With only 32 of its 302 nerves dedicated to detecting the odors that drift through its world, the lowly roundworm seems hard pressed to smell food, let alone discriminate friend from foe. But researchers have discovered a unique system of overlapping sensors that enables the creature to tell smells apart.
The system seems well designed for the nerve-challenged worm. In mice and humans, each of millions of odor sensing nerves has only one type of odor detecting receptor, allowing the brain to distinguish between odors by tracking which nerve did the sensing. But in a compromise between the need to detect many odors and the scarcity of available nerves, the roundworm's odor sensing neurons are studded with receptors for different odors. It has been a biological puzzle how a nerve that senses many odors can distinguish between them.
Scientists at the University of California, San Francisco uncovered a clever combination strategy in the worm's odor sensing nerves. Paired nerves, they found, have receptors tuned to some of the same odors, yet each member of the pair also supports receptors tuned to unique odors not detected by the partner.
With this partially overlapping detection system, the nerve pairs can sense more odors than would be possible if they had identical receptors or even if each were tuned to completely different smells, the scientists found. More importantly, the combinatorial approach allows the nerve pairs to discriminate between different odors, a lifesaving trait if the worm has to find one source of food in a bewildering array of aromas.
"The worm can solve amazingly complex sensory problems with few olfactory nerves," said senior investigator of the study, Cornelia I. Bargmann, PhD, an investigator in the Howard Hughes Medical Institute and professor and vice chair of anatomy at UCSF.
"Each nerve cell has a private window into the world of smells and a shared window with its partner. Any one nerve c
Contact: Wallace Ravven
University of California - San Francisco