Relative contribution of synaptic and non-synaptic influences to response decrements in a post-synaptic neurone.

Habituation phenomena and decrements of neural responses in isolated nervous structures have been related to depression of synaptic potentials (Bruner & Kehoe, 1970; Kandel et al. 1970; Horn & Wright, 1970; Zucker, 1972). However, previous research (Stephens, 1973) has shown that repeated intracellular stimulation of neurones in the isolated abdominal ganglion of Aplysia caUfomica produces response decrements common to trans-synaptic models of habituation (Bruner & Tauc, 1966 a, b; Buchwald, Halas, & Schramm, 1965; Kupfermann, Castellucci, Pinsker & Kandel, 1970; Thompson & Spencer, 1966). The demonstration of a decremental process resulting from intracellular stimulation and independent of synaptic modification indicates that there may be two factors contributing to trans-synaptic decrement of firing probability. Both synaptic depression and a process originating in the nonsynaptic membrane of the post-synaptic neurone could cause a decrease in firing of the post-synaptic cell. The research reported here examines some aspects of the relative influence of these two factors.