Posture and Movement

Amphibians possess most limbic centers found in mammals including the hippocampal formation (medial pallium), amygdala, septum, ventral striatum, hypothalamus, nucleus accumbens, ventral tegmental area and reticular nuclei such as the nuclei raphes and the locus coeruleus (Northcutt, 1981; Marin et al, 1996). We found evidence that-as in mammals in amphibians limbic centers play an important role in the acquisition of fear. To investigate the function of the limbic system regarding the acquisition of fear, we developed a one-trial aversive learning task in the fire-bellied toad, Bombina orientalis using honey bees (Apis m.sicula) as negative conditioning stimulus. For identification of the brain areas involved in this task, the distribution of Egr-1, a transcription factor encoded by the immediate early gene (lEG) egr-1, was investigated using immunohistochemistry. Egr-1 (also known as krox 24, zif/268, ZENK) as well as c-fos are supposed to play an important role in the consolidation of memory traces (Grimm et al., 1996; Jin et al., 1997).We found that the expression of Egr-1 in the medial amygdala, the bed nucleus of the stria terminalis and the preoptic area of the experimental group was significantly higher compared to controls fed with palatable food.