001. n = 14–15). Age and LPS both had a significant effect on overnight burrowing (Age: F1,50 = 13.34, p < 0.001. LPS: F1,50 = 28.21, p < 0.0001). In addition, an interaction between the two factors was detectable (F1,50 = 5.053, p = 0.029). To conclude, a systemic challenge of LPS led to an exacerbated and decrease in burrowing activity in 21 month old mice when compared to 4 month old mice. Next, we investigated a cerebellum dependent behaviour, the multiple static Belnacasan molecular weight rod test, which assesses the co-ordination and balance of mice on different diameter static rods (Carter et al., 1999 and Contet et al., 2001). Mice were placed on a suspended 9 mm diameter
static rod and the transit time to reach a platform after orientation was assessed in saline and LPS-treated mice (Fig. 5C and D). Chi squared analysis of baseline static rod performance showed a significant difference between young (7%, n = 30) and aged (68%, n = 25) mice in pass/fail ATM/ATR inhibition ratios on the 9 mm static rod (х2 = 22.69, d.f. = 1, p < 0.0001) ( Fig. 5C). Analysis of baseline transit times also showed a significant difference between young and aged mice (Mann Whitney test, p < 0.0001, n = 25–30 per group) ( Fig. 5D). Injection of LPS or saline did not have a significant effect on pass/fail rates at any age and there were not sufficient successful completions of the test in
the 21 month old mice to test for differences in transit times after injection. We also tested muscle strength using the climbing rod test to investigate
whether changes in muscle strength correlated with poorer static rod performance. There was a decline in climbing rod performance with age (p < 0.0001, Mann Whitney test; supplementary data Fig. 2A), but we found no difference in climbing rod performance between 21 month old mice that passed or failed the static rod test (supplementary data Fig. 2B). There was also no correlation between climbing rod test performance and static rod Methane monooxygenase transit time in 4 month old mice ( Supplementary data Fig. 2C). Finally we investigated the effect of LPS injection on the expression of inflammatory mediators in the different CNS regions of aged and young mice using quantitative real time PCR. However, we could not detect any significant increase of IL-6, IL-1β or iNOS mRNA expression 24 h after LPS injection in young or aged cerebellum or hippocampus (data not shown). In this study we have investigated the phenotype and morphological changes of microglia in eight distinct regions of the young and aged mouse brain. We show that age-related phenotype changes of microglial cells are more pronounced in the white matter, with the cerebellum, the most caudal structure studied, showing the greatest differences. Variations in microglial density have been well described in adult mouse brain with the hippocampus and substantia nigra exhibiting the highest and the cerebellar cortex the lowest density of microglia (Lawson et al., 1990).