A neural circuit for circadian regulation of arousal

Characterization of cannabinoid-1 receptors in the locus coeruleus: relationship with mu-opioid receptors

The locus coeruleus (LC)-norepinephrine system is a target of both cannabinoid and opioid actions. The present study investigated the anatomical distribution of cannabinoid-1 receptor (CB1r) in the LC and its association with mu-opioid receptor (MOR). Immunoreactivity for CB1r was localized to pre- and postsynaptic cellular profiles in the LC, 82% of which were dual-labeled for tyrosine hydroxylase (TH). Of the CB1r-immunoreactive structures, 66% were somatodendritic profiles, 22% were axon terminals, and the remaining 12% were associated with glial and small unmyelinated axon-like structures. CB1r immunoreactivity (-ir) in somatodendritic profiles was more often localized to the cytoplasm, whereas CB1r-ir located in axon terminals was more commonly localized on the plasma membrane. Somatodendritic profiles with CB1r-ir typically received input from axon terminals forming asymmetric-type synapses. In contrast, presynaptic profiles with CB1r-ir typically formed symmetric synaptic specializations. Anatomical studies confirmed the co-existence of MOR and CB1r-ir in common somatodendritic compartments of catecholaminergic neurons in the LC, and also revealed CB1r-positive axon terminals forming synaptic contact with MOR-containing dendrites. Our results provide evidence for a heterogeneous distribution of CB1r in the LC and demonstrate that CB1r and MOR co-exist in cellular profiles in this region. These data suggest important potential interactions between cannabinoid and opioid systems in LC neuronal profiles that may impact noradrenergic tone.

Halothane-induced hypnosis is not accompanied by inactivation of orexinergic output in rodents

BACKGROUND

One underexploited property of anesthetics is their ability to probe neuronal regulation of arousal. At appropriate doses, anesthetics reversibly obtund conscious perception. However, individual anesthetic agents may accomplish this by altering the function of distinct neuronal populations. Previously the authors showed that isoflurane and sevoflurane inhibit orexinergic neurons, delaying reintegration of sensory perception as denoted by emergence. Here the authors study the effects of halothane. As a halogenated alkane, halothane differs structurally, has a nonoverlapping series of molecular binding partners, and differentially modulates electrophysiologic properties of several ion channels when compared with its halogenated ether relatives.

METHODS

c-Fos immunohistochemistry and in vivo electrophysiology were used to assess neuronal activity. Anesthetic induction and emergence were determined behaviorally in narcoleptic orexin/ataxin-3 mice and control siblings exposed to halothane.

RESULTS

Halothane-induced hypnosis occurred despite lack of inhibition of orexinergic neurons in mice. In rats, extracellular single-unit recordings within the locus coeruleus showed significantly greater activity during halothane than during a comparable dose of isoflurane. Microinjection of the orexin-1 receptor antagonist SB-334867-A during the active period slowed firing rates of locus coeruleus neurons in halothane-anesthetized rats, but had no effect on isoflurane-anesthetized rats. Surprisingly, orexin/ataxin-3 transgenic mice, which develop narcolepsy with cataplexy because of loss of orexinergic neurons, did not show delayed emergence from halothane.

CONCLUSION

Coordinated inhibition of hypothalamic orexinergic and locus coeruleus noradrenergic neurons is not required for anesthetic induction. Normal emergence from halothane-induced hypnosis in orexin-deficient mice suggests that additional wake-promoting systems likely remain active during general anesthesia produced by halothane.

Development and use of a biological rhythm interview

INTRODUCTION

As several lines of evidence point to irregular biological rhythms in bipolar disorder, and its disruption may lead to new illness episodes, having an instrument that measures biological rhythms is critical. This report describes the validation of a new instrument, the Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN), designed to assess biological rhythms in the clinical setting.

METHODS

Eighty-one outpatients with a diagnosis of bipolar disorder and 79 control subjects matched for type of health service used, sex, age and educational level were consecutively recruited. After a pilot study, 18 items evaluating sleep, activities, social rhythm and eating pattern were probed for discriminant, content and construct validity, concurrent validity with the Pittsburgh Sleep Quality Index (PSQI), internal consistency and test-retest reliability.

RESULTS

A three-factor solution, termed sleep/social rhythm factor, activity factor and feeding factor, provided the best theoretical and most parsimonious account of the data; items essentially loaded in factors as theoretically intended, with the exception of the sleep and social scales, which formed a single factor. Test-retest reliability and internal consistency were excellent. Highly significant differences between the two groups were found for the whole scale and for each BRIAN factor. Total BRIAN scores were highly correlated with the global PSQI score.

DISCUSSION

The BRIAN scale presents a consistent profile of validity and reliability. Its use may help clinicians to better assess their patients and researchers to improve the evaluation of the impact of novel therapies targeting biological rhythm pathways.

Viral strategies for studying the brain, including a replication-restricted self-amplifying delta-G vesicular stomatis virus that rapidly expresses transgenes in brain and can generate a multicolor golgi-like expression

Viruses have substantial value as vehicles for transporting transgenes into neurons. Each virus has its own set of attributes for addressing neuroscience-related questions. Here we review some of the advantages and limitations of herpes, pseudorabies, rabies, adeno-associated, lentivirus, and others to study the brain. We then explore a novel recombinant vesicular stomatitis virus (dG-VSV) with the G-gene deleted and transgenes engineered into the first position of the RNA genome, which replicates only in the first brain cell infected, as corroborated with ultrastructural analysis, eliminating spread of virus. Because of its ability to replicate rapidly and to express multiple mRNA copies and additional templates for more copies, reporter gene expression is amplified substantially, over 500-fold in 6 hours, allowing detailed imaging of dendrites, dendritic spines, axons, and axon terminal fields within a few hours to a few days after inoculation. Green fluorescent protein (GFP) expression is first detected within 1 hour of inoculation. The virus generates a Golgi-like appearance in all neurons or glia of regions of the brain tested. Whole-cell patch-clamp electrophysiology, calcium digital imaging with fura-2, and time-lapse digital imaging showed that neurons appeared physiologically normal after expressing viral transgenes. The virus has a wide range of species applicability, including mouse, rat, hamster, human, and Drosophila cells. By using dG-VSV, we show efferent projections from the suprachiasmatic nucleus terminating in the periventricular region immediately dorsal to the nucleus. DG-VSVs with genes coding for different color reporters allow multicolor visualization of neurons wherever applied.

Good night and good luck: norepinephrine in sleep pharmacology

Sleep is a crucial biological process that is regulated through complex interactions between multiple brain regions and neuromodulators. As sleep disorders can have deleterious impacts on health and quality of life, a wide variety of pharmacotherapies have been developed to treat conditions of excessive wakefulness and excessive sleepiness. The neurotransmitter norepinephrine (NE), through its involvement in the ascending arousal system, impacts the efficacy of many wake- and sleep-promoting medications. Wake-promoting drugs such as amphetamine and modafinil increase extracellular levels of NE, enhancing transmission along the wake-promoting pathway. GABAergic sleep-promoting medications like benzodiazepines and benzodiazepine-like drugs that act more specifically on benzodiazepine receptors increase the activity of GABA, which inhibits NE transmission and the wake-promoting pathway. Melatonin and related compounds increase sleep by suppressing the activity of the neurons in the brain's circadian clock, and NE influences the synthesis of melatonin. Antihistamines block the wake-promoting effects of histamine, which shares reciprocal signaling with NE. Many antidepressants that affect the signaling of NE are also used for treatment of insomnia. Finally, adrenergic receptor antagonists that are used to treat cardiovascular disorders have considerable sedative effects. Therefore, NE, long known for its role in maintaining general arousal, is also a crucial player in sleep pharmacology. The purpose of this review is to consider the role of NE in the actions of wake- and sleep-promoting drugs within the framework of the brain arousal systems.

Motoneuron excitability: the importance of neuromodulatory inputs

The excitability of spinal motoneurons is both fundamental for motor behavior and essential in diagnosis of neural disorders. There are two mechanisms for altering this excitability. The classic mechanism is mediated by synaptic inputs that depolarize or hyperpolarize motoneurons by generating postsynaptic potentials. This "ionotropic" mechanism works via neurotransmitters that open ion channels in the cell membrane. In the second mechanism, neurotransmitters bind to receptors that activate intracellular signaling pathways. These pathways modulate the properties of the voltage-sensitive channels that determine the intrinsic input-output properties of motoneurons. This "neuromodulatory" mechanism usually does not directly activate motoneurons but instead dramatically alters the neuron's response to ionotropic inputs. We present extensive evidence that neuromodulatory inputs exert a much more powerful effect on motoneuron excitability than ionotropic inputs. The most potent neuromodulators are probably serotonin and norepinephrine, which are released by axons originating in the brainstem and can increase motoneuron excitability fivefold or more. Thus, the standard tests of motoneuron excitability (H-reflexes, tendon taps, tendon vibration and stretch reflexes) are strongly influenced by the level of neuromodulatory input to motoneurons. This insight is likely to be profoundly important for clinical diagnosis and treatment.

Biological rhythms, higher brain function, and behavior: Gaps, opportunities, and challenges

Increasing evidence suggests that disrupted temporal organization impairs behavior, cognition, and affect; further, disruption of circadian clock genes impairs sleep-wake cycle and social rhythms which may be implicated in mental disorders. Despite this strong evidence, a gap in understanding the neural mechanisms of this interaction obscures whether biological rhythms disturbances are the underlying causes or merely symptoms of mental disorder. Here, we review current understanding, emerging concepts, gaps, and opportunities pertinent to (1) the neurobiology of the interactions between circadian oscillators and the neural circuits subserving higher brain function and behaviors of relevance to mental health, (2) the most promising approaches to determine how biological rhythms regulate brain function and behavior under normal and pathological conditions, (3) the gaps and challenges to advancing knowledge on the link between disrupted circadian rhythms/sleep and psychiatric disorders, and (4) the novel strategies for translation of basic science discoveries in circadian biology to clinical settings to define risk, prevent or delay onset of mental illnesses, design diagnostic tools, and propose new therapeutic strategies. The review is organized around five themes pertinent to (1) the impact of molecular clocks on physiology and behavior, (2) the interactions between circadian signals and cognitive functions, (3) the interface of circadian rhythms with sleep, (4) a clinical perspective on the relationship between circadian rhythm abnormalities and affective disorders, and (5) the pre-clinical models of circadian rhythm abnormalities and mood disorders.

Light as a modulator of cognitive brain function

Humans are a diurnal species usually exposed to light while engaged in cognitive tasks. Light not only guides performance on these tasks through vision but also exerts non-visual effects that are mediated in part by recently discovered retinal ganglion cells maximally sensitive to blue light. We review recent neuroimaging studies which demonstrate that the wavelength, duration and intensity of light exposure modulate brain responses to (non-visual) cognitive tasks. These responses to light are initially observed in alertness-related subcortical structures (hypothalamus, brainstem, thalamus) and limbic areas (amygdala and hippocampus), followed by modulations of activity in cortical areas, which can ultimately affect behaviour. Light emerges as an important modulator of brain function and cognition.

Sleep and headache

There is a strong interaction between sleep and headache. Sleep and headache disorders overlap epidemiologically, and share elements of anatomy and physiology. Perhaps as a result, their treatment is often mutually interdependent. Despite this, headache and sleep disorders tend to be treated separately, by different subspecialties of neurology. The headache disorders and their relationship to sleep, the commonalities of headache and sleep pathophysiology, and headache disorders that are particularly susceptible to sleep modulation (and vice versa) are reviewed. Practical management advice for sleep-modulated headaches is provided.

Orexin neurons are necessary for the circadian control of REM sleep

STUDY OBJECTIVES

The orexin-producing neurons are hypothesized to be essential for the circadian control of sleep/wake behavior, but it remains unknown whether these rhythms are mediated by the orexin peptides or by other signaling molecules released by these neurons such as glutamate or dynorphin. To determine the roles of these neurotransmitters, we examined the circadian rhythms of sleep/wake behavior in mice lacking the orexin neurons (ataxin-3 [Atx] mice) and mice lacking just the orexin neuropeptides (orexin knockout [KO] mice).

DESIGN

We instrumented mice for recordings of sleep-wake behavior, locomotor activity (LMA), and body temperature (Tb) and recorded behavior after 6 days in constant darkness.

RESULTS

The amplitude of the rapid eye movement (REM) sleep rhythm was substantially reduced in Atx mice but preserved in orexin KO mice. This blunted rhythm in Atx mice was caused by an increase in the amount of REM sleep during the subjective night (active period) due to more transitions into REM sleep and longer REM sleep episodes. In contrast, the circadian variations of Tb, LMA, Wake, non-REM sleep, and cataplexy were normal, suggesting that the circadian timekeeping system and other output pathways are intact in both Atx and KO mice.

CONCLUSIONS

These results indicate that the orexin neurons are necessary for the circadian suppression of REM sleep. Blunting of the REM sleep rhythm in Atx mice but not in orexin KO mice suggests that other signaling molecules such as dynorphin or glutamate may act in concert with orexins to suppress REM sleep during the active period.

Paradoxical sleep deprivation: neurochemical, hormonal and behavioral alterations. Evidence from 30 years of research

Sleep comprises approximately one-third of a person's lifetime, but its impact on health and medical conditions remains partially unrecognized. The prevalence of sleep disorders is increasing in modern societies, with significant repercussions on people's well-being. This article reviews past and current literature on the paradoxical sleep deprivation method as well as data on its consequences to animals, ranging from behavioral changes to alterations in the gene expression. More specifically, we highlight relevant experimental studies and our group's contribution over the last three decades.

Developmental emergence of power-law wake behavior depends upon the functional integrity of the locus coeruleus

STUDY OBJECTIVES

Daily amounts of sleep and wakefulness are accumulated in discrete bouts that exhibit distinct statistical properties. In adult mammals, sleep bout durations follow an exponential distribution whereas wake bout durations follow a power-law distribution. In infant Norway rats, however, wake bouts initially follow an exponential distribution and only transition to a power-law distribution beginning around postnatal day 15 (P15). Here we test the hypothesis that the locus coeruleus (LC), one of several wake-active nuclei in the brainstem, contributes to this developmental transition.

DESIGN

At P7, rats were injected subcutaneously with saline or DSP-4, a neurotoxin that targets noradrenergic (NA) LC terminals. Then, at P21, sleep and wakefulness during the day and night were monitored. The effectiveness of DSP-4 treatment was verified by measuring NA, dopamine (DA), and serotonin (5-HT) concentration in cortical and non-cortical tissue using high performance liquid chromatography.

RESULTS

In relation to controls, subjects treated with DSP-4 exhibited significant reductions only in cortical and non-cortical NA concentration. Consistent with our hypothesis, the wake bout durations of DSP-4 subjects more closely followed an exponential distribution, whereas those of control subjects followed the expected power-law distribution. Sleep bout distributions were unaffected by DSP-4.

CONCLUSIONS

These results suggest that the fundamental developmental transition in the statistical structure of wake bout durations is effected in part by changes in noradrenergic LC functioning. Considered within the domain of network theory, the hub-like connectivity of the LC may have important implications for the maintenance of network function in the face of random or targeted neural degeneration.

Functional neuroanatomy of sleep and circadian rhythms

The daily sleep-wake cycle is perhaps the most dramatic overt manifestation of the circadian timing system, and this is especially true for the monophasic sleep-wake cycle of humans. Considerable recent progress has been made in elucidating the neurobiological mechanisms underlying sleep and arousal, and more generally, of circadian rhythmicity in behavioral and physiological systems. This paper broadly reviews these mechanisms from a functional neuroanatomical and neurochemical perspective, highlighting both historical and recent advances. In particular, I focus on the neural pathways underlying reciprocal interactions between the sleep-regulatory and circadian timing systems, and the functional implications of these interactions. While these two regulatory systems have often been considered in isolation, sleep-wake and circadian regulation are closely intertwined processes controlled by extensively integrated neurobiological mechanisms.

A role for sleep in brain plasticity

The idea that sleep might be involved in brain plasticity has been investigated for many years through a large number of animal and human studies, but evidence remains fragmentary. Large amounts of sleep in early life suggest that sleep may play a role in brain maturation. In particular, the influence of sleep in developing the visual system has been highlighted. The current data suggest that both Rapid Eye Movement (REM) and non-REM sleep states would be important for brain development. Such findings stress the need for optimal paediatric sleep management. In the adult brain, the role of sleep in learning and memory is emphasized by studies at behavioural, systems, cellular and molecular levels. First, sleep amounts are reported to increase following a learning task and sleep deprivation impairs task acquisition and consolidation. At the systems level, neurophysiological studies suggest possible mechanisms for the consolidation of memory traces. These imply both thalamocortical and hippocampo-neocortical networks. Similarly, neuroimaging techniques demonstrated the experience-dependent changes in cerebral activity during sleep. Finally, recent works show the modulation during sleep of cerebral protein synthesis and expression of genes involved in neuronal plasticity.

Influence of the novel antidepressant and melatonin agonist/serotonin2C receptor antagonist, agomelatine, on the rat sleep-wake cycle architecture

RATIONALE

The novel antidepressant, agomelatine, behaves as an agonist at melatonin MT(1) and MT(2) receptors and as an antagonist at serotonin (5-HT)(2C) receptors. In animal models and clinical trials, agomelatine displays antidepressant properties and re-synchronizes disrupted circadian rhythms.

OBJECTIVES

The objectives of this study were to compare the influence of agomelatine upon sleep-wake states to the selective melatonin agonists, melatonin and ramelteon, and to the selective 5-HT(2C) receptor antagonist, S32006.

METHODS

Rats were administered with vehicle, agomelatine, ramelteon, melatonin, or S32006, at the onset of either dark or light periods. Polygraphic recordings were performed and changes determined over 24 h, i.e., number and duration of sleep-wake episodes, latencies to rapid eye movement (REM) and slow-wave (SWS) sleep, power band spectra of the electroencephalogram (EEG), and circadian changes.

RESULTS

Administered at light phase onset, no changes were induced by agomelatine. In contrast, administered shortly before dark phase, agomelatine (10 and 40 mg/kg, per os) enhanced duration of REM and SWS sleep and decreased wake state for 3 h. Melatonin (10 mg/kg, per os) induced a transient enhancement in REM sleep followed by a reduction in REM and SWS sleep and an increase in waking. Ramelteon (10 mg/kg, per os) provoked a transient increase in REM sleep. Finally, S32006 (10 mg/kg, intraperitoneally), administered at dark phase onset, mimicked the increased SWS provoked by agomelatine, yet diminished REM sleep.

CONCLUSIONS

Agomelatine possesses a distinctive EEG profile compared with melatonin, ramelteon, and S32006, possibly reflecting co-joint agonist and antagonist properties at MT(1)/MT(2) and 5-HT(2C) receptors, respectively.

Local perfusion of corticosterone in the rat medial hypothalamus potentiates D-fenfluramine-induced elevations of extracellular 5-HT concentrations

The dorsomedial hypothalamus (DMH) plays an important role in coordinating physiological and behavioral responses to stress-related stimuli. In vertebrates, DMH serotonin (5-HT) concentrations increase rapidly in response to acute stressors or corticosterone (CORT). Recent studies suggest that CORT inhibits postsynaptic clearance of 5-HT from the extracellular fluid in the DMH by blocking organic cation transporter 3 (OCT3), a polyspecific CORT-sensitive transport protein. Because OCTs are low-affinity, high-capacity transporters, we hypothesized that CORT effects on extracellular 5-HT are most pronounced in the presence of elevated 5-HT release. We predicted that local application of CORT into the DMH would potentiate the effects of d-fenfluramine, a 5-HT-releasing agent, on extracellular 5-HT. These experiments were conducted using in vivo microdialysis in freely-moving male Sprague-Dawley rats implanted with a microdialysis probe into the medial hypothalamus (MH), which includes the DMH. In Experiment 1, rats simultaneously received intraperitoneal (i.p.) injections of 1 mg/kg D-fenfluramine or saline and either 200 ng/mL CORT or dilute ethanol (EtOH) vehicle delivered to the MH by reverse-dialysis for 40 min. In Experiment 2, 5 microM D-fenfluramine and either 200 ng/mL CORT or EtOH vehicle were concurrently delivered to the MH for 40 min using reverse-dialysis. CORT potentiated the increases in extracellular 5-HT concentrations induced by either i.p. or intra-MH administration of D-fenfluramine. Furthermore, CORT and D-fenfluramine interacted to alter home cage behaviors. Our results support the hypothesis that CORT inhibition of OCT3-mediated 5-HT clearance from the extracellular fluid contributes to stress-induced increases in extracellular 5-HT and 5-HT signaling.

Chronobiology and the horse: recent revelations and future directions

The circadian system provides animals with a means to adapt their internal physiology to the constantly changing environmental stimuli that exist on a rotating planet. Light information is translated into molecular timing mechanisms within pacemaker cells of the mammalian hypothalamic suprachiasmatic nucleus (SCN) via transcriptional-translational feedback loops. Humoral and neural outputs from this 'master' clock result in circadian rhythms of physiology and behaviour. The larger circadian system involves SCN synchronisation of cellular clocks throughout the organism such that individual organs can adapt their specific function to the time of day. In the short history of this scientific field, the vast majority of mammalian chronobiological research has been conducted using small laboratory animals. This review examines what these studies have revealed, discusses how recent chronobiological findings in the horse compare to what is known and highlights how the principles of circadian biology are applicable to equine husbandry and veterinary care.

Infrared thermal imaging as a physiological access pathway: a study of the baseline characteristics of facial skin temperatures

In this study we examine the baseline characteristics of facial skin temperature, as measured by dynamic infrared thermal imaging, to gauge its potential as a physiological access pathway for non-verbal individuals with severe motor impairments. Frontal facial recordings were obtained from 12 asymptomatic adults in a resting state with a high-end infrared thermal imaging system. From the infrared thermal recordings, mean skin temperature time series were generated for regions of interest encompassing the nasal, periorbital and supraorbital areas. A 90% bandwidth for all regions of interest was found to be in the 1 Hz range. Over 70% of the time series were identified as nonstationary (p<0.05), with the nonstationary mean as the greatest contributing source. Correlation coefficients between regions were significant (p<0.05) and ranged from values of 0.30 (between periorbital and supraorbital regions) to 0.75 (between contralateral supraorbital regions). Using information measures, we concluded that the greatest degree of information existed in the nasal and periorbital regions. Mutual information existed across all regions but was especially prominent between the nasal and periorbital regions. Results from this study provide insight into appropriate analysis methods and potential discriminating features for the application of facial skin temperature as a physiological access pathway.

Behavioral effects of systemic transforming growth factor-alpha in Syrian hamsters

The growth factor, transforming growth factor-alpha (TGF-alpha) is strongly expressed in the hypothalamic circadian pacemaker, the suprachiasmatic nucleus (SCN). TGF-alpha is one of several SCN peptides recently suggested to function as a circadian output signal for the regulation of locomotor activity rhythms in nocturnal rodents. When infused in the brain, TGF-alpha suppresses activity. TGF-alpha suppresses other behaviors as well including feeding, resulting in weight loss. Elevated TGF-alpha is correlated with some cancers, and it is possible the TGF-alpha and its receptor, the epidermal growth factor receptor (EGFR), mediate fatigue and weight loss associated with cancer. If true for cancers outside of the brain, then systemic TGF-alpha should also affect behavior. We tested this hypothesis in hamsters with intraperitoneal injections or week-long subcutaneous infusions of TGF-alpha. Both treatments suppressed activity and infusions caused reduced food consumption and weight loss. To identify areas of the brain that might mediate these effects of systemic TGF-alpha, we used immunohistochemistry to localize cells with an activated MAP kinase signaling pathway (phosphorylated ERK1). Cells were activated in two hypothalamic areas, the paraventricular nucleus and a narrow region surrounding the third ventricle. These sites could not only be targets of TGF-alpha produced in the SCN but could also mediate effects of elevated TGF-alpha from tumors both within and outside the central nervous system.

Circuit projection from suprachiasmatic nucleus to ventral tegmental area: a novel circadian output pathway

The suprachiasmatic nucleus (SCN) is a circadian pacemaker that synchronizes a number of vital processes. Although a great deal of research has focused on input pathways to SCN and on the central clock itself, relatively little is known about SCN output signaling pathways. The ventral tegmental area (VTA) has been extensively studied for its influence in motivated learning and, recently, for a potential role in arousal and sleep-wake regulation. Here we present data that SCN indirectly projects to VTA via the medial preoptic nucleus (MPON). Microinjection of the retrograde, transynaptic tracer pseudorabies virus (PRV) in rat VTA consistently labeled SCN neurons at time points indicative of an indirect circuit projection. To specify intermediate relay nuclei between SCN and VTA, putative relays were lesioned 1 week prior to PRV injections in VTA. Unilateral lesions of MPON reduced PRV labeling in SCN by 81.6% in the ipsilateral hemisphere and 75.8% in the contralateral hemisphere. Bilateral lesions of the caudal-dorsal lateral septum, another putative relay nucleus and dorsal injection control, did not significantly reduce PRV labeling in the SCN. Single-unit extracellular recordings under halothane anesthesia revealed a novel population of VTA neurons that selectively fired during the active circadian phase. These results show that SCN provides an indirect circuit pathway to VTA via MPON, and that VTA neurons exhibit a circadian rhythm in their impulse activity. This pathway may function in the circadian regulation of numerous behavioral processes including arousal and motivation.

Effects of cocaine, methamphetamine and modafinil challenge on sleep rebound after paradoxical sleep deprivation in rats

Sleep loss is both common and critically relevant to our society and might lead to the abuse of psychostimulants such as amphetamines, cocaine and modafinil. Since psychoactive substance abuse often occurs within a scenario of sleep deficit, the purpose of this investigation was to compare the sleep patterns of rats challenged with cocaine (7 mg/kg, ip), methamphetamine (7 mg/kg, ip), or modafinil (100 mg/kg, ip) subsequent to paradoxical sleep deprivation (PSD) for 96 h. Our results show that, immediately after 96 h of PSD, rats (10 per group) that were injected with a psychostimulant presented lower percentages of paradoxical sleep compared to those injected with saline (P < 0.01). Regarding slow wave sleep (SWS), rats injected with psychostimulants after PSD presented a late rebound (on the second night subsequent to the injection) in the percentage of this phase of sleep when compared to PSD rats injected with saline (P < 0.05). In addition, the current study has produced evidence of the characteristic effect of each drug on sleep architecture. Home cage control rats injected with modafinil and methamphetamine showed a reduction in SWS compared with the saline group. Methamphetamine affected sleep patterns most, since it significantly reduced paradoxical sleep, SWS and sleep efficiency before and after PSD compared to control (P < 0.05). Cocaine was the psychostimulant causing the least changes in sleep pattern in relation to those observed after saline injection. Therefore, our results suggest that abuse of these psychostimulants in a PSD paradigm aggravates their impact on sleep patterns.

Role of orexin input in the diurnal rhythm of locus coeruleus impulse activity

Activation of noradrenergic locus coeruleus (LC) neurons promotes wakefulness and behavioral arousal. In rats, LC neurons receive circadian inputs via a circuit that originates in the suprachiasmatic nucleus (SCN) and relays through the dorsomedial hypothalamus (DMH) to LC; this circuit input increases LC activity during the active period. DMH neurons expressing the peptide neurotransmitter orexin/hypocretin are ideally situated to act as a relay between SCN and LC due to their synaptic inputs from SCN and innervation of LC. Here, we examined the hypothesis that orexin is involved in transmitting circadian signals to LC using single-unit recordings of LC neurons in anesthetized rats maintained in 12:12 light-dark housing. We replicated earlier findings from this lab that LC neurons fire significantly faster on average during the active compared to rest periods. Local microinjection of an orexin antagonist, SB-334867-A attenuated the impulse activities of the fastest firing population of LC neurons during the active period. We also found that DMH orexin neurons project preferentially to LC and express a diurnal rhythm of activation that correlates with LC neuronal firing frequency. Therefore, we propose that DMH orexin neurons play a role in modulating the day-night differences of LC impulse activity.

Circadian distribution of generalized tonic-clonic seizures associated with murine succinic semialdehyde dehydrogenase deficiency, a disorder of GABA metabolism

Human succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disorder of GABA metabolism associated with motor impairment and epileptic seizures. Similarly, mice with targeted deletion of the Aldh5a1 gene (Aldh5a1(-/-)) exhibit SSADH deficiency and seizures early in life. These seizures begin as absence seizures the second week of life, but evolve into generalized convulsive seizures that increase in severity and become lethal during the fourth postnatal week. The seizures are alleviated and survival is prolonged when the mutant animals are weaned onto a ketogenic diet (KD). The persistence of spontaneous, recurrent, generalized tonic-clonic seizures in KD-treated adult Aldh5a1(-/-) mice allowed us to quantify their daily (circadian) distribution using a novel behavioral method based on the detection of changes in movement velocity. Adult KD-treated Aldh5a1(-/-) mice exhibited a seizure phenotype characterized by fits of wild running clonus accompanied by jumping and bouncing. These hypermotor seizures were largely spontaneous and occurred daily in a nonrandom pattern. The seizure rhythm showed a peak shortly after dark phase onset (2008 hours) with near-24-hour periodicity. Age-matched wild-type littermates showed no evidence of abnormal motor behavior. These new data suggest that generalized tonic-clonic seizures in Aldh5a1(-/-) mice are more frequent during a specific time of day and will provide useful information to clinicians for the treatment of seizures associated with human SSADH deficiency.

An endogenous circadian rhythm in sleep inertia results in greatest cognitive impairment upon awakening during the biological night

Sleep inertia is the impaired cognitive performance immediately upon awakening, which decays over tens of minutes. This phenomenon has relevance to people who need to make important decisions soon after awakening, such as on-call emergency workers. Such awakenings can occur at varied times of day or night, so the objective of the study was to determine whether or not the magnitude of sleep inertia varies according to the phase of the endogenous circadian cycle. Twelve adults (mean, 24 years; 7 men) with no medical disorders other than mild asthma were studied. Following 2 baseline days and nights, subjects underwent a forced desynchrony protocol composed of seven 28-h sleep/wake cycles, while maintaining a sleep/wakefulness ratio of 1:2 throughout. Subjects were awakened by a standardized auditory stimulus 3 times each sleep period for sleep inertia assessments. The magnitude of sleep inertia was quantified as the change in cognitive performance (number of correct additions in a 2-min serial addition test) across the first 20 min of wakefulness. Circadian phase was estimated from core body temperature (fitted temperature minimum assigned 0 degrees ). Data were segregated according to: (1) circadian phase (60 degrees bins); (2) sleep stage; and (3) 3rd of the night after which awakenings occurred (i.e., tertiary 1, 2, or 3). To control for any effect of sleep stage, the circadian rhythm of sleep inertia was initially assessed following awakenings from Stage 2 (62% of awakening occurred from this stage; n = 110). This revealed a significant circadian rhythm in the sleep inertia of cognitive performance (p = 0.007), which was 3.6 times larger during the biological night (circadian bin 300 degrees , approximately 2300-0300 h in these subjects) than during the biological day (bin 180 degrees , approximately 1500-1900 h). The circadian rhythm in sleep inertia was still present when awakenings from all sleep stages were included (p = 0.004), and this rhythm could not be explained by changes in underlying sleep drive prior to awakening (changes in sleep efficiency across circadian phase or across the tertiaries), or by the proportion of the varied sleep stages prior to awakenings. This robust endogenous circadian rhythm in sleep inertia may have important implications for people who need to be alert soon after awakening.

Circadian variation of core body temperature in Parkinson disease patients with depression: a potential biological marker for depression in Parkinson disease

BACKGROUND

The biological rhythm in comorbidity of depression and Parkinson disease (PD) is still unclear. For early diagnosis or clarification of the pathologic condition of comorbidity of depression and PD, the present study investigated the presence of circadian rhythm abnormalities in patients with depression.

METHODS

We measured the rectal temperature (RT) in 30 PD patients with or without depression during 48 consecutive hours using the maximum entropy method (MEM) and least-squares method (COSINOR). The presence of major or minor depression was evaluated by the Mini International Neuropsychiatric Interview based on the 4th edition of the Diagnostic and Statistical Manual of Mental Disorders, and the Hamilton Depression Scale.

RESULTS

The RT rhythms of patients without depression predominately showed a circadian rhythm. However, 2 of 6 patients with depression showed an infradian rhythm using MEM. COSINOR revealed that PD patients with depression showed lower amplitudes of core body temperature (p = 0.012) and higher minimum RT (p = 0.031) relative to those of patients without depression.

CONCLUSION

PD patients with depression show an altered RT circadian rhythm. The results suggest that the characteristics of core body temperature could be potentially used as a biological marker for depression in PD.

Delayed orexin signaling consolidates wakefulness and sleep: physiology and modeling

Orexin-producing neurons are clearly essential for the regulation of wakefulness and sleep because loss of these cells produces narcolepsy. However, little is understood about how these neurons dynamically interact with other wake- and sleep-regulatory nuclei to control behavioral states. Using survival analysis of wake bouts in wild-type and orexin knockout mice, we found that orexins are necessary for the maintenance of long bouts of wakefulness, but orexin deficiency has little impact on wake bouts <1 min. Since orexin neurons often begin firing several seconds before the onset of waking, this suggests a surprisingly delayed onset (>1 min) of functional effects. This delay has important implications for understanding the control of wakefulness and sleep because increasing evidence suggests that different mechanisms are involved in the production of brief and sustained wake bouts. We incorporated these findings into a mathematical model of the mouse sleep/wake network. Orexins excite monoaminergic neurons and we hypothesize that orexins increase the monoaminergic inhibition of sleep-promoting neurons in the ventrolateral preoptic nucleus. We modeled orexin effects as a time-dependent increase in the strength of inhibition from wake- to sleep-promoting populations and the resulting simulated behavior accurately reflects the fragmented sleep/wake behavior of narcolepsy and leads to several predictions. By integrating neurophysiology of the sleep/wake network with emergent properties of behavioral data, this model provides a novel framework for investigating network dynamics and mechanisms associated with normal and pathologic sleep/wake behavior.

Persistent inward currents in spinal motoneurons and their influence on human motoneuron firing patterns

Persistent inward currents (PICs) are present in many types of neurons and likely have diverse functions. In spinal motoneurons, PICs are especially strong, primarily located in dendritic regions, and subject to particularly strong neuromodulation by the monoamines serotonin and norepinephrine. Because motoneurons drive muscle fibers, it has been possible to study the functional role of their PICs in motor output and to identify PIC-mediated effects on motoneuron firing patterns in human subjects. The PIC markedly amplifies synaptic input, up to fivefold or more, depending on the level of monoaminergic input. PICs also tend to greatly prolong input time course, allowing brief inputs to initiate long-lasting self-sustained firing (i.e., bistable behavior). PIC deactivation usually requires inhibitory input and PIC amplitude can increase to repeated activation. All of these behaviors markedly increase motoneuron excitability. Thus, in the absence of monoaminergic input, motoneuron excitability is very low. Yet PICs have another effect: once active, they tend to sharply limit efficacy of additional synaptic input. All of these PIC effects have been detected in motoneuron firing patterns in human subjects and, hence, PICs are likely a fundamental component of normal motor output.

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.

Light deprivation damages monoamine neurons and produces a depressive behavioral phenotype in rats

Light is an important environmental factor for regulation of mood. There is a high frequency of seasonal affective disorder in high latitudes where light exposure is limited, and bright light therapy is a successful antidepressant treatment. We recently showed that rats kept for 6 weeks in constant darkness (DD) have anatomical and behavioral features similar to depressed patients, including dysregulation of circadian sleep-waking rhythms and impairment of the noradrenergic (NA)-locus coeruleus (LC) system. Here, we analyzed the cell viability of neural systems related to the pathophysiology of depression after DD, including NA-LC, serotoninergic-raphe nuclei and dopaminergic-ventral tegmental area neurons, and evaluated the depressive behavioral profile of light-deprived rats. We found increased apoptosis in the three aminergic systems analyzed when compared with animals maintained for 6 weeks in 12:12 light-dark conditions. The most apoptosis was observed in NA-LC neurons, associated with a significant decrease in the number of cortical NA boutons. Behaviorally, DD induced a depression-like condition as measured by increased immobility in a forced swim test (FST). DD did not appear to be stressful (no effect on adrenal or body weights) but may have sensitized responses to subsequent stressors (increased fecal number during the FST). We also found that the antidepressant desipramine decreases these neural and behavioral effects of light deprivation. These findings indicate that DD induces neural damage in monoamine brain systems and this damage is associated with a depressive behavioral phenotype. Our results suggest a mechanism whereby prolonged limited light intensity could negatively impact mood.

The 5-min pupillary alertness test is sensitive to modafinil: a placebo controlled study in patients with sleep apnea

RATIONALE

The extent of pupillary miosis during 5 min in darkness is a simple, recently introduced alertness test which may become useful in the clinical assessment of normal and pathological sleepiness.

OBJECTIVES

In this study, we further validated this test by testing its sensitivity to the effects of modafinil, a non-stimulant, alertness-promoting drug.

METHODS

Twelve unmedicated patients recently diagnosed with obstructive sleep apnea (OSA) after polysomnography, received placebo or modafinil (200 mg), according to a double-blind, cross-over design. The patients' resting pupil diameter (RPD) was sampled over 5 min in darkness before (10:00 A.M.) and after treatment (2:00 P.M.), and their light reflexes were elicited and recorded in darkness with an infrared video pupillometer.

RESULTS

We found a circadian miosis at 2:00 P.M. in the placebo treatment condition, which was reversed by modafinil. This effect correlated with modafinil-induced increase in subjective alertness, and it was greater in the most severely affected patients in terms of lowest oxygen saturation, independently of body mass index, age, or apneic episodes during sleep. Modafinil reduced the light reflex amplitude, suggesting an increase in the inhibitory input at the pupilloconstrictor Edinger-Westphal nucleus.

CONCLUSIONS

These effects of modafinil are best explained via an activation of the hypoxia-sensitive nucleus locus coeruleus. The 5-min pupillary alertness test has promising predictive validity, and it holds promise as a fast and sensitive method for the objective assessment of excessive daytime sleepiness, monitoring of disease progression, and response to treatment.

Two forces for arousal: Pitting hunger versus circadian influences and identifying neurons responsible for changes in behavioral arousal

The mechanisms underlying CNS arousal in response to homeostatic pressures are not known. In this study, we pitted two forces for CNS arousal against each other (circadian influences vs. restricted food availability) and measured the neuronal activation that occurs in a behaviorally defined group of animals that exhibited increased arousal in anticipation of feeding restricted to their normal sleeping time. The number of c-FOS+ neurons was significantly increased only in the ventromedial nucleus of the hypothalamus (VMH) in these mice, compared with control animals whose feeding was restricted to their normal active and feeding time (P < 0.01). Because the activation of VMH neurons coincides with the earliest signs of behavioral arousal preceding a change in meal time, we infer that VMH activation is involved in the increased arousal in anticipation of food.

Chronotherapeutics in a psychiatric ward

Psychiatric chronotherapeutics is the controlled exposure to environmental stimuli that act on biological rhythms in order to achieve therapeutic effects in the treatment of psychiatric conditions. In recent years some techniques (mainly light therapy and sleep deprivation) have passed the experimental developmental phase and reached the status of powerful and affordable clinical interventions for everyday clinical treatment of depressed patients. These techniques target the same brain neurotransmitter systems and the same brain areas as do antidepressant drugs, and should be administered under careful medical supervision. Their effects are rapid and transient, but can be stabilised by combining techniques among themselves or together with common drug treatments. Antidepressant chronotherapeutics target the broadly defined depressive syndrome, with response and relapse rates similar to those obtained with antidepressant drugs, and good results are obtained even in difficult-to-treat conditions such as bipolar depression. Chronotherapeutics offer a benign alternative to more radical treatments of depression for the treatment of severe depression in psychiatric wards, but with the advantage of rapidity of onset.

Brain responses to violet, blue, and green monochromatic light exposures in humans: prominent role of blue light and the brainstem

Background

Relatively long duration retinal light exposure elicits nonvisual responses in humans, including modulation of alertness and cognition. These responses are thought to be mediated in part by melanopsin-expressing retinal ganglion cells which are more sensitive to blue light than violet or green light. The contribution of the melanopsin system and the brain mechanisms involved in the establishment of such responses to light remain to be established.

Methodology/Principal Findings

We exposed 15 participants to short duration (50 s) monochromatic violet (430 nm), blue (473 nm), and green (527 nm) light exposures of equal photon flux (10¹³ph/cm²/s) while they were performing a working memory task in fMRI. At light onset, blue light, as compared to green light, increased activity in the left hippocampus, left thalamus, and right amygdala. During the task, blue light, as compared to violet light, increased activity in the left middle frontal gyrus, left thalamus and a bilateral area of the brainstem consistent with activation of the locus coeruleus.

Conclusion/Significance

These results support a prominent contribution of melanopsin-expressing retinal ganglion cells to brain responses to light within the very first seconds of an exposure. The results also demonstrate the implication of the brainstem in mediating these responses in humans and speak for a broad involvement of light in the regulation of brain function.

Knockdown of clock genes in the suprachiasmatic nucleus blocks prolactin surges and alters FRA expression in the locus coeruleus of female rats

The nature of the circadian signal from the suprachiasmatic nucleus (SCN) required for prolactin (PRL) surges is unknown. Because the SCN neuronal circadian rhythm is determined by a feedback loop of Period (Per) 1, Per2, and circadian locomotor output cycles kaput (Clock) gene expressions, we investigated the effect of SCN rhythmicity on PRL surges by disrupting this loop. Because lesion of the locus coeruleus (LC) abolishes PRL surges and these neurons receive SCN projections, we investigated the role of SCN rhythmicity in the LC neuronal circadian rhythm as a possible component of the circadian mechanism regulating PRL surges. Cycling rats on proestrous day and estradiol-treated ovariectomized rats received injections of antisense or random-sequence deoxyoligonucleotide cocktails for clock genes (Per1, Per2, and Clock) in the SCN, and blood samples were taken for PRL measurements. The percentage of tyrosine hydroxylase-positive neurons immunoreactive to Fos-related antigen (FRA) was determined in ovariectomized rats submitted to the cocktail injections and in a 12:12-h light:dark (LD) or constant dark (DD) environment. The antisense cocktail abolished both the proestrous and the estradiol-induced PRL surges observed in the afternoon and the increase of FRA expression in the LC neurons at Zeitgeber time 14 in LD and at circadian time 14 in DD. Because SCN afferents and efferents were probably preserved, the SCN rhythmicity is essential for the magnitude of daily PRL surges in female rats as well as for LC neuronal circadian rhythm. SCN neurons therefore determine PRL secretory surges, possibly by modulating LC circadian neuronal activity.

Organization of cell and tissue circadian pacemakers: a comparison among species

In most animal species, a circadian timing system has evolved as a strategy to cope with 24-hour rhythms in the environment. Circadian pacemakers are essential elements of the timing system and have been identified in anatomically discrete locations in animals ranging from insects to mammals. Rhythm generation occurs in single pacemaker neurons and is based on the interacting negative and positive molecular feedback loops. Rhythmicity in behavior and physiology is regulated by neuronal networks in which synchronization or coupling is required to produce coherent output signals. Coupling occurs among individual clock cells within an oscillating tissue, among functionally distinct subregions within the pacemaker, and between central pacemakers and the periphery. Recent evidence indicates that peripheral tissues can influence central pacemakers and contain autonomous circadian oscillators that contribute to the regulation of overt rhythmicity. The data discussed in this review describe coupling and synchronization mechanisms at the cell and tissue levels. By comparing the pacemaker systems of several multicellular animal species (Drosophila, cockroaches, crickets, snails, zebrafish and mammals), we will explore general organizational principles by which the circadian system regulates a 24-hour rhythmicity.

Active properties of motoneurone dendrites: diffuse descending neuromodulation, focused local inhibition

The dendrites of spinal motoneurones are highly active, generating a strong persistent inward current (PIC) that has an enormous impact on processing of synaptic input. The PIC is subject to regulation by descending neuromodulatory systems releasing the monoamines serotonin and noradrenaline. At high monoaminergic drive levels, the PIC dominates synaptic integration, generating an intrinsic dendritic current that is as much as 5-fold larger than the current entering via synapses. Without the PIC, motoneurone excitability is very low. Presumably, this descending control of the synaptic integration via the PIC is used to adjust the excitability (gain) of motoneurones for different motor tasks. A problem with this gain control is that monoaminergic input to the cord is very diffuse, affecting many motor pools simultaneously, probably including both agonists and antagonists. The PIC is, however, exquisitely sensitive to the reciprocal inhibition mediated by length sensitive muscle spindle Ia afferents and Ia interneurones. Reciprocal inhibition is tightly focused, shared only between strict mechanical antagonists, and thus can act to 'sculpt' specific movement patterns out of a background of diffuse neuromodulation. Thus it is likely that motoneurone gain is set by the interaction between diffuse descending neuromodulation and specific and focused local synaptic inhibitory circuits.

Selective loss of catecholaminergic wake active neurons in a murine sleep apnea model

The presence of refractory wake impairments in many individuals with severe sleep apnea led us to hypothesize that the hypoxia/reoxygenation events in sleep apnea permanently damage wake-active neurons. We now confirm that long-term exposure to hypoxia/reoxygenation in adult mice results in irreversible wake impairments. Functionality and injury were next assessed in major wake-active neural groups. Hypoxia/reoxygenation exposure for 8 weeks resulted in vacuolization in the perikarya and dendrites and markedly impaired c-fos activation response to enforced wakefulness in both noradrenergic locus ceruleus and dopaminergic ventral periaqueductal gray wake neurons. In contrast, cholinergic, histaminergic, orexinergic, and serotonergic wake neurons appeared unperturbed. Six month exposure to hypoxia/reoxygenation resulted in a 40% loss of catecholaminergic wake neurons. Having previously identified NADPH oxidase as a major contributor to wake impairments in hypoxia/reoxygenation, the role of NADPH oxidase in catecholaminergic vulnerability was next addressed. NADPH oxidase catalytic and cytosolic subunits were evident in catecholaminergic wake neurons, where hypoxia/reoxygenation resulted in translocation of p67(phox) to mitochondria, endoplasmic reticulum, and membranes. Treatment with a NADPH oxidase inhibitor, apocynin, throughout hypoxia/reoxygenation exposures conferred protection of catecholaminergic neurons. Collectively, these data show that select wake neurons, specifically the two catecholaminergic groups, can be rendered persistently impaired after long-term exposure to hypoxia/reoxygenation, modeling sleep apnea; wake impairments are irreversible; catecholaminergic neurons are lost; and neuronal NADPH oxidase contributes to this injury. It is anticipated that severe obstructive sleep apnea in humans destroys catecholaminergic wake neurons.

The role of organic cation transporter-3 in methamphetamine disposition and its behavioral response in rats

Organic cation transporter-3 (OCT3) is expressed in several tissues including the brain. We have previously demonstrated that rats with behavioral sensitization to methamphetamine (METH) increased the brain penetration of METH with decreased expression of OCT3 in brain. Considering the earlier in vitro studies demonstrating that 1) OCT3 could transport dopamine (DA) and 2) the specific transport via OCT3 could be inhibited by METH, these results suggest that decreased OCT3 might decrease the efflux of METH and/or DA from brain, subsequently causing the development of behavioral sensitization. Thus, in the present study, behavioral task related to DA and pharmacokinetic experiment were performed using rats treated with antisense against OCT3 (OCT3-AS) since no specific ligands for OCT3 are still available. The continuous infusion of OCT3-AS into the third ventricle significantly decreased the expression of OCT3 in choroid plexus (CP) epithelial cells. Both METH-induced hyperlocomotion and METH-induced extracellular DA levels in nucleus accumbens and prefrontal cortex were significantly increased in OCT3-AS-treated rats. Moreover, the concentrations of METH were significantly increased in cerebrospinal fluid as well as extracellular areas at the nucleus accumbens in OCT3-AS-treated rats. These results suggested that decreased OCT3 elevated the concentration of METH and/or DA in brain, subsequently enhancing dopaminergic neuronal transmission and increasing METH-induced hyperlocomotion. In summary, OCT3 at the CP could regulate the effect of METH by controlling the levels of METH and/or DA in brain. Thus, these results suggest that OCT3 may be a new molecular target to treat METH-related disorders such as drug abuse and schizophrenia.

Effects of kappa opioid receptor agonists on attention as assessed by a 5-choice serial reaction time task in rats

In humans, kappa opioid receptor agonists produce, among other effects, sedation and difficulty concentrating, suggesting that they may disrupt attention. The purpose of the present studies was therefore to evaluate the effects of kappa opioid receptor agonists on attention as assessed by a 5-choice serial reaction time task in rats. The kappa opioid receptor agonists (+)-U69,593 (0.1-0.56mg/kg), (+/-)-U50,488 (1.0-5.6mg/kg) and racemic GR89,696 (0.0003-0.01mg/kg) all produced dose-related decreases in the percentage of trials terminated by a correct or incorrect response and increases in the percentage of omissions. In contrast, the peripherally restricted opioid agonist ICI-204,448 was ineffective (1.0-10mg/kg). Moreover, the effects of GR89,696 were stereoselective in that (R)-GR89,696 was approximately equipotent to racemic GR89,696 and approximately 100-fold more potent than (S)-GR89,696. The opioid receptor antagonist naltrexone (0.3-3mg/kg) administered alone had no effects on performance. However, naltrexone, over the dose-range of 0.03-1.0mg/kg, produced a dose-related antagonism of the disruption produced by U69,593 (0.56mg/kg). In contrast, naltrexone, over the dose-range of 0.01-0.3mg/kg produced a dose-related antagonism of morphine (5.6mg/kg). Recent evidence has suggested that kappa opioid receptor agonists decrease dopaminergic and noradrenergic neurotransmission in prefrontal cortex and locus coeruleus. Together with previous findings, the present data indicate that kappa opioid receptor agonists disrupt performance of this attention task by decreasing the probability of responding by specific actions at central kappa opioid receptors, perhaps by decreasing dopaminergic and noradrenergic neurotransmission.

Allergic lung inflammation affects central noradrenergic control of cholinergic outflow to the airways in ferrets

Brain stem noradrenergic cell groups mediating autonomic responses to stress project to airway-related vagal preganglionic neurons (AVPNs). In ferrets, their activation produces withdrawal of cholinergic outflow to the airways via release of norepinephrine and activation of alpha(2A)-adrenergic receptors (alpha(2A)-AR) expressed by AVPNs. In these studies, we examined the effects of allergen exposure of the airway (AE) with ovalbumin on noradrenergic transmission regulating the activity of AVPNs and, consequently, airway smooth muscle tone. Experiments were performed in vehicle control (Con) and AE ferrets. Microperfusion of an alpha(2A)-AR agonist (guanabenz) in close proximity to AVPNs elicited more pronounced effects in Con than AE ferrets, including a decrease in unit activity and reflexly evoked responses of putative AVPN neurons with a corresponding decrease in cholinergic outflow to the airways. Although no differences were found in the extent of noradrenergic innervation of the AVPNs, RT-PCR and Western blot studies demonstrated that AE and repeated exposure to antigen significantly reduced expression of alpha(2A)-ARs at message and protein levels. These findings indicate that, in an animal model of allergic asthma, sensitization and repeated challenges with a specific allergen diminish central inhibitory noradrenergic modulation of AVPNs, possibly via downregulation of alpha(2A)-AR expression by these neurons.

Challenging the omnipotence of the suprachiasmatic timekeeper: are circadian oscillators present throughout the mammalian brain?

The suprachiasmatic nucleus of the hypothalamus (SCN) is the master circadian pacemaker or clock in the mammalian brain. Canonical theory holds that the output from this single, dominant clock is responsible for driving most daily rhythms in physiology and behaviour. However, important recent findings challenge this uniclock model and reveal clock-like activities in many neural and non-neural tissues. Thus, in addition to the SCN, a number of areas of the mammalian brain including the olfactory bulb, amygdala, lateral habenula and a variety of nuclei in the hypothalamus, express circadian rhythms in core clock gene expression, hormone output and electrical activity. This review examines the evidence for extra-SCN circadian oscillators in the mammalian brain and highlights some of the essential properties and key differences between brain oscillators. The demonstration of neural pacemakers outside the SCN has wide-ranging implications for models of the circadian system at a whole-organism level.

Clinical and neurobiological aspects of narcolepsy

Narcolepsy is characterized by excessive daytime sleepiness (EDS), cataplexy and/or other dissociated manifestations of rapid eye movement (REM) sleep (hypnagogic hallucinations and sleep paralysis). Narcolepsy is currently treated with amphetamine-like central nervous system (CNS) stimulants (for EDS) and antidepressants (for cataplexy). Some other classes of compounds such as modafinil (a non-amphetamine wake-promoting compound for EDS) and gamma-hydroxybutyrate (GHB, a short-acting sedative for EDS/fragmented nighttime sleep and cataplexy) given at night are also employed. The major pathophysiology of human narcolepsy has been recently elucidated based on the discovery of narcolepsy genes in animals. Using forward (i.e., positional cloning in canine narcolepsy) and reverse (i.e., mouse gene knockout) genetics, the genes involved in the pathogenesis of narcolepsy (hypocretin/orexin ligand and its receptor) in animals have been identified. Hypocretins/orexins are novel hypothalamic neuropeptides also involved in various hypothalamic functions such as energy homeostasis and neuroendocrine functions. Mutations in hypocretin-related genes are rare in humans, but hypocretin-ligand deficiency is found in many narcolepsy-cataplexy cases. In this review, the clinical, pathophysiological and pharmacological aspects of narcolepsy are discussed.