RELATIONSHIP BETWEEN EXTRACELLULAR CALCIUM CONCENTRATIONS AND THE INDUCTION OF HIPPOCAMPAL LONG-TERM POTENTIATION

The effect of varying Ca and Mg concentrations was observed on the development of long-term potentiation (LTP) in the CA [commissural anterior] 1 region of the rat hippocampus maintained in vitro. Treatments which would be expected to lower the depolarization-induced influx of Ca into neuronal elements (i.e., lowering Ca2+ or raising Mg2+ in the perfusion medium) selectively antagonized LTP, while synaptic transmission, paired-pulse and frequency facilitation, and short-term (or post-tetanic) potentiation were all maintained. LTP is probably unrelated to these short-term forms of plasticity, but is either a Ca-dependent process itself, or is dependent upon some other Ca-related phenomenon (such as transmitter release).