Relevance of the metabotropic glutamate receptor (mGluR5) in the regulation of NREM-REM sleep cycle and homeostasis: Evidence from mGluR5 (−/−) mice

Abstract

Sleep is a homeostatically regulated behavior and sleep loss evokes a proportional increase in sleep time and delta slow wave activity. Glutamate and pharmacological modulation of the metabotropic glutamate receptors (mGluR) signaling have been implicated in the organization of vigilance states. Here, the role of the mGluR5 on homeostatic regulation of sleep-wake cycle and electroencephalographic (EEG) activity was examined in mGluR5 (−/−) mice. We first characterized the sleep-wake EEG phenotype in mGluR5 (−/−) and wild-type (WT) littermates mice by continuous recording for 72h of EEG, body temperature (BT) and locomotor activity (LMA). Next, we investigated the influence of sleep deprivation on the recovery sleep and EEG slow wave activity (1–4Hz) during NREM sleep to assess whether mGluR5 deletion affects the sleep homeostasis process. Like the control animals, mGluR5 (−/−) mice exhibited a clear-cut circadian sleep-wake architecture, however they showed reduced REM sleep time during the light phase with shorter REM sleep bouts and reduced state transitions in the NREM sleep-REM sleep cycle during the first and last 24h of the spontaneous 72h recording period. In addition, mGluR5 (−/−) mice had decreased slow EEG delta power during NREM sleep and enhanced LMA associated with elevated BT during the dark phase. Moreover, mGluR5 (−/−) mice exhibited reduced slow wave activity and sleep drive after sleep deprivation, indicating altered sleep homeostatic processes. The findings strongly indicate that mGluR5 is involved in shaping the stability of NREM sleep-REM sleep state transitions, NREM slow wave activity and homeostatic response to sleep loss.