Calcium-independent activation of the secretory apparatus by ruthenium red in hippocampal neurons: a new tool to assess modulation of presynaptic function

Trudeau, Louis-Éric; Doyle, Robert T.; Emery, Dennis G.; Haydon, Philip G.

doi:10.1523/jneurosci.16-01-00046.1996

Cited by 59 publications

(69 citation statements)

References 49 publications

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“…After washout of the peptide, inter-SEAC intervals returned to 109.4 Ϯ 12.3% of control, and mean SEAC amplitudes were 117.6 Ϯ 2.1% of control. These results are entirely compatible with a merely presynaptic site of action for somatostatin (Scanziani et al, 1992;Scholz and Miller, 1992;Trudeau et al, 1996).…”

Section: Methodssupporting

confidence: 76%

“…C, The effect of somatostatin on the currentvoltage relationship in B is shown as percentage of inhibition. (Scanziani et al, 1992;Scholz and Miller, 1992;Thompson et al, 1993;Trudeau et al, 1996), presynaptic somatostatin receptors may reduce excitatory synaptic transmission via at least two independent signaling mechanisms: an inhibition of Ca 2ϩ entry and a reduction of vesicle exocytosis, which arises downstream of Ca 2ϩ entry.…”

Section: Signaling Mechanisms Of Presynaptic Somatostatin Receptorsmentioning

confidence: 99%

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Somatostatin Inhibits Excitatory Transmission at Rat Hippocampal Synapses via Presynaptic Receptors

1997

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Somatostatin is one of the major peptides in interneurons of the hippocampus. It is believed to play a role in memory formation and to reduce the susceptibility of the hippocampus to seizurelike activity. However, at the cellular level, the actions of somatostatin on hippocampal neurons are still controversial, ranging from inhibition to excitation. In the present study, we measured autaptic currents of hippocampal neurons isolated in singleneuron microcultures. Somatostatin and the analogous peptides seglitide and octreotide reduced glutamatergic, but not GABAergic, autaptic currents via pertussis toxin-sensitive G-proteins. This effect was observed whether autaptic currents were mediated by NMDA or non-NMDA glutamate receptors. Furthermore, somatostatin did not affect currents evoked by the direct application of glutamate, but reduced the frequency of spontaneously occurring excitatory autaptic currents. These results show that presynaptic somatostatin receptors of the SRIF 1 family inhibit glutamate release at hippocampal synapses. Somatostatin, seglitide, and octreotide also reduced the frequency of miniature excitatory postsynaptic currents in mass cultures without affecting their amplitudes. In addition, all three agonists inhibited voltage-activated Ca 2ϩ currents at neuronal somata, but failed to alter K ϩ currents, effects that were also abolished by pertussis toxin. Thus, presynaptic somatostatin receptors in the hippocampus selectively inhibit excitatory transmission via G-proteins of the G i /G o family and through at least two separate mechanisms, the modulation of Ca 2ϩ channels and an effect downstream of Ca 2ϩ entry. This presynaptic inhibition by somatostatin may provide a basis for its reportedly anticonvulsive action.

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Section: Methodssupporting

confidence: 76%

Section: Signaling Mechanisms Of Presynaptic Somatostatin Receptorsmentioning

confidence: 99%

Somatostatin Inhibits Excitatory Transmission at Rat Hippocampal Synapses via Presynaptic Receptors

1997

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“…However, after the BAPTA loading, carbachol still increased the sEPSC frequency. Also depletion of [Ca 2ϩ ] i stores with thapsigargin (0.5-1 M, n ϭ 4, data not shown) failed to affect the change in sEPSC frequency (27). These results show that carbachol does not enhance the sEPSC frequency by the increase in [Ca 2ϩ ] i .…”

Section: Resultsmentioning

confidence: 73%

“…However, BAPTA-loaded cells still responded to carbachol. Furthermore, thapsigargin not only failed to change [Ca 2ϩ ] i in presynaptic boutons (12) but also the frequency of sEPSCs (27) indicating that Ca 2ϩ ions released from the IP 3 -sensitive stores are not involved in this modulatory process. It is worth noting that previous immunohistochemical experiments revealed a nonuniform distribution of the IP 3 -receptors in hippocampal cells.…”

Section: Discussionmentioning

confidence: 93%

Muscarinic stimulation of synaptic activity by protein kinase C is inhibited by adenosine in cultured hippocampal neurons

Bouron

Réuter²

1997

Proc. Natl. Acad. Sci. U.S.A.

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We have studied the effect of the cholinergic agonist carbachol on the spontaneous release of glutamate in cultured rat hippocampal cells. Spontaneous excitatory postsynaptic currents (sEPSCs) through glutamatergic ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type channels were recorded by means of the patch-clamp technique. Carbachol increased the frequency of sEPSCs in a concentration-dependent manner. The kinetic properties of the sEPSCs and the amplitude distribution histograms were not affected by carbachol, arguing for a presynaptic site of action. This was confirmed by measuring the turnover of the synaptic vesicular pool by means of the f luorescent dye FM 1-43. The carbachol-induced increase in sEPSC frequency was not mimicked by nicotine, but could be blocked by atropine or by pirenzepine, a muscarinic cholinergic receptor subtype M1 antagonist. Intracellular Ca 2؉ signals recorded with the f luorescent probe Fluo-3 indicated that carbachol transiently increased intracellular Ca 2؉ concentration. Since, however, carbachol still enhanced the sEPSC frequency in bis(2-aminophenoxy)ethane-N,N,N ,N -tetra-acetate-loaded cells, this effect could not be attributed to the rise in intracellular Ca 2؉ concentration. On the other hand, the protein kinase inhibitor staurosporine as well as a down-regulation of protein kinase C by prolonged treatment of the cells with 4␤-phorbol 12-myristate 13-acetate inhibited the carbachol effect. This argues for an involvement of protein kinase C in presynaptic regulation of spontaneous glutamate release. Adenosine, which inhibits synaptic transmission, suppressed the carbachol-induced stimulation of sEPSCs by a G proteindependent mechanism activated by presynaptic A1-receptors.The occurrence of memory deficits in neurodegenerative disorders, such as Alzheimer disease, or the effects of cholinergic drugs on learning and memory have revealed an important role of the central cholinergic system in human cognitive functions (1-4). The hippocampus, which is known to be involved in memory formation (1, 4), receives cholinergic neurons from the basal forebrain. The cholinergic septohippocampal pathway modulates the activity of the hippocampus. For instance it is involved in the control of the theta rhythmic activity (5).Hippocampal cells express cholinergic nicotinic and muscarinic receptors with a predominance of the latter (5). Five muscarinic cholinergic receptor subtypes (M1-M5) have been identified (6). M1, M3, and M5 are coupled to phospholipase C activation resulting in the production of the second messengers inositol trisphosphate (IP 3 ) and diacylglycerol, whereas M2 and M4 inhibit adenylate cyclase activity (6). Immunoprecipitation studies, measurements of mRNA levels and of ligand binding sites indicate that the M1-subtype is the most abundant muscarinic receptor in the hippocampus (7).However, the role of M1-receptor activation and the subsequent signaling pathway in neurotransmitter release are only poorly understood. We have studied the effect of ...

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“…Certain agents have been reported to differentially regulate miniature release rate and evoked release probability, 15,23,46 indicating some expected divergence amongst release mechanisms. Although this is a potential limitation, a large body of evidence suggests that miniature and evoked release probabilities are regulated in parallel at presynaptic terminals.…”

Section: Discussionmentioning

confidence: 99%

Vesicle number does not predict postsynaptic measures of miniature synaptic activity frequency in cultured cortical neurons

et al. 2000

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Abstract-We tested the hypothesis that heterogeneity in the frequency of miniature synaptic activity reflects differences in the number of vesicles present in presynaptic terminals. Using imaging techniques, we measured dendritic miniature synaptic calcium transients attributed to the spontaneous release of single transmitter quanta. Following imaging, the identified neurons were processed for serial transmission electron microscopy. At sites of quantal Ca 2ϩ transients mediated by N-methyl-d-aspartate receptors, we confirmed the presence of excitatory synapses and measured the total number of vesicles and the number of docked vesicles.We observed no correlation between the frequency of spontaneous miniature activity and either the total vesicle number or the number of docked vesicles. We conclude that the presynaptic vesicle complement as measured by ultrastructural analysis does not necessarily determine the frequency of spontaneous activity at synapses mediated by N-methyl-d-aspartate receptors. ᭧ 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved.Key words: NMDA, quantal, EPSC, release, ultrastructure, electron microscopy.Studies using electron microscopy (EM) have indicated that the morphology of cortical excitatory glutamatergic synapses is highly variable. 19 Bouton size, vesicle number, vesicle diameter and postsynaptic spine volume vary widely within a relatively homogenous population of neurons. 36,41 It has been hypothesized that structural differences between synapses underlie some of the functional differences that are observed between neurons. 6,11,24 Accordingly, it is necessary to assess both synaptic structure and function at single CNS synapses.We have recently described techniques to compare structure and function at multiple synapses along a region of dendrite. 26 Using Ca 2ϩ imaging, we measured the Nmethyl-d-aspartate (NMDA) receptor-mediated component of spontaneous miniature excitatory postsynaptic currents (mEPSCs), termed the miniature synaptic Ca 2ϩ transient (MSCT). 31,32 Calcium imaging provides a method to localize synaptic responses to particular dendritic spines. 29,31,34 Sensitivity to the NMDA receptor antagonist d,l-APV suggested that under the conditions we have used, Ca 2ϩ transients associated with miniature synaptic activity are largely attributed to NMDA receptors. 31,48,34 We have previously reported a positive correlation between the MSCT amplitude and mEPSC amplitude, 32 indicating that Ca 2ϩ imaging can be used to evaluate the local characteristics of synaptic events. Following MSCT imaging, we performed serial reconstruction of transmission EM images to identify synapses at the origins of the Ca 2ϩ transients. This enabled the ultrastructural characterization of the specific synapses where MSCTs were measured. Using these techniques, we have previously reported that synapse size correlated positively with the amplitude of the NMDA component of the quantal postsynaptic response, suggesting that synapse size may place a limit on the number of postsynaptic...

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Calcium-independent activation of the secretory apparatus by ruthenium red in hippocampal neurons: a new tool to assess modulation of presynaptic function

Cited by 59 publications

References 49 publications

Somatostatin Inhibits Excitatory Transmission at Rat Hippocampal Synapses via Presynaptic Receptors

Somatostatin Inhibits Excitatory Transmission at Rat Hippocampal Synapses via Presynaptic Receptors

Muscarinic stimulation of synaptic activity by protein kinase C is inhibited by adenosine in cultured hippocampal neurons

Vesicle number does not predict postsynaptic measures of miniature synaptic activity frequency in cultured cortical neurons

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