Department of Psychology, School of Arts and Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Nicotine Tob Res. 2012 Jul;14(7):824-32. doi: 10.1093/ntr/ntr293. Epub 2012 Jan 4.
Research has identified at least two positive reinforcement-related effects of nicotine: (a) primary reinforcement and (b) enhancement of reinforcement from concurrently available stimuli. Prior examples of the reinforcement-enhancing effects with rats showed that repeated, intermittent nicotine exposure increased responding for non-nicotine reinforcers, and this effect remained robust over several weeks. However, the effects of continuous nicotine exposure on responding for a non-nicotine reinforcer are unknown, as are the effects of abruptly withdrawing continuous nicotine on behavior maintained by the same reinforcer.
Lever pressing for a visual reinforcer under a fixed ratio schedule was assessed while rats were maintained on a chronic, continuous infusion of nicotine (3.16 mg/kg/day; osmotic minipump). The effects of precipitated withdrawal on responding, following 16 days of continuous nicotine exposure, were assessed by pre-session subcutaneous injections of mecamylamine (1.0 mg/kg).
Continuous nicotine initially increased active responding for the visual reinforcer; however, continued exposure resulted in an attenuation of this effect. Precipitated withdrawal from nicotine resulted in a significant decline in active responding.
The initial increase in responding for the visual reinforcer with chronic nicotine exposure is consistent with prior research showing that intermittent exposure to nicotine acts as a reinforcement enhancer. However, the attenuation of this enhancement following prolonged nicotine exposure is in contrast with the persistent effects previously reported. Finally, the decrease in visual reinforcers below control levels (nicotine-naive animals) following nicotine withdrawal highlights a potential for affective withdrawal, which may serve as a motive for continued nicotine use.
研究已经确定了尼古丁至少有两种正强化相关的作用：（a）原发性强化和（b）增强同时存在的刺激的强化作用。先前关于老鼠的强化增强效应的例子表明，重复、间歇性的尼古丁暴露增加了对非尼古丁强化物的反应，并且这种效应在数周内仍然很强。然而，连续暴露于尼古丁对非尼古丁强化物的反应的影响尚不清楚，同样不清楚的是突然停止连续尼古丁对同一强化物维持的行为的影响。
在固定比率时间表下，通过按压杠杆来评估视觉强化物，同时老鼠持续接受慢性、连续的尼古丁输注（3.16 毫克/千克/天；渗透微型泵）。在连续 16 天暴露于尼古丁后，通过预先注射美加仑胺（1.0 毫克/千克）来评估突然戒断对反应的影响。
连续的尼古丁最初增加了对视觉强化物的主动反应；然而，持续暴露导致这种效应减弱。从尼古丁中突然戒断导致主动反应显著下降。
慢性尼古丁暴露导致对视觉强化物的反应最初增加，这与先前的研究一致，表明间歇性暴露于尼古丁充当强化增强剂。然而，与先前报道的持续效应相反，在延长的尼古丁暴露后，这种增强作用减弱。最后，在尼古丁戒断后，视觉强化物的反应降至低于对照水平（尼古丁未接触的动物），突出了可能存在的情感戒断，这可能成为继续使用尼古丁的动机。
