A method has been developed which permits monkeys to self-administer drug solutions, at will, through indwelling intravenous catheters. Psychological dependence on the effects of a drug occurs when a naive monkey voluntarily initiates and maintains self-administration of the drug. If, in addition to psychological dependence, the drug also produces psychotoxieity, either directly or upon abrupt withdrawal, it has a potential abuse liability. In the present study monkeys developedpsychological dependence on morphine, codeine, cocaine, d-amphetamine, pentobarbital, ethanol, and caffeine. All of these drugs except caffeine produced psychotoxicity. Monkeys did not develop psychological dependence on nalorphine, morphinc-nalorphine mixtures, chlorpromazine, mescaline or physiological saline.
In an in vivo autoradiographic study of immature primate trophoblast, tritiated thymidine was first found only in nuclei of cytotrophoblast but after 22 hours, labeled nuclei appeared in syncytiotrophoblast as well. Hence syncytiotrophoblast of the monkey appears to originate by differentiation of cytotrophoblast.
There is little doubt that some substance in tobacco smoke or some aspect of the act of smoking leads to habituation in many people. The experiments to be described were conducted in an effort to determine whether a similar type of habituation could be demonstrated in animals, and whether nicotine might be the substance involved.
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