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R Robitaille

Publications and source records attributed to R Robitaille.

47 records · Page 3Linked to original sources
PubMed1989

Frequency and amplitude gradients of spontaneous release along the length of the frog neuromuscular junction.

Experiments were done at the neuromuscular junctions (NMJs) of the cutaneous pectoris muscle of the frog to test the validity of the "spatial decay method" which uses simultaneous recording with two intracellular electrodes, each located in the muscle fiber near a distal end of the terminal. The miniature endplate potential (MEPP) peak amplitude recorded by each electrode is used to calculate the position of the release site producing it as well as its initial amplitude in front of its release site. The validity of the method was tested with a third focal electrode located between the two intracellular electrodes, at about 60-100 microns from one of the intracellular electrodes, the probability of spontaneous transmitter release was not uniform along the NMJ either in low or in normal Ca2++ concentration. The release sites located in the region close to the first point of contact between the axon and the muscle fibre, usually close to the center of the NMJ, were spontaneously more active than the distal release sites. The degree of the steepness of proximodistal release gradients varied among different junctions. The less active regions tended to produce smaller MEPPs than did the more active ones. In fact, a correlation was found between the logarithm of MEPP frequency in a given region and the mean corrected MEPP amplitude in that region. These results also show that MEPP frequency was modulated to a greater extent than MEPP amplitude along the frog nerve terminal. The proximodistal gradient in MEPP frequency may be related to corresponding gradients in density and length of release sites along the junction, whereas MEPP amplitude gradients may be related to gradients in the length of release sites and/or postjunctional folds.

Action Potentials↗
PubMed1989

Proximodistal gradients of the postjunctional folds at the frog neuromuscular junction: a scanning electron microscopic study.

Frog endplates were studied with the scanning electron microscope following the removal of the presynaptic terminal by collagenase and acid treatments. Endplates had 2-14 branches of primary cleft. The longest branches were parallel to the muscle fiber. Short branches oblique or perpendicular to the muscle fiber were also present near the central region of the endplates. The openings of postjunctional folds in the primary cleft were clearly visible at the bottom of the primary cleft and could be counted and measured. The longest primary cleft branches of each endplate were divided into segments of 20 microns (length corrected for shrinkage). The number of postjunctional folds per micrometer of primary cleft, the average postjunctional fold length (i.e. across the primary cleft) and the total postjunctional fold's length per micrometer of primary cleft were evaluated for each 20-microns segment of primary cleft. Negative proximodistal gradients were observed for these three parameters for the long branches of primary cleft, i.e. values were higher in the proximal region (near the motor axon) than in the distal region. These postsynaptic gradients probably reflect similar or smaller proximodistal presynaptic gradients for the active zones along the nerve.

Animals↗
PubMed1987

Interrelation between MEPP amplitude and MEPP frequency in different regions along the frog neuromuscular junction.

Experiments were done to study the relationship between miniature endplate potential (MEPP) frequency and MEPP amplitude in different regions along the frog neuromuscular junction (NMJ). The position of the release site producing a MEPP and the amplitude of a MEPP at its release site were evaluated by using the spatial decay method after simultaneous intracellular recordings at each distal end of the NMJ. The NMJ was divided in 10 regions of equal length. It was found that MEPP amplitude and MEPP frequency are smaller in distal regions than in proximal ones. Moreover, we observed a logarithmic relationship between MEPP frequency of a given region and the mean MEPP amplitude of the same region. These results suggest that the probability to produce a MEPP and the quantity of neurotransmitter liberated are two synaptic functions controlled or affected by common mechanisms.

Animals↗
PubMed1987

Non-uniform distribution of miniature endplate potential amplitudes along the length of the frog neuromuscular junction.

We studied the amplitude distribution of miniature endplate potentials (MEPPs) as a function of the release site position along the frog neuromuscular junction. Following intracellular recordings with two electrodes each located at one distal end, we used the spatial decay method to evaluate the release site position of each MEPP and the MEPP amplitude in front of its release site. Nitroblue-tetrazolium-cholinesterase staining was performed for further morphological correlation. Our results indicate that MEPP amplitude distributions are skewed to the left for distal regions, while MEPP amplitudes are more widely distributed for the proximal regions (i.e. near the last myelinated segment). This suggests that distal regions produce predominantly MEPPs with a small amplitude whereas proximal regions produce MEPPs of all sizes (small to large).

Animals↗
PubMed1987

Non-uniform release at the frog neuromuscular junction: evidence of morphological and physiological plasticity.

The frog neuromuscular junction (NMJ) is a fusiform structure parallel to the muscle fiber with a few secondary and tertiary branches. Both sprouting and regression can occur on the same nerve terminal, suggesting a continuous on-going remodelling of the mature neuromuscular junction. Thus, the frog NMJ is a dynamic structure. Ultrastructural observations of the nerve terminal suggest that the active zones are distributed equally along the mature nerve terminal. Disorganized active zones have however been observed in distal regions. The density of synaptic vesicles is also uniform throughout the whole structure. However, mitochondria appear to be more abundant in the very distal regions of the nerve terminal. The postjunctional folds and the cholinergic receptors are also uniformly distributed along the NMJ. However, during remodelling periods, the distributions of postjunctional folds and of cholinergic receptors are not uniform in the degenerating and regenerating regions. Fig. 1 summarizes these morphological data. The frequency of spontaneous release (MEPPs) at the NMJ is higher in the proximal region than in the distal regions and recent evidence suggests that the mean MEPP amplitude is higher in the proximal than in the distal portions. Evoked transmitter release is also non-uniform along the frog NMJ. As for spontaneous release, it is higher in the proximal regions than in the distal regions. Failures of the active propagation of the PNAP at low safety points, such as the end of the myelinated axon and the branching points, may be one of the mechanisms responsible for unequal evoked release. It is also possible that the PNAP does not actively invade the whole extend of the nerve terminal since Na+ channels are absent from the distal regions. Fig. 2 summarizes these physiological data.

Animals↗
PubMed1987

Incorporation of vesicular antigens into the presynaptic membrane during exocytosis at the frog neuromuscular junction: a light and electron microscopy immunochemical study.

We have studied the incorporation of vesicular membrane antigens into the presynaptic membrane during exocytosis of neurotransmitter at the frog neuromuscular junction. In a preliminary series of experiments, we first confirmed by electron microscopy that the synaptic vesicles are labelled following incubation with rabbit antisynaptic vesicle antibody of neuromuscular junction cross sections (cytoplasm and organelles reached by the antibodies). In a second series of experiments, intact neuromuscular junctions were stimulated with black widow spider venom and fixed with paraformaldehyde. The presence or absence of vesicular antigens in the presynaptic membrane was monitored with rabbit antisynaptic vesicle antibody and revealed with a second antibody coupled to peroxidase. In light microscopy, the labelled neuromuscular junctions are almost completely restricted to muscles stimulated with black widow spider venom and incubated with rabbit antisynaptic vesicle antibody. Only a few control muscles (not stimulated with black widow spider venom, but incubated with rabbit antisynaptic vesicle antibody) had labelled neuromuscular junctions. All control neuromuscular junctions, not incubated with rabbit antisynaptic vesicle antibody were unlabelled. Electron microscopy indicated that it is the presynaptic membrane of intact stimulated neuromuscular junctions which is labelled. In these intact neuromuscular junctions, the synaptic vesicles are usually unlabelled. Electron microscopy also indicated that the presynaptic membrane of only one type of control junctions (not stimulated with black widow spider venom, but incubated with rabbit antisynaptic vesicle antibody) is rarely and weakly labelled. Other types of controls (not incubated with rabbit antisynaptic vesicle antibody) are never labelled. Therefore our results are consistent with the incorporation of vesicular antigens into the plasma membrane during exocytosis produced by the black widow spider venom. The low level of labelling of unstimulated neuromuscular junctions suggest a rather complete retrieval of the vesicular proteins during endocytosis.

Animals↗
PubMed1985

Miniature endplate potential amplitudes corrected for spatial decay are not normally distributed.

Miniature endplate potentials (MEPPs) were recorded simultaneously with two intracellular electrodes placed in the muscle fiber near the ends of the frog neuromuscular junction (nmj). The MEPP amplitudes are different in each electrode and are not normally distributed. A method is proposed to correct MEPP amplitudes for spatial decay. The MEPP amplitudes corrected for spatial decay are also not normally distributed. When the class interval of the distribution is small, multiple peaks are observed.

Action Potentials↗
PubMed1984

Distribution of spontaneous release along the frog neuromuscular junction.

A new method, called the spatial decay method, is described. This method permits to localize the site of occurrence of the spontaneous release producing each miniature end-plate potential (MEPP) recorded at the frog neuromuscular junction (nmj). The method requires simultaneous intracellular recording at both distal ends of the nmj. The electrodes are positioned using Nomarksi optics. The assumptions that the MEPP amplitude is maximum in front of its release site and decays exponentially toward the recording electrodes placed distally, permit the calculation of the position of the release site producing each MEPP recorded intracellularly. The spatial decay method indicates that the occurrence of spontaneous release is not uniformly distributed along the frog nmj.

Animals↗
PubMed1979

Acupuncture analgesia in rabbits.

The aim of this study was to verify the validity and reliability of analgesia elicited by acupuncture stimulation in rabbits. Ninety-five experiments were performed using 21 adult animals. The reaction time of the avoidance response elicited by noxious heat stimulation on the snout, and the presence or absence of the start response elicited by pin-prick and clamping of the skin were studied. Bilateral electric acupuncture stimulation in the area of Tsu-san-li and Shang-chu-hsu points in the hind legs was used. The animals were either held in a soft bag, loosely attached by cords, or suspended in a hammock; the eyes were either free of blindfolded. On the basis of operational behavioral measurements, it was found that acupuncture stimulation did not produce analgesia in undisturbed, placid animals. However, during agitated or fighting periods and the immobility reflex-like state, sometimes associated with acupuncture maneuvers, long reaction times were observed. Pin-pricking and clamping stimulation of the skin were not reliable methods of noxious stimulation in the rabbit.

Acupuncture Therapy↗
PubMed1975

Interpretation of the PPD skin test in BCG-vaccinated children.

Skin testing with 5 tuberculin units (TU) of purified protein derivative (PPD) of tuberculin stabilized with polysorbate (Tween) 80 was done 3 months and 1 year after immunization with bacille Calmette-Guérin (BCG) vaccine in two groups of children: one group vaccinated at birth and another group at age 6 years. Interpretation of the PPD skin test with 5 TU is possible in children 1 year and older vaccinated with BCG at birth: if the diameter of induration is more than 10 to 12 mm the reaction cannot be ascribed to BCG vaccination and is highly suggestive of supervening infection with Mycobacterium tuberculosis or occasionally atypical mycobacteria. In contrast, the interpretation of a PPD test in children vaccinated at age 6 years is extremely difficult.

BCG Vaccine↗