RT Journal Article
SR Electronic
T1 Direct and Indirect Connections with Upper Limb Motoneurons from the Primate Reticulospinal Tract
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 4993
OP 4999
DO 10.1523/JNEUROSCI.3720-08.2009
VO 29
IS 15
A1 C. Nicholas Riddle
A1 Steve A. Edgley
A1 Stuart N. Baker
YR 2009
UL http://www.jneurosci.org/content/29/15/4993.abstract
AB Although the reticulospinal tract is a major descending motor pathway in mammals, its contribution to upper limb control in primates has received relatively little attention. Reticulospinal connections are widely assumed to be responsible for coordinated gross movements primarily of proximal muscles, whereas the corticospinal tract mediates fine movements, particularly of the hand. In this study, we used intracellular recording in anesthetized monkeys to examine the synaptic connections between the reticulospinal tract and antidromically identified cervical ventral horn motoneurons, focusing in particular on motoneurons projecting distally to wrist and digit muscles. We found that motoneurons receive monosynaptic and disynaptic reticulospinal inputs, including monosynaptic excitatory connections to motoneurons that innervate intrinsic hand muscles, a connection not previously known to exist. We show that excitatory reticulomotoneuronal connections are as common and as strong in hand motoneuron groups as in forearm or upper arm motoneurons. These data suggest that the primate reticulospinal system may form a parallel pathway to distal muscles, alongside the corticospinal tract. Reticulospinal neurons are therefore in a position to influence upper limb muscle activity after damage to the corticospinal system as may occur in stroke or spinal cord injury, and may be a target site for therapeutic interventions.