Influenza virus-induced changes in rabbit sleep and acute phase responses

Abstract

Systematic investigations of sleep after viral inoculation have not previously been described. In the present study, rabbits were inoculated intravenously (iv) with control allantoic fluid followed by two sequential inoculations of influenza virus at intervals of 24 h. After each i.v. inoculation, sleep and brain temperature (Tbr), as well as leukocyte distributions and serum levels of antiviral activity and ceruloplasmin, were monitored. The first viral inoculation elicited several acute phase responses, including increased non-rapid-eye-movement sleep (NREMS), Tbr, serum antiviral activity, and serum ceruloplasmin levels, as well as neutrophilia and lymphopenia. In contrast to the effects of the first inoculation, after the second inoculation of virus, all these acute phase parameters were diminished or absent (the hyporesponsive state). Inoculation of naive rabbits with heat-inactivated virus was similarly ineffective; however, inoculation of this group of rabbits with viable virus 24 h later did induce full-scale acute phase responses. The possible role of cytokines in mediating the acute phase response after influenza viral challenge is discussed. Results support the hypothesis that sleep is a facet of the acute phase response involved in host defense mechanisms.