Emotions, stress, hunger, and circadian rhythms all promote wakefulness and behavioral arousal. Little is known about the pathways mediating these influences, but the orexin-producing neurons of the hypothalamus may play an essential role. These cells heavily innervate many wake-promoting brain regions, and mice lacking the orexin neurons have narcolepsy and fail to rouse in response to hunger (Yamanaka et al. [2003] Neuron 38:701-713). To identify the afferents to the orexin neurons, we first injected a retrograde tracer into the orexin neuron field of rats. Retrogradely labeled neurons were abundant in the allocortex, claustrum, lateral septum, bed nucleus of the stria terminalis, and in many hypothalamic regions including the preoptic area, dorsomedial nucleus, lateral hypothalamus, and posterior hypothalamus. Retrograde labeling in the brainstem was generally more modest, but labeling was strong in the periaqueductal gray matter, dorsal raphe nucleus, and lateral parabrachial nucleus. Injection of an anterograde tracer confirmed that most of these regions directly innervate the orexin neurons, with some of the heaviest input coming from the lateral septum, preoptic area, and posterior hypothalamus. In addition, hypothalamic regions preferentially innervate orexin neurons in the medial and perifornical parts of the field, but most projections from the brainstem target the lateral part of the field. Inputs from the suprachiasmatic nucleus are mainly relayed via the subparaventricular zone and dorsomedial nucleus. These observations suggest that the orexin neurons may integrate a variety of interoceptive and homeostatic signals to increase behavioral arousal in response to hunger, stress, circadian signals, and autonomic challenges.
Narcolepsy is caused by a lack of orexin (hypocretin), but the physiologic process that underlies the sleepiness of narcolepsy is unknown. Using orexin knock-out (KO) mice as a model of narcolepsy, we critically tested the three leading hypotheses: poor circadian control of sleep and wakefulness, inadequate activation of arousal regions, or abnormal sleep homeostasis. Compared with wild-type (WT) littermates, orexin KO mice had essentially normal amounts of sleep and wake, but wake and non-rapid eye movement (NREM) bouts were very brief, with many more transitions between all behavioral states. In constant darkness, orexin KO mice had normal amplitude and timing of sleep-wake rhythms, providing no evidence for disordered circadian control. When placed in a new, clean cage, both groups of mice remained awake for ϳ45 min, demonstrating that, even in the absence of orexin, fundamental arousal regions can be engaged to produce sustained wakefulness. After depriving mice of sleep for 2-8 hr, orexin KO mice recovered their NREM and rapid eye movement sleep deficits at comparable rates and to the same extent as WT mice, with similar increases in EEG delta power, suggesting that their homeostatic control of sleep is normal. These experiments demonstrate that the fragmented wakefulness of orexin deficiency is not a consequence of abnormal sleep homeostasis, poor circadian control, or defective fundamental arousal systems. Instead, the fragmented behavior of orexin KO mice may be best described as behavioral state instability, with apparently low thresholds to transition between states.
BackgroundTrials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to determine if daily fluoxetine for 6 months after stroke improves functional outcome in Australasian and Vietnamese patients. MethodsAFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial conducted in 43 hospital stroke units in Australia (n=29), New Zealand (4), and Vietnam (10). Eligible patients were adults with a clinical diagnosis of stroke in the previous 2-15 days and a persisting neurological deficit. Patients were randomised via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20mg or matching placebo for 6 months. Patients, investigators and outcome assessors were masked to the treatment allocation. The primary outcome was functional outcome, measured by the modified Rankin scale (mRS), at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Analyses were according to the patient's treatment allocation. The trial is registered with the ACTRN registry, number 12611000774921. FindingsPowered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation 1280 patients were recruited in Australia (n=532), New Zealand (n=42) and Vietnam (n=706) between 11 January 2013 and 30 June 2019; 642 were allocated fluoxetine and 638 placebo. Adherence to trial medication (mean 167 [SD 48] days) was similar between groups. At 6 months, mRS data were available in 624 (97.2%) patients allocated fluoxetine and 632 (99.1%) placebo. The distribution of mRS categories at 6 months was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0.936, 95% CI 0.762-1.150; p=0.53), and consistent among all pre-defined subgroups. Compared to placebo, patients allocated fluoxetine had more falls (20 [3.12%] vs 7 [1.10%]; p=0.02), bone fractures (19 [2•96%] vs 6 [0.94%]; p=0.01) and epileptic seizures (10 [1.56%] vs 2 [0.31%]; p=0.04) at 6 months. InterpretationFluoxetine 20mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and seizures. These results do not support the use of fluoxetine to improve outcome after stroke.
CollaborationIMPORTANCE One in 3 adults experiences clinically significant symptoms of depression during the first year after a stroke, but evidence to support the use of antidepressants in this population remains scant.OBJECTIVE To investigate whether daily treatment with 20 mg of fluoxetine hydrochloride reduces the proportion of people affected by clinically significant symptoms of depression after stroke. DESIGN, SETTING, AND PARTICIPANTSIn this secondary analysis of the Assessment of Fluoxetine in Stroke Recovery parallel-group, randomized (1:1 assignment), double-blind, placebo-controlled clinical trial, 1221 participants in Australia, New Zealand, and Vietnam were recruited between January 11, 2013, and June 30, 2019, and were followed up for 6 months. Adults aged 18 years or older were recruited 2 to 15 days after experiencing a stroke associated with modified Rankin Scale score of 1 or higher.INTERVENTIONS Fluoxetine hydrochloride, 20 mg, or matched placebo daily for 26 weeks. MAIN OUTCOMES AND MEASURESA 9-item Patient Health Questionnaire (PHQ-9) score of 9 or lower was a prespecified secondary outcome of the trial. Assessments were completed at baseline and at 4, 12, and 26 weeks. Other outcomes of interest included participant-reported clinician diagnosis of depression, prescription of a nontrial antidepressant, or nonpharmacologic treatment of depression. Analysis was on an intention-to-treat basis.RESULTS A total of 607 participants (378 men [62.3%]; mean [SD] age, 64.3 [12.2] years) were randomly assigned treatment with placebo, and 614 participants (397 men [64.7%]; mean [SD] age, 63.4 [12.4] years) were randomly assigned treatment with 20 mg of fluoxetine hydrochloride daily. The groups were balanced for demographic and clinical measures. At baseline, 112 patients (18.5%) in the placebo group and 116 patients (18.9%) in the fluoxetine group had PHQ-9 scores of 9 or higher. During follow-up, 126 of 596 participants (21.1%) treated with placebo and 121 of 598 participants (20.2%) treated with fluoxetine had PHQ-9 scores of 9 or higher (P = .70). A similar proportion of participants with PHQ-9 scores less than 9 at baseline who were treated with fluoxetine hydrochloride and placebo developed PHQ-9 scores of 9 or higher during the trial (placebo, 72 of 488 [14.8%]; and fluoxetine, 63 of 485 [13.0%]; P = .43). A slightly higher number of participants in the placebo group than in the fluoxetine group had a participant-reported clinician diagnosis of depression (42 of 602 [7.0%] vs 26 of 601 [4.3%]; P = .05). By week 26, 14 participants (2.3%) in the placebo group and 12 participants (1.9%) in the fluoxetine group had died (P = .67). CONCLUSIONS AND RELEVANCERoutine daily treatment with 20 mg of fluoxetine did not decrease the proportion of people affected by clinically significant symptoms of depression after a stroke, nor did it affect the proportion of people prescribed an antidepressant or receiving nonpharmacologic treatments compared with placebo.
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