Systemically applied luteinizing hormone-releasing hormone (LHRH) reduces behavioural activity in rats and increases sleep activity.

Groups of each 8 male Long-Evans rats were treated with 1 or 10 micrograms/kg LHRH intraperitoneally and compared with control rats which received the vehicle fluid (NaCl-solution). Ambulatory activity in an open field (OF), entrance to central fields and the mobility index were significantly decreased by both doses. Correspondingly, wheel running and movement velocity were significantly decreased. A further group of 8 rats with chronically implanted electrodes which was habituated to sessions showed an increase of slow-wave sleep and a significant reduction of waking and active states with maximal expression 45 min after ip application of 10 micrograms/kg LHRH. Paradoxical sleep was slightly reduced. Sleep-wakefulness cyclograms showed increase of a sleep phase duration to 175% and of single slow wave sleep phase duration to 140% after LHRH. Phases of drowsiness were also prolonged.