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Biomedical subjects

R Mackel

Publications and source records attributed to R Mackel.

29 records · Page 2Linked to original sources
PubMed1986

Effects of growth, degeneration and regeneration on the sensory motor system.

Evidence was presented for regeneration and growth in the central nervous system of experimental animals and in the peripheral nervous system of man. Neurophysiological, neurohistological and neurochemical findings from the cerebellothalamocortical and the nigrostriatal projection systems as well as the motoneurons of the anterior horn and facial nucleus were presented and their possible functional implications discussed. Single unit recordings from regenerated primary afferents in human peripheral nerves were also shown and discussed in the light of their clinical relevance. The conclusions were reached that the findings of positive growth in the CNS following traumatic injury or in response to brain implants left little doubt that the CNS possesses the intrinsic capability of regeneration. The functional and clinical implications of this inherent capacity awaits further research. Recording the response behavior of regenerated primary afferents in man, on the other hand, provided more direct insight into functional deficits and their clinical correlates.

Animals↗
PubMed1985

Properties of cutaneous mechanosensitive afferents during the early stages of regeneration in man.

The technique of percutaneous microneurography was used to record single unit activity from 75 regenerated primary afferents innervating the glabrous skin of the human hand. Thirteen patients were studied, who had suffered complete transection, with subsequent suture or graft, of the median or ulnar nerves. The recordings were obtained from 7 to 23 months postoperatively (early regeneration). Three types of mechanoreceptive afferents (RA, SAI, SAII) and many deep units of unknown origin were found. No regenerated PC units could be identified. The reinnervated receptors were predominantly located in the palm and proximal fingers, comparable to those found 3 years or more postoperatively (late regeneration). Response thresholds and in general, discharge and receptive field characteristics of the majority of afferents were largely comparable to late regeneration and normal. The properties of SAII units were like normal in all respects. However, several distinct abnormalities were encountered early during regeneration: multiple receptive fields innervated by a single afferent (2/9 RA and 2/9 SAI), unusually small or large receptive fields (RA and SAI), pronounced fatigue on repetitive stimulation (7/15 SAI, 4/6 deep). Responses of reinnervated skin to sustained and repeated indentations were found to be similar to those of normal skin, and therefore, could not account for the abnormal discharge behavior. It is suggested that the transitional properties of regenerating afferents reflect unstable axon-end organ connections and immature axonal properties. Both factors would contribute to the slow course of sensory recovery, making prognosis on tactile recovery unpredictable.

Adolescent↗
PubMed1985

Human cutaneous mechanoreceptors during regeneration: physiology and interpretation.

Percutaneous microneurography was used to record activity from single cutaneous afferents reinnervating the glabrous skin of the hand. Recordings were obtained from 6 months to 10 years after complete transsection of the median and/or ulnar nerves with subsequent repair. Transitional properties in the discharge behavior and receptive field characteristics of regenerating afferents were detected during the early stages of regeneration, when axonal maturation was still in progress; these may contribute to the slow time course of sensory recovery. Properties of reinnervated receptors long after nerve repair, when regeneration can be considered complete, indicated a correlation between electrophysiological findings and the final state of clinical recovery. The insights into the neural basis of sensory deficits provided by single-unit microneurography are not yielded by conventional study of the compound action potentials. This technique reveals new information about the pathophysiological nature of peripheral nerve injury and leads to a reinterpretation of clinical deficits.

Action Potentials↗
PubMed1984

Action of tizanidine on responses of forearm flexors and extensors to torque disturbances.

The effects of tizanidine on the electromyographic responses of forearm flexors and extensors to torque disturbances were studied in normal subjects. Tizanidine had a strong depressive action on all the reflex responses, and on muscle background activity. It is concluded that the action on reflexes is not specific, but secondary to decreased spinal cord excitability.

Adult↗
PubMed1983

Transitional properties of afferents reinnervating mechanoreceptors in the human glabrous skin.

The technique of percutaneous microneurography was used to record in man from single mechanoreceptive afferents during the early stages of reinnervation. Although response properties were in several ways comparable to normal and to those of afferents studied long after nerve repair, two abnormalities were found: multiple receptive field innervation by single afferents (RA, SAI), and response fatigue with repeated stimulation (SAI). These abnormalities are considered transitional, disappearing when reinnervation is complete.

Adaptation, Physiological↗
PubMed1983

Reinnervation of mechanoreceptors in the human glabrous skin following peripheral nerve repair.

The technique of percutaneous microneurography was used to record single unit activity from 65 reinnervated and 24 normally innervated mechanoreceptors in the glabrous skin of the human hand. The results were obtained from 20 patients and 5 control subjects. The patients had suffered complete traumatic transsection, with subsequent repair, of the median or ulnar nerves. Three types of mechanoreceptors (RA, SAI, SAII) and many unidentified units located in deep tissues were found to become reinnervated. No reinnervated PC units could be identified. Response thresholds, discharge characteristics and receptive field properties of reinnervated receptors were comparable to normal, with the exception that reinnervated SA I units had slower static discharge rates and smaller receptive fields. No evidence was found for multiple peripheral innervation by a single afferent fiber. The reinnervated mechanoreceptors were predominantly located in the palm and the proximal fingers with few in the finger tips, contrary to normal. The locations and frequency of occurrence of the different types of receptors could be correlated with the goodness of sensory recovery. It is suggested that these differences result from misguidance of regenerating fibers and from poor reinnervation, and that they account for reduced sensitivity and poor tactile discrimination in patients with peripheral nerve injuries.

Adolescent↗
PubMed1981

Pattern of 'non-reciprocal' inhibition of motoneurones by impulses in group Ia muscle spindle afferents in the cat.

1. Inhibitory post-synaptic potentials (i.p.s.p.s) evoked by adequate stimulation of group Ia muscle spindle afferents of triceps surae and plantaris and by near-threshold electrical stimulation of quadriceps and hamstring nerves were recorded in a number of motoneurone species. The aim of the study was to compare the pattern of non-reciprocal Ia inhibitory actions on hind-limb motoneurones with the pattern of inhibition evoked from group Ib tendon organ afferents.2. In all the motoneurone species analysed in which i.p.s.p.s were evoked by electrical stimulation maximal for both group Ia and Ib afferents of triceps surae and plantaris, they were also evoked when these muscles were stretched and the amplitude of the stretch (10-35 mum) was below threshold for Ib afferents; 70-100% of motoneurones with Ib i.p.s.p.s showed stretch-evoked i.p.s.p.s. The stretch-evoked i.p.s.p.s appeared with latencies compatible with disynaptic and trisynaptic linkage. Since these latencies were too short to allow their mediation by group II afferents the i.p.s.p.s are attributed to a selective action of Ia afferents. The i.p.s.p.s did not appear after the nerves to triceps surae and plantaris had been cut.3. Electrical stimulation of quadriceps and hamstring nerves which was near threshold for Ia afferents and well below threshold for either the Ib component of the incoming volley or group II afferents, similarly evoked non-reciprocal i.p.s.p.s. They were found in those motoneurones in which inhibition was evoked by stimulation maximal for group I afferents. Such Ia i.p.s.p.s were evoked both in homonymous motoneurones and in motoneurones of four other hind-limb muscles. Their latencies corresponded to di- and trisynaptic coupling.4. In some motoneurones of the pretibial flexors (anterior tibial, extensor digitorum longus and peroneus longus), disynaptic i.p.s.p.s evoked from triceps surae and/or plantaris which were depressed by a conditioning ventral root stimulation (i.e. Ia reciprocal i.p.s.p.s) were followed by trisynaptic i.p.s.p.s which were not depressed in this way (Ia ;non-reciprocal' i.p.s.p.s). It thus appears that the same motoneurones may be inhibited by impulses in group Ia afferents via different spinal pathways.5. The study leads to the conclusion that the non-reciprocal inhibition from group Ia muscle spindle afferents operates in parallel with the inhibition from group Ib tendon organ afferents in all motoneurone species tested.

Animals↗
PubMed1981

Oligosynaptic excitation of motoneurones by impulses in group Ia muscle spindle afferents in the cat.

1. Intracellular recording from hind-limb motoneurones was used to investigate whether di- and trisynaptic (oligosynaptic) excitatory post-synaptic potentials (e.p.s.p.s) are evoked from group Ia muscle spindle afferents in those motoneurones in which such potentials are evoked from Ib tendon organ afferents or entire group I afferents. Ia afferents of triceps surae and plantaris were activated either selectively by single brief stretches of these muscles, or together with Ib afferents by electrical stimuli applied to the nerves.2. Muscle stretches below threshold for Ib afferents (10-35 mum) evoked e.p.s.p.s which appeared with latencies compatible with disynaptic and trisynaptic coupling between the afferents and the motoneurones. The latencies of a majority of these e.p.s.p.s were too short to allow their mediation by group II afferents, if any were activated by the applied stretches. They were also too short to be compatible with effects attributable to dorsal root reflexes. These e.p.s.p.s are thus attributed to oligosynaptic actions of Ia afferents.3. Stretch-evoked di- and trisynaptic Ia e.p.s.p.s were found in 83% of motoneurones in which e.p.s.p.s were evoked by stimuli which activated both Ia and Ib afferents; in five motoneurone species they were found in more than 90%. These observations lead to the conclusion that group Ia muscle spindle afferents evoke not only inhibitory but also excitatory actions in parallel with group Ib tendon organ afferents.4. The distribution of Ia oligosynaptic stretch-evoked excitation from ankle and toe extensor muscles was compared with the distribution of Ia non-reciprocal inhibition as described by Jankowska, McCrea & Mackel (1981b). Excitation pre-dominated in posterior biceps-semitendinosus motoneurones and inhibition in other species of motoneurones investigated, except those of intrinsic foot muscles (tibial motoneurones); similar proportions of the latter showed excitation and inhibition.5. Occurrence of oligosynaptic e.p.s.p.s as well as inhibitory post-synaptic potentials (i.p.s.p.s) of Ia origin in some motoneurone species, and in particular in individual motoneurones, is indicative of a number of reflex pathways between group I afferents and these motoneurones. Furthermore, the disappearance of some of the e.p.s.p.s evoked by near-threshold electrical stimulation following stronger stimuli indicates interactions between various functional groups of interneurones mediating group I actions.

Animals↗
PubMed1979

Segmental and descending control of the external urethral and anal sphincters in the cat.

1. The present work concerns the contribution of the somatic central nervous system to two viscero-somatic reflexes, micturition and defecation. Descending and segmental actions and properties of the motoneurones innervating the striated external urethral and external anal sphincters were studied with intracellular recording in male cats, under chloralose anaesthesia. 2. Motoneurones innervating the external urethral and external anal sphincters were intermingled and most strongly concentrated in the lateral part of the ventral horn in the S2 segment of the spinal cord. 3. Stimulation of the S1 to S3 ipsilateral dorsal roots or of the homonymous pudendal nerve branches showed that less than half of the sphincter motoneurons receive monosynaptic excitatory connexions from low threshold afferents. 4. The after-hyperpolarization recorded in the external urethral and external anal sphincter motoneurones was relatively short lasting, not long lasting as would have been expected for motoneurones innervating slow-twitch, tonic type muscles. 5. There was no evidence for recurrent inhibition in pudendal motoneurones innervating the external urethral and external anal sphincters. 6. Descending excitation and inhibition to the sphincter motoneurones originated in the nucleus reticularis gigantocellularis of the medullary reticular formation. The descending reticulospinal actions are comparable to those observed in hind limb motoneurones. 7. It is suggested that the segmental reflex connexions play a role in controlling bladder and rectal continence. The descending actions studied also modulate the segmental reflex actions and may provide voluntary control of the sphincter muscles.

Anal Canal↗
PubMed1978

Reticulospinal excitation and inhibition of neck motoneurons.

Responses of neck motoneurons to electrical stimulation of the pontomedullary reticular formation were recorded intracellularly in cerebellectomized cats anesthetized with chloralose. Stimulation of nucleus reticularis (n.r.) ventralis and the dorsal part of n.r. gigantocellularis evoked short latency, monosynaptic inhibitory postsynaptic potentials (IPSPs) in the majority of motoneurons supplying the ipsilateral splenius, biventer cervicis and complexus muscles and in 25% of motoneurons projecting in the ipsilateral spinal accessory nerve. Monosynaptic IPSPs were also evoked by stimulating the medial longitudinal fasciculus (MLF) but lesion and collision experiments indicated that these IPSPs were independent of those evoked by reticular stimulation. Monosynaptic IPSPs were also occasionally observed following stimulation of the contralateral reticular formation, especially of the dorsal part of n.r. gigantocellularis. Monosynaptic excitatory postsynaptic potentials (EPSPs) were evoked in all classes of neck motoneurons studied by stimulation of n.r. pontis caudalis, gigantocellularis and ventralis. Each reticular nucleus appeared to contribute to this excitation. The excitation was bilateral but large monosynaptic EPSPs were most often seen in motoneurons ipsilateral to the stimulus site. Data indicated that pontine EPSPs were mediated by ventromedial reticulospinal fibers while medullary EPSPs were mediated by ventrolateral reticulospinal fibers. Neck motoneurons thus receive at least three distinct direct reticulospinal inputs, two excitatory and one inhibitory.

Accessory Nerve↗