Regional transport of TNF-alpha across the blood-brain barrier in young ICR and young and aged SAMP8 mice

The blood-brain barrier (BBB) controls the exchange of regulatory substances, including tumor necrosis factor-alpha (TNF), between the brain and the blood. Transport across the BBB of some regulatory substances is altered with aging. Here, we measured the blood to brain unidirectional influx rate (Ki) for whole brain and 10 brain regions for radioactively labeled TNF in three groups of mice: young (2 mo old) ICR (the standard outbred albino laboratory mouse also termed CD-1), young SAMP8 (a strain which develops impaired learning and memory with aging that correlates with an age-related increase in brain levels of amyloid beta protein), and aged (17 mo) SAMP8 mice. In ICR mice, the hypothalamus had the fastest (1.73 microl/g-min) and the parietal cortex the slowest (0.189 microl/g-min) rates of uptake, a regional difference of about 9 fold. No differences in transport into whole brain or brain regions occurred between the ICR and young SAMP8, showing a lack of differences between strains. Transport was higher for the occipital cortex, midbrain, and striatum in aged SAMP8 mice. These results show blood-borne TNF enters some regions of the brain much more readily than others and TNF transport is increased into some brain regions of the SAMP8 mice at an age when learning and memory are impaired.

Regional variations in the transport of interleukin-1alpha across the blood-brain barrier in ICR and aging SAMP8 mice

OBJECTIVES

The blood-brain barrier (BBB) transports blood-borne interleukin-1alpha (IL-1) into the brain by a saturable process. Here, we determined whether all regions of the brain could transport IL-1 and whether transport differed between ICR and SAMP8 mice, a strain which overexpresses amyloid beta protein (Abeta) with aging.

METHODS

We used multiple-time regression analysis to measure the unidirectional influx rate (transport rate) of radioactively labeled IL-1 for 10 brain regions in young (2 months old) ICR mice and in young and aged (17 months old) SAMP8 mice. We also used radioactively labeled sucrose and albumin to determine whether the BBB was disrupted in aged SAMP8 mice.

RESULTS

In young ICR mice, eight of the 10 brain regions transported IL-1, with the pons-medulla having the fastest transport rate (0.584 +/- 0.163 microl/g x min), but no statistically significant differences occurred among regions. In SAMP8 mice, only four regions transported IL-1. In young SAMP8 mice, the pons-medulla transported IL-1 faster than any other region (0.642 +/- 0.197 microl/g x min), a rate that was significantly different (p < 0.01) from each of the other regions. Aged SAMP8 mice had a similar regional transport pattern to young SAMP8 mice, but there were no statistically significant differences among the four transporting regions. Sucrose and albumin spaces were not increased in aged SAMP8 mice, demonstrating an intact BBB.

CONCLUSIONS

The smaller number of regions transporting IL-1 in SAMP8 mice as compared to ICR mice demonstrates a genetic influence on transport which could alter the ability of blood-borne IL-1 to directly affect brain functions. No evidence of BBB disruption was found in the aged SAMP8 mice from this colony.