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L Tauc

Publications and source records attributed to L Tauc.

At least 37 records · Page 2Linked to original sources
PubMed1992

Involvement of Ca2+ uptake by a reticulum-like store in the control of transmitter release.

At an identified neuro-neuronal synapse of Aplysia, 2,5-diterbutyl 1,4-benzohydroquinone, a selective blocker of the reticulum Ca2+ pump, was found to potentiate evoked quantal release of acetylcholine through an increased accumulation of Ca2+ in the presynaptic neuron during depolarization without any accompanying changes in the presynaptic Ca2+ current. We conclude that a rapid Ca2+ buffering system, similar to that associated with the endoplasmic reticulum, must be present in the nerve terminal and play a role in the control of Ca2+ which reaches the release system.

Animals↗
PubMed1992

Presynaptic receptors for FMRFamide, histamine and buccalin regulate acetylcholine release at a neuro-neuronal synapse of Aplysia by modulating N-type Ca2+ channels.

At an identified neuro-neuronal synapse of the buccal ganglion of Aplysia, quantal release of acetylcholine (ACh) is increased by FMRFamide and decreased by histamine or buccalin. Activation of presynaptic receptors for these neuromodulators modifies a presynaptic Ca2+ current which is nifedipine-resistant and omega-conotoxin-sensitive. The voltage-sensitivity of these N-type Ca2+ channels is increased by FMRFamide and decreased by histamine through the intermediate of G proteins. Buccalin does not implicate G proteins and reduces the Ca2+ current without affecting the voltage-sensitivity of N-type Ca2+ channels. The possibility of relating the shifts in voltage-dependence of the Ca2+ current induced by FMRFamide and histamine to the phosphorylation state of the N-type Ca2+ channels is discussed. A scheme for the complex regulation of ACh release by presynaptic auto- and heteroreceptors is proposed.

Acetylcholine↗
PubMed1992

Regulation of transmitter release by presynaptic receptors at a cholinergic neuro-neuronal synapse.

The modulation of evoked transmitter release by presynaptic receptors was studied at an identified cholinergic synapse in the buccal ganglion of Aplysia. Two auto-receptors affecting acetylcholine release in opposite ways were identified. Additionally acetylcholine (ACh) release was found to be facilitated by the peptide FLRFamide and inhibited by histamine. Ca2+ channels appeared as the final effectors controlled by these non-cholinergic presynaptic receptors whereas the activation of cholinergic presynaptic receptors did not affect the Ca2+ influx. The intracellular pathway activated by FLRFamide receptors was investigated in detail. The facilitation of transmitter release induced by this peptide was prevented by bath application of H-7, a protein kinase C inhibitor. Moreover, a diacylglycerol analog mimicked the action of FLRFamide. These results suggest that activation of protein kinase C leading to the phosphorylation of Ca2+ channels could be the mechanism through which presynaptic FLRFamide receptors increase evoked quantal release of acetylcholine at this synapse.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Heterologous combinations of heavy and light chains from botulinum neurotoxin A and tetanus toxin inhibit neurotransmitter release in Aplysia.

The neuroparalytic activities of botulinum neurotoxin type A (BoNT A), tetanus toxin (TeTx), or homologous and heterologous combinations of their constituent polypeptides were examined at cholinergic and non-cholinergic synapses of Aplysia californica. When applied extracellularly, BoNT A or a mixture of its heavy (HC) and light (LC) chains were far more potent in blocking transmitter release at cholinergic than non-cholinergic synapses. The reverse was true for TeTx or a mixture its constituent chains. Such selectivity was assigned to differences in neuronal targetting and uptake of the neurotoxins since both exhibited similar potencies when injected directly into the cell body of either cell type. When bath-applied, heterologous combinations of the toxins' HC and LC appeared as effective as the parent neurotoxins from whence each HC was derived. Moreover, targetting/internalization was attributable to the analogous N-terminal moieties, H2 and beta 2, of the HC from BoNT A and TeTx. Thus, it may be postulated that the latter regions possess two functional domains, one being distinct and responsible for the divergent neuronal specificity, whereas the other serves a common role in translocating the LC of either toxin. Also, it was shown that the C-terminal portion of the HC of TeTx is unable to play the intracellular role of its counterpart in BoNT A.

Animals↗
PubMed1991

Clostridial neurotoxins: from toxins to therapeutic tools?

Tetanus toxin and botulinum toxins are powerful neurotoxins which block neurotransmitter release through an unknown mechanism my means of their light chains. The heavy chains provide the machinery for neuroselective binding, internalization, retrograde intraaxonal transport, and translocation of the L-chains into the cytosole. We have cloned and sequenced the structural genes of tetanus toxin and of five serologically distinct botulinum toxins to identify structurally and functionally conserved subdomains. The minimum essential domains of the L-chains of tetanus and botulinum toxin type A were identified by combined in vitro transcription and microinjection of L-chain specific mRNA into identified presynaptic neurons of Aplysia californica. In addition, a nontoxic mutant of tetanus was generated by replacing histidine(237) by a proline residue. The development of nontoxic neuroselective transporter molecules carrying various marker enzymes is discussed.

Amino Acid Sequence↗
PubMed1990

Receptor-mediated presynaptic facilitation of quantal release of acetylcholine induced by pralidoxime in Aplysia.

1. Possible interactions of contrathion (pralidoxime sulfomethylate), a reactivator of phosphorylated acetylcholinesterase (AChE), with the regulation of cholinergic transmission were investigated on an identified synapse in the buccal ganglion of Aplysia californica. 2. Transmitter release was evoked either by a presynaptic action potential or, under voltage clamp, by a long depolarization of the presynaptic cell. At concentrations higher than 10(-5) M, bath-applied contrathion decreased the amplitude of miniature postsynaptic currents and increased their decay time. At the same time, the quantal release of ACh was transiently facilitated. The facilitatory effect of contrathion was prevented by tubocurarine but not by atropine. Because in this preparation, these drugs block, respectively, the presynaptic nicotinic-like and muscarinic-like receptors involved in positive and negative feedback of ACh release, we proposed that contrathion activates presynaptic nicotinic-like receptors. 3. Differential desensitization of the presynaptic receptors is proposed to explain the transience of the facilitatory action of contrathion on ACh release. 4. The complexity of the synaptic action of contrathion raises the possibility that its therapeutic effects in AChE poisonings are not limited to AChE reactivation.

Acetylcholine↗
PubMed1990

Activation of protein kinase C by presynaptic FLRFamide receptors facilitates transmitter release at an aplysia cholinergic synapse.

Modulation of evoked quantal transmitter release by protein kinase C (PKC) was investigated at an identified cholinergic neuro-neuronal synapse of the Aplysia buccal ganglion. Evoked acetylcholine release was increased by a diacylglycerol analog that activates PKC and was decreased by H-7, a blocker of PKC. FLRFamide facilitated evoked quantal release by increasing presynaptic Ca2+ influx. The inhibition of PKC by H-7 prevented both the increase of presynaptic Ca2+ influx and the facilitation of evoked acetylcholine release induced by the activation of presynaptic FLRFamide receptors. These results provide evidence that the activation of PKC could be a step in the intracellular pathway by which FLRFamide receptors increase evoked quantal acetylcholine release.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Exogenous mRNA encoding tetanus or botulinum neurotoxins expressed in Aplysia neurons.

Injection of exogenous mRNA purified from various tissue preparations into cellular translation systems such as Xenopus oocytes has allowed expression of complex proteins (e.g., receptors for neurotransmitters). No evidence for expression of injected exogenous mRNA, however, has been reported in terminally differentiated neurons. If achieved, it would allow the study of long-lasting changes of properties of nerve cells in their functional context. To obtain evidence of such expression, we chose two proteins that produce a detectable effect even at very low intracellular concentrations. Tetanus toxin and botulinum neurotoxin fulfill this criterion, being the most potent neurotoxins known. Both toxins block neurotransmitter release at nanomolar intracellular concentrations. These di-chain proteins, consisting of a light chain and a heavy chain, have recently been sequenced. Their active sites are located (or partly located) on the light chain. mRNAs encoding the light chain of either toxin were transcribed in vitro from the cloned and specifically truncated genes of Clostridium tetani and Clostridium botulinum, respectively, and injected into presynaptic cholinergic neurons of the buccal ganglia of Aplysia californica. Depression of neurotransmitter release appeared in less than 1 hr, demonstrating successful expression of foreign mRNA injected into a neuron in situ.

Animals↗
PubMed1990

Histamine and FLRFamide regulate acetylcholine release at an identified synapse in Aplysia in opposite ways.

1. The effects of histamine and FLRFamide (Phe-Leu-Arg-Phe-NH2) on acetylcholine (ACh) release were studied in the buccal ganglion of Aplysia californica on an identified synapse (buccal ganglion inhibitory synapse, BGIS) involved in a small neuronal circuit controlling the feeding behaviour. The inhibitory postsynaptic current (IPSC) evoked by a presynaptic spike in the voltage-clamped postsynaptic neurone was decreased by histamine and increased by FLRFamide. 2. Histamine and FLRFamide modified the amplitude of the presynaptic spike. To test if these drugs acted directly on presynaptic calcium influx, we evoked transmitter release by 3 s depolarizations of the presynaptic neurone (to +10 mV) under voltage clamp to avoid modifications of presynaptic membrane polarization induced by changes in presynaptic voltage-dependent K+ and/or Na+ conductances. 3. Statistical analysis of this evoked long-duration (3 s) induced postsynaptic current (LDIPSC) allowed us to calculate the amplitude and the decay time of the miniature postsynaptic current and consequently the number of quanta released by the presynaptic terminal. 4. The amplitude of the LDIPSC decreased during the 3 s presynaptic depolarization. This was not due to a lack of available transmitter, since LDIPSC amplitude could be maintained constant by a 'clamp of the release of ACh' which adequately depolarized the presynaptic neurone, but rather to changes in the calcium influx into the presynaptic neurone. 5. FLRFamide increased more the initial portions of the LDIPSC than the final portions. This effect of FLRFamide was only reduced and delayed by atropine or curare, antagonists of muscarinic-like and nicotinic-like autoreceptors previously demonstrated to be present at the same terminal. Activation of the nicotinic-like receptors, which also increased transmitter release, induced a modification of the shape of the LDIPSC which was completely different from that due to FLRFamide. 6. Histamine decreased the amplitude of the LDIPSC. This effect was more pronounced at the beginning of the response. The effects of histamine were insensitive to curare and atropine, but were completely blocked by cimetidine, a specific histamine receptor antagonist. 7. The modifications of the shape and of the amplitude of the LDIPSC by FLRFamide and histamine suggested that these molecules alter presynaptic influx of calcium. This was confirmed by the analysis of calcium current recorded from the presynaptic neurone: the calcium inward current in the presynaptic neurone was increased by FLRFamide and reduced by histamine, whereas the activation of autoreceptors had no measurable effect on calcium current.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1990

Clues to the multi-phasic inhibitory action of botulinum neurotoxins on release of transmitters.

1. With the aim of gaining insight into the mechanism of Ca2(+)-dependent secretion, inhibition of transmitter release by botulinum neurotoxins or their fragments was studied at mammalian motor nerve terminals, cerebrocortical synaptosomes and PC-12 cells. 2. Relative to BoNT type A, the feeble neuromuscular paralytic activity of its two chains and the lack of activity observed with a proteolytic fragment, H2L (lacking H1, the C-terminal half of the heavy chain) highlight a requirement of the intact, disulphide-linked dichain protein for efficient targetting (binding/uptake) to peripheral cholinergic nerve endings. 3. In PC-12 cells, the renatured light chain alone proved equally potent as the whole toxin in reducing Ca2(+)-evoked noradrenaline release, when digitonin-permeabilization was used to overcome the uptake barrier. Treatment of BoNT A with 10 mM dithiothreitol, under non-denaturing conditions, was not very effective in reducing its inter-chain disulphide bond(s) and had little influence on the level of inhibition seen. 4. Altering the intra-synaptosomal concentrations of cyclic nucleotides (c-AMP, c-GMP) or protein kinase C activity failed to affect the reduction of Ca2(+)-dependent K(+)-stimulated noradrenaline release caused by BoNT A or B. On the other hand, raising the cytosolic Ca2+ concentration with the ionophore A23187 reversed the inhibitory effect of BoNT A to a greater extent than that of type B, revealing differences in their actions. 5. Whereas BoNT-induced decrease of Ca2(+)-dependent K(+)-evoked release of noradrenaline was unaffected by destruction of the actin-based cytoskeleton in synaptosomes with cytochalasin D, disassembly of microtubules with colchicine, nocodazole or griseofulvin antagonised the intracellular action of type B but not A. It is speculated that BoNT B blocks transmitter release by interfering with the proposed detachment of synaptic vesicles from microtubules. Establishing the precise involvement of tubulin in the toxin's action may provide a valuable clue to the mechanism of neurotransmitter release or its control.

Animals↗
PubMed1990

Inhibition of neurotransmitter release by botulinum neurotoxins and tetanus toxin at Aplysia synapses: role of the constituent chains.

1. The effects on the release of transmitter by botulinum neurotoxins (BoNT; types A, B, E), tetanus toxin (TeTx), constituent chains or fragments were studied on identified cholinergic and non-cholinergic synapses in Aplysia. 2. Cholinergic synapses in the buccal ganglion were found to be greater than 100 fold more sensitive to extracellular application of BoNT than to TeTx whereas in non-cholinergic synapses of the cerebral ganglion the potencies of the toxins were reversed. When intracellularly applied TeTx and BoNT were found nearly equipotent. This disparity in the susceptibilities of BoNT and TeTx to inhibit transmission was attributed to differences in the toxin's acceptors or uptake systems in the two neurone types. 3. Micro-injection into cholinergic neurones of the isolated renatured toxins' chains showed that both light and heavy chains of BoNT are intracellularly required whereas the light chain of TeTx alone is sufficient. 4. The heavy chain of BoNT as well as that of TeTx were found to mediate internalization of active moieties via its amino-terminal half. Furthermore the heavy chain of one toxin could internalize the light chain of the other.

Animals↗
PubMed1990

Molecular biology of Clostridial toxins: expression of mRNAs encoding tetanus and botulinum neurotoxins in Aplysia neurons.

mRNAs encoding the light chain of tetanus and botulinum neurotoxins were transcribed, in vitro, from the cloned and specifically truncated genes of Clostridium tetani and Clostridium botulinum, respectively, and injected into presynaptic identified cholinergic neurons of the buccal ganglia of Aplysia californica. The size of the current response measured in the voltage clamped postsynaptic neuron was taken as indicator of the quantity of acetylcholine released. Depression of neurotransmitter release similar to that observed when native light chains of the two toxins were injected but needing an additional delay of 30 to 40 minutes, demonstrated a successful expression of a foreign mRNA injected into a neuron in situ.

Acetylcholine↗
PubMed1989

Multiple domains of botulinum neurotoxin contribute to its inhibition of transmitter release in Aplysia neurons.

The binding, internalization, and inhibition of transmitter release by botulinum neurotoxin (BoNT) was investigated using the intact toxin, its heavy (HC) or light (LC) chains, and a proteolytic fragment thereof. In Aplysia neurons, blockade of acetylcholine release upon external application of BoNT types A or E was prevented by reducing the temperature to 10 degrees C, due to arresting intoxication at the membrane binding step. At this low temperature, type A HC, H2 (comprised of the N-terminal of HC), or H2L (H2 disulfide-linked to LC) antagonized the neuroparalytic action of BoNT A or E, indicating that the latter bind saturably to common ecto-acceptor via the H2 region. In contrast, H2L was unable to counteract BoNT-induced paralysis at the murine neuromuscular junction. In accordance with this species difference, unlike native BoNT, saturable binding of 125I-labeled H2L could not be detected in mammalian peripheral or central nerve terminals. Possibly, more stringent structural requirements form the basis of the toxin's greater effectiveness in inhibiting neurotransmission at mouse nerve muscle synapses than Aplysia nerve terminals. In further identification of functional domains in the toxin, an unprocessed single-chain form of BoNT type E was found to be ineffective when applied extra- or intracellularly to Aplysia neurons. Notably, bath application of the latter to a neuron preinjected with HC, but not H2L or LC, resulted in a blockade of release. This shows that the single-chain species can become internalized and requires, not only LC, but also processed HC for its inhibitory action; consistently, the proteolyzed form of BoNT E was active.

Acetylcholine↗
PubMed1989

Inhibition of transmitter release by botulinum neurotoxin A. Contribution of various fragments to the intoxication process.

1. The contribution of a proteolytic fragment (H2L) of botulinum neurotoxin type A (comprised of the aminoterminal region of the heavy-chain disulphide-linked to the light chain) to inhibition of neurotransmitter release was investigated, using central cholinergic synapses of Aplysia, rodent nerve-diaphragm preparations and cerebrocortical synaptosomes. 2. No reduction in neurotransmitter release was observed following external application to these preparations of highly purified H2L or after intracellular injection into Aplysia neurons. 3. The lack of activity was not the result of alteration in the light chain of H2L during preparation of the latter because (a) renaturation of this light chain with intact heavy chain produced a toxic di-chain form and (b) simultaneous application of heavy chain and light chain from H2L inhibited transmitter release in Aplysia. 4. Bath application of H2L and heavy chain together inhibited release of transmitter; however, at the neuromuscular junction the potency of this mixture was much lower than that of native toxin. A similar blockade resulted when heavy chain was applied intracellularly and H2L added to the bath, demonstrating that H2L is taken up into cholinergic neurons of Aplysia. This uptake is shown to be mediated by the amino-terminal moiety of heavy chain (H2), because bath application of light chain plus H2 led to a decrease in acetylcholine release from a neuron that had been injected with heavy chain. 5. A role within the neuron is implicated for a carboxy-terminal portion of heavy chain (H1) since intracellular injection of light chain and H2 did not affect transmitter release. Although the situation is unclear in mammalian nerves, these collective findings indicate that blockade of transmitter release in Aplysia neurons requires the intracellular presence of light chain and H1 (by inference), whilst H2 contributes to the internalization step.

Acetylcholine↗
PubMed1989

Light chain of tetanus toxin intracellularly inhibits acetylcholine release at neuro-neuronal synapses, and its internalization is mediated by heavy chain.

The ability of the two-chain form of tetanus toxin (TeTx), its constituent light (LC) or heavy (HC) chains, and papain fragment to block evoked acetylcholine (ACh) release in the buccal ganglia of Aplysia californica was studied electrophysiologically. Extracellularly applied, TeTx or its B fragment (consisting of LC and beta 2, the amino-terminal portion of HC) blocked ACh release, whereas LC, HC, or the beta 2 fragment did not affect it. Toxicity was restored when LC was bath applied together with HC or the beta 2 fragment. When injected into the presynaptic neuron, TeTx, the B fragment or LC, but not HC, induced inhibition of ACh release. These results indicate that the blockade of ACh release by TeTx is mimicked by intracellular action of LC, the internalization of which is mediated by the HC via its amino-terminal moiety.

Acetylcholine↗
PubMed1989

Demonstration of functional acetylcholinesterase on the soma of individual neurones of Aplysia by in vivo microspectrophotometry.

The presence of functional acetylcholinesterase is demonstrated in vivo on somatic membranes of single ganglionic neurones of Aplysia using concurrently microspectrophotometry and electrophysiology. The similarity of the effects of an irreversible blocker of acetylcholinesterase and of phospholipase C from Bacillus cereus suggests that acetylcholinesterase is anchored in the membrane via phosphatidylinositol.

Acetylcholinesterase↗
PubMed1988

Involvement of the constituent chains of botulinum neurotoxins A and B in the blockade of neurotransmitter release.

1. The abilities of botulinum neurotoxins, types A and B (single and two-chain forms) to inactivate an intraneuronal component required for transmitter release were quantified in a phrenic-nerve-diaphragm preparation, cerebrocortical synaptosomes or the buccal ganglion of Aplysia californica and compared with the mouse toxicity assay. 2. Homogeneous preparations of the individually renatured polypeptide chains of both toxin types showed low residual toxicity in the whole animal and had no effect on neurotransmission in all three systems, when tested singly. 3. Mixtures of individually renatured heavy chain, from type A or B, and either light chain proved very effective in blocking the evoked release of acetylcholine when bath-applied to the buccal ganglion of Aplysia whilst they were relatively inactive on mammalian nerve terminals, indicating a less efficient uptake of the polypeptides in the latter. 4. When renatured together, the homologous, but not the heterologous, chains of each toxin type yielded toxic, disulphide-linked two-chain species. 5. A role for the heavy chain alone in acceptor recognition and membrane translocation was implicated by the blockade of acetylcholine release produced when light chain was applied to a ganglion of Aplysia previously bathed in heavy chain and washed extensively. No blockade was observed when the order of application of the two chains was reversed. 6. These findings are discussed in the context of the intracellular requirement for both the constituent toxin chains for toxicity, and in the apparent need for these chains to be linked via a disulphide bond for uptake in rodents but not in Aplysia.

Acetylcholine↗