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Abstract
In the present study, we examined long-term effects of prenatal morphine on pain response
and on preference for sweet solutions. Pregnant Fischer 344 rats were given increasing
doses of morphine (0.75-12.0 mg/day) in slow-release emulsion, during gestational
days 12-18. Control rats were injected with vehicle and were either pair-fed to morphine
rats, or ad libitum fed. At birth, all litters were culled to 8-10 pups (half males
and half females) and cross-fostered to naive, surrogate dams. Testing began when
rats were 10-12 week old. Rats prenatally exposed to morphine exhibited higher analgesia
in response to a morphine challenge, and a greater preference for saccharin solution
as compared with both control groups. These findings indicate that prenatal morphine
induces long-lasting alterations of systems involved in reward processes and in opiate
analgesia, perhaps by modulating endogenous opiate systems.