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Memory deficits produced by marijuana arise partly via interaction of the psychoactive component, Δ 9-tetrahydrocannabinol (Δ 9-THC), with cannabinoid receptors in the hippocampus. Although cannabinoids acutely reduce glutamate release and block hippocampal long-term potentiation (LTP), a potential substrate for learning and memory, the consequences of prolonged exposure to Δ 9-THC for hippocampal function are poorly understood. Rats were injected with Δ 9-THC (10 mg/kg, ip, qd) for 1, 3, or 7 d, and electrophysiological recordings were performed in hippocampal slices 1d after the final injection. At this time, Δ 9-THC was undetectable in hippocampus using liquid chromatography–mass spectrometry (LC-MS). Hippocampal LTP generated using high-frequency (HFS) or theta burst stimulation was not observed in brain slices from the 7-d Δ 9-THC-treated animals. Δ 9-THC also blocked HFS-LTP after 3 …