Modulation of the crayfish swimmeret rhythm by octopamine and the neuropeptide proctolin
B. Mulloney, L. D. Acevedo and A. G. Bradbury Department of Zoology, University of California, Davis 95616. 1. The swimmeret system can be excited by perfusing the neuropeptide proctolin through the isolated ventral nerve cord of the crayfish. Previously silent preparations begin to generate a chara...
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Veröffentlicht in: | Journal of neurophysiology 1987-09, Vol.58 (3), p.584-597 |
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Zusammenfassung: | B. Mulloney, L. D. Acevedo and A. G. Bradbury
Department of Zoology, University of California, Davis 95616.
1. The swimmeret system can be excited by perfusing the neuropeptide
proctolin through the isolated ventral nerve cord of the crayfish.
Previously silent preparations begin to generate a characteristic motor
pattern, the swimmeret rhythm, in the nerves that innervate the swimmerets.
The response to proctolin is dose dependent and reversible. The threshold
concentration of proctolin perfused through the ventral artery is
approximately 10(-8) M. The EC50 is 1.6 X 10(-6) M. 2. Proctolin-induced
motor patterns have periods and phases similar to those of spontaneously
generated motor patterns. The durations of the bursts of impulses in
power-stroke motor neurons generated in the presence of proctolin are,
however, significantly longer than those that occur during spontaneous
activity. 3. DL-Octopamine inhibits the swimmeret system, both when the
system is spontaneously active and when it has been excited by proctolin.
The inhibition by octopamine is dose dependent and reversible. The
threshold for inhibition is approximately 10(-6) M, and the EC50 is
approximately 5 X 10(-5) M. 4. Octopamine's effect is mimicked by its
agonists, synephrine and norepinephrine. Synephrine has a lower threshold
concentration than does octopamine, but norepinephrine is much less
effective than octopamine. 5. Octopamine's inhibition is partially blocked
by an antagonist, phentolamine. 6. Phentolamine also blocks inhibition of
the swimmeret system by inhibitory command interneurons. This block is dose
dependent and can be partially overcome by stimulating the command
interneurons at higher frequencies. 7. Perfusion with 11 other suspected
crustacean neurotransmitters and transmitter analogues did not similarly
excite or inhibit the swimmeret system, so we suggest that proctolin and
octopamine are transmitters used by the neurons that normally control
expression of the swimmeret rhythm. |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.1987.58.3.584 |