Somatostatin antiserum blocks carbachol-induced increase of paradoxical sleep in the rat

The low ratio of ghrelin in plasma and cerebrospinal fluid might be beneficial to sleep

OBJECTIVE

Ghrelin is physiologically important for maintaining sleep rhythm. Cigarette smoking has been demonstrated to significantly increase the risk of insufficient sleep by regulating ghrelin at the central and peripheral levels. No research has been published to study the relationship between active smoking and sleep via ghrelin level in cerebrospinal fluid (CSF).

METHODS

A total of 139 Chinese males were recruited and divided into active smokers (n = 77) and non-smokers (n = 62). The levels of CSF and plasma ghrelin were measured. The Pittsburgh Sleep Quality Index (PSQI) was used to evaluate sleep.

RESULTS

Non-smokers had lower PSQI scores (1.71 ± 1.93) than active smokers (3.70 ± 1.78). Non-smokers have significantly lower plasma ghrelin levels and lower plasma/CSF ghrelin ratio but higher CSF ghrelin than active smokers. Among non-smokers, plasma ghrelin levels were not correlated with PSQI scores (all p > 0.05), CSF ghrelin levels were positively correlated with PSQI scores (r = 0.309, p = 0.019), and the plasma/CSF ghrelin ratio was negatively correlated with PSQI scores (r = -0.346, p = 0.008).

CONCLUSIONS

This study is the first to reveal the relationship between cigarette smoking, high CSF ghrelin levels and insufficient sleep, suggesting that maintaining a normal plasma/CSF ghrelin ratio may be the physiological mechanism of healthy sleep, and the insufficient sleep population must quit smoking.

Ghrelin and its interactions with growth hormone, leptin and orexins: implications for the sleep-wake cycle and metabolism

Several studies have shown that ghrelin administration promotes wakefulness in rodents, while in human males it induces sleep but has no effect in women. Ghrelin also plays an important role in metabolism and appetite regulation, and as described in this review may participate in the energy balance during sleep. In this review, we summarize some of the effects induced by ghrelin administration on the sleep-wake cycle in relation to the effects of other hormones, such as growth hormone, leptin, and orexin. Finally we discuss the relationship between sleep deprivation, obesity and ghrelin secretion pattern.

Microinjection of neostigmine into the pontine reticular formation of the mouse: further evaluation of a proposed REM sleep enhancement technique

Microinjections of cholinergic agonists into the pontine reticular formation (PRF) powerfully induce rapid eye movement sleep (REMS) in cats but have comparatively weaker effects in rats. Recently, the cholinomimetic neostigmine has been reported to strongly enhance REMS following microinjection into the PRF of the mouse. That study used behavioral assessments of locomotion in lieu of electrophysiological measures of muscle tone to identify REMS. We sought to confirm that the behavioral state induced in mice by PRF injections of neostigmine meets standard electroencephalogram (EEG) and electromyogram (EMG) criteria for defining REMS. Cortical EEG, nuchal muscle EMG, and PGO waves were recorded from male C57BL/6N mice with chronic indwelling cannulae for the delivery of neostigmine to the PRF. Recordings were made during midday following injections of neostigmine (8.8 mM, 50 nl), 2 h after lights on (LD 12:12). Neostigmine induced a behavioral state characterized by low amplitude, highly desynchronized cortical EEG with little theta, no PGO waves, and a sustained high muscle tone. Behavioral states meeting standard criteria for slow-wave sleep (SWS) and REMS were significantly suppressed compared to baseline recordings, and REMS onset was delayed by 3 h. Consistent with earlier reports, neostigmine did strongly suppress locomotor activity in open field tests and in the home cage. Due to the failure to meet criteria for defining REMS, we conclude that neostigmine microinjection into the PRF of the mouse induces an abnormal waking state rather than REMS.

GHRH and sleep

A significant portion of the total daily growth hormone (GH) secretion is associated with deep non-REM sleep (NREMS). GH secretion is stimulated by the hypothalamic neurohormone, GH-releasing hormone (GHRH). Exogenous GHRH promotes NREMS in various species. Suppression of endogenous GHRH (competitive antagonist, antibodies, somatostatinergic stimulation, high doses of GH or insulin-like growth factor) results in simultaneous inhibition of NREMS. Mutant and transgenic animals with a defect in GHRHergic activity display permanently reduced NREMS which cannot be reversed by means of GH supplementation. GHRH contents and mRNA levels in the hypothalamus correlate with sleep-wake activity during the diurnal cycle and sleep deprivation and recovery sleep. Stimulation of NREMS by GHRH is a hypothalamic action. GABAergic neurons in the anterior hypothalamus/preoptic region are candidates for mediating promotion of NREMS by GHRH. In contrast to NREMS, stimulation of REMS by GHRH is mediated by GH. Simultaneous stimulation of NREMS and GH secretion by GHRH may promote adjustment of tissue anabolism to sleep.

Effects of electroacupuncture at 'Anmian (Extra)' acupoints on sleep activities in rats: the implication of the caud al nucleus tractus solitarius

Electroacupuncture (EAc) possesses a broad therapeutic effect, including improvement of sleep disturbances. The mechanism of sleep improvement with EAc, however, is still unclear. The present study investigated the effects of EAc stimulation of 'Anmian (extra)' acupoints on sleep organization and the implication of an active structure, the caudal nucleus tractus solitarius (NTS). Rats were implanted with electroencephalogram (EEG) recording electrodes, and 32-gauge acupuncture needles were bilaterally inserted into 'Anmian (extra)' acupoints in the rats, followed by electrical stimulation for 20 min. Twenty-three-hour continuous EEGs were then recorded. Results showed that rapid eye movement sleep (REMS) was enhanced during the dark period when a single EAc stimulation was given 25 min prior to the onset of the dark period. REMS and slow-wave sleep (SWS) increased during the dark period after administration of EAc stimuli on 2 consecutive days. Electrical stimulation of non-acupoints produced no change in the sleep pattern. Pharmacological blockade of muscarinic cholinergic receptors by systemic administration of scopolamine dose-dependently attenuated EAc-induced changes in REMS and SWS. Furthermore, electrical lesions in the bilateral caudal NTS produced significant blockade of EAc-induced sleep enhancement. However, in rats without EAc, scopolamine increased SWS during the dark period, but caudal NTS lesions did not alter sleep. In addition, neither EAc nor scopolamine with EAc manipulation produced any change in the slow-wave activity (SWA) during SWS; however, the SWA during SWS was significantly reduced after caudal NTS lesion with EAc. These results suggest that the caudal NTS may be involved in the regulation of EAc-induced sleep alterations.

Different brain structures mediate drinking and sleep suppression elicited by the somatostatin analog, octreotide, in rats

When injected into the cerebral ventricles, the somatostatin analog, octreotide (OCT) elicits prompt drinking, vasopressin secretion and increases in blood pressure that are attributed to the activation of the intracerebral angiotensinergic system. In addition, OCT induces sleep responses that might be mediated by an inhibition of hypothalamic neurons producing growth hormone-releasing hormone (GHRH). OCT (0.02 microg in 0.2 microl) was microinjected into various brain sites to determine the structures inducing drinking and/or sleep suppression in response to OCT in rats. Drinking (>1 ml water in 10 min) was elicited in 17 rats out of 86 tested. The positive drinking sites resided in or around the subfornical organ (SFO) and the paraventricular nucleus. Both structures are part of the reported angiotensinergic dipsogenic circuit of the brain. These microinjections failed to elicit consistent sleep effects. Sleep suppression (>10% recording time in hour 1) was observed after injection of OCT either into the arcuate nucleus (n=7), where the majority of GHRHergic neurons reside, or into the medial preoptic area/anterior hypothalamus (n=8), where GHRH acts to promote sleep. Administration of OCT into far lateral sites of the lateral preoptic area and lateral hypothalamus stimulated sleep in hour 1 (n=10), perhaps via inhibiting cholinergic neurons previously implicated in arousal. The results are consistent with the hypothesis that somatostatin is involved in the regulation of both water intake and sleep, and suggest that different structures, and therefore different somatostatinergic neuronal pools, mediate these actions.

Ultradian rhythmicity of ghrelin secretion in relation with GH, feeding behavior, and sleep-wake patterns in rats

Ghrelin, an endogenous ligand for the GHS receptor, stimulates GH secretion and gastrointestinal motility and has orexigenic effects. In this study, the relationships between ghrelin, GH secretion, feeding behavior, and sleep-wake patterns were investigated in adult male rats. The half-life of exogenous ghrelin (10 microg i.v.) in plasma was about 30 min. Repeated administration of ghrelin at 3- to 4-h intervals (one during lights-on and two during lights-off periods) increased GH release and feeding activity, and decreased rapid eye movement sleep duration. Endogenous plasma ghrelin levels exhibited pulsatile variations that were smaller and less regular compared with those of GH. No significant correlation between GH and ghrelin circulating levels was found, although mean interpeak intervals and pulse frequencies were close for the two hormones. In contrast, ghrelin pulse variations were correlated with food intake episodes in the lights off period, and plasma ghrelin concentrations decreased by 26% in the 20 min following the end of the food intake periods. A positive correlation between ghrelin levels and active wake was found during the first 3 h of the dark period only. In conclusion, ghrelin, in addition to affecting GH secretion, gastrointestinal motility, and feeding activity, also modifies sleep-wake patterns. However, a direct action of ghrelin per se or the indirect effects of feeding (and all of its attendant metabolic sequelae) on sleep cannot be differentiated. Moreover, ghrelin secretion is pulsatile and directly related to feeding behavior only.

Chronic stimulation of the cat vagus nerve: effect on sleep and behavior

The effect of electrical vagus nerve stimulation (VNS) on sleep and behavior was analyzed in freely moving cats. Eight cats were prepared for 23-h sleep recordings. The left vagus nerve of four of them was stimulated during 1 min, five times at 1-h intervals, for 5 days. The VNS induces: ipsilateral myosis, blinking, licking, abdominal contractions, upward gaze, swallowing, and eventually yawning and compulsive eating, as well as an increase of ponto-geniculate-occipital (PGO) wave density and of the number of stages and total amount of rapid eye movement (REM) sleep. Besides, there was a sudden transition from waking stage to REM sleep. The present results suggest that VNS modifies sleep in the cat. This effect could be explained by an activation of the areas involved in the physiological mechanisms of sleep.

Intracerebroventricular and locus coeruleus microinjections of somatostatin antagonist decrease REM sleep in rats

In order to study the role of endogenous somatostatin in the physiologic modulation of REM sleep (REMS), we measured the effect of intracerebroventricular (ICV) injection of somatostatin antagonist (SA) cyclo-(7-aminoheptanoyl-phe-d-trp-lys-thr(bzl)) on sleep in rats. The effect of ICV SA was also tested after 24-h REMS deprivation with the platform method. To study the role of locus coeruleus (LC) as a site of the sleep inducing action for somatostatin and galanin we microinjected SA, somatostatin, and galanin locally into LC. In all experiments, vigilance state was analyzed visually from 6 h post-injection EEG/EMG recording. Injection of 0.5 and 2 nmol of SA ICV reduced spontaneous REMS and 2 nmol dose reduced also rebound REMS after REMS deprivation when compared with controls (artificial cerebrospinal fluid vehicle). Microinjection of 0.25 nmol of SA into LC reduced REMS, whereas microinjection of somatostatin, galanin, and a combined injection of them were not effective to induce REMS. The results suggest that endogenous somatostatin may contribute to facilitation of REMS. Somatostatin receptors in the LC may be one possible mediator of this effect.

The neurophysiology of sleep and waking: intracerebral connections, functioning and ascending influences of the medulla oblongata

This paper focuses on the successive historical papers related to medulla oblongata (M.O.) intracerebral connections, its activities and ascending influences regulating sleep waking behavior. The M.O. certainly influences the quantitative and qualitative processes of waking. However, its neurophysiological properties are often concealed by those of the upper-situated brain stem structures. The M.O., particularly the solitary tract nucleus, is involved in sleep-inducing processes. This nucleus seem to act as a deactivating system of the above situated reticular formation, but it also impacts directly on the thalamocortical slow wave and spindle-inducing processes. The M.O. is significantly involved in paradoxical sleep mechanisms. Indeed, the mesopontine executive centers are unable to induce paradoxical sleep without the M.O. Moreover, stimulation of the solitary tract nucleus afferents can induce paradoxical sleep, and the M.O. metabolic functioning is specifically disturbed by paradoxical sleep deprivation. Finally. there seems to be a paradoxical sleep Zeitgeber. Our current knowledge shows that this lowest brain stem level is crucial for sleep waking mechanisms. It will undoubtedly be further highlighted by future electrophysiologial and neurochemical studies.

Endogenous and exogenous factors on sleep-wake cycle regulation

A number of theories have proposed the involvement of different brain structures and neurotransmitters in order to explain the regulation of the sleep wake cycle. However, there is no clear consensus as to the mechanisms through which the brain structures and their various neurotransmitters interact to produce theses phases. Perhaps the problem is related to the fact sleep is a very fragile state, easily modified or influenced by a variety of substances or experimental manipulations. In this paper, we describe the evidence of two different groups of factors that induce important changes on the sleep wake cycle. The endogenous factors: neurotransmitters; hormone; peptides; and some substances of lipidic nature and exogenous factors: stress, food intake, learning, sleep deprivation, sensorial stimulation, exercise and temperature on the regulation the sleep-wake cycle. Likewise, we propose a hypothesis which attempts to reconcile the fact that endogenous and exogenous factors have similar effects.

Evidence against a role for the growth hormone-releasing peptide axis in human slow-wave sleep regulation

A complex interrelationship exists between sleep and somatotropic activity. In humans, intravenous injections of growth hormone-releasing hormone (GHRH) given during sleep consistently stimulate slow-wave (SW) sleep, particularly when given in the latter part of the night. In the present study, the possible somnogenic effects induced under similar conditions by GH-releasing peptide (GHRP) were investigated in seven young healthy men. Bolus intravenous injections of GHRP-2 (1 microgram/kg body wt) or saline, in randomized order, were given after 60 s of the third rapid-eye-movement period. All GHRP injections were immediately followed by transient prolactin elevations and by GH pulses of a magnitude within or around the upper limit of the physiological range. Except for a nonsignificant tendency to increased amounts of wakefulness during the 1st h after the injection, no effects of GHRP-2 administration on sleep were detected. There was in particular no enhancement of SW sleep. Thus, in contrast to GHRH, late-night single injections of GHRP-2 at a dosage resulting in similar GH elevations have no stimulatory effects on SW sleep. The present data provide evidence against the involvement of the GHRP axis in human SW sleep regulation.

Changes in rat sleep after single and repeated injections of the long-acting somatostatin analog octreotide

Somnogenic activity is attributed to both growth hormone (GH) and GH-releasing hormone (GHRH). The aim of our experiments was to study sleep after suppression of the somatotropic axis by means of administration of a long-lasting somatostatin analog, octreotide. Rats received subcutaneous injections of physiological saline (baseline), octreotide (1, 10, and 200 microg/kg), or a control solution just before light onset, and sleep-wake activity and cortical brain temperature were recorded for 23 h. Each dose of octreotide slightly promoted rapid eye movement sleep (REMS) during the 12-h light period. Non-REM sleep (NREMS) was strongly suppressed for 1 h in response to 10 and 200 microg/kg octreotide. This was followed by slight increases in NREMS time and significant enhancements in electroencephalogram slow-wave activity during NREMS after 200 microg/kg octreotide. The octreotide-induced inhibition of the somatotropic axis, as determined by plasma GH levels, vanished by the time sleep increased. Another group of rats received 10 microg/kg octreotide twice a day for 5 days. This treatment elicited persistent decreases in both NREMS time and NREMS intensity. The results support the previously reported REMS-promoting activity of somatostatin in rats. The decreases in sleep after repeated injections of octreotide are attributed to a withdrawal of the normal sleep-promoting activity of GH. The role of GHRH-GH in octreotide-induced acute suppression of NREMS is currently not clear. Other mechanisms, such as mimicking central transmitter functions of somatostatin by octreotide, should also be considered.

Differential response of rapid eye movement sleep to cholinergic blockade by scopolamine in currently depressed, remitted, and normal control subjects

The degree of cholinergic dysregulation of sleep in adult depression was evaluated using scopolamine. On separate sessions, placebo and scopolamine (4.5 micrograms/kg, IM) were administered to 14 patients with unipolar major depression, 16 recovered/remitted patients, and 18 normal controls. Scopolamine increased rapid eye movement (REM) latency (RL), reduced REM activity (RA), REM density (RD), and REM duration, and increased the percentage of stage 4 sleep in all groups. There was a differential effect of scopolamine on RL, RA, and REM duration for the first REM period, and on percentage of stage 4 sleep. Whereas a primary cholinergic hyperactivity could account for the RA and RD responses, the response profile for RL was more compatible with reduced aminergic tone as the proximal cause of the cholinergic hyperactivity. Whether the sleep abnormalities observed in remitted patients reflect an underlying vulnerability for development or recurrence of depression, and/or a scar, remains to be determined.

Chloramphenicol prevents carbachol-induced REM sleep in cats

Twenty-four cats were implanted for chronic sleep recordings. One week after the surgery, cats were divided into four groups. Two groups were treated with three i.p. injections of 150 mg/kg chloramphenicol (CAP) separated by 12 h. Carbachol (8 micrograms/1 microliter) or saline (1 microliter) was injected into the pontine reticular formation (PRF) 1 h after the last injection of CAP. The other two groups received saline or carbachol into the PRF without CAP pre-treatment. Polygraphic recordings were started immediately after the microinjection and lasted 11 h. Carbachol increased REM sleep (P < 0.001) and reduced SWS2 (P < 0.05). In contrast, chloramphenicol reduced REM sleep (P < 0.001) and increased SWS2 (P < 0.01). The combination of these drugs increased wakefulness (P < 0.01) and reduced both SWS2 and REM sleep (P < 0.001). This data shows that chloramphenicol prevents carbachol induced REM sleep. Results are discussed in terms of an interaction between brain proteins and the cholinergic system to induce REM.

Effects of somatostatin and anti-somatostatin serum on picrotoxin-kindled seizures

The effects of somatostatin, administered into different areas of the brain were studied in preliminary picrotoxin-kindled rats. The injection of somatostatin into the lateral ventrical of the brain (i.c.v.) (1.8 nmol), the hippocampus (0.6 nmol) or the amygdala (0.6 nmol), resulted in a decrease in the severity of the picrotoxin-induced convulsions. Application of the peptide into the caudate-putamen or the substantia nigra reticulata did not alter the behavioural manifestations of the kindled seizures. The local injection of anti-somatostatin serum (1:5) into the hippocampus increased the severity of the kindled convulsions and blocked the anticonvulsive effect of somatostatin, given intraventricularly. Local administration of anti-somatostatin serum into the amygdala did not alter the kindled seizures and did not abolish the anticonvulsive action of somatostatin given intraventricularly. It is concluded that somatostatin could take part in endogenous control of seizures through a suppressant influence on limbic structures; the hippocampus could be a specific site for the antiepileptic action of somatostatin.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

Preclinical and clinical studies with somatostatin related to the central nervous system

1. The tetradecapeptide somatostatin (SS) has a widespread, uneven distribution within several organs including the central nervous system (CNS), with particularly high concentration in the hypothalamus. 2. The SS-related peptides (SS28, SS28(1-12), SS28(15-28)) are originated from the precursor pre-prosomatostatin. 3. SS is suggested to be involved in a large number of CNS functions, locomotion, sedation, excitation, catatonia, body temperature, feeding, nociception, paradoxical sleep, self-stimulation, seizure, learning and memory. 4. SS influences central neurochemical processes. 5. It is possible that SS is related to various neurological and psychiatric illnesses, like Huntington's disease, multiple sclerosis, Parkinson's disease, epilepsy, eating disorders, Alzheimer's disease, schizophrenia and major depressive illness.

Reversal of desipramine-induced suppression of paradoxical sleep by a long-acting somatostatin analogue (octreotide) in rats

EEG sleep recordings were performed in rats under intraperitoneal injections of saline, desipramine (DMI, 4 mg/kg) an inhibitor of noradrenaline reuptake, and DMI plus the octapeptide somatostatin analogue (octreotide, 0.2 mg/kg). As already reported, DMI resulted in selective suppression of paradoxical sleep (PS) and increased slow wave sleep (SWS). The administration of the octapeptide somatostatin analogue totally reversed the DMI-induced suppression of PS, but had no effect on SWS. This finding confirms previous results demonstrating a role of somatostatin in the generation of PS. In addition, it suggests that the suppression of PS by DMI may be due to an inhibitory effect on somatostatin release, rather than to an alteration of brain noradrenaline.

Scopolamine-induced suppression of paradoxical sleep is reversed by the somatostatin analogue SMS 201-995 in rats

The intraperitoneal administration of the octapeptide somatostatin analogue SMS 201-995 produced a significant increase in paradoxical sleep (PS) in rats. The suppression of PS by the muscarinic receptor blocker scopolamine was reversed by SMS 201-995. These findings confirm previous results demonstrating a role of somatostatin in the generation of PS. In addition they suggest that the suppression of PS by scopolamine may be due to an inhibitory effect on somatostatin release, rather than to an alteration of cholinergic function alone.