Effects of long-term social isolation on central, behavioural and metabolic parameters in middle-aged mice

Social isolation gained discussion momentum due to the COVID-19 pandemic. Whereas many studies address the effects of long-term social isolation in post-weaning and adolescence and for periods ranging from 4 to 12 weeks, little is known about the repercussions of adult long-term social isolation in middle age. Thus, our aim was to investigate how long-term social isolation can influence metabolic, behavioural, and central nervous systemrelated areas in middle-aged mice. Adult male C57Bl/6 mice (4 months-old) were randomly divided into Social (2 cages, n = 5/cage) and Isolated (10 cages, n = 1/cage) housing groups, totalizing 30 weeks of social isolation, which ended concomitantly with the onset of middle age of mice. At the end of the trial, metabolic parameters, short-term memory, anxiety-like behaviour, and physical activity were assessed. Immunohistochemistry in the hippocampus (AFosB, BDNF, and 8OHDG) and hypothalamus (AFosB) was also performed. The Isolated group showed impaired memory along with a decrease in hippocampal AFosB at dentate gyrus and in BDNF at CA3. Food intake was also affected, but the direction depended on how it was measured in the Social group (individually or in the group) with no alteration in AFosB at the hypothalamus. Physical activity parameters increased with chronic isolation, but in the light cycle (inactive phase), with some evidence of anxietylike behaviour. Future studies should better explore the timepoint at which the alterations found begin. In conclusion, long-term social isolation in adult mice contributes to alterations in feeding, physical activity pattern, and anxiety-like behaviour. Moreover, short-term memory deficit was associated with lower levels of hippocampal AFosB and BDNF in middle age.

Automated summary

The study found that long-term social isolation can have effects on metabolism, behavior, and the central nervous system in middle-aged mice. The isolated group showed impaired memory, altered food intake, increased physical activity, and evidence of anxiety-like behavior. Short-term memory deficit was associated with lower levels of hippocampal AFosB and BDNF in middle age.