PROXIMAL CONTROL OF FETAL-RAT BEHAVIOR

We examined the influence of the amniotic sac on spontaneous movement in late gestation fetal rats. Using techniques for in vivo observation of fetal behavior, Day 21 rat fetuses were exteriorized from the uter us, with umbilical connections to the dam intact, and videotaped for 1 5 min either: (a) through the intact amniotic membranes, or (b) follow ing removal of the membranes. Analysis of fetal behavior categories re plicated the findings of previous investigators: Movements of the head , forelimbs, and rearlimbs were significantly increased by sac removal , as was the total frequency of behavior categories and the simultaneo us occurrence of different behavior categories. Frame-by-frame analysi s of videotaped behavior revealed that amniotic sac removal increased the frequency of movement bouts without altering the overall amount of time that fetuses spent moving. Movement bout durations ranged from 5 0 msec to 70 s. The average duration of movement bouts was significant ly reduced for fetuses lacking the amniotic sac as compared to fetuses within the sac, as was the overall distribution of movement bout dura tions. Frequency distributions of movement bout durations and interbou t interval (IBIs) revealed that sac removal significantly increased th e occurrence of short (1-2 s) movement bouts and reduced the frequency of protracted movement bouts and interbout intervals (> 10-s duration ). Taken together, these findings indicate that the quantitative dimen sions of fetal rat movements are influenced by proximal features of th e uterine environment. During prenatal life, the amniotic sac appears to sustain movement, possibly by providing proprioceptive feedback or physical support to the fetus, or by regulating the chemical milieu. ( C) 1994 John Wiley and Sons, Inc.