The Effects of Housing Density on Social Interactions and Their Correlations with Serotonin in Rodents and Primates

Abstract

Population density has been suggested to affect social interactions of individuals, but the underlying neural mechanisms remain unclear. In contrast, neurotransmission of monoamines such as serotonin (5-HT) and dopamine (DA) has been demonstrated to play important roles in social behaviors. Here, we investigated whether housing density affected social interactions of rodents and non-human primates housed in groups, and its correlations with monoamines. Japanese macaques exhibited higher plasma 5-HT, but not DA, concentrations than rhesus macaques. Similarly, C57BL/6 mice exhibited higher plasma and brain tissue 5-HT concentrations than DBA2 mice. Under crowding, C57BL/6 mice and Japanese macaques exhibited more prominent social avoidance with mates than DBA2 mice and rhesus macaques, respectively. Although DBA2 mice and rhesus macaques in crowding exhibited elevated plasma stress hormones, such stress hormone elevations associated with crowding were absent in C57BL/6 mice and Japanese macaques. Administration of parachlorophenylalanine, which inhibits 5-HT synthesis, increased social interactions and stress hormones in C57BL/6 mice under crowding. These results suggest that, animals with hyperserotonemia may exhibit social avoidance as an adaptive behavioral strategy to mitigate stress associated with crowding environments, which may also be relevant to psychiatric disorder such as autism spectrum disorder.

Living inside the box: environmental effects on mouse models of human disease

“…Although it is difficult to disentangle the different elements of human urban life, the issues of housing space and population density are interesting. Group size and composition clearly affect the behavior of mice ( Kappel et al, 2017 ; Lee et al, 2018 ), and crowded male mice of several strains show high levels of aggression. However, contrary to much received wisdom, the most important positive factor seems to be a rich physical and social environment, and not simply the space available, at least within the constraints of a laboratory setup ( Bailoo et al, 2018 ).…”

A bird’s-eye view of brain activity in socially interacting mice through mobile edge computing (MEC)

“…Although these reductionist approaches have clarified the causal links between neural elements and social behaviors, in most cases, the collective behaviors that arise from communication and interactions among individuals are very difficult to deduce from single brain studies, because many global properties of social groups are consequences of coordinated interactions among group members ( 1 ). In addition to the behavior level, the involvement of particular brain regions and neural circuits has been reported to be dependent on social contexts ( 2 , 3 ), necessitating the simultaneous study of two or more interacting individuals ( 4 ).…”

Monoamine and genome-wide DNA methylation investigation in behavioral addiction

“…The samples were centrifuged again at 2,000 rpm for 15 min, and 10 μL each of supernatant from these samples was applied for HPLC. Using a similar procedure described in our previous study 71 , HPLC was carried out using an HTEC-500 HPLC electrochemical detection system (Eicom, Tokyo, Japan) with the EICOMPAK SC-5ODS column and CA-ODS precolumn. The mobile phase consisting of 0.1 M acetic acid-citric acid buffer (pH 3.5) and methanol (83:17, v:v), along with 190 mg/L sodium 1-octanesulfonate and 5 mg/L EDTA-2Na, was used.…”