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

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.

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.

Hyperglycemia elicits anxiety-like behaviors in zebrafish: Protective role of dietary diphenyl diselenide

Diabetes mellitus (DM) is a chronic metabolic disease that may comorbid with various psychiatric disorders, such as anxiety and depression. The search for effective therapeutics to alleviate hyperglycemia and complications resulting from DM is continuous. Here we investigate the effects of diphenyl diselenide (DD), an organoselenium compound with several pharmacological properties, in a zebrafish model of hyperglycemia. Fish were fed for 74 days with a diet containing 3 mg/Kg DD, a concentration chosen after experiments based in a dose-response curve (DD 1, 2 and 3 mg/Kg) that did not cause overt toxicity (mortality, weight loss and neurobehavioral deficits). In the last 14 days of the experimental period, fish were concomitantly exposed to a glucose solution (111 mM). Afterwards, blood glucose levels, brain selenium (Se) content, and behavioral analysis aiming to assess anxiety-like behaviors and locomotor/exploratory activities were performed. In the novel tank diving test, glucose decreased vertical exploration and fish spent less time in the lit area when tested in the light-dark test, suggesting increased anxiety-like behavior. Moreover, DD decreased blood glucose levels in hyperglycemic fish as well as prevented the development of anxiety-related symptoms. DD diet alone did not change glycemia and behavioral parameters, but increased Se levels in the brain without affecting the cellular viability. Collectively, our findings highlight the growing utility of this zebrafish hyperglycemia model as a valuable strategy for further research in DM field and neuroprotective approaches.

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.