Passive avoidance memory consolidation and reinstatement in the young rat.

Young rats (16-30 days), trained on a one-trial passive avoidance task, were subsequently submitted to the amnesic agent hypothermia 0, 5, 10, 20 or 30 min later, and tested for retention 6 h after training. While hypothermia administered 10 min after training was no longer effective in 30-day rats, it still induced a significant retrograde amnesia in younger animals. In 16- and 18-day rats, administration of hypothermia 20 min after training could still produce a slight but statistically non-significant amnesia. Additionally, exposition to a reinstatement treatment was found to alleviate the amnesic effects of hypothermia in 20- and 30-day-old animals, while it seemed ineffective in 16- and 18-day rats. These findings suggest that the more immature the animal, the longer the consolidation period, the more vulnerable the mnemonic trace, and the less effective a reinstatement treatment for alleviation of retrograde amnesia.