Neuroscience: As the worm turns.
By Stephen S. Hall.
With the help of a tiny worm, Cornelia Bargmann is unpicking the neural circuits that drive eating, socializing and sex.
Male sexual dysfunction is never pretty, even in nematodes. In normal roundworm courtship, a slender male will sidle up to a plump hermaphrodite, make contact, and then initiate a set of steps leading up to insemination: a sinuous backwards motion as he searches for the sexual cleft, a pause to probe, and finally the transfer of sperm. The whole business is usually over in a couple of minutes. “It’s very slithery, and affectionate,” says Cornelia Bargmann, who has been observing the behaviour of this particular worm, Caenorhabditis elegans, for 25 years.
Last October, scientists in Bargmann’s laboratory at the Rockefeller University, New York, reported the discovery of a gene that seems to be crucial to successful mating. Disrupting the action of this gene causes male sexual confusion of almost epic pathos: nematodes with certain mutations poke tentatively at an inert hermaphrodite, making confused, fruitless curlicues around the potential mate. Occasionally the mutant male succeeds, but often he literally falls off the job and begins the search anew for a mate. Jennifer Garrison, a postdoc of Bargmann’s who tracked the behaviour of these males, just shakes her head as she replays the scene on her computer screen. “Really sad,” she says.
There are two punchlines to this story of thwarted invertebrate mating. One is the charming squeamishness with which Bargmann describes it, hesitating at words such as “vulva” and “spicule” and other anatomical gewgaws of roundworm reproduction. “As a well-brought-up Southern girl,” she says with a laugh, “it’s still difficult to talk about this!”
The other is scientific, supporting Bargmann’s long-standing conviction that studying these deaf, part-blind, transparent creatures, which resemble nothing so much as wriggling specks of lint, could nonetheless yield enormous insight into how a nervous system creates behaviour. Since the 1980s, Bargmann and her colleagues have systematically explained the means by which worms taste and smell, exhibit social behaviours such as feeding in groups and explore their surroundings. She and her colleagues have parsed these behaviours down to the genes and circuitry of the neural connections that drive them. Just as studies of the fruitfly laid bare the basic principles of development and studies of yeast revealed the rules of the cell cycle, Bargmann believes that the simple nematode is revealing basic secrets about how animal nervous systems — including those of humans — translate sensory information into fundamental behaviours. “What are the most basic behaviours that every animal has to show and every animal has to solve?” she asks. “You can basically say that the three would be hunger, fear and reproduction. None of those things got invented last Saturday night!” […]
Understanding the mechanics of the roundworm’s simple nervous system, says Bargmann, “may be the only chance we have of figuring out a more complex system. I’m open to the possibility that the logic is different in other animals. I just see no evidence that, at a deep level, it’s true.