Characteristics of cervical interneurones which mediate cortical motor outflow to distal forelimb muscles of cats (original) (raw)
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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...
2010
development of the motor representation in primary motor cortex. J Neurophysiol 84: [2582][2583][2584][2585][2586][2587][2588][2589][2590][2591][2592][2593][2594] 2000. The purpose of this study was to examine when the muscles and joints of the forelimb become represented in primary motor cortex (M1) during postnatal life and how local representation patterns change. We examined these questions in cats that were anesthetized (45-90 days, n ϭ 14; adults, n ϭ 3) and awake (n ϭ 4; 52-86 days). We used intracortical microstimulation (45 ms duration train, 330 Hz, 0.2-ms balanced biphasic pulses, with a leading cathodic pulse; up to 100 A). In young animals (less than day 70), we also used stimulus trains and pulses that could produce greater temporal summation (up to 200-ms train duration, down to 143-Hz stimulus frequency, up to 0.8-ms pulse width). Anesthetized animals were areflexic, and muscle tone was similar to that of the awake cats (i.e., relaxed, not weight or load bearing, with minimal resistance to passive stretch). We monitored the kinematic effects of microstimulation and changes in electromyographic (EMG) activity in forelimb muscles. There was an age-dependent reduction in the number of sites where microstimulation did not produce a motor effect (i.e., ineffective sites), from 95% in animals younger than 60 days to 33% between 81 and 90 days. In adults, 24% of sites were ineffective. Median current thresholds for evoking movements dropped from 79 A in animals younger than day 60 to 38 and 28 A in day 81-90 animals and adults, respectively. There was a proximal-to-distal development of the somatotopic organization of the motor map. Stimulation at the majority of sites in animals younger than day 71 produced shoulder and elbow movement. Wrist sites were first present by day 71, and digit sites by day 81. Sites at which multiple responses were evoked, between 1.0 and 1.5 times threshold, were present after day 71, and increased with age. A higher percentage of distal joints were corepresented with other joints, rather than being represented alone. We found that effective sites initially were scattered and new sites representing proximal and distal joints filled in the gaps between effective sites. During most of the period examined, development of the caudal M1 subregion lagged that of the rostral subregion (percent of effective sites; threshold currents), although these differences were minimal or absent in adults. Our results show that the M1 motor representation is absent at day 45 and, during the subsequent month, the motor map is constructed by progressively representing more distal forelimb joints.
The Journal of Physiology, 2007
Despite numerous investigations on the corticospinal system there is only scant information on neuronal networks mediating actions of corticospinal neurones on ipsilateral motoneurones. 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 PT fibres evoked EPSPs and/or IPSPs in 34/47 motoneurones tested. These PSPs were evoked at latencies indicating that the most direct coupling between PT neurones and motoneurones in uncrossed pathways is disynaptic. Occlusion and spatial facilitation between actions evoked by stimulation of ipsilateral PT and of reticulospinal tract fibres in the ipsilateral medial longitudinal fascicle (MLF) indicated that PT actions are mediated by reticulospinal neurones with axons in the MLF. However, after transection of the MLF in the caudal medulla, stimulation of the ipsilateral PT continued to evoke EPSPs and IPSPs with characteristics similar to when the MLF was intact (in 15/49 motoneurones) suggesting the existence of parallel disynaptic pathways via other relay neurones.
Propriospinal control of interneurons in spinal reflex pathways from tendon organs in the cat
Brain Research, 1983
Key words: spinal cord -propriospinal system -tendon organs After chronic hemisection at C3, stimulation of propriospinal fibers in the dorsal quadrant at Th 10 facilitated disynaptic PSPs from Ib afferents in hindlimb motoneurons. Recording from interneurons monosynaptically activated from group I muscle afferents, and of extraceUular focal synaptic potentials around them, revealed monosynaptic EPSPs from long propriospinal neurons. It is suggested that propriospinal neurons originating in the forelimb segments have direct excitatory connexions with interneurons oflb reflex pathways to hindlimb motoneurons. * Present address: Department•fPhysi•••gy•C•••ege•fMedicine•University•fAriz•na•Tucs•n•Ariz•na85724•U.S.A. 0006-8993 / 83/(3000-00001503.00
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.
Journal of Neurophysiology, 2011
It has previously been established that ventral spinocerebellar tract (VSCT) neurons and dorsal spinocerebellar tract neurons located in Clarke's column (CC DSCT neurons) forward information on actions of premotor interneurons in reflex pathways from muscle afferents on α-motoneurons. Whether DSCT neurons located in the dorsal horn (dh DSCT neurons) and spinocervical tract (SCT) neurons are involved in forwarding similar feedback information has not yet been investigated. The aim of the present study was therefore to examine the input from premotor interneurons to these neurons. Electrical stimuli were applied within major hindlimb motor nuclei to activate axon-collaterals of interneurons projecting to these nuclei, and intracellular records were obtained from dh DSCT and SCT neurons. Direct actions of the stimulated interneurons were differentiated from indirect actions by latencies of postsynaptic potentials evoked by intraspinal stimuli and by the absence or presence of tempo...
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
The Journal of Physiology, 1987
S. A. EDGLEY AND E. JANKOWSKA evoked via L4 interneurones would be delayed. These delays would amount to 0A4-09 ms for p.s.p.s. from group I afferents and by 0-5-2-5 ms for group II p.s.p.s. 6. In many interneurones, particularly those located ventrally, i.p.s.p.s. were evoked by group I and II muscle afferents at latencies which indicated that they were evoked disynaptically. They may therefore reflect inhibitory interactions between subpopulations of L4 interneurones. 7. The main input to L4 interneurones appears to be from group II afferents from the quadriceps and sartorius muscles. They are therefore likely to be particularly strongly activated during extension of the hip joint, when quadriceps and sartorius are stretched. The possibility is thus considered that L4 interneurones play a key role in reflexes determined by limb position.
Electroencephalography and clinical neurophysiology, 1995
Changes in motor cortex excitability induced by somatosensory afferences were evaluated in 5 subjects by testing how the short-latency cortico-spinal effects evoked by transcranial magnetic stimulation in flexor carpi radialis (FCR) motoneurones were influenced by volleys in median nerve afferent fibres. Transcranial magnetic stimulation induced two facilitatory peaks on FCR H reflex, the first at a conditioning-test interval of about -3 msec and the second at msec, separated by a phase of inhibition. If an electric shock to the median nerve at the wrist, 0.8-1 x motor threshold (MT) for thenar muscles, preceded the cortical stimulus by 18-25 msec, an increase in size of both facilitatory peaks was observed. The increase was partly due to a direct action of the median nerve volley on motoneurones. When this contribution was subtracted, two peaks of additional facilitation resulted as the effect of combined conditioning. Additional facilitation was present even during the short-lasti...