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Biomedical subjects

M Illert

Publications and source records attributed to M Illert.

At least 55 records · Page 3Linked to original sources
PubMed1986

Forearm muscles of man can reverse their function after tendon transfers: an electromyographic study.

In patients suffering from paralysis of a major synergistic muscle group tendon transfers can be considered the therapy of choice in restoring the mobility of the affected joint(s). In order to study the mechanisms underlying the subsequent reversal of function in the transferred muscles, we have recorded the EMG of several forearm muscles in parallel and compared their activation periods with control data from healthy volunteers. Slow and fast extension-flexion movements of the wrist were evaluated. The findings demonstrated a 'new' phasic EMG activity within the transferred muscles, which correlated to their new mechanical function. However, the 'old' EMG pattern was not lost. In some muscles it was present in fast and slow wrist movements, in others only in fast ones. The results indicate that the reversal of function observed in the transferred muscles can be adjusted to meet the specific needs of the movement to be performed.

Adaptation, Physiological↗
PubMed1986

Location of motoneurones projecting to the cat distal forelimb. I. Deep radial motornuclei.

The position of the motornuclei projecting through the dorsal interosseus (DR) nerve to the distal forelimb muscles has been investigated in the cat. Horseradish peroxidase (HRP) and fluorescent (Fl) compounds have been used as retrograde tracers. They were either injected into forelimb muscles or applied to the proximal end of transected forelimb nerves. Limb muscles that were not investigated have been carefully denervated. HRP was used to trace the position and the architecture of the individual motornuclei. The topographical relations between the nuclei were established with application of up to three F compounds in the same animal. The position of the labeled motornuclei was reconstructed with a computer-assisted approach which is described in the appendix. The DR representation area extends from the caudal C5 to the caudal Th1 segments. In C6 it forms a dorsoventrally oriented narrow region at the lateral border of the ventral horn; in C7 and rostral C8 it forms a broad column in the dorsolateral corner of the ventral horn. In caudal C8 and Th1 this column is shifted into a ventral direction. The motoneurones projecting to the individual DR muscles are not randomly distributed in this area, but arranged in long, slender columns. These motornuclei occupy specific positions with only minimal interindividual variations. Three nuclei (brachioradialis, extensor carpi radialis, and supinator) are located in the C6 and C7 segments. They compose about one-third of the DR cell population. The nuclei to the other radial muscles are all located in C8 and Th1. Thus most of the DR motoneurones are located in these two segments. These results, together with those from the companion paper on the location of the median and ulnar motornuclei, provide important anatomical knowledge for the investigation of the cat brachial enlargement.

Animals↗
PubMed1986

Location of motoneurones projecting to the cat distal forelimb. II. Median and ulnar motornuclei.

The position of the motornuclei projecting through the median (Mn) and ulnar (Ul) nerves to the cat distal forelimb has been investigated. Horseradish peroxidase (HRP) and fluorescent (Fl) compounds have been used as retrograde tracers. They were either injected into forelimb muscles or applied to the proximal end of transected forelimb nerves. Limb muscles that were not investigated were carefully denervated. The position and the architecture of the individual motornuclei were traced with HRP. The topographical relations between the nuclei were established with application of up to three different Fl compounds in the same animal. The Mn motoneurones had a bimodal distribution in the brachial spinal cord. The motoneurones to the pronator teres and flexor carpi radialis muscles were located in C7 and the other Mn motoneurones were located in C8 and Th1. In C7 the Mn motoneurones occupied a single representation area, which is located some distance medially of the lateral funiculus. In C8 and Th1 two Mn representation areas were found: A dorsal one that contacts the lateral funiculus and is located at the level of the central canal; a ventral one that is located ventrally in the ventral horn. The dorsal area is occupied by the motornuclei projecting to the intrinsic hand muscles and the ventral one by the nuclei projecting to the limb. The Ul motoneurones extend with an unimodal distribution from the caudal C7 to the caudal Th1 segments. They occupy a single, broad representation area. The dorsal part, which contacts the lateral funiculus, is located at the level of the central canal and harbours the nuclei to the intrinsic hand muscles. The other Ul nuclei are located ventromedially deep in the ventral horn. These results, together with those from the companion paper on the location of the deep radial motornuclei, provide important anatomical information for the investigation of the cat brachial enlargement.

Animals↗
PubMed1984

Pyramidal actions in identified radial motornuclei of the cat.

This study aimed to establish the projection from the corticospinal tract (CST) to the motoneurones innervating the deep radial (DR) forelimb muscles. In the anaesthetized cat stimulation of the contralateral pyramid and intracellular recording from identified forelimb motoneurones was used. A train of pyramidal stimuli evoked disynaptic EPSPs in DR motoneurones. The effects were very similar in the different nuclei. Pyramidal IPSPs had a slightly longer latency and occurred in most cases together with disynaptic EPSPs. It is suggested that the inhibitory actions to the distal forelimb are predominantly relayed in a trisynaptic pathway, but that a disynaptic linkage seems possible as well. The disynaptic pyramidal EPSPs remained after CST transection in C5. They were abolished after CST transections in C2. It is concluded that disynaptic corticospinal excitation of distal DR motornuclei is relayed in a short midcervical propriospinal system. Transection experiments at different cervical levels suggest that the majority of the propriospinal neurones is located in C3-C4. The CST facilitated a variety of reflex pathways to motoneurones innervating distal forelimb muscles. Disynaptic excitatory and inhibitory effects from cutaneous and low threshold group I muscle afferents were common. They were present in all investigated nuclei and powerfully facilitated from the CST. It is suggested that this allows the brain to adapt the reflex mechanisms of the distal forelimb to the synergistic-antagonistic relations between the muscles, which are changing according to the performed movement.

Animals↗
PubMed1982

Location of median and ulnar motornuclei in the cat.

In the cat we used the horseradish peroxidase (HRP) technique to investigate the location of the motor nuclei projecting through the median and the ulnar nerves. Each nucleus is described b its longitudinal extent along the rostro-caudal spinal cord axis and by its dorso-ventral and medio-lateral position within the ventral horn. The topographical relations between different nuclei are, however, only provisionally ascertained with the HRP technique, since the simultaneous use of different fluorescent tracers in the same animal is a more powerful approach to establish the spatial relations between different neuronal populations. One example with the latter technique is reported, which demonstrates the complete overlap of two different nuclei.

Animals↗
PubMed1982

Fluorescent compounds as retrograde tracers compared with horseradish peroxidase (HRP). II. A parametric study in the peripheral motor system of the cat.

Fluorescent compounds which are currently used as retrograde tracers were tested in the cat peripheral motor system and compared with horseradish peroxidase (HRP). The tracers were either injected into forelimb muscles or applied to the proximal end of transected forelimb nerves. The remaining muscles of the limb has been carefully denervated. Following intramuscular injection all fluorescent compounds labeled spinal cord motoneurons, the DAPI compounds labeled endothelial cells in addition. In the nerve application mode tracer positive motoneurons were only observed when propidium iodide (PI) and the DAPI compounds were used, whereas bisbenzimide (BB), nuclear yellow (NY) and primuline did not label any cells. The fluorescence of BB labeled motoneurons were predominantly located in the cytoplasma. NY positive motoneurons showed a different localization of the fluorescent label between the different neurons of the same motornucleus: in some neurons it was exclusively located in the nucleus, in others predominantly in the cytoplasma, in the majority in both compartments. The intracellular distribution of the BB and the NY label was independent of the pH of the fixation fluid. The fluorescent tracers labeled the motoneuronal cell columns in their complete rostrocaudal extent and in a position identical to the one obtained with HRP. However, some substances (PI, fast blue) labeled less motoneurons of a motornucleus than did HRP, none of the fluorescent tracers labeled more. The results are discussed under several aspects: use of the investigated fluorescent compounds as single tracers; use of several tracers in the same animal to map collateral projections of one and the same neuron; use of several tracers in the same animal to establish the topographical relation between several independent neuronal populations.

Animals↗
PubMed1981

Location of dorsal interosseus motor nuclei in the cat.

In the cat we have investigated the position of the motor nuclei projecting through the dorsal interosseus nerve to the distal forelimb muscles. Horseradish peroxidase was either injected into single muscles or applied to the central end of a cut nerve. The location of each nucleus is described in two ways: histograms giving the distribution of the labelled motoneurones along the rostro-caudal spinal cord axis; and regions in reconstructed cross-sections of the ventral horn which indicate the area occupied by the motoneurones of one nucleus. The relation between the nuclei was established by superposition of the reconstructed cross-sections. With this procedure we have obtained a map which shows the positions of the centres of the single radial nuclei.

Animals↗
PubMed1981

Single preganglionic sympathetic neurons of the cat branch intraspinally and project through different rami communicantes albi--a retrograde double labelling study with fluorescent tracers.

Evidence is presented that in lumbar segments of the cat, two neighbouring rami communicantes albi (white rami, WR) may contain axons of one and the same preganglionic sympathetic neurone (PSN). This was shown with bisbenzimide (Bb) and propidium iodide (PI) applied in the same cat to the central cut ends of two WR (PI to WRL1, Bb to WRL2). PSN, double labelled from both these sites, were observed in the intermediolateral and intercalate nuclei of the L1 segment. It is postulated that axons of PSN branch intraspinally and project through different WR.

Animals↗
PubMed1981

Integration in descending motor pathways controlling the forelimb in the cat. 7. Effects from the reticular formation on C3-C4 propriospinal neurones.

Effects of stimulation in the medullary reticular formation (RF) on C3-C4 propriospinal neurones (PNs) were investigated in two series of experiments: (1) indirectly by analyzing how propriospinal transmission to forelimb motoneurones is modified by reticular stimuli; (2) directly by intracellular recording from C3-C4 neurones, which were identified as propriospinal by their antidromic activation from the C6 segment. Propriospinally mediated disynaptic EPSPs evoked in motoneurones from the pyramid (Pyr) and the red nucleus (NR) were effectively facilitated by conditioning stimulation in the RF with a time course of facilitation indicating monosynaptic linkage to the PNs. Propriospinally mediated trisynaptic IPSPs were facilitated less regularly and sometimes instead depressed by conditioning stimulation in the RF. The depression is at least partly due to inhibition of the first order PNs. Recording from C3-C4 PNs revealed that many of them were excited or inhibited by single stimuli in the RF. The brief latency of the EPSPs evoked in these neurones shows monosynaptic linkage from fast reticulospinal fibres. Some IPSPs were similarly monosynaptically evoked from fast fibres and observations are presented suggesting that longer latency IPSPs are monosynaptically mediated by slower fibres. Facilitation of propriospinal transmission to motoneurones as well as the EPSPs and IPSPs in PNs were evoked from a region within or close to the nucleus reticularis gigantocellularis. Convergence of monosynaptic EPSPs from Pyr, NR, tectum, and RF was common in C3-C4 PNs. Linear summation of the EPSPs from RF with those evoked from cortico-, rubro-, or tectospinal tracts shows that the former are not due to stimulation of collaterals which the latter tracts may have in RF. Mediation of the EPSPs and IPSPs by descending, rather than by antidromically activated ascending fibres, was indicated by temporal facilitation produced by RF stimuli, subliminal for evoking monosynaptic PSPs in the PNs. Stimulation of the labyrinth did not evoke disynaptic PSPs in any of the PNs investigated. It is concluded that the C3-C4 PNs projecting to forelimb motoneurones can be excited not only from the cortico-, rubro-, and tectospinal tracts (Illert et at. 1977, 1978) but also by reticulospinal fibres.

Animals↗
PubMed1981

Cytoarchitectonic organization of lumbar preganglionic sympathetic neurons in the cat.

The location and dendritic projection of lumbar preganglionic sympathetic neurons (PSN) has been investigated in the cat. Horseradish peroxidase was either injected into lumbar paravertebral ganglia or directly applied to a lumbar ramus communicans albus. PSN were regularly found in the lateral funiculus and in the intermediate area of the ipsilateral spinal cord. They were concentrated in different nuclei: nuclei intermediolateralis pars principalis (IMLp) and pars funicularis (IMLf), nucleus intercalatus (IC) and medially near the central channel. Inconsistently, some PSN were observed in the ventral horn. Dendrites extending over a few soma were found in nearly all PSN, thus allowing description of the main dendritic projections of the preganglionic nuclei. Sometimes axons of IMLp and IC neurons could be traced into the ventral roots. In the IMLp the PSN were arranged in round clusters (up to 30 cells), which regularly followed each other in rostrocaudal direction. These clusters increased their mediolateral diameter from L1 to L4. Many cells distributed their dendrites longitudinally within the IMLp, but dendritic projections into the dorsal horn, the intermediate area and into the lateral funiculus were also frequently observed. The IMLf consisted of a few PSN only. These neurons were located in the tissue spaces between axon bundles and mediolaterally arranged, pointing towards the IMLp. The PSN of the IC were mediolaterally oriented and arranged in transverse bands extending from the lateral horn to the dorsal aspects of the central channel. All cells had mediolaterally oriented dendrites which sometimes crossed the spinal cord midline in case of the medially located neurons. The dendrites of the laterally located cells projected very often into the dorsal horn. In the medial region the PSN covered a narrow area extending from the dorsal aspects of the central channel in a ventrolateral direction up to the level of the ventral commissure. The neurons were localized in clusters and mediolaterally or longitudinally oriented. Dense clusters consisting of round cells were prevalent in the ventrolateral position. The dendrites had a rostrocaudal and mediolateral orientation and, in case of the dorsomedially located cells, sometimes crossed the spinal cord midline. The main dendritic projection areas of the different preganglionic nuclei have been compared with the location of the terminal fields of descending supraspinal and propriospinal systems and of primary afferents. It has been considered that this structural arrangement would allow for intricate interaction of the various systems with subpopulations of PSN. Thus each preganglionic nucleus might integrate specific neuronal information.

Animals↗
PubMed1978

Integration in descending motor pathways controlling the forelimb in the cat. 5. Properties of and monosynaptic excitatory convergence on C3--C4 propriospinal neurones.

Recording was made in the C3--C4 segments from cell bodies of propriospinal neurones identified by their antidromic activation from more caudal segments. Monosynaptic excitatory effects from descending motor pathways and primary afferents were investigated by electrical stimulation of higher motor centres and peripheral nerves in the forelimb and neck. The cell bodies were located mainly laterally in Rexed's layer VII. Threshold mapping for single axons showed that they descend in the lateroventral part of the lateral funicle. Antidromic stimulation at different spinal cord levels showed that some neurones terminated in the forelimb segments, others in the thoracic cord or in the lumbar segments. Terminal slowing of the conduction velocity suggested axonal branching over some segments. Monosynaptic EPSPs were evoked in the neurons by stimulation of the contralateral pyramid, red nucleus and dorsal tegmentum-superior colliculus. It is concluded that corticospinal, rubrospinal and tectospinal fibres project directly to both short and long propriospinal neurones. There was marked frequency potentiation in tectospinal synapses. Convergence from two descending tracts was common and in half of the tested cells all three tracts contributed monosynaptic excitation. Experiments with collision of descending volleys and antidromic volleys from the brachial segments demonstrated that the corticospinal and rubrospinal monosynaptic projection to the propriospinal neurones is by collaterals from fibres continuing to the forelimb segments.

Action Potentials↗
PubMed1978

Integration in descending motor pathways controlling the forelimb in the cat. 4. Corticospinal inhibition of forelimb motoneurones mediated by short propriospinal neurones.

A previously described inhibitory trisynaptic cortico-motoneuronal pathway (Illert et al., 1976a) was analysed in order to identify the two relay stations. Intracellular recording was made from motoneurones to elbow muscles. Corticospinal fibres were stimulated in the contralateral medullary pyramid. Pyramidal IPSPs were abolished by a transection of the corticospinal tract in C2 but remained after a corresponding lesion in C5. After a C5 lesion pyramidal volleys facilitated transmission in the Ia inhibitory pathway with a time course suggesting disynaptic excitatory action on the Ia inhibitory interneurones. The trisynaptic pyramidal IPSPs were depressed by volleys in the appropriate recurrent motor axon collaterals as would be expected if these IPSPs were mediated by Ia inhibitory interneurones. It is concluded that trisynaptic cortico-motoneuronal inhibition is evoked by consecutive activation of propriospinal neurones in C3--C4 and segmental Ia inhibitory interneurones.

Animals↗
PubMed1976

Integration in descending motor pathways controlling the forelimb in the cat. 1. Pyramidal effects on motoneurones.

Stimulation of the contralateral pyramid and intracellular recording from forelimb motoneurones was used to investigate corticimotoneuronal pathways in the cat. A train of pyramidal volleys evokes short-latency EPSPS in flexor motoneurones and in many extensor motoneurones. The latency for the onset after the effective pyramidal volley-usually the third - strongly indicates a disynaptic linkage. These disynaptic EPSPs were common in triceps motoneurones to fast heads but rare in those to slow heads. Pyramidal IPSPs with a slightly longer latency, suggesting a trisynaptic linkage, were found in both flexor and extensor motoneurones. They were common in motoneurones to slow heads of triceps. Disynaptic pyramidal IPSPs were found only occasionally. In addition pyramidal volleys may evoke late large EPSPs and/or IPSPs in any combination with the short-latency PSPs.

Animals↗
PubMed1976

Integration in descending motor pathways controlling the forelimb in the cat. 2. Convergence on neurones mediating disynaptic cortico-motoneuronal excitation.

With intracellular recording from forelimb motoneurones the spatial facilitation technique has been used to investigate interaction between descending pathways and forelimb afferents. As previously shown for the hindlimb, pyramidal volleys effectively facilitate interneuronal transmission in reflex pathways from different primary afferents. Evidence is presented suggesting disynaptic excitation from corticospinal fibres of interneurones in the reciprocal Ia inhibitory pathway. Interneurones of other reflex pathways from group I muscle afferents recieve monosynaptic pyramidal excitation. During pyramidal facilitation volleys in cutaneous afferents may evoke PSPs in motoneurones after a central delay of 1.3 ms suggesting that the minimal linkage is disynaptic. Information regarding convergence on the neurones intercalated in the disynaptic cortico-motoneuronal pathway was obtained by investigating the effect from primary afferents and from other descending pathways on the disynaptic pyramidal EPSPs. Volleys in cutaneous and group I muscle affferents facilitate transmission in the disynaptic cortico-motoneuronal transmission with a time course showing oligosynaptic (probably monosynaptic) action the intercalated neurone. Rubrospinal volleys likewise effectively facilitate disynaptic cortico-motoneuronal pathway with a time course showing oligosynaptic (probably monosynaptic) action on the intercalated neurone. Rubrospinal volleys likewise effectively facilitate disynaptic cortico-motoneuronal transmission with a time course showing monosynaptic action on the intercalated neurone. Spatial facilitation experiments involving three tests revealed that those intercalated neurones which receive convergent monosynaptic excitation from corticospinal and rubrospinal fibres are excited also from cutaneous forelimb afferents. Disynaptic cortico-motoneuronal transmission was also monosynaptically facilitated by stimuli in the dorsal mesencephalic tegmentum probably activating tectospinal fibres. Disynaptic, presumed tectospinal EPSPs were facilitated from cutaneous forelimb afferents. The convergence onto the neurones intercalated in the disynaptic excitatory cortico-motoneuronal pathway suggests that these neurones integrate the activity in different descending pathways and primary forelimb afferents.

Animals↗
PubMed1976

Convergence on interneurones mediating the reciprocal Ia inhibition of motoneurones. I. Disynaptic Ia inhibition of Ia inhibitory interneurones.

Interneurones identified as mediating the disynaptic reciprocal Ia inhibition of motoneurones (referred to as "Ia inhibitory interneurones") were recorded in the lumbar spinal cord of the cat. It was revealed that the Ia inhibitory interneurones themselves receive disynaptic Ia inhibition. The muscles from which this inhibition is evoked are strictly antagonistic to those supplying their Ia excitation. Similar to the Ia inhibition in motoneurones the Ia inhibition in the Ia inhibitory interneurones is decreased when preceded by an antidromic stimulation of ventral roots. Furthermore, transmission of Ia inhibition to the Ia inhibitory interneurones is facilitated from ipsilateral and contralateral primary afferents as well as several supraspinal pathways analogous to earlier findings for the Ia inhibition of motoneurones. The pattern and control of the Ia inhibition of motoneurones and of Ia inhibitory interneurones display so striking similarities that it is suggested that identical interneurones are responsible. The conclusion thus emerges that "opposite" Ia inhibitory interneurones (i.e. interneurones monosynaptically connected to antagonistic muscles) are mutually inhibiting each other. The functional significance of this organization is discussed.

Afferent Pathways↗