The free-exploratory paradigm as a model of trait anxiety in rats: Test–retest reliability

Involvement of the serotonergic, GABAergic and glutamatergic systems of the rostral anterior cingulate cortex in the trait and state anxiety of adult male Wistar rats

Despite significant advancements to understand of the neural circuitry involved in anxiety, the neurobiology of trait anxiety remains unclear. The rostral anterior cingulate cortex (rACC) and various pathways have been implicated in its regulation, making it a key to trait anxiety. The present study aimed to investigate the role of these neurotransmitter systems in the rACC in trait anxiety. Since trait anxiety is known to modulate state anxiety, we further investigated this relationship. Specifically, in Experiment I, we used animals with high trait anxiety; in Experiment II, we used animals with low trait anxiety; and in Experiment III, we used animals with medium trait anxiety. Before each behavioral assessment, drugs that either increased or decreased serotonergic (Fluoxetine or WAY-100635), GABAergic (Muscimol or Bicuculline), and glutamatergic (NMDA or Ketamine) neurotransmission in the rACC were administered, along with their respective controls. Additionally, in Experiment IV, all animals from the previous experiments were subjected to the Elevated Plus Maze (EPM) and Hole board (HB) test and evaluated without taking into account their trait anxiety levels. The results of the present study showed that, in Exp I, the modulation of the serotonergic, GABAergic and glutamatergic systems in the rACC decreased trait anxiety in highly anxious rats, while by submitting the animals to HB, the administration of fluoxetine increased state anxiety. In Exp II, the modulation of all systems increased trait anxiety in rats with low trait anxiety, whereas, in HB, state anxiety levels were increased with the administration of NMDA. In Exp III, only the modulation of the glutamatergic system, with NMDA, increased both trait and state anxiety levels. However, none of the evaluated neurotransmitter systems altered the state anxiety modeled in the EPM. Overall, the results of the present study provide new insights into the role of the neurotransmitter systems in the rACC in the regulation of trait anxiety and state anxiety.

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.

High-caloric or isocaloric maternal high-fat diets differently affect young-adult offspring behavior in anxiety-related tests and offspring sensitivity to acute fluoxetine

OBJECTIVE

to evaluate the influence of two maternal high-fat diets with different caloric contents on anxiety-like behavior in young-adult offspring and their sensitivity to acute fluoxetine.

METHODS

females Wistar rats were used and divided according to diet received during gestation and lactation: Control (CTR), high-fat/isocaloric (HI) and high-fat/high-caloric (HH). Offspring were subsequently divided into three subgroups according to acute administration of vehicle or fluoxetine (1 or 10 mg/kg). To assess animals' anxiety-like behaviors, three tests were used: open field (OF), elevated plus-maze (EPM) and free-exploratory paradigm (FEP).

RESULTS

In OF, HI and HH showed increased hyperactivity- and anxiety-related behaviors, HI being more hyperactive than HH. In response to fluoxetine, HI offspring decreased number of quadrants entered, decreased number of central entries and spent less time in rearing in peripheral areas, while HH offspring showed less time spent in rearing in the OF peripheral area. In EPM test, HI pups spent more time in closed arms than the HH pups. Fluoxetine decreased number of open arms entries for HI offspring and increased percentage of time spent in central area for HH animals. Maternal diet did not influence FEP test, neither HI nor HH presented a response after fluoxetine acute administration.

CONCLUSION

Maternal high-fat diets influence offspring anxiety-like behavior in state-anxiety tests but not in trait-anxiety test. Responsiveness to acute fluoxetine depended on maternal diet, dose and which behavioral tests were being evaluated.

Excitotoxic lesion of the medial prefrontal cortex in Wistar rats: Effects on trait and state anxiety

The neural substrate of anxiety response (state anxiety) to a threatening situation is well defined. However, a lot less is known about brain structures implicated in the individual's predisposition to anxiety (trait anxiety). Scientific evidences lead us to suppose that the medial prefrontal cortex (mPFC) is involved in both trait and state anxiety. Thus, the aim of this study was to investigate the involvement of mPFC in trait anxiety and to further evaluate its participation in state anxiety. Sixty six adult, Wistar, male rats were first tested in the free-exploratory paradigm (FEP) and were categorized according to their levels of trait anxiety (high, medium and low). Three to six days after this exposure, all animals were submitted to stereotaxic brain surgery. Half the animals from each anxiety category was allocated to the mPFC-lesioned group and the other half to the Sham-lesioned group. After seven to nine days, all animals were again tested in FEP. Eight to 10 days later, the animals were tested in the Hole Board test, a model of state anxiety. The mPFC lesion decreased levels of trait anxiety of highly anxious rats, whereas it reduced the state anxiety of all animals, regardless the level of trait anxiety. These data extend evidence of the participation of the mPFC in state anxiety and it demonstrate the involvement of this brain structure in trait anxiety, a personality trait supposed to be a predisposing factor for anxiety disorders.

Effect of Cage-Induced Stereotypies on Measures of Affective State and Recurrent Perseveration in CD-1 and C57BL/6 Mice

Stereotypies are abnormal repetitive behaviour patterns that are highly prevalent in laboratory mice and are thought to reflect impaired welfare. Thus, they are associated with impaired behavioural inhibition and may also reflect negative affective states. However, in mice the relationship between stereotypies and behavioural inhibition is inconclusive, and reliable measures of affective valence are lacking. Here we used an exploration based task to assess cognitive bias as a measure of affective valence and a two-choice guessing task to assess recurrent perseveration as a measure of impaired behavioural inhibition to test mice with different forms and expression levels of stereotypic behaviour. We trained 44 CD-1 and 40 C57BL/6 female mice to discriminate between positively and negatively cued arms in a radial maze and tested their responses to previously inaccessible ambiguous arms. In CD-1 mice (i) mice with higher stereotypy levels displayed a negative cognitive bias and this was influenced by the form of stereotypy performed, (ii) negative cognitive bias was evident in back-flipping mice, and (iii) no such effect was found in mice displaying bar-mouthing or cage-top twirling. In C57BL/6 mice neither route-tracing nor bar-mouthing was associated with cognitive bias, indicating that in this strain these stereotypies may not reflect negative affective states. Conversely, while we found no relation of stereotypy to recurrent perseveration in CD-1 mice, C57BL/6 mice with higher levels of route-tracing, but not bar-mouthing, made more repetitive responses in the guessing task. Our findings confirm previous research indicating that the implications of stereotypies for animal welfare may strongly depend on the species and strain of animal as well as on the form and expression level of the stereotypy. Furthermore, they indicate that variation in stereotypic behaviour may represent an important source of variation in many animal experiments.

Pharmacological validation of the free-exploratory paradigm in male Wistar rats: A proposed test of trait anxiety

The free-exploratory paradigm (FEP) has been proposed as a model of trait anxiety for both mice and rats. However, its pharmacological validation has only been carried out for the mice. Thus, the aim of the present study was to pharmacologically validate FEP for Wistar rats, by testing the effects of clinically established anxiolytic and anxiogenic drugs, in four different experiments. In all experiments, male Wistar rats were first tested in FEP to be categorized according to their levels of trait anxiety (high, medium and low). Then, only medium trait anxiety rats were selected to be tested again in FEP, two weeks later, after being pharmacologically treated, according to each experiment as follows: Experiment I: 0.5mg/kg of diazepam (DZP) or vehicle; Experiment II: 20mg/kg of pentylenetetrazole (PTZ) or vehicle; Experiment III: 5mg/kg of fluoxetine (FLX5) or vehicle: and Experiment IV: 0.5mg/kg of fluoxetine (FLX0.5) or vehicle. As a group, the results showed that PTZ and FLX5 increased levels of trait anxiety and reduced locomotor activity, whereas DZP and FLX0.5 decreased levels of trait anxiety, without impairing locomotor activity. These results demonstrate that FEP for rats is able to predict clinical anxiolytic and anxiogenic activities of different drugs, including fluoxetine, which is believed to present a dual effect on anxiety. Therefore, this paradigm can be proposed as an effective method for testing potential trait anxiety-reducing drugs, in rats.

Deconstructing sociability, an autism-relevant phenotype, in mouse models

Reduced sociability is a core feature of autism spectrum disorders (ASD) and is highly disabling, poorly understood, and treatment refractory. To elucidate the biological basis of reduced sociability, multiple laboratories are developing ASD-relevant mouse models in which sociability is commonly assessed using the Social Choice Test. However, various measurements included in that test sometimes support different conclusions. Specifically, measurements of time the "test" mouse spends near a confined "stimulus" mouse (chamber scores) sometimes support different conclusions from measurements of time the test mouse sniffs the cylinder containing the stimulus mouse (cylinder scores). This raises the question of which type of measurements are best for assessing sociability. We assessed the test-retest reliability and ecological validity of chamber and cylinder scores. Compared with chamber scores, cylinder scores showed higher correlations between test and retest measurements, and cylinder scores showed higher correlations with time spent in social interaction in a more naturalistic phase of the test. This suggests that cylinder scores are more reliable and valid measures of sociability in mouse models. Cylinder scores are reported less commonly than chamber scores, perhaps because little work has been done to establish automated software systems for measuring the former. In this study, we found that a particular automated software system performed at least as well as human raters at measuring cylinder scores. Our data indicate that cylinder scores are more reliable and valid than chamber scores, and that the former can be measured very accurately using an automated video analysis system in ASD-relevant models.

Susceptibility to the long-term anxiogenic effects of an acute stressor is mediated by the activation of the glucocorticoid receptors

The specificity of the response of an organism is an important variable influencing stress-related parameters and psychopathological states. We have shown that trait anxiety in C57BL/6 mice, determined by their emergence latencies in the free choice open field test, positively correlates with the long-term behavioral and neuroendocrinological changes induced by a stressor. Here, we show that this interindividual variability is caused by a different reactivity of the hypothalamus-pituitary-adrenal (HPA) axis upon exposure to a stressor. Mice with high trait anxiety (long emergence latency, LEL) display a more pronounced stress-induced activation of the HPA axis than mice with low trait anxiety (short emergence latency, SEL). Moreover, stress-induced activation of tyrosine hydroxylase and corticotropin-releasing hormone occurred in LEL but not SEL mice. In search of the molecular mechanisms underlying these differences, we found that under non-stressed conditions mRNA and protein levels of the glucocorticoid receptor in the hippocampus were higher in LEL mice compared to SEL mice. Also, systemic injection of the glucocorticoid receptor antagonist RU486 decreased the stress-induced activation of the HPA axis and the long-term anxiogenic effects of stress observed in LEL mice. Finally, the rewarding properties of cocaine were enhanced in LEL mice compared to SEL mice, suggesting a causal link between trait anxiety, stress activity and the behavioral responses to drugs of addiction.

Automation of the free-exploratory paradigm

The free-exploratory paradigm (FEP) is currently the only proposed animal model of trait anxiety, making it highly valuable to behavioural neuroscience. However, FEP has not yet been automated, so its results depend on human scoring, which can be quite imprecise. The aim of this study was, therefore, to validate an automated version of FEP, using a commercially available video-tracking system (ANY-maze(©) - Stoelting Co., USA). To achieve this, two experiments were performed. The first one evaluated the reliability of the video-based automation of FEP, and the second, assessed whether the zeolites, used as a bedding material in the first experiment to facilitate video-tracking, influenced the animals' behaviour in FEP. In experiment I, 15 drug-naive, adult, male rats were tested in FEP, while their behaviour was simultaneously evaluated by ANY-maze(©) and two human observers. Subsequently, the intraclass correlation coefficient (ICC) was calculated for the automated and manual results of the parameters "percentage of time in the novel side" (%TNS) and "total units visited" (TUV). The analysis resulted in high, significant values of ICC (%TNS: 0.9962 and TUV: 0.9453). In experiment II, 18 drug-naive, adult, male rats were allocated to two different groups: (1) tested in FEP with zeolites; and (2) tested in FEP with sawdust. The data obtained were analysed using the Student's t-test, which revealed no significant differences between the groups for the parameters %TNS and TUV. In conclusion, the data presented here show that automation of FEP, using a video-based tracking system, is not only possible, but also highly reliable.

Inheritable effect of unpredictable maternal separation on behavioral responses in mice

The long-term impact of early stress on behavior and emotions is well documented in humans, and can be modeled in experimental animals. In mice, maternal separation during early postnatal development induces poor and disorganized maternal care, and results in behavioral deficits that persist through adulthood. Here, we examined the long-term effect of unpredictable maternal separation combined with maternal stress on behavior and its transmissibility. We report that unpredictable maternal separation from birth to postnatal day 14 in C57Bl/6J mice has mild behavioral effects in the animals when adult, but that its combination with maternal stress exacerbates this effect. Further, the behavioral deficits are transmitted to the following generation through females, an effect that is independent of maternal care and is not affected by cross-fostering. The combined manipulation does not alter basic components of the hypothalamic-pituitary-adrenal axis but decreases the expression of the corticotropin releasing factor receptor 2 (CRFR2) in several nuclei of the amygdala and the hypothalamus in the brain of maternal-separated females. These results suggest a non-genomic mode of transmission of the impact of early stress in mice.

5HT-1A receptors and anxiety-like behaviours: studies in rats with constitutionally upregulated/downregulated serotonin transporter

Altered activity of brain serotonergic (5HT) system has been implicated in a wide range of behaviours and behavioural disorders, including anxiety. Functioning of 5HT-1A receptor has been suggested as a modulator of emotional balance in both, normal and pathological forms of anxiety. Here, we studied serotonergic modulation of anxiety-like behaviour using a genetic rat model with constitutional differences in 5HT homeostasis, named Wistar-Zagreb 5HT (WZ-5HT) rats. The model, consisting of high-5HT and low-5HT sublines, was developed by selective breeding of animals for extreme activities of peripheral (platelet) 5HT transporter, but selection process had affected also central 5HT homeostasis, as evidenced from neurochemical and behavioural studies. Anxiety-like behaviour in WZ-5HT rats was evaluated by two commonly used paradigms: open field and elevated-plus maze. The involvement of 5HT-1A receptors in behavioural response was assessed by measuring mRNA expression in cell bodies (raphe nuclei) and projection regions (frontal cortex, hippocampus) by use of RT-PCR and in situ hybridization, and by measuring functionality of cortical 5HT-1A receptors by use of [(3)H]8-OH-DPAT radioligand binding. Animals from the high-5HT subline exhibit increased anxiety-like behaviour and decreased exploratory activity when exposed to novel environment. No measurable differences in constitutional (baseline) functionality or expression of 5HT-1A receptors between sublines were found. The results support contribution of increased serotonergic functioning to the anxiety-like behaviour. They also validate the high-5HT subline of WZ-5HT rats as a potential model to study mechanisms of anxiety, especially of its nonpathological form, while the low-5HT subline may be useful to model sensation seeking phenotype.