Temperamental development in the rat: the first year.

Behavioral continuity and change was studied in 32 (16 male) Wistar rats observed in the hole board and canopy tests, considered to measure exploration and anxiety, respectively. Subjects were tested at 6, 11, 16, 21, 37, and 52 weeks of age. In comparison to 16-week-old rats (the standard age of rats in many experiments), juveniles seemed more anxious and exploratory, whereas mature rats were more anxious and less exploratory. There was substantial behavioral consistency between week 6 and 52, the correlations being especially high between weeks 11 and 52. Principal components analyses revealed one temperamental dimension reflecting harm avoidance in juvenile and mature rats, whereas adult rats were characterized by a further dimension, reflecting novelty seeking. Copyright 2005 Wiley Periodicals, Inc