Murine Multiple Sleep Latency Test: phenotyping sleep propensity in mice.

STUDY
OBJECTIVES: Objectives were to (1) establish a measure of sleep propensity for a more comprehensive characterization of sleepiness in murine genetics and interventional studies and (2) to characterize sample sizes necessary for statistical differences in effect.
DESIGN: Average multiple sleep latency values were compared in mice, varying strain, circadian time, and forced-wakefulness conditions.
SUBJECTS: Adult male mice of inbred strains were studied.
INTERVENTIONS: Mice were implanted with electroencephalographic and electromyographic recording electrodes. Twenty-four-hour periods of stable baseline sleep activity (> 600 minutes) were confirmed prior to baseline sleep-latency testing. Average sleep latencies were obtained across 10- and 20-minute nap opportunities within 4 consecutive 30-minute periods. Forced wakefulness protocols were performed prior to additional sleep-latency tests. MEASUREMENTS AND
RESULTS: Sleep-latency testing with 20-minute nap opportunities every 30 minutes revealed a shorter sleep latency in the lights-on period (12.4 minutes +/- 0.9 vs 16.5 +/- 1, P < .001), a substantial reduction in sleep latencies in mice subjected to 6-hour forced wakefulness (eg, C57BL/6J baseline: 12.4 +/- 0.9 minutes, and forced wakefulness, 8.5 +/- 0.9 minutes, P < .01), and strain differences in latencies following short-term forced wakefulness (P < .01). Sample sizes for 85% power to detect a 25% reduction in the 20-minute daytime Murine Multiple Sleep Latency Test require fewer than 20 mice per group for commonly used transgenic background strains.
CONCLUSIONS: The Murine Multiple Sleep Latency Test is a robust measure of sleep propensity, and the latency varies with homeostatic and circadian influences. The test requires minimal added time to standard murine sleep recordings, yet yields important additive information.