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

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.

Chromatin-derived acidic peptides modulate catecholamine release in the hypothalamus

We have studied the neuromodulatory effects of three synthetic peptides, structurally related to chromatin-derived acidic peptides (ACPs): ACP-1 (Asp-Asp-Ser-Asp-Glu-Glu-Asn), corresponding to the C-terminal fragment of the largest subunit of eukaryotic RNA polymerase II; a more lipophilic derivative, ACP-2 (Ala-Ile-Ser-Pro-Asp-Asp-Ser-Asp-Glu-Glu-Asn); and its phosphorylated form ACP-3 (Ala-Ile-Ser-Pro-Asp-Asp-Ser(P)-Asp-Glu-Glu-Asn). Rat hypothalamic synaptosomes, loaded with [(3)H]norepinephrine or [(3)H]dopamine, were perfused with the above peptides, both basally and during a depolarizing stimulus. We have found: ACP-1 inhibited both dopamine and norepinephrine release; ACP-2 inhibited dopamine release, without affecting norepinephrine release; ACP-3 was almost ineffective, except for a weak dopamine inhibiting effect only at a higher concentration.

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.

The effect of delta sleep-inducing peptide (DSIP) and phosphorylated DSIP (P-DSIP) on the apomorphine-induced hypothermia in rats

Delta sleep-inducing peptide (DSIP) and P-DSIP, phosphorylated analogue, were found to have enhancing effects on hypothermia induced by i.p. injection of apomorphine (2 mg/kg), a dopamine agonist. Further, the action of P-DSIP appeared and diminished more quickly than that of DSIP. A minimal effective dose of these peptides was 10 ng and the dose-response relationship exhibited an inverted bell-shape with a maximal effective dose of 1 microgram. By the pretreatment of anti-DSIP the enhancing effect of DSIP but not P-DSIP, was totally abolished and the action of both peptides was antagonized by haloperidol. These findings suggest that DSIP and P-DSIP have a close relation to the dopaminergic system on the thermoregulatory mechanisms.