Many simple patterns of animal behavior are innate and species-specific, varying little between individuals of a species. Examples include rhythmic activities such as walking, swimming, flying, feeding, and respiratory activity. These activities appear to be generated by stored central motor programs, the expression of which results in stereotyped patterns of behavior. We are analyzing the actions of these central motor programs (or central pattern generators) as a convenient starting point for exploring the neural basis of more complex behavior. For example, we are studying feeding behavior and its neural basis, using neurobiological and behavioral techniques. We examine the substrates of "decisions" to start feeding, to continue feeding, and to stop feeding. These studies employ caterpillars because much of their feeding behavior is well known, they have very few, well identified taste receptor cells, and their central nervous system is accessible for manipulation and recording. We have developed preparations that allow analysis of feeding at varying degrees of isolation and simplification, from intact, behaving animals to isolated central ganglia.
Gordon A. Wyse
Gordon A. Wyse
Neurobiological Basis of Insect Feeding Behavior
and of Other Innate Behavior Patterns
Feeding behavior is influenced by sensory processes: initiation and maintenance of feeding is stimulated or inhibited by taste, and feeding termination is induced by sensory signals of fullness. Nevertheless, we have substantial evidence that the rhythmic activity of chewing is controlled by a central pattern generator, both in caterpillars and in the horseshoe crab Limulus. In caterpillars, ablation of antennae and maxillae removes all external gustatory and olfactory chemoreceptors, but the animals eat normal quantities of food in normal temporal patterns without the receptors.
Furthermore, we have shown that in caterpillars and especially in Limulus, isolated central nervous systems are sufficient to produce the appropriate pattern of motor output for feeding behavior. When octopamine is perfused into the isolated Limulus nervous system, it activates this feeding motor program; moreover, octopamine injections into intact animals induce feeding behavior. Octopamine in this case could be acting as a neurotransmitter, as a hormone, or as a local neuromodulator (i.e., acting at a distance and time course intermediate between that of a hormone and a transmitter).
We are exploring the actions of octopamine and other neuroactive agents on neurons and simple neural circuits, as well as attempting to determine the behavioral roles of these agents in feeding, in and in other behavior patterns. These studies employ techniques of electrophysiological recording, behavioral analysis, pharmacology, and anatomy of identified neurons (by dye fills and by immunohistochemistry).
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