Thoracic leg motoneurons in the isolated CNS of adult Manduca produce patterned activity in response to pilocarpine,which is distinct from that produced in larvae |
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Authors: | Johnston Rebecca M Levine Richard B |
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Institution: | (1) Division of Neurobiology, Room 611 Gould Simpson Building, University of Arizona, Tucson AZ 85721, USA,;(2) Department of Physiology, University of Arizona, Tucson AZ 85721-0077, USA, |
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Abstract: | In the hawkmoth, Manduca sexta, thoracic leg motoneurons survive the degeneration of the larval leg muscles to innervate new muscles of the adult legs.
The same motoneurons, therefore, participate in the very different modes of terrestrial locomotion that are used by larvae
(crawling) and adults (walking). Consequently, changes in locomotor behavior may reflect changes in both the CNS and periphery.
The present study was undertaken to determine whether motor patterns produced by the isolated CNS of adult Manduca, in the absence of sensory feedback, would resemble adult specific patterns of coordination. Pilocarpine, which evokes a
fictive crawling motor pattern from the isolated larval CNS, also evoked robust patterned activity from leg motoneurons in
the isolated adult CNS. As in the larva, levator and depressor motoneurons innervating the same leg were active in antiphase.
Unlike fictive crawling, however, bursts of activity in levator or depressor motoneurons of one leg alternated with bursts
in the homologous motoneurons innervating the opposite leg of the same segment and the leg on the same side in the adjacent
segment. The most common mode of intersegmental activity generated by the isolated adult CNS resembled an alternating tripod
gait, which is displayed, albeit infrequently, during walking in intact adult Manduca. A detailed analysis revealed specific differences between the patterned motor activity that is evoked from the isolated
adult CNS and activity patterns observed during walking in intact animals, perhaps indicating an important role for sensory
feedback. Nevertheless, the basic similarity to adult walking and clear distinctions from the larval fictive crawling pattern
suggest that changes within the CNS contribute to alterations in locomotor activity during metamorphosis.
Electronic Publication |
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Keywords: | Insect Locomotion Crawling Walking Metamorphosis |
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