Scientists find just how discriminating a worm can be: Unique system of overlapping odor sensors ...( dor environment. They examined t...)

They examined the odor sensing abilities of a pair of olfactory neurons, known as AWC, which has been the focus of the Bargmann lab for ten years. Her research group has determined that this nerve pair not only senses at least five attractive odors, but can also distinguish between the odors.

The lab recently discovered that the two neurons, which had been thought to be identical left-right members of a pair, actually differ in one subtle, but critical respect. During the development of the nerves, an odor receptor known as STR-2 becomes active on one of the nerves but not on the other. Whether the receptor is expressed on the left or the right nerve is apparently random, they found.

Bargmann and Wes used standard techniques to search among mutant worms for those that were unable to detect the difference between benzaldehyde and butanone and then showed that these genetic mutants, known as ky542, possess an active STR-2 receptor on both members of the AWC neuron pair, unlike normal worms.

They further showed that they could induce this odor discrimination deficit in normal worms by killing one of the paired AWC cells with a laser beam. Either the mutant worms or the operated worms could sense both odors perfectly well, but with a change in one of the AWC neurons, discrimination was lost. The difference between detection and discrimination is the first step in higher processing in the senses, Bargmann said, and the experiment showed where that step occurs.

Only one of the paired AWC nerves, the one that expresses STR-2, responds to butanone, the scientists found, while both this neuron and its STR-2-silent partner can detect benzaldehyde. The nerve with the silenced STR-2 is required for discrimination between butanone and benzaldehyde, because it can smell benzaldehyde without sensing the confusing butanone odor. In turn, that silenced nerve senses a third odor, a buttery smell, that its partner can't det
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Contact: Wallace Ravven
wravven@pubaff.ucsf.edu
415-476-2557
University of California - San Francisco
4-Apr-2001