The behavioral and anatomical effects of prenatal umbilical cord clamping in the rat and their alteration by the prior maternal administration of nimodipine

This study investigated the effects of fetal rat umbilical cord compression on anatomical, biochemical, and behavioral parameters of development. Further, the study examined the ability of the calcium channel antagonist nimodipine to afford protection from this insult. Near the day of birth (E21), the umbilical cord of individual fetuses was not clamped or clamped for 2, 6, or 12 min. Before clamping, mothers were given 70 μg/kg (i.p.) nimodipine in a polyethylene glycol (PEG) vehicle or the vehicle alone. Selected animals were sacrificed for cytochrome oxidase histochemistry. The remainder of the pups were given to foster mothers and allowed to develop through adulthood. At the end of testing all animals were sacrificed and the brains weighed and measured. Histochemical analysis revealed that clamping resulted in a decrease in cytochrome oxidase reaction product in the hippocampus. The reduction in this marker of oxidative metabolism was not as pronounced in animals from drug-treated mothers. Alterations in behavior produced by clamping were detectable as early as the third day after birth (P3). At this age, pups subjected to cord clamping exhibited impaired righting and diminished avoidance of a ‘cliff’ on which they had been placed. On P67–P75, clamped animals exhibited hyperactivity in an open field, low rates of spontaneous alternation in a T-maze, and impaired learning and memory in a Pavlovian conditioned aversion-to-brightness test. The calcium channel blocker afforded protection from the effects of cord clamping, since the nimodipine-treated animals were less impaired in these behavioral tests. Animals that had been subjected to cord clamping showed reduced brain volumes and dimensions on P80. Nimodipine treatment normalized these parameters of brain development relative to non-clamped controls. Taken together, these results indicate that brief periods of umbilical cord occlusion near the time of birth can have both immediate and long-term effects on different parameters of development. In addition, the calcium channel blocker nimodipine affords partial protection from damage induced by compression of the fetal umbilical cord.