Spike timing-dependent plasticity has been reported in hippocampal slice preparations from young animals and cultures (Bi & Poo, 1998; Debanne et al. 1998). We previously reported a developmental change in the induction rules for LTP in CA1 of hippocampal slices whereby with advancing age, a postsynaptic burst of action potentials became necessary for pairing-induced LTP (Meredith et al.,SFN abstract 2002). To investigate whether GABAergic inhibition plays a role in this change, we tested whether LTP induction in the adult hippocampus was affected by blocking GABAA receptor-mediated inhibition. Patch-clamp recordings were made from CA1 pyramidal neurons in submerged hippocampal slices (300µm) from young adult C57BL6 mice (5-8weeks old,25-27oC) in the presence of 10µM of GABAA receptor antagonist, gabazine. EPSPs were alternately evoked at 0.2Hz by two stimulation electrodes placed in stratum radiatum. After a stable baseline of 12-15 minutes, one afferent input was paired with a single postsynaptic action ...