SHORT INTERTRIAL INTERVALS IMPAIR WATER MAZE PERFORMANCE IN OLD FISCHER-344 RATS

Male and female Fischer 344 rats (N = 55) aged approximately 18, 21, a nd 24 months were tested for spatial learning in the water maze with i ntertrial intervals of 1-4 min (Massed) or 23-33 min (Spaced). Animals tested in the Massed condition showed an age-related impairment on tr ials to criterion; rats aged 24 months performed more poorly than youn ger subjects. spaced animals did not differ at any age nor did they di ffer from 18- or 21 month-old Massed subjects. The youngest rats in bo th groups were comparable to animals aged 7-8 months tested under Mass ed conditions. Tests on swim distance, swim speed, and escape latency produced similar results. Our data suggest that acquisition deficits i n 24-month-old rats tested with long intertrial intervals are due at l east in part to increased susceptibility to fatigue and/or thermal str ess. Caution should be used, therefore, when interpreting age-related impairments in water maze performance.