Murine Multiple Sleep Latency Test: phenotyping sleep propensity in mice

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. Average multiple sleep latency values were compared in mice, varying strain, circadian time, and forced-wakefulness conditions. Adult male mice of inbred strains were studied. 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. 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. 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.