Dopamine has been demonstrated to be involved in the modulation of long-term potentiation (LTP) in the CA1 region of the hippocampus. As monoamine transporter blockade will increase the actions of endogenous monoamine neurotransmitters, the effect of a dopamine transporter (DAT) antagonist on LTP was assessed using field excitatory postsynaptic potentials recorded in the CA1 region of the rat hippocampal slice preparation. Application of the DAT-specific blocker GBR 12,935 produced a significant enhancement in LTP of Schaffer collateral synapses in the CA1 at concentrations as low as 100 nM. A selective D1/D5 dopamine receptor antagonist (SCH 23,390, 1 micrometer did not affect the ability of GBR 12,935 to enhance LTP, whereas application of the D3 dopamine receptor antagonist U 99,194 (1 micrometer) blocked the GBR 12,935-induced enhancement in LTP. In addition, a D3 dopamine receptor agonist (7-OH-DPAT, 1 micrometer) caused a significant increase in LTP, an effect that was also blocked by U 99,194 (3 micrometers). These results suggest that either endogenously released dopamine (facilitated by DAT blockade) or exogenously applied dopamine agonist can act to increase LTP in the CA1 of the hippocampus via activation of the D3 subtype of dopamine receptor. (Contains 6 figures.)