Please use this link to access this publication. Abstract This study was designed to test our hypothesis that an ultra-low dose of delta-9 tetrahydrocannabinol (THC) reverses age-dependent cognitive impairments in old mice and to examine the possible biological mechanisms that underlie this behavioral effect. Old female mice aged 24 months that had been injected once with 0.002 mg/kg THC (3–4 orders of magnitudes lower than doses that induce the conventional cannabinoid effects in mice) performed significantly better than vehicle-treated old mice and performed similarly to naive young mice aged 2 months, in 6 different behavioral assays that measured various aspects of memory and learning. The beneficial effect of THC lasted for at least 7 weeks. The single injection...