Abstract
The Djungarian hamster（P. sungorus）and the Roborovskii hamster（P. roborovskii）belong to the same genus, Phodopus. The Djungarian hamster is tame toward people and shows sedative behavior, but the Roborovskii hamster is not tame toward people and exhibits hyperactivity compared with Djungarian hamsters. The current study investigated whether behaviors and levels of brain monoamine and amino acid in the two species of hamster are modified by social isolation. Anxiety-like behaviors in the open field test were increased by isolation irrespective of species. However, Roborovskii hamsters, but not Djungarian hamsters, showed a positive correlation between locomotor activity and anxiety-like behavior during the open field test. In both the hippocampus and the cerebellum, levels of the branched chain amino acids, as well as those of L-histidine, L-phenylalanine, L-tyrosine and L-arginine, were higher in Roborovskii hamsters than in Djungarian hamsters, but the reverse was true for levels of taurine. In the hippocampus, Roborovskii hamsters showed higher L-serine and lower D-serine levels compared with those in Djungarian hamsters. Most monoamines and their metabolites were higher in the hippocampus of Roborovskii hamsters than in that of Djungarian hamsters. However, social isolation scarcely influenced these differences between the two hamster species. In conclusion, our results suggest that the physiologically existing differences between the two hamsters are strongly fixed and the effect of isolation in modifying the physiological response in the two hamster species may be weak.
