Synaptic transmission and effects of temperature at the squid giant synapse

Abstract

THERE have been several reports on the effects of temperature on transmitter release at synaptic junctions^1–6. Although all reports agree that synaptic transmission is affected by temperature, the relationships are often complex and may differ from one preparation to another. The preparations studied, however, have the disadvantage that the relationship of presynaptic events (such as spike amplitude) to postsynaptic response cannot be investigated. It is possible to study this relationship at the squid giant synapse where intracellular recording can be obtained from both the presynaptic terminal and the postsynaptic axon. The excitatory postsynaptic potential (e.p.s.p.) at the squid synapse usually generates an action potential in the postsynaptic axon. To study the e.p.s.p., and hence transmitter release, without the postsynaptic action potential, tetrodotoxin has often been used ^7–9; this has not permitted study of the characteristics of the presynaptic spike in relation to the e.p.s.p. In a recent investigation on transmission at the squid giant synapse, we found that lowering the temperature of the preparation abolished activation of the postsynaptic action potential by the e.p.s.p., while the presynaptic spike was still generated. This observation enabled us to investigate the relationship between the presynaptic spike and the e.p.s.p. in various experimental conditions¹⁰ and we report here the effects of changing temperature.