Social adolescent stress causes increased general anxiety in male rats and reduced social anxiety in both male and female rats

Abstract

Background: Due to the COVID-19 pandemic, the prevalence of anxiety and depression disorders increased by approximately 25-30% [1]. Reasons behind this are likely associated with the increased average daily level of stress, especially during social isolation. Since one of the main adolescence hallmarks is formation of meaningful social and love relationships, it represents a particularly vulnerable period for social stress [2]. The aim of this study was to evaluate whether isolation stress during the adolescence causes general and social anxiety in rats. Methods: Sprague-Dawley rats of both sexes were used for the adolescence social isolation experiment. From the fourth postnatal week, 24 rats were single caged and therefore subjected to the social isolation stress, while 24 non-stressed control rats remained in groups of four per cage and were handled three times a week. All rats were handled daily for one week and weighted before behavioural tests. From eleventh week, rats were subjected to the open field, elevated plus maze, and three-chamber sociability tests, with two-day gap between different tests. In open field test, time spent in the centre was measured, while in the elevated plus maze test, the time spent in open arms, normalized to time spent in all arms was measured; reduction in values of these parameters was interpreted as general anxiety. In the social preference test, social preference ratio was calculated for each animal, according to the previously published protocol [3], and reduction in this ratio was interpreted as social anxiety. 2-way ANOVA, with sex and isolation stress as factors, was used for parametric data analysis, and Fischer’s post hoc test was used to detect statistically significant between group differences. Kruskal-Wallis test was used for non-parametric data analysis, and Mann-Whitney post hoc test with multiple comparison correction was used to detect statistically significant between group differences. Results: Compared to control rats, time spent in the centre of open field (-44% [95%CI: -76%, -12%] p¼0,008) and total distance travelled (-17% [95%CI: -32%, -2%], p¼0.028) were decreased in isolated males, but not in females (p>0.1). In elevated plus maze test, time spent in the open arms was significantly decreased in male isolated rats (isolated: [median: 0.76, IQR: 0.00 – 2.06] vs control: [median: 4.96, IQR: 2.04 – 17.75], p¼0.034); however, this change did not remain significant after multiple comparisons corrections. In sociability tests, both male and female isolated rats exhibited increase in social preference ratio (+32% [95%CI: 12%, 51%], p¼0.002) and preference for novel animal over familiar one (+48% [95%CI: 10%, 86%], p¼0.015), compared to control rats. Body weight, measured after six weeks of social isolation at week ten, was increased in isolated male compared to control rats (+19% [95%CI: 14%, 24%], p<0.001), while there was no such difference observed in female rats. Conclusion: Social isolation caused increase in general anxiety in male, but not female rats. In addition, both male and female rats exhibited robust increase in preference for social interaction and novel social stimulus, which is the result opposite from the expected social anxiety as initially hypothesized.