The delta EEG (sleep)-inducing peptide (DSIP). XI. Amino-acid analysis, sequence, synthesis and activity of the nonapeptide

High-Performance Reversed-Phase Flash Chromatography Purification of Peptides and Chemically Modified Insulins

Preparative reversed-phase HPLC is the established method for the purification of peptides, but has significant limitations. We systematically investigated the use of high-performance reversed-phase flash chromatography (HPFC) to rapidly purify laboratory-scale quantities of crude, synthetic peptides and chemically modified insulins. We demonstrated these methods for a diverse set of peptides, including short, medium, and long peptides. Depending on the purity profile of the peptide, HPFC can be used either as the sole purification method, or as a pre-purification method prior to final HPLC purification. Furthermore, HPFC is suitable for the purification of peptides that are not fully in solution. We provide guidelines for the HPFC of synthetic peptides and small proteins, including the choice of columns, eluents, and gradients. We believe that HPFC is a valuable alternative to HPLC purification of peptides and small proteins.

[Olygopeptide KND as a putative endogenous prototype of delta sleep inducing peptide (DSIP). Comparative study of biological properties]

We have undertaken a comparative study on physiological activity of well known neuropeptide DSIP (WAGGDASG E) and new closely related peptide KND (WKGGNASGE) in vivo assays. The sequence of K2, N5-DSIP (KND) was found recently by the computer search for DSIP homologous sequences in available nucleotide and protein databases at 324-332 site of Lysine-specific demethylase 3 B (EC 1.14.11, Swiss-Prot: Q7LBC6.1, 1-1761aa). This human lysine-specific histone demethylase is a representative of the recently discovered family of so called JmjC-domain-containing histone demethylases encoded by JMJD1B gene and ubiquitously expressed in tissues of various mammalian species. Biological investigations performed in this work confirm our preliminary data that DSIP-related peptide KND exhibits the similar biological properties in comparison with DSIP. Assessed by us antioxidative, anticonvulsive and behavioral effects of KND were even more expressed than in DSIP case. These results provide the additional evidences to support our suggestion that KND can be a possible endogenous prototype of "real" DSIP.

JmjC-domain-containing histone demethylases of the JMJD1B type as putative precursors of endogenous DSIP

Delta sleep inducing peptide (WAGGDASGE, DSIP) is a well known multifunctional regulatory peptide. Numerous studies have confirmed its stress-protective and adaptive activity which is independent of the origin or nature of the stress or other harmful factors. However, the biosynthetic origin of DSIP remains obscure, since nothing is known of its protein precursor(s) and their encoding gene(s). We have performed a comprehensive analysis of available gene and protein databases for homologous peptide sites within mammalian resources including man. A family of Jumonji C (JmjC)-domain-containing histone demethylases was shown to contain a sequence fragment closely homologous to DSIP. One type of these ubiquitous and phylogenetically ancient proteins encoded by JMJD1B gene includes the WKGGNASGE sequence that differs from DSIP by only 2 amino acid residues in positions 2 and 5. The respective peptide was synthesized and its biological effects were evaluated in a preliminary way in the forced swimming and antitoxic tests. We suggest that the histone demethylases of the JmjC-group containing DSIP-related region can be considered as possible protein precursors of endogenous peptides with DSIP-like activity.

Antiepileptic activity of delta sleep-inducing peptide and its analogue in metaphit-provoked seizures in rats

PROBLEM

Previous studies have shown that humoral, endogenous and somnogenic, delta sleep-inducing peptide (DSIP) has influence on insomnia, pain, adaptation to stress, epilepsy, etc. We investigated the potential of DSIP and its analogue DSIP-12 (a nonapeptide with alanine in position 2 of DSIP molecule substituted by beta-alanine) to antagonize metaphit (1-[1(3-isothiocyanatophenyl)-cyclohexyl]piperidine) induced generalized, reflex audiogenic seizures in adult male Wistar albino rats.

METHODS

The rats divided in four groups received (i.p.): saline; metaphit; metaphit+DSIP; and metaphit+DSIP-12, respectively. Metaphit-treated animals displaying seizure in eight previous tests received DSIP or DSIP-12 and afterwards audiogenic stimuli were applied at hourly intervals for the next 30 h. The animals were exposed to sound stimulation 60 min after metaphit administration and further on at hourly intervals. Incidence and severity of seizures were behaviorally analyzed. Selected EEGs and power spectra were recorded and analyzed.

RESULTS AND CONCLUSIONS

Metaphit led to hypersynchronous epileptiform activity (polyspikes and spike-wave complexes) and increased power spectra 0.5-30 h after the treatment. Severity of metaphit seizures increased with time to reach the peak 7-12 h after injection. DSIP and DSIP-12 significantly (*P<0.05 and **P<0.01) increased in delta and theta frequency bands and decreased the incidence, mean seizure grade and duration of metaphit convulsions. The results suggest that DSIP and DSIP-12 may be considered as potential antiepileptics in the animal model, DSIP-12 being more efficient than DSIP.

Delta sleep-inducing peptide and its tetrapeptide analogue alleviate severity of metaphit seizures

The effects of delta sleep-inducing peptide (DSIP) and its tetrapeptide analogue, DSIP(1-4), on metaphit-induced audiogenic seizures were studied. Five groups of adult male Wistar rats were intraperitoneally treated with (1) saline, (2) metaphit, (3) DSIP, (4) metaphit+DSIP and (5) metaphit+DSIP(1-4). To examine blocking effects of DSIP and its analogue on fully developed metaphit seizures, the last two groups were injected after the eight audiogenic testing. The rats were stimulated using electric bell (on the top of the cage, generating 100+/-3 dB and frequency 5-8 kHz, for 60 s) 1 h after metaphit and afterwards at hourly intervals during the experiment. For EEG recordings and power spectra, three gold-plated screws were implanted into the skull. In metaphit-treated animals, EEGs appeared as polyspikes and spike-wave complexes while the power spectra were increasing for 30-h period. The incidence and severity of metaphit-induced audiogenic seizures reached peak value 7-12 h after the injection. Both DSIP and DSIP(1-4) significantly increased power spectra of delta waves and decreased incidence of seizures, mean seizure grade and tonic component of metaphit-induced convulsions. Taken together, these results suggest that DSIP and its analogue DSIP(1-4) should be considered as potential antiepileptics.

High delta sleep-inducing peptide-like immunoreactivity in plasma in suicidal patients with major depressive disorder

BACKGROUND

Delta sleep-inducing peptide (DSIP) supposedly involves the hypothalamus-pituitary-adrenal (HPA) axis. Previous studies have shown deviated plasma DSIP-like immunoreactivity (DSIP-LI) levels, as well as abnormal DSIP-LI responses to corticotropin-releasing hormone in patients with major depressive disorder (MDD). This study was performed to investigate plasma-DSIP-LI and its association with the dexamethasone suppression test (DST) in suicide attempters.

METHODS

Plasma-DSIP and serum cortisol were measured before and after dexamethasone intake in 34 suicide attempters and in healthy age- and sex-matched controls.

RESULTS

We found significantly elevated DSIP-LI levels in MDD patients (p < .005), and a significant correlation between predexamethasone cortisol and predexamethasone DSIP-LI levels in healthy controls. Postdexamethasone DSIP-LI levels increased in subjects with low predexamethasone DSIP-LI levels, whereas they decreased in subjects with high predexamethasone DSIP-LI levels.

CONCLUSIONS

Results give some support to the theory of glucocorticoid involvement in the regulation of DSIP, and suggest altered DSIP-LI levels in suicidal MDD patients.

Correlations between plasma-neuropeptides and temperament dimensions differ between suicidal patients and healthy controls

BACKGROUND

Decreased plasma levels of plasma-neuropeptide Y (NPY) and plasma-corticotropin releasing hormone (CRH), and increased levels of plasma delta-sleep inducing peptide (DSIP) in suicide attempters with mood disorders have previously been observed. This study was performed in order to further understand the clinical relevance of these findings.

METHODS

Examination of correlates between temperament dimensions (Karolinska Scales of Personality (KSP), the Eysenck Personality Questionnaire together with the IVE- impulsiveness scale (EPQI), and the Marke-Nyman Temperament (MNT)) and NPY, CRH and DSIP and serum-cortisol in the dexamethasone suppression test (DST) in 38 suicidal patients and matched controls.

RESULTS

NPY correlated significantly and positively with psychasthenia, irritability, and stability and significantly and negatively with validity in patients, but significantly and negatively with muscular tension, psychasthenia, verbal aggression and irritability in controls. DSIP correlated significantly and positively with impulsiveness (EPQI) in controls. CRH correlated negatively with lie in controls. Cortisol correlated significantly and positively with validity, extraversion and verbal aggression and significantly and negatively with inhibition of aggression in controls.

CONCLUSION

NPY may be related to stress tolerance. DSIP seems to be associated with impulsivity/antisocial traits.

LIMITATIONS

Non-suicidal patients were not included in the examination.

CLINICAL RELEVANCE

The state of depression or stress seems to influence the correlations studied.

Human plasma DSIP decreases at the initiation of sleep at different circadian times

Nocturnal plasma delta sleep-inducing peptide-like immunoreactivity (DSIP-LI) was determined serially in seven healthy male subjects. Time courses during nocturnal sleep (2300-0800 h), nocturnal sleep deprivation (2300-0500 h), and morning recovery sleep (0500-0800 h) after sleep deprivation were compared. A significant decrease in plasma DSIP-LI was found at the transition from wakefulness to sleep in both evening sleep (2300 h) and morning recovery sleep (0500 h). Time courses were accompanied by physiological changes in sleep electroencephalographic slow-wave activity, and in plasma concentrations of cortisol and human growth hormone. No sleep stage specificity was found. It is concluded that DSIP is influenced by the initiation of sleep.

Characterization of the release and metabolism of delta sleep-inducing peptide (DSIP) in the rat brain

In the present study, we examined whether delta sleep-inducing peptide (DSIP) was (1) secreted from neurons on depolarization and (2) degraded by membrane-associated peptidases. Incubation of DSIP with rat brain membrane resulted in the degradation of DSIP with liberation of tryptophan, an N-terminal amino acid of DSIP. Bestatin and puromycin, aminopeptidase inhibitors, significantly inhibited the degradation of DSIP and release of tryptophan. The releases of immunoreactive DSIP-like substance (irDSIP) from rat brain slices and synaptosomes were significantly stimulated by high K(+)-evoked depolarization. The released irDSIP was coeluted with native DSIP on gel filtration chromatography. High K(+)-evoked release of irDSIP did not show extracellular Ca(2+)-dependency. This Ca(2+)-independency suggests that the secretory pathway of DSIP may be different from that of other neurotransmitters. These results demonstrate that DSIP is released from nerve endings on depolarization and inactivated by membrane-associated puromycin-sensitive aminopeptidase. Therefore, DSIP may serve as a neuropeptide-like material in the central nervous systems.

Production and immunohistochemical application of monoclonal antibodies against delta sleep-inducing peptide

Monoclonal antibodies were produced following immunization of rats with delta sleep-including peptide (DSIP). The spleen cells of the rats were fused with the myeloma cell line SP2/0. The supernatants of hybridomas were screened on a solid-phase immunoassay using dot-immunobinding of DSIP and some DSIP fragments. The supernatants of six stable producer clones were found to react with DSIP. From this procedure it was also deduced that all these monoclonal antibodies recognized epitope(s) of the penta carboxy-terminal region of DSIP (DSIP5-9). Application of these monoclonal antibodies to rat median eminence sections gave a strong immunolabelling of a large population of fibres and terminal-like structures, mainly localized through the lateral areas. Elution-restaining experiments using a monoclonal antibody to DSIP and a polyclonal antiserum to luteinizing hormone-releasing hormone (LHRH) showed that the patterns of immunoreactivity respectively visualized overlap almost completely. Although numerous LHRH-immunoreactive neuronal elements were also easily demonstrated in the median eminence of the mouse, the hamster and the gerbil species, incubation of sections with monoclonal antibodies to DSIP failed to give any immunoreaction. Taken together these data argue for the independence of the DSIP/LHRH immunolabelling systems. Furthermore, it was demonstrated that DSIP5-9-related epitopes detected in the rat median eminence have no counterpart in the three other rodent species investigated. These species differences may reflect the fact that the carboxy-terminal sequence of the nonapeptide DSIP originally discovered in the rabbit is not conserved in all rodent species.

Plasma levels of DSIP in infants in the first year of life and SIDS risk

In searching for abnormalities related to the sudden infant death syndrome (SIDS), delta sleep-inducing peptide (DSIP), a regulatory peptide with sleep promoting actions, was investigated in the first year of life in four groups of children: (1) preterm infants (n = 28), (2) infants with a high mean apnea duration evaluated polysomnographically (n = 26), (3) healthy full-term infants (n = 37) and (4) siblings of SIDS-victims (n = 26). DSIP was radioimmunoassayed in plasma. Half of the infants were also investigated polygraphically during sleep. The ratio between quiet sleep and active sleep was determined. There was no age dependence of the plasma level of DSIP in the first year of life but there was an increase in the ratio of quiet/active sleep depending of maturity. The level of DSIP in healthy full-term infants was significantly higher (P less than 0.05) (median: 1885 pmol/l, interquartile range: 757 pmol/l) than in preterms (1595; 385) and in infants with a high mean apnea duration (1542; 373). There was no significant difference in DSIP concentrations between healthy full-term infants and SIDS-siblings (1605; 271).

Phosphorylation of delta sleep-inducing peptide (DSIP) by casein kinase II in vitro

A phosphorylated analogue of DSIP at Ser7 has been shown to exist endogenously by immunochemical studies. An enzyme which could phosphorylate DSIP has not yet been identified. In the present study, we examined DSIP as a substrate for in vitro phosphorylation by casein kinase II. DSIP was phosphorylated by the enzyme with apparent Km and Vmax values of 20 mM and 90.9 nmol/min/mg protein, respectively. Both ATP and GTP were utilized as phosphoryl donors. Phosphorylation of DSIP was inhibited by heparin and enhanced by spermine. These results demonstrate that DSIP can serve as a possible substrate for casein kinase II in vitro.

Characterization of delta-sleep-inducing peptide-evoked release of Met-enkephalin from brain synaptosomes in rats

Delta-sleep-inducing peptide (DSIP) stimulates the release of Met-enkephalin (Met-ENK) from superfused slices of the rodent lower brainstem in vitro. In our present study, DSIP (10(-10)-10(-9) M) induced a significant release of Met-ENK from medullary synaptosomes of rats. This DSIP-evoked release of Met-ENK was Ca2+ dependent and tetrodotoxin (TTX) insensitive. Furthermore, DSIP (10(-11)-10(-9) M) significantly increased 45Ca2+ uptake in medullary synaptosomes. These results demonstrate that DSIP acts directly on the nerve endings of Met-ENK-containing neurons to release this pentapeptide by generating a Ca2+ influx into these neurons. Effects of DSIP on Met-ENK release in other discrete brain regions were also studied. Significant DSIP-evoked Met-ENK release from synaptosomes was observed in the cortex, hypothalamus, and midbrain (at concentrations of 10(-10) and 10(-9) M) and in the hippocampus and thalamus (only at 10(-9) M), but not in the striatum. In the hypothalamus, the release of Leu-enkephalin from its synaptosomes was slightly, but not significantly, enhanced by DSIP (10(-10)-10(-8) M). Our findings demonstrate that DSIP triggered a Ca2+ influx in nerve endings to induce a subsequent release of Met-ENK from neurons in only certain brain regions.

Extraction and immunochemical characterization of delta sleep-inducing peptide-like material from the porcine pituitary and adrenal gland

The naturally occurring forms of delta sleep-inducing peptide (DSIP) are not fully identified. In the present study, porcine pituitaries and adrenal glands were extracted in water, saline or acid under various conditions and immunoreactive DSIP (IR-DSIP) quantified by radioimmunoassay. The highest concentrations were measured in anterior pituitary extracts (40.8 +/- 2.6 ng/g tissue weight) recovered using water with aprotinin. However, high performance liquid chromatography (HPLC) indicated degradation of hydrophobic forms of IR-DSIP in water extracts. Extraction in acetic acid including C18 Sep-Pak purification resulted in an elution profile of IR-DSIP in adrenal extracts with a major peak coeluting with synthetic DSIP [DSIP(1-9)], whereas anterior pituitary extract showed material of higher hydrophobicity. Approximately 30% of IR-DSIP in anterior pituitary as well as in adrenal gland extracts seemed to be glucosylated, as based on concanavalin A chromatography. One of the DSIP-immunoreactive components by immunoblotting (molecular mass 25 kDa) was identified in both pituitary and adrenal gland extracts. In conclusion, several chromatographically distinct forms of IR-DSIP are present in the porcine pituitary and adrenal gland. IR material eluting as DSIP(1-9) is present in adrenal gland extract. The procedure and solution used for tissue extraction seem to be essential in order to obtain reliable elution positions on HPLC.

Biosynthesis and processing of delta sleep-inducing peptide-like precursors in primary cultures of mouse anterior pituitary cells

The biosynthesis and processing of material resembling delta sleep-inducing peptide (DSIP) have been studied in mouse anterior pituitary primary cell cultures. Cells were pulse/chase incubated with 3H-labelled amino acids (Gly, Arg or Ala) and cell extracts were immunoprecipitated with DSIP antiserum. Labelled DSIP-related proteins were resolved by SDS/PAGE. Multiple forms of DSIP-immunoprecipitable material were observed, including three precursors of molecular mass 50-60 kDa which were processed to two major groups of intermediates of 35-45 kDa and 9-16.5 kDa. These intermediates appear to be processed to a DSIP-related peptide (molecular mass less than 3 kDa), which co-ran on reversed-phase HPLC with an endogenous form of DSIP in mouse anterior pituitary, but not with rabbit DSIP. This less than 3-kDa peptide incorporated [3H]Gly, but not [3H]Arg or [3H]Ala. In addition, it incorporated [3H]glucosamine, indicating that it was a glycopeptide. Secretion studies showed release of the less than 3-kDa DSIP-like glycopeptide and the 9-16.5-kDa group of intermediates into the medium. The present study demonstrates the biosynthesis of a small DSIP-like glycopeptide in mouse anterior pituitary cells, which is not identical with, but has similarities to, rabbit DSIP.

Delta-sleep-inducing peptide (DSIP) stimulates the release of immunoreactive Met-enkephalin from rat lower brainstem slices in vitro

We studied whether delta-sleep-inducing peptide (DSIP) acted on opioid receptor directly or indirectly. DSIP did not have binding activity to any subtype of opioid receptors. DSIP at doses of 1 pM-1 nM significantly stimulated the release of immunoreactive Met-enkephalin (iME) from superfused slices of the rat lower brainstem. The DSIP-induced release of iME was calcium-dependent. These results show that DSIP acts on opioid receptor indirectly by stimulating the release of iME in producing antinociceptive effects.

Involvement of spinal noradrenergic system in the mechanism of an antinociceptive effect of delta-sleep-inducing peptide (DSIP)

We studied whether the antinociceptive effect produced by intracerebroventricular injection of delta-sleep-inducing peptide (DSIP) to mice involved the monoaminergic pathways that descended from brainstem to spinal cord (the descending inhibitory systems). In the tail-pinch test, the antinociceptive effect of DSIP was significantly reduced by the pretreatment with reserpine (3 mg/kg i.p.) which depleted endogenous monoamines. Moreover, the intrathecal injections of monoamine antagonists were performed to evaluate the roles of the spinal noradrenergic and/or serotonergic systems in the production of the DSIP antinociception. In both tail-pinch and hot plate tests, the antinociceptive effect of DSIP was significantly antagonized by the previous intrathecal administration of phentolamine (an alpha-adrenergic blocker) or yohimbine (an alpha 2-adrenergic blocker), but was unaffected by the pretreatment with methysergide (a serotonin antagonist). These results demonstrate that the activation of the descending inhibitory systems, mainly spinal noradrenergic systems, is involved in the elicitation of DSIP antinociception.

Delta sleep-inducing peptide (DSIP)-like immunoreactivity in gut: coexistence with known peptide hormones

Delta sleep-inducing peptide-like immunoreactivity (DSIP-LI) has previously been demonstrated in brain neurons and in endocrine cells of the pituitary and the adrenal medulla. By means of three different antisera against synthetic DSIP we now describe the occurrence and distribution of DSIP-LI in several gut endocrine cells. The human gut was the richest source, where DSIP-LI was located in gastrin/CCK, secretin and PYY/glicentin cells. The rat and pig gut harbour a moderate number of immunoreactive cells in the antral mucosa but in the intestines DSIP-LI-containing cells were very few. By radioimmunoassay, the concentration of DSIP-LI was determined in extracts of various gut regions from man, pig and rat. The highest concentrations were found in all human specimens compared with corresponding samples in the pig and rat. In all three species, high-performance liquid chromatography revealed a single peak of DSIP-like material with approximately the same retention time as DSIP 3-9. Taken together, the present results provide evidence for the presence of DSIP-LI in gut endocrine cells in man, pig and rat; the human gut seems to be the richest source of DSIP-like peptides.

Reduction of immunoreactive ACTH in plasma following intravenous injection of delta sleep-inducing peptide in man

Eleven healthy male volunteers, ages 25-39 years, received a single dose of synthetic delta sleep-inducing peptide (DSIP) (25 nmol/kg BW) or saline intravenously in a randomized cross-over, double-blind study. The concentrations of neuropeptides related to the hypothalamic pituitary-adrenal (HPA) axis and cortisol were examined in serial plasma samples. In addition, cortisol and monoamine metabolites were determined in urine. A significant reduction of ACTH-like immunoreactivity (ACTH-LI) in plasma was detected for at least 3 hr after the DSIP injection, compared to the control subjects, in whom a slightly elevated concentration of ACTH-LI occurred. Plasma cortisol levels were unaffected and followed the normal diurnal decline. No differences in urinary cortisol or monoamine metabolite concentrations occurred between the two groups. The results indicate an inhibitory action of DSIP on ACTH secretion in man, as previously suggested by animal experiments.

Potent antinociceptive effect of centrally administered delta-sleep-inducing peptide (DSIP)

The effect of central administration of delta-sleep-inducing peptide (DSIP) on nociceptive responses was evaluated in mice and rats. DSIP, administered intracerebroventricularly or intracisternally to mice, produced a significant dose-dependent antinociceptive effect in the tail-pinch and hot-plate tests. Intrathecal administration of DSIP did not produce such an effect. The antinociceptive effect of DSIP was blocked by pretreatment with the opioid antagonist, naloxone. Moreover, DSIP did not produce an antinociceptive effect in morphine-tolerant mice. Similar antinociceptive effects of DSIP were observed in rats. These results suggest that DSIP produces an antinociceptive effect by acting at the supraspinal level and that this effect is mediated via the opioid receptor, either directly or indirectly. DSIP may play an important role in pain regulation in the central nervous system.

Comparison of DSIP- (delta sleep-inducing peptide) and P-DSIP-like (phosphorylated) immunoreactivity in cerebrospinal fluid of patients with senile dementia of Alzheimer type, multi-infarct syndrome, communicating hydrocephalus and Parkinson's disease

The concentrations of delta sleep-inducing peptide (DSIP)-like (DSIP-LI) and P-DSIP-like (phosphorylated, Ser7) immunoreactivity (P-DSIP-LI) were measured by specific radioimmunoassay in the cerebrospinal fluid (CSF) of patients with senile dementia of the Alzheimer type [SDAT, subdivided into early (S1), middle (S2) and late dementia (S3)], multi-infarct dementia (MD), Parkinson's disease (PD), vascular disease (VD) and communicating hydrocephalus (H), as well as in control patients (C1, C2). Mean DSIP-LI and P-DSIP-LI concentrations were found to be significantly higher in the elderly control group (C1, mean age 83 +/- 5 years) than in the middle-aged control group (C2, mean age 40 +/- 16 years). DSIP-LI and P-DSIP-LI were positively correlated with age in both control groups. Significant decreases of DSIP-LI compared with age-matched controls (C1) were observed for S2, S3, MD, PD, VD and H. In contrast, no significant differences corresponding to pathology were found for P-DSIP-LI.

The effects of delta-sleep-inducing peptide (DSIP) on wakefulness and sleep patterns in the cat

The effect of a single injection of synthetic delta-sleep-inducing peptide (DSIP, 7 nmol/kg) into the lateral ventricle of 10 cats was investigated by monitoring the sleep-wake cycle during an 8 h period. A significant decrease in sleep latency and a significant increase in total sleep and in total slow wave sleep (SWS) was found following DSIP administration. The increase in sleep resulted exclusively from a significant increase in deep slow wave sleep (S2), while light slow wave sleep (S1) was significantly decreased. Neither the total amount of REM sleep, nor hourly values of REM sleep were affected by DSIP application. Additional measures of REM sleep, like REM sleep latency, mean episode number and mean episode length were not different from those found in control conditions. DSIP was immediately effective since the amount of S2 increased to more than 50% in the first postinjection hour and the difference from the control value was highly significant. The increase in S2 was maintained over 7 h, and disappeared by the eighth hour. The increase in S2 was caused by a prolongation of S2 episodes and not by their more frequent occurrence. The results obtained suggest a sleep-facilitating property of DSIP.

The effect of subcutaneous administration of delta sleep-inducing peptide (DSIP) on some parameters of sleep in the cat

Delta sleep inducing peptide (DSIP) significantly increases deep-slow-wave sleep (DSWS) of cats after subcutaneous (SC) injection. Cats (n = 8) were SC injected with DSIP (120 nmol.kg-1) prior to polygraphic recording of EEG combined with electro-oculography, EOG) and electromyography (EMG) for 8 hours. DSIP was found to significantly increase slow-waves (delta sleep) in the sleep EEG. There was a tendency to reduced waking time and a prolongation of slow wave sleep time, and a shortening of sleep onset and REM sleep latencies but the differences from control (Ringer injection) were not statistically significant. There was no change in the amount of REM sleep. These findings support the belief that DSIP can increase sleep wave activity when administered by peripheral route.

Structure-activity relationship in the effects of delta-sleep-inducing peptide (DSIP) on rat sleep

DSIP and its analogues, [D-Trp1]-DSIP, [D-Tyr1]-DSIP, and [D-Trp1]-DSIP1-6, were injected ICV (7 nmol/kg) into rats at dark onset, and the sleep-wake activity was recorded during the 12-hr dark period and the subsequent 12-hr light period. The effects were evaluated with respect to baseline records obtained after artificial CSF injections. DSIP did not increase sleep, whereas both [D-Trp1]-DSIP and [D-Tyr1]-DSIP promoted sleep in the first part of the night. [D-Trp1]-DSIP1-6 had a prompt arousing effect. It is suggested that the sleep-promoting analogues act by facilitating slight endogenous sleep tendencies at some time after dark onset, while DSIP is degraded quickly and is therefore not effective. The increase of W after [D-Trp1]-DSIP1-6 may indicate that DSIP contains a fragment with an arousing effect. The results corroborate the notion that the active DSIP molecule has a pseudo-cyclic structure.

Sleep apnea disorders. Introduction to sleep and sleep disorders

This overview of normal and disordered sleep introduces techniques for recording and classifying sleep stages, physiological and temporal characteristics of sleep, age-related changes in sleep, consequences of sleep deprivation, theories on the function of sleep, and neurophysiological and biochemical mechanisms regulating sleep. Various categories of sleep disorders are briefly surveyed, with special emphasis on differential diagnosis of sleep apnea syndromes and other disorders characterized by symptoms of excessive daytime somnolence.

Circadian variation of dsip-like material in rat plasma

Levels of delta-sleep-inducing peptide-like immunoreactivity (DSIP-LI) in rat plasma were measured by radioimmunoassay and found to exhibit a circadian rhythm that parallelled the normal rhythm for corticosterone. The maximal plasma levels of both substances were observed to occur at about 1700h. The lowest concentrations of DSIP-LI and corticosterone were detected at 2400h and 1000h, respectively. Exposure to constant levels of illumination abolished the rhythm of DSIP-LI. It is possible that the temporal parallelism between the levels of DSIP-LI and corticosterone may represent a functional relationship between both compounds.

DSIP occurs in free form in mammalian plasma, human CSF and urine

Although delta-sleep inducing peptide was isolated and characterized several years ago, no definitive evidence has been presented for the natural existence of the free peptide. Several attempts at the partial characterization of DSIP-like immunoreactivity (DSIP-LI) have indicated that a small part of the total immunoreactivity is probably present as the free nonapeptide. Using gel chromatography (Sephadex G-100) and subsequent high performance liquid chromatography on rabbit, human, rat and dog plasma, we now show a distinct peak of DSIP-LI that has the same elution position as synthetic DSIP. Free DSIP was also found in human CSF, whereas in human urine most of the small molecular weight DSIP-LI eluted at a position corresponding to DSIP-P, the phosphorylated analog of DSIP. A newly developed antibody recognizing primarily small molecular weight DSIP-LI was used in a modified, rapid assay to facilitate demonstration of the natural occurrence of free DSIP.

Delta-sleep-inducing peptide (DSIP): a review

Since the turn of the century, it has been postulated that humoral factors induce sleep. Many compounds were proposed as sleep-factors, but only two of the sleep-peptides have been purified to homogeneity and characterized, so far. One of them, DSIP, was shown to be a nonapeptide of MW 849 and to induce mainly delta-sleep in rabbits, rats, mice, and humans, whereas in cats, the effect on REM sleep was more pronounced. A U-shaped activity curve was determined for the dose as well as for the time of infusion. DSIP-like material was found by RIA and immunohistochemistry in brain and by RIA in peripheral organs of the rat as well as in plasma of several mammals. In addition to sleep, the peptide also has been observed to affect electrophysiological activity, neurotransmitter levels in the brain, circadian and locomotor patterns, hormonal levels, psychological performance, and the activity of neuropharmacological drugs including their withdrawal.

Autoradiographic localization of binding sites for the delta sleep-inducing peptide ( [3H]DSIP) on neurons of cultured rat brainstem

Binding of the delta sleep-inducing peptide (DSIP) was studied in cultures of rat brainstem by means of autoradiography. Binding sites for [3H]DSIP were observed on small, medium-sized and large brainstem neurons but not on glial cells. Addition of unlabeled DSIP inhibited or markedly reduced binding of [3H]DSIP. It is suggested that brainstem neurons might possess receptors for this sleep-inducing peptide.

Analysis of the action of the neuropeptide-inducing delta-sleep in cats and white rats

Suboccipital administration of the oligopeptide to adult cats and white rats in a dose of 15 and 20 micrograms/kg induces the appearance of electrographic (delta-sleep) and behavioral sleep within 15-25 min. Administration of the oligopeptide induces a substantial increase in the thresholds of the response of the EEG to phonostimulation. A substantial lag (50-90 min) in the onset of paradoxical sleep is noted, which is considered by the authors as a manifestation of inhibition, exerted by the neuropeptide on the further development of the sleep mechanisms. On the basis of the data obtained it is concluded that natural sleep and that induced by the neuropeptide are nonequivalent.

Comparison of the effects of two 'sleep' peptides, delta sleep-inducing peptide and arginine-vasotocin, on single neurons in the rat and rabbit brain stem

The effects of delta sleep-inducing peptide and arginine-vasotocin were assessed on single neurons in the nucleus reticularis gigantocellularis of the brain stem in rats and rabbits. Both peptides showed predominantly excitatory actions in both species when applied by microiontophoresis. A small proportion of cells was inhibited by delta sleep-inducing peptide in the rat. Responses to delta sleep-inducing peptide were short-lasting, dose-dependent and showed no significant desensitization to repeated applications. Responses to arginine-vasotocin were of very long time course and showed profound desensitization. No statistically significant correlation was seen between cells responsive to delta sleep-inducing peptide and those responsive to arginine-vasotocin. We conclude that both 'sleep' peptides have similar actions on central neurons and that they are active in both rats and rabbits. However, no evidence was found to suggest a common mechanism of action for both substances.

Amphetamine-induced locomotor behavior of mice is influenced by DSIP

The delta sleep-inducing peptide (DSIP) has been shown to induce effects other than only delta sleep. One of these effects was the paradoxical thermoregulatory and locomotor response of rats to amphetamine after DSIP administration. In the present investigation we found similar effects of DSIP on the locomotor activity in mice. However, two different doses of DSIP (30 and 120 nmol/kg) and 3 doses of amphetamine (4, 10, and 15 mg/kg) produced a complex pattern of effects in mice tested at 22 degrees C. In general, DSIP-treated mice showed lower locomotor activity after amphetamine than controls, but under two conditions, both using 15 mg/kg amphetamine, DSIP produced higher scores; this occurred in the first two hours after amphetamine for the 30 nmol/kg DSIP group and in the third hour for mice given 120 nmol/kg DSIP. The results indicate that the effects of DSIP on locomotor behavior were dependent on the dosage of the peptide and the time of measurement as well as the level of amphetamine stimulation.

DSIP-induced changes of the daily concentrations of brain neurotransmitters and plasma proteins in rats

The influence of delta sleep-inducing peptide (DSIP) on the brain neurotransmitters 5-HT, dopamine and norepinephrine and plasma proteins/corticosterone concentrations for four time points within the 24 hr following IV injection of 30 nmol/kg was investigated in rats. DSIP administered in the morning or in the evening respectively induced changes in nearly all measured parameters. Different effects were observed for different times of administration. The most marked changes were found in the level of serotonin during daytime. In view of the multivariate results obtained by measuring several parameters at multiple time points, a method was developed to describe the time-dependent changes. By means of "circadian rhythm statistics" based on a statistical likelihood analysis we found that multiple and different changes within the factor's daily variation are induced by one injection of DSIP. A multidimensional scaling of the results provides further insights into the correlations of the DSIP-induced effects on plasma and brain factors which are therefore tentatively termed "programming functions." These apparently involve not just sleep induction but also act on multiple parameters within the 24 hr rest-activity period.

DSIP/DSIP-P and circadian motor activity of rats under continuous light

Daily intravenous injection of 30 nmol/kg DSIP (delta sleep-inducing peptide) in rats under constant illumination produced marked changes of their motor activity as compared to saline controls. Similar marked but distinctly different effects on the circadian pattern of locomotor behavior partially abolished by constant illumination were also obtained after repeated administration of 0.1 nmol/kg DSIP-P (the phosphorylated analogue of DSIP) which enhanced overall motor activity. In both instances the results additionally differed from those reported for a normal 12 hr light:dark cycle. The present results support the hypothesis that DSIP might primarily act by influencing circadian rhythmicity.

Effects of repeated DSIP and DSIP-P administration on the circadian locomotor activity of rats

Daily intravenous evening injections of 30 nmol/kg DSIP (Delta Sleep-Inducing Peptide) in rats adapted to a constant 24 hr light:dark cycle produced changes in the circadian locomotor behavior. After 3 days the normally high locomotor activity during the dark phase was reduced while during the light (sleeping) phase the animals became relatively more active. Similar, but more rapid and more marked changes were observed (with the same schedule of injections) after 0.1 nmol/kg DSIP-P (the analogue of DSIP phosphorylated at the serine in position 7). In fact the peptide and its analogue induced a relative reversal or shift of the circadian locomotor activity phases opposite to the persisting light:dark conditions (=Zeitgeber). This suggests that DSIP exerts rather complex "programming" effects on the circadian activities and has more than just a sleep-inducing activity.

The influence of synthetic DSIP (delta-sleep-inducing-peptide) on disturbed human sleep

The effects of acute intravenous administration of synthetic DSIP, 25 nmoles/kg b.wt, on disturbed human sleep were tested in 6 middle-aged chronic insomniacs. The results were: longer sleep duration and a higher quality of sleep with fewer interruptions; slightly more REM-sleep, but no day-time sedation or other side effects though the sleep enhancing capacity was seen for up to 6 h of night sleep. Sleep-promoting effects occurred only in the second hour after injection, in the first hour a slight arousing effect was indicated. The study corroborates the findings of previous investigations in healthy subjects and shows that DSIP has a normalizing influence on human sleep regulation.