Environmental enrichment and isolation rearing in the rat: Effects on locomotor behavior and startle response plasticity

Background: Laboratory rats exhibit behavioral changes that reflect a conti nuum of early life experience, from isolation-reared to socially reared to enrichment-reared conditions. In this study, we further characterize the be havioral effects of isolation, social, and enriched rearing on locomotor ac tivity, patterns of movement and exploration, startle reactivity, prepulse inhibition (PPI), and habituation in adult rats. Methods: Male Sprague-Dawley rat pups (21 days old) were housed under enric hment (three per cage with toys and exposure to enriched environments), nor mal social (three per cage), or isolation (one per cage) conditions. Fight weeks later, locomotor and exploratory behaviors, acoustic startle reactivi ty, PPI, and habituation were measured in the three groups. Results: Enrichment-reared rats exhibited reduced exploration and rapid hab ituation of locomotor activity, increased startle reactivity, and normal PP I and startle habituation compared with socially reared controls. Isolation -reared rats exhibited increased exploration and normal habituation of loco motor activity, increased startle reactivity, reduced PPI, and normal start le habituation. Conclusions: Isolation- and enrichment-reared rats exhibited opposite chang es in some behaviors and similar changes in other behaviors. Specifically, mts raised in enriched conditions appear more efficient at assimilating sti muli from their environment than do rats reared in isolation. Nevertheless, both enrichment- and isolation-rearing conditions increased startle reacti vity, whereas only isolation rearing led to disruptions of PPI in adulthood . These results suggest that isolation- and enrichment-rearing conditions p roduce some common and some differential effects on how rats process enviro nmental stimuli. For studies of isolation-rearing effects on PPI, however, the complex and resource-intensive enrichment condition seems to offer few advantages over the normal social condition. (C) 2000 Society of Biological Psychiatry.