New research identifies neural sequence for odor navigation in worms
· News-MedicalSteven Flavell, study senior author, associate professor in The Picower Institute and MIT's Department of Brain and Cognitive Sciences and investigator of the Howard Hughes Medical InstituteAcross the animal kingdom, there are just so many remarkable behaviors. With modern neuroscience tools, we are finally gaining the ability to map their mechanistic underpinnings."
Seeing the sequence
To do the research, Kramer put worms in dishes with spots of odors they'd either want to navigate toward or slither away from. With the lab's custom microscopes and software, she and her co-authors could track how the worms navigated and all the electrical activity of more than 100 neurons in their brains during those behaviors (the worms only have 302 neurons total).
The surveillance enabled Kramer, Flavell and their colleagues to observe that the worms weren't just ambling randomly until they happened to get where they'd want to be. Instead, the worms would execute turns with advantageous timing and at well-chosen angles. The worms seemed to know what they were doing as they navigated along the gradients of the odors.
Inside their heads, patterns of electrical activity among a cohort of 10 neurons (indicated by flashing green light tied to the flux of calcium ions in the cells), revealed the sequence of neural activation that enabled the worms to execute these sensible sensory-guided motions: forward, then into reverse, then into the turn, and then back to forward. Particular neurons guided each of these steps, including detecting the odors, planning the turn, switching into reverse and then executing the turns.
A couple of neurons stood out as key gears in the sequence. A neuron called SAA proved pivotal for integrating odor detection with planning movement, as its activity predicted the direction of the eventual turn. Several neurons were flexible enough to show different activity patterns depending on factors such as where the odors were and whether the worm was moving forward or in reverse.
And if the neurons are indeed turning and shifting gears, then the neuromodulator tyramine (the worm analog of norepinephrine) was the signal essential to switch their gears. After the worms started moving in reverse, tyramine from the neuron RIM enabled other neurons in the sequence to change their activity appropriately to execute the turns. In several experiments, the scientists knocked out RIM tyramine and saw that the navigation behaviors and the sequence of neural activity largely fell apart.
"The neuromodulator tyramine plays a central role in organizing these sequential brain activity patterns," Flavell says.
In addition to Flavell and Kramer, the paper's other authors are Flossie Wan, Sara Pugliese, Adam Atanas, Sreeparna Pradhan, Alex Hiser, Lillie Godinez, Jinyue Luo, Eric Bueno and Thomas Felt.
A MathWorks Science Fellowship, the National Institutes of Health, the National Science Foundation, The McKnight Foundation, The Alfred P. Sloan Foundation, the Freedom Together Foundation, and HHMI provided funding to support the work.
Source:
Journal reference: