Afterhyperpolarization mechanism in the dorsal spinocerebellar tract cells of the cat.

Abstract

The longlasting afterhyperpolarization (AHP) following single or short trains of spikes in dorsal spinocerebellar tract (DSCT) neurons of the cat was studied with intracellular recording techniques. The AHP amplitude was potential dependent, increasing with depolarization and decreasing with hyperpolarization of the membrane. With large membrane hyperpolarization, the AHP could be reversed in direction, the estimated reversal level being around 30 mV more negative than the threshold potential for spike initiation. The AHP amplitude was also little affected by Cl- ions injected into the cell. The AHP was associated with an increase in the membrane conductance, as measured with short current pulses. The major part of the conductance change was related to the AHP itself and not secondary to the hyperpolarization, i.e., to an anomalous rectification. A conductance change was also found when the membrane potential was polarized close to the AHP reversal level. There was a clear correlation between the AHP amplitude and the measured conductance changes. The AHP in DSCT neurons, as in spinal motoneurons, is apparently caused primarily by an increase in membrane conductance to K+. The time course of the conductance change underlying the AHP was calculated from the AHP voltage and a mathematical expression describing this time course was given. The properties of the AHP in DSCT cells were compared with those in spinal motoneurons and the functional significance of the differences was discussed briefly.