In order to ultimately treat neurological disorders, we must first understand how the nervous system controls normal behavior. Among the functions that any central nervous system must control are orientation movements. These include directed movements of the animal or its limbs toward or away from specific targets. Investigation of several orientation systems have shown that the control of such movements resides in relatively large populations of interneurons. Although much can be accomplished by investigating the population as a whole, at some point one must recognize the potential of each individual neuron to contribute unique properties to the system. To address these properties, one must utilize systems in which control resides in neurons that can be identified as unique individuals from animal to animal. The cockroach escape system provides just such a system. The studies described in this proposal will attempt to ask how information on wind direction is interpreted by control interneurons in the context of ever changing external and internal environmental conditions. They take advantage of years of work that have described the basic pathway of the escape system from sensory structures and wind sensitive giant interneurons through at least two populations of control interneurons to the ultimate motor neurons and leg muscles. At each level individual neurons can be identified as individuals based upon unique morphological properties. The motor neurons responsible for specific leg movements associated with escape turns will be identified. Connections will then be identified between specific thoracic interneurons and motor neurons. The pattern of connections will indicate the form of organization that is responsible for the wind evoked turn in a static environment. Modulation will then be investigated by determining the role of additional sensory cues in modifying the turn. These will include both external cues (e.g. light and sound) and internal information on the animal's limb position at the time of stimulation. The effect of substances that are known to modulate neuronal connections will also be investigated at specific critical synapses within the pathway. Techniques that will be employed include intracellular recording and dye injection from pairs of neurons to establish specific connections between identified neurons, test of effects of neuromodulatory substances at synapses and behavioral observation of the turn utilizing a high speed video system. All of these techniques are used routinely in our laboratory. The results of these investigations will provide principles that we hope can be applied generally throughout the animal kingdom to explain how individual neurons within populations process directional information in the context of other environmental conditions.
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