The transition from development to motor control function in the corticospinal system.
During early postnatal development, corticospinal (CS) system stimulation, electrical or transcranial magnetic, is minimally effective in producing muscle contraction, despite having axon terminals that excite spinal neurons. Later, after stimulation becomes more effective, the cortical motor representation develops, and movements the system controls in maturity are expressed. We determined whether development of temporal facilitation (response enhancement produced by the second of a pair of pyramidal tract stimuli, or a higher stimulus multiple of a train of stimuli) correlated with these changes. Facilitation of the monosynaptic CS response was larger in older kittens and adults than younger kittens. When facilitation was strong, strong motor responses were evoked by pyramidal stimulation with small currents and few pulses. With strong facilitation in older kittens, corticospinal axon varicosities colocalize synaptophysin like adults, suggesting a presynaptic mechanism. With effective facilitation, control signals from the cortex can be sufficiently effective to provoke muscle contraction for guiding movements.
Meng
Zhuo
Z
Center for Neurobiology and Behavior, Columbia University and New York State Psychiatric Institute, New York, New York 10032, USA.
Li
Qun
Q
Martin
John H
JH
D000200:Action Potentials / Q000502:physiology; D000367:Age Factors; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D009043:Motor Activity / Q000502:physiology*; D009044:Motor Cortex / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D009138:Musculocutaneous Nerve / Q000502:physiology; D017729:Presynaptic Terminals / Q000378:metabolism / Q000502:physiology; D011712:Pyramidal Tracts / Q000254:growth & development* / Q000502:physiology*; D013116:Spinal Cord / Q000254:growth & development / Q000502:physiology; D016708:Synaptophysin / Q000096:biosynthesis
D016708:Synaptophysin