Sections were then washed in TBS, blocked in goat serum, and incubated for 4 h in a mixture of goat anti-rabbit Alexa Fluor 555 and anti-mouse Alexa Fluor 488 (Invitrogen, Carlsbad, CA) at 1:500. regulatory brain region. Therefore, we quantified the p-eIF2-immunolabeled neurons in the BF area; Salub administration increased the number of p-eIF2-expressing noncholinergic neurons in the caudal BF. In addition, Salub also increased the intensity of p-eIF2 expression in both cholinergic and noncholinergic neurons, but this was more widespread among the noncholinergic neurons. Our findings support a hypothesis that sleep is facilitated by signals associated with the ER stress response. Keywords:protein synthesis inhibition, endoplasmic reticulum stress, phosphorylated eukaryotic initiation factor 2, basal forebrain much evidence suggests a linkbetween sleep and brain protein synthesis. Sleep is associated with increased protein synthesis in several discrete brain regions as well as the whole cerebrum (30,36). Sleep deprivation reduces the levels of SB 431542 certain proteins in rat basal forebrain (BF) (1) SB 431542 and hippocampus (15). Key components of translational control genes are preferentially expressed during sleep (7,9). Some evidence suggests that regulation of sleep is coupled to the successful execution of protein synthesis, and that non-rapid eye movement (NREM) sleep is facilitated if protein synthesis is suppressed. Administration of protein synthesis inhibitors (PSIs) usually increases NREM sleep but reduces REM sleep (33). Recently, we reported (26) that local administration of the PSI anisomycin (Ani) induced site-specific facilitation of sleep states. NREM sleep was increased by Ani administration in the lateral preoptic area and REM sleep by administration in the perifornical hypothalamic areas of rats. The sleep state facilitated by PSI administration may depend on the predominant state of sleep normally regulated by Rftn2 the brain region exposed to PSI. Arrest of protein synthesis in vivo may occur as a first line of defense against accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) lumen, identified as ER stress (16,37). A current model posits that adaptive responses to ER stress are controlled by a signaling pathway led by release of the chaperone BiP/GRP78 (37,46). An immediate adaptive response to ER stress is the phosphorylation at Ser51 of SB 431542 the -subunit of eukaryotic initiation factor 2 (eIF2), thereby blocking translation initiation and synthesis of certain classes of proteins, including membrane and secreted proteins important in brain function. The phosphorylation of eIF2 is therefore widely used as a marker of ER stress (35). All components of the unfolded protein response (UPR) were found after 6 h of sleep deprivation in mouse neocortex, including increases in p-eIF2 as well as free BiP/GRP78 and phosphorylated protein kinase-like ER kinase (PERK), a key kinase that phosphorylates eIF2 (29). Sleep deprivation has also been shown to increase the expression of BiP inDrosophila(28,39), white crowned sparrow (20), mice (25,29,41), and rats (8,38,42). On basis of the findings summarized above, our study was conceived as follows. On one hand, sleep deprivation elicits the ER stress response; sleep deprivation is followed by homeostatic facilitation of sleep. On the other hand, sleep state facilitation is coupled to facilitation of brain protein synthesis. Therefore, we hypothesized that a component of the molecular pathways of the ER stress response regulating protein synthesis could also play a role in facilitation of sleep. Because induction of p-eIF2 is a key step in the ER stress response, we hypothesized that elevation of p-eIF2 would facilitate sleep. This hypothesis was tested by administration of salubrinal (Salub), a small molecule that increases p-eIF2 by inhibiting its dephosphorylation (Ref.4; seediscussion). We administered Salub into the lateral ventricle and observed its effects on sleep. Since p-eIF2 immunolabeling was found to be more intense in the cholinergic BF area, a sleep-wake regulatory brain region, we also quantified the number of p-eIF2-immunolabeled neurons in the BF area after Salub administration. == MATERIALS AND METHODS == == Experimental subjects..