An experiment carried out in mice also indicates that biological sex and social support influence
By Maria Fernanda Ziegler
Loneliness can prolong pain and make physical recovery difficult, especially in females. This was shown in a study carried out with mice in which researchers from Unesp (Universidade Estadual Paulista) evaluated how social isolation interferes with the transition from acute to chronic pain. With the results, in the magazine Physiology Behaviorthe authors argue that loneliness should be considered a risk factor in post-operative care and pain treatments.
The work, by Fapesp, analyzed adult male and female mice isolated in individual cages or kept in groups with 4 other animals of the same sex. To simulate the transition from acute to chronic pain, all animals received a cut in the hind paw and, two weeks later, an injection of prostaglandin to reactivate hypersensitivity.
During the experiment, the researchers evaluated the mechanical sensitivity to pain, the animals’ facial expressions of discomfort and behaviors linked to anxiety and depression, such as exploring new environments and the state of apathy and anhedonia (inability to feel pleasure in activities that were previously pleasurable, such as eating) by the condition of the coat. Levels of hormones related to social bonding and pain, such as oxytocin, vasopressin and corticosterone, were also monitored.
“Only the isolated females continued to have intense pain 14 days after the cut. It was the only group that did not recover. The pain was persistent, becoming chronic, even before we carried out the additional intervention for chronification”says , professor of the Interinstitutional Postgraduate Program in Physiological Sciences, maintained by UFScar (Federal University of São Carlos) in partnership with Unesp, and one of the authors of the study.
“With this, we were able to show that social isolation delays recovery from pain. In the case, especially of mice, the results are so robust that they should not be ignored for human health”it says.
Being female impacted more than loneliness
Isolated males demonstrated greater physical resilience and showed no impairment in recovery, although they showed an exacerbation of anxiety compared to non-isolated males.
Another important aspect is that, while isolated females maintained low levels of oxytocin during all stages of the experiment, isolated males with chronic pain (after the use of prostaglandin) recovered levels of the hormone, reaching levels similar to animals that did not suffer social stress.
According to the researchers, the group of non-isolated mice showed that social support can be a protective factor, allowing them to fully recover physical sensitivity within two weeks and emotional balance after the painful stimulus.
“It is curious that, even when chronic pain was induced in females living in a group, there was a reduction in oxytocin levels. This suggests that, in them, the pain system affects this hormone more directly than the social environment”said Baptista.
The grouped male mice were those that showed greater stability and resilience.
The work is one of the first to demonstrate the impact of loneliness on the chronification of pain taking into account the biological sex of animals. “Although chronic pain is more prevalent in women, historically the inclusion of female subjects in clinical and preclinical trials has been very low. This has a number of negative implications for understanding different aspects of pain”said Baptista.
For the researcher, the findings help to explain why women are more likely to experience chronic pain, anxiety and depression and reinforce the need to consider biological sex and social support as central variables in research and personalized treatments for pain.
“The study showed that social isolation impairs the recovery of females in a more intense and lasting way than in males, affecting physical, emotional and hormonal aspects. This result opens up space for new research. We still do not fully understand the mechanisms that explain this difference, but it is already clear that social interaction and biological sex are central factors in the perception of pain”stated the researcher.
The article The interplay of social isolation, sex, and hyperalgesic priming on behavior and hormone levels in a mouse model can be read.
With information from .
