Comparative study of emotional behaviour in three inbred strains of mice.

Anxious behaviour constitutes one of the markers that best differentiated the 'non-emotional' C57BL/6 (C57) strain from the 'emotional' BALB/c (BALB) strain. Interestingly, C3H/He (C3H) mice, which possess a common genetic background to BALB, have also been found to be 'emotional' mice. The present study first illustrates that BALB and C3H mice exhibit a higher emotional level both in non-constraining situation (free-exploratory paradigm) and in a stressful one (light/dark choice test). Second, the present results confirmed the hypothesis that trait anxiety, modelled neophobic reactions in the free-exploratory paradigm, is related to GABA-benzodiazepine system rather than to the serotoninergic one, in contrast to state anxiety, modelled by the light/dark choice test. Like in BALB mice, chlordiazepoxide was able to counteract the neophobic responses in C3H mice confronted with the free-exploratory paradigm, in contrast to 8-OH-DPAT which did not modify C3H behaviour in this test. Conversely, both chlordiazepoxide and 8-OH-DPAT reduced anxious reactions of BALB and C3H mice in the light/dark choice test, showing that BALB and C3H mice are sensitive to serotonin-interacting drugs only when confronted with a stressful situation. Furthermore, chlordiazepoxide and 8-OH-DPAT were found to be devoid of anxiolytic-like effect in C57 mice. The lack of anxiolytic-like activity of these compounds in C57 mice can be related to the low basal level of emotional reactions of this strain. Finally, the present results showed that chronic stress was able to blunt general emotional level of mice in both experimental situations and that both BALB and C3H mice were more sensitive to chronic stress than C57 ones. In conclusion, BALB and C3H may be two strains of choice for testing potential anti-anxiety treatments which might be of great long-term benefit in the chronically anxious patients. Furthermore, these strains constitute interesting material for determining hereditary factors which presumably underlie the development of some chronic anxiety disorders. Finally, since C3H and BALB mice appeared particularly susceptible to chronic stress, it can be proposed that these strains may be a useful tool to examine the possible common origins of anxiety disorders and chronic stress-related disorders, such as certain forms of depression.