Cellular neuroscienceDifferential efficiency of the endocytic machinery in tonic and phasic synapses
Section snippets
Experimental animals and tissue processing
Trunk segments of lamprey (Lampetra fluviatilis) spinal cords were dissected out as described before (Gad et al., 2000) and incubated either in low Ca2+ Ringer’s solution (0.1 mM CaCl2, 4 mM MgCl2) for 2 h at 4 °C to reduce the level of spontaneous synaptic activity in the preparation (four animals) or in high K+ Ringer’s solution (30 mM KCl) for 30 min at 4 °C to induce synaptic activity and vesicle cycling (three animals). To inhibit ATP production at synapses 40 mM NaN3 was added to the
Results
To compare levels of proteins involved in synaptic vesicle recycling in the tonic dorsal column synapse versus the phasic reticulospinal synapse in the lamprey spinal cord, we used the post-embedding immunogold technique. Contrary to pre-embedding techniques this approach provides equal access for the antibody to the antigen exposed to the surface of the section (Ottersen, 1989). Labeling of the two types of synapse was performed in the same section. To examine the difference in particle
Discussion
A number of studies have demonstrated that when phasic central synapses are challenged with tonic stimulation, a depletion of synaptic vesicles is typically observed (Model et al 1975, Wickelgren et al 1985, Gad et al 1998). In the lamprey giant synapse the massive fusion of vesicles during high-frequency stimulation results in large expansion of the synaptic vesicle membrane (Gad et al., 1998), which is then retrieved predominantly via the clathrin-mediated endocytic mechanism, although some
Acknowledgments
This work was supported by Swedish Research Council grants (K2005-32X-13473-06A, O.S.; K2004-33X-11287-10A, L.B.) and Svenska Läkaresällskapet (O.S.). We would like to thank Dr. P. De Camilli for the generous gift of DG-1 antibodies, Dr. M. McNiven for MC60 antibodies, and Dr. R. Jahn for SV2 antibodies.
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2011, Seminars in Cell and Developmental BiologyCitation Excerpt :Ca2+ influx and dephosphorylation-triggered migration of endocytic dephosphin proteins along with synapsin away from the SV cluster may not only promote endocytosis, but also destabilize the intravesicular matrix making SVs available for fusion. Interestingly, endocytic proteins that undergo stimulation-dependent migration cycles, show differential levels in tonic and phasic synapses [80], suggesting a differential organization of the intravesicular matrix in synapses with different release patterns. We thus hypothesize that complex formation between synapsin I and endocytic dephosphins may contribute to SV clustering in an activity-regulated fashion.
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2009, NeuroscienceCitation Excerpt :Differences in compensatory endocytic machineries in two central glutamatergic synapses with phasic and tonic patterns of activity have recently been observed in the lamprey spinal cord. Proteins that undergo migration to the periactive zone during onset of clathrin-mediated endocytosis, such as dynamin, amphiphysin, and intersectin, were found to display higher levels of labeling per vesicle in tonic dorsal column synapses as compared with phasic reticulospinal synapses (Evergren et al., 2006). Synaptic vesicle protein 2 (SV2) immunoreactivity was not significantly different in the two types of synapses.