Sacchetti B, Ambroqi Lorenzini C, Baldi E, Tassoni G, Bucherelli C
Dipartimento di Scienze Fisiologiche, Università di Firenze, Italy.
Arch Ital Biol. 1999 Aug;137(4):235-48.
In fear-conditioned Wistar rats freezing was induced by the delivery of a series of footshocks paired to tones (CS) in a specific conditioning chamber (context). CS and contextual fear were acquired in the same single conditioning session without preexposition to the conditioning chamber (day 1). Different groups of animals were conditioned employing three increasing US (footshock) intensities (0.25, 0.5, 0.75 mA). During the retention sessions context and CS conditioned freezing (fear response) were measured using a paradigm that fulfilled the following conditions: i) CS freezing retention was measured in a context different from the conditioning one; ii) CS and context freezing were measured at increased delays after the training session (days 3 and 4, 14 and 15, 28 and 29). The results show that there are significant differences between CS and context freezing retention, which are clearly related to delay after the initial session and to US intensity. In particular: 1) conditioned freezing to a discrete tone is better retained than conditioned freezing to context (irrespective of US intensity); 2) context freezing is directly related to US intensity much more than to tone freezing; 3) context freezing is easier to extinguish than tone freezing. The results are discussed in relation to previous ones and to their relevance to freezing genesis neural correlates.
在恐惧条件化的Wistar大鼠中，通过在特定的条件化箱（环境）中给予一系列与音调（条件刺激）配对的足部电击来诱发僵住反应。条件刺激和环境恐惧在同一个单次条件化训练中习得，且在训练前未对条件化箱进行预暴露（第1天）。不同组的动物采用三种递增的非条件刺激（足部电击）强度（0.25、0.5、0.75毫安）进行条件化训练。在记忆保持阶段，使用满足以下条件的范式测量环境和条件刺激诱发的僵住反应（恐惧反应）：i）在与条件化环境不同的环境中测量条件刺激诱发的僵住反应的记忆保持；ii）在训练后不同的延迟时间（第3和4天、第14和15天、第28和29天）测量条件刺激和环境诱发的僵住反应。结果表明，条件刺激和环境诱发的僵住反应的记忆保持之间存在显著差异，这明显与初次训练后的延迟时间和非条件刺激强度有关。具体而言：1）对离散音调的条件化僵住反应比环境条件化僵住反应保留得更好（与非条件刺激强度无关）；2）环境僵住反应比音调僵住反应更直接地与非条件刺激强度相关；3）环境僵住反应比音调僵住反应更容易消退。结合之前的研究结果及其与僵住反应发生的神经相关性的关联对这些结果进行了讨论。
