Analysis of Muscular Activity in Neonatal Animals to Screen for Mutations and/or Drugs that Alter Sleep and Wake States ( 99072)
Northwestern investigators have developed a high-throughput screening method for novel genes and/or drug compounds associated with the sleep and wake state. Previously it has not been possible to screen a large number of sleep-related drugs and/or genes in rodents because of the time, cost and invasive nature of recording sleep via brain electrical activity (electroencephalography (EEG) in adult animals. The novelty of this method is two-fold: 1) the sleep-wake state in the neonatal animal has been demonstrated to represent the sleep-wake state in the adult animal and, 2) the sleep-wake state in neonatal rodents can be measured accurately and non-invasively by recording only muscular activity (electromyography (EMG). Thus this novel technology allows accurate, high-throughput screening for sleep-related genes and/or drug compounds in neonates that are significantly more time and cost-effective than the present methodology used with adult animals. Recently these investigators identified a mutant rodent that shows prolonged wakefulness with the use of this novel screening method. The mutant phenotype segregates in a manner that is consistent with the hypothesis that a single gene has been mutated giving rise to a dominant or semi-dominant high wake phenotype.
SCIENTIFIC BACKGROUND: In adult animals the only way to accurately determine and characterize vigilance states (ie. wake and the two primary stages of sleep, NREM and REM sleep) is to monitor EEG and EMG activity using chronic electrodes previously implanted under deep anesthesia. For studies in adult animals this typically requires extensive surgical procedures making it very expensive and time consuming to record EEG and EMG sleep from a large number of animals. This technology involves the use of recording just muscular activity for 1–3 hours in neonatal rodents as a marker of vigilance states. Such an approach allows one to distinguish what is termed Active Sleep (AS, analogous to REM sleep in adults) from Quiet Sleep (QS, analogous to NREM sleep in adults) from wake. Because of the unique presence of abundant muscular twitches during AS which are reflected on EMG activity, this criterion allows for the clear recognition of AS from QS during the first two weeks of age. These investigators have demonstrated that alterations observed in sleep characteristics in neonatal rats are consistent with those observed in adult animals in two different strains of rats. As opposed to EMG analysis, behavioral observations (e.g. by video camera) are not precise enough to perceive small twitches and to appreciate the general muscular tone which is low in QS and flat in AS. In addition, unlike EEG, the EMG signal can be processed on-line for automatic analysis as sleep-wake states and other parameters.
SUMMARY: This technology allows screening for altered sleep phenotypes, and ultimately altered sleep genes at a very early age which is highly cost effective. The “non-invasive” aspect of this method allows for the use of the animals for other phenotypic screening purposes, which is difficult after invasive surgery needed for EEG recording. This novel approach will also allow screening of thousands of drugs in a more cost and time effective manner within a single year. Furthermore those drugs which influence sleep and/or wake states in neonates can then be tested in adulthood when regular EEG sleep can be monitored to further analyze sleep in more detail, e.g. circadian rhythm of sleep-wake states, analysis of EEG signal including power spectral analysis. Use of this method may lead to the identification of novel compounds which not only alter the sleep-wake state but also influence human fatigue, alertness, performance, cognition, memory and learning as well as other aspects of human biochemistry, metabolism and/or behavior that are affected by the quantity and quality of the sleep-wake cycle.
U.S. Patent 6,477,408 issued on November 5, 2002 and is available for licensing.
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