Lobster neuromuscular junctions treated with black widow spider venom: correlation between ultrastructure and physiology

Comparative proteomic analysis to probe into the differences in protein expression profiles and toxicity bases of Latrodectus tredecimguttatus spiderlings and adult spiders

The early reports and our previous work confirmed the existence of the toxic proteinaceous components in the body of the L. tredecimguttatus newborn and adult spiders. For revealing the differences in the protein expression profiles and toxicity bases of the spiders at different developmental stages, the spiderling and adult spider proteins were comparatively analyzed using a proteomic strategy. Totals of 429 and 958 proteins were identified from the spiderlings and adult spiders, respectively, with 239 proteins being identified from both of them. Although some similarities between the spiderling and adult spider proteomes exist, there are obvious differences between the two proteomes in size, complexity, molecular weight (MW) distribution, acid-base property, and hydropathicity, etc. Gene ontology (GO) analysis demonstrates that, comparing based on the percentages of proteins, the spiderling and adult spider proteins have generally similar distribution profiles with respect to the subcellular localization, molecular function and biological process. However, there are still some differences between these two sets of proteins in some classifications of the three GO categories. For the adult spiders, latrotoxins together with other toxins and toxin-like proteins, etc. constitute their toxicity basis, whereas the toxicity of the spiderlings depends mainly on the synergistic action of atypical latrotoxins and toxin-like proteins, most of which are different from those of the adult spiders, demonstrating that the spiders at different developmental stages have largely different toxicity mechanisms.

Drosophila stoned proteins regulate the rate and fidelity of synaptic vesicle internalization

At an initial step during synaptic vesicle recycling, dynamin and adaptor proteins mediate the endocytosis of synaptic vesicle components from the plasma membrane. StonedA and stonedB, novel synaptic proteins encoded by a single Drosophila gene, have predicted structural similarities to adaptors and other proteins implicated in endocytosis. Here, we test possible roles of the stoned proteins in synaptic vesicle internalization via analyses of third instar larval neuromuscular synapses in two Drosophila stoned (stn) mutants, stn(ts) and stn(8P1). Both mutations reduce presynaptic levels of stonedA and stonedB, although stn(ts) has relatively weak effects. The mutations cause retention of synaptic vesicle proteins on the presynaptic plasma membrane but do not alter the levels or distribution of endocytosis proteins, dynamin, alpha-adaptin, and clathrin. In addition, stn(8P1) mutants exhibit depletion and enlargement of synaptic vesicles. To determine whether these defects arise from altered synaptic vesicle endocytosis or from defects in synaptic vesicle biogenesis, we implemented new methods to assess directly the efficiency of synaptic vesicle recycling and membrane internalization at Drosophila nerve terminals. Behavioral and electrophysiological analyses indicate that stn(ts), an allele with normal evoked release and synaptic vesicle number, enhances defects in synaptic vesicle recycling shown by Drosophila shi(ts) mutants. A dye uptake assay demonstrates that slow synaptic vesicle recycling in stn(ts) is accompanied by a reduced rate of synaptic vesicle internalization after exocytosis. These observations are consistent with a model in which stonedA and stonedB act to facilitate the internalization of synaptic vesicle components from the plasma membrane.

alpha-latrocrustatoxin increases neurotransmitter release by activating a calcium influx pathway at crayfish neuromuscular junction

alpha-latrocrustatoxin (alpha-LCTX), a component of black widow spider venom (BWSV), produced a 50-fold increase in the frequency of spontaneously occurring miniature excitatory postsynaptic potentials (mEPSPs) at crayfish neuromuscular junctions but did not alter their amplitude distribution. During toxin action, periods of high-frequency mEPSP discharge were punctuated by periods in which mEPSP frequency returned toward control levels. EPSPs were increased in amplitude during periods of enhanced mEPSP discharge. alpha-LCTX had no effect when applied in Ca(2+)-free saline, but subsequent addition of Ca(2+) caused an immediate enhancement of mEPSP frequency even when alpha-LCTX was previously washed out of the bath with Ca(2+)-free saline. Furthermore removal of Ca(2+) from the saline after alpha-LCTX had elicited an effect immediately blocked the action on mEPSP frequency. Thus alpha-LCTX binding is insensitive to Ca(2+), but toxin action requires extracellular Ca(2+) ions. Preincubation with wheat germ agglutinin prevented the effect of alpha-LCTX but not its binding. These binding characteristics suggest that the toxin may bind to a crustacean homologue of latrophilin/calcium-independent receptor for latrotoxin, a G-protein-coupled receptor for alpha-latrotoxin (alpha-LTX) found in vertebrates. alpha-LCTX caused "prefacilitation" of EPSP amplitudes, i.e., the first EPSP in a train was enhanced in amplitude to a greater degree than subsequent EPSPs. A similar alteration in the pattern of facilitation was observed after application of the Ca(2+) ionophore, A23187, indicating that influx of Ca(2+) may mediate the action of alpha-LCTX. In nerve terminals filled with the Ca(2+) indicator, calcium green 1, alpha-LCTX caused increases in the fluorescence of the indicator that lasted for several minutes before returning to rest. Neither fluorescence changes nor toxin action on mEPSP frequency were affected by the Ca(2+) channel blockers omega-agatoxin IVA or Cd(2+), demonstrating that Ca(2+) influx does not occur via Ca(2+) channels normally coupled to transmitter release in this preparation. The actions of alpha-LCTX could be reduced dramatically by intracellular application of the Ca(2+) chelator, bis-(o-aminophenoxy)-N,N,N', N'-tetraacetic acid. We conclude that induction of extracellular Ca(2+) influx into nerve terminals is sufficient to explain the action of alpha-LCTX on both spontaneous and evoked transmitter release at crayfish neuromuscular junctions.

Cysteine string protein is required for calcium secretion coupling of evoked neurotransmission in drosophila but not for vesicle recycling

The entire deletion of the cysteine string protein (CSP) gene causes a temperature-sensitive (ts) block of evoked neurotransmission in Drosophila. CSP has been found to interact in vitro with the clathrin-uncoating ATPase HSC70, suggesting a potential role of CSP in vesicle recycling. Using FM1-43 imaging, we analyzed whether the ts block of neurotransmission in csp mutants is caused by a defect in vesicle exocytosis or vesicle recycling. We determined that FM1-43-labeled synaptic boutons of csp mutant neuromuscular junctions fail to destain at 32 degrees C after K+ depolarization, and that FM1-43 dye uptake cannot be evoked by K+ stimulation at 32 degrees C. However, when we stimulated dye uptake independent of depolarization by using black widow spider venom (BWSV), we observed endocytotic uptake of FM1-43. This suggests that endocytosis exhibits no primary ts defect. In addition, we found no ts defect of vesicle recycling at 32 degrees C that would correlate with the ts block of neurotransmission. We also discovered that BWSV and the calcium ionophore calcimycin stimulate FM1-43 destaining and quantal release in csp mutants at 32 degrees C when depolarization fails to evoke any response. The wild-type-like, calcimycin-induced response in csp null mutants indicates that some aspect of the depolarization-dependent calcium signaling pathway must be impaired, either calcium entry, calcium action, or both. Collectively, our results indicate that the csp mutation affects calcium secretion coupling of evoked exocytosis but not vesicle recycling. This supports the hypothesis that CSP links synaptic vesicles to calcium secretion coupling.

Effects of black widow spider venom and latrocrustatoxin on crustacean nerve cells: electrophysiological and ultrastructural study

1. Black widow spider venom (BWSV), or crustacean-specific toxin purified from it (named latrocrustatoxin, LCT) were lethal for the crayfish. 2. Distortions in the EMG and motor activity pattern after LCT injection indicated venom effects on the crayfish nervous system. 3. In the isolated ventral nerve cord, transient activation of the "silent" interneurons and motoneurons occurred after BWSV or LCT application. 4. In the isolated nerve-muscle preparation, LCT application elicited an intense transmitter release resulting in the complete blockade of neuromuscular transmission. 5. Electron microscopic study of the nervous and muscle tissue in venom treated crayfish demonstrated certain destructive changes in the nervous cells especially in the nerve terminals. 6. The results suggest that the LCT acts as a presynaptic neurotoxin in the central and peripheral nervous system of the crayfish.

Monitoring of black widow spider venom (BWSV) induced exo- and endocytosis in living frog motor nerve terminals with FM1-43

The neurotoxin Black Widow Spider Venom (BWSV) triggers massive release of neurotransmitter at synapses. Here we demonstrate that the action of BWSV on the frog neuromuscular junction can be visualized in vivo by the use of the fluorescent styryl dye FM1-43. This vital dye stains recycled synaptic vesicles upon nerve stimulation. Motor nerve terminals were stained with FM1-43 via electrical stimulation, washed and then exposed to BWSV or alpha-Latrotoxin. All terminals destained completely, independent of external calcium. Exposure of frog nerve terminals to BWSV in the presence of FM1-43 and calcium led to staining of terminals. The staining pattern appeared to be exactly the same as in control preparations, stimulated electrically via the nerve. When the same experiment was performed in the absence of calcium, only a minute quantity of dye was taken up into the nerve terminals, and the synapses looked swollen and puffed. Addition of external calcium to these preparations elicited an immediate shrinking of the nerve terminals, indicating endocytosis. These observations support electron-microscopic data that suggest an important role for extracellular calcium in endocytosis of BWSV poisoned nerve terminals.

Spontaneous release of multiquantal miniature excitatory junction potentials induced by a Drosophila mutant

1. Intracellular recordings were made from muscle fibre No. 6 of the dorsal longitudinal flight muscle (DLM) of Drosophila melanogaster in both wild-type flies and the temperature-sensitive paralytic mutant, shibirets-1 (shi). 2. Continuous recordings of the miniature excitatory junction potentials (MEJPs) in this fibre were made as the temperature was changed from 19 to 29 degrees C, and back to 19 degrees C. In shi flies, synapses become depleted of vesicles at 29 degrees C due to a temperature-dependent blockage in the recycling process, while transmitter release proceeds normally. When the temperature is lowered to 19 degrees C, recycling is allowed to proceed and recovery of the full complement of synaptic vesicles gradually occurs in about 20 min. 3. It was observed that the MEJP amplitude distribution in shi flies was unimodal at 19 degrees C prior to heating (as was wild-type), but during recovery from 8 min exposure to 29 degrees C became multimodal, with peaks at roughly integral multiples of the original peak prior to heating. This effect was never seen in wild-type flies. 4. Also, during recovery, the MEJP did not occur randomly, but rather occurred in a clustered fashion. 5. It is concluded that during recovery from depletion in shi neuromuscular junctions, a condition exists which causes the synchronization of spontaneous release, causing multiquantal MEJPs or clustering of MEJPs, depending on the degree of synchronization. 6. The possible role of Ca2+ in this phenomenon is discussed.

Time course and frequency dependence of synaptic vesicle depletion and recovery in electrically stimulated sympathetic ganglia

The mammalian superior cervical sympathetic ganglion has been extensively used to study the kinetics of ACh metabolism and release. The present investigation examined the time course of changes in the number of synaptic vesicles and abundance of plasma membrane at preganglionic nerve terminals using stimulation protocols similar to those used in previous biochemical and electrophysiological studies. Continuous stimulation of the preganglionic trunk to the cat superior cervical ganglion in vivo produced an initially rapid fall in the number of clear synaptic vesicles followed by a subsequent plateau. Reciprocal changes in plasma membrane occurred with a similar time course. The plateau phase is interpreted as a steady-state where vesicle exocytosis is balanced by the rate of vesicle reformation from plasma membrane. During quiescent recovery, restoration of normal resting ultrastructure is initially rapid but slows with time as vesicle number and plasma membrane abundance approach pre-stimulation values, indicating that the rate of vesicle reformation at the end of stimulation is high and proportional to the number of vesicles incorporated into the plasma membrane. These results are interpreted as consistent with the 'vesicle hypothesis' of neurotransmitter release.

Transient and enduring morphological correlates of synaptic activity and efficacy change in the rat hippocampal slice

This study examined anatomical correlates of: (1) long-term potentiation (LTP); (2) equivalent low frequency synaptic activity; (3) continuous high frequency synaptic activation which did not produce LTP; and (4) synaptic inactivation by high Mg2+/low Ca2+ incubation in hippocampal subfield CA1 in the in vitro slice, and examined the persistence of changes at 10-15 min, 2 h and 8 h after stimulation. After potentiating stimulation (6 trains at 100 Hz for 1 s or 200 Hz for 0.5 s), compared to an equivalent number of low frequency stimuli (1 Hz for 600 s), there were increases in numbers of shaft and sessile spine synapses (synapses on stubby, headless spines). This suggested an increase in the number of shaft synapses onto inhibitory interneurons and/or an enhancement of synapse formation on pyramidal neurons possibly involving initial formation of shaft synapses and a transition from shaft, to sessile spine, to full grown spine synapses. Postsynaptic spine heads also assumed a rounder shape, as indicated by decreases in spine perimeter to area ratios, contact lengths, and the percentage of 'cup' shaped spines. There was no effect of potentiating stimulation on bouton or spine areas. After continuous high frequency synaptic activation (40 Hz or 100 Hz for 10 min), which produced no apparent LTP, there were no changes in synapse numbers or spine head shape parameters. However, in contrast to effects of LTP, there was an increase in bouton mitochondrial area and a marginal increase in bouton area compared to the low frequency condition. Inactivation did not affect any of these measures. LTP-associated increases in numbers of shaft and sessile spine synapses persisted over an 8 h incubation period, while the effect on spine shape disappeared after 2 h. Physiologically-demonstrable LTP persisted over the 8 h period. Effects of continuous high level activation on mitochondrial and bouton areas were even more transient, disappearing 2 h after stimulation. These findings: (1) confirm previously reported effects of potentiating stimulation on synapse numbers and spine shape; (2) indicate that spine shape changes are not necessary for the maintenance of LTP; and (3) indicate that continuous high frequency activation which does not produce potentiation has different and non-persisting effects from potentiating stimulation.

Retinal illumination produces synaptic inhibition of a neurosecretory organ in the crayfish, Pacifastacus leniusculus (Dana)

We have identified a cluster of neurosecretory cells in the crayfish eyestalk that possess dendrites in the second optic neuropil (Medulla) and project axons to the first optic neuropil (Lamina). Illumination of the ipsilateral retina produces a synaptic inhibition of these cells that is mimicked by iontophoresis of gamma-aminobutyric acid within the medullary neuropil. The neurosecretory nature of the cells, the efferent projection of their axons, and the strong inhibition of their spiking activity upon retinal illumination suggest that they may be involved in the feedback control of dark adaptation and/or circadian changes in visual sensitivity.

Neurotransmitter release and nerve terminal morphology at the frog neuromuscular junction affected by the dye Erythrosin B

1. The quantal release of neurotransmitter and the fine structure of frog neuromuscular junctions has been examined in the presence of the xanthene dye Erythrosin B.2. At concentrations of 10 muM or greater, Erythrosin B produced time- and dose-dependent increases in transmitter release from presynaptic nerve terminals.3. Miniature end-plate potential (m.e.p.p.) frequency increased in an exponential manner during continuous exposure to the dye. The rate constant for this exponential was dose-dependent, increasing with concentrations from 10 muM to 1 mM.4. The amplitude of evoked end-plate potentials (e.p.p.s) also increased exponentially during dye treatment, primarily due to an increase in quantal content. Rate constants for this effect were also dose-dependent, and were approximately 1/5 as large as those for m.e.p.p.s.5. While the frequency of m.e.p.p.s was increasing, their amplitude distribution did not qualitatively change. Thus the dye has little effect on the size of individual quanta.6. The presynaptic effects of Erythrosin B were irreversible under these experimental conditions. Brief exposure to the dye caused increases in m.e.p.p. frequency and e.p.p. amplitude which were maintained at steady levels during extensive rinsing with dye-free Ringer solution.7. Prolonged exposure to the dye caused an eventual decrease in m.e.p.p. frequency and abolition of e.p.p.s. Coincident with this decline ;giant' m.e.p.p.s as large as 40 mV were observed.8. At dye concentrations greater than approximately 200 muM, Erythrosin B rapidly and reversibly increased the membrane potential and input resistance of muscle fibres. This post-synaptic effect was small and variable in normal saline, but was pronounced in low potassium solutions.9. During the period that release was enhanced by Erythrosin B, presynaptic nerve terminals contained the normal complement of synaptic vesicles and other organelles. Mitochondria were swollen in this condition.10. After m.e.p.p. frequency declined below normal levels and ;giant' m.e.p.p.s appeared, the number of synaptic vesicles within nerve terminals declined and dilated cisternae were present. Mitochondria were swollen further.11. These results do not reveal any mechanism to explain the ability of Erythrosin B to increase transmitter release, but the decline in release may be caused by partial depletion of synaptic vesicles. The ;giant' m.e.p.p.s could be due to the discharge of acetylcholine from cisternae.

Black widow spider bites

Black widow spiders (Latrodectus species) are found worldwide. Envenomation of humans usually occurs as the result of chance intrusion into the spider's domain by the human. The venom is regarded as one of the most potent biologic toxins. The venom acts by destabilization of cell membranes and degranulation of nerve terminals resulting in the release of neurotransmitters. The clinical picture is characterized by painful muscle spasm and hypertension. The very young, the elderly or enfeebled, and those with cardiovascular disease are at greatest risk. While not always necessary, the most effective treatment is specific antiserum. Muscle relaxants, analgesics and intravenous calcium are useful adjuvant treatment.

The ionic dependence of black widow spider venom action at the stretch receptor neuron and neuromuscular junction of crustaceans

The effects of black widow spider venom (BWSV) on the crayfish stretch receptor and the lobster neuromuscular junction were examined. In crayfish stretch receptor neurons, BWSV caused a slight hyperpolarization followed by a large depolarization. The venom-induced depolarization of the stretch receptor was caused by an increase in membrane conductance to Na+ and Ca2+. Black widow spider venom also caused an increase in the frequency of miniature inhibitory postsynaptic potentials recorded in the stretch receptor. The ability of BWSV to increase the frequency of miniature excitatory postsynaptic potentials (MEPSPs) at the lobster neuromuscular junction was dependent on the divalent cation composition of the bathing medium. Ringer solutions containing Ca2+ supported the greatest venom-induced increase in MEPSP frequency, Mg2+ and Mn2+ supported a moderate increase in MEPSP frequency, while Co2+ and Zn2+ blocked this venom effect entirely. Black widow spider venom did not block axonal conduction in lobster walking leg axons or in the axon of the crayfish stretch receptor. The results suggest that in crustaceans, BWSV interacts specifically with membrane of the soma-dendritic region of the stretch receptor and with nerve terminal membrane, causing an increase in Na+ and Ca2+ conductance.

Differentiation of identifiable lobster neuromuscular synapses during development

The ultrastructure of physiologically identified low and high release synapses arising from a single axon on fibres of the distal accessory flexor muscle (DAFM) in a mature lobster was examined by serial section electron microscopy. Low release neuromuscular terminals located only on the proximal fibre were characterized by large synapses (mean area 2.084 micron2), small presynaptic dense bars (mean are 0.021 micron2) and hence a low (2.3%) ratio of dense bar area to synaptic area. In contrast high output terminals located only on the distal fibre had smaller synapses (mean area 0.625 micron2), large dense bars (mean area 0.066 micron2) and a high (23.9%) ratio of bar area to synaptic area. A similar ratio was consistently found for each synaptic type in several other examples of mature lobsters. Hence it was used as a criterion for determining the point at which differentiation occurs during development. In the first larval stage (24 h old) the innervation was localized and undifferentiated. In the fourth (2 week old) and twelfth (1 y old) stage lobsters, the innervation had proliferated to small bundles of proximal and distal fibres. During development synapses increase in their mean surface area in the proximal fibre while remaining constant in the distal fibre. The mean surface area of the dense bars is similar in all stages except for the proximal fibres of the twelfth stage where it is smaller by 50%. Similarly the ratio fo dense bar area to synaptic area is not significantly different for all stages except for the twelfth stage proximal fibres where it is half the value. Consequently differentiation of low and high release neuromuscular terminals occurs by the twelfth stage with an increase in the mean surface area of synapses and a decrease in the mean surface area of dense bars. This morphological differentiation is enhanced in the mature lobster.

On the quantal release of endogenous glutamate from the crayfish neuromuscular junction

1. The abdominal slow flexor muscle was isolated from the crayfish (Cambarus clarkii) and placed in 150 microliters. Harreveld solution. The concentrations of glutamate and aspartate in this solution were measured by mass fragmentography. 2. Application of black widow spider venom (BWSV) produced a marked increase in the frequency of miniature excitatory post-synaptic potentials (m.e.p.s.p.s). During the high frequency discharge of m.e.p.s.p.s, the glutamate content in the solution was significantly increased. There was an approximately linear relationship between the increase in the glutamate efflux produced by BWSV and the variance of the membrane potential fluctuation during high frequency discharge of m.e.p.s.p.s. 3. In most cases, the efflux of aspartate during control rest periods was smaller than that of glutamate. During the discharge of m.e.p.s.p.s produced by BWSV, the increase in the aspartate efflux was very small compared to glutamate. 4. Nerve stimulation caused a significant increase in the efflux of glutamate, but the change in the aspartate efflux was very small and not significant. 5. Application of methylene blue increased the frequency of m.e.p.s.p.s and glutamate efflux, but little, if any, increase was found in aspartate efflux. 6. It is concluded that glutamate is preferentially released from nerve terminals in a quantal fashion.