Norepinephrine-like effects of neuropeptide Y on LH release in the rat

Neuropeptide Y, a recently isolated neuropeptide exhibited norepinephrine-like effects on LH release after intracerebroventricular administration at doses from 0.5 to 10 micrograms. While it promptly suppressed LH release in ovariectomized rats, there was a dose-related stimulation of LH secretion in ovarian steroid primed-ovariectomized rats. In view of the evidence that neuropeptide Y may coexist with adrenergic neurotransmitters, these findings suggest that it may play a role in regulation of LH release in the rat, either independently or in concert with catecholamines.     

The effects of pancreatic polypeptides and neuropeptide Y on the rat vas deferens

In order to study the physiological significance of the coexistence of pancreatic polypeptide and norepinephrine (NE) in peripheral noradrenergic nerves, the effects of pancreatic polypeptides of several species were tested on the isolated rat vas deferens. Neuropeptide Y (NPY) was also studied because of its sequence homology to the pancreatic polypeptides. The contractile responses, which were mediated predominantly by activation of noradrenergic nerves following electrical stimulation, were inhibited by bovine pancreatic polypeptide (BPP), human pancreatic polypeptide (HPP), avian pancreatic polypeptide (APP) and NPY in a dose-dependent manner using a constant flow bath. The decreasing order of the inhibitory responses was as follows: BPP = HPP greater than NPY greater than APP. The inhibitory responses produced by BPP and HPP lasted more than 1 hr and displayed a marked tachyphylaxis. In contrast, the inhibitory effects induced by NPY and APP usually returned to the control level after 20-30 min and had minimal tachyphylaxis. The inhibitory action of NPY was still present during alpha-adrenergic blockade. Contractions produced by a single submaximal dose of exogenous NE or serotonin (5-HT) in unstimulated preparations were not affected by pretreatment with NPY. The amplitude of contractions was partially reduced 1 min after pretreatment with BPP or HPP; recovery occurred about 15 min after peptide pretreatment in a constant flow bath. These results suggest that an NPY receptor exists presynaptically in the rat vas deferens and that stimulation of the receptor by NPY inhibits the release of NE from noradrenergic nerves.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of neuropeptide Y on rat body temperature in normal conditions and after ethanol administration]

It was shown that intracerebroventricular (icv) administration of 2 micrograms neuropeptide Y (NPY) increased the rectal temperature in rats 2.5 hours postinjection. During 5 days we analysed dynamics of the effect of NPY on alcohol-induced hypothermia in this particular interval. 2 micrograms of NPY were given daily 30 min prior to 25% solution of ethanol (3 g/kg weight rat) intraperitoneal injection. It was found that NPY can prevent the attenuation of alcohol hypothermia on the 3-d and 4-th injection day. It was supposed that the inhibitory effect of NPY on the development of alcohol tolerance may be due to the capacity of NPY to increase food behavior. So it's known that activation of other competitor motivation may inhibit the development of alcoholism.     

Naloxone blocks 'anxiolytic' effects of neuropeptide Y

Intracerebroventricular injection of neuropeptide Y (NPY) produces potent 'anxiolytic' effects in animal models of anxiety. Administration of opioid receptor antagonists suppresses NPY-induced food intake and thermogenesis. The present study examined whether the opiate antagonist naloxone would also suppress the 'anxiolytic' effects of neuropeptide Y. Following training and stabilization of responding in an operant conflict model of anxiety, rats were injected with either NPY or diazepam. Both NPY (veh., 2, 4, 6 microg, i.c.v.) and chlordiazepoxide (veh., 2, 4, 6 mg/kg, i.p.) produced a dose-dependent increase in punished responding in the conflict test. The 'anxiolytic' effects of NPY were not blocked by the administration of flumazenil (3, 6, 12 mg/kg, i.p.). The administration of naloxone (0.25-2.0 mg/kg, s.c.) antagonized the effects of NPY. Central administration of the selective mu opiate antagonist CTAP (1 microg, i.c.v.) partially blocked NPY-induced conflict responding. These results support the hypothesis that NPY may play an important role in experimental anxiety independent of the benzodiazepine receptor and further implicate the opioid system in the behavioral expression of anxiety.     

Distribution of neuropeptide Y immunoreactivity in the forebrain of the rat

The distribution of neuropeptide Y (NPY) like immunoreactivity was investigated in the forebrain of the rat with immunohistochemical methods. Specificity of the antisera was established by the absence of all immunoreactive staining in tissue incubated in antisera which had been preabsorbed with the pure NPY antigen. NPY containing cells were distributed widely in the forebrain. These included neocortex, basal forebrain, septum, bed nucleus of the stria terminalis, neostratium, hypothalamic arcuate nucleus, and intergeniculate leaflet. This study also demonstrated an extensive network of NPY fibers in various areas of the forebrain such as the prepotic area, the hypothalamus and the paraventricular nucleus of the thalamus. The distribution of avian pancreatic polypeptide and NPY was compared, and the possible importance of NPY is briefly discussed.     

Stress-induced changes of circulating neuropeptide Y in the rat: comparison with catecholamines

Circulating concentrations of neuropeptide Y-like immunoreactivity (NPY), noradrenaline (NA) and adrenaline (AD) were measured in conscious, chronically catheterized rats submitted to various stress protocols. Basal plasma levels of NPY, NA and AD (194 +/- 52 fmol/ml, 0.90 +/- 0.11 pmol/ml and 0.52 +/- 0.07 pmol/ml) were increased by handling (+132%, +76% and +629%, respectively) and rose further during electric shock treatment. Adrenalectomy resulted in the complete disappearance of circulating adrenaline but did not alter either control or stress values of noradrenaline. In comparison circulating levels of NPY were reduced, but not significantly in adrenalectomized animals. Insulin stress induced a large increase in plasma AD levels and cold stress induced an increase in plasma NA levels, without any parallel change in NPY concentrations. These results demonstrate that NPY, which is colocalized with catecholamines in the peripheral nervous systems, is also released during stress responses and that its release parallels more closely changes in circulating NA than AD. Furthermore, stress-induced changes in circulating NPY-like immunoreactivity do not originate from the adrenal gland but mainly from the peripheral nervous system, and the release of NPY is dependent upon the nature of the stimulus.     

Daily variation of rat brain fucosyltransferase

Glycoprotein fucosyltransferase activity was investigated in rat brain during 24 h periods. Up to 50 % variations were detected without correlations with either lights on or off, while acetylcholinesterase located in same membrane fractions showed no level variations.     

Tumor anorexia: effects on neuropeptide Y and monoamines in paraventricular nucleus

Paraventricular (PVN) concentrations of neuropeptide Y (NPY), serotonin (5-HT) and dopamine (DA) in anorectic tumor-bearing (TB) rats were measured before and after tumor resection. At onset of anorexia in TB versus non-tumor bearing (NTB) Controls 5-HT increased from 12.19+/-0.49 pg/microg to 14.89+/-0.81 pg/microg ( P<0.05 ) while DA and NPY decreased from 7.34+/-0.42 pg/microg to 4.97+/-0.56 pg/microg and 23.47+/-4.27 pg/microg to 13.64+/-1.44 pg/microg, respectively ( P<0.05 ). After tumor resection, these neuromediators normalized when compared to sham-operated NTB rats. NTB pair-fed Controls were also studied. We conclude that the increased 5-HT and the decreased DA and NPY concentrations in PVN are associated with cancer anorexia and that the NPY food stimulatory effect is linked to serotoninergic and dopaminergic systems in hypothalamus.     

Plasma concentration of neuropeptide Y in patients with adrenal hypertension.

The mechanisms of hypertension during primary hyperaldosteronism and Cushing's syndrome are not completely understood. An enhanced vascular sensitivity to noradrenaline has been described in both situations. Neuropeptide Y (NPY) induces direct vasoconstriction and potentiates the action of noradrenaline. Sodium retention and dexamethasone have been shown to increase circulating NPY levels in animals and the expression of NPY in neuroendocrine cells. In order to determine if NPY could be involved in the enhanced vascular sensitivity to noradrenaline associated with adrenocortical hyperactivity, we measured plasma NPY in patients with Cushing's syndrome (n = 26) and primary hyperaldosteronism (n = 15) and compared it with that of hypertensive patients with pheochromocytomas (n = 13) or essential hypertension (n = 51) and with normotensive controls (n = 47). The concentration of NPY-Like immunoreactivity (NPY-Li) (mean +/- S.E.) in controls was 39.6 +/- 3.0 pg/ml. Elevated concentrations were found in 77% of the samples collected from pheochromocytoma patients (1180.4 +/- 394.0 pg/ml). NPY-Li levels in patients with essential hypertension (35.0 +/- 2.6 pg/ml), primary hyperaldosteronism (31.3 +/- 3.9 pg/ml) and Cushing's syndrome (33.1 +/- 4.8 pg/ml) were not different from that of controls. NPY-Li levels in hypertensive and normotensive patients with Cushing's syndrome were similar (38.5 +/- 7.5 vs 24.2 +/- 3.7 pg/ml). No correlation was found between the NPY-Li level and the mean blood pressure at the time of sampling. Our results suggest that NPY is unlikely to be involved in the pathogenesis of hypertension associated with primary hyperaldosteronism and Cushing's syndrome.     

Daily changes of neuropeptide Y-like immunoreactivity in the suprachiasmatic nucleus of the rat

Most of the biochemical, physiological and behavioural events in living organisms show diurnal fluctuations, normally synchronized with 24-h environmental rhythms, such as the light-dark cycle. The suprachiasmatic nucleus (SCN) of the hypothalamus is considered to be a pacemaker of the circadian rhythms in several mammals. The light-dark cycle is the primary synchronizing agent for many of the circadian rhythms which are regulated by the SCN. The photic information reaches the SCN also through a neuropeptide Y(NPY)-like immunoreactive pathway from the ventro-lateral geniculate nucleus. We found that in 12-h-dark and 12-h-light housed rats the NPY-like immunoreactive innervation of the ventro-lateral part of the SCN shows a 24 h rhythm with values rising gradually during the light phase and falling during the dark phase. Besides this rhythm, we found two peaks corresponding to the switching on and switching off of the light. The average level of NPY-like immunoreactivity, as assessed by means of semiquantitative immunocytochemistry and expressed in 'arbitrary units', is reduced in rats housed in total darkness for 2 weeks. These results confirm the physiological role of NPY in the timing of the circadian activity of the SCN.     

Divergent effects of peripheral and global neuropeptide Y deletion

Objectives:Neuropeptide Y (NPY) is involved in the coordination of bone mass and adiposity. However, multiple NPY sources exist and their individual contribution to the skeleton and adiposity not known. The objectives of our study were to evaluate the effects of peripheral mesenchymal derived NPY to the skeleton and adiposity and to compare them to the global NPY^KO model.Methods:To study the role of mesenchymal-derived NPY, we crossed conditional NPY (NPY^fl/fl) mice with Prx1cre to generate PrxNPY^KO mice. The bone phenotype was assessed using micro-CT. The skeletal phenotype of PrxNPY^KO mice was subsequently compared to global NPY^KO model. We evaluated body weight, adiposity and functionally assessed the feeding response of NPY neurons to determine whether central NPY signaling was altered by Prx1cre.Results:We identified the increase in cortical parameters in PrxNPY^KO mice with no changes to cancellous bone. This was the opposite phenotype to global NPY^KO mice generated from the same conditional allele. Male NPY^KO mice have increased adiposity, while PrxNPY^KO mice showed no difference, demonstrating that local mesenchymal-derived NPY does not influence adiposity.Conclusion:NPY mediates both positive and negative effects on bone mass via separate regulatory pathways. Deletion of mesenchymal-derived NPY had a positive effect on bone mass.     

Isolation and sequence of rat peptide YY and neuropeptide Y

Rat peptide YY and rat neuropeptide Y have been isolated in parallel from colon and brain extracts respectively, using salt fractionation, gel filtration chromatography, cation-exchange HPLC, and reverse phase phenyl-silica HPLC. Immunoreactivity was identified using a combination of 3 NPY immunoassays which exhibit differing cross-reactivities for PYY (90%, less than 0.01% and 30% respectively). The yield at the final purification step was 1.2 nmol rPYY and 0.5 nmol rNPY. Half of each purified peptide was subjected to complete microsequence analysis. This showed that while rat NPY was structurally identical to human NPY, the sequence of PYY from rat colon was the same as porcine PYY isolated from extracts of duodenum.     

Central thermoregulatory effects of neuropeptide Y and orexin A in rats

Orexin A and neuropeptide Y that are known to induce a feeding response when applied centrally, in the present studies also caused hypothermia. Neuropeptide Y elicited hypothermia by depressing metabolic rate (without affecting heat loss mechanisms), while orexin A acted through enhancing peripheral heat loss (without affecting metabolic rate). Neither peptide induced coordinated thermoregulatory changes, both of them appeared to influence thermoregulation via different effector mechanisms.     

The effects of selective amino acid substitution upon neuropeptide Y antisecretory potency in rat jejunum mucosa

The antisecretory potency of NPY and a series of truncated and structural analogues of NPY have been tested upon mucosal preparations of rat small intestine. Single amino acid substitutions, i.e., [Ile34]NPY, [Pro34]NPY, resulted in severe attenuation and loss of biological activity, respectively, and neither peptide affected NPY responses. An agonist order of potency: NPY greater than or equal to [Glu16,Ser18,Ala22,Leu28,31]NPY (ESALL-NPY) greater than [Cys2,Aoc5-24,DCys27]NPY (C2-NPY) greater than [Aoc5-24]NPY greater than [Des-Ser3,Des- Lys4]C2-NPY much greater than [Cys5,Aoc7-20,DCys24]NPY (C5-NPY) greater than equal to [DCys7,Aoc8-17, Cys20]NPY (C7-NPY) greater than [Aoc8-17]NPY greater than or equal to [Ile34]C7-NPY much greater than [Aoc2-27]NPY much greater than [Pro34]C2-NPY was obtained. The use of analogues based upon the tertiary structural model of NPY with varying amounts of N- and C-terminal helical regions removed and replaced with a single 8-aminooctanoic acid residue (Aoc) has allowed us to assess the structural requirements for activation of the regions in close apposition to each other. The polyproline helix, beta-turn and majority of the amphipathic alpha-helix serve a structural role bringing N- and C-terminal residues together for optimal receptor recognition and activation.     

Dexamethasone treatment increases neuropeptide Y levels in rat hypothalamic neurones

Immunoreactive glucocorticoid receptors (GR) have previously been demonstrated in neuropeptide Y (NPY) neurones of the rat hypothalamus. To determine whether NPY synthesis is influenced by glucocorticoids, the effect of dexamethasone (DEX) on the levels of immunoreactive NPY in rat hypothalamic neurones was investigated in vivo and in vitro. Daily injections of DEX (0.1 mg/day) for 5 days increased the NPY content of the mediobasal hypothalamus in female rats by 117% (p less than 0.002). Primary cultures of hypothalamic neurones were also sensitive to the effect of glucocorticoids. Intracellular NPY levels were significantly increased (p less than 0.001) compared to control values by 151%, 222% and 268% when cultures were maintained in a defined serum free medium containing DEX 10(-9), 10(-8) and 10(-7) M respectively.     

Intracerebroventricular neuropeptide Y suppresses open field and home cage activity in the rat

Effects of intracerebroventricular administration of neuropeptide Y on open field behaviour, behavioural habituation and corticosterone response to open field testing, and on home cage activity have been investigated in the rat. In the open field, NPY reduced activity in a dose-dependent manner. Behavioural habituation was not influenced. After 5 days of recovery, NPY-treated animals did not differ from non-treated in any of the measured parameters. Peripheral corticosterone levels were not significantly affected, although there was a strong tendency towards an increase. Injection of 2 nmol NPY did not produce any gross neurological deficits. At this dose, NPY greatly suppressed home cage activity. The effect lasted throughout the recording period of 22 h, abolishing the normal circadian variation in activity. After 5 days of recovery, the effect was no longer present. Our interpretation of these findings is, that NPY is a highly potent endogenous agent capable of producing certain important aspects of behavioural sedation in a reversible manner. Since NPY did not decrease the corticosterone response to a novel stimulus, its pattern of actions seems to differ from synthetic sedative drugs.     

Effect of age and photoperiodic conditions on metabolism and oxidative stress related markers at different circadian stages in rat liver and kidney

It has been shown that some cytochrome P450-dependent enzyme activities could present daily fluctuations, particularly CYP3A isoenzymes which are enhanced during the dark period. The aim of this study was to investigate whether age and photoperiodic conditions at different circadian stages could influence these fluctuations. Young mature (10 weeks) and old (22 months) Wistar rats were initially exposed to light-dark cycles 12:12 during 4 weeks, and secondly 18:6 for either one week or six weeks. Erythromycin N-demethylase (CYP3A-dependent), 7-ethoxycoumarin O-deethylase (CYP1A-dependent) and aniline 4-hydroxylase (CYP2E-dependent) activities were determined in liver and kidney microsomes at different hours after darkness onset (HADO). In addition, liver and kidney GSH, GSHPx, ATP, TBARS were determined. During the LD 12:12 cycle, while no significant modification was observed in CYP1A- and 2E-dependent enzyme activities as functions of HADO, erythromycin N-demethylase activity (CYP3A-dependent) showed a significant increase during the second third of the dark period in both young and old rats. After switching to a LD 18:6 cycle, this variation was still observed during second third of the dark period, to a lesser but still significant degree, with no difference between one week and six weeks exposure to the new photoperiod. It can be noted that the old rats showed a significantly lower level of erythromycin N-demethylase activity than the young rats, in parallel to a decrease in GSH, GSHPx and ATP, and an increase in TBARS.These results confirm the lower resistance of old animals to oxidative stress. The observed variations in metabolism parameters underline the need for study designs in pharmaco-toxicology taking into account the possible risks induced by circadian changes, especially in aged subjects.     

Daily and circadian variation in the electroretinogram of the domestic fowl: effects of melatonin

Visual and circadian function are integrally related in birds, but the precise nature of their interaction is unknown. The present study determined whether visual sensitivity measured electroretinographically (ERG) in 7-week-old cockerels varies over the time of day, whether this rhythm persists in constant darkness (DD) and whether exogenous melatonin affects this ERG rhythmicity. ERG b-wave amplitude was rhythmic in LD and persisted in DD with peak amplitude during mid- to late afternoon in LD and mid-subjective day in DD, indicating that the ERG rhythm is endogenously generated. No daily or circadian variation in a-wave amplitude was observed, and ERG component latency and durations were not rhythmic. Intramuscular injection of 10 g/kg melatonin at ZT10 in LD significantly decreased b-wave amplitude but had no effect on a-wave. Intraocular injection of 600 pg melatonin, however, had no effect on any aspect of the ERG. These data indicate that a circadian clock regulates ocular sensitivity to light and that melatonin may mediate some or all of this effect. The level at which melatonin modulates retinal sensitivity is not known, but the present data suggest a central site rather than a direct effect of the hormone in the eye.Abbreviations DD constant darkness - ERG electroretinography - EW Edinger-Westphal nuclei - IMEL iodomelatonin - IO isthmooptic nucleus - LD light-dark cycle - SCG superior cervical ganglion - SCN suprachiasmatic nuclei - vSCN visual suprachiasmatic nucleus