Early Environmental Stimulation Produces Long-Lasting Changes on β-Adrenoceptor Transduction System

Abstract

Long-term behavioral and biochemical effects of exposure to differential early stimulation (postnatal handling and/or enriched environment) were studied in 18- to 20-month-old Sprague-Dawley rats. Postnatal handling treatment was given between 1 and 22 postnatal days. In the enriched environment procedure, the pups were maintained under enriched conditions from weaning until postnatal Day 100. At 18 months of age animals were tested for working memory in an object recognition test, based on the differential exploration of familiar and new objects. Animals reared in the enriched environment performed better in the working memory test than did control or postnatally handled rats. No interaction was observed between postnatal handling and environmental enrichment on cognitive parameters. At 20 months of age, the animals were sacrificed and cyclic AMP formation was determined under basal conditions and after activation of β-adrenoceptors in cerebral cortex and hippocampus. Both postnatal handling and its combination with exposure to enriched environment significantly increased basal cyclic AMP accumulation in cerebral cortex, but not in the hippocampus. Environmental enrichment was able to induce a long-lasting modification in the responsiveness of the β-adrenergic neurotransmitter system as reflected by a decreased cyclic AMP accumulation after β-adrenoceptor activation by means of isoprenaline, in either anatomical structure. It is suggested that manipulations of the environment early in life leading to a reduction in age-related memory deficits produce subtle but long-lasting modifications of noradrenergic transmission.