Trait anxiety: a hidden variable in physiological and pathological processes

Human subjects display a great variability in the predisposition to respond anxiogenically to stimuli, i.e. trait anxiety. This susceptibility has been studied in rodents through the creation of selected strains for anxiety-like behaviour, to obtain extreme anxiety traits. Moreover, anxiety has been shown to variously affect physiological processes, such as a cognitive task performance, both in humans and selected rodents strains. However, interindividual differences in basal anxiety level in naïve rats and how they may affect cognitive functioning have been poorly investigated. Therefore, the aim of this study is to provide an evidence of the huge interindividual differences in anxiety levels in a population of naïve Wistar rats and demonstrate how they can affect a widely used cognitive test, the Novel Object Recognition (NOR) test. Following this line of research, in this study we also investigate if trait anxiety could affect pathological processes, such as the susceptibility on the onset of a neurological disease, the temporal lobe epilepsy, in a population of C57Bl/6J mice. Finally, we evaluate if the exposure to a strong stressful factor for mice, such as a predator odor, could induce an increase of the pathological process in chronic phase of the illness, for example in the number of seizures, in the same epileptic animals. These results could show the relevance to consider trait anxiety, the propension to response in a manner more or less anxious to a specific stimulus, of each subject, in order to avoid interpretative errors during the evaluation of a specific behaviour shown by the subject. Therefore we claim the need to consider interindividual differences in emotionality (e.g. anxiety) in general, and the need to assess anxiety level while studying rats cognitive abilities. It will be possible to include it as a covariate in the statistical analysis, in studies that schedule behavioural factors, in order to avoid interpretative errors dued to this hidden variable.