Ventrolateral Preoptic Neurons Research Articles

Orexin neurons inhibit sleep to promote arousal

Humans and animals lacking orexin neurons exhibit daytime sleepiness, sleep attacks, and state instability. While the circuit basis by which orexin neurons contribute to consolidated wakefulness remains unclear, existing models posit that orexin neurons provide their wake-stabilizing influence by exerting excitatory tone on other brain arousal nodes. Here we show using in vivo optogenetics, in vitro optogenetic-based circuit mapping, and single-cell transcriptomics that orexin neurons also contribute to arousal maintenance through indirect inhibition of sleep-promoting neurons of the ventrolateral preoptic nucleus. Activation of this subcortical circuit rapidly drives wakefulness from sleep by differentially modulating the activity of ventrolateral preoptic neurons. We further identify and characterize a feedforward circuit through which orexin (and co-released glutamate) acts to indirectly target and inhibit sleep-promoting ventrolateral preoptic neurons to produce arousal. This revealed circuitry provides an alternate framework for understanding how orexin neurons contribute to the maintenance of consolidated wakefulness and stabilize behavioral state.

Activation of the Ventrolateral Preoptic Neurons Projecting to the Perifornical-Hypothalamic Area Promotes Sleep: DREADD Activation in Wild-Type Rats.

The ventrolateral preoptic area (VLPO) predominantly contains sleep-active neurons and is involved in sleep regulation. The perifornical-hypothalamic area (PF-HA) is a wake-regulatory region and predominantly contains wake-active neurons. VLPO GABAergic/galaninergic neurons project to the PF-HA. Previously, the specific contribution of VLPO neurons projecting to the PF-HA (VLPO > PF-HAPRJ) in sleep regulation in rats could not be investigated due to the lack of tools that could selectively target these neurons. We determined the contribution of VLPO > PF-HAPRJ neurons in sleep regulation by selectively activating them using designer receptors exclusively activated by designer drugs (DREADDs) in wild-type Fischer-344 rats. We used a combination of two viral vectors to retrogradely deliver the Cre-recombinase gene, specifically, in VLPO > PF-HA neurons, and further express hM3Dq in those neurons to selectively activate them for delineating their specific contributions to sleep–wake functions. Compared to the control, in DREADD rats, clozapine-N-oxide (CNO) significantly increased fos-expression, a marker of neuronal activation, in VLPO > PF-HAPRJ neurons (2% vs. 20%, p < 0.01) during the dark phase. CNO treatment also increased nonREM sleep (27% vs. 40%, p < 0.01) during the first 3 h of the dark phase, when rats are typically awake, and after exposure to the novel environment (55% vs. 65%; p < 0.01), which induces acute arousal during the light phase. These results support a hypothesis that VLPO > PF-HAPRJ neurons constitute a critical component of the hypothalamic sleep–wake regulatory circuitry and promote sleep by suppressing wake-active PF-HA neurons.

Astrocytes in the Ventrolateral Preoptic Area Promote Sleep.

Although ventrolateral preoptic (VLPO) nucleus is regarded as a center for sleep promotion, the exact mechanisms underlying the sleep regulation are unknown. Here, we used optogenetic tools to identify the key roles of VLPO astrocytes in sleep promotion. Optogenetic stimulation of VLPO astrocytes increased sleep duration in the active phase in naturally sleep-waking adult male rats (n = 6); it also increased the extracellular ATP concentration (n = 3) and c-Fos expression (n = 3-4) in neurons within the VLPO. In vivo microdialysis analyses revealed an increase in the activity of VLPO astrocytes and ATP levels during sleep states (n = 4). Moreover, metabolic inhibition of VLPO astrocytes reduced ATP levels (n = 4) and diminished sleep duration (n = 4). We further show that tissue-nonspecific alkaline phosphatase (TNAP), an ATP-degrading enzyme, plays a key role in mediating the somnogenic effects of ATP released from astrocytes (n = 5). An appropriate sample size for all experiments was based on statistical power calculations. Our results, taken together, indicate that astrocyte-derived ATP may be hydrolyzed into adenosine by TNAP, which may in turn act on VLPO neurons to promote sleep.SIGNIFICANCE STATEMENT Glia have recently been at the forefront of neuroscience research. Emerging evidence illustrates that astrocytes, the most abundant glial cell type, are the functional determinants for fates of neurons and other glial cells in the central nervous system. In this study, we newly identified the pivotal role of hypothalamic ventrolateral preoptic (VLPO) astrocytes in the sleep regulation, and provide novel insights into the mechanisms underlying the astrocyte-mediated sleep regulation.

GABAergic ventrolateral pre‑optic nucleus neurons are involved in the mediation of the anesthetic hypnosis induced by propofol.

Intravenous anesthetics have been used clinically to induce unconsciousness for seventeen decades, however the mechanism of anesthetic-induced unconsciousness remains to be fully elucidated. It has previously been demonstrated that anesthetics exert sedative effects by acting on endogenous sleep-arousal circuits. However, few studies focus on the ventrolateral pre-optic (VLPO) to locus coeruleus (LC) sleep-arousal pathway. The present study aimed to investigate if VLPO is involved in unconsciousness induced by propofol. The present study additionally investigated if the inhibitory effect of propofol on LC neurons was mediated by activating VLPO neurons. Microinjection, target lesion and extracellular single-unit recordings were used to study the role of the VLPO-LC pathway in propofol anesthesia. The results demonstrated that GABAA agonist (THIP) or GABAA antagonist (gabazine) microinjections into VLPO altered the time of loss of righting reflex and the time of recovery of righting reflex. Furthermore, propofol suppressed the spontaneous firing activity of LC noradrenergic neurons. There was no significant difference observed in firing activity between VLPO sham lesion and VLPO lesion rats. The findings indicate that VLPO neurons are important in propofol-induced unconsciousness, however are unlikely to contribute to the inhibitory effect of propofol on LC spontaneous firing activity.

Armodafinil-induced wakefulness in animals with ventrolateral preoptic lesions.

Armodafinil is the pharmacologically active R-enantiomer of modafinil, a widely prescribed wake-promoting agent used to treat several sleep-related disorders including excessive daytime sleepiness associated with narcolepsy, shift work sleep disorder, and obstructive sleep apnea/hypopnea syndrome. Remarkably, however, the neuronal circuitry through which modafinil exerts its wake-promoting effects remains unresolved. In the present study, we sought to determine if the wake-promoting effects of armodafinil are mediated, at least in part, by inhibiting the sleep-promoting neurons of the ventrolateral preoptic (VLPO) nucleus. To do so, we measured changes in waking following intraperitoneal administration of armodafinil (200 mg/kg) or the psychostimulant methamphetamine (1 mg/kg) in rats with cell-body specific lesion of the VLPO. Rats with histologically confirmed lesions of the VLPO demonstrated a sustained increase in wakefulness at baseline, but the increase in wakefulness following administration of both armodafinil and methamphetamine was similar to that of intact animals. These data suggest that armodafinil increases wakefulness by mechanisms that extend beyond inhibition of VLPO neurons.

A Physiologically Based Model of Orexinergic Stabilization of Sleep and Wake

The orexinergic neurons of the lateral hypothalamus (Orx) are essential for regulating sleep-wake dynamics, and their loss causes narcolepsy, a disorder characterized by severe instability of sleep and wake states. However, the mechanisms through which Orx stabilize sleep and wake are not well understood. In this work, an explanation of the stabilizing effects of Orx is presented using a quantitative model of important physiological connections between Orx and the sleep-wake switch. In addition to Orx and the sleep-wake switch, which is composed of mutually inhibitory wake-active monoaminergic neurons in brainstem and hypothalamus (MA) and the sleep-active ventrolateral preoptic neurons of the hypothalamus (VLPO), the model also includes the circadian and homeostatic sleep drives. It is shown that Orx stabilizes prolonged waking episodes via its excitatory input to MA and by relaying a circadian input to MA, thus sustaining MA firing activity during the circadian day. During sleep, both Orx and MA are inhibited by the VLPO, and the subsequent reduction in Orx input to the MA indirectly stabilizes sustained sleep episodes. Simulating a loss of Orx, the model produces dynamics resembling narcolepsy, including frequent transitions between states, reduced waking arousal levels, and a normal daily amount of total sleep. The model predicts a change in sleep timing with differences in orexin levels, with higher orexin levels delaying the normal sleep episode, suggesting that individual differences in Orx signaling may contribute to chronotype. Dynamics resembling sleep inertia also emerge from the model as a gradual sleep-to-wake transition on a timescale that varies with that of Orx dynamics. The quantitative, physiologically based model developed in this work thus provides a new explanation of how Orx stabilizes prolonged episodes of sleep and wake, and makes a range of experimentally testable predictions, including a role for Orx in chronotype and sleep inertia.

Sedative and hypnotic activity of N6-(3-methoxyl-4-hydroxybenzyl) adenine riboside (B2), an adenosine analog

N6-(3-methoxyl-4-hydroxybenzyl) adenine riboside (B2) is an N6-substitued adenosine analog. Previous studies have shown that B2 binds to the adenosine A1 and A2A receptors with moderate affinity and produces protective effects on serum deprivation-induced cell damage. However, central nervous system effects of B2 have not been studied. We aimed to investigate the sedative and hypnotic effects and the mechanism of action of B2 in mice. Our behavioral studies showed that oral administration of B2 decreased spontaneous locomotor activity and potentiated the hypnotic effect of pentobarbital in mice. Sleep architecture analyses revealed that B2 decreased wakefulness and increased non-rapid eye movement (NREM) sleep in both normal mice and mice with caffeine-induced insomnia. Using immunohistochemistry, we showed that B2 increased c-Fos expression, a cellular marker for neuronal activity, in the ventrolateral preoptic (VLPO) area, a sleep center in the anterior hypothalamus. Altogether, these results indicate that oral administration of B2 produces sedative and hypnotic effects. Furthermore, the activation of VLPO neurons may be involved in the central depressant effects of B2.

Opiates, Sleep, and Pain

Opiates, Sleep, and Pain

Alpha 2-Adrenoceptor-mediated presynaptic modulation of GABAergic transmission in mechanically dissociated rat ventrolateral preoptic neurons.

The ventrolateral preoptic nucleus (VLPO) is a key nucleus involved in the homeostatic regulation of sleep-wakefulness. Little is known, however, about the cellular mechanisms underlying its role in sleep regulation and how the neurotransmitters, such as GABA and noradrenaline (NA), are involved. In the present study we investigated GABAergic transmission to acutely dissociated VLPO neurons using an enzyme-free, mechanical dissociation procedure in which functional terminals remained adherent and we investigated how this GABAergic transmission was modulated by NA. As previously reported in slices, NA hyperpolarized multipolar VLPO neurons and depolarized bipolar VLPO neurons. NA also inhibited the release of GABA onto multipolar VLPO neurons but had no effect on GABAergic transmission to bipolar neurons. The inhibition of release was mediated by presynaptic alpha(2) adrenoceptors coupled to N-ethylmaleimide (NEM)-sensitive G-proteins which appeared to act via inhibition of adenylate cyclase and subsequent decreases in protein kinase A activity. The inhibition of GABA release did not, however, involve an inhibition of external Ca(2+) influx. The results indicate that all VLPO neurons contain GABAergic inputs and that the different morphological subgroups of VLPO neurons are correlated not only to different postsynaptic responses to NA but also to different presynaptic NA responses. Furthermore our results demonstrate an additional mechanism by which NA can modulate the excitability of multipolar VLPO neurons which may have important implications for its role in regulating sleep/wakefulness.

Perchance to sleep…

Why and how do we sleep? The history of sleep research is full of stories of dedicated human researchers living in caves, and experiments on animal brainstems, but we still do not really know the answers to the fundamental questions of how and why (and therefore also why not). The latest research, however, is beginning to confirm the answer to how.From the results of in vivo animal experiments, neurons that induce the onset of sleep are thought to reside in the ventrolateral preoptic nucleus (VLPO) at the base of the forebrain1xActivation of ventrolateral preoptic neurons during sleep. Sherin, J.E. et al. Science. 1996; 271: 216–219Crossref | PubMedSee all

The Possible Role of c-fos Protein in Hypothalamus in Sleep Disturbance in Chronic Uremic Rats

Sleep disturbance is very common in patients with chronic renal failure, but its mechanism is not clear. The activity of c-fos protein (FOS) in ventrolateral preoptic neurons (VLPO) is associated with the sleep pattern. The purpose of this study was to evaluate the relationship between sleep disturbance and the expression of FOS in VLPO of chronic uremic rats. Chronic uremia was induced by the 5/6 nephrectomized model. The movements of the rats were measured with infrared monitoring during the daytime (8.00–20.00) and nighttime (20.00–8.00). Rats were killed at 10.00 or 16.00 h for the daytime (uremic rats 7, control 8) and at 22.00 h for the nighttime (uremic rats 7, control 9). The expression of FOS in VLPO was examined with the immunohistochemical method. The number of recorded daytime movements in uremic rats was significantly higher than in control rats (458 ± 185 vs. 222 ± 41, p < 0.001), but the number of recorded nighttime movements in uremic rats was lower than in control rats (949 ± 430 vs. 1,618 ± 261, p < 0.001). In the daytime, the number of FOS immunoreactive cells in uremic rats was lower than in control rats (18.4 ± 5.3 vs. 42.8 ± 6.3, p < 0.001), but there was no difference between two groups in the nighttime (10.8 ± 8.4 vs. 12.5 ± 5.1, p = 0.62). There was a strong negative correlation between the number of recorded movements and the number of FOS immunoreactive cells in VLPO (r = –0.700, p < 0.001). This finding suggests that sleep disturbances in chronic uremic rats might be related to the decreased expression of FOS in VLPO.

Activation of Ventrolateral Preoptic Neurons During Sleep

The rostral hypothalamus and adjacent basal forebrain participate in the generation of sleep, but the neuronal circuitry involved in this process remains poorly characterized. Immunocytochemistry was used to identify the FOS protein, an immediate-early gene product, in a group of ventrolateral preoptic neurons that is specifically activated during sleep. The retrograde tracer cholera toxin B, in combination with FOS immunocytochemistry, was used to show that sleep-activated ventrolateral preoptic neurons innervate the tuberomammillary nucleus, a posterior hypothalamic cell group thought to participate in the modulation of arousal. This monosynaptic pathway in the hypothalamus may play a key role in determining sleep-wake states.

HYPOTHALAMIC REGULATION OF SLEEP IN RATS. AN EXPERIMENTAL STUDY

The essential role of the nervous system in the regulation of the sleep-waking rhythm of higher animals is now widely recognized. No less a person than von Economo, however, drew attention to the fact that the phenomenon of sleep cannot be accounted for by a mere functional change of the central nervous system from its condition during the waking state. It is indeed an important fact that the function of sleep, instead of being characteristic of higher animals, is also observed in organisms which do not possess a central nervous system, and even in several vegetable species. It is therefore impossible to attribute this mysterious function to any special organ. Since all experimental work on sleep has hitherto been confined to mammals, chiefly to cats and monkeys, practically no data concerning the comparative physiology of this phenomenon are available. Nevertheless, it seems probable that during the phylogenetic development the function of sleep, together with many other mechanisms, was progressively centralized into the nervous system from which organ all changes, characteristic of sleep, were ultimately effected. This centralization proceeded so far that the alternation of wake and sleep seems to be governed in mammals by a circumscribed area of the central nervous system, capable of determining physical and psychical activities. The existence of this “centre” for the regulation of sleep is generally accepted by students of this subject.