Suppression of lever-pressing behavior in rats reared in differentially enriched environment

In order to elucidate the suppression mechanism of lever pressing or getting fewer food pellets by rats, reared in an enriched environment in comparison with those reared in an impoverished environment, three experiments were carried out, using Fisher 344 rats. In Experiment I, differential rearing was introduced early in life (75 days, 30 through 105 days after birth), while in Experiment II it was introduced rather late (160 days, 110 through 270 days after birth), and Experiment III it was introduced at the lates (322 days, 245 through 567 after birth). In all three experiments, the suppression of lever pressing was observed. In Experiment I, the real lever-pressing time is shorter for rats reared in an impoverished environment. In Experiment II, rats reared in an impoverished environment become instantaneously aroused, when reinforcement ratio decreases. In Experiment III rats lost weight significantly and increased mortality, who were reared in an impoverished emvironment latest in life.