Sleep induction and temperature lowering by medial preoptic α1 adrenergic receptors

Galanin neurons in the ventrolateral preoptic area promote sleep and heat loss in mice

The preoptic area (POA) is necessary for sleep, but the fundamental POA circuits have remained elusive. Previous studies showed that galanin (GAL)- and GABA-producing neurons in the ventrolateral preoptic nucleus (VLPO) express cFos after periods of increased sleep and innervate key wake-promoting regions. Although lesions in this region can produce insomnia, high frequency photostimulation of the POA^GAL neurons was shown to paradoxically cause waking, not sleep. Here we report that photostimulation of VLPO^GAL neurons in mice promotes sleep with low frequency stimulation (1-4 Hz), but causes conduction block and waking at frequencies above 8 Hz. Further, optogenetic inhibition reduces sleep. Chemogenetic activation of VLPO^GAL neurons confirms the increase in sleep, and also reduces body temperature. In addition, chemogenetic activation of VLPO^GAL neurons induces short-latency sleep in an animal model of insomnia. Collectively, these findings establish a causal role of VLPO^GAL neurons in both sleep induction and heat loss.

Hypothalamic or Extrahypothalamic Modulation and Targeted Temperature Management After Brain Injury

Targeted temperature management (TTM) has been recognized to protect tissue function and positively influence neurological outcomes after brain injury. While shivering during hypothermia nullifies the beneficial effect of TTM, traditionally, antishivering drugs or paralyzing agents have been used to reduce the shivering. The hypothalamic area of the brain helps in controlling cerebral temperature and body temperature through interactions between different brain areas. Thus, modulation of different brain areas either pharmacologically or by electrical stimulation may contribute in TTM; although, very few studies have shown that TTM might be achieved by activation and inhibition of neurons in the hypothalamic region. Recent studies have investigated potential pharmacological methods of inducing hypothermia for TTM by aiming to maintain the TTM and reduce the shivering effect without using antiparalytic drugs. Better survival and neurological outcome after brain injury have been reported after pharmacologically induced TTM. This review discusses the mechanisms and modulation of the hypothalamus with other brain areas that are involved in inducing hypothermia through which TTM may be achieved and provides therapeutic strategies for TTM after brain injury.

Role of dorsal vagal complex A2 noradrenergic neurons in hindbrain glucoprivic inhibition of the luteinizing hormone surge in the steroid-primed ovariectomized female rat: effects of 5-thioglucose on A2 functional biomarker and AMPK activity

Neuro-glucostasis is required for normal expression of the steroid positive-feedback-induced preovulatory pituitary luteinizing hormone (LH) surge, a critical element of female reproduction. Glucoprivic signals from the caudal hindbrain restrain this surge, but the cellular source of this stimulus is unclear. Norepinephrine (NE) exerts well-defined stimulatory effects on the reproductive neuroendocrine axis. Our studies show that medullary A2 noradrenergic neurons are both estrogen- and glucoprivic-sensitive. Here, we investigated the premise that the LH surge is inhibited by A2 cell reactivity to hindbrain glucopenia and diminished preoptic NE neurotransmission. Estradiol- and progesterone-primed ovariectomized (OVX) female rats were injected into the caudal fourth ventricle (CV4) with the glucose anti-metabolite, 5-thioglucose (5TG) or saline (SAL) prior to onset of the LH surge. Pretreatment by intra-CV4 delivery of the selective catecholamine neurotoxin, 6-OHDA, attenuated LH output, but prevented inhibition by 5TG. 5TG modified patterns of steroid feedback-associated Fos staining of A2, but not other medullary catecholamine cell groups. Intra-preoptic administration of the alpha₁-adrenergic receptor agonist, methoxamine, elicited site-specific reversal of hindbrain glucoprivic suppression of gonadotropin-releasing hormone (GnRH) neuron Fos labeling and LH release. Western blotting of laser-microdissected A2 neurons revealed glucoprivic stimulation of Fos, but inhibition of the catecholamine synthetic enzyme, dopamine-β-hydroxylase; 5TG also diminished A2 estrogen receptor (ER)-α and progesterone receptor profiles, but augmented ER-β protein. Intriguingly, A2 AMPK activity was decreased in 5TG-treated rats, despite down-regulation of GLUT3 and no change in MCT2 protein expression. Rostral preoptic GnRH neurons also exhibited decreased AMPK activation simultaneous with apparent reduction of neuropeptide signaling to the pituitary. The present studies demonstrate that hindbrain glucoprivation inhibits the LH surge, in part, by reducing preoptic noradrenergic input, and furthermore implicate A2 neurons as a source of this altered signal. Results also suggest that AMPK sensor deactivation does not supersede the impact of pharmacological inhibition of glucose catabolism on A2 cell function nor afferent signaling of hindbrain glucopenia on GnRH neurons. Further studies are needed to determine if decreased AMPK activation in these cell populations reflect compensatory gain in positive energy balance and/or direct effects of estrogen on AMPK.

Metabolic activity in the insular cortex and hypothalamus predicts hot flashes: an FDG-PET study

CONTEXT

Hot flashes are a common side effect of adjuvant endocrine therapies (AET; leuprolide, tamoxifen, aromatase inhibitors) that reduce quality of life and treatment adherence in breast cancer patients. Because hot flashes affect only some women, preexisting neurobiological traits might predispose to their development. Previous studies have implicated the insula during the perception of hot flashes and the hypothalamus in thermoregulatory dysfunction.

OBJECTIVE

The aim of the study was to understand whether neurobiological factors predict hot flashes.

DESIGN

[18F]-Fluorodeoxyglucose (FDG) positron emission tomography (PET) brain scans coregistered with structural magnetic resonance imaging were used to determine whether metabolic activity in the insula and hypothalamic thermoregulatory and estrogen-feedback regions measured before and in response to AET predict hot flashes. Findings were correlated with CYP2D6 genotype because of CYP2D6 polymorphism associations with tamoxifen-induced hot flashes.

OUTCOME MEASURES

We measured regional cerebral metabolic rate of glucose uptake (rCMRglu) in the insula and hypothalamus on FDG-PET.

RESULTS

Of 18 women without hot flashes who began AET, new-onset hot flashes were reported by 10 (55.6%) and were detected objectively in nine (50%) participants. Prior to the use of all AET, rCMRglu in the insula (P ≤ 0.01) and hypothalamic thermoregulatory (P = 0.045) and estrogen-feedback (P = 0.007) regions was lower in women who reported developing hot flashes. In response to AET, rCMRglu was further reduced in the insula in women developing hot flashes (P ≤ 0.02). Insular and hypothalamic rCMRglu levels were lower in intermediate than extensive CYP2D6 metabolizers.

CONCLUSIONS

Trait neurobiological characteristics predict hot flashes. Genetic variability in CYP2D6 may underlie the neurobiological predisposition to hot flashes induced by AET.

Noradrenergic modulation of wakefulness/arousal

The locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. State-dependent neuronal discharge activity of locus coeruleus noradrenergic neurons has long-suggested a role of this system in the induction of an alert waking state. Work over the past two decades provides unambiguous evidence that the locus coeruleus, and likely other noradrenergic nuclei, exert potent wake-promoting actions via an activation of noradrenergic β- and α₁-receptors located within multiple subcortical structures, including the general regions of the medial septal area, the medial preoptic area and, most recently, the lateral hypothalamus. Conversely, global blockade of β- and α₁-receptors or suppression of norepinephrine release results in profound sedation. The wake-promoting action of central noradrenergic neurotransmission has clinical implications for treatment of sleep/arousal disorders, such as insomnia and narcolepsy, and clinical conditions associated with excessive arousal, such as post-traumatic stress disorder.

c-Fos expression in neurons projecting from the preoptic and lateral hypothalamic areas to the ventrolateral periaqueductal gray in relation to sleep states

The ventrolateral division of the periaqueductal gray (vlPAG) and the adjacent deep mesencephalic reticular nucleus have been implicated in the control of sleep. The preoptic hypothalamus, which contains populations of sleep-active neurons, is an important source of afferents to the vlPAG. The perifornical lateral hypothalamus (LH) contains populations of wake-active neurons and also projects strongly to the vlPAG. We examined nonREM and REM sleep-dependent expression of c-Fos protein in preoptic-vlPAG and LH-vlPAG projection neurons identified by retrograde labeling with Fluorogold (FG). Separate groups of rats (n=5) were subjected to 3 h total sleep deprivation (TSD) followed by 1 h recovery sleep (RS), or to 3 h of selective REM sleep deprivation (RSD) followed by RS. A third group of rats (n=5) was subjected to TSD without opportunity for RS (awake group). In the median preoptic nucleus (MnPN), the percentage of FG+ neurons that were also Fos+ was higher in TSD-RS animals compared to both RSD-RS rats and awake rats. There were significant correlations between time spent in deep nonREM sleep during the 1 h prior to sacrifice across groups and the percentage of double-labeled cells in MnPN and ventrolateral preoptic area (VLPO). There were no significant correlations between percentage of double-labeled neurons and time spent in REM sleep for any of the preoptic nuclei examined. In the LH, percentage of double-labeled neurons was highest in awake rats, intermediate in TSD-RS rats and lowest in the RSD-RS group. These results suggest that neurons projecting from MnPN and VLPO to the vlPAG are activated during nonREM sleep and support the hypothesis that preoptic neurons provide inhibitory input to vlPAG during sleep. Suppression of excitatory input to the vlPAG from the LH during sleep may have a permissive effect on REM sleep generation.

Leptin-sensitive neurons in mouse preoptic area express alpha 1A- and alpha 2A-adrenergic receptor isoforms

Leptin binding to its functional receptor stimulates the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signalling pathway, finally resulting in nuclear translocation of the phosphorylated STAT3 (P-STAT3). Systemic treatment with leptin (3mg/kg; intraperitoneal injection) induced the appearance of P-STAT3-immunoreactive cells in adult mouse preoptic area (POA). Here we show that the vast majority of leptin-responsive cells were located in medial POA (mPOA), followed by the median preoptic nucleus. Rare, scattered and weakly stained cells were found in ventromedial preoptic nucleus and lateral preoptic area. Co-localization studies disclosed that mPOA leptin-responsive cells were neurons, and that a large proportion expressed the alpha(1A)- and/or alpha(2A)-adrenergic receptor (AR) isoforms. Although understanding the functional relevance of leptin-responsive POA neurons requires further investigation, the finding that they bear alpha-ARs suggests that they may be targeted by the ascending noradrenergic system, which densely innervates the mPOA, and thus be involved in thermoregulation, arousal and/or the sleep-wake cycle.

Heat loss responses and blockade of prostaglandin E2-induced thermogenesis elicited by alpha1-adrenergic activation in the rostromedial preoptic area

The unilateral microinjection of noradrenaline (NA), but not vehicle solution, into the rostromedial preoptic area (POA) elicited simultaneous increases in cutaneous temperatures of the tail and sole of the foot and decreases in the whole-body O(2) consumption rate, heart rate, and colonic temperature in urethane-chloralose-anesthetized rats, suggesting a coordinate increase in heat loss and decrease in heat production. The magnitude of these responses increased dose-dependently over the range of 1-100 pmol, except for the metabolic and bradycardic responses. Similar hypothermic responses were elicited by the microinjection of 40 pmol methoxamine (an alpha(1)-adrenergic agonist), but not by that of clonidine (an alpha(2)-agonist) or isoproterenol (a beta-agonist). Sites at which microinjection of NA elicited hypothermic responses were in the vicinity of the organum vasculosum of the lamina terminalis including the median preoptic nucleus, whereas no thermal or metabolic response was elicited when NA was microinjected into the lateral POA or caudal part of the medial POA. The microinjection of 130 fmol prostaglandin (PG) E(2) into the NA-sensitive site always elicited thermogenic, tachycardic, and hyperthermic responses. Furthermore, the PGE(2)-induced febrile responses were greatly attenuated by prior administration of NA at the same site. These results demonstrate that NA in the rostromedial POA exerts alpha(1)-adrenoceptor-mediated hypothermic effects and opposes PGE(2)-induced fever.

Noradrenergic modulation of arousal

Through a highly divergent efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. State-dependent neuronal discharge activity of locus coeruleus neurons has long-suggested a role of this system in the induction of an alert waking state. More recent work supports this hypothesis, demonstrating robust wake-promoting actions of the locus coeruleus-noradrenergic system. Norepinephrine enhances arousal, in part, via actions of beta- and alpha1-receptors located within multiple subcortical structures, including the general regions of the medial septal area and the medial preoptic areas. Recent anatomical studies suggest that arousal-enhancing actions of norepinephrine are not limited to the locus coeruleus system and likely include the A1 and A2 noradrenergic cell groups. Thus, noradrenergic modulation of arousal state involves multiple noradrenergic systems acting within multiple subcortical regions. Pharmacological studies indicate that the combined actions of these systems are necessary for the sustained maintenance of arousal levels associated with spontaneous waking. Enhanced arousal state is a prominent aspect of both stress and psychostimulant drug action and evidence indicates that noradrenergic systems likely play an important role in both stress-related and psychostimulant-induced arousal. These and other observations suggest that the dysregulation of noradrenergic neurotransmission could well contribute to the dysregulation of arousal associated with a variety of behavioral disorders including insomnia and stress-related disorders.

Alpha-1 adrenergic receptors in the medial preoptic area are involved in the induction of sleep

This paper reviews the recent studies that led to the conclusion that the noradrenergic neurons projecting to the medial preoptic area (mPOA) are hypnogenic and that they mediate this action through alpha(1) adrenergic receptors. Microinjection of noradrenaline (NA) into the mPOA induced arousal. Studies using alpha(2) adrenergic drugs showed that the arousal induced by intrapreoptic injection of NA was due to its action on presynaptic alpha(2) adrenergic receptors. A combination of lesion and chemical stimulation techniques demonstrated that when NA acted on the postsynaptic alpha(1 )receptors in the mPOA, it induced sleep. Intrapreoptic injection of alpha(1) agonist, methoxamine could induce sleep, when the hypothermia, which was simultaneously produced, was behaviorally compensated for by the animal. Increased arousal produced by the destruction of noradrenergic fibers in the mPOA further confirmed the hypnogenic role of these fibers.