PubMed Health⌕ Search

Biomedical subjects

M Pecot-Dechavassine

Publications and source records attributed to M Pecot-Dechavassine.

13 recordsLinked to original sources
PubMed1997

Selective motor hyperreinnervation using motor rootlet transfer: an experimental study in rat brachial plexus.

Misdirection of sensory fibers into motor pathways is, in part, responsible for the poor results obtained after peripheral nerve repair. After avulsion of the C-5 root in rats, the authors connected a C-4 ventral rootlet to the musculocutaneous nerve by means of a sural nerve graft. In this way, they were able to increase the number of regenerating motor fibers and avoid growth of sensory fibers into the nerve grafts. Functional recovery was evaluated electrophysiologically and histologically. The origin of the axons that reinnervated the nerve graft was analyzed by means of morphological studies including retrograde labeling procedures. Motor neurons survived and regenerated after the rootlet transfer and there was no functional impairment. Many neurons were retrograde labeled in the ventral horn and widespread biceps muscle reinnervation was demonstrated with recovery of nearly normal electrophysiological properties. Motor hyperreinnervation of the musculocutaneous nerve was observed. This high degree of reinnervation in a long (40-mm) graft was attributed to the good chance that a muscle fiber can be reinnervated by a motor fiber when the number of regenerating motor neurons is increased and when competitive sensory fibers are excluded from reinnervation.

Animals↗
PubMed1995

The rat brachial plexus and its terminal branches: an experimental model for the study of peripheral nerve regeneration.

Despite the introduction of microsurgical techniques into clinical practice, the results of surgical procedures involving the brachial plexus and peripheral nerves are still far from spectacular. We therefore studied the rat brachial plexus and its terminal branches in 203 rats. Detailed anatomic and morphologic analyses of the biceps brachii and musculocutaneous nerve, finger flexors, flexor carpi radialis, and the median nerve were performed. Various sources of conventional and vascularized nerve grafts were explored. After musculocutaneous nerve section or median nerve section, there were no articular contractures or automutilations, which constitutes an advantage for these experimental models over the sciatic nerve model. The brachial plexus and its terminal branches provide a good experimental model which can be used to assess the development and normal control of muscle function, examine the mechanisms underlying functional recovery, and test the effects of treatments to enhance recovery.

Animals↗
PubMed1990

Presynaptic actions of botulinal neurotoxins at vertebrate neuromuscular junctions.

1. In the present paper we review some presynaptic aspects of the mode of action of botulinal toxins (BoTxs) at vertebrate neuromuscular junctions with emphasis on studies carried out in our laboratories using electrophysiological and morphological techniques. 2. Spontaneous quantal transmitter release recorded as miniature end-plate potentials is drastically affected by BoTxs. The low probability of release at poisoned terminals can be enhanced by carbonyl cyanide m-chlorophenylhydrazone (CCCP), Cd2+ and La3+. However, CCCP and La3+ which drastically deplete clear synaptic vesicles from unpoisoned terminals failed to markedly affect the density of synaptic vesicles at poisoned terminals. It is concluded that poisoned terminals have a reduced sensitivity to the release-promoting action of Ca2+, Cd2+ and La3+. 3. When comparing the effect of the various BoTxs on nerve-impulse evoked transmitter release it appears that increasing phasic Ca2+ entry into the terminals enhances evoked synchronized quantal release only from terminals poisoned with serotypes A and E. In contrast, enhanced Ca2+ entry into terminals poisoned with serotypes B, D and F induced a period of high frequency asynchronous release suggesting that these BoTxs may affect a presynaptic step beyond the influx of Ca2+, that may be involved in the synchronization of transmitter quanta. These data suggest that the actions of BoTxs involve several steps of the acetylcholine release process. 4. The analysis of presynaptic currents which depend on both Ca2+ entry and intraterminal background Ca2+ levels strongly suggests that neither Ca2+ entry nor intraterminal Ca2+ levels are altered by BoTxs. Furthermore, poisoned terminals are no more efficient than unpoisoned ones in dealing with Ca2+ overloads. 5. Finally, the morphological examination of junctions paralysed by BoTx-A indicates that the toxin triggers a particularly important overgrowth of the nerve terminals and suggests that the in vivo functional recovery may occur from an extension of the original nerve terminal arborization and the concomitant remodelling of postsynaptic structures.

Animals↗
PubMed1989

Formation of functional endplates by spinal axons regenerating through a peripheral nerve graft. A study in the adult rat.

Peripheral nerve (PN) autografts were used in the adult rat to join the midcervical spinal cord to a nearby denervated skeletal muscle. Retrograde tracing, morphological and electrophysiological studies indicated the following: 1) a great number of neurons, located bilaterally, between C3 and C7 in most laminae of the grey matter, extended axons into the PN grafts, 2) a lesser number of neurons regenerated up to the reconnected muscle, but most of them were typical motoneurons, 3) neuromuscular junctions were formed in ectopic locations, around the tip of the grafted nerve, and at the sites of original endplates, 4) these junctions were functional and formed by axons that had regenerated into the PN bridges, as muscle contraction was obtained by electrical stimulation of the grafted nerves, 5) they were proved to be cholinergic since endplate potentials, evoked by stimulating the PN graft, were suppressed by curare. These results strongly suggest that spinal neurons, and especially motoneurons, are involved in the formation, through PN bridges, of new functional cholinergic connections with denervated skeletal muscles.

Action Potentials↗
PubMed1988

Effects of carbonyl cyanide m-chlorophenylhydrazone on quantal transmitter release and ultrastructure of frog motor nerve terminals.

The quantal acetylcholine release and the ultrastructural effects of the metabolic inhibitor carbonyl cyanide m-chlorophenylhydrazone have been examined at frog neuromuscular junctions. Carbonyl cyanide m-chlorophenylhydrazone (2 microM) caused a temperature-dependent block of evoked quantal transmitter release accompanied by an increase in the rate of spontaneous quantal release. The carbonyl cyanide m-chlorophenylhydrazone-induced increase in miniature endplate potential frequency was neither antagonized nor prevented by tetrodotoxin. It also occurred in a Ca2+-free medium and after replacement of Ca2+ by Sr2+, indicating that it does not depend upon a Na+ or Ca2+ influx from the external medium but may act by releasing Ca2+ from intraterminal stores. Spontaneous quantal transmitter release was exhausted irreversibly within 4 h of carbonyl cyanide m-chlorophenylhydrazone (2 microM) action, during which time an average of 4.7 x 10(5) acetylcholine quanta were released per junction. The morphologic analysis revealed a significant temperature and time-dependent reduction in the number of synaptic vesicles with swelling and dispersion of mitochondria within the motor nerve terminals. Changes in synaptic vesicle number appear to be directly related to the intensity of transmitter release. The good correlation observed between the number of quanta secreted and the number of vesicles lost by nerve terminals in the absence of vesicle recycling provides an estimate of the initial store of transmitter quanta.

Acetylcholine↗
PubMed1988

[Functional reinnervation of a skeletal muscle by means of a peripheral nerve autograft to the spinal cord by dorsal approach. Study in the adult rat].

Peripheral nerve grafts were used in adult rats to join the spinal cord to a denervated skeletal muscle. From 2 to 5 months later, results of electrophysiological, histological and retrograde horseradish peroxidase labelling studies showed that spinal neurons, and especially motoneurons, were probably involved in the formation of new functional cholinergic neuromuscular junctions through these bridges.

Animals↗
PubMed1987

An improved combined cholinesterase stain and silver impregnation method for quantitative analysis of innervation patterns in frog muscle.

The original method combining Karnovsky's cholinesterase stain and Bodian silver impregnation has been modified to stain both myelinated and unmyelinated axons and to reduce background staining. The improvements were obtained by adding nitric acid to a paraformaldehyde-acetone fixative and by carrying out the silver impregnation of axons in an alcoholic solution. The method is especially suitable for quantitative estimation of the different kinds of nerve sprouting as well as for study of the remodeling of neuromuscular junctions in normal and experimental frog muscles.

Animals↗
PubMed1985

Effects of isaxonine on skeletal muscle reinnervation in the rat: an electrophysiologic evaluation.

Electrophysiologic detection of the first signs of gastrocnemius muscle reinnervation shows that after a single localized freezing of the rat sciatic nerve, isaxonine does not significantly increase the rate of axonal regeneration. However, this drug does significantly enhance axonal sprouting, as it induces an increase of 50% in the number of muscle fibers with multiple innervation 10-30 days after freezing. After 30 days, the proportion of multiinnervated fibers decreases in both the control and isaxonine-treated rats, and the differences between them gradually disappear.

Animals↗
PubMed1979

A combined silver and cholinesterase method for studying exact relations between the pre- and the postsynaptic elements at the frog neuromuscular junction.

Combination of Karnovsky's cholinesterase staining with silver impregnation of axons (modified Bodian's technique) offers a new means of studying the relation between the pre- and postsynaptic elements in the frog neuromuscular junction. The method can be applied to whole muscles so that synapses of individual superficial muscle fibers which have previously been investigated by electrophysiological techniques can be identified after staining. In this way synaptic activity can be correlated with such synaptic features as number of axon branches, length of the occupied synaptic gutter, axonal sprouts, etc. The distinction between occupied and unoccupied parts of the synaptic gutters is useful when studying reinnervation, regression, or growth of a synapse.

Animals↗