Biomedical subjects

M Nicolet

Publications and source records attributed to M Nicolet.

At least 19 recordsLinked to original sources

PubMed1992

Cytotactin is involved in synaptogenesis during regeneration of the frog neuromuscular system.

The expression of cytotactin, an extracellular matrix glycoprotein involved in morphogenesis and regeneration, was determined in the normal and regenerating neuromuscular system of the frog Rana temporaria. Cytotactin was expressed in adult brain and gut as two major components of Mr 190,000 and 200,000 and a minor form of higher molecular weight, but was almost undetectable in skeletal muscle extract. However, cytotactin was concentrated at the neuromuscular junctions as well as at the nodes of Ranvier. After nerve transection, cytotactin staining increased in the distal stump along the endoneurial tubes. In preparations of basal lamina sheaths of frog cutaneous pectoris muscle obtained by inducing the degeneration of both nerve and muscle fibers, cytotactin was found in dense accumulations at original synaptic sites. In order to define the role of cytotactin in axonal regeneration and muscle reinnervation, the effect of anti-cytotactin antibodies on the reinnervation of the basal lamina sheaths preparations was examined in vivo. In control preparations, regenerating nerve terminals preferentially reinnervate the original synaptic sites. In the presence of anti-cytotactin antibodies, axon regeneration occurred with normal fasciculation and branching but with altered preterminal nerve fibers pathways. Ultrastructural observations showed that synaptic basal laminae reinnervation was greatly delayed or inhibited. These results suggest that cytotactin plays a primordial role in synaptogenesis, at least during nerve regeneration and reinnervation in the adult neuromuscular system.

Animals↗

PubMed1992

N-cadherin and N-CAM in myoblast fusion: compared localisation and effect of blockade by peptides and antibodies.

The expression and distribution of two cell adhesion molecules, N-cadherin and N-CAM, at the surface of cultured leg muscle cells from 11-day-old chicken embryos were studied and compared. N-cadherin, which was expressed by fusing myoblasts, was down-regulated on old myotubes while N-CAM was still present. Both molecules, as viewed by confocal microscopy, appeared to have coaccumulated at the areas of contact between fusing myoblasts. However, immunogold electron microscopy did not reveal significant colocalization of N-cadherin and N-CAM, and their segregation after antibody-induced patching suggested the absence of direct interactions between N-cadherin and N-CAM. The role of the Ca2+ dependent cell adhesion molecule N-cadherin in myogenesis was investigated. Myoblast fusion was inhibited (1) with a synthetic peptide containing the H-A-V sequence and (2) with a monoclonal anti-N-cadherin antibody, demonstrating that N-cadherin-mediated cell adhesion is required for myoblast fusion. Under the same conditions no effect of anti-N-CAM antibodies was observed. Taken together these observations suggest that N-cadherin, acting independently from N-CAM, is a major cell adhesion molecule involved in embryonic myoblast fusion in vitro.

Amino Acid Sequence↗

PubMed1991

Phosphatidylinositol is involved in the attachment of tailed asymmetric acetylcholinesterase to neuronal membranes.

1. We analyzed the mode of attachment of 16 S tailed acetylcholinesterase (AChE; EC 3.1.1.7) to rat superior cervical ganglion (SCG) neuronal membranes. Using extractions by high-salt (HS) and nonionic detergent (Triton X-100), we found two pools of 16 S AChE. 2. The detergent-extracted (DE) 16 S AChE was tightly bound to membranes through detergent-sensitive, high-salt insensitive interactions and was distinct from high-salt-soluble 16 S AChE. The detergent-extracted (DE) 16 S AChE constituted a significant proportion of about one-third of the total 16 S AChE. 3. Treatment of the neuronal membranes by a phosphatidylinositol-specific phospholipase C (PIPLC) resulted in the release of some, but not all DE 16 S AChE, indicating that a significant amount of the neuronal DE 16 S AChE, about one-third, is anchored to membranes through a phosphatidylinositol containing residue. Thus, a covalent association of a glycolipid and catalytic or structural AChE polypeptidic chains occurs not only for dimeric AChE but also for the asymmetric species of AChE. 4. The complex polymorphism of AChE is due not only to different globular or asymmetric associations of catalytic and structural subunits but also to the alternative existence of a transmembrane domain or a glycolipid membrane anchor.

Acetylcholinesterase↗

PubMed1990

[Dieulafoy's simple stomach ulcer: apropos of 5 cases].

Dieulafoy's ulcer is a probably congenital arterial malformation which may produce severe upper gastrointestinal haemorrhage. It represents about 1% of all cases of acute upper gastrointestinal haemorrhage (3/249 in our department during 1989). We report 5 cases in whom haemostatic endoscopic treatment was successful and propose therefore that this therapy should be the initial treatment of choice. Surgical intervention should be considered only if endoscopic therapy fails.

Adult↗

PubMed1990

Cell modulation of hydrophobic tailed 16S acetylcholinesterase by intracellular calcium in rat superior cervical ganglion neurons.

In primary cell cultures of rat superior cervical ganglia (SCG) the tailed asymmetric 16S molecular form of acetylcholinesterase (AChE) possesses hydrophilic (high-salt soluble, HSS) and hydrophobic (detergent extracted, DE) variants. Hydrophobic tailed acetylcholinesterase is associated with membranes through a glycolipid anchor. In the presence of tunicamycin, an antibiotic which inhibits protein glycosylation, the cellular amount of the hydrophobic DE 16S AChE is increased. Exposure of the cells to the calcium ionophore A 23187 leads to a decrease in DE 16S AChE and a correlated increase in hydrophilic HSS 16S AChE. These results suggest the existence of an endogenous processing of tailed AChE, transforming the hydrophobic variant into an hydrophilic one controlled through glycosylation and intracellular calcium.

Acetylcholinesterase↗

PubMed1989

Scoring atopic dermatitis: the simpler the better?

Two scoring methods evaluating the severity of atopic dermatitis have been compared. One was simple, quick and compatible with a busy outpatients clinic. The other was more complicated and time consuming; it took into account most of the evaluable clinical signs of disease activity in each involved site. There was a highly significant correlation between the two methods of scoring, thus validating the simplest one; furthermore, the more complicated method was less reproducible than the simplest when used by two physicians on the same patient. This suggests that a simple and feasible scoring method is meaningful in keeping records at each visit in any patient with atopic dermatitis. Such records may then be used in retrospect for the evaluation of any new therapy.

Adolescent↗

PubMed1988

Distribution and role in regeneration of N-CAM in the basal laminae of muscle and Schwann cells.

The neural cell adhesion molecule (N-CAM) is a membrane glycoprotein involved in neuron-neuron and neuron-muscle adhesion. It can be synthesized in various forms by both nerve and muscle and it becomes concentrated at the motor endplate. Biochemical analysis of a frog muscle extract enriched in basal lamina revealed the presence of a polydisperse, polysialylated form of N-CAM with an average Mr of approximately 160,000 as determined by SDS-PAGE, which was converted to a form of 125,000 Mr by treatment with neuraminidase. To define further the role of N-CAM in neuromuscular junction organization, we studied the distribution of N-CAM in an in vivo preparation of frog basal lamina sheaths obtained by inducing the degeneration of both nerve and muscle fibers. Immunoreactive material could be readily detected by anti-N-CAM antibodies in such basal lamina sheaths. Ultrastructural analysis using immunogold techniques revealed N-CAM in close association with the basal lamina sheaths, present in dense accumulation at places that presumably correspond to synaptic regions. N-CAM epitopes were also associated with collagen fibrils in the extracellular matrix. The ability of anti-N-CAM antibodies to perturb nerve regeneration and reinnervation of the remaining basal lamina sheaths was then examined. In control animals, myelinating Schwann cells wrapped around the regenerated axon and reinnervation occurred only at the old synaptic areas; new contacts between nerve and basal lamina had a terminal Schwann cell capping the nerve terminal. In the presence of anti-N-CAM antibodies, three major abnormalities were observed in the regeneration and reinnervation processes: (a) regenerated axons in nerve trunks that had grown back into the old Schwann cell basal lamina were rarely associated with myelinating Schwann cell processes, (b) ectopic synapses were often present, and (c) many of the axon terminals lacked a terminal Schwann cell capping the nerve-basal lamina contact area. These results suggest that N-CAM may play an important role not only in the determination of synaptic areas but also in Schwann cell-axon interactions during nerve regeneration.

Animals↗

PubMed1986

Globular and asymmetric acetylcholinesterase in frog muscle basal lamina sheaths.

After denervation in vivo, the frog cutaneus pectoris muscle can be led to degenerate by sectioning the muscle fibers on both sides of the region rich in motor endplate, leaving, 2 wk later, a muscle bridge containing the basal lamina (BL) sheaths of the muscle fibers (28). This preparation still contains various tissue remnants and some acetylcholine receptor-containing membranes. A further mild extraction by Triton X-100, a nonionic detergent, gives a pure BL sheath preparation, devoid of acetylcholine receptors. At the electron microscope level, this latter preparation is essentially composed of the muscle BL with no attached plasmic membrane and cellular component originating from Schwann cells or macrophages. Acetylcholinesterase is still present in high amounts in this BL sheath preparation. In both preparations, five major molecular forms (18, 14, 11, 6, and 3.5 S) can be identified that have either an asymmetric or a globular character. Their relative amount is found to be very similar in the BL and in the motor endplate-rich region of control muscle. Thus, observations show that all acetylcholinesterase forms can be accumulated in frog muscle BL.

Acetylcholinesterase↗

PubMed1985

Rapid axonal transport of three molecular forms of acetylcholinesterase in the frog sciatic nerve.

Acetylcholinesterase occurs in the frog sciatic nerve under five stable molecular forms with distinct sedimentation coefficients in sucrose gradients: 3 globular forms (3.6S, 6S and 10.5S) and two asymmetric ones (14S and 18S). Whereas in birds and mammals, the asymmetric tailed forms of acetylcholinesterase are present in trace amounts in peripheral nerves and account for only a small part of the enzyme activity submitted to a rapid axonal transport, the two asymmetric 14S and 18S forms represent nearly 50% of total activity in the frog sciatic nerve and account for 60-70% of the acetylcholinesterase activity accumulated at both sides of a nerve transection, the rest being due to an accumulation of globular molecules. We showed that the three forms, 10.5S, 14S and 18S, are all carried with the fast phase of axonal transport at a velocity of 100-120 mm/day in the anterograde direction and 20-30 mm/day in the retrograde direction. The velocity of transport for the light molecular forms 3.6S and 6S could not be calculated. In addition, we observed that large amounts not only of the 10.5S but also of the asymmetric 14S and 18S forms appear to be stationary along the frog sciatic nerve, contrary to the situation described for peripheral nerves in birds or mammals. Our results thus reveal that some axonal transport parameters for the asymmetric forms of acetylcholinesterase greatly differ in the peripheral nerves of amphibians on the one hand and of birds and mammals on the other, suggesting that these heavy molecular forms might have distinct functions in the nerves of lower and higher vertebrates.

Acetylcholinesterase↗

PubMed1982

[Histochemical study of skeletal muscles of the frog, Rana temporaria].

Histochemical profiles of muscles were identified based on staining for myosin ATPase activity. They reveal typical arrangement of muscular fibres with a zoned pattern. Tonic fibres have a unique histochemical profile and are mixed with the most oxydative fast fibres to form toxic zones. Muscles show fast profiles in thigh and tonic or mixed profiles in fore-arm.

Adenosine Triphosphatases↗

PubMed1981

[Molecular forms of acetylcholinesterase in frog skeletal muscle: effects of denervation].

In the muscles of the frog, four main molecular forms of acetylcholinesterase are present, with sedimentation coefficients of 5.7, 10.4, 13 and 17.6 S. The heaviest forms, 13 S and 17.6 S are found in both nerve-free segments and endplates zones of sartorius muscle. They decrease in long-term denervation experiments. Consequently, these two forms are not specifically localized in endplates containing regions. However, they depend either on muscle activity or on neural influence or both.

Acetylcholinesterase↗

PubMed1976

[Tetanic fatigue and proximate post-tetanic recuperation in sartorius and flexor carpi radialis muscles of the male frog. Effects of iodoacetic acid (author's transl)].

The time-course of the isometric tension output, at 20 degrees C, during a long tetanus and after a short period of rest, was investigated in two isolated frog muscles : the sartorius and flexor carpi radialis muscles. To prevent aerobie and glycolytic recovery processes, some muscles were poisoned with 0,4 mM iodoacetic acid (IAA) and nitrogen, for 20 or 40 min. 1. For the unpoisoned sartorius muscle, tetanic tension declined quickly, but after a 0,8 sec period of rest, the muscle was able to develop high tension. Poisoning with IAA-N2 increased fatigue without suppressing the property of a proximate post-tetanic recuperation. 2. In the flexor carpi radialis muscle resistance to fatigue was very large before poisoning and diminished after poisoning. Proximate recuperation was very weak. 3. The results show that the recovery processes are not a primary factor of the development of the short-term fatigue ; they enhance the hypothesis that a failure of the electromechanical coupling can explain the rate of the tension fall in tetanized sartorius muscles.

Anaerobiosis↗

PubMed1975

Tonic properties of the Flexor carpi radialis muscle of the male frog (Rana temporaria).

The mechanical acitvity of the isolated flexor carpi radialis muscle (FCRM) of the mature male frog (Rana temporaria) was compared to that of the sartorius muscle. Muscles were stimulated directly by massive shocks at 20 degrees C and isometric tension was recorded during single twitch, twitch series, long tetani and long tetanus series. Some groups of muscles were poisoned with IAA-N2 or FDNB. The FCRM showed a high resistance to fatigue during a tetanus series and a "fatigue contracture" during a twitch series. The rate of the tetanic tension rise was smaller by five to six times than in the sartorius muscle (0 to 50% Po) and the twitch/tetanus ratio was always very small. During continuous activity and after the blocking of recovery metabolic pathways, FCRM used its energetic stores two to three times slower than the sartorius muscle. These stores did not seem to be more important. The results indicate that the FCRM is not a "tonic" muscle but, quite possibly, is composed of several types of fibre like many other frog muscles. However, some characteristics of mechanical response cannot be explained by the common classification into two types of fibre.

Animals↗

PubMed1974