Have you ever wondered how social distancing and self-isolation can affect your brain? An international research team led by Erin Schumann of the Max Planck Institute for Brain Research has discovered a brain molecule that functions as a “thermometer” for the presence of other people in an animal’s environment. Zebras “sense” the presence of others through the mechanical sensation and movement of water – which includes brain hormone.
Changing social conditions can cause lasting changes in animal behavior. Social isolation, for example, can have devastating consequences for humans and other animals, including the zebra. However, the brain systems that perceive the social environment are not well understood. To study whether neuronal genes respond to dramatic changes in the social environment, graduate student Lucas Anesser and colleagues raise zebras either alone or with relatives for different periods of time. The researchers used RNA sequencing to measure the expression levels of thousands of neuronal genes.
Tracking social density
“We found a constant change in the expression of a handful of genes in fish raised in social isolation. One of them was the parathyroid hormone 2 (pth2), which encodes a relatively unknown peptide in the brain. but also their density. Surprisingly, when the zebrafish were isolated, pth2 disappeared into the brain, but its expression levels rose rapidly, similar to a thermometer reading when other fish were added to the tank, “explains Anneser.
Excited by this discovery, the scientists tested whether the effects of isolation could be reversed by placing previously isolated fish in a social environment. “After only 30 minutes of swimming with their relatives, there was a significant recovery in pth2 levels. After 12 hours with native pth2 levels, they were indistinguishable from those seen in socially raised animals,” says Anneser. “This really strong and rapid regulation was unexpected and showed a very close link between gene expression and the environment.”
So which sensory modality do animals use to detect others and cause changes in gene expression? “It turned out that the sensory modality that controls the expression of pth2 is not sight, taste or smell, but rather mechanization – they actually” feel “the physical movements of swimming neighboring fish,” explains Schumann.
Sensation of water movements
Fish perceive movement (“mechanical sensation”) in their immediate vicinity through a sensory organ called a lateral line. To test the role of mechanosensation in stimulating pth2 expression, the team mechanically ablated sensitive cells in the lateral line of the fish. In previously isolated animals, ablation of lateral line cells prevents the rescue of the neurohormone, which is usually caused by the presence of other fish.
Just as we humans are sensitive to touch, zebrafish seem to be specifically set up to swim other fish. Scientists have noticed changes in pth2 levels caused by the movement of water, which is caused by specific substances in the tank. “Zebra fish larvae swim in short bursts. We mimicked this water stimulation by programming an engine to create artificial movements of the fish. Interestingly, in previously isolated fish, artificial movements save pth2 levels just like real neighboring fish,” he explains. Anneser.
“Our data show a surprising role for a relatively unexplored neuropeptide, Pth2 – it monitors and responds to population density in the animal’s social environment. It is clear that the presence of others can have dramatic consequences for the animal’s access to resources and ultimate survival. in this way, it is likely that this neurohormone regulates social brain and behavioral networks, ”concludes Schumann.
Social experiences affect zebrafish from an early age
Lukas Anneser et al., The neuropeptide Pth2 dynamically senses others through a mechanical sensation, Nature (2020). DOI: 10.1038 / s41586-020-2988-z
Provided by the Max Planck Society
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