Integrating the open field, elevated plus maze and light/dark box to assess different types of emotional behaviors in one single trial

Abstract

Current anxiety tests do not provide, individually, a pure and complete picture of an animal's emotional profile. Therefore, many authors test their experimental hypotheses using a series of anxiety-related tests, which are thought to reflect different facets of emotionality. The objective of this study was to investigate the potential usefulness of integrating three widely used behavioral tests, the open field (OF), elevated plus maze (EPM), and light/dark box (LDB), to assess a wider range of emotional and non-emotional behaviors within one single trial. A protocol was developed where rats could freely explore an OF that was physically connected to an EPM and a LDB during 15 min. Classical anxiety- and locomotion-related behaviors from each test were measured. Lewis and spontaneously hypertensive rats (SHR) inbred strains, known to present genetic differences in each of the individual tests, differed for all anxiety-related behaviors from the combined apparatus. Factor analyses revealed that similar anxiety- and locomotion-related factors were produced by the three tests applied either separately or in combination. Under both conditions, each test produced its own anxiety-related factor. Two benzodiazepines, chlordiazepoxide (at 5 and 10 mg/kg) and midazolam (at 0.75 mg/kg), facilitated the approach towards the EPM open arms, whereas pentylenetetrazole (10 mg/kg) specifically inhibited exploration of the three aversive areas (OF center, EPM open arms, LDB light compartment). Together, these results suggest that the new integrated apparatus may contribute to the study of anxiety, by providing a rapid, comprehensive and reliable method of assessing emotionality-related behaviors and its underlying components.