Effect of prolonged isolation on learning, biogenic amine turnover and aggressive behaviour in three strains of mice

Abstract

Two albino strains (MF-1 and CF-1) and one non-albino inbred strain (DBA/2J) of mice were compared for shuttle-box avoidance acquisition and fighting behaviour following a 5-week isolation period. Brain levels and turnover rates of norepinephrine and serotonin were also measured in groups of isolated mice. Mice housed in groups of five (aggregated) served as control subjects. Only the albino strains became aggressive after isolation; DBA/2J mice did not fight when paired. Results obtained in order of increasing facility of avoidance acquisition and a higher level of spontaneous activity were: DBA/2J mice > CF-1 mice > MF-1 mice. These results were correlated with whole-brain steady-state levels of norepinephrine among the strains. No differences in avoidance acquisition or serotonin levels and turnover rates were observed between isolated and aggregated mice within the same strain. CF-1 mice had lower levels and a faster turnover rate of serotonin compared with the other strains. Norepinephrine turnover rates were unchanged in CF-1 and DBA/2J mice following isolation, but were significantly slowed in MF-1 isolated mice compared with their controls. It is concluded that no clear-cut relationship exists among learning ability, aggressive behaviour and biogenic amine turnover rates in isolated or aggregated mice.