Salubrinal, an inhibitor of protein synthesis, promotes deep slow wave sleep.

Previous work showed that sleep is associated with increased brain protein synthesis and that arrest of protein synthesis facilitates sleep. Arrest of protein synthesis is induced during the endoplasmic reticulum (ER) stress response, through phosphorylation of eukaryotic initiation factor 2alpha (p-eIF2alpha). We tested a hypothesis that elevation of p-eIF2alpha would facilitate sleep. We studied the effects of intracerebroventricular infusion of salubrinal (Salub), which increases p-eIF2alpha by inhibiting its dephosphorylation. Salub increased deep slow wave sleep by 255%, while reducing active waking by 49%. Delta power within non-rapid eye movement (NREM) sleep was increased, while power in the sigma, beta, and gamma bands during NREM was reduced. We found that Salub increased expression of p-eIF2alpha in the basal forebrain (BF) area, a sleep-wake regulatory brain region. Therefore, we quantified the p-eIF2alpha-immunolabeled neurons in the BF area; Salub administration increased the number of p-eIF2alpha-expressing noncholinergic neurons in the caudal BF. In addition, Salub also increased the intensity of p-eIF2alpha 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.

Effects on sleep of microdialysis of adenosine A1 and A2a receptor analogs into the lateral preoptic area of rats.

Evidence suggests that adenosine (AD) is an endogenous sleep factor. The hypnogenic action of AD is mediated through its inhibitory A1 and excitatory A2A receptors. Although AD is thought to be predominantly active in the wake-active region of the basal forebrain (BF), a hypnogenic action of AD has been demonstrated in several other brain areas, including the preoptic area. We hypothesized that in lateral preoptic area (LPOA), a region with an abundance of sleep-active neurons, AD acting via A1 receptors would induce waking by inhibition of sleep-active neurons and that AD acting via A2A receptors would promote sleep by stimulating the sleep-active neurons. To this end, we studied the effects on sleep of an AD transport inhibitor, nitrobenzyl-thio-inosine (NBTI) and A1 and A2A receptor agonists/antagonists by microdialyzing them into the LPOA. The results showed that, in the sleep-promoting area of LPOA: 1) A1 receptor stimulation or inhibition of AD transport by NBTI induced waking and 2) A2A receptor stimulation induced sleep. We also confirmed that NBTI administration in the wake promoting area of the BF increased sleep. The effects of AD could be mediated either directly or indirectly via interaction with other neurotransmitter systems. These observations support a hypothesis that AD mediated effects on sleep-wake cycles are site and receptor dependent.

GABA-mediated control of hypocretin- but not melanin-concentrating hormone-immunoreactive neurones during sleep in rats.

The perifornical-lateral hypothalamic area (PF-LHA) has been implicated in the regulation of behavioural arousal. The PF-LHA contains several cell types including neurones expressing the peptides, hypocretin (HCRT; also called orexin) and melanin-concentrating hormone (MCH). Evidence suggests that most of the PF-LHA neurones, including HCRT neurones, are active during waking and quiescent during non-rapid eye movement (non-NREM) sleep. The PF-LHA contains local GABAergic interneurones and also receives GABAergic inputs from sleep-promoting regions in the preoptic area of the hypothalamus. We hypothesized that increased GABA-mediated inhibition within PF-LHA contributes to the suppression of neuronal activity during non-REM sleep. EEG and EMG activity of rats were monitored for 2 h during microdialytic delivery of artificial cerebrospinal fluid (aCSF) or bicuculline, a GABAA receptor antagonist, into the PF-LHA in spontaneously sleeping rats during the lights-on period. At the end of aCSF or bicuculline perfusion, rats were killed and c-Fos immunoreactivity (Fos-IR) in HCRT, MCH and other PF-LHA neurones was quantified. In response to bicuculline perfusion into the PF-LHA, rats exhibited a dose-dependent decrease in non-REM and REM sleep time and an increase in time awake. The number of HCRT, MCH and non-HCRT/non-MCH neurones exhibiting Fos-IR adjacent to the microdialysis probe also increased dose-dependently in response to bicuculline. However, significantly fewer MCH neurones exhibited Fos-IR in response to bicuculline as compared to HCRT and other PF-LHA neurones. These results support the hypothesis that PF-LHA neurones, including HCRT neurones, are subject to increased endogenous GABAergic inhibition during sleep. In contrast, MCH neurones appear to be subject to weaker GABAergic control during sleep.

Preoptic area warming inhibits wake-active neurons in the perifornical lateral hypothalamus.

Activation of the preoptic area (POA) warm sensitive neurons is known to promote non-REM (NREM) sleep and inhibit neuronal discharge in arousal-related brain structures. The perifornical area of the lateral hypothalamus (PF/LH) was recently recognized to be an additional important arousal promoting region. We studied the behavior of PF/LH neurons in rats during the normal sleep-wake cycle and in response to local POA warming. Most PF/LH neurons were wake-active, and exhibited low discharge throughout NREM. Seventy four percent of these wake-active neurons exhibited moderate or strong activation in REM sleep compared to NREM sleep. A substantial group (26%) exhibited very low discharge in REM as well as NREM sleep. Fifty two percent of units in the PF/LH area were responsive to POA warming; 90% of responsive neurons exhibited a significant reduction (-26.47+/-2.16% for 1 degrees C of POA warming) in their discharge rate. The inhibitory effect of POA warming on PF/LH neurons was not associated with EEG slowing. This study supports the hypothesis that sleep induction by POA warm sensitive neurons is mediated through the inhibition of multiple arousal-related structures.