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Interleukin‐8 promotes non‐rapid eye movement sleep in rabbits and rats

Interleukin‐8 (IL‐8) is a cytokine found in the brain. In this study, the ability of IL‐8 to induce sleep in rabbits and rats was investigated. Twenty‐seven Sprague–Dawley rats and 16 male New Zealand White rabbits were provided electroencephalographic (EEG) electrodes, a brain thermistor, and a lateral intracerebroventricular cannula. The animals were injected intracerebroventricularly (i.c.v.) with pyrogen‐free saline and, one of the following doses of IL‐8 on a separate day: 1.25 or 12.5 ng in rabbits and 10, 50, or 100 ng in rats. EEG, brain temperature, and motor activity were recorded for 23 h after the i.c.v. injections. IL‐8 increased time spent in non‐rapid eye movement sleep (NREMS) without affecting rapid eye movement sleep (REMS). In rabbits, both doses of IL‐8 promoted NREMS. In rats, the 10 and 50 ng doses of IL‐8 failed to affect sleep, but the 100 ng dose of IL‐8 enhanced NREMS. EEG slow‐wave activity during NREMS was increased after the high dose of IL‐8 in rabbits. IL‐8 also induced fever in rabbits but not rats. Heat inactivated IL‐8 did not alter any of the parameters measured. Current results support the notion that the brain cytokine network plays a role in sleep regulation.