PERINATAL TREATMENT OF RATS WITH OPIATES AFFECTS THE DEVELOPMENT OF THE BLOOD-BRAIN-BARRIER TRANSPORT-SYSTEM PTS-1

Previous results have shown that treatment of rats with morphine durin g the neonatal period can influence development of peptide transport s ystem-1 (PTS-1), the blood-brain barrier transport system for Tyr-MIF- 1 and methionine enkephalin. Previous work has suggested that the acti vity level of PTS-1 correlates with the concentration of methionine en kephalin in the brain. We show here that rats treated peripherally wit h morphine sulfate (MS) in both the prenatal and neonatal periods have enhanced activity of PTS-1. The degree of enhancement increases with age to reach a 66% increase in comparison with controls at age 9 weeks . The mu agonist MS was more powerful than the kappa agonist ethylketo cyclazocine (EKC) or the delta agonist [D-Pen(2,5),pCl-Phe(4)]enkephal in (pCl-DPDPE) in producing this effect. Opiate antagonists had comple x effects with methylnaltrexone blocking the action of MS on PTS-1. Th ese results show that the level of PTS-1 activity in adult rats can be modified by perinatal events that affect opiate tone during developme nt. Copyright (C) 1996 Elsevier Science Inc.