Stress is warping these fish brains

It is well known that stress can have negative effects on animal brains, with social stress leading to an accumulation of oxidative stress. This imbalance between free radicals and antioxidants can result in various health issues, from cancer to neurological disorders to arthritis.

To understand how social stress transforms into oxidative stress, scientists are studying a social and hierarchical fish species called cichlids. The social hierarchy in cichlids seems to increase oxidative stress levels in the brains of low-status individuals, although caution is advised when comparing this to human experiences. The findings are outlined in a study published on November 26 in the journal Frontiers in Behavioral Neuroscience.

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“We found that low rank was generally associated with higher levels of oxidative stress in the brain,” stated study co-author and biologist Peter Dijkstra from Central Michigan University. “The patterns of oxidative stress in the brain are likely influenced by social experiences that modulate cellular processes in the brain.”

Cichlids comprise over 1,300 species and are primarily found in tropical regions of America, Africa, Madagascar, and Asia. These freshwater fishes exhibit a strict social hierarchy, with dominant males being larger, more aggressive, and more colorful than subordinate males. Due to their physiology and social structure, cichlids serve as a valuable model for studying the impact of social stress on oxidative stress levels in the brain.

In the study, researchers set up 15 large tanks divided into two sections. Each section contained six females and two males, allowing the fish to interact within their groups and visually with neighboring groups in transparent tanks. By introducing a territory for dominant males to defend, a hierarchy quickly formed within each group, remaining stable throughout the experiment.

The scientists conducted blood sampling, brain dissections, and measurements of gonad size relative to body size in male cichlids. Larger gonads indicate higher androgen levels in these fish. The researchers evaluated markers of oxidative stress and antioxidant capacity in different brain regions, aiming to understand the impact of social status on oxidative stress.

Low-status fish exhibited higher oxidative stress levels and lower antioxidant capacity compared to high-status fish. While high-status fish showed higher oxidative stress indicators in their blood, their brains appeared more protected. Reproductive activity, associated with high status, correlated with higher antioxidant levels and lower oxidative stress in the brain.

The team suggested a link between hormone levels and neuroprotection in the brain, with low-status fish having smaller gonads and lower hormone levels potentially impacting brain protection from oxidative stress. However, the effects of social status on oxidative stress proved to be complex, as different brain regions showed varied responses to social stress.

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Dijkstra emphasized that the observed patterns of oxidative stress in the brain may not necessarily be detrimental to the animals. Future studies may explore the fitness consequences of oxidative stress in the brain, shedding light on how social stressors contribute to oxidative stress and brain diseases.

It is crucial not to draw direct comparisons between cichlid society and human society. The cichlid hierarchy serves as a model system for understanding the impact of social stress on the brain in this specific species, requiring more focused studies to elucidate the relationship between social stress and oxidative stress in different brain regions.

“We have identified intriguing patterns across various brain regions,” Dijkstra stated. “The next step is to delve deeper into the regulation of oxidative stress and its modulation by social stress, necessitating further rigorous experimental investigations.”