The objective of this study is to determine the role of prior prolonged low frequency stimulation (900 pulses at 1 Hz) on the further induced long-term potentiation (LTP) and depression (LTD) of synaptic activity in the rat hippocampal CA1 area. Hippocampal slices and standard extracellular field potential recording techniques were employed. LTP and LTD were induced using stimulation at 5 Hz (900 pulses) paired with or without simultaneous application of 1 microM isoproterenol respectively, at either normal CA1 synapses or CA1 synapses that were pre-conditioned with prolonged low frequency stimulation at 1 Hz. LTD could be successfully induced upon 900 pulses of stimulation given at 5 Hz at normal synapses (82.1 +/- 2.9%; n = 5); it was, however, reduced to 96.5 +/- 4.7% (n = 6) at the preconditioned synapses. When paired with application of isoproterenol, 900 pulses of stimulation given at 5 Hz produced LTP (139.9 +/- 9.6%, n = 5) at normal synapses. The magnitude of LTP is decreased to (130 +/- 13.2%) (n = 6) at pre-conditioned synapses, though the difference is not significant. These results suggest that at a given CA1 synapses the expression of LTP and LTD is dependent on their history of use.