- Scientists expose rats to others being bullied by big rats
- Bystanders developed symptoms of depression, including social withdrawal and an inability to experience pleasure
- New neurons in the region of the hippocampus associated with memory and sensory perception fail to survive
- Normal mental function and neurogenesis returned when rats were given Prozac, but some had to return weeks later
New research from Japan suggests that rats are empathetic and can become depressed when they see other rodents being bullied.
A team from the Tokyo University of Science believes that exposure to protracted stress leads to a degeneration of neurons in the hippocampus, which they see as an important factor in depression.
Scientists said this so-called ‘second-hand’ depression may provide insight into how humans develop and treat mental health issues.
“I want people to think about how stress can change not only the minds of people with depression, but ours — those who see us,” said lead author Akiyoshi Saitoh, professor of pharmacology. Vice told.
Mice made to watch other rodents developed symptoms of depression, including social withdrawal and an inability to experience pleasure.
The researchers decided to look at how stress affected neurogenesis in the hippocampus, a small but complex brain structure that sits beneath each temporal lobe and is associated with learning, emotion and memory.
Saitoh said, ‘We decided to focus on possible mechanisms of psychological stress in adult hippocampal neurogenesis, to understand its role in depressive disorders. said in a release.
Neurogenesis is the process by which new neurons are formed in the brain.
Saitoh and his colleague’s research exposed mice to a form of ‘chronic vicarious social defeat stress’, which helped them repeatedly overcome another mouse.
They put two rats in a cage, one larger than the other, and pushed the smaller one into the larger rodent’s territory.
In the brains of spectator rats, there was a decrease in the survival rate of new neurons in the dentate gyrus, a region of the hippocampus related to memory and sensory perception. The authors believe the fall contributed greatly to his depression.
The larger mouse would aggressively defend its location, but it wasn’t the smaller mouse the team was interested in: It was a third mouse, safe in its cage, watching the whole ordeal.
Even though they were not at risk, the spectator rats developed depressive symptoms.
After 10 days, they displayed signs of anhedonia, or the inability to experience pleasure – a major symptom of depression in humans.
‘If you give rats the choice to drink sweetened or regular water, they will almost always go for the sweetened drink because it is more pleasant,’ Saitoh said vice. ‘But the rat that saw the social defeat was not,’ he said, indicating a decreased desire for pleasure.
The study was recently published in the journal behavioral brain research.
Saitoh described witnesses as ‘almost like hikikomori’, young adults in Japan who become so isolated in their parents’ homes that they are unable to work or go to school.
“They weren’t interested in other rats, which is unusual, because rats are sociable creatures,” he said.
There was also a physiological change: the spectator rats had a decreased survival rate of new neurons in the dentate gyrus, a region of the hippocampus related to memory and sensory perception.
The authors believe that the fall contributed greatly to his depression.
Neuron survival rates improved after viewers were given the antidepressant fluoxetine, a selective serotonin reuptake inhibitor, commonly known as Prozac.
But he didn’t make a ‘sudden, full recovery,’ Saitoh said. In fact, for some, symptoms returned weeks later.
He said it is important to understand how depression in humans is not treated quickly.
Co-author Toshinori Yoshioka said in the release that the team believes the experiment will play an important role in ‘clarifying the pathophysiology of depression and the development of a corresponding novel drug.’
The dentate gyrus is one of only a few brain organs where neuron growth continues into adulthood for many mammals, including rats and primates.