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: 3.33). 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
  • [Show abstract] [Hide abstract]
    ABSTRACT: Anatomically incomplete spinal cord injuries are often followed by considerable functional recovery in patients and animal models, largely because of processes of neuronal plasticity. In contrast to the corticospinal system, where sprouting of fibers and rearrangements of circuits in response to lesions have been well studied, structural adaptations within descending brainstem pathways and intraspinal networks are poorly investigated, despite the recognized physiological significance of these systems across species. In the present study, spontaneous neuroanatomical plasticity of severed bulbospinal systems and propriospinal neurons was investigated following unilateral C4 spinal hemisection in adult rats. Injection of retrograde tracer into the ipsilesional segments C3-C4 revealed a specific increase in the projection from the ipsilesional gigantocellular reticular nucleus in response to the injury. Substantial regenerative fiber sprouting of reticulospinal axons above the injury site was demonstrated by anterograde tracing. Regrowing reticulospinal fibers exhibited excitatory, vGLUT2-positive varicosities, indicating their synaptic integration into spinal networks. Reticulospinal fibers formed close appositions onto descending, double-midline crossing C3-C4 propriospinal neurons, which crossed the lesion site in the intact half of the spinal cord and recrossed to the denervated cervical hemicord below the injury. These propriospinal projections around the lesion were significantly enhanced after injury. Our results suggest that severed reticulospinal fibers, which are part of the phylogenetically oldest motor command system, spontaneously arborize and form contacts onto a plastic propriospinal relay, thereby bypassing the lesion. These rearrangements were accompanied by substantial locomotor recovery, implying a potential physiological relevance of the detour in restoration of motor function after spinal injury.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 10/2014; 34(40):13399-410. DOI:10.1523/JNEUROSCI.0701-14.2014 · 6.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background: Acoustic startle reflex (ASR) can be used as a tool to examine reticulospinal excitability. The potential role of reticulospinal mechanisms in the development of spasticity has been suggested but not tested. Objective: To examine reticulospinal excitability at different stages of motor recovery in patients with chronic stroke using the ASR. Methods: Sixteen subjects with hemiplegic stroke participated in the study. We examined ASR responses at rest and contralateral motor overflow during voluntary elbow flexion. Results: ASR responses in impaired biceps muscles showed different patterns at different stages. In subjects without spasticity, ASR responses were less frequent (10% on impaired side) and had normal duration (<200 ms). In subjects with spasticity, the responses were more frequent (58.3% on impaired side) and longer lasting (up to 1 minute). However, no correlation between exaggerated reflex responses and Modified Ashworth Scale (MAS) scores was observed. During voluntary elbow flexion on the impaired side, similar positive linear force-electromyogram (EMG) relationships were found in subjects with and without spasticity. Electromyographic activity of the resting nonimpaired limb increased proportionally in subjects with spasticity (r = 0.6313, P = .0004), but no such correlation was found in subjects without spasticity (r = 0.0191, P = .9612). Conclusions: Preliminary findings of exaggerated ASR responses and associated contralateral overflow only in spastic biceps muscles in patients with chronic stroke suggest the important role of reticulospinal mechanisms in the development of spasticity.
    Topics in Stroke Rehabilitation 07/2014; 21(4):358-370. DOI:10.1310/tsr2104-358 · 1.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Little attention has been given to how age affects the neural processing of movement within the brainstem. Since the brainstem plays a critical role in motor control throughout the whole body, having a clear understanding of deficits in brainstem function could provide important insights into movement deficits in older adults. A unique property of the startle reflex is its ability to involuntarily elicit planned movements, a phenomenon referred to as startReact. The noninvasive startReact response has previously been used to probe both brainstem utilization and motor planning. Our objective was to evaluate deficits in startReact hand extension movements in older adults. We hypothesized that startReact hand extension will be intact but delayed. Electromyography was recorded from the sternocleidomastoid (SCM) muscle to detect startle and the extensor digitorum communis (EDC) to quantify movement onset in both young (24 ± 1) and older adults (70 ± 11). Subjects were exposed to a startling loud sound when prepared to extend their hand. Trials were split into those where a startle did (SCM+) and did not (SCM-) occur. We found that startReact was intact but delayed in older adults. SCM+ onset latencies were faster than SCM- trials in both the populations, however, SCM+ onset latencies were slower in older adults compared to young (Δ = 8 msec). We conclude that the observed age-related delay in the startReact response most likely arises from central processing delays within the brainstem.
    06/2014; 2(6). DOI:10.14814/phy2.12025


1 Download
Available from