Portugal George S, Kenney Justin W, Gould Thomas J
Department of Psychology, Neuroscience Program, Weiss Hall, Temple University, Philadelphia, PA 19122, USA.
Neurobiol Learn Mem. 2008 Feb;89(2):106-13. doi: 10.1016/j.nlm.2007.05.002. Epub 2007 Jun 20.
Acute nicotine enhances contextual fear conditioning, whereas withdrawal from chronic nicotine produces impairments. However, the nicotinic acetylcholine receptors (nAChR) that are involved in nicotine withdrawal deficits in contextual fear conditioning are unknown. The present study used genetic and pharmacological techniques to investigate the nAChR subtype(s) involved in the effects of nicotine withdrawal on contextual fear conditioning. beta2 or alpha 7 nAChR subunit knockout (KO) and corresponding wild-type (WT) mice were withdrawn from 12 days of chronic nicotine treatment (6.3mg/kg/day), and trained with 2 conditioned stimulus (CS; 85 dB white noise)--unconditioned stimulus (US; 0.57 mA footshock) pairings on day 13. On day 14, mice were tested for contextual and cued freezing. beta2 KO mice did not show nicotine withdrawal-related deficits in contextual fear conditioning, in contrast to WT mice and alpha 7 KO mice. A follow-up study investigated if nicotine withdrawal disrupts acquisition or recall of contextual fear conditioning. The high affinity nAChR antagonist dihydro-beta-erythroidine (DH beta E; 3mg/kg) was administered prior to training or testing to precipitate withdrawal in chronic nicotine-treated C57BL/6 mice. Deficits in contextual fear conditioning were observed in chronic nicotine-treated mice when DH beta E was administered prior to training, but not when administered at testing. These results indicate that beta2-containing nAChRs, such as the alpha 4 beta 2 receptor, mediate nicotine withdrawal deficits in contextual fear conditioning. In addition, nicotine withdrawal selectively affects acquisition but not recall or expression of the learned response.
急性尼古丁增强情境恐惧条件反射,而长期尼古丁戒断则会产生损害。然而,参与情境恐惧条件反射中尼古丁戒断缺陷的烟碱型乙酰胆碱受体(nAChR)尚不清楚。本研究使用基因和药理学技术来研究参与尼古丁戒断对情境恐惧条件反射影响的nAChR亚型。从12天的慢性尼古丁治疗(6.3毫克/千克/天)中撤药后,对β2或α7 nAChR亚基敲除(KO)小鼠和相应的野生型(WT)小鼠进行实验,并在第13天用2次条件刺激(CS;85分贝白噪声)-非条件刺激(US;0.57毫安足部电击)配对进行训练。在第14天,对小鼠进行情境和线索性僵住测试。与WT小鼠和α7 KO小鼠相比,β2 KO小鼠在情境恐惧条件反射中未表现出与尼古丁戒断相关的缺陷。一项后续研究调查了尼古丁戒断是否会破坏情境恐惧条件反射的获得或回忆。在训练或测试前给予高亲和力烟碱型乙酰胆碱受体拮抗剂二氢β-刺桐啶(DHβE;3毫克/千克),以促使慢性尼古丁治疗的C57BL/6小鼠出现戒断反应。当在训练前给予DHβE时,慢性尼古丁治疗的小鼠出现情境恐惧条件反射缺陷,但在测试时给予则未出现。这些结果表明,含β2的nAChR,如α4β2受体,介导情境恐惧条件反射中的尼古丁戒断缺陷。此外,尼古丁戒断选择性地影响学习反应的获得,但不影响回忆或表达。