The plus maze and scototaxis test are not valid behavioral assays for anxiety assessment in the South African clawed frog

There are no behavioral models for testing anxiety in amphibians, a group of animals widely used for developmental, ecotoxicological, and genetic research. We aimed to validate two common rodent paradigms, the plus maze and the scototaxis test, for use in the aquatic African clawed frog (Xenopus laevis). We predicted: (a) that frogs would prefer the dark, vs. light, portions of the testing arenas (face validity), (b) that this behavior could be altered with acute administration of anxio-selective drugs (construct validity), and (c) that time spent in the dark portions of the arenas would be positively correlated (predictive validity). Prior to testing, frogs were treated with fluoxetine (selective serotonin reuptake inhibitor [SSRI]), desipramine (serotonin- and norepinephrine-reuptake inhibitor), caffeine (methylxanthine, adenosine receptor antagonist, phosphodiesterase inhibitor), saline, or were left unmanipulated. Each drug was administered acutely (1 h prior to testing; ca