PubMed Health⌕ Search

Biomedical subjects

J E Esquerda

Publications and source records attributed to J E Esquerda.

32 records · Page 2Linked to original sources
PubMed1990

Type A botulinum toxin disorganizes quantal acetylcholine release and inhibits energy metabolism.

The physiological, morphological and biochemical effects of type A Botulinum toxin (BoTX) were analysed in the electric organ of Torpedo, a modified neuromuscular system. The quantal content of the postsynaptic potential, or electroplaque potential (EPP), was reduced by BoTX but the quantum size remained unchanged till complete failure of the neurally evoked transmission. BoTX also suppressed the occurrence of spontaneous electroplaque potentials (MEPPs) of a quantal size but potentials of a smaller amplitude still kept on occurring in the intoxicated synapses. BoTX inhibited the evoked release of acetylcholine (ACh; biochemically measured) but the rate of spontaneous ACh release transiently increased during the period when evoked release went down. On the other hand, there were no significant change of ACh content, of ACh turnover, of ACh repartition in the vesicular and free compartments, or in the number of synaptic vesicles. Surprisingly, the amount of ATP was reduced to 50% in BoTX treated tissue at the time of transmission failure; also the level of creatine phosphate (CrP) was lowered to less than 20% and the rate of activity of creatine kinase was reduced. It was concluded that, electrophysiologically, BoTX affects synaptic transmission in a very similar way in the electric organ and in the neuromuscular junctions. On the other hand, the shortage of ATP supply found in the present study may play a role in the pathophysiology of intoxication and should be taken into account in investigations designed to see whether BoTX affects various phosphorylations in cholinergic nerve terminals.

Acetylcholine↗
PubMed1989

Absence of histochemical immunoreactivity to calcitonin gene-related peptide (CGRP) in spinal cord motoneurons from (+)-tubocurarine-treated chick embryos.

A physiological neuronal death that implicates about 50% of the motoneuron population occurs in the chick embryo between the 6th (E6) and 9th (E9) day of incubation. This natural death can be prevented by administration of neuromuscular blocking agents (e.g. (+)-tubocurarine ((+)-Tc)). In this study, calcitonin gene-related peptide-like immunoreactivity (CGRP-LIR) was studied in spinal cord motoneurons from normal and (+)-Tc-treated chick embryos. In normal embryos CGRP-LIR was found in a neuronal subpopulation of the spinal cord lateral motor column (LMC) that was maximal between the 14th (E14) and 16th (E16) embryonic days with a subsequent decrease. In LMC neurons from (+)-Tc-treated chick embryos examined at E14-16 days no histochemically detectable CGRP-LIR could be observed.

Animals↗
PubMed1989

Synaptic localization of a 66-kDa soluble protein from skeletal muscle: evidence for its developmental and neural regulation.

Soluble proteins from normal, adult denervated, and developing rat muscles were studied in order to identify common molecular species undergoing developmental regulation and nerve dependence. Significant increases in 66- and 30-kDa proteins were found as a consequence of 14 days of denervation. Subsequent reinnervation restores normal adult levels. During development, high levels of the 66-kDa protein were found in neonatal muscles but slowly decreased concomitant with the following postnatal maturation period; the adult levels were reached at Postnatal Day (P) 21. From the immunocytochemical studies it is deduced that both proteins were concentrated mainly at the end-plate region in adult normal muscle. Following denervation, the proteins were found distributed over the entire cell. For the 66-kDa protein, a similar pattern of extensive distribution was seen in immature muscle. Although no data for functional implications for these proteins are available at present, the properties described here make them of interest in understanding nerve-muscle interactions.

Animals↗
PubMed1987

Phylogenetic polymorphism on lectin binding to junctional and non-junctional basal lamina at the vertebrate neuromuscular junction.

The histochemical binding of seven fluoreceinated lectins was comparatively studied in muscular tissue from twenty three different animal species including mammalians, amphibians, avians and fishes. Special interest was taken in the exploration of the differential lectin-binding properties at the neuromuscular synapse. Binding to synaptic sites was demonstrated using lectins that recognizes N-acetylgalactosamine and among of them, Dolichus biflorus agglutinin (DBA), was the most specific. Nevertheless, DBA fails to stain endplates in the muscle from most of the avians and the fishes (including the Torpedo electric organ) indicating that a polymorphic distribution of glycoconjugates exist at the vertebrate neuromuscular junction. Other lectins such as Concanavalin A (ConA) or Wheat germ agglutinin (WGA), share a similar staining properties in all animals that we examined making an intense label over the complete muscle surface. Although the species-related polymorphism on lectin binding does not reveal a clear relationship with the evolutionary tree, they give an evidence on the chemical heterogeneity of molecules specifically concentrated at the neuromuscular junction.

Animals↗
PubMed1987

Receptors to agglutinin from Dolichus biflorus (DBA) at the synaptic basal lamina of rat neuromuscular junction. A histochemical study during development and denervation.

The binding of agglutinin from Dolichus biflorus (DBA) and other lectins (Concanavalin A, agglutinin from wheat germ and lectin from Bandeiraea simplicifolia) to synaptic and extrasynaptic portions of the basal lamina of muscle fibers, was studied with histochemical methods. In rat muscle, DBA-binding is specifically detected at the basal lamina of neuromuscular junction. However, long-term (6 months) denervated end-plate in adult rat muscle failed to bind DBA. During normal development, synaptic DBA receptors appear later than acetylcholine receptors or acetylcholinesterase at the rat neuromuscular junction. Generalized DBA-binding to motor end-plates is first visualized in 3-day-old rats, but section of sciatic nerve in 1-day-old rats prevents the appearance of synaptic DBA-binding on the leg end-plates. It is suggested, therefore, that the synaptic DBA receptors could be related to the postnatal stabilization of rat neuromuscular synapses.

Aging↗
PubMed1987

Structural changes at pure cholinergic synaptosomes during the transmitter release induced by A-23187 in Torpedo marmorata. A freeze-fracture study.

Pure cholinergic synaptosomes isolated from the electric organ of Torpedo marmorata were stimulated by calcium ionophore A-23187. The effect of time course of stimulation on the changes in intramembrane particles (IMPs) on presynaptic membranes was studied by quick-freezing and aldehyde-fixation freeze-fracture. We showed that the decrease of small-particle density at the P-face and the increase of large-particle density at the E-face was maximum after 30 sec of A-23187 stimulation. Later, the density of synaptic vesicles decreased. We suggest that the redistribution of IMPs on the presynaptic membrane and acetylcholine (ACh) release from pure cholinergic synaptosomes have a similar time course when triggered by A-23187.

Acetylcholine↗
PubMed1987

Botulinum toxin inhibits quantal acetylcholine release and energy metabolism in the Torpedo electric organ.

1. Type A Botulinum toxin (BoTX) blocked nerve-electroplaque transmission in small fragments of Torpedo marmorata electric organ incubated in vitro. The effect was observed either with the crystalline toxin complex (associated with haemagglutinin) or with the purified neurotoxin (molecular weight approximately 150,000). 2. The quantal content of the evoked post-synaptic response was reduced by BoTX but the quantum size remained unchanged till complete blockade of the evoked response. 3. Spontaneous electroplaque potentials were composed of two populations: one with a bell-shaped amplitude distribution (miniature potentials or quanta) and a population of small events with a skewed distribution (subminiatures). In BoTX-poisoned tissue, the bell-distributed miniatures progressively disappeared, but the subminiatures kept on occurring. Occasionally, larger spontaneous potentials with a slow time course were recorded; they were also BoTX resistant. 4. A biochemical assay showed that evoked acetylcholine (ACh) release was impaired by BoTX. During the period when evoked transmission was blocked, spontaneous ACh release transiently increased. 5. At the time of transmission blockade, there was no significant change of ACh content, of ACh turnover, of ACh repartition in the vesicle-bound and free compartments, or of the number of synaptic vesicles. 6. The amount of ATP was reduced to 50% by BoTX, and that of creatine phosphate (CrP) to less than 20%. The ATP-CrP-converting enzyme, creatine kinase, was inhibited in BoTX-poisoned tissue. 7. Thus, the electrophysiological effects of BoTX are very similar at the nerve-electroplaque and the neuromuscular junctions. The present work suggests in addition that suppression of quantal release by BoTX is related to marked alterations of the energy metabolism in the tissue.

Acetylcholine↗
PubMed1982

Binding of beta-bungarotoxin to Torpedo electric organ synaptosomes. A high resolution autoradiographic study.

Isolated pure cholinergic synaptosomes from Torpedo electric organ were incubated in vitro with beta-bungarotoxin for 15, 30 and 60 min and processed for electron microscopy. It was found that no morphological damage was seen after 15 min but by contrast, severe disruption of synaptosomes was present at 30 or 60 min after incubation with toxin. Synaptosomes were incubated also for 15 min in the presence of 125I-labelled beta-bungarotoxin and the binding was evaluated by electron microscopic autoradiography. The toxin was found to bind to the presynaptic membrane. The surface density of toxin binding sites was calculated to be around 3000/micron2. In a minor population of synaptosomes, the toxin was translocated into large vesicles suggesting that the toxin-receptor complexes underwent endocytosis in such vesicles. These results give further support to the view that inhibition of transmitter release by the toxin is produced by its action on plasma membrane.

Animals↗
PubMed1981

Effects of ouabain and electrical stimulation on the fine structure of nerve endings in the electric organ of Torpedo marmorata.

The cycle of synaptic vesicles was studied in isolated nerve terminals and in the electric tissue of Torpedo marmorata. The synaptosomes, as used in this investigation, were a pure cholinergic subcellar fraction that captured dextran particles as an extracellular marker. This endocytotic phenomenon was enhanced by potassium depolarization. Field electrical stimulation (1 Hz and 10 Hz) of the electric organ induced the appearance of membrane foldings into presynaptic terminals. Morphometric studies showed that the number of synaptic vesicles did not decline until after at least 30 min. On the other hand, at 10 Hz these changes were accompanied by an increase in length of the membrane of the terminal. At 15 min of recovery after prolonged stimulation, there was a great increase in density of synaptic vesicles with a large number of vesicles of small diameter. This increase was accompanied by a decrease of membrane length, suggesting that reformation of vesicles is related to retrieval of membrane. Pharmacological stimulation with ouabain produced changes similar to those of long-term electrical stimulation. These changes in membrane were accompanied by a decrease of the population of synaptic vesicles and a wide variation in their diameters. It is concluded that structural changes reported here could not be correlated with kinetics of the transmitter release.

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↗
PubMed1976

Erythropoietic protoporphyria. A light, electron, and polarization microscopical study of the liver in three patients.

Two of three patients with erythropoietic protoporphyria showed pigment deposits with typical red porphyrin fluorescence on liver biopsy specimens. Birefringence of this pigment by polarized light is due to its crystalline nature, as demonstrated by electron microscopy. There was slight portal inflammation in these cases. A liver biopsy specimen from a third patient was normal.

Adult↗