The Effect of a Disrupted Light-Dark Schedule on Fear in Mice

Abstract

The objective of the present study was to assess the effect of a disrupted light-dark (LD) schedule on fear and body weight in mice. Female and male Swiss Webster mice (N = 71) were exposed to either a normal 12 : 12 hr LD schedule or a disrupted 12 : 12 hr LD schedule for 35 days, after which fear was assessed in two behavioral assays. To assess to the effect of LD disruption on body weight, body weights were measured every 5 days during the course of the LD disruption. Possible differences between females and males were also explored. For all but one variable in the behavioral tests, results showed that LD disruption no effect on fear. However, increased defecation frequency in animals exposed to the disrupted schedule shows a fear-increasing effect of LD disruption. Increased time in the periphery as well as increased defecation in males in the open field show that males were more fearful than females. However, more time in the light section of the light-dark box and longer latency to enter the dark section of the box show that males were less fearful than females in the light-dark box. Females made more frequent entries to the light section, indicative of reduced fear as well as higher locomotor activity in females than males in the light-dark box, a finding which is consistent with the literature. LD disruption also did not affect body weight. Because of contrasting results from variables in the behavioral tests, the effect of the disrupted LD schedule on fear in the present study is unclear.