Substance P enhancement of inhibitory avoidance learning: Mediation by the N-terminal sequence

Abstract

Experiments were performed to investigate the effects of intraperitoneally administered undecapeptide substance P (SP), its N-terminal fragment SP(1–7) (SPN) and the C-terminal analog [pGlu 6]-SP(6–11) (SPC) on inhibitory avoidance learning, using a one-trial up-hill avoidance task. In Experiment 1 rats were injected with either SP (50 μg/kg), SPN (3.3, 33, 167, 333 μg/kg) or SPC (2.7, 27, 134, 268 μg/kg) immediately after the training trial. Controls received the diluent vehicles. When tested 24 hr later, rats injected with 50 μg/kg SP (37 nmol/kg) and 167 μg/kg SPN (185 nmol/kg) exhibited longer step-up latencies than vehicle-treated controls. None of the other doses of SPN nor of the C-terminal fragment influenced performance. In Experiment 2, 167 μg/kg SPN or vehicle was injected posttrial either immediately or 5 hr after the training trial. Retention latencies 24 hr later were longer for rats treated with 167 μg/kg SPN immediately after the training trial. Performance of the SPN 5-hr delay group did not differ from that of the vehicle-injected controls, ruling out proactive effects of SPN on recall.