Gulick Danielle, Gould Thomas J
Department of Psychology, Neuroscience Program, Center for Substance Abuse Research, Temple University, Philadelphia, PA 19122, USA.
Neuropsychopharmacology. 2009 Aug;34(9):2167-79. doi: 10.1038/npp.2009.45. Epub 2009 Apr 29.
The current study examined the effects of nicotine infusion into the dorsal hippocampus or anterior cingulate on fear conditioning and on ethanol-induced deficits in fear conditioning, and whether these effects involved receptor activation or inactivation. Conditioning consisted of two white noise (30 s, 85 dB)-foot-shock (2 s, 0.57 mA) pairings. Saline or ethanol was administered to C57BL/6 mice 15 min before training and saline or nicotine was administered 5 min before training or before training and testing. The ability of the high-affinity nicotinic acetylcholinergic receptor (nAChR) antagonist dihydro-beta-erythroidine (DHbetaE) to modulate the effects of ethanol and nicotine was also tested; saline or DHbetaE was administered 25 (injection) or 15 (infusion) minutes before training or before training and testing. Infusion of nicotine into the hippocampus enhanced contextual fear conditioning but had no effect on ethanol-induced learning deficits. Infusion of nicotine into the anterior cingulate ameliorated ethanol-induced deficits in contextual and cued fear conditioning but had no effect on learning in ethanol-naive mice. DHbetaE blocked the effects of nicotine on ethanol-induced deficits; interestingly, DHbetaE alone and co-administration of subthreshold doses of DHbetaE and nicotine also ameliorated ethanol-induced deficits but failed to enhance learning. Finally, DHbetaE failed to ameliorate ethanol-induced deficits in beta2 nAChR subunit knockout mice. These results suggest that nicotine acts in the hippocampus to enhance contextual learning, but acts in the cingulate to ameliorate ethanol-induced learning deficits through inactivation of high-affinity beta2 subunit-containing nAChRs.
本研究考察了向背侧海马体或前扣带回注入尼古丁对恐惧条件反射以及乙醇诱导的恐惧条件反射缺陷的影响,以及这些影响是否涉及受体激活或失活。条件反射由两次白噪声(30秒,85分贝)-足部电击(2秒,0.57毫安)配对组成。在训练前15分钟给C57BL/6小鼠注射生理盐水或乙醇,在训练前5分钟或训练及测试前注射生理盐水或尼古丁。还测试了高亲和力烟碱型乙酰胆碱能受体(nAChR)拮抗剂二氢-β-刺桐啶(DHbetaE)调节乙醇和尼古丁作用的能力;在训练前或训练及测试前25分钟(注射)或15分钟(注入)给予生理盐水或DHbetaE。向海马体注入尼古丁增强了情境恐惧条件反射,但对乙醇诱导的学习缺陷没有影响。向前扣带回注入尼古丁改善了乙醇诱导的情境和线索性恐惧条件反射缺陷,但对未接触过乙醇的小鼠的学习没有影响。DHbetaE阻断了尼古丁对乙醇诱导缺陷的作用;有趣的是,单独使用DHbetaE以及亚阈值剂量的DHbetaE与尼古丁共同给药也改善了乙醇诱导的缺陷,但未能增强学习效果。最后,DHbetaE未能改善β2 nAChR亚基基因敲除小鼠中乙醇诱导的缺陷。这些结果表明,尼古丁在海马体中起作用以增强情境学习,但在扣带回中起作用,通过使含高亲和力β2亚基的nAChRs失活来改善乙醇诱导的学习缺陷。