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J Tomas

Publications and source records attributed to J Tomas.

At least 19 recordsLinked to original sources
PubMed2001

IgM monoclonal antibody against terminal moiety of GM2, GalNAc-GD1a and GalNAc-GM1b from a pure motor chronic demyelinating polyneuropathy patient: effects on neurotransmitter release.

We describe a patient with a pure motor chronic demyelinating polyneuropathy with an IgM monoclonal component showing anti-GM2, GalNAc-GD1a and GalNAc-GM1b reactivity whose common epitope appears to be -[GalNAcbeta1-4Gal(3-2alphaNeuAc)beta1]. We used intracellular recording to study how IgM from this patient affected neurotransmitter release in the mouse diaphragm in vitro. Adding serum (and specifically, the purified monoclonal IgM component) blocked the nerve-evoked response in both quantal content and evoked endplate potential (EPP) amplitude in a complement-independent and reversible manner. The IgM increased the frequency of spontaneous miniature endplate potentials (MEPPs) in a complement-dependent and reversible manner but had no effect on MEPP amplitude.

Adult↗
PubMed2001

Pertussis toxin-sensitive G-protein and protein kinase C activity are involved in normal synapse elimination in the neonatal rat muscle.

Individual skeletal muscle fibers in most new-born rodents are innervated at a single endplate by several motor axons. During the first postnatal weeks, the polyneuronal innervation decreases in a process of synaptic elimination. Previous studies showed that the naturally occurring serine-protease thrombin mediates the activity-dependent synapse reduction at the neuromuscular junction (NMJ) in vitro and that thrombin-receptor activation may modulate nerve terminal consolidation through a protein kinase mechanism. To test whether these mechanisms may be operating in vivo, we applied external thrombin and its inhibitor hirudin, and several substances affecting the G protein-protein kinase C system (GP-PKC) directly over the external surface of the neonatal rat Levator auris longus muscle. Muscles were processed for immunocytochemistry to simultaneously detect acetylcholine receptors (AChRs) and axons for counting the percentage of polyinnervated NMJ. We found that exogenous thrombin accelerated synapse loss and hirudin blocked axonal removal. Phorbol-12-myristate-13-acetate, a potent PKC activator, had a similar effect as thrombin, whereas the PKC inhibitors, calphostin C and staurosporine, prevented axonal removal. Pertussis toxin, an effective blocker of GP function, blocked synapse elimination. These findings suggest that the normal synapse elimination in the neonatal rat muscle may be modulated, at least in part, by the pertussis-sensitive G-protein and PKC activity and that thrombin could play a role in the postnatal synaptic maturation in vivo.

Animals↗
PubMed2000

Topological differences along mammalian motor nerve terminals for spontaneous and alpha-bungarotoxin-induced sprouting.

Spontaneous sproutings can be observed in end plates from normal adult vertebrate muscles and motor end plates develop increased growth signs and sprouts when target muscle cells become less active or paralysed. Nevertheless, very little is known about where in the motor nerve terminal arborization spontaneous and experimentally induced sprouts originate, their similarities and differences and also about their final maturation or elimination. In this study we investigate the topological properties of both spontaneous and alpha-bungarotoxin-induced sprouts (during different periods of intoxication and after recovery) along the motor nerve terminal branches of the Levator auris longus muscle of Swiss mice (between 48-169 day old). Muscles were processed for immunocytochemistry to simultaneously detect postsynaptic AChRs and axons. This procedure permits us to make an accurate identification of the fine sprouts and a morphometric study of the presynaptic branching pattern profile in control muscles, during the toxin action and after recovery from paralysis. The results show that in normal muscles, the initial and trunk segments (those between branch points) of the terminal arborization sprouted proportionally more branches when taking their relative lengths into account than the distal free-end segments. In contrast, every micrometer of alpha-bungarotoxin-treated muscles throughout the full terminal arborization have the same probability of generating a sprout. Moreover, the toxin-induced sprouts can consolidate as new branches once recovered from the paralysis without changing the total length of the nerve terminal arborization.

Aging↗
PubMed1997

Physiological activity-dependent ultrastructural plasticity in normal adult rat neuromuscular junctions.

The major finding of the present study is that the ultrastructural organization of the neuromuscular synapse can be modified by a small, 4-week-long, physiological increase in the locomotor activity of the extensor digitorum longus muscle of normal adult rats trained to walk. This study measures these plastic adaptations using several synaptic morphological parameters. The observed changes in neuromuscular junctions affect both pre- and postsynaptic membranes. In particular, the presynaptic membrane densities in the active zones and the postsynaptic adaxonal membrane densities become larger, which shows that in the normal adult mammal neuromuscular junction, there is an activity-dependent modulation of the neurotransmission-related structures in response to slight physiologic functional demands. The nature and magnitude of these changes are discussed.

Animals↗
PubMed1993

Activity-dependent plastic changes in the motor nerve terminals of the adult rat.

Small and short-lasting physiologic variations in the locomotor activity of normal adult rats can induce remodelling in the motor nerve endings of the fast extensor digitorum longus muscle. The specificity and relative importance of the different plastic adaptations occurring in the presynaptic axonal tree have been studied, in silver impregnated nerve endings, by using an automatic image analysis treatment of the nerve terminals' geometric properties and a discriminant analysis of the morphometric parameters. Changes observed, like selective length variations in certain terminal segments and positional rearrangements, agree with a mechanism of neural connectivity regulation in the adult that arises as a consequence of normal neuromuscular activity.

Adaptation, Physiological↗
PubMed1992

Pattern of arborization of the motor nerve terminals in the fast and slow mammalian muscles.

A silver impregnation method and a morphometric approach were used to define differences existing in the motor nerve terminal branching pattern between a fast-twitch muscle (extensor digitorum longus) and a slow-twitch one (soleus) of the normal adult rat. Because no single measure can describe precisely all geometrical properties (ie both topology and metrics) of the nerve terminals, we evaluated morphologic parameters defining length and angular characteristics in the different terminal segments classified according to their centrifugal order. The main results indicate that the distal free-end segments in the extensor digitorum longus muscle are shorter and less divergent than in the soleus nerve terminals. The endings in the two muscles have different fractal dimensions. Findings are discussed in the context of the hypothetical mechanisms governing motor nerve terminal size and complexity.

Animals↗
PubMed1991

Excretion of the Escherichia coli alpha-haemolysin by Serratia marcescens.

Serratia marcescens 2170 derivative strains harbouring either the haemolytic plasmid pANN202-312 or pANN202-312R, were able to produce extracellular haemolysin to a greater extent than the corresponding Escherichia coli 5K strains. The haemolysin recovered from S. marcescens cultures supernatants had a molecular weight of 110 kD, and its extracellular production was maximal near the end of the exponential growth phase. The hlyR sequence, which belongs to the haemolytic determinant located in the plasmid pHly152 and enhances haemolysin expression and secretion in E. coli, appeared not to play an equivalent role in S. marcescens.

Blotting, Western↗
PubMed1990

Branching pattern of the motor nerve endings in a skeletal muscle of the adult rat.

We have performed a morphometric analysis of the branching pattern of the rat sternomastoid motor nerve terminals in normal and regenerated singly-innervated synaptic areas, in junctions with an accessory ending and also in dually-innervated synaptic areas. We tried to seek measurable differences related to the terminal complexity and size in these different situations. The number of sole-plate nuclei is always significantly correlated with the nerve terminal parameters and unrelated to the muscle cell diameter. A significant correlation between the terminal complexity and the postsynaptic size is found only in the smallest endings whereas correlation is lost with the increase in nerve terminal complexity. In normal singly-innervated areas, the mean length of the distal free-end segments of the terminal arborisation becomes reduced with the increase in complexity of the terminals, whereas the mean length of the segments between branching points and the mean angle of branch emergence is, on average, constant. Whereas the accessory endings show the same branching pattern as the endings during the initial days of regeneration, the parent ending can be considered as a miniature version of the endings in normal singly-innervated junctions. In dually-innervated areas, the smallest endings show a similar branching pattern to the accessory endings and the endings during the initial process of reinnervation, whereas the larger endings show a significant reduction in the length of the distally placed segments compared to the normal endings in singly-innervated areas. Results indicate that the terminal branching pattern is not haphazard but, on the contrary, general rules and tendencies can be measured.

Animals↗
PubMed1989

Motor nerve terminal morphologic plasticity induced by small changes in the locomotor activity of the adult rat.

The possible existence of plastic changes in the branching pattern and the complexity of silver-impregnated motor nerve terminals was studied in the extensor digitorum longus muscle of adult rats housed in metabolic cages or trained to walk. Results indicate a precise inverse relation between the amount of locomotor activity and the complexity finally attained by the motor nerve terminals.

Animals↗
PubMed1980

Calcium fluxes in isolated pure cholinergic nerve endings from the electric organ of Torpedo marmorata.

1. Ca fluxes were studied in a pure cholinergic preparation of nerve endings from Torpedo electric organ. In standard physiological saline solution (280 mM Na+, 3 mM K+) the calcium uptake was at the rate of 8 nmole per mg of protein per minute, equivalent to a calcium influx of 0.6 pmole/cm2 x sec. 2. The rate of calcium uptake was enhanced when synaptosomes were depolarized, increasing potassium concentration in the external medium. Maximum stimulation was reached when the potassium concentration was over 50 mM and averaged 20 nmole Ca2+ per mg protein per minute, equivalent to calcium influx of about 1.5 pmole/cm2 x sec. 3. Protoveratrine and tytiustoxin also stimulated calcium uptake into the nerve terminals and their effect was blocked by tetrodotoxin. Tetrodotoxin didn't block calcium uptake in K+-stimulated synaptosomes. Some inhibitors of transmitter release such as Dantrolene, Verapamil, BetaBungarotoxin and adenine nucleotides prevented the stimulatory effect on calcium uptake by depolarizing agents. 4. The calcium entry increased roughly linearly with a slope proportional to external calcium concentrations up to 20 mM. This effect was greatly increased when either 100 mM K+ or protoveratrine were added to the external medium. 5. Most of the loss of isotope from 45Ca-loaded synaptosomes occurred by a sodium-dependent calcium efflux mechanism with half-activation at 13 mM Na+. This may be equivalent to 1.65 pmole/cm2 x sec. 6. In sodium-free and calcium-free solutions, a residual efflux (5 nmole per mg protein per min) is observed. Metabolic inhibitors such as CN- enhanced this residual efflux. 7. Morphological studies using sodium-free fixation solutions and radioautographic detection of 45Ca are consistent with calcium sequestration by intracellular organelles by a similar mechanism to the calcium buffering system described in disrupted synaptosomes. Synaptic vesicles may play an important role in this calcium sequestration.

Adenine Nucleotides↗