Social Involvement Modulates the Response to Novel and Adverse Life Events in Mice

Abstract

Epidemiological findings suggest that social involvement plays a major role in establishing resilience to adversity, however, the neurobiology by which social involvement confers protection is not well understood. Hypothesizing that social involvement confers resilience by changing the way adverse life events are encoded, we designed a series of behavioral tests in mice that utilize the presence or absence of conspecific cage mates in measuring response to novel and adverse events. We found that the presence of cage mates increased movement after exposure to a novel environment, increased time spent in the open arms of the elevated plus maze, and decreased freezing time after a foot shock as well as expedited fear extinction, therefore significantly changing the response to adversity. This is a first description of a mouse model for the effects of social involvement on adverse life events. Understanding how social involvement provides resilience to adversity may contribute to the future treatment and prevention of mental and physical illness.

Social isolation is closely linked to a marked reduction in physical activity in male mice

“…We next asked: how soon after placement in the PhenoTyper environment do isolated mice decrease their activity? Based on our prior observations (Colnaghi et al., 2016), we hypothesized that the effect of social isolation would have an immediate effect on locomotion. We measured distance traveled and time spent moving in the first 5 min after the mice were placed in the PhenoTyper, during the light cycle.…”

“…One such basic cue is the presence of peers. Based on our previous research demonstrating that mice tend to move less when facing adverse or novel experiences in the absence of conspecifics, we reasoned that the absence of a cage mate in the home cage environment will result in a decrease in locomotion similar to the responses to other anxiogenic contexts that we have previously characterized (Colnaghi et al., 2016). Indeed, we found that socially isolated mice have a lower level of activity compared to paired mice, and that this reduction is reversible.…”

“…We next asked: how soon after placement in the PhenoTyper environment do isolated mice decrease their activity? Based on our prior observations (Colnaghi et al, 2016), we hypothesized that the effect of social isolation would have an immediate effect on locomotion.…”

“…Unlike for social isolation, many molecular mechanisms by which physical activity potentiates health and longevity are known, such as increased heart rate variability, increased brain-derived neurotrophic factor leading to increased neurogenesis, better neuroprotection, and improved cognitive function, as well as an increase in mitochondrial density in multiple tissues including brain and skeletal muscle (Bayod et al, 2015;Poirier, 2014;Warburton et al, 2006). Previously, we had demonstrated that mice tend to move less when alone in the context of an adverse or novel environment (Colnaghi et al, 2016). Hypothesizing that social isolation is closely linked to reduced physical activity also in the absences of adversity, we set out to examine the connection between social isolation and movement in mice.…”

Optogenetic reactivation of prefrontal social memory trace mimics social buffering of fear

“…Squirrel monkeys exhibit ameliorated stress responses after exposure to a fearful stimulus (a snake) if social companions were present during exposure [26]. In rats, stress responses to fearful stimuli were reduced in the presence of a same-sex partner [27,28], and in mice, the presence of cage-mates reduces anxiolytic responses to novel and aversive stimuli [29].…”