Summary: A neuroimaging study on house sparrows reveals changes in the dopaminergic system could be a physiological mechanism underlying the negative behavioral effects of chronic stress. The findings shed light on stress and resilience in wildlife and humans.
Source: Louisiana State University
A biologist at Louisiana State University conducted a pioneering research study that could help us to better understand the role of dopamine in stress resilience in humans through analyzing wild songbirds. This study could lead to increased prevention and treatment of stress-related disorders.
Dopamine is a chemical in the brain that is important for learning and memory. Department of Biological Sciences Assistant Professor Christine Lattin, and colleagues conducted this study of wild songbirds showing that dopamine is important in responding to chronic stressors, which can help wildlife conservation efforts in response to environmental stressors such as habitat destruction, natural disasters, extreme weather events and increases in predation.
Lattin, who is the lead author on the study published in Nature’s Scientific Reports, applied a biomedical imaging technology called Positron Emission Tomography, or PET, scans that are used commonly on humans but rarely on wild animals to quantify dopamine receptors in house sparrows.
“This study is exciting because it is the first time PET scans have been used in wildlife to quantify dopamine receptors in the brain. Developing this technique has opened the door to being able to scan animals and release them back into the wild,” she said.
“We need to know how these wild birds are coping with stressors and responding to changes to the environment so we can understand how to best protect them.”
In addition to the biomedical imaging, Lattin and colleagues tracked changes in the birds’ body mass and hormone levels, and observed their behavior using a remotely operated video camera to study wild house sparrows’ response to captivity over four weeks. The birds were scanned after being brought in to the lab and then again four weeks later. By using PET scans, they were able to study how the stress of captivity affected the birds over time.
They found that one type of dopamine receptor decreased over time during captivity, which suggests that birds became less resilient to stress over time. The greater the decrease in dopamine receptors, the more they exhibited anxiety-related behaviors such as feather-ruffling. All of the wild birds also decreased body mass.
“These physiological, neurobiological and behavioral changes suggest that songbirds are not able to habituate to captivity, at least over short periods of time. It is very important that scientists studying stress in wildlife find more ways to study them in their natural habitat,” Lattin said.
This research complies with all existing laws and regulations and the Ornithological Council’s Guidelines for the Use of Wild Birds in Research.
In vivo imaging of D2 receptors and corticosteroids predict behavioural responses to captivity stress in a wild bird
Individual physiological variation may underlie individual differences in behavior in response to stressors. This study tested the hypothesis that individual variation in dopamine and corticosteroid physiology in wild house sparrows (Passer domesticus, n = 15) would significantly predict behavior and weight loss in response to a long-term stressor, captivity. We found that individuals that coped better with captivity (fewer anxiety-related behaviors, more time spent feeding, higher body mass) had lower baseline and higher stress-induced corticosteroid titres at capture. Birds with higher striatal D2 receptor binding (examined using positron emission tomography (PET) with 11C-raclopride 24 h post-capture) spent more time feeding in captivity, but weighed less, than birds with lower D2 receptor binding. In the subset of individuals imaged a second time, D2 receptor binding decreased in captivity in moulting birds, and larger D2 decreases were associated with increased anxiety behaviors 2 and 4 weeks post-capture. This suggests changes in dopaminergic systems could be one physiological mechanism underlying negative behavioral effects of chronic stress. Non-invasive technologies like PET have the potential to transform our understanding of links between individual variation in physiology and behavior and elucidate which neuroendocrine phenotypes predict stress resilience, a question with important implications for both humans and wildlife.