Prenatal exposure to addictive drug during mother's pregnancy will cause a series of problems to the offsprings incluing the increase of addictive susceptibility,impairment of learning and memory or cognitive functions. The neral mechanism underlying the learning impairment is not clear. With the chick embryo as unique model in the developmental research field, the present study examined the critical time window to impair learning and memory and enhance susceptibility to addictive drug during the embronic periods following the morphine exposure, and investigated the opoid and GABAgernic mechanism in the memory impairment. The results showed that prenatal morphine exposure during the embryonic days 5-8 (E5-8) but not E17-20 impaired the learning behaviors in chicks, in contrast, prenatal morphine during E17-20 but not E5-8 increased the addictive susceptibility. Delta opioid receptor antagonist can improve the learning impairment effect and mu opioid receptor antagonist can reverse the susceptiblility caused by prenatal morphine exposure. Since opioid receptors were distributed in GABA neuons,it is hypothesized that prenatal morphine will alter the developmental process of GABA neurons in offspring. The intermediate medial mesopallium (IMM), a region of the chick forebrain, is intimately involved in the early lea
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