The effect of the cannabinoid receptor agonist and antagonist on the light-induced changes in the suprachiasmatic nucleus of rats.

The CB1 cannabinoid receptors have been found in the rodent suprachiasmatic nucleus, and their activation suppresses the light-induced phase shift in locomotor rhythmicity of mice and hamsters. Here, we show that the CB1 receptor agonist CP55940 significantly attenuates the light-induced phase delay in rats as well. Furthermore, it blocks the light induction of c-Fos and light-induced downregulation of pERK1/2 in the SCN, and the CB1 antagonist AM251 prevents the photic induction of pERK1/2 and reduces pGSK3β after photic stimulation.

The day/night difference in the circadian clock's response to acute lipopolysaccharide and the rhythmic Stat3 expression in the rat suprachiasmatic nucleus.

The circadian clock in the suprachiasmatic nucleus (SCN) regulates daily rhythms in physiology and behaviour and is an important part of the mammalian homeostatic system. Previously, we have shown that systemic inflammatory stimulation with lipopolysaccharide (LPS) induced the daytime-dependent phosphorylation of STAT3 in the SCN. Here, we demonstrate the LPS-induced Stat3 mRNA expression in the SCN and show also the circadian rhythm in Stat3 expression in the SCN, with high levels during the day.