Prolonged in utero meconium exposure impairs spatial learning in the adult rat: Central Prize Award

Objective The purpose of this study was to examine the effects of prolonged in utero meconium exposure on adult learning and memory, as measured by the Morris water maze. Study design Timed pregnant Long-Evans rats were studied. On gestational day 20 (term, 21 days of gestation), laparotomy was performed, and each maternal animal received an injection of clear amniotic fluid or meconium-stained amniotic fluid into each gestational sac. The laparotomy incision was closed, and the animals received postoperative monitoring through delivery. On postnatal days 145 to 148, the offspring underwent Morris water maze testing. The mean (±SEM) for the latency time was reported for each day's trial and compared between groups. Results There were significant differences between meconium-stained amniotic fluid group and clear amniotic fluid group in the mean time to platform on day 1 (82.7 ± 1.8 seconds vs 75.9 ± 3.0 seconds; P=.04), day 2 (60.5 ± 3.5 seconds vs 47. 8 ± 4.6 seconds; P=.03), and day 3 (56.5 ± 4.5 seconds vs 34.7 ± 4.4 seconds; P=.001). However, there were no differences on days 4 and 5. There were also no differences between recall and response learning trials that were done after a 12-day retention period. Conclusion In the absence of hypoxia or infection, prolonged in utero meconium exposure is associated with a delay of spatial learning in the adult rat.