The influence of experience during brain development was investigated on juvenile behavior, adult amphetamine sensitization, and neuronal structural plasticity in rats. Two experiential factors (i.e., tactile stimulation and stress) were studied either before or soon after birth. Early experience feminized social behavior in males; however, only stress enhanced anxiety-like behavior in males. Repeated amphetamine administration resulted in the development and persistence of behavioral sensitization. However, tactile stimulation attenuated the drug-induced behavioral sensitization whereas stress failed to influence the degree of sensitization. Neuroanatomical findings revealed that early experience altered the cortical and subcortical structures. Furthermore, drug exposure reorganized the brain structures involved in addiction but early experience prevented the drug-associated changes. Early adverse experience influences the subsequent exposure to a drug of abuse at anatomical level whereas a favorable experience has an effect both at behavioral and anatomical levels and thus may play a protective role against drug-induced sensitization and addiction. / xii, 263 leaves : ill. ; 29 cm