Hypothalamic injection of prolactin or its antibody alters the rat sleep-wake cycle

Several studies have suggested an interaction between prolactin and the sleep-wake cycle. In this study ovine prolactin (oPRL) and anti-prolactin antibody were microinjected into the rat dorsolateral hypothalamus, which contains prolactin-like immunoreactive neurons. Results indicate that during the light period, prolactin injection induced an increase in paradoxical sleep duration, whereas it caused a decrease when injected during the dark period. Anti-prolactin antibody injection during the dark period also decreased paradoxical sleep duration. There was no effect of oPRL or antibody on slow wave sleep duration irrespective of injection time. These results suggest that prolactin injection may have an inhibitory effect on hypothalamic prolactin neurons.