Role of hypocretin in the medial preoptic area in the regulation of sleep, maternal behavior and body temperature of lactating rats.

Abstract

The hypocretins (HCRT), also known as orexin, includes two neuroexcitatory peptides, HCRT-1 and HCRT-2 (orexin A y B, respectively), synthesized by neurons located in the postero-lateral hypothalamus, whose projections and receptors are widely distributed throughout the brain, including the medial preoptic area (mPOA). HCRT have been associated with a wide range of physiological functions including sleep-wake cycle, maternal behavior and body temperature, all regulated by the mPOA. Previously we showed that HCRT in the mPOA facilitates certain active maternal behaviors, while the blockade of HCRT-R1 increased the time spent in nursing. As mother rats mainly sleep while they nurse, we hypothesize that HCRT in the mPOA of lactating rats reduce sleep and nursing, while the intra-mPOA administration of the dual orexin receptor antagonist (DORA) would generate the opposite effect. Therefore, the aim of this study was to determine the role of HCRT within the mPOA, in the regulation and integration of the sleep-wake cycle, maternal behavior and body temperature of lactating rats. To evaluate this idea, we assessed the sleep-wake states, maternal behavior and body temperature of lactating rats following microinjections of HCRT-1 (100 and 200 M) and DORA (5mM) into the mPOA. As expected, our data shows that HCRT-1 in mPOA promoted wakefulness and a slightly increase in body temperature, whereas DORA increased both NREM and REM sleep along with nursing and milk ejection. Taken together, our results strongly suggest that the reduction of the endogenous HCRT within the mPOA of lactating rats is important to promote sleep, nursing and milk ejection.