James D. Angstadt, Ph.D. - US grants

This project introduces a laboratory component to an existing Neurobiology course and adds computer capability to promote independent student projects in a current Animal Physiology course. The equipment added includes Macintosh IIsi computers, a data acquisition and analysis system (MacLab), and supporting hardware and software. The Neurobiology course focuses on the medicinal leech and covers such techniques as intracellular recording with microelectrodes, voltage clamp measurements of ionic currents, and computer-assisted data acquisition and analysis. Equipment includes anti-vibration tabletops, Leitz and Huxley micromanipulator, A-M Systems intracellular amplifiers, an Axoclamp voltage clamp amplifier, and a Flaming- Brown microelectrode puller. In both laboratories students, working in teams of three, first learn a basic technique or principle and then formulate and test their own related hypothesis either by designing a mini-independent research project or redesigning the parameters for the basic laboratory.

The basic patterns of rhythmic motor behavior are generated by central nervous system circuits called neural oscillators. The oscillatory activity under investigation in this study, induced by suppression of calcium currents, is unusual in that it depends on sodium currents (rather than calcium currents as observed in other animals) and because the oscillations occur synchronously in all neurons of the same invertebrate nervous systems. These novel features will allow several questions of broad significance to be addressed. First, what cellular mechanisms generate these sodium-dependent oscillations and why are sodium-dependent oscillators so rare compared to calcium-dependent oscillators? Second, what cellular mechanisms are used to synchronize oscillatory activity within neural networks? To answer these questions, Dr. Angstadt will 1) develop an isolated neuron preparation that expresses oscillatory activity similar to that observed in intact ganglia, 2) identify and characterize the role of persistent ionic currents in generating the oscillations, and 3) determine the cellular mechanisms responsible for synchronizing the oscillations in different neurons. His approach will be to remove identified neurons from invertebrate ganglia, isolate these neurons in cell culture, and study their ionic currents using voltage clamp techniques. In other experiments, mechanisms underlying synchronization of oscillations will be investigated in experiments on intact ganglia. These studies are important because they will further understanding of persistent sodium conductances in nerve cells, including their functional role in the generation of oscillatory activity, and may provide a model system for studies of cellular mechanisms underlying the synchronized neuronal activity associated with epileptic and other seizures in more complex nervous systems.

JAMES D. ANGSTADT - PROJECT SUMMARY

Ionic Conductances Underlying Serotonergic Modulation of Rhythmic Motor
Behavior

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.