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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.


Convergence of pyramidal and rubral effects after C5 DLF transection. (A), intracellular recordings from a LRN neuron showing spatial facilitation disynaptic EPSPs when applying a train of two stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the second pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). Note that the rubral conditioning stimulation was given synchronously with the second pyramidal stimulation. (B,C), distribution of EPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively. Measurements were made from the last effective volley of the train in this and the following latency histograms. (D), intracellular recording from another LRN neuron showing spatial facilitation of IPSPs when applying a train of three stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the third pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). (E,F), distribution of IPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively.
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Figure 3: Convergence of pyramidal and rubral effects after C5 DLF transection. (A), intracellular recordings from a LRN neuron showing spatial facilitation disynaptic EPSPs when applying a train of two stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the second pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). Note that the rubral conditioning stimulation was given synchronously with the second pyramidal stimulation. (B,C), distribution of EPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively. Measurements were made from the last effective volley of the train in this and the following latency histograms. (D), intracellular recording from another LRN neuron showing spatial facilitation of IPSPs when applying a train of three stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the third pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). (E,F), distribution of IPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively.

Mentions: After C5 DLF transection of cortico-and rubrospinal fibers, leaving descending connections with the LRN neurons and C3-C4 PNs, but not with interneurons in the forelimb segments, monosynaptic EPSPs and disynaptic and late EPSPs and IPSPs could be evoked in the LRN from the contralateral pyramid and NR. The expected minimal disynaptic linkage of pyramidal and rubral EPSPs and IPSPs to LRN via C3-C4 PNs is 2.1 ms, and the maximal linkage is 2.9 ms (based on a conduction velocity of 60 m/s for the corticospinal fibers and 26 m/s for the ascending branch of the C3-C4 PNs; Alstermark et al., 1981a). Disynaptic pyramidal EPSPs were found in 28% (19/67 neurones) and IPSPs in 55% (36/66 neurones). Disynaptic rubral EPSPs were observed in 16% (11/69 neurones) and IPSPs in 46% (32/69 neurones). The higher frequencies of the IPSPs most likely reflect the fact that the membrane potential decreased after electrode impalement of the LRN cells, making it easier to record IPSPs than EPSPs. Figure 3 shows spatial facilitation of disynaptic pyramidal and rubral EPSPs and IPSPs in LRN neurones following stimulation of cortico- and rubrospinal fibers with a short train of 2–3 volleys after C5 DLF transection (Figures 3A,B), as well as the distribution of latencies (measured from the effective stimulation pulse) in Figures 3C,D.


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

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

Convergence of pyramidal and rubral effects after C5 DLF transection. (A), intracellular recordings from a LRN neuron showing spatial facilitation disynaptic EPSPs when applying a train of two stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the second pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). Note that the rubral conditioning stimulation was given synchronously with the second pyramidal stimulation. (B,C), distribution of EPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively. Measurements were made from the last effective volley of the train in this and the following latency histograms. (D), intracellular recording from another LRN neuron showing spatial facilitation of IPSPs when applying a train of three stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the third pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). (E,F), distribution of IPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively.
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Related In: Results  -  Collection

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Figure 3: Convergence of pyramidal and rubral effects after C5 DLF transection. (A), intracellular recordings from a LRN neuron showing spatial facilitation disynaptic EPSPs when applying a train of two stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the second pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). Note that the rubral conditioning stimulation was given synchronously with the second pyramidal stimulation. (B,C), distribution of EPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively. Measurements were made from the last effective volley of the train in this and the following latency histograms. (D), intracellular recording from another LRN neuron showing spatial facilitation of IPSPs when applying a train of three stimuli to the contralateral pyramid alone (left panel), combined with conditioning single stimulus to the contralateral NR (middle panel) and when the third pyramidal stimulus was removed but the conditioning rubral stimulation remained (right panel). (E,F), distribution of IPSP latencies measured from the incoming volley evoked by stimulation in the contralateral pyramid and NR, respectively.
Mentions: After C5 DLF transection of cortico-and rubrospinal fibers, leaving descending connections with the LRN neurons and C3-C4 PNs, but not with interneurons in the forelimb segments, monosynaptic EPSPs and disynaptic and late EPSPs and IPSPs could be evoked in the LRN from the contralateral pyramid and NR. The expected minimal disynaptic linkage of pyramidal and rubral EPSPs and IPSPs to LRN via C3-C4 PNs is 2.1 ms, and the maximal linkage is 2.9 ms (based on a conduction velocity of 60 m/s for the corticospinal fibers and 26 m/s for the ascending branch of the C3-C4 PNs; Alstermark et al., 1981a). Disynaptic pyramidal EPSPs were found in 28% (19/67 neurones) and IPSPs in 55% (36/66 neurones). Disynaptic rubral EPSPs were observed in 16% (11/69 neurones) and IPSPs in 46% (32/69 neurones). The higher frequencies of the IPSPs most likely reflect the fact that the membrane potential decreased after electrode impalement of the LRN cells, making it easier to record IPSPs than EPSPs. Figure 3 shows spatial facilitation of disynaptic pyramidal and rubral EPSPs and IPSPs in LRN neurones following stimulation of cortico- and rubrospinal fibers with a short train of 2–3 volleys after C5 DLF transection (Figures 3A,B), as well as the distribution of latencies (measured from the effective stimulation pulse) in Figures 3C,D.

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.