Interaction dynamics of two diffusing particles: contact times and influence of nearby surfaces.

Interactions of diffusing particles are governed by hydrodynamics on different length and timescales. The local hydrodynamics can be influenced substantially by simple interfaces. Here, we investigate the interaction dynamics of two micron-sized spheres close to plane interfaces to mimic more complex biological systems or microfluidic environments. Using scanned line optical tweezers and fast 3D interferometric particle tracking, we are able to track the motion of each bead with precisions of a few nanometers and at a rate of 10 kilohertz. From the recorded trajectories, all spatial and temporal information is accessible. This way, we measure diffusion coefficients for two coupling particles at varying distances h to one or two glass interfaces. We analyze their coupling strength and length by cross-correlation analysis relative to h and find a significant decrease in the coupling length when a second particle diffuses nearby. By analysing the times the particles are in close contact, we find that the influence of nearby surfaces and interaction potentials reduce the diffusivity strongly, although we found that the diffusivity hardly affects the contact times and the binding probability between the particles. All experimental results are compared to a theoretical model, which is based on the number of possible diffusion paths following the Catalan numbers and a diffusion probability, which is biased by the spheres' surface potential. The theoretical and experimental results agree very well and therefore enable a better understanding of hydrodynamically coupled interaction processes.

[Type II Charcot-Marie-Tooth and dopa-sensitive Parkinson disease]. / Maladie de Charcot-Marie-Tooth type II et syndrome parkinsonien dopasensible.

The occurrence of a dopa-sensitive parkinsonian syndrome 25 years after a neuropathy suggestive of Charcot-Marie-Tooth disease type II raised the possibility of a relationship between these two diseases. Apart from Machado-Joseph-Azorean disease, an association of this kind seems to be exceptional and it can not be excluded that it was fortuitous. However, the recent description of 7 familial and sporadic cases of a syndrome characterized by a peripheral neuropathy, familial in 5 of the 7 cases, followed, a few years later, by a dopa-sensitive parkinsonian syndrome, makes it possible to consider that this association might have a common genetic origin.

[Sciatic radiculalgia with muscular hypertrophy]. / Radiculalgie sciatique avec hypertrophie musculaire.

A 52-year-old male developed hypertrophy of the right calf after several bouts of right lumbar pain with sciatica. Electromyography disclosed evidence of demyelination in the territories of the right S1 and S2 roots. Microscopic studies showed both atrophic muscle fibers scattered among fibers of normal caliber and a large number of hypertrophic fibers. Post-sciatica hypertrophy of the calf is a true muscle hypertrophy with muscle weakness. Electromyography may show unusual tracings with repeated complex bursts or continuous activity of motor units. Muscle enzyme levels may be elevated. The size of hypertrophied fibers varies across cases. The cause of the muscle fiber hypertrophy may be either stretching due to the action of antagonists or unusual electrical activity.

[Involuntary leakage of urine in women]. / Les pertes urinaires insensibles de la femme.

Involuntary leakage of urine in women is often the result of ill-understood pathological conditions which, it seems to us, can most often be related to neurological troubles or to post-operative urethral scarring with or without weak sphincter action associated with urethral instability. They are responsible for a large fraction of the poor results that have been obtained after treatment of bladder instability or of urinary incontinence due to the transmission defect. They should be looked for carefully in every pre-treatment work-out of a patient. The treatment consists mainly in using oestrogen and in re-educating the sphincter muscles with the help of a biofeed-back technique, as well as finally giving-anticholinergic drugs. When they are associated with stress incontinence of urine due to faulty transmission they do not represent an absolute contra-indication to surgery, so long as it is understood that the outcome of the surgery will always, in these cases, be less favourable.

[Contribution of electromyography to the diagnosis of acute radicular or medullary cervical disc palsies (author's transl)]. / Apport de l'électromyographie au diagnostic des paralysies aiguës radiculaires ou médullaires cervicales d'origine discale.

Operative treatment was employed in 38 patients with cervical disc lesions. These had produced either compression of spinal cord nerves, especially C6 or C7 (22 cases), or cervical ischemic lesions (16 cases) of the centromedullary region, either isolated or associated with symmetrical, bilateral cord lesions. A study of pre- and post-operative clinical and electromyographic correlations enabled differentiation of acute cervical radioculopathies from myelopathies and definition of their progression as a function of the surgical treatment employed.

[Contribution of EMG to the diagnosis of facial nerve and muscle involvement in neurinoma of the VIIIth nerve]. / Apport de l'EMG au diagnostic des atteintes faciales par neurinome du VIII.

An examination of 5 cases of acoustic nerve neurinoma, and 3 cases where the diagnosis was suspected, showed that EMG signs of a possible facial nerve compression in the ponto-cerebellar angle were represented by abnormal activity at rest, sub-clinical signs of progressive neurogenic atrophy in the hemi-facial muscles, and a significant increase in the latency of the oligosynaptic R1 reflex response.

[Fisher's syndrome. Peripheral or central origin (author's transl)]. / Syndrome de Fisher. Origine périphérique ou centrale?

The syndrome described by M. Fisher in 1956 includes ophtalmoplegia, ataxia, and generalized loss of reflexes. It is classically considered to be of peripheral origin and its relation to Guillain and Barre's syndrome in its mesencephalic form is debatable. The authors review 5 cases and discuss the question of a probable central origin. They base their opinion on the pathognomonic features of these cases and those in the literature, as well as the results of their oculographic and electromyographic studies. They stress the importance of the nature of the ataxia; the severe equilibrium disturbances noted in these patients could result, contrary to usual thinking, more from a central vestibular syndrome than from a cerebellar lesion.