Site of action of sleep-inducing muramyl peptide isolated from human urine: microinjection studies in rabbit brains.

1. Sleep-promoting muramyl peptide purified from human urine (SPU) was injected through chronically implanted guide tubes into defined regions of the basal forebrain and brain stem of unanesthetized rabbits. Electroencephalogram (EEG) and body movements were recorded subsequent to each injection. 2. Of 52 injection sites, there were 8 in which microinjection of SPU induced significant increases of slow-wave sleep (SWS) for 5 or more hours. Each active site was tested twice with SPU and once with vehicle control. 3. Seven of the active sites were located in a region extending from the basal forebrain at the level of the optic chiasm to the mesodiencephalic junction. No active sites were found in the lower brain stem. 4. The behavioral and EEG characteristics of the excess SWS induced by microinjection of SPU appeared normal and similar to the excess sleep that follows intraventricular infusions of sleep factor. However, the responses occurred sooner after injections into an active site than after infusion into a lateral ventricle.