Antagonism of the effect of delta sleep-inducing peptide by naloxone in the rat

Phosphorylated delta sleep inducing peptide restores spatial memory and p-CREB expression by improving sleep architecture at high altitude

AIMS

Sleep loss at high altitude (HA) play major role in worsening of neuropsychological functions, such as attention, memory and decision making. This study investigates the role of phosphorylated delta sleep inducing peptide (p-DSIP) in improving sleep architecture during chronic hypobaric hypoxia (HH) exposure and restoration of spatial navigational memory.

METHODS

Morris water maze (MWM) trained rats were exposed to HH at 7620 m. p-DSIP was injected intra-peritoneally (10 μg/Kg bw) during HH exposure as an intervention against sleep alteration. Sleep architecture was recorded telemetrically before and during HH exposure. Monoamines were estimated by high performance liquid chromatography from brain stem (BS) and hypothalamus. CREB and p-CREB level in hippocampus was studied by western blotting and expression of different monoamine regulatory enzymes in BS was measured by flow cytometry. Naloxone (1 mg/kg bw), a μ opioid receptor antagonist of sleep inducing effect of DSIP was also studied.

KEY FINDINGS

p-DSIP injection daily in circadian active period (18.30 h) during chronic HH enhanced non rapid eye movement sleep, rapid eye movement sleep as well as improved MWM performance of rats. p-DSIP treatment showed lower monoamine level and tyrosine hydroxylase (TH) expression and increased monoamine oxidase A (MAO A), glutamic acid decarboxylase (GAD) and Choline acetyltransferase (ChAT) expression. Further, naloxone altered navigational memory by decreasing the CREB and p-CREB level in hippocampus suggesting suppression of sleep inducing effect of p-DSIP.

SIGNIFICANCE

Our study demonstrates that improvement of sleep quality by p-DSIP restores spatial memory by up regulating CREB phosphorylation during simulated high altitude hypoxia.

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.

The phosphorylated analogue of DSIP enhances slow wave sleep and paradoxical sleep in unrestrained rats

Continued 10-h nocturnal intracerebroventricular infusion of 0.5 nmol P-DSIP, the phosphorylated analogue of delta-sleep-inducing peptide (DSIP), significantly increased slow wave sleep (22%) and paradoxical sleep (81%) in unrestrained rats. The increase in the amount of sleep was largely due to an increase in the number of sleep episodes. Larger and smaller doses were ineffective in doses ranging from 0.025 to 25 nmol. The sleep-promoting potency of P-DSIP was 5 times greater than that of DSIP compared by the same assay.

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.

DSIP--a tool for investigating the sleep onset mechanism: a review

Delta-Sleep-Inducing Peptide (DSIP) has several physiological effects in addition to its ability to promote sleep in animals under certain conditions. These effects include modification in thermoregulation, heart rate, blood pressure, pain threshold, and in the lymphokine system. DSIP effects are circadian cycle-dependent. Moreover, some of DSIP effects appear before neurological or behavioral signs of sleep. DSIP may promote peripheral preparatory physiological mechanisms associated with sleep onset.

Delta-sleep-inducing peptide (DSIP): an update

The isolation and characterization of delta-sleep-inducing peptide (DSIP) achieved from 1963 to 1977 were reviewed in 1984. The first reports describing sleep as well as extra-sleep effects of DSIP also were included in that work. Only two years later, much additional literature concerning DSIP has accumulated. Besides further sleep-inducing and/or -supporting effects of DSIP in animals, considerable work has been carried out to evaluate the potential use of the peptide for therapeutic purposes such as treatment of insomnia, pain, and withdrawal. Immunohistochemical as well as radioimmunochemical studies provided further insights into the natural occurrence of the nonpeptide and the distribution of DSIP-like material in the body, suggesting possible relations of the peptide to certain diseases. Various physiological functions of DSIP and a possible mechanism of action involving the modulation of adrenergic transmission remain to be established.

DSIP affects adrenergic stimulation of rat pineal N-acetyltransferase in vivo and in vitro

The natural occurrence, sleep, and extra-sleep effects of delta sleep-inducing peptide (DSIP) have been shown by different laboratories. However, neither an in vitro assay system nor a probable mechanism of action of the peptide have been conclusively demonstrated so far. The recent finding that DSIP influences the nocturnal rise of N-acetyltransferase (NAT) activity in rat pineal led us to investigate a possible effect on pharmacologically induced NAT activity in vivo and in vitro. Stimulation of the enzyme with adrenergic drugs such as isoproterenol and phenylephrine was reduced by DSIP at doses of 150 and 300 micrograms/kg injected subcutaneously. In vitro, 6, 150 and 300 nM DSIP attenuated isoproterenol stimulation of the enzyme in cultured pineals, whereas 150 nM DSIP effectively reduced stimulation induced by a combination of the two drugs. The peptide alone did not influence NAT activity in vitro, but produced a slight stimulation in vivo. To our knowledge, these results represent the first report of a direct interaction of DSIP with adrenergic transmission. The in vitro system could prove useful for establishing possible mechanism(s) of action of the 'sleep peptide.'