Knowing that whole-body exposure to high-frequency ultrasound increases human brain activity, they used rats — which enjoy high-frequency ultrasound vocalizations (USV) — to explore ultrasonic effects on the mechanisms underlying depression.
Researchers used rats, including some without olfactory lobes (organs that regulate neurotransmission), to study agitation and anxiety-like behavior. with and without exposure to USV for 24 hours. Olfactory bulbectomized (OB) rats were used because they experience changes in neurotransmitters, endocrine secretions and behavior similar to humans with depression.
“Since studies on ultrasound exposure have been primarily conducted on human subjects, we needed to establish robust animal models to elucidate underlying mechanisms using invasive techniques,” Tokyo University of Science Professor Akiyoshi Saitoh said in a news release. “In our current study, we have used OB rats to study the effects of ultrasound on neural activity and behavior.”
First, they compared wild rats and OB rats to see how they responded to being attacked, being startled, presented with a struggle and initiating a fight.
Then, the researchers monitored levels of a hormone that is released in response to stress, plasma corticosterone, in blood samples and used a maze to trigger anxiety.
The researchers found that the OB rats that had been exposed to USV had significantly less hyperemotionality and lower plasma corticosterone levels than rats that had not been exposed to USV. They also found that USV-exposed rats seemed to have less anxiety in the maze after the ultrasound exposure.
The researchers said their study, published in NeuroReport, is the first of its kind that demonstrates potential anti-depressant effects of ultrasound exposure in rats.
“Unlike drug therapy, ultrasound exposure is non-invasive and easy to use,” Saitoh said. “An ultrasound-based therapeutic device may therefore aid the treatment and prevention of mental disorders in patients while they go about their daily lives.“