Uncrossed actions of feline corticospinal tract neurones on hindlimb motoneurones evoked via ipsilaterally descending pathways (original) (raw)
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The Journal of Physiology, 2007
We have previously demonstrated double crossed pathways through which pyramidal tract neurones can influence ipsilateral motoneurones, via contralaterally descending reticulospinal neurones and spinal commissural interneurones. The aim of the present study was to examine the effects of stimulation of pyramidal tract (PT) fibres mediated via ipsilaterally descending pathways and to find out which neurones relay these effects. This was done by using intracellular recordings from 96 lumbar motoneurones in deeply anaesthetized cats. To eliminate actions of fibres descending on the side contralateral to the location of the motoneurones, the spinal cords were hemisected on this side at a low-thoracic level. Stimuli that selectively activated ipsilateral
The Journal of Physiology, 2006
Coupling between pyramidal tract (PT) neurones and ipsilateral hindlimb motoneurones was investigated by recording from commissural interneurones interposed between them. Near maximal stimulation of either the left or right PT induced short latency EPSPs in more than 80% of 20 commissural interneurones that were monosynaptically excited by reticulospinal tract fibres in the medial longitudinal fascicle (MLF). The EPSPs were evoked at latencies that were only 1-2 ms longer than those of EPSPs evoked from the MLF, compatible with a disynaptic coupling between PT fibres and these commissural interneurones. EPSPs evoked by PT stimulation were frequently associated with IPSPs which either followed or preceded the EPSPs. The latencies of the IPSPs (on average about 1 ms longer than latencies of the earliest EPSPs) indicated that they were mediated via single additional inhibitory interneurones. Records from a sample of nine commissural interneurones from a different population (with monosynaptic input from group I and/or II muscle afferents, and disynaptically excited from the MLF) suggest that actions of PT fibres on such interneurones are weaker because only four of them were excited by PT stimuli and at longer latencies. By demonstrating disynaptic coupling between PT neurones and commissural interneurones via reticulospinal fibres, the results provide a direct demonstration of trisynaptic coupling in the most direct pathways between PT neurones and ipsilateral motoneurones, and thereby strengthen the proposal that the double crossed pathways between PT neurones and ipsilateral motoneurones might be used to replace crossed actions of damaged PT neurones.
Ipsilateral Actions of Feline Corticospinal Tract Neurons on Limb Motoneurons
Journal of Neuroscience, 2004
Contralateral pyramidal tract (PT) neurons arising in the primary motor cortex are the major route through which volitional limb movements are controlled. However, the contralateral hemiparesis that follows PT neuron injury on one side may be counteracted by ipsilateral of actions of PT neurons from the undamaged side. To investigate the spinal relays through which PT neurons may influence ipsilateral motoneurons, we analyzed the synaptic actions evoked by stimulation of the ipsilateral pyramid on hindlimb motoneurons after transecting the descending fibers of the contralateral PT at a low thoracic level. The results show that ipsilateral PT neurons can affect limb motoneurons trisynaptically by activating contralaterally descending reticulospinal neurons, which in turn activate spinal commissural interneurons that project back across to motoneurons ipsilateral to the stimulated pyramidal tract. Stimulation of the pyramids alone did not evoke synaptic actions in motoneurons but potently facilitated disynaptic EPSPs and IPSPs evoked by stimulation of reticulospinal tract fibers in the medial longitudinal fascicle. In parallel with this doublecrossed pathway, corticospinal neurons could also evoke ipsilateral actions via ipsilateral descending reticulospinal tract fibers, acting through ipsilaterally located spinal interneurons. Because the actions mediated by commissural interneurons were found to be stronger than those of ipsilateral premotor interneurons, the study leads to the conclusion that ipsilateral actions of corticospinal neurons via commissural interneurons may provide a better opportunity for recovery of function in hemiparesis produced by corticospinal tract injury.
Brain Research, 1975
Previous investigations have shown that disynaptic excitation from the corticospinal tract to forelimb motoneurones is mediated by propriospinal neurones with their cell bodies located in the segments C3-C43. Transmission to these propriospinal neurones is facilitated by rubrospinal volleys and by impulses in low threshold cutaneous forelimb afferents, possibly monosynaptically a. These conclusions were derived indirectly from intracellular recording of EPSPs in motoneurones after various spinal cord lesions at different cervical levels. The aim of the present study was to find such propriospinal neurones and to investigate their properties directly. Experiments were made on 7 cats anaesthetized with chloralose (50-60 mg/kg) and additional small amounts of Nembutal, given in the course of the experiment. The third cervical segment (C3) was explored with conventional microelectrode recording technique. Cell bodies of propriospinal neurones were identified by antidromic invasion on stimulation of their axons in more caudal segments. For this purpose several sets of bipolar silver electrodes were placed on the surface of the ipsilateral lateral funiculus (LF) ranging from C6 to L5. The dorsal column (DC) was transected in C5 in order to avoid effects from its concomitant activation by LF stimulation in C6. Another set of stimulating electrodes on the surface of the DC in C4 allowed investigation of the effect of stimulation of primary afferents. Methods for stimulation of the medullary pyramid (Pyr), the red nucleus (NR) and the dorsal tegmentum of the midbrain (Tegm) were described previously 2-4. The present results are based on recordings from 38 propriospinal neurones monosynaptically excited from the pyramid; 26 of them were recorded from intracellularly. With extracellular recording the criterion for antidromic invasion was the fixed latency of the spike evoked at liminal stimulation and the ability to follow high
Pyramidal excitation in long propriospinal neurones in the cervical segments of the cat
Experimental Brain Research, 1991
1. The effect of stimulating the contralateral pyramid has been investigated with intracellular recording from 128 long propriospinal neurones (long PNs) in the C3-Th1 segments of the cat. Long PNs were identified by the antidromic activation from the Th13 segment. They were located in laminae VII-VIII of Rexed. Single pyramidal stimulation evoked monosynaptic EPSPs in 15/40 of the long PNs in cats with intact pyramid. In 15 other long PNs, a train of three to four pyramidal stimuli evoked EPSPs with latencies indicating a minimal disynaptic linkage. The remaining 25% of the long PNs lacked mono- or disynaptic pyramidal EPSPs. In a few cases longer latency excitation was observed. 2. The location of the intercalated neurones which mediate the disynaptic pyramidal EPSPs was investigated by making four different lesions of the corticofugal fibres: 1) at the border of the C5 and C6 segments, 2) at the border of the C2 and C3 segments, 3) at the caudal part of the pyramid; three mm rostral to the decussation and 4) at the level of the trapezoid body. Stimulation of the corticofugal fibres was made either rostral to lesion 3 (rPyr) in order to activate neurones in a cortico-bulbospinal pathway or caudal to lesion 3 (cPyr) to activate neurones in a corticospinal pathway. In the former case, in one experiment, stimulation was made in the pyramid between lesions 3 and 4 (double pyramidal lesion). In case of cPyr stimulation, lesions 1 and 2 were added sequentially in order to investigate if the corticospinal excitation was mediated via C3-C4 PNs. All lesions were made mechanically, except lesion 2 which in some of the experiments was performed by reversible cooling. 3. Stimulation in the pyramid rostral to lesion 3 and in between lesions 3 and 4 evoked disynaptic EPSPs in the long PNs, which shows that they were mediated via reticulospinal neurones. Stimulation in cPyr after lesion 3 elicited disynaptic EPSPs, which remained after lesion 1 but were abolished after adding lesion 2. It is concluded that the disynaptic cPyr EPSPs were mediated via intercalated neurones in the C3-C4 segments. 4. When the disynaptic cPyr EPSP was conditioned with a single volley in nucleus ruber and/or in tectum, it was markedly facilitated, especially when the conditioned volley was applied simultaneously with the effective cPyr volley. The results show that the intercalated neurones in the C3-C4 segments receive monosynaptic convergence from cortico-, rubro- and tectospinal fibres. Stimulation in the lateral reticular nucleus (LRN) evoked monosynaptic EPSPs.(ABSTRACT TRUNCATED AT 400 WORDS)
Ipsilateral actions from the feline red nucleus on hindlimb motoneurones
The Journal of Physiology, 2008
The main aim of the study was to investigate whether neurones in the ipsilateral red nucleus (NR) affect hindlimb motoneurones. Intracellular records from motoneurones revealed that both EPSPs and IPSPs were evoked in them via ipsilaterally located premotor interneurones by stimulation of the ipsilateral NR in deeply anaesthetized cats in which only ipsilaterally descending tract fibres were left intact. When only contralaterally descending tract fibres were left intact, EPSPs mediated by excitatory commissural interneurones were evoked by NR stimuli alone while IPSPs mediated by inhibitory commissural interneurones required joint stimulation of the ipsilateral NR and of the medial longitudinal fascicle (MLF, i.e. reticulospinal tract fibres). Control experiments led to the conclusion that if any inadvertently coactivated axons of neurones from the contralateral NR contributed to these PSPs, their effect was minor. Another aim of the study was to investigate whether ipsilateral actions of NR neurones, pyramidal tract (PT) neurones and reticulospinal tract neurones descending in the MLF on hindlimb motoneurones are evoked via common spinal relay neurones. Mutual facilitation of these synaptic actions as well as of synaptic actions from the contralateral NR and contralateral PT neurones showed that they are to a great extent mediated via the same spinal neurones. A more effective activation of these neurones by not only ipsilateral corticospinal and reticulospinal but also rubrospinal tract neurones may thus contribute to the recovery of motor functions after injuries of the contralateral corticospinal tract neurones. No evidence was found for mediation of early PT actions via NR neurones.
Journal of Neuroscience, 2010
Trunk muscles are important for postural adjustments associated with voluntary movements but little has been done to analyse mechanisms of supraspinal control of these muscles at a cellular level. The present study therefore aimed to investigate the input from pyramidal tract (PT) neurons to motoneurons of the m. longissimus lumborum of the erector spinae and to analyse to what extent it is relayed by reticulospinal (RS) neurons. Intracellular records from motoneurons were used to evaluate effects of electrical stimulation of medullary pyramids and of axons of RS neurons descending in the medial longitudinal fasciculus (MLF). The results revealed that similar synaptic actions were evoked from the ipsilateral and contralateral PTs, including disynaptic and trisynaptic EPSPs and trisynaptic IPSPs. Stimulation of the MLF evoked monosynaptic and disynaptic EPSPs and disynaptic or trisynaptic IPSPs in the same motoneurons. All short latency PSPs of PT origin were abolished by transection of the MLF, while they remained after transection of PT fibers at a spinal level. Hence, RS neurons might serve as the main relay neurons of the most direct PT actions on m. longissimus. However, longer latency IPSPs remaining after MLF or PT spinal lesions and after ipsilateral or contralateral hemisection of spinal cord indicate that PT actions are also mediated by ipsilaterally and/or contralaterally located spinal interneurons. The bilateral effects of PT stimulation thereby provide an explanation why trunk movements after unilateral injuries of PT neurons (e.g. stroke) are impaired to a lesser degree than movements of the extremities.
Propriospinal control of last order interneurones of spinal reflex pathways in the cat
Brain Research, 1973
In studies from our laboratory on the supraspinal control of segmental spinal mechanisms, the problem has occasionally arisen as to whether some segmental effects evoked by stimulation of a supraspinal tract were due to activation of long propriospinal neurones. For this and other reasons it became necessary to obtain more information about long propriospinal neurones, not only with respect to their segmental origin, the trajectory of their axons and their synaptic activation, but also regarding their effects on segmental mechanisms. To analyze segmental synaptic effects evoked by propriospinal fibres we chose to stimulate the axons directly at the low thoracic level, and limited ourselves to effects on motoneurones and last order interneurones in spinal reflex pathways. In this report it will be shown that propriospinal fibres terminate on some interneurones which project directly to motoneurones, and that these iriterneurones are interposed in two well defined segmental reflex pathways. Both conclusions are based on intracellular records of postsynaptic potentials (PSPs) evoked in motoneurones (in L6-SI spinal segments) by stimulation ofpropriospinal and peripheral nerve fibres, and on an analysis of interactions between effects evoked from these two sources.
Journal of Neurophysiology, 2006
The aim of the study was to analyze interactions between neuronal networks mediating centrally initiated movements and reflex reactions evoked by peripheral afferents; specifically whether interneurons in pathways from group Ib afferents and from group II muscle afferents mediate actions of reticulospinal neurons on spinal motoneurons by contralaterally located commissural interneurons. To this end reticulospinal tract fibers were stimulated in the contralateral medial longitudinal fascicle (MLF) in chloralose-anesthetized cats in which the ipsilateral half of the spinal cord was transected rostral to the lumbosacral enlargement. In the majority of interneurons mediating reflex actions of group Ib and group II afferents, MLF stimuli evoked either excitatory or inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) or both EPSPs and IPSPs attributable to disynaptic actions by commissural interneurons. In addition, in some interneurons EPSPs were evoked at latencies compat...