Reticulospinal neurons in the pontomedullary reticular formation of the monkey (Macaca fascicularis)

Department of Psychology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA.
Neuroscience (Impact Factor: 3.36). 08/2009; 163(4):1158-70. DOI: 10.1016/j.neuroscience.2009.07.036
Source: PubMed

ABSTRACT Recent neurophysiological studies indicate a role for reticulospinal neurons of the pontomedullary reticular formation (PMRF) in motor preparation and goal-directed reaching in the monkey. Although the macaque monkey is an important model for such investigations, little is known regarding the organization of the PMRF in the monkey. In the present study, we investigated the distribution of reticulospinal neurons in the macaque. Bilateral injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) were made into the cervical spinal cord. A wide band of retrogradely labeled cells was found in the gigantocellular reticular nucleus (Gi) and labeled cells continued rostrally into the caudal pontine reticular nucleus (PnC) and into the oral pontine reticular nucleus (PnO). Additional retrograde tracing studies following unilateral cervical spinal cord injections of cholera toxin subunit B revealed that there were more ipsilateral (60%) than contralateral (40%) projecting cells in Gi, while an approximately 50:50 ratio contralateral to ipsilateral split was found in PnC and more contralateral projections arose from PnO. Reticulospinal neurons in PMRF ranged widely in size from over 50 microm to under 25 microm across the major somatic axis. Labeled giant cells (soma diameters greater than 50 microm) comprised a small percentage of the neurons and were found in Gi, PnC and PnO. The present results define the origins of the reticulospinal system in the monkey and provide an important foundation for future investigations of the anatomy and physiology of this system in primates.

1 Follower
35 Reads
  • Source
    • "While the corticospinal tract offers the most direct access to the spinal cord, the corticobular pathway connecting through the reticular formation provides an alternative pathway (Lemon 2008). While the reticulospinal tract has well-established role in posture and locomotion (Deliagina et al. 2008; Honeycutt et al. 2009; Honeycutt and Nichols 2010; Mori 1987; Mori et al. 1989; Musienko et al. 2008; Schepens et al. 2008; Stapley and Drew 2009), new evidence expands this traditional view highlighting its role during voluntary movements like reaching (Buford and Davidson 2004; Davidson et al. 2007; Sakai et al. 2009). Although this type of task is known to also be mediated by corticospinal pathways, recordings from the reticular formation demonstrate that these cells are strongly modulated during reaching. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The reticulospinal tract was recently shown to have synaptic connections to the intrinsic muscles of the fingers in non-human primates, indicating it may contribute to hand function long thought to be controlled exclusively through corticospinal pathways. Our objective was to obtain evidence supporting the hypothesis that these same anatomical connections exist in humans. StartReact, an involuntary release of a planned movement via the startle reflex, provides a non-invasive means to examine the reticulospinal tract in humans. We found that startReact was triggered during coordinated grasp but not individuated finger movements. This result suggests that the reticulospinal tract does have connections to the intrinsic muscles of the fingers in humans but its functional role is limited to coordinated movement of the whole hand. These results do not diminish the well-established role of corticospinal pathways in the control of hand movement. Indeed, they cement the significance of corticospinal pathways in individuated finger movement control. Still, these results point to an updated and expanded view of distal hand control where reticulospinal and corticospinal pathways work in parallel to generate a large repertoire of diverse, coordinated movement in the hand. Finally, the presence of reticulospinal pathways to the muscles of the hand makes this pathway an attractive therapeutic target for clinical populations where the corticospinal tract is absent or injured.
    Journal of Neurophysiology 07/2013; 110(7). DOI:10.1152/jn.00866.2012 · 2.89 Impact Factor
  • Source
    • "The reticulospinal tract is a brain stem pathway that originates in the gigantocellular reticular nucleus (lateral/medullary reticulospinal tract) and caudal and oral pontine reticular nuclei (medial/ pontine reticulospinal tract) and descends in the brain stem both bilaterally and uncrossed, respectively (Kuypers 1964). Both tracts terminate in spinal gray matter bilaterally with minimal ipsilateral predominance (Sakai et al. 2009) across multiple spinal segments (Matsuyama et al. 1997). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The effect of reticular formation excitability on maximum voluntary torque (MVT) generation and associated muscle activation at the shoulder and elbow was investigated through natural elicitation (active head rotation) of the asymmetric tonic neck reflex (ATNR) in 26 individuals with stroke and 9 age-range-matched controls. Isometric MVT generation at the shoulder and elbow was quantified with the head rotated (face pointing) contralateral and ipsilateral to the paretic (stroke) and dominant (control) arm. Given the dominance of abnormal torque coupling of elbow flexion with shoulder abduction (flexion synergy) in stroke and well developed animal models demonstrating a linkage between reticular formation and ipsilateral elbow flexors and shoulder abductors, we hypothesized that constituent torques of flexion synergy, specifically elbow flexion and shoulder abduction, would increase with contralateral head rotation. The findings of this investigation support this hypothesis. Increases in MVT for 3 out of 4 flexion synergy constituents (elbow flexion, shoulder abduction, and shoulder external rotation) were observed during contralateral head rotation only in individuals with stroke. EMG data of the associated muscle co-activations were non-significant however are presented for consideration in light of a likely underpowered statistical design for this specific variable. This study provides evidence for not only the re-emergence of ATNR following stroke, but also indicates a common neuroanatomical link, namely an increased reliance on ipsilateral reticulospinal pathways, as the likely mechanism underlying the expression of both ATNR and flexion synergy that results in the loss of independent joint control.
    Journal of Neurophysiology 09/2012; 108(11). DOI:10.1152/jn.01030.2011 · 2.89 Impact Factor
  • Source
    • "They were targeted towards the PMRF using co - ordinates adapted from stereotaxic atlases of the macaque brain ( Smith et al . 1972 ; Martin & Bowden , 1996 ) and from the parasagittal templates provided by Sakai et al . ( 2009 ) . Electrodes were arranged in a 4 × 4 array ( 0 . 5 mm inter - electrode spacing ) . With this configuration , the recording microdrive and amplifiers were located caudal to the skull ( above the spinal column , with electrodes heading rostrally through the occiput ) , while the TMS coil was on the skull ' s dorsal surface over M1 . T"
    [Show abstract] [Hide abstract]
    ABSTRACT: Transcranial magnetic stimulation (TMS) of cerebral cortex is a popular technique for the non-invasive investigation of motor function. TMS is often assumed to influence spinal circuits solely via the corticospinal tract. We were interested in possible trans-synaptic effects of cortical TMS on the ponto-medullary reticular formation in the brainstem, which is the source of the reticulospinal tract and could also generate spinal motor output. We recorded from 210 single units in the reticular formation of three anaesthetized macaque monkeys whilst TMS was performed over primary motor cortex. Short latency responses were observed consistent with activation of a cortico-reticular pathway. However, we also demonstrated surprisingly powerful responses at longer latency, which often appeared at lower threshold than the earlier effects. These late responses seemed to be generated partly as a consequence of the sound click made by coil discharge, and changed little with coil location. This novel finding has implications for the design of future studies using TMS, as well as suggesting a means of non-invasively probing an otherwise inaccessible important motor centre.
    The Journal of Physiology 06/2012; 590(Pt 16):4045-60. DOI:10.1113/jphysiol.2011.226209 · 5.04 Impact Factor
Show more


35 Reads
Available from