Meeting Abstract
23.1 Jan. 5 Variation in entrainment of fictive swimming in lampreys due to bending stimuli at successive longitudinal positions TYTELL, E.D.*; COHEN, A.H.; University of Maryland; University of Maryland tytell@umd.edu
In fishes, undulatory swimming is produced by sets of spinal interneurons constituting central pattern generators (CPGs). Coupling among successive oscillators in spinal cord produces in a consistent longitudinal phase lag that results in the traveling wave for swimming. Sensory input can modulate the wave; for example, bending the body entrains it to the stimulus frequency. Swimming bends the body along its entire length, but most previous studies of mechanical entrainment in fishes have examined bending at single points close to the spinal cord�s ends. It is not known whether different portions of the cord respond to bending stimuli differently. If they do, the variation may contribute to both hydrodynamic and mechanical performance. First, it may affect the final form and speed of the neural traveling wave, which in turn affects the body�s swimming wave, an important feature for hydrodynamic performance. It may also contribute to the phase lag between muscle activation and body bending. In many fishes, anterior muscle turns on during shortening, producing energy for locomotion, while posterior muscle is active during lengthening, absorbing energy and potentially reducing the mechanical performance. Entrainment by sinusoidal bending was examined at successive points along the spinal cord of fictively swimming lampreys while recording from ventral roots. A gradient in entrainment phase was observed. Caudal ventral root bursts occurred around the time of maximum stretch on the same side as the nerve, while central segments tended to burst later in the stimulus cycle, similar to the pattern observed in vivo. Entrainment was examined in spinal cord sections with different numbers of segments to determine how much of this gradient resulted from coupling among segments, in comparison to variation in responses to sensory stimuli.
