression-like behavior induced by LPS injection, besides reducing the levels of inflammatory cytokines such as matrix metalloproteinase-2, c-reactive protein, interleukin-6, tumor necrosis factor-alpha and nuclear factor kappa-light-chain-enhancer of activated B cells. It also prevented the decrease of the brain-derived neurotrophic factor levels and neuronal cell viability in the prefrontal cortex of LPS-treated mice. Furthermore, we observed that gut permeability was reduced, there was an improved short-chain fatty acid profile and reduced gut dysbiosis in the LPS mice fed with B. breve Bif11. Similarly, we observed a decrease in behavioural deficits and restoration of gut permeability in chronic mild stress. Together, these results would help in deciphering the role of probiotics in the management of neurological disorders where depression, anxiety and inflammation are prominent clinical features.

Antidepressant-like activity of a brain penetrant HCN channel inhibitor in mice

Changes in Hyperpolarization-Activated Cyclic Nucleotide-Gated (HCN) channel function have been linked to depressive-like traits, making them potential drug targets. However, there is currently no peer-reviewed data supporting the use of a small molecule modulator of HCN channels in depression treatment. Org 34167, a benzisoxazole derivative, has been patented for the treatment of depression and progressed to Phase I trials. In the current study, we analysed the biophysical effects of Org 34167 on HCN channels in stably transfected human embryonic kidney 293 (HEK293) cells and mouse layer V neurons using patch-clamp electrophysiology, and we utilised three high-throughput screens for depressive-like behaviour to assess the activity of Org 34167 in mice. The impact of Org 34167 on locomotion and coordination were measured by performing rotarod and ledged beam tests. Org 34167 is a broad-spectrum inhibitor of HCN channels, slowing activation and causing a hyperpolarising shift in voltage-dependence of activation. It also reduced I _h-mediated sag in mouse neurons. Org 34167 (0.5 mg/kg) reduced marble burying and increased the time spent mobile in the Porsolt swim and tail suspension tests in both male and female BALB/c mice, suggesting reduced depressive-like behaviour. Although no adverse effects were seen at 0.5 mg/kg, an increase in dose to 1 mg/kg resulted in visible tremors and impaired locomotion and coordination. These data support the premise that HCN channels are valid targets for anti-depressive drugs albeit with a narrow therapeutic index. Drugs with higher HCN subtype selectivity are needed to establish if a wider therapeutic window can be obtained.

Chronic corticosterone improves perseverative behavior in mice during sequential reversal learning

BACKGROUND

Stressful life events can both trigger development of psychiatric disorders and promote positive behavioral changes in response to adversities. The relationship between stress and cognitive flexibility is complex, and conflicting effects of stress manifest in both humans and laboratory animals.

OBJECTIVE

To mirror the clinical situation where stressful life events impair mental health or promote behavioral change, we examined the post-exposure effects of stress on cognitive flexibility in mice.

METHODS

We tested female C57BL/6JOlaHsd mice in the touchscreen-based sequential reversal learning test. Corticosterone (CORT) was used as a model of stress and was administered in the drinking water for two weeks before reversal learning. Control animals received drinking water without CORT. Behaviors in supplementary tests were included to exclude non-specific confounding effects of CORT and improve interpretation of the results.

RESULTS

CORT-treated mice were similar to controls on all touchscreen parameters before reversal. During the low accuracy phase of reversal learning, CORT reduced perseveration index, a measure of perseverative responding, but did not affect acquisition of the new reward contingency. This effect was not related to non-specific deficits in chamber activity. CORT increased anxiety-like behavior in the elevated zero maze test and repetitive digging in the marble burying test, reduced locomotor activity, but did not affect spontaneous alternation behavior.

CONCLUSION

CORT improved cognitive flexibility in the reversal learning test by extinguishing prepotent responses that were no longer rewarded, an effect possibly related to a stress-mediated increase in sensitivity to negative feedback that should be confirmed in a larger study.

Fast antidepressant action of ketamine in mouse models requires normal VGLUT1 levels from prefrontal cortex neurons

The NMDA antagonist ketamine demonstrated a fast antidepressant activity in treatment-resistant depression. Pre-clinical studies suggest that de novo synthesis of the brain-derived neurotrophic factor (BDNF) in the PFC might be involved in the rapid antidepressant action of ketamine. Applying a genetic model of impaired glutamate release, this study aims to further identify the molecular mechanisms that could modulate antidepressant action and resistance to treatment. To that end, mice knocked-down for the vesicular glutamate transporter 1 (VGLUT1+/-) were used. We analyzed anhedonia and helpless behavior as well as the expression of the proteins linked to glutamate transmission in the PFC of mice treated with ketamine or the reference antidepressant reboxetine. Moreover, we analyzed the acute effects of ketamine in VGLUT1+/- mice pretreated with chronic reboxetine or those that received a PFC rescue expression of VGLUT1. Chronic reboxetine rescued the depressive-like phenotype of the VGLUT1+/- mice. In addition, it enhanced the expression of the proteins linked to the AMPA signaling pathway as well as the immature form of BDNF (pro-BDNF). Unlike WT mice, ketamine had no effect on anhedonia or pro-BDNF expression in VGLUT1+/- mice; it also failed to decrease phosphorylated eukaryote elongation factor 2 (p-eEF2). Nevertheless, we found that reboxetine administered as pretreatment or PFC overexpression of VGLUT1 did rescue the antidepressant-like activity of acute ketamine in the mice. Our results strongly suggest that not only do PFC VGLUT1 levels modulate the rapid-antidepressant action of ketamine, but also highlight a possible mechanism for antidepressant resistance in some patients.

In vivo overexpression of synaptogyrin-3 promotes striatal synaptic dopamine uptake in LRRK2R1441G mutant mouse model of Parkinson's disease

BACKGROUND

Leucine-rich repeat kinase 2 (LRRK2) mutation is a common genetic risk factor of Parkinson's disease (PD). Presynaptic dysfunction is an early pathogenic event associated with dopamine (DA) dysregulation in striatum of the brain. DA uptake activity of DA uptake transporter (DAT) affects synaptic plasticity and motor and non-motor behavior. Synaptogyrin-3 (SYNGR3) is part of the synaptogyrin family, especially abundant in brain. Previous in vitro studies demonstrated interaction between SYNGR3 and DAT. Reduced SYNGR3 expression was observed in human PD brains with unclear reasons.

METHODS

Here, we further explored whether inducing SYNGR3 expression can influence (i) cellular DA uptake using differentiated human SH-SY5Y neuronal cells, (ii) striatal synaptosomal DA uptake in a mutant LRRK2^R1441G  knockin mouse model of PD, and (iii) innate rodent behavior using the marble burying test.

RESULTS

Young LRRK2 mutant mice exhibited significantly lower SYNGR3 levels in striatum compared to age-matched wild-type (WT) controls, resembling level in aged WT mice. SYNGR3 is spatially co-localized with DAT at striatal presynaptic terminals, visualized by immuno-gold transmission electron microscopy and immunohistochemistry. Their protein-protein interaction was confirmed by co-immunoprecipitation. Transient overexpression of SYNGR3 in differentiated SH-SY5Y cells increased cellular DA uptake activity without affecting total DAT levels. Inducing SYNGR3 overexpression by adeno-associated virus-7 (AAV7) injection in vivo into striatum increased ex vivo synaptosomal DA uptake in LRRK2 mutant mice and improved their innate marble burying behavior.

CONCLUSION

Brain SYNGR3 expression may be an important determinant to striatal DA homeostasis and synaptic function. Our preliminary behavioral test showed improved innate behavior after SYNGR3 overexpression in LRRK2 mutant mice, advocating further studies to determine the influence of SYNGR3 in the pathophysiology of DA neurons in PD.

Single cannabidiol administration affects anxiety-, obsessive compulsive-, object memory-, and attention-like behaviors in mice in a sex and concentration dependent manner

RATIONALE

The behavioral effects of cannabidiol (CBD) are understudied, but are important, given its therapeutic potential and widespread use as a natural supplement.

OBJECTIVE

The objective of this study was to test whether a single injection of CBD affected anxiety-like or attention-like behavior, or memory in wildtype mice or mice with reported trait anxiety due to a targeted gene-deletion in a voltage-dependent potassium channel, Kv1.3.

METHODS

Wildtype C57BL/6 J and Kv1.3-/- mice of both sexes were reared to adulthood and then administered an intraperitoneal injection of 10 or 20 mg/kg CBD. Mice were behaviorally-phenotyped using the marble-burying test, the light-dark box (LDB), short (1 h) and long-term (24 h) object memory test, the elevated-plus maze (EPM), and the object-based attention task in order to assess obsessive compulsive-, anxiety-, and attention-like behaviors, and memory.

RESULTS

We discovered that acute CBD treatment reduced marble burying in male, but not female mice. CBD was effective in lessening anxiety-like behaviors determined by the LDB test in both male and female wildtype mice, whereby the effective dose required to observe the effect in females was less. In Kv1.3-/- mice, CBD increased anxiety-like behaviors in the LDB in both sexes at the higher concentration of CBD and it similarly increased anxiety-like behavior in females in the EPM at the lower concentration of CBD. Long-term object memory was reduced in male wildtype mice at the lower concentration of CBD. Finally, ADHD- or attention-like behaviors were not altered by CBD in wildtype mice, but in Kv1.3-/- mice, females were observed to have a loss in attention while males demonstrated improved attention.

CONCLUSIONS

We conclude that administration of a single dose of CBD has immediate effects on mouse behavior that is dose, sex, and anxiety-state dependent - and that these behavioral outcomes are important to examine in parallel human trials.

Animal Behavior in Psychedelic Research

Psychedelic-assisted psychotherapy holds great promise in the treatment of mental health disorders. Research into 5-hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelic compounds has increased dramatically over the past two decades. In humans, these compounds produce drastic effects on consciousness, and their therapeutic potential relates to changes in the processing of emotional, social, and self-referential information. The use of animal behavior to study psychedelics is under debate, and this review provides a critical perspective on the translational value of animal behavior studies in psychedelic research. Acute activation of 5-HT_2ARs produces head twitches and unique discriminative cues, disrupts sensorimotor gating, and stimulates motor activity while inhibiting exploration in rodents. The acute treatment with psychedelics shows discrepant results in conventional rodent tests of depression-like behaviors but generally induces anxiolytic-like effects and inhibits repetitive behavior in rodents. Psychedelics impair waiting impulsivity but show discrepant effects in other tests of cognitive function. Tests of social interaction also show conflicting results. Effects on measures of time perception depend on the experimental schedule. Lasting or delayed effects of psychedelics in rodent tests related to different behavioral domains appear to be rather sensitive to changes in experimental protocols. Studying the effects of psychedelics on animal behaviors of relevance to effects on psychiatric symptoms in humans, assessing lasting effects, publishing negative findings, and relating behaviors in rodents and humans to other more translatable readouts, such as neuroplastic changes, will improve the translational value of animal behavioral studies in psychedelic research. SIGNIFICANCE STATEMENT: Psychedelics like LSD and psilocybin have received immense interest as potential new treatments of psychiatric disorders. Psychedelics change high-order consciousness in humans, and there is debate about the use of animal behavior studies to investigate these compounds. This review provides an overview of the behavioral effects of 5-HT_2AR agonist psychedelics in laboratory animals and discusses the translatability of the effects in animals to effects in humans. Possible ways to improve the utility of animal behavior in psychedelic research are discussed.

Sex differences in long-term fear and anxiety-like responses in a preclinical model of PTSD

With a high prevalence of posttraumatic stress disorder (PTSD) in females, studying sex differences in preclinical models is of substantial importance. We have previously employed behavioural criteria to identify and characterize a subpopulation of rats that presented impaired fear extinction and long-term fear and anxiety responses following fear conditioning. We now exposed male and female rats to fear conditioning and extinction and segregated the animals into weak- (WE) and strong-extinction (SE) groups based on behavioural scores during extinction. Animals were subsequently tested for tone and context recall, as well as anxiety-like responses in the marble burying and novelty suppression of feeding (NSF) tests. Vaginal lavages were collected to characterize the phase of the estrous cycle during fear extinction. We found that females had reduced freezing during tone recall and a lower latency to feed in the NSF test. No differences were found in females undergoing extinction during high and low estrogen phases of the cycle in any of the performed tests. Overall, the percentage of animals that presented WE and SE phenotypes was similar in males and females. Both, WE males and females had increased freezing during tone and context recall. Along with our previous reports, WE males presented anxiety-like responses, particularly in the NSF compared to SE animals. In contrast, WE females buried less marbles than their SE mates. Future investigation including a larger number of behavioural tests are certainly required to corroborate our findings and ascertain potential mechanisms to explain the differences observed in our study.

A Novel Automated Approach for Improving Standardization of the Marble Burying Test Enables Quantification of Burying Bouts and Activity Characteristics

The marble burying test is a commonly used paradigm to describe phenotypes in mouse models of neurodevelopmental and psychiatric disorders. The current methodological approach relies predominantly on reporting the number of buried marbles at the end of the test. By measuring the proxy of the behavior (buried marbles), many important characteristics regarding the temporal aspect of this assay are lost. Here, we introduce a novel, automated method to quantify mouse behavior during the marble burying test with the focus on the burying bouts and movement dynamics. Using open-source software packages, we trained a supervised machine learning algorithm (the "classifier") to distinguish burying behavior in freely moving mice. In order to confirm the classifier's accuracy and characterize burying events in high detail, we performed the marble burying test in three mouse models: Ube3a^m-/p+ [Angelman syndrome (AS) model], Shank2 ^-/- (autism model), and Sapap3 ^-/- [obsessive-compulsive disorder (OCD) model] mice. The classifier scored burying behavior accurately and consistent with the previously reported phenotype of the Ube3a^m-/p+ mice, which showed decreased levels of burying compared with controls. Shank2 ^-/- mice showed a similar pattern of decreased burying behavior, which was not found in Sapap3 ^-/- mice. Tracking mouse behavior throughout the test revealed hypoactivity in Ube3a^m-/p+ and hyperactivity in the Shank2 ^-/- mice, indicating that mouse activity is unrelated to burying behavior. Reducing activity with midazolam in Shank2 ^-/- mice did not alter the burying behavior. Together, we demonstrate that our classifier is an accurate method for the analysis of the marble burying test, providing more information than currently used methods.

Role of Nociceptin/Orphanin FQ-NOP Receptor System in the Regulation of Stress-Related Disorders

Nociceptin/orphanin FQ (N/OFQ) is a 17-residue neuropeptide that binds the nociceptin opioid-like receptor (NOP). N/OFQ exhibits nucleotidic and aminoacidics sequence homology with the precursors of other opioid neuropeptides but it does not activate either MOP, KOP or DOP receptors. Furthermore, opioid neuropeptides do not activate the NOP receptor. Generally, activation of N/OFQ system exerts anti-opioids effects, for instance toward opioid-induced reward and analgesia. The NOP receptor is widely expressed throughout the brain, whereas N/OFQ localization is confined to brain nuclei that are involved in stress response such as amygdala, BNST and hypothalamus. Decades of studies have delineated the biological role of this system demonstrating its involvement in significant physiological processes such as pain, learning and memory, anxiety, depression, feeding, drug and alcohol dependence. This review discusses the role of this peptidergic system in the modulation of stress and stress-associated psychiatric disorders in particular drug addiction, mood, anxiety and food-related associated-disorders. Emerging preclinical evidence suggests that both NOP agonists and antagonists may represent a effective therapeutic approaches for substances use disorder. Moreover, the current literature suggests that NOP antagonists can be useful to treat depression and feeding-related diseases, such as obesity and binge eating behavior, whereas the activation of NOP receptor by agonists could be a promising tool for anxiety.

In silico Screening and Behavioral Validation of a Novel Peptide, LCGA-17, With Anxiolytic-Like Properties

The aim of the study was to develop better anxiolytics and antidepressants. We focused on GABA_A receptors and the α2δ auxiliary subunit of V-gated Ca²⁺ channels as putative targets because they are established as mediators of efficacious anxiolytics, antidepressants, and anticonvulsants. We further focused on short peptides as candidate ligands because of their high safety and tolerability profiles. We employed a structural bioinformatics approach to develop novel tetrapeptides with predicted affinity to GABA_A receptors and α2δ. In silico docking studies of one of these peptides, LCGA-17, showed a high binding score for both GABA_A receptors and α2δ, combined with anxiolytic-like properties in a Danio rerio behavioral screen. LCGA-17 showed anxiolytic-like effects in the novel tank test, the light–dark box, and the social preference test, with efficacy comparable to fluvoxamine and diazepam. In binding assays using rat brain membranes, [³H]-LCGA-17 was competed more effectively by gabapentinoid ligands of α2δ than ligands of GABA_A receptors, suggesting that α2δ represents a likely target for LCGA-17. [³H]-LCGA-17 binding to brain lysates was unaffected by competition with ligands for GABA_B, glutamate, dopamine, serotonin, and other receptors, suggesting specific interaction with α2δ. Dose-finding studies in mice using acute administration of LCGA-17 (i.p.) demonstrated anxiolytic-like effects in the open field test, elevated plus maze, and marble burying tests, as well as antidepressant-like properties in the forced swim test. The anxiolytic effects were effectively blocked by bicuculline. Therefore, LCGA-17 is a novel candidate anxiolytic and antidepressant that may act through α2δ, with possible synergism by GABA_A receptors.

Sex-Dependent Signatures, Time Frames and Longitudinal Fine-Tuning of the Marble Burying Test in Normal and AD-Pathological Aging Mice

The marble burying (MB) test, a classical test based on the natural tendency of rodents to dig in diverse substrates and to bury small objects, is sensitive to some intrinsic and extrinsic factors. Here, under emerging neuroethological quantitative and qualitative analysis, the MB performance of 12-month-old male and female 3xTg-AD mice for Alzheimer’s disease and age-matched counterparts of gold-standard C57BL6 strain with normal aging unveiled sex-dependent signatures. In addition, three temporal analyses, through the (1) time course of the performance, and (2) a repeated test schedule, identified the optimal time frames and schedules to detect sex- and genotype-dependent differences. Besides, a (3) longitudinal design from 12 to 16 months of age monitored the changes in the performance with aging, worsening in AD-mice, and modulation through the repeated test. In summary, the present results allow us to conclude that (1) the marble burying test is responsive to genotype, sex, aging, and its interactions; (2) the male sex was more sensitive to showing the AD-phenotype; (3) longitudinal assessment shows a reduction in females with AD pathology; (4) burying remains stable in repeated testing; (5) the time-course of marbles burying is useful; and (6) burying behavior most likely represents perseverative and/or stereotyped-like behavior rather than anxiety-like behavior in 3xTg-AD mice.

The non-benzodiazepine anxiolytic etifoxine limits mechanical allodynia and anxiety-like symptoms in a mouse model of streptozotocin-induced diabetic neuropathy

More than 450 million people worldwide suffer from diabetes, or 1 in 11 people. Chronic hyperglycemia degrades patients’ quality of life and the development of neuropathic pain contributes to the burden of this disease. In this study, we used the mouse model of streptozocin-induced diabetic type 1 neuropathy to assess the analgesic potential of etifoxine. Etifoxine is a prescribed anxiolytic that increases GABAAA receptor function through a direct positive allosteric modulation effect and, indirectly, by stimulating the production of endogenous GABAA receptor positive modulators such as allopregnanolone-type neurosteroids. We show that a post-symptomatic or preventive treatment strongly and durably reduces mechanical hyperalgesia and anxiety in diabetic neuropathic mice. This analgesic and neuroprotective effect on painful symptoms and emotional comorbidities is promising and should now be clinically evaluated.

(E)-3-furan-2-yl-N-phenylacrylamide (PAM-4) decreases nociception and emotional manifestations of neuropathic pain in mice by α7 nicotinic acetylcholine receptor potentiation

Clinical intervention of pain is often accompanied by changes in affective behaviors, so both assays of affective and sensorial aspects of nociception play an important role in the development of novel analgesics. Although positive allosteric modulation (PAM) of α7 nicotinic acetylcholine receptors (nAChRs) has been recognized as a novel approach for the relief of sensorial aspects of pain, their effects on affective components of pain remain unclear. Therefore, we investigated whether PAM-4, a highly selective α7-nAChR PAM, attenuates inflammatory and neuropathic pain, as well as the concomitant depressive/anxiety comorbidities. The anti-nociceptive activity of PAM-4 was assessed in mice using the formalin test and chronic constriction injury (CCI)-induced neuropathic pain model. The anxiolytic- and antidepressant-like activity of PAM-4 was evaluated using the marble burying test and forced swimming test. Acute systemic administration of PAM-4 dose-dependently reversed formalin-induced paw licking behavior and CCI-induced mechanical allodynia without development of any motor impairment. PAM-4 reversed the decreased swimming time and number of buried marbles in CCI-treated mice, suggesting that this ligand attenuates chronic pain-induced depression-like behavior and anxiogenic-like effects. The effects of PAM-4 were inhibited by the α7-selective antagonist methyllycaconitine, indicating molecular mechanism mediated by α7-nAChRs. Indeed, electrophysiological recordings showed the PAM-4 enhances human α7 nAChRs with higher potency and efficacy compared to rat α7 nAChRs. These findings suggest that PAM-4 reduces both sensorial and affective behaviors induced by chronic pain in mice by α7-nAChR potentiation. PAM-4 deserves further investigations for the management of chronic painful conditions with comorbidities.

Salidroside Improves Chronic Stress Induced Depressive Symptoms Through Microglial Activation Suppression

Depression is a severe neurological disorder highly associated with chronic mental stress stimulation, which involves chronic inflammation and microglial activation in the central nervous system (CNS). Salidroside (SLDS) has been reported to exhibit anti-neuroinflammatory and protective properties on neurological diseases. However, the mechanism underlying the effect of SLDS on depressive symptoms has not been well elaborated. In the present study, the effects of SLDS on depressive behaviors and microglia activation in mice CNS were investigated. Behavioral tests, including Forced swimming test (FST), Open field test (OFT) and Morris water maze (MWM) revealed that SLDS treatment attenuated the depressive behaviors in stress mice. SLDS treatment significantly reduced the microglial immunoreactivity for both Iba-1 and CD68, characteristic of deleterious M1 phenotype in hippocampus of stress mice. Additionally, SLDS inhibited microglial activation involving the suppression of ERK1/2, P38 MAPK and p65 NF-κB activation and thus reduced the expression and release of neuroinflammatory cytokines in stress mice as well as in lipopolysaccharide (LPS)-induced primary microglia. Also, SLDS changed microglial morphology, attachment and reduced the phagocytic ability in LPS-induced primary microglia. The results demonstrated that SLDS treatment could improve the depressive symptoms caused by unpredictable chronic stress, indicating a potential therapeutic application of SLDS in depression treatment by interfering microglia-mediated neuroinflammation.

Anxiety and Alzheimer's disease: Behavioral analysis and neural basis in rodent models of Alzheimer's-related neuropathology

Alzheimer's disease (AD) pathology is commonly associated with cognitive decline but is also composed of neuropsychiatric symptoms including psychological distress and alterations in mood, including anxiety and depression. Emotional dysfunction in AD is frequently modeled using tests of anxiety-like behavior in transgenic rodents. These tests often include the elevated plus-maze, light/dark test and open field test. In this review, we describe prototypical behavioral paradigms used to examine emotional dysfunction in transgenic models of AD, specifically anxiety-like behavior. Next, we summarize the results of studies examining anxiety-like behavior in transgenic rodents, noting that the behavioral outcomes using these paradigms have produced inconsistent results. We suggest that future research will benefit from using a battery of tests to examine emotional behavior in transgenic AD models. We conclude by discussing putative, overlapping neurobiological mechanisms underlying AD-related neuropathology, stress and anxiety-like behavior reported in AD models.

Diazepam causes sedative rather than anxiolytic effects in C57BL/6J mice

Diazepam has been broadly accepted as an anxiolytic drug and is often used as a positive control in behavioral experiments with mice. However, as opposed to this general assumption, the effect of diazepam on mouse behavior can be considered rather controversial from an evidence point of view. Here we revisit this issue by studying the effect of diazepam on a benchmark task in the preclinical anxiety literature: the elevated plus maze. We evaluated the minute-by-minute time-course of the diazepam effect along the 10 min of the task at three different doses (0.5, 1 and 2 mg/kg i.p. 30 min before the task) in female and male C57BL/6J mice. Furthermore, we contrasted the effects of diazepam with those of a selective serotoninergic reuptake inhibitor (paroxetine, 10 mg/kg i.p. 1 h before the task). Diazepam had no anxiolytic effect at any of the tested doses, and, at the highest dose, it impaired locomotor activity, likely due to sedation. Noteworthy, our results held true when examining male and female mice separately, when only examining the first 5 min of the task, and when animals were subjected to one hour of restrain-induced stress prior to diazepam treatment. In contrast, paroxetine significantly reduced anxiety-like behavior without inducing sedative effects. Our results therefore suggest that preclinical studies for screening new anxiolytic drugs should be cautious with diazepam use as a potential positive control.

Antidepressant Screening Demonstrated Non-Monotonic Responses to Amitriptyline, Amoxapine and Sertraline in Locomotor Activity Assay in Larval Zebrafish

Antidepressants are well-known drugs to treat depression and major depressive disorder for humans. However, the misuse and abuse of antidepressants keep increasing with several side effects reported. The aim of this study was to assess the potential adverse effects of 18 antidepressants by monitoring zebrafish larval locomotor activity performance based on the total distance traveled, burst movement count, and total rotation count at four dark-light intercalated phases. In general, zebrafish larvae displayed sedative effects after antidepressant exposure by showing a significant reduction in all of the locomotor activity-related endpoints. However, three antidepressants i.e., amitriptyline, amoxapine, and sertraline were able to trigger a significantly high locomotor activity in zebrafish larvae during the light cycle. These differences might be due to the pharmacologic differences among the antidepressants. In addition, since each antidepressant possesses a different dosage range from the other, overdoses of these antidepressants might also be the causes of these differences. Furthermore, based on these results, a further study was conducted to observe the effect of these three antidepressants in lower concentrations. From the results, biphasic effects in terms of zebrafish larval locomotor activity were demonstrated by these drugs. Even though further studies are still required to validate the mechanism, these findings indicate that these antidepressants might share a common mechanism responsible for their effects on zebrafish larval locomotor activity although there were some differences in potency of these effects.

Hnrnph1 is a novel regulator of alcohol reward

BACKGROUND

Hnrnph1 is a validated quantitative trait gene for methamphetamine behavioral sensitivity that encodes for heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1). This RNA-binding protein is involved in all stages of RNA metabolism that impacts mesocorticolimbic dopamine neurotransmission to influence addiction-related behavior.

METHODS

We characterized the alcohol behavioral phenotypes of mice heterozygous for a deletion in the first coding exon of Hnrnph1 (Hnrnph1+/-). We examined alcohol intake under both continuous- and limited-access procedures, as well as alcohol-induced place-conditioning. Follow-up studies examined genotypic differences in the psychomotor-activating and sedative-hypnotic effects of acute and repeated alcohol, and a behavioral test battery was employed to determine the effects of Hnrnph1 deletion on the manifestation of negative affect during alcohol withdrawal.

RESULTS

Relative to wild-type (WT) controls, Hnrnph1+/- males exhibited blunted intake of high alcohol concentrations under both drinking procedures. Hnrnph1 deletion did not impact the conditioned rewarding properties of low-dose alcohol, but reversed the conditioned place-aversion elicited by higher alcohol doses (2 and 4 g/kg), with more robust effects in male versus female mice. No genotypic differences were observed for alcohol-induced locomotor activity. Hnrnph1+/- mice exhibited a modest increase in sensitivity to alcohol's sedative-hypnotic effects, but did not differ from WT mice with regard to tolerance to alcohol's sedative-hypnotic effects or alcohol metabolism, Inconsistent effects of Hnrnph1 deletion were observed in models for withdrawal-induced negative affect.

CONCLUSIONS

These data identify Hnrnph1 as a novel, male-selective, driver of alcohol consumption and high-dose alcohol aversion that is potentially relevant to the neurobiology of alcohol abuse and alcoholism.

Negative Modulation of the Metabotropic Glutamate Receptor Type 5 as a Potential Therapeutic Strategy in Obesity and Binge-Like Eating Behavior

Obesity is a multifactorial disease, which in turn contributes to the onset of comorbidities, such as diabetes and atherosclerosis. Moreover, there are only few options available for treating obesity, and most current pharmacotherapy causes severe adverse effects, while offering minimal weight loss. Literature shows that metabotropic glutamate receptor 5 (mGluR5) modulates central reward pathways. Herein, we evaluated the effect of VU0409106, a negative allosteric modulator (NAM) of mGluR5 in regulating feeding and obesity parameters. Diet-induced obese C57BL/6 mice were treated for 14 days with VU0409106, and food intake, body weight, inflammatory/hormonal levels, and behavioral tests were performed. Our data suggest reduction of feeding, body weight, and adipose tissue inflammation in mice treated with high-fat diet (HFD) after chronic treatment with VU0409106. Furthermore, a negative modulation of mGluR5 also reduces binge-like eating, the most common type of eating disorder. Altogether, our results pointed out mGluR5 as a potential target for treating obesity, as well as related disorders.

Digging Signatures in 13-Month-Old 3xTg-AD Mice for Alzheimer's Disease and Its Disruption by Isolation Despite Social Life Since They Were Born

The severity of this pandemic's scenarios will leave significant psychological traces in low resistant and resilient individuals. Increased incidence of depression, anxiety, obsessive-compulsive disorder (OCD), and post-traumatic stress disorder has already been reported. The loss of human lives and the implementation of physical distance measures in the pandemic and post-COVID scenarios may have a greater impact on the elderly, mostly in those with dementia, as OCD and other neuropsychiatric symptoms (NPS) are quite prevalent in this population. Modeling NPS in animals relies in neuroethological perspectives since the response to new situations and traumatic events, critical for survival and adaptation to the environment, is strongly preserved in the phylogeny. In the laboratory, mice dig vigorously in deep bedding to bury food pellets or small objects they may find. This behavior, initially used to screen anxiolytic activity, was later proposed to model better meaningless repetitive and perseverative behaviors characteristic of OCD or autism spectrum disorders. Other authors found that digging can also be understood as part of the expression of the animals' general activity. In the present brief report, we studied the digging ethograms in 13-month-old non-transgenic and 3xTg-AD mice modeling normal aging and advanced Alzheimer's disease (AD), respectively. This genetic model presents AD-like cognitive dysfunction and NPS-like phenotype, with high mortality rates at this age, mostly in males. This allowed us to observe the digging pattern's disruption in a subgroup of 3xTg-AD mice that survived to their cage mates. Two digging paradigms involving different anxiogenic and contextual situations were used to investigate their behavior. The temporal course and intensity of digging were found to increase in those 3xTg-AD mice that had lost their "room partners" despite having lived in social structures since they were born. However, when tested under neophobia conditions, this behavior's incidence was low (delayed), and the temporal pattern was disrupted, suggesting worsening of this NPS-like profile. The outcomes showed that this combined behavioral paradigm unveiled distinct features of digging signatures that can be useful to study these perseverative behaviors and their interplay with anxiety states already present in the AD scenario and their worsening by naturalistic/forced isolation.

Magic Shotgun Nature with Scattergun Approach of Curcumin Repurposing in Obsessive-compulsive Disorder: A Novel Metaphysician of Drug Discovery

BACKGROUND

Obsessive-Compulsive Disorder (OCD) is an intricate, debilitating neuropsychiatric disorder. Exclusively, Selective Serotonin Reuptake Inhibitors (SSRIs) are effective agents used for the treatment of OCD. However, SSRIs are not a magic pill-they do not respond adequately to everybody. In this consideration, a single drug target (magic bullet) is only a slightly superior option for all patients with a lot of pathognomonic signs.

OBJECTIVE

The principal aim of the current study was to check the potential contribution of repurposing of magic shotgun nature of curcumin (rhizomes of Curcuma longa) with scattergun approach- proceeding a pioneer 'fine-tune' for obsessive-compulsive disorder.

METHOD

Swiss albino mice (male 20 to 25 gram) were grouped into different groups (n = 6) used for the MBB (marble-burying behaviour) and MA (motor activity) test as a model for evaluation of anti-compulsive activity (Anti-OCD). Ethanolic extract of Curcuma longa (EECL-10, 15, 25, 40 mg/kg), or SSRI (fluoxetine 5, 10, 15 mg/kg) followed by pre-treated with either sub effective dose of fluoxetine attenuated MBB without effected the MA, or neurotoxin p-chlorophenyl alanine induced compulsive behavior and specific 5-HT receptors agonists/ antagonist, intraperitoneally revealed neuromodulation.

RESULTS

EECL (40 mg/kg) significantly attenuated the MBB. Although, during treatments, none of the above had any critical impact on MA. p < 0.05 was considered significant in every case.

CONCLUSION

Multiple drug-target interactions with multifarious biogenic receptors, supervene unexpected side effects followed by the repurposing of wanted effects (scattergun effect) were evoked by curcumin treatment. Finally, the study shows that EECL (curcumin) has anti-compulsive activity, which is mediated by neuromodulation with 5-HT receptors.

Investigating the role of 5-HT2A and 5-HT2C receptor activation in the effects of psilocybin, DOI, and citalopram on marble burying in mice

Psychedelic drugs acting as 5-hydroxyptryptamine 2A receptor (5-HT_2AR) agonists have shown promise as viable treatments of psychiatric disorders, including obsessive-compulsive disorder. The marble burying test is a test of compulsive-like behavior in mice, and psychedelics acting as 5-HT_2AR agonists can reduce digging in this test. We assessed the 5-HT₂R contribution to the mechanisms of two 5-HT_2A agonists on digging behavior in female NMRI mice, using citalopram as a reference compound. While the 5-HT_2AR antagonist M100907 blocked the effect of DOI and the 5-HT_2CR antagonist SB242084 blocked the effect of citalopram, neither antagonist blocked the effect of psilocybin. This study confirms 5-HT_2AR agonism as a mechanism for reduced compulsive-like digging in the MB test and suggests that 5-HT_2A and 5-HT_2CRs can work in parallel on this type of behavior. Our results with psilocybin suggest that a 5-HT₂R-independent mechanism also contributes to the effect of psilocybin on repetitive digging behavior.

Attenuation of Anxiety-Like Behavior by Helichrysum stoechas (L.) Moench Methanolic Extract through Up-Regulation of ERK Signaling Pathways in Noradrenergic Neurons

The long-term use of anxiolytic and antidepressant drugs can cause a plethora of side effects and the use of complementary and alternative medicine, which is generally considered safer than conventional medicine, is consistently increasing. Helichrysum stoechas (L.) Moench methanolic extract (HSE) has shown MAO-A inhibitory properties in previous studies. With the aim of obtaining innovative and safer therapies for mood disorders, this study investigated the potential activity of HSE in the management of anxiety- and depression-related symptoms. HSE showed dose-dependent (30-100 mg/kg p.o.) anxiolytic-like activity in the light dark box and marble burying tests, without any antidepressant-like activity, as shown by the results of the tail suspension test. Additionally, HSE did not have any effect on the modulation of pain, which highlights its selectivity in the control of anxiety-related behavior. At active doses, HSE did not produce any sedative effect or result in impaired motor coordination and memory functions. Western blotting experiments showed the ability of HSE to counteract the reduction in the phosphorylation of ERK44/42, to restore brain-derived neurotrophic factor (BDNF) expression and to return cyclic AMP response element binding (CREB) levels to basal levels in noradrenergic hippocampal neurons of mice exposed to an anxiety-related environment, which indicates a protective role against anxiety behavior. These results suggest that oral administration of HSE might represent an interesting opportunity for the management of anxiety disorders.

Effects of delivery mode on behavior in mouse offspring

Cesarean section (CS) has been associated with an increased risk of mental disorders in the offspring. This could possibly be explained by an inadequate microbial colonization early in life with a consequential disturbed gut-brain interaction. To investigate the link between delivery mode and behavior and develop a suitable animal model for further research of the gut-brain axis, the aim of this study was to characterize the gut microbiota (GM) together with the behavioral response in various behavioral tests in CS-delivered mice. We hypothesized that mice delivered by CS would present with disturbances in normal physiological behavior possibly due to an inadequate microbial colonization. C57BL/6 mice delivered by CS or vaginal delivery (VD) were cross fostered and, as adults, observed for anxiety-related behavior in the open field test, social deficits in a sociability test and compulsive behavior in the marble burying test. GM was analyzed by 16S rRNA gene amplicon sequencing. The open field test showed that CS-delivered mice had a decreased activity and accelerated defecation compared to VD-delivered mice. In addition, CS-delivered female mice spend less time interacting with cage mates in the sociability test, whereas there was no effect of CS delivery on the average number of marbles buried. In conclusion, CS-delivered mice had a more pronounced anxiety-like behavior and showed less preference for sociability in female offspring.

Exploring test batteries for depression- and anxiety-like behaviours in female and male ICR and black Swiss mice

Objective and rationale: Animal models are critical for the study of mental disorders and their treatments but are repeatedly criticized for problems with validity and reproducibility. One approach to enhance validity and reproducibility of models is to use test batteries rather than single tests. Yet, a question regarding batteries is whether one can expect a consistent individual behavioural phenotype in mice across tests that can be presumed to be part of the same construct. This study was designed to explore the relationship between the behaviours of mice across tests in some variations of test batteries for depression- and anxiety-like behaviours. Methods: Female and male healthy, intact, and untreated mice from the ICR and black Swiss strains were used in four separate experiments. With some variations, mice were exposed to a battery of behavioural tests representing affective- and anxiety-like behaviours. Data were analysed for differences between sexes and for correlations between behaviours within and across the tests in the battery. Results: No differences were found between the sexes. With very few exceptions, we found correlations within tests (when one test has more than one measure or is repeated) but not across different tests within the battery. Conclusions: The results cast some doubt on the utility of behavioural test batteries to represent different facets of emotional behaviour in healthy intact outbred mice, without any interventions or treatments. Additional studies are designed to explore whether stronger relationship between the tests will appear after manipulations or drug treatments.

Long-lasting analgesic and neuroprotective action of the non-benzodiazepine anxiolytic etifoxine in a mouse model of neuropathic pain

Neuropathic pain is frequently associated with anxiety and major depressive disorders, which considerably impact the overall patient experience. Favoring GABAergic inhibition through the pain matrix has emerged as a promising strategy to restore proper processing of nociceptive and affective information in neuropathic pain states. In this context, the non-benzodiazepine anxiolytic etifoxine (EFX), known to amplify GABAergic inhibition through positive modulation of GABA_A receptors and neurosteroidogenesis, presents several advantages. Therefore, we sought to investigate the preclinical therapeutic potential of EFX on the somatosensory and affective components of neuropathic pain. Here, we used a murine model in which neuropathic pain was induced by the implantation of a compressive cuff around the sciatic nerve (mononeuropathy). We showed that the intraperitoneal EFX treatment for five consecutive days (50 mg/kg) relieved mechanical allodynia in a sustained manner. Besides its effect on evoked mechanical hypersensitivity, EFX also alleviated aversiveness of ongoing pain as well as anxiodepressive-like consequences of neuropathic pain following cuff-induced mononeuropathy. This effect was also seen 12 weeks after induction of the neuropathy when allodynia was no longer present. Analgesic and neuroprotective actions of EFX were also seen by the absence of neuropathic pain symptoms if a second sciatic nerve constriction injury was applied to the contralateral hindpaw. Mass spectrometry analysis revealed a normalization of brainstem serotonin levels in EFX-treated animals and an increase in norepinephrine. This study suggests that EFX presents promising therapeutic potential for the relief of both somatosensory and affective consequences of neuropathic pain, a beneficial effect that is likely to involve monoamine descending controls.

Neurobehavioral effects of neonatal opioid exposure in mice: Influence of the OPRM1 SNP

Opioid use among pregnant women is a growing public health concern in the United States. Infants exposed to opioids in utero are at risk of exhibiting neonatal opioid withdrawal syndrome (NOWS). The biological mechanisms underlying short and long-term consequences of in utero opioid exposure and NOWS are unknown. A potential genetic factor is a single-nucleotide polymorphism (SNP) in the mu-opioid receptor gene (OPRM1 A118G). Opioid exposed infants with the G-allele spend less time in hospitals after birth. To determine whether this SNP modulates the neurobehavioral effects of neonatal opioid exposure and withdrawal, we used mice possessing the equivalent Oprm1 SNP (A112G). Pups were treated chronically with saline or morphine from postnatal days (PNDs) 1 to 14, a developmental period equivalent to the third trimester of a human pregnancy and a sensitive period for opioid exposure in rodents. Morphine treatment produced significant developmental delays regardless of genotype and increased total ultrasonic vocalizations in males during spontaneous withdrawal. Animals were aged and tested for anxiety and drug response during adolescence and adulthood, respectively. AA morphine-treated animals showed reduced activity in the marble burying task compared with saline controls; however, this effect was absent in AG and GG animals. As adults, AA males exposed to morphine from PNDs 1 to 14 exhibited enhanced development of locomotor sensitization to morphine, whereas females showed reduced locomotor sensitization. These data suggest the involvement of the Oprm1 SNP for certain outcomes of neonatal opioid exposure and highlight the importance of considering sex and genetic variability for the prognosis of NOWS.

Chronic Voluntary Binge Ethanol Consumption Causes Sex-Specific Differences in Microglial Signaling Pathways and Withdrawal-associated Behaviors in Mice

BACKGROUND

Microglia are the resident immune cells in the brain where they play essential roles in the development and maintenance of physiological functions of this organ. Aberrant activation of microglia is speculated to be involved in the pathogenesis of a variety of neurological disorders, including alcohol use disorders. Repeated binge ethanol (EtOH) consumption can have a profound impact on the function and integrity of the brain resulting in changes in behaviors such as withdrawal and reward. However, the microglial molecular and cellular pathways associated with EtOH binge consumption remain poorly understood.

METHOD

In this study, adult C57BL/6J male and female mice were subjected daily to a gelatin-based drinking-in-the-dark voluntary EtOH consumption paradigm (3 h/d for 4 months) to characterize EtOH consumption and withdrawal-associated and anxiety-like behaviors. Brain microglia were isolated at the end and analyzed for protein expression profile changes using unbiased mass spectrometry-based proteomic analysis.

RESULTS

Both male and female mice consistently consumed binge quantities of EtOH daily, resulting in blood EtOH levels > 80 mg/dl measured at the end of the 3-hour daily consumption period. Although female mice consumed a significantly greater amount of EtOH than male mice, EtOH withdrawal-associated anxiety-like behaviors measured by marble-burying, light-dark box, and elevated plus maze tests were predominantly observed in male mice. Proteomic analysis of microglia isolated from the brains of animals at the end of the 4-month binge EtOH consumption identified 117 and 37 proteins that were significantly up- or downregulated in EtOH-exposed male and female mice, respectively, compared to their pair-fed controls. Protein expression profile-based pathway analysis identified several cellular pathways that may underlie the sex-specific and EtOH withdrawal-associated behavioral abnormalities.

CONCLUSION

Taken together, our findings revealed sex-specific changes in EtOH withdrawal-associated behaviors and signaling pathways in the mouse brain microglia and may help advance our understanding of the molecular, cellular, and behavioral changes related to human binge EtOH consumption.

Human-Derived Bifidobacterium dentium Modulates the Mammalian Serotonergic System and Gut-Brain Axis

BACKGROUND & AIMS

The human gut microbiota can regulate production of serotonin (5-hydroxytryptamine [5-HT]) from enterochromaffin cells. However, the mechanisms underlying microbial-induced serotonin signaling are not well understood.

METHODS

Adult germ-free mice were treated with sterile media, live Bifidobacterium dentium, heat-killed B dentium, or live Bacteroides ovatus. Mouse and human enteroids were used to assess the effects of B dentium metabolites on 5-HT release from enterochromaffin cells. In vitro and in vivo short-chain fatty acids and 5-HT levels were assessed by mass spectrometry. Expression of tryptophan hydroxylase, short-chain fatty acid receptor free fatty acid receptor 2, 5-HT receptors, and the 5-HT re-uptake transporter (serotonin transporter) were assessed by quantitative polymerase chain reaction and immunostaining. RNA in situ hybridization assessed 5-HT-receptor expression in the brain, and 5-HT-receptor-dependent behavior was evaluated using the marble burying test.

RESULTS

B dentium mono-associated mice showed increased fecal acetate. This finding corresponded with increased intestinal 5-HT concentrations and increased expression of 5-HT receptors 2a, 4, and serotonin transporter. These effects were absent in B ovatus-treated mice. Application of acetate and B dentium-secreted products stimulated 5-HT release in mouse and human enteroids. In situ hybridization of brain tissue also showed significantly increased hippocampal expression of 5-HT-receptor 2a in B dentium-treated mice relative to germ-free controls. Functionally, B dentium colonization normalized species-typical repetitive and anxiety-like behaviors previously shown to be linked to 5-HT-receptor 2a.

CONCLUSIONS

These data suggest that B dentium, and the bacterial metabolite acetate, are capable of regulating key components of the serotonergic system in multiple host tissues, and are associated with a functional change in adult behavior.

Similarities and dissimilarities in the effects of benzodiazepines and specific serotonin reuptake inhibitors (SSRIs) in the defensive marble burying test: A systematic review and meta-analysis

One problem areas of animal models and tests for neuropsychiatric disorders is unclear reproducibility, including both internal and external validity. One way to examine external validity is with systematic reviews and meta-analyses, a standard practice in clinical research that is relatively neglected in preclinical research. Considering the need to evaluate the validity and reproducibility of frequently used animal models, this study presents a meta-analysis of the effects of prototypic benzodiazepines and specific serotonin reuptake inhibitors (SSRIs) in the mouse defensive marble burying test (MBT). These drug groups were selected because although they differ in their biological targets as well as in their clinical use, they are both commonly used for the treatment of anxiety disorders. A PubMed literature search was performed to identify studies that examined the effects of benzodiazepines (diazepam, alprazolam, chlordiazepoxide, clonazepam) or SSRIs (fluoxetine, citalopram, escitalopram, fluvoxamine, paroxetine) in the MBT in mice. For benzodiazepines, 73 experiments were included. Benzodiazepines effect size was 2.04 and Q statistics was 1959 with a significant correlation between dose and effect size (r = 0.31, p = 0.007). For SSRIs we identified 47 experiments. Effect size of SSRIs was 2.24 and Q statistics was 493.38. No correlation was found between dose and effect size (r = 0.23, p = 0.12). The current results support the external validity of the defensive marble burying test as a screening test for anxiolytic effects. However, these results indicate that significant attention should be given to the administration schedules of benzodiazepines and SSRIs.

The selective 5-HT2A receptor agonist 25CN-NBOH: Structure-activity relationship, in vivo pharmacology, and in vitro and ex vivo binding characteristics of [3H]25CN-NBOH

The remarkable effects exhibited by classical psychedelics in recent clinical trials have spawned considerable interest in 5-HT_2A receptor (5-HT_2AR) activation as a treatment strategy for several psychiatric/cognitive disorders. In this study we have continued our development of 25CN-NBOH, one of the most 5-HT_2AR-selective agonists reported to date, as a pharmacological tool for exploration of 5-HT_2AR expression and functions. The importance of the 2' and 3' positions in 25CN-NBOH as structural hotspots for its 5-HT_2AR activity was investigated by synthesis and pharmacological characterization of six novel analogs at 5-HT_2AR and 5-HT_2CR in binding and functional assays. While the 5-HT_2AR activity of 25CN-NBOH was retained in 3'-methyl, 2',3'-chroman, 2',3'-dihydrofuran and 2',3'-furan analogs, the 3'-methoxy and 3'-ethyl analogs displayed substantially lower binding affinities and agonist potencies than 25CN-NBOH. Interestingly, the 2',3'-substitution pattern was also a key determinant of agonist efficacy, as all six analogs exhibited low-efficacy partial agonism or de facto antagonism at the 5-HT_2AR in the functional assays. Systemic administration of 25CN-NBOH and its close structural analog 25CN-NBMD induced robust head-twitch response in mice, a well-established behavioural effect of 5-HT_2AR activation in vivo, and 25CN-NBOH mediated robust reductions in the activity of mice in an anxiety-related marble burying assay, which supports the proposed beneficial effects of 5-HT_2AR activation on disorders characterized by cognitive rigidity. Finally, tritiated 25CN-NBOH exhibited high 5-HT_2AR binding affinity (K_D ~1 nM) and selectivity against 5-HT_2BR and 5-HT_2CR in equilibrium and kinetic binding studies of the recombinant receptors, and in concordance [³H]25CN-NBOH displayed substantial specific, ketanserin-sensitive binding to cortex and small levels of binding to choroid plexus in rat brain slices in autoradiography studies. In conclusion, this work delineates the subtle molecular determinants of the 5-HT_2AR activity in 25CN-NBOH, substantiates the potential in this compound and its analogs as tools for in vivo studies of the 5-HT_2AR, and introduces a novel selective agonist radioligand as another potentially valuable tool for future explorations of this receptor.

A critical inquiry into marble-burying as a preclinical screening paradigm of relevance for anxiety and obsessive-compulsive disorder: Mapping the way forward

Rodent marble-burying behavior in the marble-burying test (MBT) is employed as a model or measure to study anxiety- and compulsive-like behaviors or anxiolytic and anticompulsive drug action. However, the test responds variably to a range of pharmacological interventions, and little consensus exists regarding specific methodologies for its execution. Regardless, the test is widely applied to investigate the effects of pharmacological, genetic, and behavioral manipulations on purported behaviors related to the said neuropsychiatric constructs. Therefore, in the present review we attempt to expound the collective translational significance of the MBT. We do this by (1) reviewing burying behavior as a natural behavioral phenotype, (2) highlighting key aspects of anxiety and obsessive-compulsive disorder from a translational perspective, (3) reviewing the history and proof of concept of the MBT, (4) critically appraising potential methodological confounds in execution of the MBT, and (5) dissecting responses of the MBT to various pharmacological interventions. We conclude by underlining that the collective translational value of the MBT will be strengthened by contextually valid experimental designs and objective reporting of data.

3Rs-based optimization of mice behavioral testing: The habituation/dishabituation olfactory test

BACKGROUND

There is clear evidence that most of the paradigms that are used in the field of behavioral neuroscience suffer from a lack of reliability mainly because of oversimplification of both testing procedures and interpretations. In the present study we show how an already existing behavioral test, the olfactory habituation / dishabituation task, can be optimized in such a way that animal number and animal distress could be minimized, number/confidence of behavioral outcomes and number of explored behavioral dimensions could be increased.

NEW METHOD

We used ethologically relevant technical and procedural changes associated with videotracking-based automated quantification of sniffing behavior to validate our new setup. Mainly internal and construct validity were challenged through the implementation of a series of simple experiments.

RESULTS

We show that the new version of the test: 1) has very good within and inter laboratory replicability, 2) is sensitive to some environmental / experimental factors while insensitive to others, 3) allows investigating hedonism, both state and trait anxiety, efficacy of anxiolytic molecules, acute stress, mental retardation-related social impairments and learning and memory. 4) We also show that interest for both nonsocial and social odors is stable over time which makes repetitive testing possible.

CONCLUSIONS

This work paves the way for future studies showing how behavioral tests / procedures may be improved by using ethologically relevant changes, in order to question laboratory animals more adequately. Refining behavioral tests may considerably increase predictivity of preclinical tests and, ultimately, help reinforcing translational research.

Marble-burying behavior test as a murine model of compulsive-like behavior

Object burying by rodents is a popular screening tool for anxiolytic agents. However, modulation of marble-burying by serotonin reuptake inhibitors prompted its link to obsessive-compulsive disorder/compulsive-like behavior. The Marble-burying behavior test is an acute test; however, some investigators incorporate the sub-acute treatment regimen as an essential component for screening anti-compulsive agents. The test exhibits between-laboratory methodological differences and demonstrates positive treatment responses to an array of pharmacotherapies, creating doubts about its predictive validity and construct validity. Numerous reviews are available on marble-burying behavior test, which incorporates the test as a part of anti-compulsive behavior-like screens, but none has made it a sole subject-matter for discussion. This review attempts to provide a comprehensive account of the marble-burying test as a model of compulsive-like disorders. It envisages the model's scientific origins, the preclinical research done and its correlation with the clinical research outcomes, and a detailed discussion about its validity. In conclusion, there appears a need to address the issue of construct and predictive validity of the model authoritatively; or the paradigm may remain squandered in the field of obsessive-compulsive disorder research.

Preclinical characterization of ACH-000029, a novel anxiolytic compound acting on serotonergic and alpha-adrenergic receptors

Anxiety disorders are serious and common mental diseases, yet there is still a need for the development of more effective anxiolytics with better safety profiles than benzodiazepines and serotonin reuptake inhibitors. The serotonergic and noradrenergic systems have reciprocal interactions and are intricately related to the pathogenesis of anxiety. In this study, the anxiolytic-like effect of the novel compound ACH-000029, 3-(2-(4-(2-methoxyphenyl) piperazine-1-yl) ethyl) quinazoline-4(3H)-one, is reported. This compound acts at selected serotonergic (5-HT1A and 5-HT1D partial agonism and 5-HT2A antagonism) and α-adrenergic (α-1A, 1B and 1D antagonism) receptors, with good selectivity over other G-protein-coupled receptors. ACH-000029 exhibited high blood-brain barrier permeation and acute anxiolytic effects in the marble burying (MB) and light-dark box (LDB) models of anxiety over the dose ranges of 8-32 mg/kg i.p. and 16-30 mg/kg p.o. The anxiolytic activity was comparable to that observed for serotonin reuptake inhibitors (paroxetine and fluoxetine) and benzodiazepines (alprazolam, diazepam and clobazam). The analysis of the whole-brain c-fos expression following oral dosing showed that ACH-000029 regulated regions highly associated with the processing of environmental stimuli and anxiety behavior, such as the amygdala, paraventricular nucleus of the thalamus, retrosplenial dorsal, pallidum, bed nuclei of the stria terminalis, and locus ceruleus. No safety concerns were identified for ACH-000029 in the functional observational battery up to 50 mg/kg i.p. and in the nonprecipitated withdrawal test up to 30 mg/kg p.o. twice daily for 20 days. This work supports the further development of ACH-000029 as a drug candidate for the treatment of anxiety disorders. The analysis of the in vitro pharmacology and brain regions regulated by this compound may also lead to the exploration of other indications within the psychiatry field.

The 5-hydroxytryptamine 2A receptor agonists DOI and 25CN-NBOH decrease marble burying and reverse 8-OH-DPAT-induced deficit in spontaneous alternation

5-Hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelics are increasingly recognized as potentially useful treatments of psychiatric disorders, such as obsessive-compulsive disorder, depression, anxiety, and drug dependence. There is limited understanding of the way they exert their therapeutic action, but inhibition of rigid behavior and cognition has been suggested as a key factor. To examine the role of 5-HT_2ARs in modulating repetitive behavior, we tested two 5-HT_2AR agonists, DOI, and the selective 25CN-NBOH, in two mouse tests of compulsive-like behavior. Using adult C57BL/6JOlaHsd male mice, we examined the effects of the two compounds on digging behavior in the marble burying test and on 8-OH-DPAT-disrupted spontaneous alternation behavior in the Y-maze. Both compounds dose-dependently decreased digging behavior in the marble burying test, indicating anti-compulsivity effects, which were not related to non-specific locomotor inhibition. Both 5-HT_2AR agonists also reversed 8-OH-DPAT-reduced alternation ratio in the spontaneous alternation behavior test, although the effects were less pronounced than in the marble burying test. This suggests that the 5-HT_2AR promotes exploratory behavior, but that the deficit produced by 8-OH-DPAT is too excessive to be fully reversed by 5-HT_2AR agonists. This study shows that agonism of 5-HT_2AR reduces repetitive behavioral patterns, supporting the theory that this is a potential new treatment approach to disorders of cognitive or behavioral inflexibility. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Microglia morphology and proinflammatory signaling in the nucleus accumbens during nicotine withdrawal

Smoking is the largest preventable cause of death and disease in the United States. However, <5% of quit attempts are successful, underscoring the urgent need for novel therapeutics. Microglia are one untapped therapeutic target. While previous studies have shown that microglia mediate both inflammatory responses in the brain and brain plasticity, little is known regarding their role in nicotine dependence and withdrawal phenotypes. Here, we examined microglial changes in the striatum-a mesolimbic region implicated in the rewarding effects of drugs and the affective disruptions occurring during withdrawal. We show that both nicotine and withdrawal induce microglial morphological changes; however, proinflammatory effects and anxiogenic behaviors were observed only during nicotine withdrawal. Pharmacological microglial depletion during withdrawal prevented these effects. These results define differential effects of nicotine and withdrawal on inflammatory signaling in the brain, laying the groundwork for development of future smoking cessation therapeutics.

A Psycho-Behavioral Perspective on Modelling Obsessive-Compulsive Disorder (OCD) in Animals: The Role of Context

Obsessive-compulsive disorder is a heterogeneous and debilitating condition, characterized by intrusive thoughts and compulsive repetition. Animal models of OCD are important tools that have the potential to contribute significantly to our understanding of the condition. Although there is consensus that pre-clinical models are valuable in elucidating the underlying neurobiology in psychiatric disorders, the current paper attempts to prompt ideas on how interpretation of animal behavior can be expanded upon to more effectively converge with the human disorder. Successful outcomes in psychopharmacology involve rational design and synthesis of novel compounds and their testing in well-designed animal models. As part of a special journal issue on OCD, this paper will 1) review the psychobehavioral aspects of OCD that are of importance on how the above ideas can be articulated, 2) briefly elaborate on general issues that are important for the development of animal models of OCD, with a particular focus on the role and importance of context, 3) propose why translational progress may often be less than ideal, 4) highlight some of the significant contributions afforded by animal models to advance understanding, and 5) conclude by identifying novel behavioral constructs for future investigations that may contribute to the face, predictive and construct validity of OCD animal models. We base these targets on an integrative approach to face and construct validity, and note that the issue of treatment-resistance in the clinical context should receive attention in current animal models of OCD.

8-OH-DPAT Induces Compulsive-like Deficit in Spontaneous Alternation Behavior: Reversal by MDMA but Not Citalopram

Rodents exhibit natural exploratory behaviors, which can be measured by the spontaneous alternation behavior (SAB) test. Perseverance in this test induced by the 5-hydroxytryptamine 1A receptor (5-HT_1AR) agonist, 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT), resembles compulsive behaviors observed in humans and manifests as reduced alternation ratio. This study characterized 8-OH-DPAT-induced perseverance in the SAB test in C57BL/6JOlaHsd male mice by coadministration of WAY100635, citalopram and the 5-HT releasing agent, 3,4-methylenedioxymethamphetamine (MDMA), to deepen the understanding of 5-HT-dependent mechanisms. The 5-HT_1AR mechanism of 8-OH-DPAT (1.0 mg/kg, p < 0.01) on perseverance was confirmed by coadministration of the 5-HT_1AR antagonist, WAY100635 (2.0 mg/kg, p < 0.05), which attenuated the effects of 8-OH-DPAT. Such effects could also be reversed by MDMA (1.0 mg/kg, p < 0.05; 10.0 mg/kg, p < 0.001) but not citalopram. These findings confirm the importance of 5-HT in regulating perseverative behavior. Future investigations are required to determine the predictive validity of the 8-OH-DPAT-disrupted SAB test as an inducible mouse model of compulsivity.

Null mutation in P4h-tm leads to decreased fear and anxiety and increased social behavior in mice

HIF prolyl 4-hydroxylases (HIF-P4Hs, also known as PHDs and EGLNs) are crucial enzymes that modulate the hypoxia inducible factor (HIF) response and help to maintain cellular oxygen homeostasis. This function is especially well-known for cytoplasmic or nuclear enzymes HIF-P4H-1-3 (PHDs 1-3, EGLNs 2, 1 and 3, respectively), but the physiological role is still obscure for a fourth suggested HIF-P4H, P4H-TM that is a transmembrane protein and resides in the endoplasmic reticulum. Recently however, both experimental and clinical evidence of the P4H-TM involvement in CNS physiology has emerged. In this study, we first investigated the expression pattern of P4H-TM in the mouse brain and found a remarkably selective abundance in brains areas that are involved in social behaviors and anxiety including amygdala, lateral septum and bed nucleus of stria terminalis. Next, we performed behavioral assays in P4h-tm^-/- mice to investigate a possible phenotype associated to these brain areas. In locomotor activity tests, we found that P4h-tm^-/- mice were significantly more active than their wild-type (WT) littermate mice, and habituation to test environment did not abolish this effect. Instead, spatial learning and memory seemed normal in P4h-tm^-/- mice as assessed by Morris swim task. In several tests assessing anxiety and fear responses, P4h-tm^-/- mice showed distinct courageousness, and they presented increased interaction towards fellow mice in social behavior tests. Most strikingly, P4h-tm^-/- mice practically lacked behavioral despair response, a surrogate marker of depression, in forced swim and tail suspension tests. Instead, mutant mice of all other Hif-p4h isoforms lacked such a behavioral phenotype. In summary, this study presents a remarkable anatomy-physiology association between the brain expression of P4H-TM and the behavioral phenotype in P4h-tm^-/- mice. Future studies will reveal whether P4H-TM may serve as a novel target for anti-depressant and anti-anxiety pharmacotherapy.