Effects of prenatal capsaicin treatment on fetal spontaneous activity, opiate receptor binding, and acid phosphatase in the spinal cord

Abstract Although the effects of capsaicin in neonatal and adult animals have been reported, the effects of prenatal capsaicin treatment are not known. We examined the teratologic and neurotoxic potential of capsaicin treatment in fetal rats. Capsaicin was injected into pregnant rats at various times during gestation. No gross external or internal malformations resulted. After injection on days 16 and 17 of gestation, a decrease in fetal spontaneous activity occurred as well as a loss of fetal responsiveness to morphine. This accompanied a loss of [ 3 H]naloxone binding in the fetal spinal cord but not in the brain stem. [ 3 H]Naloxone binding returned to normal by 24 days postnatally. Acid phosphatase, which normally appears in the substantia gelatinosa postnatally, was permanently reduced after capsaicin treatment at 16 and 17 days of gestation.