Because of its relative simplicity, the leech is one of only a handful of organisms in which it has been possible to trace a continuous neural pathway from sensory input to the muscles that generate the actual movements. One of the most important functions of the nervous system is to control rhythmic movements such as walking, swimming and flying. To survive, an animal must also be able to modify its behavior to meet the demands of a changing environment. In response to increasing hunger, for example, an animal may increase the probability that a given sensory stimulus, such as detection of potential prey, will lead to activation of behaviors that move the animal toward the prey. In Dr. Angstadt's new research project, the effects of the neurohormone serotonin on motor neurons controlling swimming behavior in the medicinal leech will be examined.
Hungry leeches have higher levels of serotonin in their blood and are more likely to swim.
However, it is not yet understood exactly how serotonin affects the neurons to change the probability of swimming. An explanation could, in the long run, lead to human health benefits. Angstadt, whose primary research interest is the question of how neural circuits generate and control rhythmic motor behavior, has been studying neurons in worms for nearly 20 years. First it was the nematode Ascaris, a large parasitic roundworm with three pairs of lips. The attachment continued when he came to Siena in 1991.