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Carlfredrik Ekerot - One of the best experts on this subject based on the ideXlab platform.
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the Lateral Reticular Nucleus integration of descending and ascending systems regulating voluntary forelimb movements
Frontiers in Computational Neuroscience, 2015Co-Authors: Bror Alstermark, Carlfredrik EkerotAbstract: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.
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the Lateral Reticular Nucleus a precerebellar centre providing the cerebellum with overview and integration of motor functions at systems level a new hypothesis
The Journal of Physiology, 2013Co-Authors: Bror Alstermark, Carlfredrik EkerotAbstract:The Lateral Reticular Nucleus (LRN) is a major precerebellar centre of mossy fibre information to the cerebellum from the spinal cord that is distinct from the direct spinocerebellar paths. The LRN ...
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the Lateral Reticular Nucleus in the cat
Experimental Brain Research, 1990Co-Authors: Carlfredrik EkerotAbstract:Intracellular recordings were obtained from 204 neurones in the Lateral Reticular Nucleus (LRN). LRN neurones contacted by the bVFRT were identified by the responses evoked on stimulation of descending fibres in the contraLateral ventral quadrant of the spinal cord (cVQ) at cervical (C5cVQ) and lumbar (L2cVQ) levels. Stimulation of the cVQ evoked excitatory or inhibitory responses in 124 of the 204 LRN neurones. EPSPs were evoked in 45, IPSPs in 52 and both EPSPs and IPSPs in 27 LRN neurones. The shortest latencies of the responses evoked from the cVQ indicated that both EPSPs and IPSPs were disynaptic. This finding was confirmed by direct stimulation of the ascending fibres in the ipsiLateral ventroLateral funiculus at C3 (C3iVLF) or LI (LliVLF). In most LRN neurones activated or inhibited from the cVQ, stimulation of the iVLF evoked similar responses at a monosynaptic latency. These results indicate that the bVFRT consists of roughly equally large groups of excitatory and inhibitory neurones monosynaptically connected with the LRN. Excitatory and inhibitory bVFRT neurones had similar peripheral receptive fields and termination areas in the LRN. LRN neurones were divided into those contacted by cervical bVFRT neurones and lumbar bVFRT neurones. The former group consisted of LRN neurones responding to C5cVQ stimulation at latencies below 5 ms, whereas the latter group contained LRN neurones responding to stimulation of the L2cVQ. Cervical bVFRT neurones projected to most parts of the LRN whereas the projection of lumbar bVFRT neurones were confined to the ventroLateral part of the Nucleus. Excitatory and inhibitory bVFRT neurones of each group had similar termination areas. About half of the LRN neurones contacted by cervical bVFRT neurones did not respond to stimulation of the contraLateral forelimb (cF) nerve. These bVFRT neurones formed a separate group which terminated in the dorsomedial part of the LRN. Cervical bVFRT neurones activated by the cF terminated in the ventroLateral part of the Nucleus. The conduction velocity between the L1 and C3 segments was determined for axons of lumbar bVFRT neurones. The velocities ranged between 55–137 m/s (mean 90.6 m/s) for excitatory neurones and between 35–120 (mean 87.5 m/s) for inhibitory neurones. Monosynaptic responses, particularly EPSPs, were frequently evoked from the L1iVLF in LRN neurones with a bVFRT input from cervical segments only. The results suggest that many excitatory cervical bVFRT neurones have fast conducting descending axon branches projecting to the lumber cord. Long descending axon branches seemed to be less common among inhibitory cervical bVFRT neurones.
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the Lateral Reticular Nucleus in the cat vi excitatory and inhibitory afferent paths
Experimental Brain Research, 1990Co-Authors: Carlfredrik EkerotAbstract:: The afferent paths from the spinal cord and from trigeminal afferents to the Lateral Reticular Nucleus (LRN) were investigated by intracellular recording from 204 LRN neurones in preparations with a spinal cord lesion at C3 that spared only the ipsiLateral ventral quadrant. Stimulation of nerves in the limbs evoked EPSPs and JPSPs in 201 of 204 tested LRN neurones. The strongest input was from the ipsiLateral forelimb (iF) which evoked EPSPs in 49% and IPSPs in 73% of the LRN neurones. Each of the other limbs evoked EPSPs in approximately 20% and IPSPs in approximately 25% of the neurones. Stimulation of the ipsiLateral trigeminal nerve (iTrig) evoked EPSPs in 32% and IPSPs in 46% of the neurones. The shortest latencies of the EPSPs and IPSPs indicated a disynaptic connection between primary afferents in the iF and iTrig and the LRN. The most direct pathways for excitatory and inhibitory responses from the other limbs were trisynaptic. Stimulation of the ventral part of the ipsiLateral funiculus (iVLF) at C3 (C3iVLF) evoked monosynaptic responses in 189 of 201 tested LRN neurones. Monosynaptic EPSPs were recorded in 104 neurones and monosynaptic IPSPs in 126 neurones. Monosynaptic EPSPs and IPSPs were encountered in all parts of the LRN. Stimulation of the iVLF at L1 (L1iVLF) evoked monosynaptic EPSPs and IPSPs in the ventroLateral part of the LRN. The termination areas of excitatory and inhibitory fibres appeared to be the same. LRN neurones without monosynaptic EPSPs or IPSPs from the L1iVLF were located mainly in the dorsal part of the magnocellular division. Stimulation of the dorsal funiculi (DF) at C2 and the ipsiLateral trigeminal nerve (iTrig) evoked excitatory and inhibitory responses in the LRN. The shortest latencies of EPSPs and IPSPs indicated disynaptic connections.
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the Lateral Reticular Nucleus in the cat vii excitatory and inhibitory projection from the ipsiLateral forelimb tract if tract
Experimental Brain Research, 1990Co-Authors: Carlfredrik EkerotAbstract:: Intracellular recording from neurones in the Lateral Reticular Nucleus (LRN) demonstrated that, in addition to the previously identified excitatory ipsiLateral forelimb tract (iF tract) (Clendenin et al. 1974c) there is an inhibitory tract mediating information from the ipsiLateral forelimb to the LRN. The excitatory and inhibitory tracts were similarly organized. The tract neurones were monosynaptically activated by afferents in the ipsiLateral forelimb and projected to the same area of the LRN. They will be considered as excitatory and inhibitory components of the iF tract and denoted the excitatory and inhibitory iF tract (EiF and IiF tracts). Stimulation of the descending ipsiLateral dorsoLateral funiculus (iDLF) in the C3 segment evoked disynaptic EPSPs and IPSPs in LRN neurones contacted by the EiF and IiF tracts. The responses in individual LRN neurones evoked from the iDLF were similar to the responses evoked from the forelimb nerves suggesting that the EiF and IiF tracts are monosynaptically activated by fibres in the iDLF. The dorsal portion of the magnocellular part of the LRN constituted the main termination area of both the EiF and IiF tracts. Neurones in this area have previously been shown to project ipsiLaterally to lobule V in the pars intermedia of the cerebellar anterior lobe and to the paramedian lobule (Clendenin et al. 1974a). IPSPs evoked from the IiF tract in LRN neurones outside the main termination area had smaller amplitudes and longer latencies. This finding suggests that these responses were generated by thin axon colLaterals given off from dorsally located stem axons.
B. A. Flumerfelt - One of the best experts on this subject based on the ideXlab platform.
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Afferent organization of the Lateral Reticular Nucleus in the rat: An anterograde tracing study
Anatomy and Embryology, 1992Co-Authors: N. Rajakumar, A. W. Hrycyshyn, B. A. FlumerfeltAbstract:The organization of the afferent projections to the Lateral Reticular Nucleus of the rat was investigated following placement of horseradish peroxidase-conjugated wheatgerm agglutinin into the red Nucleus, fastigial Nucleus, various levels of the spinal cord or the sensorimotor area of the cerebral cortex. The pattern of distribution of anterogradely labelled profiles visualized with tetramethylbenzidine revealed that the caudal three-fourths of the Lateral Reticular Nucleus received a large, topographically organized projection from the entire length of the contraLateral spinal cord. The Lateral part of the rostral half of the Lateral Reticular Nucleus received a small projection from the contraLateral red Nucleus, the dorsal part of the middle third of the Nucleus received a diffuse projection from the contraLateral fastigial Nucleus, and the extreme rostromedial part of the Nucleus received a sparse projection from the contraLateral cerebral cortex. The dorsal part of the middle third of the Lateral Reticular Nucleus also received a small projection from the ipsiLateral cervical spinal cord. The distribution of afferent fibres from different levels of the spinal cord, red Nucleus, and fastigial Nucleus overlapped substantially in the middle third of the Lateral Reticular Nucleus, whereas the cerebral cortical receiving area was separate. These data suggest that the middle third of the Lateral Reticular Nucleus integrates spinal and supraspinal impulses to the cerebellum, while the rostral part of the Nucleus is involved in a separate cerebral cortico-cerebellar pathway.
Tom J. H. Ruigrok - One of the best experts on this subject based on the ideXlab platform.
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lack of a biLateral projection of individual spinal neurons to the Lateral Reticular Nucleus in the rat a retrograde non fluorescent double labeling study
Neuroscience Letters, 1995Co-Authors: S K E Koekkoek, Tom J. H. RuigrokAbstract:The projection of spinal neurons to the Lateral Reticular Nucleus of the rat was investigated with a non-fluorescent double retrograde tracing technique. Either a gold-lectin tracer or cholera toxin-b-subunit was injected into the Lateral Reticular Nucleus on each side of the brain. Retrogradely labeled neurons were encountered biLaterally throughout the spinal cord. Double labeled neurons, however, were seldom seen (< 2% of the total number of labeled neurons) and those that were could, at least partly, be ascribed to inadvertent labeling of passing fibers. It is concluded that most spinoReticular neurons project to either the ipsi- or contraLateral Lateral Reticular Nucleus, suggesting that each side receives a unique spinal input.
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Connections of the Lateral Reticular Nucleus to the Lateral Vestibular Nucleus in the Rat. An Anterograde Tracing Study with Phaseolus vulgaris Leucoagglutinin
European Journal of Neuroscience, 1995Co-Authors: Tom J. H. Ruigrok, F. Cella, Jan VoogdAbstract:Efferent projections from the Lateral Reticular Nucleus in the rat were investigated with anterograde transport of Phaseolus vulgaris leucoagglutinin. Besides the well known mossy fibre connections to the cerebellar cortex and colLaterals to the cerebellar nuclei, a substantial biLateral projection to the Lateral vestibular Nucleus was found. Terminal arborizations found within this Nucleus appeared to detach from the reticulocerebellar fibres in the cerebellar white matter and enter the Lateral vestibular Nucleus from dorsally. This projection may have functional relevance for the control, by ascending spinal pathways, of the descending Lateral vestibulospinal tract.
Timothy J Ness - One of the best experts on this subject based on the ideXlab platform.
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visceral nociceptive input to the area of the medullary Lateral Reticular Nucleus ascends in the Lateral spinal cord
Neuroscience Letters, 2005Co-Authors: Meredith T Robbins, Tyler Uzzell, Timothy J NessAbstract:In halothane-anesthetized rats, neurons stereotaxically located in the region of the medullary Lateral Reticular Nucleus (LRN) and responsive to urinary bladder distension (UBD) were characterized using extracellular electrodes. Most neurons excited by UBD were also excited by noxious stimuli applied to biLateral receptive fields comprising at least half of the body surface. These biLateral nociceptive specific (bNS) neurons exhibited graded responses to graded intensities of UBD. Neuronal responses to noxious UBD were highly positively correlated with responses to noxious colorectal distension, suggesting a convergence of visceral sensory information in the area of LRN. BiLateral Lateral mid-cervical spinal cord lesions virtually abolished activity of bNS neurons evoked by noxious UBD, while dorsal midline lesions had no significant effect. These data support a role for neurons in the region of the LRN in visceral nociception and implicate traditional Lateral spinal cord pain pathways in the transmission of visceral information to caudal ventroLateral medullary structures.
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characterization of neurons in the area of the medullary Lateral Reticular Nucleus responsive to noxious visceral and cutaneous stimuli
Brain Research, 1998Co-Authors: Timothy J Ness, Kenneth A Follett, John G Piper, B A DirksAbstract:Abstract In halothane-anesthetized rats, 283 caudal medullary neurons responsive to colorectal distension (CRD) were characterized using extracellular electrodes. Neurons inhibited by CRD ( n =82) were in the area dorsal to the Lateral Reticular Nucleus (LRN). Most neurons excited by CRD ( n =130) were located within or immediately adjacent to the LRN, were excited by noxious heat and/or noxious pinch of at least half the body surface and were called biLateral nociceptive specific (bNS) neurons. bNS neurons had accelerating responses to graded CRD (threshold: 20±2 mmHg). Ten of twelve bNS neurons tested could be antidromically activated by electrical stimulation of the midline cerebellum. Other neurons excited by CRD ( n =71) had mixed responses to cutaneous stimuli and were generally located in the area dorsal to the LRN. Increases in blood pressure due to intravenous phenylephrine did not significantly alter the spontaneous activity of neurons excited by CRD, but altered spontaneous activity (12 excited, four inhibited) in all neurons tested which were inhibited by CRD. Decreases in blood pressure produced by intravenous nitroprusside produced a reciprocal response in most neurons inhibited by CRD and had a delayed onset (20–30 s after bolus administration) excitatory effect on 21 of 27 units excited by CRD. Combined with other studies, these data suggest a role for neurons within and adjacent to the LRN in the modulation of visceral nociception. They also implicate a role for the cerebellum in visceral nociceptive processing.
David K Ryugo - One of the best experts on this subject based on the ideXlab platform.
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projections of the Lateral Reticular Nucleus to the cochlear Nucleus in rats
The Journal of Comparative Neurology, 2007Co-Authors: Xiping Zhan, David K RyugoAbstract:The Lateral Reticular Nucleus (LRN) resides in the rostral medulla and caudal pons, is implicated in cardiovascular regulation and cranial nerve reflexes, and gives rise to mossy fibers in the cerebellum. Retrograde tracing data revealed that medium-sized multipolar cells from the magnocellular part of the LRN project to the cochlear Nucleus (CN). We sought to characterize the LRN projection to the CN using BDA injections. Anterogradely labeled terminals in the ipsiLateral CN appeared as boutons and mossy fibers, and were examined with light and electron microscopy. The terminal field in the CN was restricted to the granule cell domain (GCD), specifically in the superficial layer along the anteroventral CN and in the granule cell lamina. Electron microscopy showed that the smallest LRN boutons formed 1–3 synapses, and as boutons increased in size, they formed correspondingly more synapses. The largest boutons were indistinguishable from the smallest mossy fibers, and the largest mossy fiber exhibited 15 synapses. Synapses were asymmetric with round vesicles and formed against thin dendritic profiles characterized by plentiful microtubules and the presence of fine filopodial extensions that penetrated the ending. These structural features of the postsynaptic target are characteristic of the terminal dendritic claw of granule cells. LRN projections are consistent with known organizational principles of non-auditory inputs to the GCD. J. Comp. Neurol. 504:583–598, 2007. © 2007 Wiley-Liss, Inc. Indexing terms: auditory; granule cells; mossy fibers; synapse
