Behavioral differences in black Swiss mice from separate colonies: implications for modeling domains of mania.

Recent work demonstrated the advantages of using black Swiss (BS) mice to model behavioral domains of mania including reward-seeking, risk-taking, vigor, and sensitivity to psychostimulants. Until recently BS mice were only available from Taconic (TAC) farms, but a colony was recently established by Charles River (CR). The present study compared the behavioral phenotype of mice from the new CR colony to the TAC animals to evaluate if mice from CR also have the advantages as model animals for mania. TAC and CR mice were compared in a battery of tests related to domains of mania, and the effects of lithium were tested in the CR mice. CR mice showed lower activity levels and preference for sweet solution and higher immobility in the forced swim test compared with TAC mice. Furthermore, in contrast with the antimanic-like effects of lithium previously described in TAC mice, in CR mice lithium only had an antidepressant-like effect in the forced swim test. The results indicate that the CR BS mice lack the behavioral properties that make the TAC BS mice advantageous for modeling domains of mania.

It is darkness and not light: Depression-like behaviors of diurnal unstriped Nile grass rats maintained under a short photoperiod schedule.

Circadian rhythms are strongly implicated in affective disorders and some recent studies suggested that diurnal rodents might be advantageous model animals for them. In line with this possibility, previous work demonstrated that in the diurnal fat sand rat, short photoperiod conditions result in depression- and anxiety-like behavioral phenotype that is relieved with bright light treatment. To further explore the possibility of using diurnal species as model animals for affective disorders, the present study examined the effects of short photoperiod schedule in an additional diurnal rodent, the unstriped Nile grass rat. Results indicate that 6 weeks short photoperiod (5 h light/19 h dark) regimen induced depression-like behavior in the forced swim test and the saccharin preference test compared with animals maintained in a neutral photoperiod regimen (12 h light/12 h dark). No effects were shown in the light/dark box model of anxiety or in a test for spontaneous activity. These results demonstrate that photoperiod manipulations in diurnal rodents induce affective-like behavioral change and support the possibility that diurnal rodents might provide a good potential as model animals for depression spectrum disorders.