Meeting Abstract

S1.6  Tuesday, Jan. 4  Flexibility in the patterning and control of axial locomotor networks in lamprey BUCHANAN, J.T.; Marquette Univ james.buchanan@marquette.edu

In lower vertebrates, locomotor burst generators for axial muscles generally produce unitary bursts that alternate between the two sides of the body. In lamprey, a lower vertebrate fish, locomotor activity in the axial ventral roots of the isolated spinal cord can exhibit flexibility in the timings of bursts to dorsally-located myotomes versus ventrally-located myotomes. These episodes of decreased synchrony can occur spontaneously, especially in the rostral spinal cord where the propagating body waves of swimming originate. Application of serotonin, an endogenous spinal neurotransmitter known to presynaptically inhibit excitatory synapses in lamprey, can promote decreased synchrony of dorsal-ventral bursting. These observations suggest the possible existence of dorsal and ventral locomotor networks with modifiable coupling strength. Intracellular recordings of motoneurons during locomotor activity provide some support for this model. Pairs of motoneurons innervating myotomes of similar ipsilateral dorsoventral location tend to have higher correlations of fast synaptic activity during fictive locomotion than do pairs of motoneurons innervating myotomes of different ipsilateral dorsoventral locations, suggesting their control by different premotor interneuron populations. Further, these different motoneuron pools receive different patterns of excitatory and inhibitory synaptic inputs from individual reticulospinal neurons, conveyed in part by different sets of premotor interneurons. Perhaps, then, the lamprey locomotor networks are not simply unitary burst generators on each side of the cord, but may exist as coupled burst generators, each associated with pools of motoneurons innervating different dorsoventral myotomal levels. The coupling strength between these networks may be modifiable, perhaps weakening when greater maneuverability is required.