[Effect of cytochalasin D on the structure of mixed synapses and their electrotonic conductivity]

By methods of qualitative and quantitative electronmicroscopy the ultrastructure of mixed synapses of the goldfish Mauthner cell (MC) and their ability to strengthen electrotonic transmission after application of cytochalasin D, a highly specific inhibitor of actin polymerization. On the background of cytochalasin action tetranization of afferent rootlets of acoustic nerve, terminated with mixed synapses on the MC lateral dendrite, failed to induce any long-term potentiation of electronic coupling. On the contrary, a long-term depression of electrotonic transmission was evoked in this case. On the ultrastructureal level such a depression of synaptic conductivity was seen to correlate with a decrease in the number and total length per synaptic apposition of the desmosome-like contacts, known as actin-containing structures, as compared with unstimulated control preparations. In addition, experimental preparations were characterized with unusual quantity of asymmetric desmosome-like contacts, hemidesmosome, whose number during a long-term depression became 4 fold higher than in the control synapses. The data obtained support our recent suggestion on the role of filamentous actin in induction and long-term maintenance of enhanced electrotonic conductivity at mixed synapses.