In this study, we wish to test the role of β-adrenergic receptors in modulating associated-LTP & LTD induced at a weak synaptic input of Shaffer collateral fibers onto CA1 pyramidal cells, after it was paired with a separated strong Shaffer collateral input in hippocampal slices. The experimental procedures were same as a paper presented in this meeting (Lin et at, SFN 2002 Annul Meeting). As shown in the Figure, bath application of 1 μM isoproterenol (Iso) resulted in LTP of weak input after paired with a strong input with +15 ms (weak leaded strong) delay; this pairing protocol however resulted in no LTP of the weak input in control condition. Application of Iso did not significantly changed LTP induced by pairing protocol of +10 ms delay. In contrast, LTD of weak input was induced by pairing protocol of -100 ms (strong leaded weak) delay in control condition; it was blocked upon application of Iso. The above effects of Iso on LTP & LTD were prevented in slices pretreated with H-89. Our results therefore...