The Journal of Neuroscience, November 15, 2002, 22(22):9997-10008
Synchronization of Motor Neurons during Locomotion in the
Neonatal Rat: Predictors and Mechanisms
Matthew C.
Tresch and
Ole
Kiehn
Department of Neuroscience, Karolinska Institutet, 17177 Stockholm,
Sweden
We describe here the robust synchronization of motor neurons at a
millisecond time scale during locomotor activity in the neonatal rat.
Action potential activity of motor neuron pairs was recorded
extracellularly using tetrodes during locomotor activity in the
in vitro neonatal rat spinal cord. Approximately 40% of motor neuron pairs recorded in the same spinal segment showed significant synchronization, with the duration of the central peak in
cross-correlograms between motor neurons typically ranging between
~30 and 100 msec. The percentage of synchronized motor neuron pairs
was considerably higher for pairs with similar locomotor-related activity and strong rhythmic modulation. We also found synchronization between the activities of different motor pools, even if located several segments apart. Such distant synchronization was abolished in
the absence of chemical synapses, although local coupling between motor
neurons persisted. On the other hand, both local and distant coupling
between motor neurons were preserved after antagonism of gap junction
coupling between motor neurons. These results demonstrate that motor
neuron activity is strongly synchronized at a millisecond time scale
during the production of locomotor activity in the neonatal rat. These
results also demonstrate that chemical synaptic inputs, in addition to
electrical synapses, contribute to this synchronization, suggesting the
existence of multiple mechanisms underlying motor neuron
synchronization in the neonatal rat. The fast synchronization described
here might be involved in activity-dependent processes during
development or in the coordination of individual motor neurons into a
functional population underlying behavior.
Key words:
motor neuron; synchronization; gap junction; locomotion; development; pattern generation
Copyright © 2002 Society for Neuroscience 0270-6474/02/22229997-12$05.00/0
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