The localization of orexin neuropeptides in the lateral hypothalamus has focused interest on their role in ingestion. The orexigenic neurones in the lateral hypothalamus, however, project widely in the brain, and thus the physiological role of orexins is likely to be complex. Here we describe an investigation of the action of orexin A in modulating the arousal state of rats by using a combination of tissue localization and electrophysiological and behavioral techniques. We show that the brain region receiving the densest innervation from orexinergic nerves is the locus coeruleus, a key modulator of attentional state, where application of orexin A increases cell firing of intrinsic noradrenergic neurones. Orexin A increases arousal and locomotor activity and modulates neuroendocrine function. The data suggest that orexin A plays an important role in orchestrating the sleep-wake cycle.Since the discovery of the orexins (1) investigations of their functions have been guided by evidence for their hypothalamic distribution (1, 2), focusing on feeding, energy homeostasis (1, 3), and neurocrine functions (3). Our studies now show the presence of orexin A immunoreactive fibers and varicosities in extrahypothalamic areas, particularly the locus coeruleus, and demonstrate that the functions of orexin A extend beyond the hypothalamus.Orexin A and B are derived from a 130-aa precursor, prepro-orexin, which is encoded by a gene localized to human chromosome 17q21 (1). Prepro-orexin, or preprohypocretin (2), was identified in the rat hypothalamus by directional tag PCR subtractive hybridization (2) and has been shown by Northern blot analysis to be abundant in the brain and detectable at low levels in testes but not in a variety of other tissues (1, 2). Hypocretins had been identified as hypothalamic neuropeptides, but their biological role was not described (2). Nucleotide sequence alignment shows that hypocretins 1 and 2 have sequence in common with orexins A and B, respectively, but additional amino acids are present in both hypocretins. In situ hybridization maps confirm dense prepro-orexin mRNA expression in the hypothalamus (1, 2). Immunocytochemical mapping of orexin A has identified a population of mediumsized neurones within the hypothalamus, median eminence (3), and ventral thalamic nuclei of rat brain (1, 3). This distribution has been confirmed in human tissue (4).Orexin A binds with high affinity to the novel G proteincoupled receptors orexin 1 (OX 1 ) (IC 50 20 nM) and orexin 2 (OX 2 ) (IC 50 38 nM). Calcium mobilization assays in transfected HEK293 cells confirm that orexin A is a potent agonist at both OX 1 (EC 50 30 nM) and OX 2 (EC 50 34 nM) (1). Emerging evidence suggests the existence of an extensive extrahypothalamic projection of orexin-immunoreactive neurones. Peyron et al. (5), in addition to confirming the presence of immunoreactive cell somata within the hypothalamus, reported immunolabeled fibers throughout extrahypothalamic regions, including septal nuclei, substantia nigra, and raphe nucle...

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The effects of intraperitoneally administered melatonin on sleep and brain neurochemistry in the rat were studied by use of EEG recording and standard fluorescence techniques. Melatonin, 10 mg/kg, reduced time to sleep onset and time spent awake but increased both slow wave and paradoxical sleep. Qualitatively similar but smaller effects were produced by a dose of 2.5 mg/kg. Neither dose of melatonin altered normal EEG patterns or disrupted normal sleep behaviour. Melatonin, 20 mg/kg, did not significantly alter concentrations of tryptophan, 5‐hydroxytryptamine, 5‐hydroxyindoleacetic acid, noradrenaline or dopamine in any part of the brain. It is concluded that the sleep promoting activity of melatonin cannot be related to gross changes in brain indoleamine and catecholamine levels.

Reduction of the pressor responses to adrenaline in the rabbit following administration of prostaglandin E1 has been confirmed. The effect is, however, nonspecific since noradrenaline, angiotensin and vasopressin are also antagonized. Analogous responses were observed in blood flow experiments on the cat hind limb but not on the rabbit isolated auricles or the rabbit isolated duodenum. Contractions of the cat nictitating membrane produced by sympathetic preganglionic stimulation or by adrenaline were not decreased following injection of prostaglandin E1 but the relaxation period was shorter. Contractions of the rabbit vas deferens induced in vivo by adrenaline were smaller after prostaglandin E1 and this effect tended to be longlasting.In 1938, Euler observed that pressor responses to adrenaline in the rabbit were reduced following an intravenous injection of prostaglandin. Steinberg, Vaughan, Nestel & Bergstr6m (1963) have recently made a similar observation using pure prostaglandin E1. These authors have also shown that the break-down of triglyceride in adipose tissue induced by catechol amines is antagonized. In this investigation we have confirmed the action of prostaglandin E1 on pressor responses to catechol amines and have shown that this effect is nonspecific since responses to angiotensin and vasopressin are also reduced. METHODSBlood pressure experiments. Blood pressure was recorded from a carotid artery using either a mercury manometer or a Statham pressure transducer. Cats were anaesthetized with pentobarbitone sodium (40 mg/kg), rabbits and rats with urethane (1.75 g/kg) injected intraperitoneally. In some experiments rats were anaesthetized with ether and pithed using a strong wire introduced through an orbit and passed down the cerebrospinal axis.Cat hind-limb blood flow. Cats, weighing 2.5 to 4.5 kg, were anaesthetized with pentobarbitone sodium (40 mg/kg) injected intraperitoneally. The trachea, a carotid artery and both external jugular veins were cannulated. Blood pressure was recorded by a mercury manometer. Venous outflow from a hind-limb was recorded by passing blood from the femoral vein through a Palmer drop-chamber connected to a Gaddum drop-recorder, the blood being returned into a jugular vein. The artery supplying the gracilis muscle was cannulated with fine polyethylene tubing connected to a three-way tap for retrograde intra-arterial injections. Heparin (1,000 U/kg) was injected intravenously and further doses of 500 U/kg were given every 2 hr. Contractions of the hind-limb muscles produced by stimulation of