Effect of Long-Term Social Isolation on Behavior and Brain Dopaminergic System in Mice

The central dopaminergic system is implicated in the regulationof various physiological processes and behavioral responses, includingsocial behavior. Although long-term individual housing of rodentsis well known to alter their behavioral and neurochemical parameters,data interpretation remains ambiguous. In this work, we studiedthe effects of long-term social isolation on the behavior and stateof the central dopaminergic system in male C57Bl/6 mice. The animalsof the experimental group, aged 40–42 days, were housed singly inindividual cages for six weeks, while the age-matched mice of thecontrol group were housed in a group. Isolation did not affect locomotorand exploratory activity in the open field test compared to grouphousing. At the same time, singly-housed animals demonstrated alonger duration of social contacts in a resident–intruder model,as well as a weakened stereotypical behavior in the marble buryingtest compared to group-housed rats. These behavioral changes wereaccompanied by an increase in striatal mRNA levels of the genesencoding dopamine D1 and D2 receptors. Moreover, the level of the dopaminemetabolite 3,4-dihydroxyphenylacetic acid (DOPAC) decreased in thehypothalamus and increased in the frontal cortex in singly-housedcompared to group-housed mice. The results provide a better insightinto the effects of long-term social isolation on the behavior anddopaminergic system in mice.