Our previous studies have shown that
agmatine inhibited
morphine-induced conditioned place preference and locomotor sensitization in rats. In the present study, we further investigated the effects of
agmatine on the discriminative stimulating effects produced by
morphine in rats.
Agmatine, at the dose range of 10-80 mg/kg (i.g.), neither induced drug discrimination, nor substituted for
morphine stimulus in rats that were previously treated with
morphine, suggesting that
agmatine itself has no psychomotor-stimulating potential. However, pretreatment with
agmatine (40, 80 mg/kg, i.g.) significantly inhibited the acquisition, but not expression, of
morphine-induced drug discrimination as assessed by the correct nose-poke response. Further, chronic administration of
agmatine (40, 80 mg/kg/day x 12 days, i.g., 25 min prior to
morphine) also significantly accelerated the extinction of the discrimination induced by
morphine. These data suggest that
agmatine inhibits the acquisition and accelerates the extinction of
morphine-induced discrimination, supporting possible use of
agmatine in the treatment of
opioid dependence.