Bending the lamprey spinal cord causes a slowly-decaying increase in the frequency of fictive swimming.
It is well known that rhythmic lateral bending of the isolated lamprey spinal cord/notochord can entrain the central pattern generator (CPG) for locomotion. During entrainment, the CPG's frequency is equal to the bending frequency. We report here that bending can also have a slowly-decaying excitatory effect on the CPG's frequency. Experiments were performed in which the caudal end of a 30-50 segment piece of spinal cord/notochord was repeatedly rhythmically bent for 0.5-12 cycles. A slowly-decaying excitation was said to be present if after the termination of bending the CPG's frequency was significantly greater than baseline and decayed back to baseline with a time constant of one or more cycles. In 14 of 16 animals, a slowly-decaying excitation could be evoked by bending. In five of the nine animals tested, this slowly-decaying excitation could be evoked with bending frequencies both faster and slower than the baseline frequency. Depending on the animal, the slowly-decaying excitation could be elicited by as little as one-half cycle of bending and by bending amplitudes as small as 6-21 degrees peak deflection. We interpret these data as evidence of a second effect of bending distinct from the phase-dependent effect that produces entrainment.
Kiemel
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Department of Biology, University of Maryland, College Park, MD 20742, USA. kiemel@glue.umd.edu
Cohen
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AH
D000818:Animals; D007798:Lampreys / Q000502:physiology*; D009672:Notochord / Q000502:physiology; D010507:Periodicity; D013116:Spinal Cord / Q000502:physiology*; D013314:Stress, Mechanical; D013550:Swimming / Q000502:physiology*