Sleep deficits in diabetic rats: restoration following chronic intravenous or intracerebroventricular infusions of insulin

The role of insulin in sleep was investigated in the present study by using streptozotocin-induced insulin deficiency in rats. Our previous studies showed a selective increase in the daily duration of slow wave sleep following either peripheral or central administration of insulin in normal rats. We now report sleep deficits following the pharmacological destruction of pancreatic B insulin-producing cells. The daily duration of both slow wave sleep (SWS) and paradoxical sleep (PS) were decreased on the third day following the injection of streptozotocin. However, only SWS remained lower than the control levels two weeks after the treatment whereas PS returned to normal values. The continuous intravenous infusion of exogenous insulin (2 IU per 24 hr) brought about a selective restoration of SWS in insulin-deficient and hyposomniac rats. A dose-dependent restoration of SWS was also observed when exogenous insulin was continuously administered intracerebroventricularly in streptozotocin-treated diabetic rats. Although the mechanism of the induction of sleep by insulin remains to be elucidated, these results clearly support its hypnogenic properties. A possible direct action of insulin on brain cells is suggested.