The Delta-Sleep Inducing Peptide in Cerebral Mechanisms of Emotional Stress

The problem of the anti-stressor effect of the delta-sleep inducing peptide (DSIP) and of its neurophysiological mechanisms of action is considered. Physiological data are exposed that indicate an intraventricular administration of DSIP in rats to results in an increase of resistance to emotional stress, according to behavioral and autonomous reactions, and in a decrease of excitability of the brain structures responsible for protective reaction. Radioimmunological evidence is presented for the resistance of animals to emotional stress to depend on the content in hypothalamus of certain oligopeptides, such as -endorphin, DSIP, and the substance P. It was shown that animals resistant to emotional stress had a higher content of these oligopeptides in hypothalamus than those predisposed to stress. The issue is discussed that the prolonged anti-stressor effects after the DSIP administration are determined by considerable changes of the content of other polypeptides and hormones in hypothalamus and blood, which are involved in the reaction under the effect of DSIP.     

Analysis of the mechanism of the stress-protective action of delta sleep-inducing peptide

By RIA there were studied the contents of corticosterone, ACTH, beta-endorphin and insulin in the blood plasma, met- and leu-enkephalin in different regions of the rat brain and in the adrenal glands after a 6-hour immobilization. The stress increased the content of corticosterone, ACTH, beta-endorphin, but not insulin in the blood plasma, and the levels of met-enkephalin in the adrenal glands, but decreased the met-enkephalin contents in the striatum. The injection of DSIP (0.1 mg/kg, i/p) blocked partly the elevation of corticosterone only. The authors propose, that stress-protective action of DSIP is realized with the involvements of the hypothalamo-pituitary-adrenal gland system.     

Electroencephalographic analysis of inter-central relations in hypothalamo-reticulo-limbic brain structures during treatment with corticosteroids and neuropeptides

Intercentral relations between hypothalamus, limbic system and reticular formation were studied in rabbits and rats under systemic and central action of DSIP, ACTH, corticosteroids and stress (aggressive-defensive behaviour). The results obtained demonstrate changes in the adrenal cortex resulting from stress-inducing adrenocortical hormone content. The increase was achieved by the rise in ACTH level resulting in corticosteroid level elevation (endogenous elevation-aggressive behaviour) and by corticosteroid injections (exogenous elevation). Correlation analysis of structural interrelations after ACTH and corticosteroid injections demonstrated an increased correlation between hypothalamo-reticular-limbic structures. DSIP was shown to have an opposite effect. Correlation analysis revealed the potentials for the formation of new functional interrelations between hypothalamo-reticular-limbic structure in the motivation of aggression (stress) and the levels of corticosterone and DSIP. DSIP action depends on the initial corticosteroid blood level and is more marked in stress-inducing concentrations.     

Effects of ethanol on the concentration of neuropeptides, ACTH and corticosterone during immobilization stress

It was shown, that stress increased the level of ACTH, beta-endorphin and corticosterone in the blood plasma of the rat. Injection of ethanol (1 g/kg) decreased the level of ACTH, but increased the levels of beta-endorphin in the rat subjected to immobilization stress. The immobilization lowered the levels of met-enkephalin in the striatum and medulla oblongata, but increased the content of neuropeptide in the adrenal glands. The concentration of leu-enkephalin and DSIP remained unchanged following the stress. Ethanol reversed the action of immobilization on the level of met-enkephalin in the striatum, but increased the content of DSIP in the thalamus. These results indicate that ethanol modified the activity of pituitary-adrenal-axis during stress and probably the stress-protective action of ethanol partly performed with the involvement of DSIP.     

The delta sleep-inducing peptide as a factor enhancing the content of substance P in the hypothalamus and the resistance of rats to emotional stress]

The influence of the delta-sleep inducing peptide (DSIP, 60 and 120 nmol/kg, intraperitoneally) on the content of substance P (SP) in rats hypothalamus was studied on males of August line. DSIP administration significantly increased the mean SP content in the hypothalamus and also its content in animals, stable and predisposed to emotional stress. Daily DSIP administration before putting the rats in conditions of stress increased the SP content in the hypothalamus decreased at the emotional stress. Preliminary single DSIP administration to the animals subjected to stress also increased the SP content. Single DSIP administration in a dose of 60 nmol/kg sharply reduced classical stress manifestations, such as hypertrophy of adrenals and thymus involution.     

Aminopeptidase P from rat brain. Purification and action on bioactive peptides.

Aminopeptidase P (EC 3.4.11.9) was purified from rat brain cytosol. A subunit Mr of 71,000 was determined for the reduced, denaturated protein whereas an Mr of 143,000 was determined for the native enzyme. The purified aminopeptidase P selectively liberated all unblocked, preferentially basic or hydrophobic ultimate amino acids from di-, tri- and oligopeptides with N-terminal Xaa-Pro- sequences. Corresponding peptides with penultimate Ala instead of Pro were cleaved with much lower rates; oligopeptides with residues other than Pro or Ala in the penultimate position appeared not to be substrates for the enzyme. Several bioactive peptides with Xaa-Pro sequences, especially bradykinin, substance P, corticortropin-like intermediate lobe peptide, casomorphin and [Tyr]melanostatin were shortened by the N-terminal amino acid by aminopeptidase P action. Rat brain aminopeptidase P was optimally active at pH 7.6-8.0 in the presence of Mn2+. Chelating agents and SH-reacting reagents inhibited the enzyme, but common inhibitors of aminopeptidases, like amastatin or bestatin, of prolidase or of dipeptidyl peptidases II and IV, like N-benzoyloxycarbonyl-proline or epsilon-benzyl-oxycarbonyl-lysyl-proline, as well as antibiotics like beta-lactam ones, bacitracin or puromycin, had little or no effect.     

Obliteration of alpha-melanocyte-stimulating hormone derived from POMC in pituitary and brains of PC2-deficient mice

Alpha-melanocyte-stimulating hormone (alpha-MSH) is a neuropeptide expressed in pituitary and brain that is known to regulate energy balance, appetite control, and neuroimmune functions. The biosynthesis of alpha-MSH requires proteolytic processing of the proopiomelanocortin (POMC) precursor. Therefore, this study investigated the in vivo role of the prohormone convertase 2 (PC2) processing enzyme for production of alpha-MSH in PC2-deficient mice. Specific detection of alpha-MSH utilized radioimmunoassay (RIA) that does not crossreact with the POMC precursor, and which does not crossreact with other adrenocorticotropin hormone (ACTH) and beta-endorphin peptide products derived from POMC. alpha-MSH in PC2-deficient mice was essentially obliterated in pituitary, hypothalamus, cortex, and other brain regions (collectively), compared to wild-type controls. These results demonstrate the critical requirement of PC2 for the production of alpha-MSH. The absence of alpha-MSH was accompanied by accumulation of ACTH, ACTH-containing imtermediates, and POMC precursor. ACTH was increased in pituitary and hypothalamus of PC2-deficient mice, evaluated by RIA and reversed-phase high pressure liquid chromatography (RP-HPLC). Accumulation of ACTH demonstrates its role as a PC2 substrate that can be converted for alpha-MSH production. Further analyses of POMC-derived intermediates in pituitary, conducted by denaturing western blot conditions, showed accumulation of ACTH-containing intermediates in pituitaries of PC2-deficient mice, which implicate participation of such intermediates as PC2 substrates. Moreover, accumulation of POMC was observed in PC2-deficient mice by western blots with anti-ACTH and anti-beta-endorphin. In addition, increased beta-endorphin1-31 was observed in pituitary and hypothalamus of PC2-deficient mice, suggesting beta-endorphin1-31 as a substrate for PC2 in these tissues. Overall, these studies demonstrated that the PC2 processing enzyme is critical for the in vivo production of alpha-MSH in pituitary and brain.     

Comparative immunocytochemical localization of putative opioid ligands in the central nervous system

We report a detailed comparative immunocytochemical mapping of enkephalin, CCK and ACTH/beta-endorphin immunoreactive nerves in the central nervous system of rat and guinea pig. Enkephalin immunoreactivity was detected in many groups of nerve cell bodies, fibers and terminals in the limbic system, basal ganglia, hypothalamus, thalamus, brain stem and spinal cord. beta-endorphin and ACTH immunoreactivity was limited to a single group of nerve cell bodies in and around the arcuate nucleus and in fibers and terminals in the midline areas of the hypothalamus, thalamus and mesencephalic periaqueductal gray with lateral extensions to the amygdaloid area. Cholecystokinin immunoreactive nerve fibers and terminals displayed a distribution similar to that of enkephalin in many regions; but striking differences were also found. An immunocytochemical doublestaining technique, which allowed simultaneous detection of two different peptides in the same tissue section, showed that enkephalin-, CCK- and ACTH/beta-endorphin-immunoreactive nerves although closely intermingled in many brain areas, occurred separately. The distributions of nerve terminals containing these neuropeptides showed striking overlaps and also paralleled the distribution of opiate receptors. This may suggest that enkephalin, CCK, ACTH and beta-endorphin may interact with each other and with opiate receptors.     

Effects of cortisol treatment on brain and adrenal corticotropin-releasing hormone (CRH) content and other parameters regulated by CRH

Corticotropin-releasing hormone (CRH) has been found in both hypothalamic and extrahypothalamic sites of the brain and also in the adrenal medulla. To study the timing and location of delayed glucocorticoid action in rats, we measured the effects of 2-day and 7-day cortisol treatment on immunoreactive CRH concentrations in hypothalamus, cerebral cortex, hippocampus, cerebellum, and adrenal gland. The activity of the hypothalamo-pituitary-adrenal (HPA) axis and the sympathoadrenal system were also measured. Studies were carried out both in the afternoon and/or in the morning, to get information about possible circadian changes. CRH contents were not changed in any brain areas studied, except there was a trend of decrease in the hypothalamus compared to vehicle in the afternoon due to the lack of circadian increase after 7-day cortisol treatment. Pituitary ACTH content decreased significantly after 7-day treatment, while beta-endorphin did not. Plasma levels of ACTH, corticosterone, norepinephrine and epinephrine and adrenal ACTH and beta-endorphin contents decreased after 2-day, adrenal CRH content after 7-day treatment with cortisol. Our findings suggest, that chronic cortisol treatment inhibits the circadian activation of the HPA axis at all levels but has variable effects on baseline measures because it causes different changes in release and synthesis at different sites.     

Effects of beta endorphin and delta-sleep inducing peptide on resistance to emotional stress

Enzyme immunoassay was used to study the contents of beta-endorphin and delta-sleep inducing peptide (DSIP) in blood and hypothalamus in rats of Wistar and August lines under acute emotional stress. The stress-resistance of the animals was determined by using preliminary behavior tests. The rats were divided into two groups and predisposed to acute emotional stress. It was found that the contents of these peptides in Wistar-rats, which are more resistant to emotional stress, were higher compared with the August-rats, which are more predisposed to emotional stress. It was shown that the contents of beta-endorphin and DSIP in Wistar-rats is higher than in predisposed Wistar-rats.     

Substance P in the central mechanism of the rabbit feeding response evoked by stimulation of the lateral hypothalamus

The effects of substance P on the central mechanisms of food motivation elicited by electrical stimulation of the lateral hypothalamus were studied in chronic experiments on rabbits. Intravenous injection of substance P (30 micrograms/kg) brought about a dramatic reduction in the excitability of the "food center" in the hypothalamus, which returned to normal 45-60 minutes after injection. Higher concentrations of substance P provoked food behavior inversion up to the replacement of food motivation by avoidance behavior. Intravenous injections of substance P disturbed the relationships between the hippocamp, midbrain reticular formation and hypothalamus seen in health. This manifested in complete cessation of the inhibitory effects of the dorsal hippocamp and facilitating influences of the midbrain reticular formation on the excitability of the hypothalamic "food center". It is assumed that disorders of the central mechanisms of food motivation may arise from the effects produced by substance P directly on the central nervous system or on the brain via changes in the hormonal balance and responses of the autonomous nervous system.     

Effect of beta-endorphin on catecholamine levels in the rat hypothalamus and cerebral cortex

The present paper deals with the effect of beta-endorphin on catecholamine content in the hypothalamus and cerebral cortex of male rats. beta-endorphin was found to decrease catecholamine content in the rat brain, with the degree of reduction depending on the brain topography and the time following the peptide administration. 5 min later no changes in catecholamine content were observed either in the hypothalamus or in the cerebral cortex. 20 min later beta-endorphin induced a statistically significant fall of catecholamine concentration in the hypothalamus. A tendency towards its decrease was also observed in the cerebral cortex. 60 min later beta-endorphin produced an insignificant decrease in catecholamine level in both brain areas under study. It may be therefore suggested that beta-endorphin-induced decrease of catecholamine content in the hypothalamus and cerebral cortex represents one of the mechanisms underlying beta-endorphin stimulating action on a number of trophic functions of the hypophysis.     

Comparison of structural and functional organization of adrenocorticotropic hormone and wasp kinin]

A comparative study of structural and functional organization of the polypeptides -- ACTH and wasp kinin was made. The effects of fragments Lys 17, 18-ACTH11(-18)-NH2--(I) and WK4(-12)--(II), possessing "common" fragments and a cluster of basic amino-acids, on the lipolytic and steroidogenic effects of ACTH and myotropic effects of bradykinin were studied. Both fragments I and II potentiate ACTH-induced lipolysis and steroidogenesis in isolated rat fat and adrenal cells but suppress the myotropic effect of bradykinin on guinea pig ileum. The similarity of biological effects of ACTH and WK fragments support our supposition on the similarity in structurally functional organization of these peptides.     

Substance P in the central mechanisms of the escape reaction

The role of substance P in the central mechanisms of escape reaction elicited by electrical stimulation of the ventromedial hypothalamus was investigated in chronic experiments on rabbits. Intravenous injection of substance P (30 micrograms/kg) led to a short-term (less than 10 min) increase in the threshold of stimulation of the ventromedial hypothalamus and to more stable (up to 1.5 h) disorders of the hippocampal-hypothalamic relations. After substance P injection the inhibitory effects of the dorsal hippocampus but not the facilitating influences of the midbrain reticular formation on excitability of the hypothalamic motivation center were found to be lacking. Disorders of the central mechanisms of escape reaction after substance P injection correlated with new patterns of the main EEG rhythms in different areas of the brain cortex in response to the ascending excitations of the limbic-midbrain structures. Interpreting the mechanisms of substance P involvement in escape reaction the authors point to the ability of the given peptide to interact with different transmitter systems of the brain and opiate receptors and to alter the brain blood circulation.     

Distribution of the delta sleep-inducing peptide in the brain of rabbits: study by immunofluorescence

Using the indirect immunofluorescence method, the distribution of the Delta Sleep Inducing Peptide (DSIP)-containing neurons was studied in the rabbit brain. DSIP antisera were raised in rat by multiple injections of synthetic DSIP conjugated to thyroglobulin. Some DSIP immunoreactive cell bodies were detected in the diagonal band of Broca and anterior part of the hypothalamus. Large populations of immunofluorescent fibers and terminals were visualized mainly through the organum vasculosum of the lamina terminalis, the preoptic areas, the subfornical organ, the thalamus, the ventromedial hypothalamus and infundibulum. Further, most of the cells of the intermediate lobe of the hypophysis displayed DSIP-immunoreactivity. The predominant localization of DSIP-immunoreactive fibers and terminals in certain circumventricular organs suggests that DSIP could play a specific role in the neurohumoral regulation.     

Content of endogenous opiates and adrenocorticotropic hormone in the brain structures of rats of different ages

The contents of beta-endorphin (BE), methionine-enkephalin (MEK), and adrenocorticotropic hormone (ACTH) in the hypophysis and hypothalamus of intact 4- to 6-week-old and 16-week-old Wistar rats was studied. The maximum BE concentration was found in the hypophysis, whereas the maximum MEK and ACTH concentrations were found in the hypothalamus. Aging was followed by a decrease in the concentrations of all above substances, except BE, whose concentration in the hypophysis of the older rat group was markedly higher than in the hypophysis of 4- to 6-week-old animals.     

Substance P enhances cation permeability of neuronal cell lines

Substance P stimulated the uptake of guanidinium in neuroblastoma X glioma hybrid cells and neuroblastoma cells but not in polyploid glioma cells. Guanidinium has previously been shown to pass the action potential Na+ channel in the two neuronal cell lines. Half-maximal stimulation was reached at 3 microM substance P and, with the hybrid cells, a saturation was seen above 10 microM. The analogue (D-Pro2,D-Trp7,9)-substance P, recently described as a substance P antagonist, caused a stimulation of guanidinium uptake comparable to that seen in the presence of substance P and did not inhibit the stimulation exerted by substance P. The pharmacological properties of the substance P-activated ion channel were investigated. Tubocurarine, phentolamine and propranolol blocked the substance P-stimulated guanidinium uptake with half-maximal inhibitory concentrations of 0.5, 5 and 50 microM. A similar characteristics has been found previously with the veratridine-activated Na+ channel in the cell lines investigated here. Peptides structurally related to substance P such as physalaemin and eledoisin, or others such as neurotensin, bradykinin, D-Ala2, Met5-enkephalinamide and ACTH(1-24) did not affect guanidinium uptake. In view of the high concentrations of substance P required for eliciting an effect in the cell lines, the involvement of specific receptors is questioned. A direct interaction of the peptide with the action potential Na+ channel is discussed.     

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.     

Endogenous Peptides That Inhibit Brain Cyclic AMP Phosphodiesterase

Peptide extracts of rat brain powerfully inhibited the cyclic AMP phosphodiesterase activity of rat brain homogenate. Similar extracts of ox brain showed comparable although less potent activity. Preliminary investigation of the physicochemical properties of brain extracts indicated that the rat brain extract contained an active peptide of low molecular weight (about 1400), whereas ox brain contained two such peptides (about 1400 and 900). These studies indicate that endogenous oligopeptides that inhibit cyclic AMP phosphodiesterase are present in brain. Experiments on several pure peptides known to be present in brain. Experiments on several pure peptides known to be present in the CNS showed that the majority were inactive against brain phosphodiesterase, but ACTH(1-24), somatostatin, substance P and Lys8-vasopressin, in descending order of potency, were active. To help distinguish the peptides found in rat and ox brain extracts from known peptides, preliminary analyses of amino acid composition were performed. These suggested that the peptides found in brain extracts were distinct from known peptides having the ability to inhibit cyclic AMP phosphodiesterase.     

Effect of beta-endorphin on endocrine function

It has been disclosed that beta-endorphin exerts marked effect on the secretion of ACTH, prolactin, corticosterone, aldosterone and somatotrophin formation in the pituitary but does not produce any effect on blood thyrotropin. Maximal rise in the concentration of the hormones was seen at the 20th minute, despite the fact that an elevation in the content of some hormones was recorded at the 5th minute following intravenous injection of beta-endorphin. At the 60th minute after beta-endorphin injection the content of prolactin, corticosterone and aldosterone in the blood dropped to the control level, while ACTH content remained significantly higher than in intact animals. One of the possible mechanisms underlying the action of beta-endorphin on the secretion of the hormones indicated might be the changes in the ratio of brain monoamines (a decrease in dopamine).