Neuropeptide Y: Role in light-dark cycle entrainment of hamster circadian rhythms

Microinjection of neuropeptide Y (NPY) into the suprachiasmatic region of the hypothalamus (SCN) phase shifted the circadian activity rhythm of hamsters housed in constant light. NPY advanced the phase when injected during the 12 h that preceded the daily onset of activity and tended to phase delay the activity cycle when injected during the 12 h after activity onset. In contrast, injection of saline into the SCN or NPY into the ventricular system had no effect on circadian phase. These and other data suggest that NPY functions as a chemical messenger important for the light-dark cycle entrainment of circadian rhythms.     

Serotonin1A autoreceptor activation by S 15535 enhances circadian activity rhythms in hamsters: evaluation of potential interactions with serotonin2A and serotonin2C receptors

Mammalian circadian activity rhythms are generated by pacemaker cells in the suprachiasmatic nucleus (SCN). As revealed by the actions of diverse agonists, serotonergic input from raphe nuclei generally inhibits photic signaling in the suprachiasmatic nucleus. In contrast, the serotonin (5HT)1A partial agonist, 4-(benzodioxan-5-yl)1-(indan2-yl)piperazine (S 15535), was found to enhance the phase-shifting influence of light on hamster circadian rhythms [Gannon, Neuroscience 119 (2003) 567]. Herein, we extend this observation in showing that S 15535 (5.0 mg/kg, i.p.) markedly (275%) enhanced the light-induced phase shift in circadian activity rhythms: further, this action was dose-dependently abolished by the highly-selective 5HT1A receptor antagonist, WAY 100,635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]N-2-pyridinyl-cyclohexane-carboxamide maleate) (0.1-0.5 mg/kg, i.p.). WAY 100,635, which was inactive alone, shares the antagonist actions of S 15535 at postsynaptic 5HT1A sites, yet blocks its effects at their presynaptic counterparts. Thus, 5HT1A autoreceptor activation must be involved in this effect of S 15535 which contrasts with the opposite, inhibitory influence upon phase shifts of the "full" agonist, 8-OH-DPAT, which acts by stimulation of postsynaptic 5HT1A receptors [Rea et al., J Neurosci 14 (1994) 3635]. Despite the occurrence of 5HT2A and 5HT2C receptors in the (rat) suprachiasmatic nucleus, their influence on circadian rhythms is unknown since actions of selective ligands have never been evaluated. This issue was investigated with the most selective agents currently available. However, the 5HT2A agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.25 and 0.5 mg/kg), and the 5HT2C agonist, alphaS-6-chloro-5-fluoro-a-methyl-1H-indole-1-ethanamine fumarate (Ro-60-0175) (1.0 and 5.0 mg/kg), failed to affect light-induced phase shifts in hamsters. Moreover, even over broad dose-ranges, the 5HT2A antagonist, (+)-(2,3-dimethoxy-phenyl)-[1-[2-(4-fluoro-phenyl)-ethyl]-piperidin-4-yl]methanol (MDL 100,907) (0.1-1.0 mg/kg), and the 5HT2C antagonist, 6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy)pyridin-3-yl carbamoyl]indoline (SB 242,084) (1.0-10.0 mg/kg), were likewise inactive. In view of evidence that 5HT2A and 5HT2C sites functionally interact with 5HT1A receptors, we also examined the influence of these agents upon the actions of S 15535, but no significant alteration was seen in its enhancement of rhythms. In conclusion, S 15535 elicits a striking enhancement of light-induced phase shifts in circadian rhythms by specifically recruiting 5HT1A autoreceptors, which leads to suppression of serotonergic input to the suprachiasmatic nucleus. Surprisingly, no evidence for a role of 5HT2A or 5HT2C sites was found, though comparable functional studies remain to be undertaken in rats. Indeed, the present work underlines the importance of comparative studies of circadian rhythms in various species, as well as the need for further study of potential interactions among 5HT receptor subtypes in their control.     

Release of neuropeptide Y upon haemorrhagic hypovolaemia in relation to vasoconstrictor effects in the pig

Neuropeptide Y is co-stored with noradrenaline in peripheral sympathetic nerves, but is not present in the adrenal chromaffin cells in the pig. Plasma levels of neuropeptide Y-like immunoreactivity and catecholamines were studied upon haemorrhagic shock in the anaesthetized pig. The animals were bled in two successive steps (30 and 10 ml kg^–), resulting in a reduction of the mean arterial blood pressure by 44% and 53 %, respectively. Plasma levels of noradrenaline increased abruptly after the first bleeding from 1.21 ± 0.27 to 26.5 ± 6.3 nmol 1^-1. Plasma neuropeptide Y showed a progressive increase from 62 ± 8 pmol 1^–1 in the basal state to 365 ± 98 pmol 1^–1 at 60 min after the first bleeding. After the second bleeding plasma neuropeptide Y and noradrenaline showed a largely parallel increase and finally reached levels of 2524 ± 580 pmol 1^–1 and 316 ± 117 nmol 1^–1, respectively. A veno-arterial gradient of neuropeptide Y and noradrenaline indicating local release was present over the spleen after both bleeding steps. The overflow of neuropeptide Y was delayed about 15 min compared to noradrenaline after the initial bleeding. Depletion of the neuropeptide Y content after shock in the heart and skeletal muscle supported local release also from these organs. Infusions of neuropeptide Y to obtain similar plasma concentrations as during shock (nM range) caused reduction in blood flow as determined by the radionuclide-labelled microsphere technique in several organs including spleen and skeletal muscle (threshold response at 319 ± 22 pmol 1^–1) but not in heart and brain. In conclusion, both neuropeptide Y and noradrenaline were markedly elevated in plasma upon haemorrhagic shock, suggesting release from sympathetic nerve terminals. Neuropeptide Y could therefore have a role as a sympathetic neurotransmitter, and during severe stress, circulating plasma levels are in the range where vasoconstriction is evoked by exogenous NPY.     

Effect of neuropeptide Y on behavior and on the time course of the brain noradrenalin level

Laboratory of General Physiology of Functional Systems, P. K. Anokhin Research Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Institute of Pathophysiology, Szeged Medical University, Hungary. (Presented by Academician of the Academy of Medical Sciences of the USSR I. P. Ashmarin). Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 108, No. 8, pp. 132–135, August, 1989.     

Reserpine-induced potentiation of the inhibitory action of neuropeptide Y on the rat vas deferens neurotransmission

The inhibitory action of neuropeptide Y (NPY) on the muscular activity of the prostatic end of the rat vas deferens elicited by transmural electrical stimulation was examined in control and in reserpinized rats. Pretreatment with 1 mg/kg reserpine for 48 h induced a 6-fold increase in NPY potency. Likewise, the potency of clonidine to inhibit the electrically induced muscular activity or noradrenaline to contract the ductus musculature was also potentiated. It is hypothesized that reserpine via a denervation super-sensitivity-like process increases the density of the NPY receptors. The functional significance of NPY in the motor activity of the vas deferens is discussed.     

NAN-190 potentiates the circadian response to light and speeds re-entrainment to advanced light cycles

Health problems can arise from de-synchrony between the external environment and the endogenous circadian rhythm, yet the circadian system is not able to quickly adjust to large, abrupt changes in the external daily cycle. In this study, we investigated the ability of NAN-190 to potentiate the circadian rhythm response to light as measured by phase of behavioral activity rhythms. NAN-190 (5 mg/kg, i.p.) was able to significantly potentiate the response to light both in dark-adapted and entrained hamsters. Furthermore, NAN-190 was effective even when administered up to 6 h after light onset. Response to a light pulse was both greater in magnitude and involved fewer unstable transient cycles. Finally, NAN-190 was able to speed re-entrainment to a 6 h advance of the light/dark cycle by an average of 6 days when compared with vehicle-treated animals. This work suggests that compounds like NAN-190 may hold great potential as a pharmaceutical treatment for jetlag, shift work, and other circadian disorders.     

The homeostatic role of neuropeptide Y in immune function and its impact on mood and behaviour

Neuropeptide Y (NPY), one of the most abundant peptides in the nervous system, exerts its effects via five receptor types, termed Y1, Y2, Y4, Y5 and Y6. NPY's pleiotropic functions comprise the regulation of brain activity, mood, stress coping, ingestion, digestion, metabolism, vascular and immune function. Nerve‐derived NPY directly affects immune cells while NPY also acts as a paracrine and autocrine immune mediator, because immune cells themselves are capable of producing and releasing NPY. NPY is able to induce immune activation or suppression, depending on a myriad of factors such as the Y receptors activated and cell types involved. There is an intricate relationship between psychological stress, mood disorders and the immune system. While stress represents a risk factor for the development of mood disorders, it exhibits diverse actions on the immune system as well. Conversely, inflammation is regarded as an internal stressor and is increasingly recognized to contribute to the pathogenesis of mood and metabolic disorders. Intriguingly, the cerebral NPY system has been found to protect against distinct disturbances in response to immune challenge, attenuating the sickness response and preventing the development of depression. Thus, NPY plays an important homeostatic role in balancing disturbances of physiological systems caused by peripheral immune challenge. This implication is particularly evident in the brain in which NPY counteracts the negative impact of immune challenge on mood, emotional processing and stress resilience. NPY thus acts as a unique signalling molecule in the interaction of the immune system with the brain in health and disease.     

Prehatch entrainment of circadian rhythms in the domestic chick using different light regimes

The onset of circadian rhythms in many animals occurs during prenatal development. We conducted four experiments, using the domestic chick as a model, to assess when these rhythms can first be entrained and the type of light zeitgeber necessary. In Experiment 1, the presence of circadian rhythms was assessed using tonic immobility, an antipredator behavior, whereas in Experiments 2 to 4 body temperature was studied. We demonstrate that (a) circadian rhythms can be entrained during the late stage of the chick's 21-day incubation period (prehatch Days 13-18), (b) only 1 day of light cues [12:12 hr light:dark (12L:12D)] on prehatch Day 13 is necessary for entrainment, and (c) short bouts of light, which simulate the light cues embryos typically experience during natural incubation, can act as zeitgebers although they are not as effective as 12L:12D. The onset of entrainment is earlier than predicted and suggests that the brain structures mediating circadian rhythms mature sooner than proposed by previous research.     

Time-dependent effects of ischaemia on neuropeptide Y mechanisms in pig renal vascular control in vivo

We have investigated the effects of ischaemia on neuropeptide Y (NPY) mechanisms involved in sympathetic vascular control of the pig kidney in vivo. Reperfusion after 2 h of renal ischaemia was associated with local overflow of noradrenaline (NA) but not of NPY-like immunoreactivity (-LI). Renal sympathetic nerve stimulation 10 min into reperfusion evoked markedly reduced vasoconstrictor effects and significantly less overflow of NA (reduced by 70% from the pre-ischaemic conditions), whereas NPY-LI overflow was unaltered. Renal vasoconstrictor responses to exogenous peptide YY (PYY), phenylephrine and angiotensin II were strongly attenuated after this ischaemic period, while vasoconstriction to α,β-methylene ATP was maintained to a larger extent. The renal vascular responses and NA overflow had become partially normalized within a 2 h recovery period. In contrast, the renal vasoconstrictor response and the overflow of NPY-LI upon sympathetic nerve stimulation were enhanced after 15 min of renal ischaemia. In parallel, the PYY-evoked renal vasoconstriction was selectively and markedly prolonged after the 15 min of ischaemia. In the presence of the NPY Y₁ receptor antagonist BIBP 3226, the augmented vascular response to nerve stimulation was significantly attenuated. We conclude that reperfusion after 2 h of renal ischaemia is associated with local overflow of NA, whereas the sympathetic nerve-evoked release of NA and the reactivity of the renal vasculature to vasoconstrictor stimuli are reversibly reduced. Furthermore, possibly due to an impaired local degradation, the role of neurogenically released NPY in renal sympathetic vasoconstriction is enhanced after short-term (15 min) ischaemia compared with control conditions.     

Electro-acupuncture as a peroperative analgesic method and its effects on implantation rate and neuropeptide Y concentrations in follicular fluid

BACKGROUND: In a previous study on the effect of electro-acupuncture (EA) in combination with a paracervical block (PCB) as an analgesic method during oocyte aspiration in IVF treatment, EA appeared to increase the pregnancy rate. This study was designed to test the hypothesis that EA as an analgesic during oocyte aspiration would result in: (i) a better IVF pregnancy rate than with alfentanil; (ii) peroperative analgesia that was as good as that produced by alfentanil; (iii) less postoperative abdominal pain, nausea and stress; and (iv) a reduction in the use of additional analgesics. Neuropeptide Y (NPY) concentrations in follicular fluid (FF) were analysed when possible. METHODS AND RESULTS: In this prospective, randomized, multicentre clinical trial, 286 women undergoing oocyte aspiration were randomly allocated to the EA group (EA plus a PCB) or to the alfentanil group (alfentanil plus a PCB). No significant differences were found between the EA and alfentanil groups in any of the IVF variables. NPY concentrations in FF were significantly higher in the EA group compared with the alfentanil group. No correlation between pregnancy rate and NPY concentrations was found in either analgesic group. Both EA plus a PCB and alfentanil plus a PCB induced adequate peroperative analgesia during oocyte aspiration evaluated using the visual analogue scale. After 2 h, the EA group reported significantly less abdominal pain, other pain, nausea and stress than the alfentanil group. In addition, the EA group received significantly lower amounts of additional alfentanil than the alfentanil group. CONCLUSION: EA does not improve pregnancy rate in the present clinical situation. The observation that NPY concentrations in FF were higher in the EA group may be important for human ovarian steroidogenesis. The analgesic effects produced by EA are as good as those produced by conventional analgesics, and the use of opiate analgesics with EA is lower than when conventional analgesics alone are used.     

Attenuation of circadian light induced phase advances and delays by neuropeptide Y and a neuropeptide Y Y1/Y5 receptor agonist

Circadian rhythms can be synchronised to photic and non-photic stimuli. The circadian clock, anatomically defined as the suprachiasmatic nucleus in mammals, can be phase shifted by light during the night. Non-photic stimuli reset the circadian rhythm during the day. Photic and non-photic stimuli have been shown to interact during the day and night. Precise mechanisms for these complex interactions are unknown. A possible pathway for non-photic resetting of the clock is thought to generate from the intergeniculate leaflet, which conveys information to the suprachiasmatic nucleus (SCN) through the geniculohypothalamic tract and utilises neuropeptide Y (NPY) as its primary neurotransmitter.Interactions between light and NPY were investigated during the early (2 h after activity onset) and late (6 h after activity onset) night in male Syrian hamsters. NPY microinjections into the region of the SCN significantly attenuated light-induced phase delay, during the early subjective night. Phase advances to light were completely inhibited by the administration of NPY during the late night.The precise mechanism by which NPY attenuates or blocks photic phase shifts is unclear, but the NPY Y5 receptor has been implicated in the mediation of this inhibitory effect. The NPY Y1/Y5 receptor agonist, [Leu(31),Pro(34)]NPY, was administered via cannula microinjections following light exposure during the early and late night. [Leu(31),Pro(34)]NPY significantly attenuated phase delays to light during the early night and blocked phase advances during the late night, in a manner similar to NPY.These results show the ability of NPY to attenuate phase shifts to light during the early night and block light-induced phase advances during the late night. Furthermore, this is the first in vivo study implicating the involvement of the NPY Y1/Y5 receptors in the complex interaction of photic and non-photic stimuli during the night. The alteration of photic phase shifts by NPY may influence photic entrainment within the circadian system.     

Serotonergic pre-treatments block in vitro serotonergic phase shifts of the mouse suprachiasmatic nucleus circadian clock

The suprachiasmatic nucleus (SCN) contains a circadian clock that maintains its time-generating and phase-modulating capacities in vitro. Previous studies report clear differences in the ability of serotonergic stimuli to phase-shift the SCN clock when applied directly to the SCN either in vivo or in vitro: while mice and rat circadian clocks are readily phase-shifted by serotonin (5-HT) or 5-HT agonists applied in vitro, hamster and mice circadian clocks respond inconsistently to 5-HT agonists injected directly into the SCN in vivo. Here we have investigated one possible explanation for these differences: that the SCN isolated in vitro experiences reduced endogenous 5-HT signaling, which increases clock sensitivity to subsequent 5-HT stimulation. For these experiments we treated mouse SCN brain slices with low concentrations of compounds that increase serotonin signaling: 5-HT, a 5-HT agonist (8-OH-DPAT), the 5-HT precursor, l-tryptophan, or the 5-HT re-uptake inhibitor, fluoxetine. Pretreatment with each of these substances completely blocked subsequent phase-shifts induced by mid-subjective day treatment with either 5-HT or 8-OH-DPAT, while they did not block phase-shifts induced by the adenylate cyclase activator, forskolin. Time-course data on l-tryptophan-induced inhibition are consistent with this treatment inducing receptor internalization, while timing of the recovery from inhibition is consistent with receptor reinsertion. Together these data support the hypothesis that SCN clock sensitivity to serotonergic phase modulation is affected by the amount of prior serotonin signaling present in the SCN, and that this signaling alters the density of surface 5-HT receptors on SCN clock neurons.     

Coexistence of neuropeptide Y and somatostatin in rat and human cortical and rat hypothalamic neurons

The distribution and coexistence of neuropeptide Y (NPY) and somatostatin (SOM) were evaluated in rat and human cerebral cortex and in the rat hypothalamic arcuate nucleus (n) using double immunofluorescent staining in which primary antisera were raised in different species. The results of the study indicate extensive coexistence of NPY and SOM in both rat and human cortex but only occasional coexistence in the rat arcuate n.     

Action and localization of neuropeptide Y in the human fallopian tube

Using indirect immunohistochemistry, neuropeptide Y-like immunoreactivity was found in nerve fibers around blood vessels and in the muscle layers of the human fallopian tube. Apart from a network of immunoreactive nerve fibers in connection with the luminary epithelium of the isthmus, the distribution resembled that of adrenergic, tyroxine hydroxylase immunoreactive, nerve fibers. Neuropeptide Y was found to have a dose-dependent inhibitory action on the adrenergic contractile response to field stimulation in the external longitudinal muscle layer of the isthmus. Furthermore, neuropeptide Y inhibited [3H]noradrenaline release from isthmic preparations during field stimulation, suggesting a prejunctional inhibitory action on adrenergic neurotransmission.     

海洛因依赖对大鼠直肠神经肽Y表达的影响

目的探讨海洛因依赖期间大鼠直肠内神经肽Y（NPY）免疫反应阳性细胞的形态学改变。方法选取成年SD大鼠,分为海洛因依赖组、盐水对照组和正常对照组,皮下注射海洛因建立大鼠海洛因依赖模型,取直肠组织用免疫组织化学SABC法及图像分析法进行研究。结果与正常及盐水对照组比较,海洛因依赖组大鼠直肠NPY阳性细胞的细胞数均增多。图像分析显示海洛因依赖期间大鼠直肠内NPY阳性细胞的平均灰度值均低于正常及盐水对照组（P〈0.05）;以17 d时间组最低（P〈0.05）。结论海洛因依赖期间直肠NPY阳性细胞的平均灰度值发生变化,提示NPY合成和分泌增多。     

Immunohistochemical analysis of the early ontogeny of the neuropeptide Y system in rat brain

The distribution of neuropeptide Y in the developing rat brain was studied with immunocytochemistry, using the peroxidase-antiperoxidase method. Immunoreactive perikarya were first seen on embryonic day 13 and staining of fibres appeared from embryonic day 15 onwards: perikaryal staining was generally more intense prenatally than after birth. Areas rich in neuropeptide Y immunostaining included the monoaminergic regions of the brain stem from embryonic day 13 (especially the lateral reticular nucleus and the medullary reticular formation), the dorsal mesencephalon (with spots of immunoreactivity in the outer subventricular zone at embryonic days 13 or 14 and many cells and fibres in the inferior colliculus from embryonic days 16-20) and the olfactory tubercle/ventral striatum from embryonic day 15 until birth. The period of development of cortical neurones extended from embryonic day 19 until postnatal day 21. A hitherto unreported feature unique to neuropeptide Y was the presence in certain parts of the cerebral cortex of transient cells at the base of the cortical plate bearing radial processes which transverse its width. They were present from embryonic day 17 until postnatal day 4 and were maximally developed at embryonic days 20 or 21, contributing at this age a substantial fibre projection through the immature corpus callosum. The abundance of neuropeptide Y in the prenatal rat brain suggests it may play an important role in development.     

Occurrence of neuropeptide Y (NPY)-like immunoreactivity in catecholamine neurons in the human medulla oblongata

We report here the coexistence of a neuropeptide and catecholamines in neurons of the human brain. Using indirect immunofluorescence histochemistry, combined with elution and restaining experiments, neurons in the medulla oblongata of man were demonstrated to contain both a neuropeptide Y-like peptide and the catecholamine synthesizing enzyme tyrosine hydroxylase.