Reproduction is one of the most important activities of all animal species, Wagenaar notes, but in leeches, as in other sexually reproducing species, it has proven difficult to understand how this critical behavior is produced by activity in the nervous system.
"Few animals will execute reproductive behaviors while they are being subjected to neurobiological recording methods," Wagenaar says.
Wagenaar and his colleagues got around the relative reticence of the leeches by injecting them with a type of hormone found in a wide variety of animals. In humans and in other mammals, two versions of this hormonevasopressin and oxytocinplay a powerful role in reproductive physiology and pair-bonding. Leeches also produce a member of this hormone family, called hirudotocin. The groups at UCSD and Caltech discovered that the hormone plays a role in normal leech mating behavior.
Within minutes after a leech has received an injection of hirudotocin, it displays a variety of courtship behaviors, even if it is alone in a container. During courtship, leeches open their mouths wide and explore the bodies of potential partners by running the mouth along the skin, while also twisting their bodies like a corkscrew. These behaviors were known to be elicited by hirudotocin and other closely related members of the vasopressin molecular family.
"Hirudotocin is produced by the leech, but under ordinary conditions it may be present in very small quantities," Wagenaar says. "By injecting a relatively large quantity of the hormone, we may, in a sense, overwhelm the system. Whereas small doses only increase the tendency toward the behavior, allowing other cues to override it (as in the natural case), larger doses make this tendency so strong that nothing else can get in the way."
Using progressively more reduced leech preparationsthat is, smaller and smaller pieces of a leechthe scientists identified the part of its central
|Contact: Kathy Svitil|
California Institute of Technology