Effect of repetitive activation on the afterhyperpolarization in dorsal spinocerebellar tract neurones.

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Abstract
The changes in the afterhyperpolarization (AHP) with repetitive activation were studed in dorsal spinocerebellar tract cells of the cat using intracellular recording techniques. The AHP following a single spike was conditioned at different interspike intervals by a single preceding spike. In the majority of neurons the AHP following a spike added approximately linearly with that generated by a preceding spike. In other cells the AHP following a spike was instead depressed by a preceding spike. This depression was approximately constant at interspike intervals less than the AHP duration (50-100 ms). Thereafter the AHP slowly recovered during the next 100-300 ms. There was no associated decrease in the initial brief hyperpolarizing undershoot. With shortlasting repetitive activation at high frequency (> 100 impulses/s) the AHP peak amplitude increased progressively with successive spikes (5-15 spikes). No change in the time constant of decay was observed. A good correspondence was found between the observed increase in peak amplitude of the AHP and that given by a theoretical linear superposition of the successive AHP. Changes in the brief hyperpolarizing undershoot with repetitive activation were also described.