Kovac&Davis1980 - JOURNALOF NEUROPHYSIOLOGY Vol. 43,...

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JOURNALOF NEUROPHYSIOLOGY Vol. 43, No. 2, February 1980. Printed in U.S.A. Neural Mechanism Underlying Behavioral Choice in Pleurobmzchaea MARK I? KOVAC AND W. J. DAVIS The Thimann Laboratories, University of California, Santa Crux, California 95064 SUMMARY AND CONCLUSIONS 1. Feeding behavior normally takes prec- edence over withdrawal from tactile stimula- tion in Pleurobranchaea ‘s behavioral hier- archy (2, 4), an adaptation that presumably prevents withdrawal from food. Here we analyze the neuronal interactions between the feeding and withdrawal motor systems in order to determine the neural mechanisms by which this instance of behavioral choice is mediated. 2. Evidence is presented that the with- drawal motor system is organized as a simple reflex in which primary sensory inputs activate a withdrawal-command interneuron, which in turn excites a population of with- drawal motoneurons. The data suggest that sensory inputs also directly activate the withdrawal motoneurons. A neuronal cor- relate of the withdrawal response can be evoked by electrical stimulation of the large oral veil nerve and recorded as a character- istic extracellular discharge from the small oral veil nerve. 3. Electrical activation of the feeding system by stomatogastric nerve stimula- tion (6) suppresses the electrically evoked withdrawal response in semi-intact prepara- tions and in isolated nervous systems. There- fore, the suppression occurs independently of sensory feedback and is mediated by central neurons. 4. A microelectrode survey of neurons in the feeding motor system revealed a reidentifiable pair of corollary discharge (CD) neurons in the buccal ganglion that is capable of suppressing the withdrawal re- sponse. Intracellular” analysis of these neurons showed that they are coactive with feeding and capable of fully suppressing withdrawal at physiological discharge fre- quencies. Silencing both CD neurons by hyperpolarization abolishes most of the suppression of withdrawal output during feeding output. Therefore, this pair of iden- tified neurons is both necessary and sufficient to account for most of the suppression of withdrawal during feeding. 5. Intracellular recording from putative withdrawal motoneurons while activating the withdrawal motor system revealed a train of large, unitary EPSPs from a presynaptic neuron, the “withdrawal-command neuron.” These EPSPs occur with the same time course as the withdrawal response, which they presumably underlie. EPSPs from this command neuron are abolished by activa- tion of the feeding system or by intra- cellular stimulation of the aforementioned CD neurons. 6. The data presented collectively suggest that feeding takes precedence over with- drawal in Pleurobranchaea’s behavioral hierarchy because the identified pair of CD neurons that is part of the feeding network inhibits the withdrawal-command
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This note was uploaded on 04/21/2008 for the course BIO 101 taught by Professor Pott-santone during the Spring '08 term at Northeastern.

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Kovac&Davis1980 - JOURNALOF NEUROPHYSIOLOGY Vol. 43,...

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