Dockendorf Ella R, Burrell Brian D
Division of Basic Biomedical Sciences, Sanford School of Medicine, Center for Brain and Behavior Research (CBBRe), University of South Dakota, Vermillion, South Dakota.
PLoS One. 2025 Jun 12;20(6):e0326039. doi: 10.1371/journal.pone.0326039. eCollection 2025.
Studies of pain/nociception often rely on simple reflexes to assess pain-related changes in behavior. However, there is considerable interest in utilizing more complex, self-initiated behaviors in place of stimulus-evoked reflexes. In this study we report an operant conditioning assay using Hirudo verbana (the medicinal leech) to assess the effects of injury on motivational and cognitive processes. Animals were placed in an arena consisting of an illuminated and a dark chamber with a connecting section in between. The connecting section was partially filled with gravel, which acted as an obstacle and delayed escape from the illuminated to the dark side. With repeated experience H. verbana learned to overcome the gravel obstacle, reflected as a decreased escape latency from the illuminated chamber. The capacity for this enhanced escape behavior was retained for up to two hours. In animals that received an injury to the posterior sucker, learning and memory of this operant escape task was disrupted. Injured animals also exhibited mechanosensory sensitization, changes in locomotion, changes in exploratory behavior, and increased negative phototaxis. Over 12 days, changes in locomotion, exploratory behavior, and phototaxis recovered to pre-injury levels, although mechanosensory sensitization remained. Disruptions in cognitive behavior also recovered during this period with the capacity for operant conditioning returning six days after injury and two hour retention of conditioning returning by day 12. This study shows that injury produces a complex and coordinated set of sensory, motor, and integrative changes in H. verbana that may be relevant to understanding the biological processes behind pain in vertebrates.
对疼痛/伤害感受的研究通常依赖于简单反射来评估行为中与疼痛相关的变化。然而，人们对利用更复杂的、自发的行为来取代刺激诱发的反射有着浓厚的兴趣。在本研究中，我们报告了一种使用欧洲医蛭（Hirudo verbana）的操作性条件反射试验，以评估损伤对动机和认知过程的影响。将动物放置在一个由一个明亮室和一个黑暗室组成的场地中，中间有一个连接部分。连接部分部分填充有砾石，其作为障碍物，延迟了从明亮室到黑暗室的逃脱。随着反复的经验，欧洲医蛭学会了克服砾石障碍，这表现为从明亮室逃脱的潜伏期缩短。这种增强的逃脱行为能力可保持长达两小时。在接受后吸盘损伤的动物中，这种操作性逃脱任务的学习和记忆受到破坏。受伤的动物还表现出机械感觉过敏、运动变化、探索行为变化以及负趋光性增加。在12天内，运动、探索行为和趋光性的变化恢复到受伤前的水平，尽管机械感觉过敏仍然存在。在此期间，认知行为的破坏也得到恢复，操作性条件反射能力在受伤后六天恢复，条件反射的两小时保持能力在第12天恢复。这项研究表明，损伤在欧洲医蛭中产生了一系列复杂且协调的感觉、运动和整合变化，这可能与理解脊椎动物疼痛背后的生物学过程相关。
