The suprachiasmatic nucleus changes the daily activity of the arcuate nucleus α-MSH neurons in male rats.

Timing of metabolic processes is crucial for balanced physiology; many studies have shown the deleterious effects of untimely food intake. The basis for this might be an interaction between the arcuate nucleus (ARC) as the main integration site for metabolic information and the suprachiasmatic nucleus (SCN) as the master clock. Here we show in male rats that the SCN influences ARC daily neuronal activity by imposing a daily rhythm on the α-MSH neurons with a peak in neuronal activity at the end of the dark phase. Bilateral SCN lesions showed a complete disappearance of ARC neuronal rhythms and unilateral SCN lesions showed a decreased activation in the ARC at the lesioned side. Moreover light exposure during the dark phase inhibited ARC and α-MSH neuronal activity. The daily inhibition of ARC neuronal activity occurred in light-dark conditions as well as in dark-dark conditions, demonstrating the inhibitory effect to be mediated by increased SCN (subjective) day neuronal activity. Injections into the SCN ...