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(2+) 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.
Subject(s)
Neurons/physiology , Synaptic Vesicles/metabolism , Animals , Calcium/metabolism , Cells, Cultured , Cerebral Cortex/cytology , Excitatory Postsynaptic Potentials/physiology , Fetus/cytology , Microscopy, Confocal , Microscopy, Electron , Neurons/ultrastructure , Presynaptic Terminals/metabolism , Presynaptic Terminals/ultrastructure , Rats , Rats, Wistar , Receptors, N-Methyl-D-Aspartate/physiology , Synaptic Vesicles/ultrastructureABSTRACT
We have tested the hypothesis that functional differences between synapses are associated with ultrastructure in cultured cortical neurons. Using Ca(2+) imaging, we measured NMDA receptor-mediated miniature synaptic calcium transients attributed to the spontaneous release of single transmitter quanta. After imaging, the identified neurons were processed for serial transmission electron microscopy. At sites of quantal NMDA receptor-dependent Ca(2+) transients, we confirmed the presence of excitatory synapses and measured spine size and synaptic contact area. Our results demonstrate that synapse size correlates positively with the amplitude of the NMDA receptor-mediated postsynaptic response, suggesting that larger synapses express a greater number of NMDA receptors. Therefore, regulation of quantal amplitude may involve processes that alter synapse size.
Subject(s)
Cerebral Cortex/ultrastructure , Synapses/ultrastructure , Animals , Calcium/physiology , Cells, Cultured , Cerebral Cortex/physiology , Excitatory Postsynaptic Potentials , Image Processing, Computer-Assisted , Microscopy, Confocal , Microscopy, Electron , Neuroglia/physiology , Neuroglia/ultrastructure , Neurons/physiology , Neurons/ultrastructure , Patch-Clamp Techniques , Rats , Receptors, N-Methyl-D-Aspartate/physiology , Synapses/physiologyABSTRACT
A silicon mask-etching technique was used to prepare grooved surfaces that control the direction of outgrowths of human gingival explants. The method used to produce the grooves is excellent in terms of both the uniformity of the grooves and the control with which surfaces of the desired specifications can be obtained.
