Harvey J A, Gormezano I, Cool-Hauser V A
J Pharmacol Exp Ther. 1983 Apr;225(1):42-9.
Classical conditioning of the rabbit nictitating membrane response was accomplished by presenting tone- and light-conditioned stimuli for 800 msec before delivery of a 100-msec shock as the unconditioned stimulus. Scopolamine significantly retarded the rate of acquisition and final asymptotic performance of conditioned responses to the tone- and light-conditioned stimuli. Methylscopolamine was approximately 20 times less potent than scopolamine in retarding the rate of acquisition, and had no effect on the final asymptotic performance of conditioned responses. The retardation in acquisition of conditioned responses produced by scopolamine could still be detected 5 days after cessation of drug injections, indicating that the effects of scopolamine were on acquisition and not performance. In contrast, scopolamine and methylscopolamine had no affect on the development of long-term habituation produced by the unpaired presentations of tone, light and shock stimuli. Control experiments indicated that the acquisition of conditioned responses by animals injected with saline, scopolamine or methylscopolamine was not contaminated by the presence of changes in base-line responding, sensitization or pseudoconditioning. In addition, scopolamine and methylscopolamine did not affect the unconditioned nictitating membrane reflex. In previously trained animals, scopolamine produced a significant, approximately 25-db elevation in the intensity threshold of a tone-conditioned stimulus for elicitation of conditioned responses. It was concluded that scopolamine blocks the excitatory properties of tone stimuli and this accounts for its ability to retard the rate of acquisition of conditioned responses.
兔瞬膜反应的经典条件反射是通过在给予100毫秒的电击作为非条件刺激之前，呈现800毫秒的音调及光条件刺激来完成的。东莨菪碱显著延缓了对音调及光条件刺激的条件反应的习得率和最终渐近表现。甲基东莨菪碱在延缓习得率方面的效力比东莨菪碱低约20倍，并且对条件反应的最终渐近表现没有影响。东莨菪碱引起的条件反应习得延缓在停止注射药物后5天仍可检测到，这表明东莨菪碱的作用是在习得阶段而非表现阶段。相比之下，东莨菪碱和甲基东莨菪碱对由音调、光和电击刺激的不配对呈现所产生的长期习惯化的发展没有影响。对照实验表明，注射生理盐水、东莨菪碱或甲基东莨菪碱的动物对条件反应的习得没有受到基线反应变化、敏感化或假性条件反射的影响。此外，东莨菪碱和甲基东莨菪碱不影响非条件瞬膜反射。在先前受过训练的动物中，东莨菪碱使引发条件反应的音调条件刺激的强度阈值显著升高约25分贝。得出的结论是，东莨菪碱阻断了音调刺激的兴奋性特性，这解释了它延缓条件反应习得率的能力。
