Reciprocal interaction between the suprachiasmatic nucleus and the immune system tunes down the inflammatory response to lipopolysaccharide

- There is a day night rhythm in the cytokine response to LPS that depends on the SCN.
- The SCN is activated by a peripheral injection of LPS.
- Lesioning the SCN causes a 10 fold increase in the immune response.
- The SCN inhibits the inflammatory response to LPS.

Several studies have shown circadian variations in the response of the immune system suggesting a role of the suprachiasmatic nucleus (SCN). Here we show that lipopolysaccharide (LPS) administration in the beginning of the active period induced more severe responses in temperature and cytokines than LPS given in the rest period. Moreover night administered LPS increased SCN basal neuronal activity indicating a direct influence of inflammation on the SCN. Bilateral lesions of the SCN resulted in an increased inflammatory response to LPS demonstrating that an interaction between the SCN and the immune system modulates the intensity of the inflammatory response.