HSERM, School of Applied Sciences, University of Mississippi, Oxford, MS, USA.
HSERM, School of Applied Sciences, University of Mississippi, Oxford, MS, USA; Neurobiology and Anatomical Sciences, Medical School, University of Mississippi Medical Center, Jackson, MS, USA; Department of Biomolecular Sciences, School of Pharmacy, University of Mississippi, Oxford, MS, USA.
Behav Brain Res. 2022 Jan 24;417:113613. doi: 10.1016/j.bbr.2021.113613. Epub 2021 Oct 1.
Previous studies show that intermittent social defeat (ISD) stress increases self-administration of psychostimulants, which suggests that ISD promotes reward-seeking behavior and, ultimately, increases vulnerability to develop drug abuse. The present study investigates whether ISD alters cost/benefit evaluations to promote reward-seeking behavior and whether these alterations are time-dependent. Male rats performed two different tasks that assessed their motivation to seek and consume food rewards. An effort-discounting task in which rats chose between less and more effortful options (i.e., 1 lever-press versus 2, 5, 10 or 20 lever-presses) associated with low- and high-reward (i.e., 1 sugar pellet versus 3 sugar pellets), respectively; and a progressive ratio task in which rats had to increase their effort (more lever presses) to obtain a sugar pellet. ISD consisted of exposing animals to social defeat once every three days for ten days (4 stress episodes). Rats were tested 24-48 h after stress episodes, and 1 week and 6 weeks after the last stress episode. In the effort-discounting task, stressed animals showed a decrease in their preference for high rewards associated with more effort (i.e., 10 and 20 lever-presses). These effects were transient and not maintained one week after stress. In the progressive ratio task, stressed animals showed an increase in the number of lever presses to obtain rewards that emerged six weeks after the last stress episode. These results suggest different short- and long-term effects on the motivation for rewards after ISD and indicate temporal dynamic adaptations in the function of the brain reward system.
先前的研究表明，间歇性社会挫败（ISD）应激会增加精神兴奋剂的自我给药，这表明 ISD 促进了寻求奖励的行为，最终增加了滥用药物的易感性。本研究调查了 ISD 是否会改变成本/收益评估以促进寻求奖励的行为，以及这些改变是否具有时间依赖性。雄性大鼠进行了两项不同的任务，评估了它们寻求和消耗食物奖励的动机。一项是努力折扣任务，其中大鼠在更少和更多努力的选项（即 1 次按压与 2、5、10 或 20 次按压）之间进行选择，分别与低回报（即 1 个糖丸）和高回报（即 3 个糖丸）相关联；另一项是渐进比例任务，其中大鼠必须增加他们的努力（更多的按压）才能获得糖丸。ISD 包括每隔三天对动物进行一次社会挫败，持续十天（4 个应激发作）。大鼠在应激发作后 24-48 小时、最后一次应激发作后 1 周和 6 周进行测试。在努力折扣任务中，应激动物表现出对高回报的偏好降低，而与更多努力（即 10 次和 20 次按压）相关。这些影响是短暂的，在应激后一周内没有维持。在渐进比例任务中，应激动物在获得奖励时表现出按压次数的增加，这种现象出现在最后一次应激发作后 6 周。这些结果表明，ISD 后对奖励的动机有不同的短期和长期影响，并表明大脑奖励系统功能的时间动态适应性。
