Transient sex differences in the between-sessions but not in the within-session memory underlying an active place avoidance task in weanling rats

Spatial abilities were tested in male and female rats by training them to a void an area in which there was a mild footshock while the arena rotated at 1 revolution/minute. The to-be-avoided area was stable in the coordinates of the room, so extramaze landmarks had to be used for accurate navigation, as the rotation made intramaze cues and substrate-based path integration u seless for the avoidance. From Postnatal Day (PD) 19, rats were trained for 22 consecutive days. When the shock area was the same across sessions male rats reached optimal performance on PDs 23-24, 10 days before female rats, but when the location of the shock changed daily there were no sex differe nces. The results indicate that there are separate memory components underl ying spatial competence: a within-session component that develops similarly in male and female rats and a between-sessions component that lasts at lea st 24 hr and appears earlier in male than in female rats.