9514483 O'Gara The experiments described in this proposal will examine how the nervous system controls the feeding behavior of the medicinal leech. The physiological mechanisms used by the leech nervous system to control behavior are similar to those found in higher animals, including humans. The relative simplicity of the leech nervous system allows us to examine some of these physiological mechanisms in ways that are difficult or impossible in higher animals. An additional justification for studying feeding in the leech is the re- emergence of the use of leeches following plastic and reconstructive surgery. When an amputated part of the body (like a finger or an ear) is reattached, it is relatively easy for the surgeon to reattach the arteries in the affected body part. However, veins are more delicate and blood is more likely to clot in them. Because of these problems, blood within the reattached body part has no way to return to the rest of the body. Pressure builds up in the reattached part and blood flow stops. Without treatment, the tissue will die. When these problems occur, the surgeon can restore blood flow to the affected tissue using leeches. The leech will feed on the congested tissue and drain it of blood. In addition, the bite mark left by the leech will ooze blood for a number of hours. These two actions will allow new blood to flow into the reattached tissue and keep it alive. Efforts to mimic these actions artificially have been unsuccessful; thus, there is no substitute for the use of leeches in these situations. A better understanding of how leech feeding is controlled may allow doctors to more efficiently utilize leeches in this role. Nerve cells (called neurons) communicate with other neurons and muscle cells by releasing a chemical called a neurotransmitter. The neurotransmitter changes the behavior of the recipient neuron or causes a change in tension of a muscle cell. The neurotransmitter is sens ed by the recipient cell using protein molecules called receptors. Receptors for a particular neurotransmitter usually come in a number of varieties. The different receptors can be preferentially activated using specific drugs that resemble the neurotransmitter. Feeding behavior of the leech is dependent on the neurotransmitter serotonin. The experiments in this proposal will examine the effects of serotonin on the nervous system and muscle cells of the gut. In the first series of experiments, we will examine the effects of serotonin (and similar acting drugs) on biting behavior and blood consumption. By the use of specific drugs that activate only certain types of serotonin receptors, we will examine the role of the various receptors in feeding. We will also record the electrical activity of the muscles involved in feeding using very fine wires implanted in these muscles. These experiments will allow us to examine how serotonin turns on feeding behavior. In a second set of experiments we will examine the effects of serotonin-like drugs on the contractions of the leech pharynx after we have removed it from the body. The pharynx is the first part of the gut and actually generates the suction that draws blood from the victim. These experiments are designed to allow us to deduce what types of serotonin receptors are present on the muscles of the pharynx, and the role of each receptor type in controlling contractions of the pharynx. The last series of experiments will examine the effects of serotonin-like drugs on individual pharyngeal muscle cells. Using fine microelectrodes that are inserted into individual cells, we will examine the effects of these drugs on the muscle cell membrane. We will examine the effects of serotonin-like drugs on the permeability of the cell membrane to ions (charged atoms). The movement of ions across the cell membrane triggers the events that eventually lead to muscle contraction. These studies will a llow us to examine the role of various serotonin receptors in regulating muscle contraction at the level of the individual cell.
