RUI: Ionic Conductances Underlying Serotonergic Modulation of Rhythmic Motor Behavior

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JAMES D. ANGSTADT - PROJECT SUMMARYIonic Conductances Underlying Serotonergic Modulation of Rhythmic MotorBehavior One of the most important functions of the nervous system is to control movement. Walking, swimming and flying are examples of rhythmic motor behaviors that consist of a relatively stereotyped pattern of muscle contractions. To survive, an animal must also be able to modify its motor and other behaviors 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 motor behaviors that move the animal toward the prey. Thus, an important goal in neurobiology is to understand how the neural circuits underlying motor behavior are modified over time. One way that changes in circuit function are achieved in both invertebrate and vertebrate animals is to alter the electrical and synaptic properties of neurons with chemicals called neuromodulators. One of the most well studied neuromodulators of motor behavior is a chemical called serotonin. In this project, the effects of serotonin on motor neurons controlling swimming behavior in the medicinal leech will be examined. 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 pathway from sensory input to the rhythm-generating circuit and then out to the muscles that generate the actual movements. Hungry leeches have higher levels of serotonin in the blood surrounding their neurons and, as a result, are more likely to swim. Moreover, serotonin affects the electrical properties of several types of neurons found in the swim behavior pathway. However, it is not yet understood exactly how serotonin affects these neurons to cause the increased probability of swimming. This information will be obtained by measuring directly, under controlled conditions, the ionic currents in swim motor neurons of the leech before and after exposure to serotonin. After identifying those ionic currents modified by serotonin, the specific changes induced by this neuromodulator will be identified. Comparison of the resulting data with research on modulation of motor behaviors in a variety of invertebrate and vertebrate species will contribute to the elucidation of general principles underlying the control of motor behavior in all animals, including humans.