EFFECTS OF NALOXONE TREATMENT ON MEMORY-ENHANCING PROPERTIES OF POST-TRAINING ADMINISTRATION OF SUBSTANCE-P

The present study investigated the effects of post-trial systemic inje ctions of the neurokinin substance P (SP) on inhibitory avoidance lear ning in rats treated with naloxone before conditioning and/or test tri als. Rats were trained in a step-down or uphill inhibitory avoidance t ask and tested 24 h later. The animals received, 30 min before trainin g and/or testing an i.p. injection of saline or naloxone (Nx) at doses of 0.5; 1.0; 5.0 or 50 mg/kg. Immediately after training they were ad ministered SP 50 mug/kg or vehicle. Animals that received Nx both befo re conditioning and test trials (5.0 and 50 mg/kg), in combination wit h SP, showed better test performance for the uphill and step-down avoi dance then those treated only with SP. Nx administered only before tra ining (5.0 and 50 mg/kg) or before test (0.5 to 50 mg/kg) reduced the effects of SP. These data are discussed in terms of the possibility th at Nx produces a state-dependent learning when combined with SP.