Can we learn from a worm?

Notes from Planet Earth

The short answer is yes — most decidedly. In fact this worm, known as Caenorhabditis elegans has played an important role in biologic science since 1974. It was at that time that biologist Sydney Brenner first used this small round worm (nematode) as a research animal much as we have used inbred mice and fruit flies.

Since that date several scientists have won a Noble prize for their work with this tiny creature. The worm’s simple anatomy offers an opportunity to study many biologic processes that would be enormously difficult with higher organisms. Although only 1 mm long, it is, like humans, bilaterally symmetrical and most of its organs are analogous to those in mammals. The great majority of individuals are hermaphrodites (able to produce both sperm and eggs), while only one in 2000 is a male. When a male mates with a hermaphrodite the number of progeny is often more than 1,000, whereas self-fertilized hermaphrodites lay only about 300 eggs.

C. elegans, which normally feeds on bacteria, can survive being stored in liquid nitrogen (-196○C). Indeed, some even survived the Columbia Space Shuttle disaster in 2003 when these worms were on board to study their response to prolonged weightlessness. They have also proven to be useful in studying nicotine dependence, showing behaviors analogous to mammals when exposed to this drug. But one of the most valuable of its features is that it contains only about 1,000 cells and less than 400 neurons in its entire nervous system. Each nerve cell has now been fully mapped as to its connections with both other neurons and to its muscles and other organs. And the fate of each cell in the early embryo has been followed to its final position in the adult worm.

The first multicellular organism to have its genome fully sequenced, C. elegans contains many of the same genes controlling the same functions that are found in higher organisms. Recently it has been shown that these worms make two small proteins quite analogous to two important hormones we secrete from our pituitary gland. In mammals one of these peptides (vasopressin) acts on the kidney to control water balance and salt intake, while the other peptide (oxytocin) regulates sexual and reproductive behavior including maternal behavior, social cognition, and pair bonding. The two closely related peptides in C. elegans have been named “nematocin-1” and “nematocin-2” and nematocin-1 has been shown to play an important role in determining the behavior of males during mating. In its absence (in mutants) males are very inefficient in their approach to mating and mate less successfully than normal male worms. Additionally, mutants lacking these genes showed an inability to learn to avoid salt.

The subtle and complicated responses that nerve cells make to multiple inputs from other nerve cells or sensory organs and the resulting outputs to nerve cells controlling behavior are much more easily studied in these simple animals and will greatly help us understand how these complex nerve nets function in the brains of higher animals including ourselves.

Questions and suggestions from readers are welcomed and will be responded to in future editions of this column. Contact me at cwdingman2@frontier.com.

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