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Biomedical subjects

R G Hallin

Publications and source records attributed to R G Hallin.

At least 37 records · Page 2Linked to original sources
PubMed1993

Functional recovery in primates with brachial plexus injury after spinal cord implantation of avulsed ventral roots.

Intraspinal replantation of avulsed spinal nerve roots as a surgical treatment for motor deficits after severe brachial plexus injury was investigated in primates. Under general anaesthesia hemi-laminectomy was performed in cynomolgus monkeys (Macaca fascicularis). Ventral roots within the brachial plexus were then avulsed by traction and subsequently implanted into the ventrolateral aspect of the spinal cord. No dysfunction in the long fibre tracts was seen following surgery. Postoperatively there was a flaccid paralysis of the arm on the lesioned side. Severe atrophy developed within 5-7 weeks in the muscles supplied by the avulsed roots and EMG revealed denervation activity. Two to three months after surgery there were EMG signs of reinnervation, which were shortly followed by evidence of clinical recovery. A gradual improvement in the function of the affected arm occurred and the animals' motor behaviour normalised. One year after surgery there was a full range of motion in the arm, but the EMG activity in the reinnervated muscles at maximal force was reduced. Tracing of regenerated motor neurons with horseradish peroxidase (HRP) injected into the biceps muscle revealed retrogradely labelled motor neurons confined to the ipsilateral ventral horn. It was concluded that intraspinal replantation of avulsed ventral roots in primates significantly promotes motor recovery in the muscles supplied by the lesioned spinal cord segments.

Animals↗
PubMed1992

Somatosensory and autonomic deficiencies following trauma in man; evaluation of symptomatology by studying peripheral neural correlates and induced tissue reactions.

Careful clinical and experimental studies in well-diagnosed groups of selected patients can give valuable information concerning unknown mechanisms involved in certain disease states. In particular, microneurographic techniques can be applied to assess the underlying neural pathophysiology. It is anticipated that future studies performed along these guidelines will contribute to an improved diagnosis and/or therapy in a number of clinical conditions.

Adult↗
PubMed1991

Segregation by modality of myelinated and unmyelinated fibers in human sensory nerve fascicles.

Thin diameter concentric needle electrodes with a small recording surface were used to explore the characteristics of neighboring fibers in sensory median nerve fascicles. Fibers which were close neighbors in the fascicle, were not randomly distributed intraneurally. Instead there was an intrafascicular segregation by modality of both myelinated and unmyelinated fibers. In addition, evidence was obtained which suggested that the contents of different Schwann cells vary. Some Schwann cell systems envelop afferent C fibers whereas others hold efferent sympathetic C axons. The results imply a modality segregation amongst both A and C fibers in human peripheral sensory nerve fascicles.

Adult↗
PubMed1990

Microneurography in relation to intraneural topography: somatotopic organisation of median nerve fascicles in humans.

Microneurography was performed in median nerve sensory fascicles with concentric needle electrodes and with conventional tungsten microneedles. The latter electrodes preferentially recorded activity from the myelinated fibres in the whole fascicle. By contrast, due to its special design, a concentric needle can record activity selectively from even a small part of a fascicle. High amplitude signals in C fibres can be discriminated close to Schwann cells that envelope unmyelinated axons. Apart from being biased for activity in thin fibres, the concentric needles can also record signals from nearby myelinated fibres. The palmar receptive fields of such fibre groups were not congruent with the areas traditionally attributed to multiunit skin afferents in humans, namely the innervation zone(s) of one or two adjacent digital nerve(s). Instead, the multiunit fields often comprised small parts of a digital nerve innervation area, frequently only the pulp of a finger. Single units were always localised within previously screened multiunit areas. Contrary to some previously accepted tenets it is probable that single unit activity in myelinated fibres in these studies is recorded extra-axonally near to a node of Ranvier. The findings also suggest the presence of a somatotopy in human limb nerve fascicles, comparable to that previously established in the spinal cord and the somatosensory cortex.

Adrenergic Fibers↗
PubMed1986

Percutaneous microneurography in man does not cause pressure block of almost all axons in the impaled nerve fascicle.

Neural activity from the median nerve was recorded in 5 volunteers with a concentric needle electrode that has two recording surfaces in very close proximity at the tip. The aim of this study was to establish the probability of recording activity in the nerve from both surfaces simultaneously. We wanted to test one aspect of a recent critique of the microneurographic technique (Wall and McMahon, Pain, 21 (1985) 209-229), namely the suggestion that the recording electrode in these types of studies causes pressure block of almost all fibers in the impaled nerve fascicle. In 80% of our experiments it was possible to record neural activity at both surfaces simultaneously. These results indicate that the physiological state of the peripheral nerves during microneurographic explorations is not necessarily highly abnormal due to pressure block of nearly 100% of the nerve fibers close to the recording electrode tip. Our results thus speak against this aspect of the criticism of the microneurographic technique.

Adult↗
PubMed1984

Do large diameter cutaneous afferents have a role in the transmission of nociceptive messages?

In recent studies, it has been reported that high-frequency stimulation restricted to A alpha beta fibers in man can be perceived as painful and evoke a nociceptive flexion reflex. These results would indicate that some patterns of activity in low-threshold mechanoreceptors can lead to painful sensations. Because of the theoretical importance of this question, the above studies were extended by recording the evoked neural activity with the technique of percutaneous microneurography. Painful sensations and the nociceptive reflex did not appear unless the evoked nerve response contained activity in A delta fibers. The results support the theory that painful sensations occur in normal man only when nociceptor afferents are activated.

Acoustic Stimulation↗
PubMed1984

The influence of the sympathetic system on mechanoreception and nociception. A review.

Physiological evidence, including some recent microneurographic data obtained in man, that suggests the existence of a sympathetic influence on somatosensory input is reviewed. Following nerve injury abnormal sympathetic-afferent connections might occur. Hypothetically, such abnormalities could be of significance in clinical states involving nerve injuries where sensory and trophic dysfunctions are also prominent characteristics.

Adrenergic Fibers↗
PubMed1982

Nociceptors and warm receptors innervated by C fibres in human skin.

The properties of 125 C fibre units recorded from the peripheral nerves of conscious man were studied. On the basis of receptive field properties and responses to natural stimulation, 120 of the units were classified as polymodal C nociceptors. Five of the units were identified as specific C warm receptors. In contrast to the polymodal nociceptors, which often had comparatively large and complex receptive fields with several receptive maxima, receptive fields of the thermo-receptors consisted of one single spot. Polymodal nociceptors responded readily to moderately intense and noxious mechanical stimuli whereas the warm receptors produced inconsistent responses to even intense mechanical skin stimulation. Thermal stimulation in the innocuous range, perceived as warmth, optimally excited the thermoreceptors whereas the polymodal C nociceptors fired most intensely to noxious painful heat.

Adult↗
PubMed1981

Neurophysiological studies of peripheral nerve functions after neural regeneration following nerve suture in man.

Eleven patients, of which the majority had sustained total transection of the median nerve at the wrist, were investigated at least 5 years after epineural nerve suture. Electrophysiological examinations included conventional electromyography and electroneurography, as well as percutaneous microelectrode exploration of the sutured nerves proximal to the site of injury. In all cases the functional neural recovery was incomplete as evaluated by electrophysiological techniques. The most satisfactory clinical and electrophysiological recovery was observed in the youngest patients with the shortest delay from injury to nerve suture. Aside from reduced conduction velocity single regenerated myelinated fibres had qualitatively normal response characteristics and receptive fields as revealed by recording with microelectrodes. Multi-unit recordings however disclosed abnormal fascicular receptive fields which consisted of two to four separate skin patches in reinnervated skin. This misdirection of regenerated nerve fibres may account for faulty sensory localization of light tactile stimuli in the area of reinnervation. The clinical implications of the appearance of this phenomenon during the process of reinnervation are discussed.

Adolescent↗