Sex, smell, and appetite. (Endocrinology).

Does the smell of movie-theater popcorn send you dashing for a supersize bucket? Oddly enough, a study of sexual dysfunction in mutated mice may help explain such connections between smell and appetite.

The mice are genetically engineered to lack melanin-concentrating hormone, or MCH, which is made in the brain and is known to stimulate feeding. Mice with this mutation have little appetite and tend to be lean. During mice-breeding experiments, researchers at the Joslin Diabetes Center in Boston noted that it took about twice as long as normal for MCH-deficient mice to have litters, though they bred normally when crossed with unmutated mice.

So, Gabriella Segal-Lieberman and her colleagues videotaped the animals' sexual behavior. They found that female mice lacking MCH were less receptive to mating, and that male mice lacking MCH were less successful in their mounting behavior. These behaviors are linked to chemical cues called pheromones, Segal-Liebennan says.

When put into a cage containing one cotton swab dipped in water and another in female mouse urine, which is known to contain pheromones, normal males flock to the one with the urine. However, many of the mutant males didn't, Segal-Lieberman says. Her team has also found that mice lacking MCH are less sensitive to food odors. And that, Segal-Lieberman concludes, probably explains why these animals eat less than normal mice: Their food smells less appetizing.--D.C.