EFFECTS OF POTASSIUM CHANNEL BLOCKERS ON SYNAPTIC PLASTICITY IN THE CORTICOSTRIATAL PATHWAY

High-frequency stimulation (HFS) of the cerebral cortex or underlying white matter usually induces long-term depression (LTD) in the cortico striatal pathway. Long-term potentiation (LTP) has been described in s triatal cells exposed to extracellular tetraethylammonium (TEA). The f acilitating effect of TEA may be due to blockade of K+ channels in the postsynaptic neurone or alternatively to presynaptic effects on the r elease of neurotransmitters such as glutamate or dopamine. We compared the effects of HFS on LTP in striatal cells in four groups of neurone s. HFS in control conditions induced LTD (- 28.6 +/- 2.0% at 20 min, n = 10) whereas HFS in extracellular TEA (30 mM) induced LTP (+ 51.0 +/ - 24.2% at 20 min, n = 7). LTP was not induced in cells loaded with in tracellular Cs (- 20.3 +/- 11.4% at 20 min, n = 10) or intracellular T EA (-11.8 +/- 8.9% at 20 min, n = 10), despite comparable effects on p ostsynaptic responses to HFS. Since the effects of the intracellular K C channel blockers are limited to the cell being recorded from, these findings suggest that the facilitating effect of extracellular TEA on LTP induction involves a presynaptic action. (C) 1998 Published by Els evier Science Ltd. All rights reserved.