Strain differences in sleep and other pathophysiological sequelae of influenza virus infection in naive and immunized mice.

To characterize behavioral and physiological alterations induced by viral respiratory infection, C57BL/6 and BALB/c strains of mice were monitored for 2 days before and 4 days after intranasal inoculation with influenza virus. Both strains developed hypothermia, decrease locomotor activity, and decreased delta-wave amplitude during sleep within 24 h after inoculation. However, infected C57BL/6 mice also spent more time in slow-wave sleep, but infected BALB/c mice did not. The increased SWS in C57BL/6 mice occurred during the lights-off phase of the circadian cycle, and resulted in loss of the normal circadian rhythmicity of sleep. Increased sleep also occurred after viral challenge of immunized C57BL/6 mice, but was not observed after secondary challenge of immunized BALB/c mice. These data indicate that sleep alterations may accompany viral infections in some, but not all, strains of mice. The dissimilar sleep patterns seen in C57BL/6 and BALB/c mice after influenza infection may reflect differences in their immune response to influenza virus.