Applying electric shock to a 1 mm long roundworm sounds difficult to explain, but scientists at Nagoya City University have used this special stimulus to discover some strange behaviors of Caenorhabditis elegans. These behaviors can further deepen our understanding of human emotional mechanisms and then treat diseases.
Caenorhabditis elegans has been a major subject of research for human medicine and therapeutics (such as studying anti-aging mechanisms) because they share genes and other surprising biological commonalities.
In this study, C. elegans was electrically stimulated and began to move away from the stimulus at high speeds. While this is not unusual, as most animals instinctively flee from perceived danger, these worms continued to "run" for one to two minutes after stimulation stopped. In most animals, the abnormal behavior ceases once stimulation ceases.
"We unexpectedly found that the high-speed responses of C. elegans persisted after electric shock," the researchers noted.
The researchers believe the worms' behavior suggests a unique mechanism at work that resembles a primitive emotional response. Corroborating this, the worms also ignored their usual food priority, bacteria, in favor of what they deemed more important for survival. Because they also use food sources to read environmental information critical to their survival, this is an unexpected change from primitive, instinctive behavior.
"The fact that they did not respond to food during and after our electrical stimulation may also be evidence that electrically induced emotional states influence responses to food, which is a completely different stimulus," the researchers note. "Taken together, these results may suggest that the animals' response to electrical shock represents an emotion, perhaps similar to fear."
Not all worms behave the same. Genetic analysis shows that some animals, with mutations in certain genes, are unable to produce neuropeptides, which are similar to human hormones. In these worms, running behavior lasts much longer than in other animals.
This longer-lasting "fear" response gives scientists clues about how big a role genetics may play in emotion regulation -- both in the well-studied worm C. elegans and in humans.
Emotional responses to stimuli may not be naturally attenuated but may be attenuated by genetic mechanisms that control their activity. Researchers believe there may be new genes that regulate emotional responses, providing new ways to treat diseases such as depression and anxiety.
Previous studies of the neurosensory behavior of these tiny worms have examined their processing abilities, and another study also noted their aversive behavior in response to thermal stimuli.
The latest research is published in the journal Genetics.