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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 from the isolated C3 DLF segment. (A), intracellular recordings from a LRN showing disynaptic EPSPs when applying a train of three stimuli to the isolated C3 DLF. (B), intracellular recordings from a LRN showing disynaptic EPSPs and IPSPs when applying a train of three stimuli to the isolated C3 DLF. The same traces are shown at a slow (upper panels) and fast (lower panels) sweep speed. Note, the lower panels only show part of the upper records, indicated by the horizontal black line. (C,D), distribution of EPSP respectively IPSP latencies measured from the incoming volley evoked by stimulation in the isolated C3 DLF segment.
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Figure 4: Effects evoked from the isolated C3 DLF segment. (A), intracellular recordings from a LRN showing disynaptic EPSPs when applying a train of three stimuli to the isolated C3 DLF. (B), intracellular recordings from a LRN showing disynaptic EPSPs and IPSPs when applying a train of three stimuli to the isolated C3 DLF. The same traces are shown at a slow (upper panels) and fast (lower panels) sweep speed. Note, the lower panels only show part of the upper records, indicated by the horizontal black line. (C,D), distribution of EPSP respectively IPSP latencies measured from the incoming volley evoked by stimulation in the isolated C3 DLF segment.

Mentions: In order to further delineate the LRN effects of C3-C4 PN activation, the DLF was transected in C2 and C5. The isolated C2 to C5 strip of DLF was then stimulated electrically using a monopolar tungsten electrode. Figure 4 shows that stimulation of cortico- and rubro-spinal fibers in the C3 DLF evoked disynaptic EPSPs and IPSPs in LRN neurones with latencies within the expected disynaptic range of 1.6–2.4 ms. These data further indicate that the disynaptic LRN effects of cortico- and rubro-spinal excitation are mediated by PNs located in the C3 to C4 segments.


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

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

Effects evoked from the isolated C3 DLF segment. (A), intracellular recordings from a LRN showing disynaptic EPSPs when applying a train of three stimuli to the isolated C3 DLF. (B), intracellular recordings from a LRN showing disynaptic EPSPs and IPSPs when applying a train of three stimuli to the isolated C3 DLF. The same traces are shown at a slow (upper panels) and fast (lower panels) sweep speed. Note, the lower panels only show part of the upper records, indicated by the horizontal black line. (C,D), distribution of EPSP respectively IPSP latencies measured from the incoming volley evoked by stimulation in the isolated C3 DLF segment.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525057&req=5

Figure 4: Effects evoked from the isolated C3 DLF segment. (A), intracellular recordings from a LRN showing disynaptic EPSPs when applying a train of three stimuli to the isolated C3 DLF. (B), intracellular recordings from a LRN showing disynaptic EPSPs and IPSPs when applying a train of three stimuli to the isolated C3 DLF. The same traces are shown at a slow (upper panels) and fast (lower panels) sweep speed. Note, the lower panels only show part of the upper records, indicated by the horizontal black line. (C,D), distribution of EPSP respectively IPSP latencies measured from the incoming volley evoked by stimulation in the isolated C3 DLF segment.
Mentions: In order to further delineate the LRN effects of C3-C4 PN activation, the DLF was transected in C2 and C5. The isolated C2 to C5 strip of DLF was then stimulated electrically using a monopolar tungsten electrode. Figure 4 shows that stimulation of cortico- and rubro-spinal fibers in the C3 DLF evoked disynaptic EPSPs and IPSPs in LRN neurones with latencies within the expected disynaptic range of 1.6–2.4 ms. These data further indicate that the disynaptic LRN effects of cortico- and rubro-spinal excitation are mediated by PNs located in the C3 to C4 segments.

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.