Retention of internal experiences in juvenile and adult rats

Abstract

An equal number of adult and juvenile female Sprague-Dawley rats (n = 14) received one of four treatments during Phase 1 of the study. Phase 1 consisted of four sucrose-saline pairings (S), four illness experiences (I), four sucrose-illness pairings (SI), or four saline injections (C). After the last Phase 1 treatment, all subjects received a 30-min exposure to sucrose and water followed by a LiCl injection during the second phase of the experiment. Phase 2 began either 1 or 28 days following the last injection. Each subject continued to receive sucrose-illness experience until a suppression criterion was reached or for a maximum of 4 test days. Adult and juvenile animals that had received sucrose-illness pairings in Phase 1 and tested 1 or 28 days later drank significantly less sucrose than their appropriate control animals. The I treatment adult and juvenile rats at the 1-day retention interval developed the taste aversion more slowly than control animals. Furthermore, the adult, but not the juvenile, rats given sucrose exposures prior to conditioning drank more sucrose than their control rats on Day 2 of training at both intervals. At the 28-day retention test, suppression of sucrose intake was equivalent in adult and juvenile rats in I and C animals. These results show that young and adult animals can recall prior taste aversion experiences over a 28-day interval but apparently do not remember illness-alone experiences 28 days later.