Selected contribution: circadian rhythm of tumor necrosis factor-alpha uptake into mouse spinal cord

Circadian variations in the actions of tumor necrosis factor-alpha (TNF-alpha) have been observed. Because a saturable transport system at the blood-brain barrier mediates most of the influx of TNF-alpha from blood to the central nervous system (CNS), the circadian variation of the CNS effects of TNF-alpha could be related to changes in this transport system. Accordingly, we measured the uptake of intravenously injected TNF-alpha into various CNS regions at different times and compared these measurements with the uptake into a peripheral control (muscle). We found that the spinal cord, but not the brain, showed a circadian rhythm in the uptake of TNF-alpha. This pattern is similar to that of leptin but different from that of interleukin-1. The circadian rhythm of the influx of TNF-alpha into this region of the CNS suggests a functional role for the spinal cord in the physiological actions of TNF-alpha.