High Ca2+/low Mg2+ solution induces long-term depression in rat CA1 pyramidal neurons

Inducing long-term depression (LTD), one type of synaptic plasticity, typically requires electrical stimulation. Using rat hippocampal slices, we show that increasing the Ca2+ of the extracellular solution to 4 mM and decreasing the Mg2+ to 0.1 mM induced LTD in the CA1 region in the absence of electrical stimulation. The ionically-induced-LTD occluded electrical stimulation-induced LTD and was not blocked by application of 50 mu M D-2-amino-5-phosphonopentanoic acid (an N-methyl-D-aspartate receptor antagonist) or by 1 mM (RS)-alpha-methyl-4-carboxyphenylglycine (a metabotropic glutamate receptor antagonist) alone. However, LID was not ionically induced in the presence of both inhibitors. Our findings suggest that altering tissue excitability by changing the ionic environment mim ics electrical stimulation in the induction of LTD. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.