Low-level lead exposure effects on spatial reference memory and working memory in rats

BACKGROUND: Studies have demonstrated that lead exposure can result in cognitive dysfunction and behavior disorders. However, lead exposure impairments vary under different experimental conditions. OBJECTIVE: To detect changes in spatial learning and memory following low-level lead exposure in rats, in Morris water maze test under the same experimental condition used to analyze lead exposure effects on various memory types and learning processes. DESIGN AND SETTING: The experiment was conducted at the Animal Laboratory, Institute of Psychology, Chinese Academy of Science between February 2005 and March 2006. One-way analysis of variance (ANOVA) and behavioral observations were performed. MATERIALS: Sixteen male, healthy, adult, Sprague Dawley rats were randomized into normal control and lead exposure groups (n = 8). METHODS: Rats in the normal control group were fed distilled water, and those in the lead exposure group were fed 250 mL of 0.05% lead acetate once per day. At day 28, all rats performed the Morris water maze test, consisting of four phases: space navigation, probe test, working memory test, and visual cue test. MAIN OUTCOME MEASURES: Place navigation in the Morris water maze was used to evaluate spatial learning and memory, probe trials for spatial reference memory, working memory test for spatial working memory, and visual cue test for non-spatial cognitive function. Perkin-Elmer Model 300 Atomic Absorption Spectrometer was utilized to determine blood lead levels in rats. RESULTS: (1) In the working memory test, the time to reach the platform remained unchanged A between the control and lead exposure groups (F(1,1) = 0.007, P = 0.935). A visible decrease in escape latencies was observed in each group (P = 0.028). However, there was no significant difference between the two groups (F(1,1) = 1.869, P = 0.193). The working memory probe test demonstrated no change between the two groups in the time spent in the target quadrant during the working memory probe test (F(1,1) = 1.869, P = 0.193). However, by day 4, differences were observed in the working memory test (P < 0.01). (2) Multivariate repetitive measure and ANOVA in place navigation presented no significant difference between the two groups (F(1,1) = 0.579, P 0.459). (3) Spatial probe test demonstrated that the time to reach the platform was significantly different between the two groups (F(1,1) = 4.587, P = 0.048), and one-way ANOVA showed no significant difference in swimming speed between the two groups (F(1,1) = 1.528, P= 0.237). (4) In the visual cue test, all rats reached the platform within 15 seconds, with no significant difference (F(1, 1) = 0.579, P = 0.459). (5) During experimentation, all rats increased in body mass, but there was no difference between the two groups (F(1,1) = 0.05, P= 0.943). At day 28 of 0.05% lead exposure, the blood lead level was 29.72 mu g/L in the lead exposure group and 5.86 mu g/L in the control group (P < 0.01). CONCLUSION: The present results revealed low-level lead exposure significantly impaired spatial reference memory and spatial working memory, but had no effect on spatial learning.