Ontogeny of spatial navigation in rats: A role for response requirements?

Three experiments investigated the role of response requirements in the Mor ris water maze for pre- and postweanling rats. Fischer-344N pups were requi red to locate a hidden platform using extramaze cues in a tank modified for the pups' immature response repertoire. Weanlings (20-22 days) displayed s patial learning in a pool 1/2 the size of the adults' (Experiment 1); by 26 -28 days of age, probe performance was comparable to adults on quadrant pre ference and platform-crossing measures. Preweanlings (17 days). in a pool 1 /3 the original size, significantly reduced escape latencies and displayed quadrant preference and platform-crossing scores indicative of spatial navi gation. These results suggest that despite its protracted postnatal develop ment, the preweanling hippocampus allows neural integration of visual-spati al information; however, the capacity to demonstrate such learning is depen dent on task parameters and the pup's response repertoire.