A cellular mechanism of classical conditioning in Aplysia.
A cellular mechanism of classical conditioning in Aplysia.
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发表时间：
1984-09
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通讯作者：
R. Hawkins
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作者：
R. Hawkins
海兔的防御性虹吸和鳃收缩是一种简单的反射，由一个明确的神经回路调节，对尾巴的强烈刺激表现出敏感化反应。当对虹吸或外套架的弱刺激(条件性刺激或CS)与对尾部的电击(非条件性刺激或US)配对时，虹吸回反射也表现出经典的条件反射。细胞研究表明，这种条件反射的机制与反射敏化机制相同：由于cAMP介导的K+电流减少而导致的突触前易化，以及由此导致的感觉神经元动作电位的拓宽。因此，尾部休克(美国)产生更大的单突触EPSP从感觉到运动神经元，如果休克之前感觉神经元的尖峰活动比如果它没有尖峰活动(敏化)发生，或者如果休克和尖峰活动以一种特别不成对的模式出现。这种活动依赖的易化放大涉及成对感觉神经元的动作电位比未成对感觉神经元的动作电位更大的展宽，这似乎是由于参与敏化的相同的5-羟色胺和cAMP敏感的K+电流受到更大的抑制。这些结果表明，戒断反射的经典条件反射机制是对敏化的潜在机制的阐述。以此类推，学习的高阶特征的机制，如偶然性的影响，可以从这些简单学习形式的分子机制的组合中建立起来。
The defensive siphon and gill withdrawal of Aplysia is a simple reflex, mediated by a well-defined neural circuit, that exhibits sensitization in response to strong stimulation of the tail. The siphon withdrawal reflex also exhibits classical conditioning when a weak stimulus to the siphon or mantle shelf (the conditioned stimulus or CS) is paired with a shock to the tail (the unconditioned stimulus or US). Cellular studies indicate that the mechanism of this conditioning shares aspects of the mechanism of sensitization of the reflex: presynaptic facilitation due to a cAMP-mediated decrease in K+ current and consequent broadening of action potentials in the sensory neurones. Thus, tail shock (the US) produces greater facilitation of the monosynaptic EPSP from a sensory to a motor neurone if the shock is immediately preceded by spike activity in the sensory neurone than if it occurs without spike activity (sensitization), or if the shock and spike activity are presented in a specifically unpaired pattern. This activity-dependent amplification of facilitation involves a greater broadening of action potentials in paired than in unpaired sensory neurones and appears to be due to a greater depression of the same serotonin- and cAMP-sensitive K+ current involved in sensitization. These results indicate that a mechanism of classical conditioning of the withdrawal reflex is an elaboration of the mechanism underlying sensitization. By analogy, the mechanisms of higher-order features of learning, such as the effect of contingency, may be built from combinations of the molecular mechanisms of these simple forms of learning.