Repetitive firing: quantitative analysis of encoder behavior of slowly adapting stretch receptor of crayfish and eccentric cell of Limulus.

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Abstract
Techniques developed for determining summed encoder feedback in conjunction with the leaky integrator and variable-.gamma. models for repetitive firing are applied to spike train data obtained from the slowly adapting crustacean [Procambarus clarki] stretch receptor and the eccentric cell of Limulus polyphemus. Input stimuli were intracellularly applied currents. Analysis of data from cells stringently selected by reproducibility criteria gave a consistent picture for the dynamics of repetitive firing. The variable-.gamma. model with appropriate summed feedback was most accurate for describing encoding behavior of both cell types. The leaky integrator model, while useful for determining summed feedback parameters, was inadequate to account for underlying mechanisms of encoder activity. For the stretch receptor, 2 summed feedback processes were detected: one had a short time constant; the other, a long one. Appropriate tests indicated that the short time constant effect was from an electrogenic Na pump, and the same is presumed for the long time constant summed feedback. Both feedbacks show seasonal and/or species variations. Short hyperpolarizing pulses inhibited the feedback from the long time constant process. The eccentric cell showed 2 summed feedback processes: 1 due to self inhibition, the other probably a short time constant electrogenic Na pump similar to that described in the stretch receptor.