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Journal of Experimental Biology 52,217-231 (1970)
Published by Company of Biologists 1970

Characteristics of Transmission Failure in the Squid Stellate Ganglion: A Study of a Simple Habituating System

G. HORN ¹ and M. J. WRIGHT ²

¹ Department of Anatomy, University of Cambridge
² The Psychological Laboratory, University of Cambridge

1. Failure of transmission was studied in the squid stellate ganglion by delivering shocks to the mantle connective and recording extracellularly from the last stellar nerve.

2. When the mantle connective was repeatedly stimulated by trains of shocks, it was invariably possible to select stimulus parameters at which the number of impulses evoked in the giant axon of the last stellar nerve declined.

3. The course of transmission failure with repeated stimulation was studied over a wide range of stimulus parameters. It was closely similar to the course of habituation which has been described for interneurones in more complex systems.

4. When a train of shocks was delivered to the mantle connective the synaptic potential evoked by successive shocks in the train declined. The time of initiation of the synaptic potential remained constant, but the slope of its leading edge decreased so that the time of spike initiation became progressively more delayed. Ultimate failure to generate a spike is accounted for by the failure of the synaptic potential to reach the threshold for spike initiation which was unchanged.

5. Recovery occurred with the passage of time. If a second train of shocks was delivered before restoration was complete the number of impulses evoked was usually fewer than those evoked by the previous train. This is because the synaptic potential is depressed and fewer shocks are needed to depress it still further to and below the level necessary for spike initiation.

6. Possible mechanisms responsible for the progressive failure of the synaptic potential are discussed.