Lifelong Exercise Enhances Spatial Maze Performance In Female Sprague-Dawley Rats

Abstract

Animal research has shown that exercise improves while sedentary behavior impairs maze performance. Despite the importance of exercise to cognitive function, access to exercise is often overlooked in animal experiments and laboratory animals usually have little or no access to physical activity outside of a standard cage. PURPOSE: This study compared spatial maze performance in female Sprague-Dawley rats over their life span with different access to physical activity: 1) none outside a standard cage, (SED) 2) twice-weekly physical activity in a large box (PA), and 3) regular running wheel exercise (EX). The study aims to examine brain-derived neurotrophic factor (BDNF) in the hippocampus to determine whether BDNF expression in the dorsal hippocampus mediates the effect of lifelong exercise on spatial learning and memory in adult animals. METHODS: 108 rats were divided into three groups. Monthly spatial maze performances were monitored for 23 months by evaluating total time to collect 5 reinforcements (correct responses), working errors (returning to the same arm that contained the reinforcement), and reference errors (going to any of the three arms that never contained reinforcements). BDNF mRNA expression and protein levels were measured in ventral and dorsal hippocampus using quantitative real-time reverse transcription polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assays (ELISA). RESULTS: On average, over 23 months of spatial maze testing, EX animals completed the maze in less time (113.5 ± 5.2 sec) than both PA and SED animals (145.3 ±/- 2.7 and 147.8 ± 3.0 sec, respectively; p < 0.05) and, in turn, EX had a greater number of correct responses (4.33 ±0.15) than PA and SED animals (3.42 ± 0.12 and 3.44 ±0.12, respectively; p < 0.05). CONCLUSION: Compared with animals that resided in a standard cage and those with twice weekly hourly access to physical activity, animals with regular access to running wheel exercise had enhanced spatial maze performance over their life span, indicated by less time needed to complete the task and more correct responses. We hypothesized that animals with lifelong access to exercise will have higher BDNF gene expression in hippocampal tissue which, is associated with cognitive function.