Platelet activating factor and its metabolite promote sleep in rabbits

Platelet activating factor (PAF) is a key inflammatory mediator. PAF and its receptor are found in brain and PAF affects or is affected by the production of sleep promoting cytokines such as interleukin-1. PAF also interacts with several other sleep-regulatory substances such as nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, nitric oxide, prostaglandins, and prolactin. We thus hypothesized that PAF would increase sleep. In these experiments, each rabbit received an injection of 25 microl of 2% DMSO to obtain control values, and on a separate day received PAF or lyso-PAF, a metabolite of PAF. Ten, 100 and 500 nmol for each substance was injected intracerebroventricularly. Both PAF and lyso-PAF enhanced non-rapid eye movement (NREM) sleep but not REM sleep. Lyso-PAF, but not PAF, induced hyperthermia. Results are consistent with the hypothesis that the brain cytokine network is involved in physiological sleep regulation.