Early programming of astrocyte organization in the mouse suprachiasmatic nuclei by light.

The principal pacemaker in mammals, controlling physiology and behavior, is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Early photic experience has long-term effects on the animal's rhythmic behavior, as indicated by alterations in the phase shift induced by a light pulse, and in the expression of the circadian rhythm of locomotor activity under light-dark (LD), constant light (LL), and constant darkness (DD) environments. However, the brain substrates targeted by early light have not yet been identified.