Localization of the site of effect of a wasp's venom in the cockroach escape circuitry |
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Authors: | F Libersat G Haspel J Casagrand K Fouad |
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Institution: | (1) Department of Life Sciences, The Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel, IL |
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Abstract: | The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward the head ganglia (the brain and subesophageal ganglion). In the present study, our aim was to identify
the head ganglion that is the target of the venom and the mechanisms by which the venom blocks the thoracic portion of the
escape neuronal circuitry. Because the escape responses elicited by a wind stimulus in brainless and sham-operated animals
were similar, we propose that the venom effect is on the subesophageal ganglion. Apparently, the subesophageal ganglion modulates
the thoracic portion of the escape circuit. Recordings of thoracic interneuron responses to the input from the abdominal giant
interneurons showed that the thoracic interneurons receive synaptic drive from these interneurons in control and in stung
animals. Unlike normal cockroaches, which use both fast and slow motoneurons for producing rapid escape movements, stung animals
activate only the slow motoneuron. However, we show that in stung animals, the fast motoneuron still can be recruited with
bath application of pilocarpine, a muscarinic agonist. These results indicate that the descending control from the subesophageal
ganglion is presumably exerted on the premotor thoracic interneurons to motoneurons connection of the thoracic escape circuitry.
Accepted: 19 December 1998 |
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Keywords: | Insects Venom Thoracic interneurons Wasp Subesophageal ganglion |
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