Physiological Properties of Chemically Transmitting Synapses in the Resting State

Abstract

Only with one type of chemically transmitting synapse, the giant synapses of the squid stellate ganglion, has it been possible to insert electrodes simultaneously into both presynaptic elements (Fig.8A),and so to investigate the electrical interaction between these two elements (Bullock and Hagiwara 1957; Hagiwara and Tasaki 1958). The negligible level of the electrical coupling between the presynaptic and postsynaptic components of the synapse is shown in Fig. 8D, F, where on hyperpolarizing the postsynaptic membrane there is no detectable change in presynaptic membrane potential, the small potential shift in D, being exactly duplicated in the extracellular record, F. Likewise, on hyperpolarizing the presynaptic membrane (Fig. 8C), there is no detectable potential change in the postsynaptic membrane. However, before these definitive investigations were made, it was recognized that there was a high degree of electrical uncoupling across chemically transmitting synapses. With intracellular recording there is no detectable potential change across the postsynaptic membrane when the presynaptic impulse propagates into the presynaptic terminals (Fatt and Katz 1951; Brock, Coombs and Eccles 1952). This is also convincingly demonstrated in the squid giant synapse (Figs. 8B; 12A–D; Bullock and Hagiwara 1957; Hagiwara and Tasaki 1958).