Influence of long-term social isolation on the behavior and dopamine system of the brain in mice

The dopamine brain system is involved in the regulation of various physiological processes and behavioral responses, including social behavior. It was shown in rodents that prolonged social isolation can lead to changes in behavioral parameters and neurochemical parameters, but these data remain unclear. In this work, we studied the effects of prolonged social isolation on the behavior and state of the brain dopamine system in male C57Bl/6 mice. Animals of the experimental group from the age of 40 - 42 days were kept individually in separate cages for six weeks, while the mice of the control group were kept in-group conditions. Isolation did not affect locomotor and exploratory activity in the “open field” test compared to the content in the group. At the same time, animals subjected to prolonged isolation demonstrated a longer duration of social contacts in the “resident-intruder” model and a weakening of stereotypical behavior in the “marbles burying” test compared to the control group. These behavioral changes were accompanied by an increase in mRNA levels of the genes encoding dopamine D1 and D2 receptors in the striatum of mice. In addition, the level of the dopamine metabolite DOPAC decreased in the hypothalamus and increased in the frontal cortex of mice due to the effect of social isolation compared with the control group. The results contribute to the understanding of the effects of prolonged social isolation on the behavior and dopamine brain system in mice.