Abstract
To the ill patient with diabetes, the behavioral symptoms of sickness such as fatigue and apathy are debilitating and can prevent recuperation. Here we report that peripherally administered insulin-like growth factor 1 (IGF-1) attenuates LPS-dependent depression of social exploration (sickness) in nondiabetic (db/+) but not in diabetic (db/db) mice. We show that the insulin/IGF-1 mimetic vanadyl sulfate (VS) is effective at augmenting recovery from sickness in both db/+ and db/db mice. Specifically, peak illness was reached at 2 h for both VS and control animals injected with LPS, and VS mice recovered 50% faster than non-VS-treated animals. Examination of the mechanism of VS action in db/+ mice showed that VS paradoxically augmented peritoneal macrophage responsivity to LPS, increasing both peritoneal and ex vivo macrophage production of IL-1beta and IL-6 but not TNF-alpha. The effects of VS in promoting recovery from sickness were not restricted to LPS, because they were also observed after direct administration of IL-1beta. To explore the possibility that VS impairs immune-to-brain communication via vagal afferents, the vagally mediated satiety-inducing effects of cholecystokinin 8 were tested in db/+ mice. Cholecystokinin decreased food intake in saline-injected mice but not in VS-treated mice. VS also inhibited LPS-dependent up-regulation of IL-1beta and IL-6 mRNA in the brain, while increasing by 50% the cerebral expression of transcripts of the specific antagonist of IL-1 receptors IL-1RA and IL-1R2. Taken together, these data indicate that VS improves recovery from LPS-induced sickness by blocking vagally mediated immune-to-brain signaling and by up-regulating brain expression of IL-1beta antagonists.