吗啡对不同距离条件下大鼠信号追踪和目标追踪的影响

Effects of Administration of Morphine on Sign-tracking/Goal-tracking under Different Distances

条件刺激短暂呈现并消失后,奖赏立即呈现,多次匹配后诱导出动物对条件刺激(信号追踪)或奖赏呈现装置如食盒(目标追踪)的接近。条件刺激与食盒间的距离是影响信号/目标追踪反应和损害联结学习的重要变量,成瘾药物能够增加奖赏的诱因动机,进而增加个体的奖赏寻求行为。距离能否通过损害联结学习而减弱成瘾药物的动机放大作用尚未见到报道。本实验采用autoshaping模型,考察8、30和60 cm距离条件下吗啡处理对大鼠信号追踪和目标追踪的影响。结果发现:(1)信号追踪随距离增加而减少,目标追踪对距离不敏感。(2)急性吗啡处理减少8、30和60 cm条件下信号追踪而增加8和60 cm条件下目标追踪,慢性吗啡处理在8和30 cm条件下减少信号追踪增加目标追踪;消退检测中,吗啡前暴露减少8和60 cm条件下信号追踪而增加60 cm条件下目标追踪。(3)辨别反转学习中,吗啡前暴露使30和60 cm条件下的大鼠偏爱旧信号、辨别力受损,减少8、30和60 cm条件下大鼠对新信号的接触。这些结果提示,距离较少影响吗啡的信号追踪抑制作用和目标追踪增强效应,而易化吗啡前暴露对反转学习的损害。说明距离是易化成瘾药物对联结学习不利影响而非反转其动机放大作用的重要因素。

Pairings of a conditioned （CS） and unconditioned （US） stimulus can result in approach to either the CS （sign tracking） or the US （goal tracking）. The distance between the conditioned stimulus and the site of US delivery affects the sign / goal tracking response and impairs the associative learning; the addictive drugs can enhance the incentive effects of a reward and thus increase individual reward seeking behavior. There are no reports on the relationship between impairments of associative learning by the distance and the incentive amplifying effects of addictive drugs. Therefore, this experiment attempted to investigate the effects of administration of morphine on sign-tracking and goal-tracking when the spatial separation between the CS and a US food was 8, 30 and 60 cm. Fifty-six male Sprague-Dawley rats participated in the approach conditioning experiment of different distances consisted of habituation, food receptacle training, acquisition, administration of morphine which was given daily injection of morphine （5mg/kg） or saline for 7 days, extinction phases and reversal learning. Two different material objects served as CS＋ and CS-, and a 10-sec food as US while approach duration of the CS （sign-tracking） and US （goal-tracking） was measured. Each CS＋ was always followed by food delivery any of the experiment phases except the extinction phases, whereas the CS- was not. The results were as following： （1） Sign tracking of rats developed when the CS was 60 cm from the US.Increasing the spatial separation between the CS and US resulted in a decline in sign tracking and had no effect on goal tracking under non-drug conditions. （2） Acute administration of morphine （5.0 mg/kg） decreased measures of sign-tracking, from 8 to 60cm, while simultaneously increasing measures of goal-tracking when the CS was 8 and 60 cm from the source of the US. Repeated administration of morphine decreased measures of sign-tracking while simultaneously increasing measures of goal-tracking when the CS was 8 and 30 cm from the source of the US. In the extinction test, prior morphine exposure decreased sign-tracking when the CS was 8 and 60cm from the source of the US, and increased goal-tracking when the spatial separation between the CS and US was 60 era. （3） In the discrimination reversal learning, rats pre-exposed to morphine showed less contact to new CS＋ compared to saline controls from 8 to 60cm, showed worse discrimination and biased to old CS＋ when the spatial separation was 30 and 60 cm. The results of this study suggested that distance had little effect on suppression of sign-tracking but had enhancing effects on goal-tracking by morphine. Morphine pre-exposure impairing discrimination reversal learning was facilitated by distance. Research shows the distance is an important factor, which facilitates impairments of associative learning and has no effect on the incentive amplifying effects of following administration of addictive drug.