Trait or state anxiety: refined methods to measure emotion-related behaviour in fish models
Anxiety-associated disorders impose tremendous burden on society. Despite extensive research, these conditions remain poorly understood, a problem which could be improved through the advancement of pre-clinical models. Anxiety tests applied in pre-clinical research are based on measuring species-specific behaviour controlled by an internal anxiety-like drive comparable to that of humans. Although these tests are sensitive for anxiolytic drugs, they show poor inter-test correlations at the individual level. This inconsistency might be traced back to fluctuating emotional states of the individual in between tests, temporarily masking its anxious traits. Based on our current findings using rodent models we attempted to develop a high-throughput method in order to increase test reliability and to reduce individual variance in zebrafish (Danio rerio), a model extensively used for pharmacological screening, and paradise fish (Macropodus opercularis), a classical ethological model. We performed a three-time sampling serial, using the Open Tank, Light-Dark and Swimming Plus-Maze tests, where animals underwent all tests each day in a semi-random order. Using spacio-temporal variables we drew summary-measures (SuMs) which we compared to commonly used single-test measures (SiMs). Similarly to our findings in rodent models, SuMs consistently showed stronger inter-test correlation compared to SiMs in paradise fish. Surprisingly, we did not find such an effect in zebrafish. In conclusion, while our results suggest that great care should be exercised when using zebrafish as a translational model of anxiety, through the use of summary-measures it is possible to delineate the emotional trait of paradise fish in a high-throughput manner.