Neuropeptide substance P improves water maze performance in aged rats.

The effects of the peripherally administered neuropeptide substance P (SP) on spatial learning capacities were investigated in 27-month-old rats using a water-maze task. Old rats were injected intraperitoneally once daily for 6 days with 50 or 250 micrograms/kg SP or vehicle 30 min prior to acquisition trials. Improvement in maze performance was observed following injections of 250 micrograms/kg SP only. Furthermore, vehicle-treated old rats showed significantly poorer acquisition rates than vehicle-treated 12-week-old rats. Thus, the improvement in performance after the 250 micrograms/kg dose of SP can be interpreted in terms of a compensation of performance deficit in the old rats.