Ronald Szymusiak

Salubrinal, an endoplasmic reticulum stress blocker, modulates sleep homeostasis and activation of sleep- and wake-regulatory neurons

Endoplasmic reticulum (ER) stress has been associated with the regulation of sleep and wake. We have previously shown that i.c.v. administration of a specific ER stress modulator, Salubrinal (SALUB), which inhibits global protein translation by blocking the dephosphorylation of eukaryotic initiation factor 2α (p-eIF2α), increased non-rapid eye movement (NREM) sleep. Here we report on the relationship between ER stress response and sleep homeostasis by measuring the amount and intensity of homeostatic recovery sleep in response to the i.c.v. administration of SALUB in adult freely behaving rats. We have also tested the hypothesis that SALUB induces sleep by activating sleep-promoting neurons and inhibiting wake-promoting neurons in the basal forebrain (BF) and hypothalamus by quantifying the effects of SALUB treatment on c-Fos expression in those neuronal groups. The present study found that i.c.v. administration of SALUB significantly modified the homeostatic sleep response. SALUB administered during sleep deprivation increased sleep intensity, indicated by slow-wave activity (SWA), during recovery sleep, whereas its administration during recovery sleep increased the amount of recovery sleep. We also found that SALUB induced c-Fos activation of GABAergic neurons in the sleep-promoting rostral median preoptic nucleus while simultaneously reducing c-Fos activation of wake-promoting lateral hypothalamic orexin-expressing neurons and magnocellular BF cholinergic neurons. The current findings suggest that ER stress pathway plays a role in the homeostatic control of NREM sleep in response to sleep deprivation and provides a mechanistic explanation for the sleep modulation by molecules signaling the need for brain protein synthesis.