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The lateral reticular nucleus; integration of descending and ascending systems regulating voluntary forelimb movements.

Alstermark B, Ekerot CF - Front Comput Neurosci (2015)

Bottom Line: Individual motoneurones do not have projections to spino-cerebellar neurons.The LRN projections to the deep cerebellar nuclei exert a direct excitatory effect on descending motor pathways via the reticulospinal, vestibulospinal, and other supraspinal tracts, and might play a key role in cerebellar motor control.Our results support the hypothesis that the LRN provides the cerebellum with highly integrated information, enabling cerebellar control of complex forelimb movements.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Medical Biology, Section of Physiology, Umeå University Umeå, Sweden.

ABSTRACT
Cerebellar control of movements is dependent on mossy fiber input conveying information about sensory and premotor activity in the spinal cord. While much is known about spino-cerebellar systems, which provide the cerebellum with detailed sensory information, much less is known about systems conveying motor information. Individual motoneurones do not have projections to spino-cerebellar neurons. Instead, the fastest route is from last order spinal interneurons. In order to identify the networks that convey ascending premotor information from last order interneurons, we have focused on the lateral reticular nucleus (LRN), which provides the major mossy fiber input to cerebellum from spinal interneuronal systems. Three spinal ascending systems to the LRN have been investigated: the C3-C4 propriospinal neurones (PNs), the ipsilateral forelimb tract (iFT) and the bilateral ventral flexor reflex tract (bVFRT). Voluntary forelimb movements involve reaching and grasping together with necessary postural adjustments and each of these three interneuronal systems likely contribute to specific aspects of forelimb motor control. It has been demonstrated that the command for reaching can be mediated via C3-C4 PNs, while the command for grasping is conveyed via segmental interneurons in the forelimb segments. Our results reveal convergence of ascending projections from all three interneuronal systems in the LRN, producing distinct combinations of excitation and inhibition. We have also identified a separate descending control of LRN neurons exerted via a subgroup of cortico-reticular neurones. The LRN projections to the deep cerebellar nuclei exert a direct excitatory effect on descending motor pathways via the reticulospinal, vestibulospinal, and other supraspinal tracts, and might play a key role in cerebellar motor control. Our results support the hypothesis that the LRN provides the cerebellum with highly integrated information, enabling cerebellar control of complex forelimb movements.

No MeSH data available.


Effects evoked via the cervical bVFRT. (A), intracellular recordings from a LRN neuron showing disynaptic EPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (B,C), distribution of EPSP latencies by electrical stimulation of the LVST in the coVQ in C4 respectively C6. (D), intracellular recordings from a LRN neuron showing disynaptic IPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (E,F), distribution of IPSP latencies by electrical stimulation of the coVQ in the C4 and C6 segments, respectively.
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Figure 6: Effects evoked via the cervical bVFRT. (A), intracellular recordings from a LRN neuron showing disynaptic EPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (B,C), distribution of EPSP latencies by electrical stimulation of the LVST in the coVQ in C4 respectively C6. (D), intracellular recordings from a LRN neuron showing disynaptic IPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (E,F), distribution of IPSP latencies by electrical stimulation of the coVQ in the C4 and C6 segments, respectively.

Mentions: We also tested the effects of cervical bVFRT neurones on the LRN by stimulation of the lateral vestibulospinal tract in the contralateral (coVQ) in C4 or C6. We confirmed earlier findings by Clendenin et al. (1974b) and by Ekerot (1990b) that disynaptic excitation and inhibition in the LRN could be evoked by cervical bVFRT stimulation, as shown in two different LRN neurones in Figures 6A,D. Figure 6A illustrates disynaptic EPSPs evoked by the second and third volley (shown at higher sweep speed in the right panel). Figure 6D illustrates disynaptic IPSPs evoked by the first volley alone. In the right panel, taken at higher sweep speed, a second IPSP can be observed at trisynaptic latency (arrowhead). Note the prolongation of the minimal latencies when stimulating in C6 compared to C4, as shown in Figures 6B,C,E,F, respectively. This is expected because the bVFRT neurons are located downstream of the stimulation site.


The lateral reticular nucleus; integration of descending and ascending systems regulating voluntary forelimb movements.

Alstermark B, Ekerot CF - Front Comput Neurosci (2015)

Effects evoked via the cervical bVFRT. (A), intracellular recordings from a LRN neuron showing disynaptic EPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (B,C), distribution of EPSP latencies by electrical stimulation of the LVST in the coVQ in C4 respectively C6. (D), intracellular recordings from a LRN neuron showing disynaptic IPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (E,F), distribution of IPSP latencies by electrical stimulation of the coVQ in the C4 and C6 segments, respectively.
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Related In: Results  -  Collection

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Figure 6: Effects evoked via the cervical bVFRT. (A), intracellular recordings from a LRN neuron showing disynaptic EPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (B,C), distribution of EPSP latencies by electrical stimulation of the LVST in the coVQ in C4 respectively C6. (D), intracellular recordings from a LRN neuron showing disynaptic IPSPs when stimulating the LVST with a train of three stimuli in the (coVQ) in the C6 segment. The right panel was taken at a higher sweep speed and is expanded from the section indicated by the horizontal line in the left panel. (E,F), distribution of IPSP latencies by electrical stimulation of the coVQ in the C4 and C6 segments, respectively.
Mentions: We also tested the effects of cervical bVFRT neurones on the LRN by stimulation of the lateral vestibulospinal tract in the contralateral (coVQ) in C4 or C6. We confirmed earlier findings by Clendenin et al. (1974b) and by Ekerot (1990b) that disynaptic excitation and inhibition in the LRN could be evoked by cervical bVFRT stimulation, as shown in two different LRN neurones in Figures 6A,D. Figure 6A illustrates disynaptic EPSPs evoked by the second and third volley (shown at higher sweep speed in the right panel). Figure 6D illustrates disynaptic IPSPs evoked by the first volley alone. In the right panel, taken at higher sweep speed, a second IPSP can be observed at trisynaptic latency (arrowhead). Note the prolongation of the minimal latencies when stimulating in C6 compared to C4, as shown in Figures 6B,C,E,F, respectively. This is expected because the bVFRT neurons are located downstream of the stimulation site.

Bottom Line: Individual motoneurones do not have projections to spino-cerebellar neurons.The LRN projections to the deep cerebellar nuclei exert a direct excitatory effect on descending motor pathways via the reticulospinal, vestibulospinal, and other supraspinal tracts, and might play a key role in cerebellar motor control.Our results support the hypothesis that the LRN provides the cerebellum with highly integrated information, enabling cerebellar control of complex forelimb movements.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Medical Biology, Section of Physiology, Umeå University Umeå, Sweden.

ABSTRACT
Cerebellar control of movements is dependent on mossy fiber input conveying information about sensory and premotor activity in the spinal cord. While much is known about spino-cerebellar systems, which provide the cerebellum with detailed sensory information, much less is known about systems conveying motor information. Individual motoneurones do not have projections to spino-cerebellar neurons. Instead, the fastest route is from last order spinal interneurons. In order to identify the networks that convey ascending premotor information from last order interneurons, we have focused on the lateral reticular nucleus (LRN), which provides the major mossy fiber input to cerebellum from spinal interneuronal systems. Three spinal ascending systems to the LRN have been investigated: the C3-C4 propriospinal neurones (PNs), the ipsilateral forelimb tract (iFT) and the bilateral ventral flexor reflex tract (bVFRT). Voluntary forelimb movements involve reaching and grasping together with necessary postural adjustments and each of these three interneuronal systems likely contribute to specific aspects of forelimb motor control. It has been demonstrated that the command for reaching can be mediated via C3-C4 PNs, while the command for grasping is conveyed via segmental interneurons in the forelimb segments. Our results reveal convergence of ascending projections from all three interneuronal systems in the LRN, producing distinct combinations of excitation and inhibition. We have also identified a separate descending control of LRN neurons exerted via a subgroup of cortico-reticular neurones. The LRN projections to the deep cerebellar nuclei exert a direct excitatory effect on descending motor pathways via the reticulospinal, vestibulospinal, and other supraspinal tracts, and might play a key role in cerebellar motor control. Our results support the hypothesis that the LRN provides the cerebellum with highly integrated information, enabling cerebellar control of complex forelimb movements.

No MeSH data available.