Study in Rodents Reveals Consequences of Isolation on Brain Cellularity and Social Recognition Ability

Depression is a complex and multifactorial condition that affects millions of people worldwide. Social isolation is one of the multiple factors that can induce depression in humans and other animals, but the detailed mechanisms of how the lack of social contact can affect brain structure and promote mental health issues remain unclear.

To better understand this mechanism, researchers from the Institute of Biomedical Sciences at the Federal University of Rio de Janeiro (UFRJ), in collaboration with the D’Or Institute for Research and Education (IDOR), investigated the brain changes caused by social isolation in rodents, finding significant differences compared to the brains of non-isolated animals. The study was published in the scientific journal Brain Structure and Function. The research was led by Dr. Daniel Menezes Guimarães, a researcher at IDOR’s Image Processing Laboratory (LPI), as part of his PhD thesis at UFRJ.

Social Isolation in Mice

To understand the impact of social isolation on rodents, scientists isolated mouse pups from their peers immediately after weaning. They then assessed various behavioral and anatomical aspects throughout the isolation period.

Isolated rodents exhibited lower weight and mild behavioral impairments, such as a decline in the ability to perceive, remember, and interact with other members of their species. The impairment in social cognition suggests that social isolation during development can have long-lasting effects on individuals’ lives.

Social Isolation and Brain Cell Composition

In addition to evaluating the animals’ behavior and cognition, the scientists focused on the physical changes that social isolation could cause in the rodents’ brains, analyzing alterations in cell composition and the structure of the brain’s white matter, responsible for neural connections.

The researchers particularly evaluated the effect of social isolation on oligodendrocytes, a type of cell in the central nervous system essential for producing the myelin sheath, which facilitates nerve impulse conduction.

For this analysis of brain cellularity, the researchers used the isotropic fractionator method, which provides a robust estimate of the number of neurons and oligodendrocytes in dissected brain regions. They also employed neuroimaging techniques to analyze the white matter’s microstructure.

Isolated animals showed a lower number of oligodendrocytes in different brain regions when isolated from the 21st day of age. The reduction was more pronounced when the isolation continued until the age of 90 days, compared to a shorter isolation period (until the age of 60 days).

The duration of isolation also impacted the number of neurons, especially in the hippocampus, a brain region related to learning and memory. Significant changes in white matter were not detected through neuroimaging, but the parallel reduction in the number of neurons and oligodendrocytes might indicate a direct relationship between these cell populations.

Cellular Changes in Depression May Be Key to Treatments

The study indicates that social isolation affects the behavior and brain cell composition of mice. Although this is a rodent study, the findings reveal processes that may help guide future investigations and therapeutic approaches for depression in humans.

This research emphasizes the importance of understanding the biological mechanisms associated with depression and how external factors, such as social isolation, can influence the development of this and other pathologies. A better understanding of these connections could be an essential step in developing effective interventions to help those suffering from this debilitating and stigmatized disease.

Written by Maria Eduarda Ledo de Abreu.