The environmental enrichment effect upon cortical growth is neutralized by concomitant pharmacological suppression of active sleep in female rats

Abstract

In order to examine the hypothesis that active (REM) sleep contributes to the enhanced brain development which is observed in rats reared under enriched conditions, 3 groups of female rats were assigned at 28 days after birth to either: (a) daily 2.5 h exposure to an enriched environment, followed immediately by active sleep deprivation (clonidine injection); (b) daily environmental enrichment plus vehicle only; or (c) daily vehicle injection, but continuous rearing under standard laboratory conditions. In addition, so as to control for a possible direct pharmacological effect upon cortical growth, another series of rats was chronically injected with clonidine or saline under standard conditions. At 65 days of age all the animals were sacrificed and the brains dissected into different regions for weighing. A significant increase in total brain weight (mainly due to a heavier cerebral cortex) was found in the enriched-saline group as compared with the standard-saline controls. In contrast, the enriched-clonidine rats showed no differences from the standard-saline group. Moreover, no significant differences were found between clonidine- and saline-injected rats reared in the standard environment. The results indicate that active sleep and central NA activity play a role in growth-promoting effects of environmental stimulation upon specific brain regions.