Recurrente Hemmung der Extensor-Fusimotoneurone?

Summary The antidromic effect of ventral root or muscle nerve stimulation has been studied on functionally isolated -efferents to the medial gastrocnemius muscle in the intercollicular decerebrate cat. Tetanic stimulation of the ventral root at levels below the threshold for the investigated -efferents decreases the activity of 10 out of 19 -motoneurones. This effect is greater in cats with intact contralateral dorsal roots. Tetanic stimulation of synergic muscular nerves inhibits some of the investigated -motoneurones, whereas tetanic stimulation of antagonistic muscular nerves fails to have any inhibitory effect. It is suggested that the recurrent inhibition of -motoneurones is mediated via at least one additional interneuron between the Renshaw cell and the -motoneuron.

     

Effects of combining static and dynamic fusimotor stimulation on the response of the muscle spindle primary ending to sinusoidal stretching.

1. A pair of fusimotor fibres, one static and the other dynamic, were stimulated simultaneously to test their combined action on the response of muscle spindle primary endings in the cat soleus to sinusoidal stretching. A frequency of 1 Hz was chiefly used, with a wide range of amplitudes (10 micronm-2 mm). The response of the ending was assessed from the parameters of the sine fitted to its firing averaged throughout the course of the cycle; this was felt useful even though the responses to the larger stretches showed certain non-linear features. 2. With small stretches (up to about 50 micronm amplitude) static action dominated, and the modulation of firing during conbined stimulation was little or no larger than that found during the static stimulation on its own, and much smaller than that found during the static stimulation on its own, and much smaller than that found during the dynamic stimulation. The phase of the response was, however, much the same for all three conditions. 3. With larger stretches the modulation with combined stimulation was intermediate between the values found on stimulating either fusimotor fibre on its own; the dynamic contribution increased progressively with the amplitude of stretching. 4. With larger stretches the phase of the response during combined stimulation was appreciably closer to that for static action than to that for dynamic action. But the differences between the various conditions were small (below 20 degrees) and seem attributable to various distortions of the response wave from away from a true sinusoid, rather than betokening a difference in the ratio of velocity to length sensitivity under the various conditions. This view was supported by the effects on phase of grading the rate of stimulation of one fusimotor fibre while holding that of the other constant. 5. Detailed comparison of the cycle histograms obtained under different conditions showed an interestingly asymmetrical pattern of summation and occlusion of the effects of the two kinds of fusimotor fibre. At the peak of the response to a large stretch static action summed with dynamic action, which was here the stronger, so that at this phase of the cycle the firing was greater with the combined stimulation than with either fibre on its own. But, in the trough of the response to the same stretch static action occluded any dynamic action, which was now the weaker, so that at this phase of the cycle the firing with combined stimulation was virtually the same as that with static stimulation on its own. With a small stretch, static action normally occluded dynamic action throughout the cycle; this is in line with the firing during static action now usually being greater than that during dynamic action for all phases of the cycle.     

Evidence for a non-orthostatic origin of orthostatic tremor

OBJECTIVES: Orthostatic tremor was first described by Heilman in 1984. It usually occurs in the legs during stance and decreases markedly during sitting or walking. The aim of this study was to determine if orthostatic tremor is invariably associated with the orthostatic and weight bearing conditions in the arms and legs, and to investigate the features of orthostatic tremor under different levels of peripheral loading. METHODS: Multichannel surface EMG recordings were obtained under different conditions (body posture and peripheral loading) from the proximal arm and leg muscles of seven patients fulfilling the clinical and electrophysiological criteria of orthostatic tremor. RESULTS: In weight bearing positions (stance; weight bearing on the hands on all fours), all patients showed 13 Hz-16 Hz tremor activity, predominantly in the active limb. No tremor activity could be found in a supine position with muscles at rest. Isometric contraction of the limbs in the supine position led to synchronous 13 Hz-16 Hz rhythmic activity in five patients. No tremor was seen when the subjects were suspended in a harness with relaxed legs. Isometric contraction of the legs in this position produced tremor in two patients. A stepwise reduction of the body weight by a harness reduced the tremor activity. Additional loading (10 kg-20 kg) during stance led to an increase in tremor amplitude, but tremor frequency remained unchanged. CONCLUSIONS: Orthostatic tremor is invariably present during stance or other weight bearing positions. It is not, however, always associated with orthostasis. In at least some patients it can be classified as an orthostasis independent action tremor. The failure of peripheral loading to modify tremor frequency indicates that orthostatic tremor may have a central, rather than a peripheral, origin.     

Cytocompatibility of a novel, longitudinally microstructured collagen scaffold intended for nerve tissue repair

Traumatic injury to the nervous system induces functional deficits as a result of axonal destruction and the formation of scar tissue, cystic cavitation, and physical gaps. Bioengineering bridging materials should ideally act as cell carriers for the implantation of axon growth-promoting glia, as well as supporting integration with host cell types. Here, we describe the cytocompatibility of a novel, micro-structured porcine collagen scaffold containing densely packed and highly orientated channels that, in three-dimensional (3D) tissue culture, supports attachment, proliferation, aligned process extension, and directed migration by populations of glial cells (olfactory nerve ensheathing cells and astrocytes) and orientated axonal growth by neurons (differentiated human SH-SY5Y neuroblastoma cell line). The seeded glia required several weeks to penetrate deeply into the highly porous scaffold, where they adopted an orientated morphology similar to that displayed in simple 2D cultures. The direct interaction between SH-SY5Y-derived nerve fibers and the collagen scaffold also resulted in highly orientated axonal growth. It is likely that biocompatible scaffolds that are capable of promoting glial cell attachment, migration, and highly orientated process outgrowth will be important for future repair strategies for traumatically injured nervous tissues.     

Acute exacerbations of idiopathic pulmonary fibrosis

The natural history of idiopathic pulmonary fibrosis (IPF) has been characterized as a steady, predictable decline in lung function over time. Recent evidence suggests that some patients may experience a more precipitous course, with periods of relative stability followed by acute deteriorations in respiratory status. Many of these acute deteriorations are of unknown etiology and have been termed acute exacerbations of IPF. This perspective is the result of an international effort to summarize the current state of knowledge regarding acute exacerbations of IPF. Acute exacerbations of IPF are defined as acute, clinically significant deteriorations of unidentifiable cause in patients with underlying IPF. Proposed diagnostic criteria include subjective worsening over 30 days or less, new bilateral radiographic opacities, and the absence of infection or another identifiable etiology. The potential pathobiological roles of infection, disordered cell biology, coagulation, and genetics are discussed, and future research directions are proposed.     

Computer-based screening of chest X-rays for vertebral compression fractures as an osteoporosis index in men

We evaluated the recognition of osteoporosis in the veteran male population through a computer-based review of chest X-ray (CXR) reports in the Veterans Affairs Northern California Health Care System database, looking for unrecognized vertebral fractures. All CXR reports between January 1, 2000 and December 31, 2001, were scanned for the terms "compression" or "wedg (where the " indicates a wild card search encompassing such terms as "wedge" or "wedging")". During this time, 26,994 CXR examinations were performed on 18,069 patients. 22,494 (83.3% of the total) CXR examinations were done in 14,561 men >or=50 years of age. 780 CXR reports (3.5%) encompassing 664 men (4.5%) contained at least one key phrase suggesting osteoporosis. Three years later, 495 of these 664 men were still living. 99 of these (20%) had been diagnosed with osteoporosis, 72 (15%) had a dual-energy X-ray absorptiometry (DXA) scan, and 89 (18%) had ever been prescribed a bisphosphonate. Overall, only 126 (25%) men had chart documentation indicating some recognition by the provider of the abnormality reported on CXR. We conclude that a significant fraction of men >50 years old may have unrecognized osteoporosis severe enough to result in vertebral fracture. We conclude that computerized screening of CXR reports may represent an effective strategy to aid clinicians in identifying men at risk for further debilitating fractures.