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Freeze‐fracture study of the large myelinated club ending synapse on the goldfish Mauthner cell: Special reference to the quantitative analysis of gap junctions
Author(s) -
Tuttle Rebecca,
Masuko Sadahiko,
Nakajima Yasuko
Publication year - 1986
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902460206
Subject(s) - gap junction , postsynaptic potential , connexon , biology , synapse , mauthner cell , biophysics , neuroscience , neurotransmission , synaptic vesicle , anatomy , vesicle , membrane , microbiology and biotechnology , intracellular , genetics , receptor , connexin , fishery , fish <actinopterygii> , biochemistry
The large myelinated club endings (LMCEs) of primary eighth nerve afferents form mixed synapses on the lateral dendrite of the giant Mauthner cell. The double replica freeze‐fracture technique was employed to examine the intramembrane fine structure of these LMCE synapses. Morphological correlates of both chemical and electrical transmission were found at the LMCE synapses. Electrical synaptic junctions, or gap junctions, were located over much (10‐20%) of the synaptic contact. These were seen in both preand postsynaptic membrane as tightly packed P face particle aggregates and corresponding aggregates of E face pits. Specializations characteristic of chemical synaptic junctions were most prominent at the periphery of the synaptic contact. These specializations consisted of postsynaptic E face particle aggregates which were subjacent to presynaptic active zones. The active zones were distinguishable as regions with an increased density of large particles and vesicle attachment sites represented by P face depressions and E face protuberances. Quantitative analysis of gap junction particle (connexon) number at five LMCEs revealed 24,000‐106,000 connexons per LMCE. Comparison with data from electrophysiological studies of single LMCEs indicates that only a small fraction of the connexon channels are open at any given time during electrotonic transmission at an LMCE synapse.