Effects of early postnatal handling on brain beta-adrenoceptors and behavior in tests related to stress.

The present study investigated the effects of early postnatal handling and temporary maternal isolation, between the 5th and 20th postnatal days, on various behaviors related to stress measured in adulthood in male Wistar rats. In addition, beta-adrenoceptor binding in the brain was measured. The handling consisted of daily 3-min sessions during which a pup was gently held by an investigator. The isolated rat pups were kept separated from their nursing mothers for 1 h daily. Subsequently, it was found that the time spent immobile in Porsolt's swim test was shortened, and voluntary alcohol (5% v/v) consumption was reduced in the handled rats, as compared with the non-handled and isolated animals. No differences in the measure of anxiety--food consumed in a novel environment--or the time spent in social, aggressive and defensive behaviors in a resident-intruder paradigm, were noted. Neither did the density or affinity of beta-adrenoceptors in the frontal cortex or hippocampus differ significantly between the groups. The results indicate that short-lasting maternal separation does not cause sustained effects on behavior in the rat. Early postnatal handling leads to shortened immobility in the swim test and reduced voluntary alcohol consumption, suggesting that handled rats show an improved ability to cope with stress.