Fig. 1.

Performance by Young (2 months old) and Old (20 months old) male rats that were either castrated (GDX) or sham castrated (Sham) during 25 days of testing in an 8-arm radial maze (n = 10–12/group). Entry rates and memory errors (mean ± SEM) are divided into 5-day blocks in the left-hand graphs and averaged across blocks in the right-hand graphs. Letters designate groups that differed significantly from each other within blocks (p < 0.05). (A) Arm entry rate increased significantly over the testing blocks (p < 0.0005), and Young rats entered arms at a significantly faster rate than Old rats (*p < 0.0005). There was no effect of castration on arm entry rate. (B) Rats performed significantly fewer WMEs on later testing blocks (p = 0.037), and Young rats performed significantly fewer WMEs than Old rats (*p < 0.0005). There was no main effect of castration, but on the final testing block (days 21–25), the Old/GDX group performed significantly more WMEs than all of the other groups. (C) There was no effect of block or castration on RMEs, but the Old rats performed significantly fewer RMEs than the Young rats (*p < 0.0005). (D) Rats performed significantly fewer WREs on later testing blocks (p = 0.003), and Young rats performed significantly fewer WREs than Old rats (*p < 0.0005). There was no main effect of castration for WREs, but on the final testing block the Old/Sham group performed at a level intermediate between the Old/GDX group and the Young groups.