Effects of permanent residence with foster mothers and new siblings upon numbers of mast cells within the thalamus of preweaned rats

In a split-litter, cross-fostered design, the numbers of mast cells per 10 micrometer sections within the thalamic boundaries in rats that had been re ared by 8 natural or 8 foster mothers were counted 5 days and 10 days after the transfer had occurred on postnatal Day 10. The rats from 4 litters wit h the highest numbers of thalamic mast cells exhibited marked reductions in these numbers when fostered by mothers of the 4 litters with the fewest nu mbers of thalamic mast cells. The reverse influence was not observed, These results suggest that adaptation to changing maternal environments for rats with congenitally elevated numbers of mast cells may increase the risk of degranulation and transient anomalies within cerebral vasculature or the bl ood-brain barrier.