Prolonged responsiveness to the maternal pheromone in the postweanling rat.

When rat young reach 27 days of age they stop responding to a pheromone carried in the feces of the lactating female. Because the consumption of such feces promotes the deposition of brain myelin, we suggested that response to the pheromone might continue as long as the amount of myelin per gram brain remained below adult levels. Our data support the suggestion. Pups deficient in myelin responded to the pheromone after 27 days of age.