Intracerebroventricular injection of a neuropeptide Y-Y1 receptor agonist increases while BIBP3226, a Y1 antagonist, reduces the infarct volume following transient middle cerebral artery occlusion in rats

The role of NPY signaling pathway in diagnosis, prognosis and treatment of stroke

Neuropeptide Y (NPY), an extensively distributed neurotransmitter within the central nervous system (CNS), was initially detected and isolated from the brain of a pig in 1982. By binding to its G protein-coupled receptors, NPY regulates immune responses and contributes to the pathogenesis of numerous inflammatory diseases. The hippocampus contained the maximum concentration in the CNS, with the cerebral cortex, hypothalamus, thalamus, brainstem, and cerebellum following suit. This arrangement suggests that the substance has a specific function within the CNS. More and more studies have shown that NPY is involved in the physiological and pathological mechanism of stroke, and its serum concentration can be one of the specific biomarkers of stroke and related complications because of its high activity, broad and complex effects. By summarizing relevant literature, this article aims to gain a thorough understanding of the potential clinical applications of NPY in the treatment of stroke, identification of stroke and its related complications, and assessment of prognosis.

Adequate expression of neuropeptide Y is essential for the recovery of zebrafish motor function following spinal cord injury

In strong contrast to limited repair within the mammalian central nervous system, the spinal cord of adult zebrafish is capable of almost complete recovery following injury. Understanding the mechanism underlying neural repair and functional recovery in zebrafish may lead to innovative therapies for human spinal cord injury (SCI). Since neuropeptide Y (NPY) plays a protective role in the pathogenesis of several neurological diseases, in the present study, we evaluated the effects of NPY on neuronal repair and subsequent recovery of motor function in adult zebrafish following SCI. Real-time quantitative PCR (qRT-PCR), in situ hybridization and immunostaining for NPY revealed decreased NPY expression at 12 hours (h), 6 and 21 days (d) after SCI. Double-immunostaining for NPY and islet-1, a motoneuron marker, showed that NPY was expressed in spinal cord motoneurons. Morpholino (MO) treatment for suppressing the expression of NPY inhibited supraspinal axon regrowth and locomotor recovery, in which double-staining for proliferating cell nuclear antigen (PCNA) and islet-1 showed a reduction in motoneuron proliferation. Similarly, a downregulated mRNA level of Y1 receptor of NPY (NPY1R) was also detected at 12 h, 6 and 21 d after injury. Immunostaining for NPY and in situ hybridization for NPY1R revealed that NPY1R was co-localized with NPY. Collectively, the results suggest that NPY expression in motoneurons promotes descending axon regeneration and locomotor recovery in adult zebrafish after SCI, possibly by regulating motoneuron proliferation through activation of NPY1R.

Relations of neuropeptide Y and heme oxygenase-1 expressions with fetal brain injury in rats with intrahepatic cholestasis of pregnancy

PURPOSE

To investigate the relations of neuropeptide Y (NPY) and heme oxygenase-1 (HO-1) expressions with fetal brain injury in rats with intrahepatic cholestasis of pregnancy (ICP).

METHODS

Sixty rats pregnant for 15 days were randomly divided into experimental and control groups. The ICP model was established in experimental group. On the 21st day, the blood biochemical test, histopathological examination of pregnant rat liver and fetal brain tissues and immunohistochemical analysis of fetal rat brain tissues were performed.

RESULTS

On the 21st day, the alanineaminotransferase, aspartate aminotransferase and total bile acid levels in experimental group were significantly higher than control group (P<0.01). Compared with control group, there was obvious vacuolar degeneration in pregnant rat liver tissue and fetal brain tissue in experimental group. NPY expression in fetal brain tissue was negative in control group and positive in experimental group. HO-1 expression in fetal brain tissue was strongly positive in control group and positive in experimental group. There was significant difference of immunohistochemical staining optical density between two groups (P<0.01).

CONCLUSION

In fetal brain of ICP rats, the NPY expression is increased, and the HO-1 expression is decreased, which may be related to the fetal brain injury.

Neuropeptide Y treatment induces retinal vasoconstriction and causes functional and histological retinal damage in a porcine ischaemia model

PURPOSE

To investigate the effects of intravitreal neuropeptide Y (NPY) treatment following acute retinal ischaemia in an in vivo porcine model. In addition, we evaluated the vasoconstrictive potential of NPY on porcine retinal arteries ex vivo.

METHODS

Twelve pigs underwent induced retinal ischaemia by elevated intraocular pressure clamping the ocular perfusion pressure at 5 mmHg for 2 hr followed by intravitreal injection of NPY or vehicle. After 4 weeks, retinas were evaluated functionally by standard and global-flash multifocal electroretinogram (mfERG) and histologically by thickness of retinal layers and number of ganglion cells. Additionally, the vasoconstrictive effects of NPY and its involved receptors were tested using wire myographs and NPY receptor antagonists on porcine retinal arteries.

RESULTS

Intravitreal injection of NPY after induced ischaemia caused a significant reduction in the mean induced component (IC) amplitude ratio (treated/normal eye) compared to vehicle-treated eyes. This reduction was accompanied by histological damage, where NPY treatment reduced the mean thickness of inner retinal layers and number of ganglion cells. In retinal arteries, NPY-induced vasoconstriction to a plateau of approximately 65% of potassium-induced constriction. This effect appeared to be mediated via Y1 and Y2, but not Y5.

CONCLUSION

In seeming contrast to previous in vitro studies, intravitreal NPY treatment caused functional and histological damage compared to vehicle after a retinal ischaemic insult. Furthermore, we showed for the first time that NPY induces Y1- and Y2- but not Y5-mediated vasoconstriction in retinal arteries. This constriction could explain the worsening in vivo effect induced by NPY treatment following an ischaemic insult and suggests that future studies on exploring the neuroprotective effects of NPY might focus on other receptors than Y1 and Y2.

Neuropeptide Y Y2 and Y5 receptors as promising targets for neuroprotection in primary neurons exposed to oxygen-glucose deprivation and in transient focal cerebral ischemia in rats

It was postulated that neuropeptide Y (NPY)-ergic system could be involved in the ischemic pathophysiology, however, the role of particular subtypes of NPY receptors (YRs) in neuroprotection against ischemia is still not well known. Therefore, we investigated the effect of NPY and YR ligands using in vitro and in vivo experimental ischemic stroke models. Our in vitro findings showed that NPY (0.5-1μM) and specific agonists of Y2R (0.1-1μM) and Y5R (0.5-1μM) but not that of Y1R produced neuroprotective effects against oxygen-glucose deprivation (OGD)-induced neuronal cell death, being also effective when given 30min after the end of OGD. The neuroprotective effects of Y2R and Y5R agonists were reversed by appropriate antagonists. Neuroprotection mediated by NPY, Y2R and Y5R agonists was accompanied by the inhibition of both OGD-induced calpain activation and glutamate release. Data from in vivo studies demonstrated that Y2R agonist (10μg/6μl; i.c.v.) not only diminished the infarct volume in rats subjected to transient middle cerebral artery occlusion (MCAO) but also improved selected gait parameters in CatWalk behavioral test, being also effective after delayed treatment. Moreover, we found that a Y5R agonist (10μg/6μl; i.c.v.) did not reduce MCAO-evoked brain damage but improved stride length, when it was given 30min after starting the occlusion. In conclusion, our studies indicate that Y5 and especially Y2 receptors may be promising targets for neuroprotection against ischemic damage.

Multifaces of neuropeptide Y in the brain--neuroprotection, neurogenesis and neuroinflammation

Neuropeptide Y (NPY) has been implicated in the modulation of important features of neuronal physiology, including calcium homeostasis, neurotransmitter release and excitability. Moreover, NPY has been involved as an important modulator of hippocampal and thalamic circuits, receiving particular attention as an endogenous antiepileptic peptide and as a potential master regulator of feeding behavior. NPY not only inhibits excessive glutamate release (decreasing circuitry hyperexcitability) but also protects neurons from excitotoxic cell death. Furthermore, NPY has been involved in the modulation of the dynamics of dentate gyrus and subventricular zone neural stem cell niches. In both regions, NPY is part of the chemical resource of the neurogenic niche and acts through NPY Y1 receptors to promote neuronal differentiation. Interestingly, NPY is also considered a neuroimmune messenger. In this review, we highlight recent evidences concerning paracrine/autocrine actions of NPY involved in neuroprotection, neurogenesis and neuroinflammation. In summary, the three faces of NPY, discussed in the present review, may contribute to better understand the dynamics and cell fate decision in the brain parenchyma and in restricted areas of neurogenic niches, in health and disease.

Galanin systems and ischemia: peptide and receptor plasticity in neurons and oligodendroglial precursors

Cerebral cortex contains few if any galanin neurons, but receives galanin-ergic inputs from subcortical areas. Apart from our earlier study on the response to cortical spreading depression, little is known about the presence and function of galanin in normal or injured cortex and to gain more insight into its possible roles, we investigated the temporal effects of focal ischemia on the expression of galanin and galanin receptors (GalRs). Focal ischemia induced in the rat by unilateral middle cerebral artery occlusion increased galanin and GalR1 mRNAs in penumbral/undamaged areas on the first and second day post-ischemia, while increased GalR2 mRNA was observed in the same regions only on the second day. Immunohistochemical studies revealed galanin immunoreactive neurons in the frontal/ cingulate cortex and abundant galanin-immunoreactivity in nerve axons/fibres within the penumbral areas, between the third and the seventh day after ischemia. Galanin mRNA and immunoreactivity was also increased in a population of small cells thought to be NG2-positive oligodendrocyte precursors. Up-regulation of galanin and GalRs in various cell populations following severe ischemic injury further demonstrates the marked plasticity of galanin and GalR1/2 expression after brain injury, and together with data reported elsewhere in this volume, suggests a functional role for galanin signalling in such pathophysiological conditions.

Neuroprotective effects of neuropeptide Y-Y2 and Y5 receptor agonists in vitro and in vivo

It is generally assumed that neurodegeneration is connected with glutamatergic hyperactivity, and that neuropeptide Y (NPY) inhibits glutamate release. Some earlier studies indicated that NPY may have neuroprotective effect; however, the results obtained so far are still divergent, and the role of different Y receptors remains unclear. Therefore in the presented study we investigated the neuroprotective potential of NPY and its Y2, Y5 or Y1 receptor (R) ligands against the kainate (KA)-induced excitotoxicity in neuronal cultures in vitro, as well as in vivo after intrahippocampal KA injection and also in an ischemic middle cerebral artery occlusion model after intraventricular injection of Y2R agonist. NPY compounds were applicated 30 min, 1, 3 or 6 h after the start of the exposure to KA, or 30 min after the onset of ischemia. Our results indicate the neuroprotective activity of NPY and its Y2R and Y5R ligands against the kainate-induced excitotoxicity in primary cortical and hippocampal cultures. Importantly, NPY was effective when given as late as 6 h, while Y2R or Y5R agonists 3 h, after starting the exposure to KA. In in vitro studies those protective effects were inhibited by the respective receptor antagonists. Neuroprotection was also observed in vivo after intrahippocampal injection of Y2R and Y5R agonists 30 min or 1 h after KA. No protection was found either in vitro or in vivo after the Y1R agonist. The Y2R agonist also showed neuroprotective activity in the ischemic model. The obtained results indicate that neuropeptide Y produces neuroprotective effect via Y2 and Y5 receptors, and that the compounds may be effective after delayed application.

The effect of cardiac ischemic preconditioning on rat left ventricular gene expression profile

Ischemic preconditioning (IPC) is a phenomenon where heart is rendered more resistant to subsequent ischemia-reperfusion (I-R)-induced injury by one or more brief episodes of I-R. The mechanisms responsible for cardio-protective effects of IPC are not well characterized. The objective of the study was to characterize gene expression profiles in the left ventricle of male Wistar rat hearts exposed to I-R or IPC followed by I-R. Group 1 included hearts that were only perfused for 30 min. Group 2 included hearts that underwent 30 min perfusion followed by 40 min I and 30 min R. Group 3 comprised 30 min perfused hearts that were subjected to IPC (5 min I + 10 min R + 5 min I + 10 min R) followed by I-R. Total RNAs were isolated from left ventricular tissues. Codelink gene expression system (GE Healthcare) was used for cRNA target preparation, hybridization of microarrays (Rat UniSet 10 K CodeLink bioarrays, GE Healthcare) and detection. Microarrays were scanned with Affymetrix 428 Array scanner. Data analyses were carried out with GeneSifter microarray data analysis software. We determined a total of 140 transcripts (> or =2-fold change) whose expressions were changed (44 up-regulated and 96 down-regulated) accompanying to I-R injury compared to perfused only hearts. Twenty-three transcripts including Ryr3, Crk, Dio1, Npy1r, Ptpra, Cyp51 that were down-regulated by I-R injury, were up-regulated by cardiac IPC. IPC down-regulated the expression of several transcripts including Atf3 (activating transcription factor 3), carboxypeptidase A1 (Cpa1), Slc38a4, Blk which were up-regulated by I-R. In conclusion, evaluation of global gene expression profiling via microarray-based technologies provides a molecular portrait of cardiac IPC of the left ventricular tissue of rat heart.

Neuropeptide Y-Y1 receptor agonist worsens while antagonist improves survival of cultured Y1-expressing neuronal cells following oxygen and glucose deprivation

In this in vitro study, we investigated the influence of neuropeptide Y (NPY) Y1 receptor activation or inhibition on the viability of cultured neuronal or glial cells following oxygen glucose deprivation (OGD). Viability of cultured cells was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. When compared to the vehicle-treated control group, treatment with NPY or [Leu31,Pro34]-NPY (Y1 agonist) reduced viability of cultured SK-N-MC (Y1-expressing) human neuronal cells at 24 h after 1 h of OGD, while BIBP3226 (Y1 antagonist) improved viability. Except at the highest concentration of NPY used in the study, treatment with NPY or NPY3-36 (Y2 agonist) did not influence viability of cultured SH-SY5Y (Y2-expressing) human neuronal cells at 24 h after 1 h of OGD. In addition, treatment with NPY, [Leu31,Pro34]-NPY, NPY3-36, or BIBP3226 did not affect viability of cultured primary astrocytes at 24 h after 4 h of OGD. The present results agree with those of a recent in vivo study. Activation of NPY-Y1 receptors may mediate ischemic pathophysiological processes, and inhibiting the Y1 receptors may be protective. The combination of OGD and cultured neuronal cells may be useful in future studies on the neuroprotective and harmful mechanisms of NPY-Y1 receptor inhibition and activation during ischemia, respectively.

Neuropeptide Y and its receptor analogs differentially modulate the immunoreactivity for neuronal or endothelial nitric oxide synthase in the rat brain following focal ischemia with reperfusion

An intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) or [Leu31, Pro34]-NPY (non-Y2 receptor agonist) given during middle cerebral artery occlusion (MCAO) increases the infarct volume and nitric oxide (NO) overproduction in the rat brain. An i.c.v. injection of NPY3-36 (non-Y1 receptor agonist) has no effects, while BIBP3226 (selective Y1 receptor antagonist) reduces the infarct volume and NO overproduction. This study examined the effects of NPY or its receptor analog on the immunoreactivity (ir) for three isoforms of NO synthase (NOS) following 1 h of MCAO and 3 h of reperfusion. Focal ischemia/reperfusion led to increased ir for neuronal NOS (nNOS) within the ipsilateral caudate putamen and insular cortex. NPY or [Leu31, Pro34]-NPY enhanced but BIBP3226 suppressed such increase in the nNOS-ir. Focal ischemia/reperfusion also led to an ipsilateral increase in extent and/or intensity of the ir for endothelial NOS (eNOS) in the caudate putamen and/or parietal cortex. NPY or [Leu31, Pro34]-NPY suppressed but BIBP3226 enhanced such change in the eNOS-ir. NPY3-36 did not consistently influence the nNOS-ir or eNOS-ir following MCAO. Specific ir for inducible NOS was undetectable. These opposing effects of NPY-Y1 receptor activation or inhibition on nNOS and eNOS may lead to harmful or beneficial consequences following ischemia/reperfusion.

Galanin-like peptide stimulates vasopressin, oxytocin and adrenocorticotropic hormone release in rats

Galanin-like peptide is a recently identified neuropeptide. We examined the effects of stressful stimuli on expression of c-Fos protein in galanin-like peptide neurons, and the effects of central infusion of galanin-like peptide on release of stress hormones, vasopressin, oxytocin and adrenocorticotropic hormone, in male rats. Foot shock stress induced expression of c-Fos protein in galanin-like peptide neurons in the hypothalamus. Intracerebroventricular injection of galanin-like peptide significantly increased plasma concentrations of vasopressin, oxytocin and adrenocorticotropic hormone. Galanin-like peptide also increased blood pressure, heart rates and plasma glucose concentrations, but significantly changed neither plasma osmolality nor blood haemoglobin concentration. A neuropeptide Y-Y1 receptor antagonist, BIBP3226, did not significantly change galanin-like peptide-induced hormone release. It is possible that galanin-like peptide is involved in vasopressin, oxytocin and adrenocorticotropic hormone release from the pituitary during stress.

Melatonin reduces nitric oxide level during ischemia but not blood-brain barrier breakdown during reperfusion in a rat middle cerebral artery occlusion stroke model

Melatonin is a potent antioxidant and free radical scavenger. Previously, we showed that a single injection of melatonin before ischemia significantly reduced the infarct volume in both permanent and 3-hr middle cerebral artery occlusion (MCAO) rat stroke models. Nitric oxide (NO) and other free radicals play an important role in the pathogenesis of cerebral ischemia, and they have been postulated to mediate the breakdown of the blood-brain barrier (BBB) during ischemia. In this study, we evaluated the influence of melatonin, given at 30 min before MCAO, on brain NO concentration and BBB breakdown. Brain NO concentration was measured at 15 min of MCAO using electron paramagnetic resonance spectroscopy. BBB breakdown at 3 hr of reperfusion following 3 hr of MCAO was assessed using Evans blue extravasation. The relative brain NO concentration was increased to 141.69 +/- 9.71% (mean +/- S.E.M.; n = 9) at 15 min of MCAO. Treatment with melatonin at 1.5, 5, or 50 mg/kg significantly reduced the brain NO concentration to 104.20 +/- 11.20% (n = 8), 55.67 +/- 5.58% (n = 11), and 104.86 +/- 12.56% (n = 9), respectively. Melatonin at 5 mg/kg did not affect Evans blue extravasation. Our results suggest that a single injection of melatonin protects against focal cerebral ischemia partly via inhibition of ischemia-induced NO production and that this regimen does not prevent BBB breakdown following ischemia-reperfusion.