Study shows that a single neuron’s parallel outputs can coordinate many aspects of behavior

A new MIT study funded by the U.S. National Science Foundation focuses on a single cell in one of nature’s simplest nervous systems. It provides an in-depth illustration of how individual neurons can use multiple means to drive complex behaviors.

In the C. elegans worm, which only has 302 nerve cells, a single neuron named HSN uses multiple chemicals and connections to orchestrate egg-laying and locomotion over the course of several minutes. 

HSN releases several chemicals and makes multiple connections along its length, not only to control egg-laying and locomotion, but to then slow down the worm for several minutes after the eggs are laid. For the latter phase of this behavior, HSN transfers the neurotransmitter serotonin to a fellow neuron, which re-releases the neurotransmitter to influence behavior minutes later.

"Our results reveal that a single neuron can influence many behaviors over multiple timescales and show that neurons can 'borrow' serotonin from one another to control behavior," the researchers write in Current Biology. The study’s senior author is Steven Flavell.

How this single neuron has seemingly paradoxical effects on behavior, the speeding up for egg-laying, then slowing down afterward, was a mystery. Flavell’s team discovered that HSN uses parallel neurotransmitter outputs in different ways to control the animal’s behavior.

"The finding that neurons can take up and re-release serotonin produced by other neurons to control behavior reveals a novel feature of serotonin signaling that could have important medical implications," Flavell said. The molecule that takes up serotonin, SERT/MOD-5, is the target of serotonin-specific re-uptake inhibitors (SSRIs) like Prozac. This study raises the possibility that SSRIs may influence how neurons share serotonin with each other, which could be relevant for their mode of action in treating psychiatric disorders.