Study objectives: Sleep in mice has typically been determined from electroencephalograms and electromyograms recorded via cables in tethered animals. However, the relatively small physical size of mice can produce concerns in recording with cables that may not be seen in larger animals. To examine the influence of implantation and tethering on mice, we recorded activity and sleep in 2 strains while they were attached to 3 cable configurations that varied in weight and flexibility.
Design: Activity was recorded prior to surgery and after surgery without tethering. Afterward, the mice were habituated to 3 cable configurations (light [L]: 1.5 g; medium [M]: 2.2 g; heavy [H]: 3.0 g), and activity and sleep were recorded for 2 consecutive days under each configuration.
Setting: N/A.
Patients or participants: Studies were conducted in 2 mouse strains that differ significantly in levels of spontaneous activity (more-active strain: BALB/cJ [C]; less-active strain: DBA/2J [D2]).
Interventions: N/A.
Measurements and results: Significant postsurgery reductions in activity in nontethered mice were found only in the more-active C strain. Activity in both strains was reduced in a graded manner as cable weight increased and flexibility decreased. In contrast, changes in sleep were not graded across cables, and changes in rapid eye movement sleep showed more variability. In addition, the effects of varying cables were not consistent across strains.
Conclusions: The differential impact that variations in the weight and flexibility of recording cables can have on the amount and patterns of sleep is an important consideration in conducting and interpreting sleep studies in mice.