Suppression of locomotor activity in female C57Bl/6J mice treated with interleukin-1β: Investigating a method for the study of fatigue in laboratory animals

Abstract

Fatigue is a disabling symptom in patients with multiple sclerosis and Parkinson's Disease, and is also common in patients with traumatic brain injury, cancer, and inflammatory disorders. Little is known about the neurobiology of fatigue, in part due to the lack of an approachto induce fatigue in laboratory animals. Fatigue is a common response to systemic challenge by pathogens, a response in part mediated through action of the pro-inflammatory cytokineinterleukin-1 beta (IL-1β). We investigated the behavioral responses of mice to IL-1β. Female C57Bl/6J mice of 3 ages were administered IL-1β at various doses i.p. Interleukin-1β reducedlocomotor activity, and sensitivity increased with age. Further experiments were conducted with middle-aged females. Centrally administered IL-1β dose-dependently reduced locomotoractivity. Using doses of IL-1β that caused suppression of locomotor activity, wemeasured minimal signs of sickness, such as hyperthermia, pain or anhedonia (as measured withabdominal temperature probes, pre-treatment with the analgesic buprenorphine and through sucrose preference, respectively), all of which are responses commonly reported with higherdoses. We found that middle-aged orexin-/- mice showed equivalent effects of IL-1β on locomotor activity as seen in wild-type controls, suggesting that orexins are not necessary for IL-1β -induced reductions in wheel-running. Given that the availability and success of therapeutic treatments for fatigue is currently limited, we examined the effectiveness of two potentialclinical treatments,modafinil and methylphenidate.We found that these treatments were variably successful in restoring locomotor activity after IL-1β administration. This provides onestep toward development of a satisfactory animal model of the multidimensional experience of fatigue, a model that could allow us to determine possible pathways through which inflammationinduces fatigue, and could lead to novel treatments for reversal of fatigue.