Short light—dark cycles and paradoxical sleep in the rat: Effect of strain difference and hypophysectomy

Abstract

Rats were exposed to short light—dark cycles to study the redistribution of paradoxical sleep (PS). PS predominated during the short dark periods in the albino strain, and to a lesser extent in the pigmented strain. Hypophysectomy did not affect the predominance of PS during the dark periods. We conclude that neither the albino condition nor the presence of the pituitary gland is a prerequisite for the redistribution of PS to short dark periods.