A comparison of behavior paradigms assessing spatial memory in tree shrew

Abstract

Spatial cognition enables animals to navigate the environment. Impairments in spatial navigation are often preclinical signs of Alzheimer’s disease (AD) in human. Therefore, evaluating spatial memory deficits is valuable when assessing incipient AD in animal models. The Chinese tree shrew, a close relative of primates, possesses many features that make it suitable for AD research. However, there is a scarcity of reliable behavior paradigms to monitor changes in spatial cognition in this species. To address this, we established reward-based paradigms in the radial-arm maze and the cheeseboard maze for tree shrew, and tested spatial memory of a group of twelve male animals in both tasks, along with a control water maze test, before and after bilateral lesions to the hippocampus, the brain region essential for spatial navigation. Tree shrews memorized target positions during training, and their task performance improved gradually until reaching a plateau in all three mazes. After the lesion, spatial learning was compromised in both newly-developed tasks, whereas memory retrieval was impaired in the water maze. Furthermore, individual task performance in both dry-land paradigms depended heavily on the size of remaining hippocampal tissue. Notably, all lesioned animals displayed spatial memory deficits in the cheeseboard task, but not in the other two paradigms. Our results suggest that the cheeseboard task currently represents the most sensitive paradigm for assessing spatial memory in tree shrew, with the potential to monitor progressive cognitive declines in aged or genetically modified animals developing AD-like symptoms.Significance StatementCognitive tests that monitor impairments in spatial memory play a crucial role in evaluating animal models with early-stage Alzheimer’s disease (AD). The Chinese tree shrew possesses many features suitable for an AD model, yet behavior tests assessing spatial cognition in this species are lacking. Here we developed novel behavior paradigms tailored to measure spatial memory in tree shrews and evaluated their sensitivity to changes in spatial learning by examining a group of hippocampus-lesioned animals. Our results indicate that the cheeseboard task effectively detects impairments in spatial memory and holds potential for monitoring the progressive cognitive decline in aged or genetically modified tree shrews that develop AD-like symptoms. This research may facilitate the use of tree shrew model in AD research.