Short-term, preweaning treatment with tetracycline affects physical development and behavior in rats.

Tetracycline (TC) was administered indirectly to rat pups through maternal milk, giving mothers diluted TC solutions as a single source of drinking water, during 13-16 days of postnatal age (PND) in Experiment 1. In Experiment 2, using rats of a different strain, TC dose and its application period were reduced from 0.5 mg/ml to 0.25 mg/ml and from PND 13-16 to PND 13-15, respectively. In Experiment 3, TC was administered directly to the pups via stomach intubation during PND 13-16. The effects of these short-term treatments were tested in adulthood. Brain weight decreased, although no abnormal changes were found histologically in the cerebral cortex. Immobility time in the forced swimming test was decreased more in the TC group as compared to the controls. These results suggest that even a small amount of TC could affect physiological development and behavior. In Experiment 4, mothers were given TC in their drinking water (0.5 mg/ml) for 1 to 5 days, beginning on PND 12. On each of the treatment days, measurements were made of the weight of brain and body, and of the concentration of TC in the brain and in gastric curd of offspring. The greater the TC intake by dams was, the more remarkable was the decrease in the brain weight of offspring. TC concentration of gastric curd was on the order of 1-3.5 micrograms/g curd.