Baldi Elisabetta, Lorenzini Carlo Ambrogi, Bucherelli Corrado
Department of Physiological Sciences, University of Florence, Viale G.B. Morgagni 63, I-50134 Florence, Italy.
Neurobiol Learn Mem. 2004 May;81(3):162-6. doi: 10.1016/j.nlm.2004.02.004.
The relationship between US (footshock) intensity and the two conditioned freezing responses (to acoustic CS and to "context") was investigated in fear conditioning. Administered footshock intensity was 0.00, 0.15, 0.30, 0.60, 0.90, and 1.20 mA to six different groups of 70-day-old male Albino Wistar rats. To measure contextual freezing, the animals were again placed inside the conditioning apparatus without acoustic CS and US presentation. To measure acoustic CS freezing, the animals were placed in a totally different apparatus and only the acoustic CS was presented. The 0.15 mA footshock intensity was not sufficient to condition the animals, in fact no freezing was exhibited as in the non-shocked control group. The 0.30 mA footshock intensity was sufficient only to condition the animals to the acoustic CS, whereas the 0.60 mA was sufficient to condition the animals both to acoustic CS and to context. Footshock intensities (0.90 and 1.20 mA) did not elicit any significant increase in conditioned freezing for either acoustic CS or context but at the highest one the generalization phenomenon appeared (freezing in the different context before presentation of acoustic CS). Acoustic CS freezing to all over-threshold intensities was longer than that to context. In conclusion, freezing responses to acoustic CS and context after increasing footshock intensities follow distinct patterns, and intermediate footshock intensities (0.60 and 0.90 mA) appear to be the most useful for eliciting conditioned freezing responses to acoustic CS and to context without inducing a generalized fear status contamination.
在恐惧条件反射实验中，研究了美国（足部电击）强度与两种条件性僵住反应（对听觉条件刺激和对“环境”）之间的关系。对六组70日龄雄性白化Wistar大鼠施加的足部电击强度分别为0.00、0.15、0.30、0.60、0.90和1.20毫安。为了测量环境性僵住，将动物再次置于条件反射装置中，不呈现听觉条件刺激和美国刺激。为了测量听觉条件刺激引起的僵住，将动物置于完全不同的装置中，只呈现听觉条件刺激。0.15毫安的足部电击强度不足以使动物形成条件反射，事实上，与未受电击的对照组一样，没有出现僵住现象。0.30毫安的足部电击强度仅足以使动物对听觉条件刺激形成条件反射，而0.60毫安的强度足以使动物对听觉条件刺激和环境都形成条件反射。足部电击强度（0.90和1.20毫安）在听觉条件刺激或环境方面均未引起条件性僵住的显著增加，但在最高强度时出现了泛化现象（在呈现听觉条件刺激之前在不同环境中僵住）。对所有阈上强度的听觉条件刺激的僵住时间比对环境的僵住时间长。总之，足部电击强度增加后，对听觉条件刺激和环境的僵住反应遵循不同的模式，中等强度的足部电击（0.60和0.90毫安）似乎最有助于引发对听觉条件刺激和环境的条件性僵住反应，而不会引起泛化恐惧状态的污染。
