INDUCTION OF LTD BY INCREASING EXTRACELLULAR CA2-LEVEL IN THE DENTATEGYRUS IN-VITRO( FROM A LOW)

Long-term depression (LTD) of field excitatory postsynaptic potentials was induced in the medial path of the dentate gyrus in juvenile rats in vitro by a protocol involving returning the Ca2+ concentration of t he external media to the control level (2 mM) following a period (30 m in) in low Ca2+ (1.2 mM), with stimulation at the test frequency throu ghout. Directly increasing Ca2+ from the control level did not induce LTD (or long-term potentiation). Such LTD showed mutual occlusion with low frequency stimulation (LFS, 1 Hz, 900 stimuli)-induced LTD. The C a2+-induced LTD was shown to be induced by the procedure of elevating the Ca2+ from the low to the control concentration, and not by the pro cedure of lowering of Ca2+, as full amplitude LFS induced LTD could be induced in the low Ca2+ media. Ca2+-induced LTD was inhibited by Ni2 (25 mu M) and 2-amino-5-phosphonopentanoate (50 mu M), demonstrating the necessity for activation of T/R-type voltage-gated Ca2+ channels a nd N-methyl-D-aspartate receptors, respectively, (C) 1998 Elsevier Sci ence Ireland Ltd. All rights reserved.