Effect of different illumination levels on rat behavior in the elevated plus-maze

Social isolation and post-weaning environmental enrichment effects on rat emotional behavior and serotonergic system

Social isolation (SI) is related to adverse neurobehavioral effects and neurochemical changes when it occurs early in development. On the other hand, environmental enrichment (EE) is associated with a reduction in anxiety-like and depression-like behavior, as well as an increase in serotonin (5-HT) levels in the prefrontal cortex and hippocampus in rodents. This study systematically reviewed the effects of SI and EE on emotional behavior and serotonergic system components in rats after weaning. Primary experimental studies that used subgroups of rats subjected to SI, EE, and normal social conditions after weaning were considered eligible. Studies that used transgenic rodents, ex vivo studies, in vitro studies, human research, or in silico studies were ineligible. Two authors completed searches in Medline/PubMed, LILACS, Scopus, Web of Science, EMBASE, and Open Gray. The Kappa index was calculated to assess agreement between reviewers and assess study quality. The results showed that the animals exposed to EE showed better adaptation to a new environment. Furthermore, EE increased 5-HT levels in the hippocampus and prefrontal cortex of rodents. Thus, it appears that an EE during the critical period of development may reduce anxiety/depression-like behaviors, as well as increase long-term neurotransmitter response.

Multidimensional behavioral profiles associated with resilience and susceptibility after inescapable stress

Clinical depression is characterized by multiple concurrent symptoms, manifesting as a complex heterogeneous condition. Although some well-established classical behavioral assessments are widespread in rodent models, it remains uncertain whether rats also display stress-induced depression-related phenotypes in a multidimensional manner, i.e., simultaneous alterations in multiple behavioral tests. Here, we investigated multivariate patterns and profiles of depression-related behavioral traits in male Wistar rats subjected to inescapable footshocks (IS) or no-shocks (NS), followed by a comprehensive battery of behavioral tests and ethological characterization. We observed generalized stronger intra-test but weaker inter-test correlations. However, feature clustering of behavioral measures successfully delineated variables linked to resilience and susceptibility to stress. Accordingly, a noteworthy covariation pattern emerged, characterized by increased open field locomotion, reduced time in the elevated plus maze open arms, lower sucrose preference, and increased shuttle box escape failures that consistently differentiated IS from NS. Surprisingly there is little contribution from forced swim. In addition, individual clustering revealed a diversity of behavioral profiles, naturally separating NS and IS, including subpopulations entirely characterized by resilience or susceptibility. In conclusion, our study elucidates intricate relationships among classical depression-related behavioral measures, highlighting multidimensional individual variability. Our work emphasizes the importance of a multivariate framework for behavioral assessment in animal models to understand stress-related neuropsychiatric disorders.

Withdrawal from repeated nicotine vapor exposure increases somatic signs of physical dependence, anxiety-like behavior, and brain reward thresholds in adult male rats

Nicotine vapor consumption via electronic nicotine delivery systems has increased over the last decade. While prior work has shed light on the health effects of nicotine vapor inhalation, its unique effects on the brain and behavior have not been thoroughly explored. In this study we assessed markers of withdrawal following 14 days of nicotine vapor exposure. For Experiment 1, 21 adult male rats were exposed to ambient air or 6, 12, or 24 mg/mL nicotine vapor for 14 consecutive days. Following exposure on day 14, rats were injected with the nicotinic receptor antagonist mecamylamine (3.0 mg/mL) and assessed for somatic withdrawal signs and anxiety-like behavior in the elevated plus maze. For Experiment 2, 12 adult male rats were tested for intracranial self-stimulation (ICSS) immediately following exposure to vehicle vapor (50%/50%, vegetable glycerin/propylene glycol) or 24 mg/mL nicotine vapor, for 14 consecutive days. ICSS behavior was assessed for an additional 14 days, following cessation of repeated vapor exposure. Results reveal that rats with repeated nicotine vapor exposure display an increase in behavioral indicators of withdrawal following injection of mecamylamine (precipitated withdrawal). Additionally, increases in ICSS stimulation thresholds, indicative of reduced brain reward sensitivity, persist following cessation of repeated nicotine vapor exposure (spontaneous withdrawal). These data suggest that repeated e-cigarette use leads to nicotine dependence and withdrawal that affects behavior and brain reward function. Further characterization of the health effects of nicotine vapor is necessary to improve treatment strategies for nicotine use disorder and public health policies related to novel nicotine delivery systems.

Ventral CA1 Population Codes for Anxiety

The ventral hippocampus is a critical node in the distributed brain network that controls anxiety. Using miniature microscopy and calcium imaging, we recorded ventral CA1 (vCA1) neurons in freely moving mice as they explored variants of classic behavioral assays for anxiety. Unsupervised behavioral segmentation revealed clusters of behavioral motifs that corresponded to exploratory and vigilance-like states. We discovered multiple vCA1 population codes that represented the anxiogenic features of the environment, such as bright light and openness, as well as the moment-to-moment anxiety state of the animals. These population codes possessed distinct generalization properties: neural representations of anxiogenic features were different for open field and elevated plus/zero maze tasks, while neural representations of moment-to-moment anxiety state were similar across both experimental contexts. Our results suggest that anxiety is not tied to the aversive compartments of these mazes but is rather defined by a behavioral state and its corresponding population code that generalizes across environments.

Behavioral comparison of the C57BL/6 inbred mouse strain and their CB6F1 siblings

A large portion of basic biomedical research studies are conducted using genetically defined, inbred mouse strains. The C57BL/6 mouse strain is the most widely used genetic background in current rodent research. The rationale for using inbred strains is that all individuals are genetically identical with minimal phenotypic variation, allowing for more statistically powerful analyses. F1 hybrids between two inbred strains are also genetically identical to one another but are heterozygous at every locus at which the parental strains differ rather than homozygous. Both theoretical and empirical evidence suggests that this heterozygosity in F1 hybrids allow for potentially greater resilience in response to the inevitable stresses of laboratory environments. The purpose of this study was to characterize the differences in commonly used tests of physical performance (forelimb grip strength and rotarod) and anxiety-like behavior between the F1 hybrids created from BALB/c females mated to C57BL/6 males (called CB6F1 mice) and one of its parental strains, C57BL/6. We used a natural cross-fostering breeding scheme to minimize maternal care effects and emphasize the effects of genetic differences. We found significant correlations between anxiety-like behavioral measures and physical performance measures which are not traditionally associated with anxiety-like behavior, and which differ between strains. Findings from this study should be taken into consideration when designing behavioral studies and choosing model organisms.

Color-Coding Method Reveals Enhancement of Stereotypic Locomotion by Phenazepam in Rat Open Field Test

One of the most important tasks in neuroscience is the search for theoretical foundations for the development of methods for diagnosing and treating neurological pathology, and for assessing the effect of pharmacological drugs on the nervous system. Specific behavioral changes associated with exposure to systemic influences have been invisible to the human eye for a long time. A similar pattern of changes is characteristic of phenazepam, a drug with a wide range of effects on the brain. In this study, we used a color-coding method, which consists of combining three time positions in one image, the present (0 s), the near future (0.33 s) and the far future (1.6 s). This method made it possible to identify movement patterns, such as the initialization of ahead movements, side turns and 180° turns (back), and also to determine the degree of predictability of future movements. The obtained data revealed a decrease in the number of turns to the sides while maintaining ahead movement, as well as an increase in the predictability of movements in rats under the influence of phenazepam. Thus, sedative doses of phenazepam do not exhibit general depression of brain functions, but the inhibition of specific centers, including the medial prefrontal cortex and postsubiculum, which are involved in stereotypic locomotive behavior.

Acute and long-term sex-dependent effects of social instability stress on anxiety-like and social behaviours in Wistar rats

Adolescence is a critical time of social learning in which both the quantity and quality of social interactions shape adult behavior and social function. During adolescence, social instability such as disrupting or limiting social interactions can lead to negative life-long effects on mental health and well-being in humans. Animal models on social instability are critically important in understanding those underlying neurobiological mechanisms. However, studies in rats using these models have produced partly inconsistent results and can be difficult to generalize. Here we assessed in a sex and age consistent manner the long-term behavioural consequences of social instability stress (SIS - 1-hr daily isolation and change in cage mate between postnatal day (PD30-45)) in Wistar rats. Female and male rats underwent a battery of tests for anxiety-like, exploratory, and social behaviour over five days beginning either in adolescence (PD46) or in adulthood (PD70). Social instability led to reduced anxiety-like behaviour in the elevated plus maze in both sexes in adolescence and in adulthood. Social interactions were also reduced in rats that underwent SIS - an effect that was independent of sex and age when tested. SIS improved social recognition memory in both sexes whereas a sex-dependent effect was seen in the social novelty preference test where male rats that underwent SIS spent more time in social approach toward a novel peer than toward their cage mate. In comparison, control male and female groups did not differ in this test, in time spent with novel versus the cage mate. Thus, overall, social instability stress in Wistar rats altered the behavioural repertoire, with enduring alterations in social behaviour, enhanced exploratory behaviour, and reduced anxiety-like behaviour. In conclusion, the social instability stress paradigm may better be interpreted as a form of enrichment in Wistar rats than as a stressor.

Exploring the light/dark box test: Protocols and implications for neuroscience research

BACKGROUND

Knowledge on the neurobiological systems underlying psychiatric disorders has considerably evolved due to findings on basic research using animal models. Anxiety-like behaviors in rodents are widely explored in neuroethological apparatuses, such as the light-dark box (LDB) test through different protocols, which have been shown to influence the behavioral outcomes and probably the activation of the hypothalamic-pituitary-adrenal (HPA) axis.

NEW METHOD

Adult male Wistar rats were submitted to LDB in different room illumination conditions (25/0, 65/0 and/or 330/0 lux), initial positioning in the LDB compartments and previous stressful experience in the Elevated Plus Maze (EPM) or restraint stress (RS). Rats' behavior (exploratory and risk assessment) was registered during a 15 min period, divided into blocks of 5 min RESULTS: Exploration of the lit compartment decreased in higher luminosity condition, as after positioning rats in the dark compartment or previous exposure to the EPM, while low luminosity increased exploration of the LDB. No differences were observed on serum corticosterone in all groups and experimental conditions.

COMPARISON WITH EXISTING METHODS

Light intensity and test duration influenced exploration of the LDB jeopardizing the anxiolytic/anxiogenic effects. Low light intensity increased exploration, while high intensity decreased it. These results suggest that 65/0 lux is a neutral condition to investigate possible anxiolytic/anxiogenic effects of drugs and/or exposure to previous aversive stimuli as the EPM.

CONCLUSIONS

Different factors impact on exploratory and risk assessment behaviors which may be related to safety maximization behavior. Unraveling how different factors affect behavior may be a crucial step towards understanding its expression and the contributions on advances in the physiopathology 1 and treatment of psychiatric disorders.

Prenatal ethanol exposure leads to persistent anxiety-like behavior during adulthood indicated by reduced horizontal and vertical exploratory behaviors

Background

Fetal alcohol spectrum disorders (FASD) caused by prenatal ethanol exposure (PE) consist of many cognitive/behavioral deficits. Studies have reported that PE leads to impairments of learning and memory, attention, executive function, and anxiety. Open field (OF) is a common behavioral model which offers comprehensive ethological information. Here, we analyzed multiple parameters of OF to examine anxiety behavior and habituation after PE.

Material and Methods

Pregnant Sprague Dawley rats were gavaged twice/day with 0 or 3 g/kg/treatment ethanol (15% w/v) during gestational day (GD) 8-20, mimicking second-trimester heavy PE in humans. The control and PE adult offspring were subjected to OF task in different ambient light levels with or without acute stress.

Results

Prenatal ethanol exposure did not influence the overall locomotor activities or habituation in the OF. In lower ambient light, no PE effects could be detected. In higher ambient light, female PE rats showed less activities in the center zone, indicative of increased anxiety. Males show lower activities in the center zone only after acute stress. Rats spent <2% of the time in the center zone compared to >75% of the time in the corner zone where they engaged in frequent rearing activities (vertical exploration; exploratory rearing). Prenatal ethanol exposure led to lower rearing activities in the corner in both males and females. Acute stress masks the PE effects in males but not in females.

Discussion

The results support that heavy PE leads to persistent anxiety-like behavior during adulthood in both sexes. This conclusion is supported by using multiple parameters of exploratory behavior in the OF, including the rearing activities in the corner to reach reliable quantification of anxiety-like behavior.

Effects of chronic fluoxetine treatment on anxiety- and depressive-like behaviors in adolescent rodents - systematic review and meta-analysis

Background

Drugs prescribed for psychiatric disorders in adolescence should be studied very extensively since they can affect developing and thus highly plastic brain differently than they affect the adult brain. Therefore, we aimed to summarize animal studies reporting the behavioral consequences of chronic exposure to the most widely prescribed antidepressant drug among adolescents i.e., fluoxetine.

Methods

Electronic databases (Medline via Pubmed, Web of Science Core Collection, ScienceDirect) were systematically searched until April 12, 2022, for published, peer-reviewed, controlled trials concerning the effects of chronic fluoxetine administration vs. vehicle on anxiety and depression measures in naïve and stress-exposed adolescent rodents. All of the relevant studies were selected and critically appraised, and a meta-analysis of eligible studies was performed.

Results

A total of 18 studies were included in the meta-analysis. In naïve animals, chronic adolescent fluoxetine administration showed dose-related anxiogenic-like effects, measured as a reduction in time spent in the open arms of the elevated plus maze. No significant effects of chronic adolescent fluoxetine on depression-like behavior were reported in naïve animals, while in stress-exposed rodents chronic adolescent fluoxetine significantly decreased immobility time in the forced swim test compared to vehicle.

Conclusions

These results suggest that although chronic fluoxetine treatment proves positive effects in animal models of depression, it may simultaneously increase anxiety in adolescent animals in a dose-related manner. Although the clinical implications of the data should be interpreted with extreme caution, adolescent patients under fluoxetine treatment should be closely monitored.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-022-00420-w.

The Reversal of Empathy-Induced Hypernociception in Male Mice by Intra-Amygdala Administration of Midazolam and Cannabidiol Depends on 5-HT3 Receptors

Introduction: Empathy is a fundamental prosocial behavior. It has been defined as perception, awareness, and understanding of others' emotional states, including painful processes. Mice living in pairs with conspecific chronic suffering from constriction injury exhibit pain hypersensitivity mediated by the amygdaloid complex. Nevertheless, the underlying mechanisms in the amygdala responsible for this response remain to be determined. This study investigated if the anxiolytic benzodiazepine midazolam (MDZ) and cannabidiol (CBD), a phytocannabinoid with multiple molecular targets, would attenuate this behavioral change. We also investigated if serotonergic and γ-aminobutyric acid (GABA)ergic mechanisms in the amygdala are involved in this effect. Materials and Methods: Male Swiss mice were housed in pairs for 28 days. The pairs were divided into two groups on the 14th day: cagemate nerve constriction and cagemate sham. On the 24th day, cagemates underwent a stereotaxic surgery and, on the 28th day, were evaluated on the writhing test. Results: The results showed that living with chronic pain leads to hypernociception in the cagemate and increases the expression of 5-HT₃ receptor (5-HT₃R) and glutamic acid decarboxylase 67 within the amygdala. MDZ (3.0 and 30 nmol) and CBD (30 and 60 nmol) attenuated the hypernociceptive behavior. The 5-HT₃R antagonist ondansetron (0.3 nmol) prevented the antinociceptive effects of MDZ and CBD. Conclusion: These findings indicate that 5-HT₃R and GABAergic mechanisms within the amygdala are involved in the pain hypersensitivity induced by the empathy for pain model. They also suggest that MDZ and CBD could be a new potential therapy to alleviate emotional pain disorders.

Decrease in the rewarding value of spatial novelty due to the contamination of the stimulus field with light - evidence from a free exploration test involving rats

It has been shown that rearranging the spatial properties of a familiar environment consistently elicits a positive response in rats directed toward the source of novelty. Previous studies have been conducted under red light or darkness. The purpose of this study was to test the effect of rearranging the spatial properties of a familiar environment in conjunction with a change in lighting conditions. The results have shown specific effects of the light presence and its intensity on different behavioral measures. We propose that this study provides a basis for hypothesizing a two-way mechanism of the behavioral response to light regulation in rats. The first is based on ON/OFF states. This level may be related to fundamental, evolutionarily early, emergent components of behavioral antipredator adaptations. Another level of behavioral regulation involves mechanisms sensitive to light intensity. These appear to be involved in the regulation of more advanced behavioral acts, such as exploratory responses. This may suggest that light intensity analysis may require the involvement of more advanced cognitive components in the behavioral regulation system.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Effects of personality on assessments of anxiety and cognition

Individual variation in responses to commonly used tests of anxiety and spatial memory is often reported. While this variation is frequently considered to be 'noise', evidence suggests that it is, at least partially, related to consistent individual differences in behavioral responses (i.e., personality). The same tests used to assess anxiety are often used to profile personality traits, but personality differences are rarely considered when testing treatment differences in anxiety. Focusing on the rat literature, we describe fundamental principles involved in anxiety and spatial memory tests and we discuss how personality differences and housing conditions can influence behavioral responses in these tests. We propose that an opportunity exists to increase stress resiliency in environmentally sensitive individuals by providing environmental enrichment. We conclude by discussing different approaches to incorporating personality measures into the design and analysis of future studies; given the potential that variation masks research outcomes, we suggest that a strategy which considers the individual and its housing can contribute to improving research reproducibility.

Lateralization in hemi-parkinsonian rats is affected by deep brain stimulation or glutamatergic neurotransmission in the inferior colliculus

After unilateral lesion of the medial forebrain bundle (MFB) by 6-OHDA rats exhibit lateralized deficits in spontaneous behavior or apomorphine-induced rotations. We investigated whether such lateralization is attenuated by either deep brain stimulation (DBS) or glutamatergic neurotransmission in the inferior colliculus (IC) of Wistar rats. Intracollicular DBS did not affect spontaneous lateralization but attenuated apomorphine-induced rotations. Spontaneous lateralization disappeared after both glutamatergic antagonist MK-801 or the agonist NMDA microinjected in the IC. Apomorphine-induced rotations were potentiated by MK-801 but were not affected by NMDA intracollicular microinjection. After injecting a bidirectional neural tract tracer into the IC, cell bodies and/or axonal fibers were found in the periaqueductal gray, superior colliculus, substantia nigra, cuneiform nucleus and pedunculo-pontine tegmental nucleus, suggesting the involvement of these structures in the motor improvement after IC manipulation. Importantly, the side of the IC microinjection regarding the lesion (ipsi- or contralateral) is particularly important and this effect may not involve the neostriatum directly.Significance StatementThe inferior colliculus, usually viewed as an auditory structure, when properly manipulated may counteract motor deficits in Parkinsonian rats. Indeed, the present study showed that 30 Hz deep brain stimulation or glutamatergic neural network in the inferior colliculus reduced body asymmetry induced by medial forebrain bundle unilateral 6-OHDA lesion in rats, an animal model of Parkinsonism. Understanding how glutamatergic mechanisms in the inferior colliculus influence motor control, classically attributed to the basal nuclei circuitry, could be useful in the development of new therapeutics to treat Parkinson's disease and other motor disorders.

Blockade of the mineralocorticoid receptors in the medial prefrontal cortex prevents the acquisition of one-trial tolerance in mice

One-trial tolerance (OTT) is characterized by the lack of anxiolytic-like effects of benzodiazepines in animals submitted to a trial 2 in the elevated plus-maze (EPM) and is described to be influenced by learning mechanisms. Mineralocorticoid receptors (MR) in the infralimbic subregion (IL) of the medial prefrontal cortex (mPFC) are important modulators of emotional learning, but the MR involvement in the establishment of OTT remains unclear. We investigated the effects of intra-IL infusions of RU 28318 (an MR antagonist) on the OTT to the anxiolytic effects of midazolam (MDZ, GABA_A-benzodiazepine agonist) in mice exposed to a two-trial protocol in the EPM. First, mice were treated with saline or MDZ (2mgkg^-1, i.p.) 30minutes before trial 1 or 2 in the EPM, to characterize the OTT. To investigate the role of MR in the OTT, independent groups of mice received intra-IL infusions of vehicle or RU 28318 (5 or 10ng 0.1µL^-1) immediately before or after first trial in the EPM. Twenty-four hours later, the same mice received injections of saline or MDZ and were re-tested in the EPM. The MDZ decreased anxiety-like behaviors in trial 1, but the same anxiolytic-like effect was not observed in MDZ-mice prior to the second EPM test, confirming the OTT. Blockade of MR in the IL before, but not after, trial 1 restored the anxiolytic effects if MDZ administered in trial 2. These findings indicate that the MR in the IL-mPFC contributing to the OTT by mediating the acquisition, but not the consolidation of emotional learning.

Anxiolytic-like Effects of the Positive GABAB Receptor Modulator GS39783 Correlate with Mice’s Individual Basal Anxiety and Stress Reactivity

Positive gamma-aminobutyric acid type B (GABA_B) receptor modulators such as GS39783 have showed anxiolytic-like effects in several studies while such effects were absent in other studies. These conflicting findings led us hypothesize that the anxiolytic-like effects of such compounds depend on the individual basal anxiety and/or the anxiogenic properties of the used tests. The present study addresses this hypothesis by testing GS39783 effects on mice’s anxiety-like behavior in a light–dark box. We found that GS39783 had no effects on a whole-group level. However, after grouping the mice for their basal anxiety, GS39783 reduced anxiety-like behavior in the subgroup with highest basal anxiety. Moreover, GS39783 effects correlated with individual basal anxiety. Next, the anxiogenic properties of the light–dark box test were increased by prior stress exposure. Again, GS39783 was not effective on a whole-group level. However, GS39783 had an anxiolytic-like effect in the most stress-responsive subgroup. Moreover, GS39783 effects correlated with individual stress responsiveness. Finally, we show that GS39783 brain levels were within a behaviorally relevant range. Overall, our study demonstrates that GS39783 effects depend on individual basal anxiety and stress responsiveness. This suggests that anxiety tests should generally be designed to capture individual basal anxiety and/or stress responsiveness as well as individual compound effects.

Motor, memory, and anxiety-like behavioral impairments associated with brain-derived neurotrophic factor and dopaminergic imbalance after inhalational exposure to deltamethrin

Believed to cause damage to the nervous system and possibly being associated with neurodegenerative diseases, deltamethrin (DM) is a type II pyrethroid used in pest control, public health, home environment, and vector control. The objective of this study was to evaluate the motor, cognitive and emotional changes associated with dopaminergic and BDNF imbalance after DM exposure in rats. Sixty Wistar rats (9-10 months-old) were used, under Ethics Committee on Animal Research license (ID 19/2017). The animals were randomly divided into four groups: control (CTL, 0.9% saline), DM2 (2mg DM in 1.6mL 0.9% saline), DM4 (4mg of DM in 1.6mL of 0.9% saline), and DM8 (8mg of DM in 1.6mL of 0.9% saline). DM groups were submitted to 9 or 15 inhalations, one every 48hours. Half of the animals from each group were randomly selected and perfused 24hours after the 9th or 15th inhalation. Throughout the experiment, the animal's behavior were evaluated using catalepsy test, open field, hole-board test, Modified Elevated Plus Maze, and social interaction. At the end of the experiments, the rats were perfused transcardially and their brains were processed for Tyrosine Hydroxylase (TH) and Brain derived neurotrophic factor (BDNF) immunohistochemistries. The animals submitted to 9 inhalations of DM showed a reduction in immunoreactivity for TH in the Substantia nigra pars compacta (SNpc), ventral tegmental area (VTA), and dorsal striatum (DS) areas, and an increase in BDNF in the DS and CA1, CA3 and dentate gyrus (DG) hippocampal areas. Conversely, the animals submitted to 15 inhalations of DM showed immunoreactivity reduced for TH in the SNpc and VTA, and an increase in BDNF in the hippocampal areas (CA3 and DG). Our results indicate that the DM inhalation at different periods induce motor and cognitive impairments in rats. Such alterations were accompanied by dopaminergic system damage and a possible dysfunction on synaptic plasticity.

5-HT3 receptor within the amygdaloid complex modulates pain hypersensitivity induced by empathy model of cohabitation with a partner in chronic pain condition in mice

Cohabitation with a partner undergoing chronic pain induces pain hypersensitivity. Among a lot of other neurochemical pathways, the serotonin (5-HT) role, specifically the 5-HT₃ receptor (5-HT₃R), in the amygdala has never been evaluated in this model. Here we studied the effects of the amygdala's chemical inhibition, its neuronal activation pattern, and 5-HT, 5-HIAA, and 5-HT turnover within the amygdala. Furthermore, the systemic and intra-amygdala 5-HT₃R activation and blockade in mice that cohabited with a conspecific subjected to chronic constriction injury were investigated. Male Swiss mice were housed in partners for 28 days. The dyads were divided into two groups on the 14^th day: cagemate nerve constriction (CNC) and cagemate sham (CS). On the 24^th day, cagemates underwent a stereotaxic surgery (when necessary) and, on the 28^th day, they were evaluated on the writhing test. The amygdala inactivation promotes pain-hypersensitivity behaviors in groups and dyads; cohabitation with a partner with chronic pain did not change FosB-labeled cells in the amygdala's nucleus and increases 5-HT turnover in cagemates. Systemic and intra-amygdala 5-HT₃R activation attenuated and enhanced the number of writhes, respectively. In contrast, 5-HT₃R blockade reduced hypersensitivity pain response. Results suggest the involvement of amygdala serotonergic signaling via 5-HT₃R in empathy-like behavior.

Oxidative stress and neuroinflammation in a rat model of co-morbid obesity and psychogenic stress

BACKGROUND

There is growing recognition for a reciprocal, bidirectional link between anxiety disorders and obesity. Although the mechanisms linking obesity and anxiety remain speculative, this bidirectionality suggests shared pathophysiological processes. Neuroinflammation and oxidative damage are implicated in both pathological anxiety and obesity. This study investigates the relative contribution of comorbid diet-induced obesity and stress-induced anxiety to neuroinflammation and oxidative stress.

METHODS

Thirty-six (36) male Lewis rats were divided into four groups based on diet type and stress exposure: 1) control diet unexposed (CDU) and 2) exposed (CDE), 3) Western-like high-saturated fat diet unexposed (WDU) and 4) exposed (WDE). Neurobehavioral tests were performed to assess anxiety-like behaviors. The catalytic concentrations of glutathione peroxidase and reductase were measured from plasma samples, and neuroinflammatory/oxidative stress biomarkers were measured from brain samples using Western blot. Correlations between behavioral phenotypes and biomarkers were assessed with Pearson's correlation procedures.

RESULTS

We found that WDE rats exhibited markedly increased levels of glial fibrillary acidic protein (185 %), catalase protein (215 %), and glutathione reductase (GSHR) enzymatic activity (418 %) relative to CDU rats. Interestingly, the brain protein levels of glutathione peroxidase (GPx) and catalase were positively associated with body weight and behavioral indices of anxiety.

CONCLUSIONS

Together, our results support a role for neuroinflammation and oxidative stress in heightened emotional reactivity to obesogenic environments and psychogenic stress. Uncovering adaptive responses to obesogenic environments characterized by high access to high-saturated fat/high-sugar diets and toxic stress has the potential to strongly impact how we treat psychiatric disorders in at-risk populations.

Effects of test experience, closed-arm wall color, and illumination level on behavior and plasma corticosterone response in an elevated plus maze in male C57BL/6J mice: a challenge against conventional interpretation of the test

The elevated plus maze test is a widely used test for assessing anxiety-like behavior and screening novel therapeutic agents in rodents. Previous studies have shown that a variety of internal factors and procedural variables can influence elevated plus maze behavior. Although some studies have suggested a link between behavior and plasma corticosterone levels, the relationships between them remain unclear. In this study, we investigated the effects of experience with a battery of behavioral tests, the wall color of the closed arms, and illumination level on the behavior and plasma corticosterone responses in the elevated plus maze in male C57BL/6J mice. Mice were either subjected to a series of behavioral tests, including assessments of general health and neurological function, a light/dark transition test, and an open field test, or left undisturbed until the start of the elevated plus maze test. The mice with and without test battery experience were allowed to freely explore the elevated plus maze. The other two independent groups of naïve mice were tested in mazes with closed arms with different wall colors (clear, transparent blue, white, and black) or different illumination levels (5, 100, and 800 lx). Immediately after the test, blood was collected to measure plasma corticosterone concentrations. Mice with test battery experience showed a lower percentage of open arm time and entries and, somewhat paradoxically, had lower plasma corticosterone levels than the mice with no test battery experience. Mice tested in the maze with closed arms with clear walls exhibited higher open arm exploration than mice tested in the maze with closed arms with black walls, while there were no significant differences in plasma corticosterone levels between the different wall color conditions. Illumination levels had no significant effects on any measure. Our results indicate that experience with other behavioral tests and different physical features of the maze affect elevated plus maze behaviors. Increased open arm time and entries are conventionally interpreted as decreased anxiety-like behavior, while other possible interpretations are considered: open arm exploration may reflect heightened anxiety and panic-like reaction to a novel situation under certain conditions. With the possibility of different interpretations, the present findings highlight the need to carefully consider the test conditions in designing experiments and drawing conclusions from the behavioral outcomes in the elevated plus maze test in C57BL/6J mice.

Differential modulation of the anterior cingulate and insular cortices on anxiogenic-like responses induced by empathy for pain

Mice cohabiting with a conspecific in chronic pain display anxiogenesis in the elevated plus-maze (EPM). Given that the anterior cingulate (ACC) and insular (InC) cortices play a role in the modulation of anxiety, pain, and emotional contagion, we investigated (a) the FosB activation in both brain areas and (b) the effects of intra-ACC or -InC injection of cobalt chloride (CoCl₂, a synaptic blocker), on the anxiety of mice cohabiting with a cagemate suffering pain. Twenty-one days after birth, male Swiss mice were housed in pairs for 14 days to establish familiarity. On the 14th day, mice were divided into two groups: cagemate sciatic nerve constriction (CNC; i.e., one animal of each pair was subjected to sciatic nerve constriction), and cagemate sham (CS; i.e., a similar procedure but without suffering nerve constriction). After that, both groups were housed again with the same pairs for the other 14 days. On the 28th day, mice had their brains removed for the immunoassays analyses (Exp. 1). For experiments 2 and 3, on the 23rd day, the cagemates received guide cannula implantation bilaterally in the ACC or InC and, on the 28th day, they received local injections of saline or CoCl₂, and then were exposed to the EPM. Results showed that cohabitation with a conspecific with chronic pain decreases and increases neuronal activation (FosB) within the ACC and InC, respectively. Intra-ACC or InC injection of CoCl₂ reversed the anxiogenic effect in those animals that cohabited with a conspecific in chronic pain. ACC and InC seem to modulate anxiety induced by emotional contagion in animals cohabitating with a conspecific suffering pain.

Moderate Adolescent Ethanol Vapor Exposure and Acute Stress in Adulthood: Sex-Dependent Effects on Social Behavior and Ethanol Intake in Sprague-Dawley Rats

Adolescent alcohol use can lead to numerous consequences, including altered stress reactivity and higher risk for later anxiety and alcohol use disorders. Many studies have examined the consequences of heavy ethanol exposure in adolescence, but far less is understood about lower levels of intoxication. The present study examined moderate adolescent ethanol exposure as a possible factor in increasing stress reactivity in adulthood, measured through general and social anxiety-like behaviors, as well voluntary ethanol intake. Male and female Sprague-Dawley rats underwent an adolescent chronic intermittent ethanol (aCIE) vapor exposure during early adolescence, reaching moderate blood ethanol concentrations. Animals then underwent two days of forced swim stress in adulthood. We found that ethanol-exposed males consumed more ethanol than their air counterparts and an interesting stress and ethanol exposure interaction in males. There were no significant effects on voluntary drinking in females. However, the social interaction test revealed increased play-fighting behavior in ethanol-exposed females and reduced social preference in females after two days of stress exposure. Overall, this work provides evidence for sex-specific, long-term effects of moderate aCIE and susceptibility to acute stress in adulthood.

Interactions of the estrous cycle, novelty, and light on female and male rat open field locomotor and anxiety-related behaviors

Animal behavior can be modulated by multiple interacting factors. In rodents such as rats, these factors include, among others, the female estrous cycle, exposure to a novel environment, and light. Here, we used the open field test to disassociate differences in behavior resulting from each of these factors by testing the hypothesis that locomotor and anxiety-related behaviors differ between estrous cycle phases in female rats and that novelty and light exposure concurrently influence these behaviors in both female and male rats. Adult female rats were tested twice under red or white light in estrus and diestrus estrous cycle phases. Adult male rats were also tested twice under either red or white light. In females, an interaction between novelty and estrous cycle phase influenced locomotor and anxiety-related behaviors. In males, novelty influenced locomotor and anxiety-related behaviors differentially under red and white light. Light exposure increased anxiety-related behaviors in both males and females, but reduced locomotor behavior only in females. These findings reveal the complexities of behavioral testing and highlight the importance of factors such as the estrous cycle, novelty, and light exposure.

Blockade of the endovanilloid receptor, TRPV1, and of the endocannabinoid enzyme, FAAH, within the nucleus accumbens shell elicits anxiolytic-like effects in male rats

RATIONALE

The functional role of the endocannabinoid system (ECS) and Transient Receptor Potential Vanilloid type-1 (TRPV1) within the Nucleus Accumbens shell (NAc shell) remains unknown. Preclinical studies in rodents have reported that the ECS modulates emotional responses such as anxiety. The NAc shell has a high density of synaptically co-localized cannabinoid receptor type-1 (CB1R) and TRPV1, suggesting a potential involvement in the modulation of anxiety.

OBJECTIVES

The present study aims to establish the role of ECS-TRPV1 interactions within the NAc shell and its effects on anxiety. It is hypothesized that the neurochemical regulation elicited by ECS within the NAc shell mediates anxiety-like behaviors in rodents.

METHODS

In this study, male Sprague Dawley rats were implanted with bilateral brain cannula targeting the NAc shell. Following recovery from surgery, animals received microinfusion pretreatments (0, 0.125, 0.5 nmol/0.4 μl) of N-arachidonoyl-serotonin (AA-5-HT), a dual blocker of the endocannabinoid-inactivating enzyme, fatty acid amide hydrolase (FAAH) and a TRPV1 antagonist in the NAc shell. Following treatment, animals were tested in an elevated plus maze (EPM) paradigm for a period of 5 minutes. At the end of the experiment, animals were sacrificed and their brains collected for histological and biochemical analysis.

RESULTS

Results showed that animals treated with AA-5-HT in a dose dependent manner spent significantly more time in the open arms than vehicle-treated animals. In addition, AA-5-HT administration induced a significant downregulation of CB1R expression in the NAc shell.

CONCLUSIONS

The present findings suggest that the ECS within the NAc shell modulates anxiety-like behaviors via FAAH and CB1R activity.

Empathy for Pain: Insula Inactivation and Systemic Treatment With Midazolam Reverses the Hyperalgesia Induced by Cohabitation With a Pair in Chronic Pain Condition

Empathy for pain is the ability to perceive and understand the pain in the other individual. Recent studies suggested that rodents have this social ability. GABAergic system has receptors in the brain structures involved in emotional processes as well as in the insular cortex. This area has been described as an important key in modulation of pain and empathy. The present study has investigated the role of insula and its Benzodiazepine-GABAA system on social modulation of pain induced by cohabiting with a mouse submitted to sciatic nerve constriction, a neuropathic pain model. The insular cortex function was assessed by the structure inactivation (Experiments 1 and 2); the role of GABA system was evaluated by systemic treatment of midazolam (MDZ 0.5, 1, and 2 mg/kg) (Experiment 3); and the role of GABAA receptors of insula were studied by bilateral MDZ (3 and 30 nmol/0.1 μl) microinjections in the structure (Experiment 4). Male Swiss mice were housed in groups or dyads. On dyads, after 14 days of cohabitation they were divided into two groups: cagemate nerve constriction and cagemate sham (CS). After 14 days of familiarity, cagemates were evaluated on the writhing test. For group-housed, insula inactivation did not change nociception. For dyad-housed, cohabiting with a mouse in chronic pain increased the nociceptive response and the insula inactivation has reverted this response. Systemic MDZ attenuated nociception and intra-insula MDZ did not alter it. Our results suggest that cohabitation with a pair in chronic pain induces hypernociception, insula possibly modulates this response and the GABA system is also possibly involved, but not its insular mechanisms.

The critical role of amygdala subnuclei in nociceptive and depressive-like behaviors in peripheral neuropathy

The amygdala is an important component of the limbic system that participates in the control of the pain response and modulates the affective-motivational aspect of pain. Neuropathic pain is a serious public health problem and has a strong affective-motivational component that makes it difficult to treat. The central (CeA), basolateral (BLA) and lateral (LA) nuclei of the amygdala are involved in the processing and regulation of chronic pain. However, the roles of these nuclei in the maintenance of neuropathic pain, anxiety and depression remain unclear. Thus, the main objective of this study was to investigate the role of amygdala subnuclei in the modulation of neuropathic pain, including the affective-motivational axis, in an experimental model of peripheral neuropathy. The specific goals were as follows: (1) To evaluate the nociceptive responses and the patterns of activation of the CeA, BLA and LA in neuropathic rats; and (2) To evaluate the effect of inactivating the amygdala nuclei on the nociceptive response, anxiety and depressive behaviors, motor activity, and plasma stress hormones in animals with neuropathic pain. Thus, mechanical hyperalgesia and allodynia, and the pattern of c-Fos staining in the amygdala subnuclei were evaluated in rats with chronic constriction of the sciatic nerve, as well as sham-operated and naïve rats. Once the amygdala subnuclei involved in neuropathic pain response were defined, those subnuclei were pharmacological inactivated. The effect of muscimol inactivation on the nociceptive response (hyperalgesia and allodynia), anxiety (elevated plus-maze), depressive-like behavior (forced swim test), motor activity (open field), and plasma stress hormone levels (corticosterone and adrenocorticotropic hormone) were evaluated in sham-operated and neuropathic animals. The results showed that the anterior and posterior portions of the BLA and the central portion of the CeA are involved in controlling neuropathic pain. The inactivation of these nuclei reversed hyperalgesia, allodynia and depressive-like behavior in animals with peripheral neuropathy. Taken together, our findings improve our understanding of the neurocircuitry involved in persistent pain and the roles of specific amygdala subnuclei in the modulation of neuropathic pain, including the neurocircuitry that processes the affective-motivational component of pain.

Inflammatory and neuropathic pain conditions do not primarily evoke anxiety-like behaviours in C57BL/6 mice

BACKGROUND

Chronic pain is often accompanied by comorbidities like anxiety and depression. The temporal correlations, as well as the underlying mechanisms of these reciprocal correlations, are unclear. Moreover, preclinical studies examining emotional behaviour are very controversial, and a chronological analysis of anxiety-like behaviour in mouse pain models considering both genders has not been performed so far.

METHODS

We used several behavioural tests to assess and validate anxiety-like behaviour in complete Freund's adjuvant (CFA) and spared nerve injury (SNI) pain models in C57BL/6 mice. Among these were the elevated plus maze test, open field test, hole-board test and light-dark test. Additionally, we included a late stage analysis of depression-like behaviour using the forced swim test. All tests were applied once for each cohort of mice. Importantly, we used C57BL/6N mice of both genders; we investigated the effect of social isolation, the impact of pain induction to either the right or left hind limb and also investigated C57BL/6J mice.

RESULTS

The validity of test conditions was confirmed using the anxiogenic drugs Yohimbine and Pentylenetetrazol. Anxiety-like behaviour was analysed throughout the time period when mice exhibited hypersensitivity to mechanical stimuli. We did not observe any consistent alteration in anxiety-like behaviour at any of the investigated time points between 1 and 14 days following CFA-induced inflammation or 3 and 84 days following SNI surgery using different behavioural tests.

CONCLUSIONS

Inflammatory and neuropathic pain conditions do not primarily evoke anxiety- and depression-like behavioural alterations within the herein investigated time period.

SIGNIFICANCE

Anxiety-like behaviour is not primarily altered following CFA and SNI in C57BL6 mice, irrespective of the gender, mouse sub-strain, housing conditions or affected body side within the herein investigated time period.

Intra-vermis H4 receptor agonist impairs performance in anxiety- and fear-mediated models

The neural histaminergic system modulates cognitive performance in various animal models. However, little is known about the effects of the H4 histaminergic receptor in the central nervous system. The purpose of this study was to investigate the effect of histaminergic H4 agonist VUF-8430 microinjection into the cerebellar vermis on the consolidation of emotional memory in mice subjected to the elevated plus maze (EPM) and inhibitory avoidance task (IAT). All experiments were performed on two consecutive days: exposure (T1 and D1) and 24h after, which we called re-exposure (T2 and D2). The animals received saline (SAL) or VUF (0.15 nmol; 0.49 nmol; 1.48 nmol/0.1μl) administered post-exposure. Experiment 1 was conducted in the EPM, and the animals were free to explore the maze for 5min. In T1, immediately after exposure, the pharmacological treatment was given; in T2, there was only re-exposure to the EPM. Experiment 2 involved the IAT, and the pharmacological treatment was provided post-D1; in D2, the animals were only re-exposed to the IAT. In Experiment 1, increased open arm exploration (% open arm entries and% open arms time) for 0.49 and 1.48nmol of VUF were recorded in T2 compared to T1. In Experiment 2, a significant decrease in consolidation latency was recorded for the group that received 1.48nmol of VUF compared to the SAL group in D2. These results indicate that a 1.48nmol VUF microinjection into the cerebellar vermis impaired performance in both models, even though one model was anxiety-mediated (EPM) and the other was fear-mediated (IAT).

The Impact of Environmental Light Intensity on Experimental Tumor Growth

BACKGROUND/AIM

Cancer research requires for consistent models that minimize environmental variables. Within the typical laboratory animal housing facility, animals may be exposed to varying intensities of light as a result of cage type, cage position, light source, and other factors; however, studies evaluating the differential effect of light intensity during the light phase on tumor growth are lacking.

MATERIALS AND METHODS

The effect of cage face light intensity, as determined by cage rack position was evaluated with two tumor models using the C57Bl/6NHsd mouse and transplantable B16F10 melanoma cells or Lewis lung carcinoma (LLC) cells. Animals were housed in individually-ventilated cages placed at the top, middle, or bottom of the rack in a diagonal pattern so that the top cage was closest to the ceiling light source, and cage face light intensity was measured. Following a two-week acclimation period at the assigned cage position, animals were subcutaneously administered either 1.3×10⁶ B16F10 melanoma cells or 2.5×10⁵ Lewis lung carcinoma cells. Weights of excised tumors were measured following euthanasia 18 days (melanoma) or 21 days (LCC) after tumor cell administration.

RESULTS

Cage face light intensity was significantly different depending on the location of the cage, with cages closest to the light source have the greatest intensity. Mean tumor weights were significantly less (p<0.001 for melanoma; p≤0.01 for LCC) in middle light intensity mice compared to high and low light intensity mice.

CONCLUSION

The environmental light intensity to which experimental animals are exposed may vary markedly with cage location and can significantly influence experimental tumor growth, thus supporting the idea that light intensity should be controlled as an experimental variable for animals used in cancer research.

Wistar audiogenic rats display abnormal behavioral traits associated with artificial selection for seizure susceptibility

Accumulating evidence from different animal models has contributed to the understanding of the bidirectional comorbidity associations between the epileptic condition and behavioral abnormalities. A strain of animals inbred to enhance seizure predisposition to high-intensity sound stimulation, the Wistar audiogenic rat (WAR), underwent several behavioral tests: forced swim test (FST), open-field test (OFT), sucrose preference test (SPT), elevated plus maze (EPM), social preference (SP), marble burying test (MBT), inhibitory avoidance (IAT), and two-way active avoidance (TWAA). The choice of tests aimed to investigate the correlation between underlying circuits believed to be participating in both WAR's innate susceptibility to sound-triggered seizures and the neurobiological substrates associated with test performance. Comparing WAR with its Wistar counterpart (i.e., resistant to audiogenic seizures) showed that WARs present behavioral despair traits (e.g., increased FST immobility) but no evidence of anhedonic behavior (e.g., increased sucrose consumption in SPT) or social impairment (e.g., no difference regarding juvenile exploration in SP). In addition, tests suggested that WARs are unable to properly evaluate degrees of aversiveness (e.g., performance on OFT, EPM, MBT, IAT, and TWAA). The particularities of the WAR model opens new venues to further untangle the neurobiology underlying the co-morbidity of behavioral disorders and epilepsy. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Early deprivation increases high-leaning behavior, a novel anxiety-like behavior, in the open field test in rats

The open field test is one of the most popular ethological tests to assess anxiety-like behavior in rodents. In the present study, we examined the effect of early deprivation (ED), a model of early life stress, on anxiety-like behavior in rats. In ED animals, we failed to find significant changes in the time spent in the center or thigmotaxis area of the open field, the common indexes of anxiety-like behavior. However, we found a significant increase in high-leaning behavior in which animals lean against the wall standing on their hindlimbs while touching the wall with their forepaws at a high position. The high-leaning behavior was decreased by treatment with an anxiolytic, diazepam, and it was increased under intense illumination as observed in the center activity. In addition, we compared the high-leaning behavior and center activity under various illumination intensities and found that the high-leaning behavior is more sensitive to illumination intensity than the center activity in the particular illumination range. These results suggest that the high-leaning behavior is a novel anxiety-like behavior in the open field test that can complement the center activity to assess the anxiety state of rats.

Cholinergic agonist reverses H1-induced memory deficit in mice

This study investigated the effects of bilateral intraamygdalar microinjections of PNU-282987, a nicotinic cholinergic agonist, on anxiety and the reversal of amnesia induced by chlorpheniramine (CPA), an H1 histaminergic antagonist, in mice subjected to the elevated plusmaze (EPM). Two experiments were performed with seventy-nine adult male Swiss mice. The isolated microinjections of PNU-282987 did not produce effects on emotional memory; however, the combined microinjections of PNU-282987 and CPA were able to reverse the deficit in memory induced by CPA (ANOVA, p<0.05). Taken together, these results suggest that intraamygdalar injections of PNU-282987 did not induce effects on anxiety and emotional memory per se; however, concurrent microinjections of PNU-282987 and CPA-reverse amnesia induced-CPA which is suggestive of an interaction between the histaminergic and cholinergic systems in the modulation of emotion memory acquisition in mice.

The expression of amphetamine sensitization is dissociable from anxiety and aversive memory: Effect of an acute injection of amphetamine

The repeated administration of amphetamine can lead to locomotor sensitization. Although the repeated administration of amphetamine has been associated with anxiety and impaired working memory, it is uncertain if expression of amphetamine sensitization is associated with modifications of emotional memories. To address this issue, rats were injected once daily with amphetamine for five consecutive days (1.5mg/kg). After four days of withdrawal, rats were delivered an acute amphetamine injection to assess the expression of sensitization. A single exposure to an elevated plus maze (EPM), 24h after the last injection of amphetamine, showed that amphetamine sensitization is not accompanied by anxiety. Next, aversive memory was assessed using an 11day inter-trial interval between the EPM Trial 1 and EPM Trial 2. Rats administered with saline showed a percentage of open arms time (% OAT) in Trial 2 that was comparable to Trial 1, demonstrating a reduction in the retrieval of aversive memory. However, rats sensitized after the EPM Trial 1 showed a significant decrease in the % OAT in Trial 2. Importantly, a decrease in the % OAT in Trial 2 compared to Trial 1 was also observed after a single injection of amphetamine 24h before Trial 2. These results show a facilitation in the retrieval of aversive memory, and suggest that a previous amphetamine injection is enough to produce a protracted activation of neural circuits necessary for the retrieval of aversive memory.

Rats can acquire conditional fear of faint light leaking through the acrylic resin used to mount fiber optic cannulas

Rodents are exquisitely sensitive to light and optogenetic behavioral experiments routinely introduce light-delivery materials into experimental situations, which raises the possibility that light could leak and influence behavioral performance. We examined whether rats respond to a faint diffusion of light, termed caplight, which emanated through the translucent dental acrylic resin used to affix deep-brain optical cannulas in place. Although rats did not display significant changes in locomotion or rearing to caplight in a darkened open field, they did acquire conditional fear via caplight-footshock pairings. These findings highlight the potential confounding influence of extraneous light emanating from light-delivery materials during optogenetic analyses.

Intra-amygdala microinjections of chlorpheniramine impair memory formation or memory retrieval in anxiety- and fear-mediated models

H1 receptor histaminergic antagonist, chlorpheniramine (CPA) participates in cognitive performance in various animal models. However, little is known regarding the effects of CPA microinjection into the amygdala on emotional behavior. The purpose of this study was to investigate whether CPA microinjection into the amygdala has the same effect on two models, one anxiety- and the other fear-mediated, in various memory stages using the elevated plus maze (EPM) and the inhibitory avoidance task (IAT) tests. Two experiments were performed with seventy-two adult male Swiss mice. Behavioral testing was performed on two consecutive days, and in both experiments, before each trial, the animals received bilateral microinjections of saline (SAL) or CPA (0.16 nmol). The animals were re-exposed to the EPM or IAT 24h after the first trial. Four experimental groups were tested: SAL-SAL, SAL-CPA, CPA-SAL and CPA-CPA. In experiment 1, a decreased open arm exploration (% open arm entries, %OAE and% open arms time, %OAT) for SAL-SAL and SAL-CPA was showed, while these measures did not decrease for the CPA-SAL and CPA-CPA groups in Trial 2. In experiment 2, an increase of retention latency in relation to training 2 for the groups SAL-SAL and CPA-SAL and a significant decrease in latency for the group SAL-CPA was revealed. These results indicate that chlorpheniramine microinjection into the amygdala impairs emotional memory acquisition and/or consolidation in the EPM and retrieval of IAT.

κ Opioid receptor activation in different brain regions differentially modulates anxiety-related behaviors in mice

κ Opioid receptor system is widely implicated in the regulation of emotion. However, the findings about the role on anxiety in rodents are highly controversial, since both anxiogenic- and anxiolytic-like effects have been reported with κ opioid receptor activation. The mechanism and the underlying neuroanatomical substrates are unexplored. In the present study, we first investigated the effects of κ agonist U50,488H on anxiety-related behaviors over a wide range of doses, and we found that U50,488H produced dual effects in anxiety, with low dose being anxiogenic and high dose being anxiolytic. To assess the potential neuroanatomical substrates, we used phosphorylation of extracellular signal-related kinase1/2 (pERK1/2) to map the underlying neural circuits. We found that the anxiogenic effect of U50,488H was paralleled by an increase of pERK1/2 in the nucleus accumbens, whereas the anxiolytic effect was paralleled by an increase of pERK1/2 in the lateral septal nucleus. We then examined the behavioral consequences with locally microinjection of U50,488H, and we found that microinjection of U50,488H into the nucleus accumbens exerted anxiogenic-like effects, whereas microinjection of U50,488H into the lateral septal nucleus. Both effects can be abolished by κ antagonist nor-BNI pretreatment. To the best of our knowledge, the present work firstly provides the neuroanatomical sites that mediating the dual anxiogenic- and anxiolytic-like effects of U50,488H in mice. This study may help to explain current controversial role of κ receptor activation in anxiety-related behaviors in rodents, and may open new perspectives in the areas of anxiety disorders and κ receptor function.

Preclinical animal anxiety research - flaws and prejudices

The current tests of anxiety in mice and rats used in preclinical research include the elevated plus-maze (EPM) or zero-maze (EZM), the light/dark box (LDB), and the open-field (OF). They are currently very popular, and despite their poor achievements, they continue to exert considerable constraints on the development of novel approaches. Hence, a novel anxiety test needs to be compared with these traditional tests, and assessed against various factors that were identified as a source of their inconsistent and contradictory results. These constraints are very costly, and they are in most cases useless as they originate from flawed methodologies. In the present report, we argue that the EPM or EZM, LDB, and OF do not provide unequivocal measures of anxiety; that there is no evidence of motivation conflict involved in these tests. They can be considered at best, tests of natural preference for unlit and/or enclosed spaces. We also argued that pharmacological validation of a behavioral test is an inappropriate approach; it stems from the confusion of animal models of human behavior with animal models of pathophysiology. A behavioral test is developed to detect not to produce symptoms, and a drug is used to validate an identified physiological target. In order to overcome the major methodological flaws in animal anxiety studies, we proposed an open space anxiety test, a 3D maze, which is described here with highlights of its various advantages over to the traditional tests.

Ameliorating effects of gypenosides on chronic stress-induced anxiety disorders in mice

BACKGROUND

Ethanol extract from Gynostemma pentaphyllum (GP) shows anti-stress and anxiolytic functions in mice, and also protects dopamine neurons in 6-hydroxydopamine-lesioned rat model of Parkinson's disease. In addition, gypenosides (the gypenoside-enriched components of GP, GPS) have a protective effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease. In this study, the ameliorating effects of GPS on chronic stress-induced anxiety disorders in mice were investigated.

METHODS

Mice were orally treated with GPS (100 and 200 mg/kg) once a day for 10 days, followed by exposure to electric footshock (EF) stress (0.6 mA, 1 s every 5 s, 3 min). After the final administration of either GPS, water extract of GP (GP-WX) or ethanol extract of GP (GP-EX, positive control), the behavioral tests such as elevated plus-maze, marble burying and locomotor activity tests, and the biochemical parameters including dopamine, serotonin and corticosterone levels, and c-Fos expression were examined.

RESULTS

Treatment with GPS (100 and 200 mg/kg) increased the number of open arm entries and the time spent on open arms in elevated plus-maze which were reduced by chronic EF stress. GPS (100 and 200 mg/kg) reduced the number of marbles buried which increased by chronic EF stress. In these states, the brain levels of dopamine and serotonin decreased by chronic EF stress and they were recovered by GPS. The serum levels of corticosterone increased by chronic EF stress were also reduced by GPS (100 and 200 mg/kg). Finally, chronic EF stress-induced c-Fos expression was markedly reduced by GPS (100 and 200 mg/kg) in the brain. GPS (100 and 200 mg/kg) also showed an equivalent efficacy on anxiolytic functions, as compared with GP-EX (50 mg/kg). However, GP-WX (50 mg/kg) showed a less effect on anxiety disorders than GP-EX (50 mg/kg) and GPS (100 and 200 mg/kg).

CONCLUSION

These results suggest that GPS (100 and 200 mg/kg) has anxiolytic effects on chronic EF stress-induced anxiety disorders by modulating dopamine and serotonin neuronal activities, c-Fos expression and corticosterone levels. GPS may serve as a phytonutrient in chronic stress-induced anxiety disorders.

Relative luminosity in the plus maze upon the exploratory behaviour of female Wistar rats

Objective This study evaluated the provision of two configuration of the Elevated Pluz-Maze (EPM) by analizing the exploratory behaviour of female Wistar rats in different phases of the estrous cycle in EPMs with different gradients of luminosity between the open and enclosed arms (O/E∆Lux).Methods Female Wistar rats were treated with Midazolam (MDZ, 1.0 mg.kg-1) and were tested for their exploratory behaviour in either the EPM 10 O/E∆Lux or EPM 96 O/E∆Lux.Results A multiple regression analysis indicated that the O/E∆Lux is negatively associated with the %Open arm entries and %Open arm time, suggesting that as O/E∆Lux increases, the open arm exploration decreases. The estrous cycle phase did not influence the open-arm exploration in either EPM. MDZ- induced anxiolysis was detected in 96 O/E∆Lux EPM in all phases of the EC.Discussion Results of this study suggest the importance of the O/E∆Lux to establish the arm preference in the EPM, and to preserve the predictive validity of the EPM.

Repeated social defeat stress enhances the anxiogenic effect of bright light on operant reward-seeking behavior in rats

Repeated stress can trigger episodes of depression, along with symptoms of anhedonia and anxiety. Although often modeled separately, anxiogenic factors potently modulate hedonic, or appetitive, behavior. While repeated stress can increase anxiety and decrease appetitive behavior, it is not clear whether repeated stress can influence the impact of anxiogenic factors on appetitive behavior. This study tests whether repeated stress shifts behavior in a task that measures anxiogenic-appetitive balance. To test this, adult male rats were trained to lever press for sucrose pellet reward, and the effect of anxiogenic bright light on this behavior was measured. The impact of the bright light anxiogenic stimulus on lever pressing was compared between groups exposed to either daily repeated social defeat stress or control handling. We found that repeated stress reduced exploration in the open field and decreased social interaction, but had minimal effect on baseline lever pressing for reward. Repeated stress substantially enhanced the effect of anxiogenic bright light on lever pressing. This effect was greater two days after the last stress exposure, and began to diminish within two weeks. These data demonstrate that the anxiogenic and anhedonic features induced by repeated stress can be separately measured, and that the impact of anxiogenic stimuli can be greatly enhanced after repeated stress, even in the face of appetitive drive. The data also demonstrate that some apparent anhedonic-like effects of repeated stress can be due to increased sensitivity to anxiogenic stimuli, and may reflect an imbalance in an appetitive approach-withdrawal continuum.