Acta Neuropsychiatr. 2021 Jun;33(3):148-155. doi: 10.1017/neu.2021.3. Epub 2021 Feb 17.
Whereas numerous experimental and clinical studies suggest a complex involvement of serotonin in the regulation of anxiety, it remains to be clarified if the dominating impact of this transmitter is best described as anxiety-reducing or anxiety-promoting. The aim of this study was to assess the impact of serotonin depletion on acquisition, consolidation, and expression of conditioned fear.
Male Sprague-Dawley rats were exposed to foot shocks as unconditioned stimulus and assessed with respect to freezing behaviour when re-subjected to context. Serotonin depletion was achieved by administration of a serotonin synthesis inhibitor, para-chlorophenylalanine (PCPA) (300 mg/kg daily × 3), (i) throughout the period from (and including) acquisition to (and including) expression, (ii) during acquisition but not expression, (iii) after acquisition only, and (iv) during expression only.
The time spent freezing was significantly reduced in animals that were serotonin-depleted during the entire period from (and including) acquisition to (and including) expression, as well as in those being serotonin-depleted during either acquisition only or expression only. In contrast, PCPA administrated immediately after acquisition, that is during memory consolidation, did not impact the expression of conditioned fear.
Intact serotonergic neurotransmission is important for both acquisition and expression of context-conditioned fear.
尽管大量的实验和临床研究表明，5-羟色胺在焦虑的调节中具有复杂的作用，但仍需阐明这种递质的主要影响是减轻焦虑还是促进焦虑。本研究旨在评估 5-羟色胺耗竭对条件性恐惧的获得、巩固和表达的影响。
雄性 Sprague-Dawley 大鼠接受足底电击作为非条件刺激，并在重新暴露于环境时评估其冻结行为。通过给予 5-羟色胺合成抑制剂对氯苯丙氨酸（PCPA）（300mg/kg 每日×3）来实现 5-羟色胺耗竭，（i）在获得至表达的整个期间，（ii）在获得期间但不在表达期间，（iii）仅在获得后，和（iv）仅在表达期间。
在整个获得至表达期间以及仅在获得期间或仅在表达期间进行 5-羟色胺耗竭的动物，其冻结时间明显减少。相比之下，在获得后立即给予 PCPA，即在记忆巩固期间，并不影响条件性恐惧的表达。
完整的 5-羟色胺能神经传递对环境条件性恐惧的获得和表达都很重要。
