Neuropeptide Y and the ocular innervation of rat, guinea pig, cat and monkey

Tear neuropeptide Y as a non-invasive marker of peripheral microvascular complications in type 1 diabetes

AIMS

To investigate tear neuropeptide Y (NPY) and substance P concentrations in individuals with type 1 diabetes, comparing those with and without both diabetic retinopathy (DR) and peripheral neuropathy.

METHODS

This cross-sectional study involved 41 participants with type 1 diabetes and none to moderate DR, and 22 healthy controls. Assessments included clinical ocular surface parameters, quantification of corneal nerve attributes (based on in vivo confocal microscopy imaging), DR grading, and evaluation for small and large fibre neuropathy. Concentrations of NPY and substance P in tear samples were measured using enzyme-linked immunosorbent assay.

RESULTS

Mean (±standard deviation) tear NPY concentrations in participants with type 1 diabetes and length-dependent small fibre neuropathy (SFN) was lower than in controls (10.84±4.10 ng/mL vs 14.72±3.12 ng/mL; p=0.004), but not significantly different from type 1 diabetes participants without SFN (13.39±4.66 ng/mL; p=0.11). Tear NPY levels were lower in individuals with type 1 diabetes and mild/moderate non-proliferative DR (10.44±3.46 ng/mL) compared to none/minimal DR (13.79±4.76 ng/mL; p=0.0005) and controls. In separate linear regression models, both the presence of SFN ((β=-0.75, p=0.02) and the presence of mild/moderate DR (β=-0.84, p=0.009) were significantly associated with tear NPY levels relative to controls, after adjusting for participant age, sex, and dry eye disease. There were no inter-group differences for tear substance P concentrations.

CONCLUSIONS

Tear NPY has potential utility as an indicator of peripheral microvascular complications associated with type 1 diabetes.

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Seasonal Differences in Expression of Neuropeptide Y (NPY) in Visual Centers of Spotted Munia (Lonchura punctulata)

The visual perception of birds is an incredibly exciting subject of research. Birds have significantly higher visual acuity than most other animals, which helps them stay safe in flight and detect their prey. Understanding how the eyes send information to the brain for additional processing is crucial. The brain has sections (nuclei) that accept input from the retina. The key areas where information is processed are the hyperpallium apicale (HA), hippocampus (HP), optic tectum (TeO), nucleus rotundus (RoT), and the geniculatus lateralis ventralis (Glv); among these, the RoT is one of the most investigated nuclei for vision. This study looked at how the visual centers of non-photoperiodic songbirds (Spotted Munia) adapt in different life history stages by looking at NPY expression. We immunohistochemically quantified NPY expression in four different seasons, including pre-breeding (June), breeding (September), post-breeding (December), and regressed (March) in the brain of Spotted Munia. We evaluated changes in the expression levels of the peptide throughout the year, by determining the expression at four different periods throughout the year. Peptide expression levels were projected to fluctuate within photoperiod-induced seasons. It was discovered that the parts of the brain related to vision (RoT, HA, and HP) have a higher number of immunoreactive cells during their mating season, i.e., during the summer. The appearance of NPY, a non-photic marker, in brain areas linked with light perception, was fascinating. Indirectly, NPY aids avian reproduction in a variety of ways. These findings demonstrate the importance of these nuclei in the process of reproduction, as well as the involvement of NPY in the visual brain areas of Spotted Munia.

Short and long-term effect of dexamethasone on the transcriptome profile of primary human trabecular meshwork cells in vitro

In the quest of identifying newer molecular targets for the management of glucocorticoid-induced ocular hypertension (GC-OHT) and glaucoma (GCG), several microarray studies have attempted to investigate the genome-wide transcriptome profiling of primary human trabecular meshwork (TM) cells in response to dexamethasone (DEX). However, no studies are reported so far to demonstrate the temporal changes in the expression of genes in the cultured human TM cells in response to DEX treatment. Therefore, in the present study, the time-dependent changes in the genome-wide expression of genes in primary human TM cells after short (16 hours: 16 h) and long exposure (7 days: 7 d) of DEX was investigated using RNA sequencing. There were 199 (118 up-regulated; 81 down-regulated) and 525 (119 up-regulated; 406 down-regulated) DEGs in 16 h and 7 d treatment groups respectively. The unique genes identified in 16 h and 7 d treatment groups were 152 and 478 respectively. This study found a distinct gene signature and pathways between two treatment regimes. Longer exposure of DEX treatment showed a dys-regulation of Wnt and Rap1 signaling and so highlighted potential therapeutic targets for pharmacological management of GC-OHT/glaucoma.

The Role of Neuropeptides in Pathogenesis of Dry Dye

Neuropeptides are known as important mediators between the nervous and immune systems. Recently, the role of the corneal nerve in the pathogenesis of various ocular surface diseases, including dry eye disease, has been highlighted. Neuropeptides are thought to be important factors in the pathogenesis of dry eye disease, as suggested by the well-known role between the nervous and immune systems, and several recently published studies have elucidated the previously unknown pathogenic mechanisms involved in the role of the neuropeptides secreted from the corneal nerves in dry eye disease. Here, we reviewed the emerging concept of neurogenic inflammation as one of the pathogenic mechanisms of dry eye disease, the recent results of related studies, and the direction of future research.

The anatomical and functional relationship between allergic conjunctivitis and allergic rhinitis

There are numerous anatomic connections between the allergic conjunctivitis and allergic rhinitis. The most obvious reason is the physical connection via the nasolacrimal apparatus. However, a closer look at innervation, circulatory, lymphatic, and neurogenic systems reveals much more than a physical connection. The eye is richly innervated by parasympathetic nerves that enter the eyes after traveling in conjunction with the parasympathetic input to the nasal cavity. Parasympathetic innervation governing the tear film and nasal secretion can intersect at the pterygopalatine ganglion. Neurogenic inflammation affects both the eye and the nose as evidenced by the presence of the same neurogenic factors. Venous flow is in the SOV area connecting the eye and the nose, once thought to be without valves. In the past, this thinking is the basis for concern about the danger triangle of the face. Recent literature has shown otherwise. Although valves are present, there are still pathways where bidirectional flow exists and a venous connection is made. The most likely area for venous communication is the pterygoid plexus and cavernous sinus. The venous flow and connections also offers a pathway for allergic shiners. Understanding the mutual connections between the nasal mucosa and the ocular surface can also affect treatment strategies.

Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.

Retinal vascular image analysis as a potential screening tool for cerebrovascular disease: a rationale based on homology between cerebral and retinal microvasculatures

The retinal and cerebral microvasculatures share many morphological and physiological properties. Assessment of the cerebral microvasculature requires highly specialized and expensive techniques. The potential for using non-invasive clinical assessment of the retinal microvasculature as a marker of the state of the cerebrovasculature offers clear advantages, owing to the ease with which the retinal vasculature can be directly visualized in vivo and photographed due to its essential two-dimensional nature. The use of retinal digital image analysis is becoming increasingly common, and offers new techniques to analyse different aspects of retinal vascular topography, including retinal vascular widths, geometrical attributes at vessel bifurcations and vessel tracking. Being predominantly automated and objective, these techniques offer an exciting opportunity to study the potential to identify retinal microvascular abnormalities as markers of cerebrovascular pathology. In this review, we describe the anatomical and physiological homology between the retinal and cerebral microvasculatures. We review the evidence that retinal microvascular changes occur in cerebrovascular disease and review current retinal image analysis tools that may allow us to use different aspects of the retinal microvasculature as potential markers for the state of the cerebral microvasculature.

Action of biologically active peptides on monkey iris sphincter and dilator muscles

Biologically active peptides modulate pupillary responsiveness in many non-primate mammals. We examined the action of seven different peptides on iris sphincter and dilator muscles of rhesus monkey. Iris sphincter and dilator muscle preparations from rhesus monkeys were mounted in an organ bath, and tension changes were recorded by an isometric transducer. Electrical field stimulation (100Hz, 0.3 msec, 10V) was applied through a pair of platinum plate electrodes. Monkey iris sphincter and dilator muscles produced simple cholinergic and adrenergic excitatory responses respectively to electrical field stimulation. Strong field stimulation did not elicit slow Substance P (SP) mediated contractions like those in rabbit iris sphincter. Exogenously applied pituitary adenylate cyclase-activating peptide (PACAP) enhanced in a concentration-dependent manner (0.3 nM-0.1 microm) the sphincter response to field stimulation, while neuropeptide Y (NPY) and somatostatin (SRIF) attenuated it. These three peptides did not affect sphincter contractions induced by acetylcholine, and therefore were acting at presynaptically. SP, calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and galanin (GAL) had no effect (at 0.1 microm) on iris sphincter. None of seven exogenously applied peptides had an effect on monkey iris dilator muscle. The innervation of primate irises may be relatively simple compared to non-primates because each of the peptides in this study can modulate miosis or mydriasis in non-primate mammals. Future studies will be expected on the functional significance of species differences in iridial innervation.

Characterisation of WE-14 in porcine ocular tissue

WE-14 is derived from the cell-specific posttranslational processing of chromogranin A (CgA) in subpopulations of neuroendocrine cells and neurons. Region- and site-specific chromogranin A, pancreastatin and WE-14 antisera were employed to study the generation of WE-14 in porcine ocular tissues. No chromogranin A or pancreastatin immunostaining was detected in ocular tissue. Immunohistochemistry detected WE-14 immunostaining in a network of nerve fibre bundles and nerve fibres throughout the limbus, cornea, iris and ciliary body with sparse nerve fibres detected throughout the choroid and sclera. Retinal analysis detected intense WE-14 immunostaining in large ovoid cells in the ganglion cell layer with weak immunostaining in a population of small cells in the inner nuclear layer; weak immunostaining was detected within the fibre layers in the inner plexiform layer. Quantitatively, the highest WE-14 tissue concentration was recorded in aqueous retinal and corneal extracts with lower concentrations in the sclera, choroid and anterior uveal tissues. Chromatographic profiling resolved a minor chromogranin A-like immunoreactant and a predominant immunoreactant co-eluting with synthetic human WE-14. This is the first study to demonstrate that WE-14 is generated in neuronal fibres primarily innervating the anterior chamber and in select cell populations in the retina.

Corneal nerves: structure, contents and function

This review provides a comprehensive analysis of the structure, neurochemical content, and functions of corneal nerves, with special emphasis on human corneal nerves. A revised interpretation of human corneal nerve architecture is presented based on recent observations obtained by in vivo confocal microscopy (IVCM), immunohistochemistry, and ultrastructural analyses of serial-sectioned human corneas. Current data on the neurotransmitter and neuropeptide contents of corneal nerves are discussed, as are the mechanisms by which corneal neurochemicals and associated neurotrophins modulate corneal physiology, homeostasis and wound healing. The results of recent clinical studies of topically applied neuropeptides and neurotrophins to treat neurotrophic keratitis are reviewed. Recommendations for using IVCM to evaluate corneal nerves in health and disease are presented.

Distribution of peptidergic nerve fibres in the guinea pig trabecular meshwork

A quantitative analysis of peptidergic nerve fibres located in the trabecular meshwork of the guinea pig has been performed. Our results confirm that this structure contains VIP-, NPY- and substance P-like immunoreactivity as major neurotransmitters. These findings were obtained using immunohistochemical techniques. For this purpose serial sections of the eye were stained by immunohistochemistry for each of three neurotransmitters and stained sections were analysed by quantitative image analysis. Our findings demonstrate that SP-positive, NPY-positive and VIP-positive nerve fibres occupy 11.2, 4.9 and 2.4%, respectively, of the observed area (expressed as conventional units, C.U.) in the trabecular meshwork of the guinea pig eye. It is relevant to emphasize that the area containing these three types of peptidergic nerve fibres appears to be large (18.5 +/- 6.6 C.U.) in proportion to the total observed area. The innervation of the drainage angle of the guinea pig eye has been well described by many authors. This is the first study to report quantitative measurements of three types of peptidergic nerve fibres identified and measured in this area. The presence of these three neurotransmitters in the trabecular meshwork of guinea pig eye suggests their possible participation in aqueous humor regulation.

Superior cervical ganglionectomy-induced lowering of intraocular pressure in rabbits: role of prostaglandins and neuropeptide Y

At 22-24 h after unilateral ganglionectomy (SX), intraocular pressure (IOP) was significantly (p < 0.001) reduced in SX eyes compared either with the contralateral, normally innervated eyes or with baseline measurements. SX raised prostaglandin E2 (PGE2), PGF2alpha, and neuropeptide Y (NPY) concentrations in the aqueous humor but reduced these levels in the iris-ciliary body. At 22-24 h after bilateral SX, flurbiprofen (0.03%) significantly (p < 0.001) inhibited the reduction of IOP and the elevation of PGE2 and PGF2alpha levels in the aqueous humor. We conclude that PGs mediate the reduction of IOP at 22-24 h after SX.

Peptidergic innervation of the rat cornea

Corneal nerves regulate corneal epithelial integrity, proliferation, and wound healing. The mechanisms by which the nerves mediate their effects remain poorly understood; however, the release of biologically active neuropeptides has been hypothesized. The purpose of the current investigation was to determine the relative densities, distribution patterns, and origins of rat corneal nerves containing each of eight different neuropeptides, calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL), neuropeptide Y (NPY), methionine-enkephalin (M-ENK), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), and cholecystokinin (CCK). In the first set of experiments, immunohistochemical demonstrations of the above neuropeptides were performed on free-floating corneal sections cut tangential to the corneal surface. The results showed that six of the peptides, CGRP, SP, GAL, NPY, M-ENK, and VIP were present in rat corneal nerves. The innervation patterns of corneal nerves containing each of these six peptides were then documented by mapping all fibers in serial sections from select corneal quadrants onto a series of line drawings by using a drawing tube. In the second set of experiments, the origins of the corneal peptidergic nerve fibers were determined by selective ocular denervations. Unilateral combined sensory and sympathetic ocular denervations or unilateral sympathetic ocular denervations were performed in adult rats by transecting the ophthalmomaxillary nerve and/or removing the superior cervical ganglion. After 5-7 days, each of the ipsilateral corneas was sectioned and processed immunohistochemically for the presence of one of the six peptides found in experiment one, and the fibers that survived the ocular denervations were plotted onto line drawings. Ocular denervations revealed that corneal peptidergic nerves have sensory (CGRP, SP, and GAL), sympathetic (NPY), and parasympathetic (GAL, NPY, M-ENK, and VIP) origins. The results of this investigation have shown that the peptidergic innervation of the rat cornea is more extensive and complex than previously reported. This is the first investigation to show the presence of GAL in the rat cornea, and the first to demonstrate the presence of NPY-, VIP-, and M-ENK-IR nerve fibers in the cornea of any species.

Parasympathetic innervation of the rat cornea

The mammalian cornea receives a dense sensory innervation and a modest sympathetic innervation. The purpose of the current study was to determine if the rat cornea is also innervated by parasympathetic nerves. In the first set of experiments, unilateral combined sympathetic and sensory ocular denervations were performed in adult rats by surgical removal of the superior cervical ganglion and intracranial transection of the trigeminal ophthalmomaxillary nerve. Completeness of the denervation procedure was verified postmortem by a variety of macroscopic and immunohistochemical methods. Five to twelve days later, the corneas were serially sectioned tangential to the ocular surface and processed immunohistochemically with antibodies against the pan-neuronal markers, protein gene product 9.5 (PGP-9.5) and peripherin. In every animal a small, but constant, population of corneal and limbal immunoreactive fibers were unaffected by the surgical denervations and were concluded to derive from parasympathetic ganglia. In the second set of experiments, the origins of the rat corneal innervation were determined by applying the neuroanatomical tracer, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to the central cornea. Two to four days later, the trigeminal, superior cervical, ciliary, accessory ciliary and pterygopalatine ganglia were sectioned and analysed for the presence of HRP-labeled neurons. Examination of the corneal application site and associated ocular tissues revealed no evidence of tracer spread into neighbouring structures. Small numbers (0-6 per animal) of HRP-labeled neurons were observed in the ipsilateral ciliary and accessory ciliary ganglia of most animals. The results of these carefully controlled studies provide strong anatomical evidence of a modest parasympathetic innervation of the rat cornea.

Innervation of melanocytes in human skin

Communication between the nervous system and epidermal melanocytes has been suspected on the basis of their common embryologic origin and apparent parallel involvement in several disease processes, but never proven. In this study, confocal microscopic analysis of human skin sections stained with antibodies specific for melanocytes and nerve fibers showed intraepidermal nerve endings in contact with melanocytes. This intimate contact was confirmed by electron microscopy, which further demonstrated thickening of apposing plasma membranes between melanocytes and nerve fibers, similar to synaptic contacts seen in nervous tissue. Since many intraepidermal nerve fibers are afferent nerves that act in a "neurosecretory" fashion through their terminals, cultured human melanocytes were stimulated with calcitonin gene-related peptide (CGRP), substance P, or vasoactive intestinal peptide, neuropeptides known to be present in cutaneous nerves, to examine their possible functions in the epidermal melanin unit. CGRP increased DNA synthesis rate of melanocytes in a concentration- and time-dependent manner. Cell yields after 5 d were increased 25% compared with controls maintained in an otherwise optimized medium. Furthermore, stimulation by CGRP induced rapid and dose-dependent accumulation of intracellular cAMP, suggesting that the mitogenic effect is mediated by the cAMP pathway. These studies confirm and expand a single earlier report in an animal model of physical contact between melanocytes and cutaneous nerves and for the first time strongly suggest that the nervous system may exert a tonic effect on melanocytes in normal or diseased human skin.

Regional involvement of an endothelium-derived contractile factor in the vasoactive actions of neuropeptide Y in bovine isolated retinal arteries

1. In vitro experiments in a microvascular myograph were designed in order to investigate the effects of human neuropeptide Y (NPY), its receptor subtype and the mechanisms underlying NPY actions in bovine isolated retinal proximal (PRA) and distal (DRA) arteries. 2. A single concentration of NPY (10 nM) induced a prompt and reproducible contraction which reached a plateau within 1-4 min, after which the response returned to baseline over the next 2-10 min. Cumulative addition of NPY induced concentration-dependent contractions of bovine retinal arteries, with an EC50[M] of 1.7 nM and a maximal response equal to 54 +/- 8% of Emax (absolute maximal contractile levels of vessels) and not different from that obtained by a single addition of the peptide. There were no significant differences in either sensitivity or maximal response to NPY between PRA and DRA. 3. Porcine NPY and the selective Y1-receptor agonist, [Pro34]NPY, also induced concentration-dependent contractions of the retinal arteries with a potency and maximal response not significantly different from those of human NPY; in contrast, the selective Y2-receptor agonist, NPY(13-36), caused only a 5% contraction at the highest concentration used. 4. Removal of extracellular Ca2+ or pretreatment with the 1,4-dihydropyridine Ca(2+)-channel blocker, nifedipine (1 microM), reduced the contractile response of 10 nM NPY to 18.4 +/- 3.3% (n = 6) and 18.6 +/- 3.9% (n = 6); respectively, of the controls. 5. Mechanical removal of the endothelium depressed the maximal contraction elicited by NPY in PRA but did not affect either sensitivity or maximal response to the peptide in DRA. In endothelium-intact arteries, blockade of the cyclo-oxygenase pathway with 3 microM indomethacin increased resting tension in both PRA and DRA and significantly inhibited sensitivity and maximal contraction to NPY of PRA and DRA, respectively. The thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor antagonist, SQ30741, reduced both sensitivity and maximal contraction to NPY in PRA but not in DRA. 6. In endothelium-denuded PRA, indomethacin but not SQ30741 significantly reduced NPY maximal response and induced a marked increase in resting tension suggesting a basal release of a vasodilator prostanoid from smooth muscle cells. 7. Superoxide dismutase (SOD) (150 u ml-1) reduced the maximal contraction to NPY in PRA. Inhibition of the nitric oxide (NO) synthase with NG-nitro-L-arginine (L-NOARG) (30 microM), enhanced sensitivity and maximal contraction to NPY in both PRA and DRA. In the presence of L-NOARG, SOD did not further inhibit NPY responses in PRA. 8. NPY (10 nM) induced a 2.9 fold leftwards shift of the noradrenaline concentration-response curves in PRA and increased maximal response by 50 +/- 16%. Neither 1 nor 10 nM NPY affected noradrenaline responses in DRA. [Pro34]NPY (10 nM), but not NPY(13-36), mimicked the potentiating effect of NPY on noradrenaline responses in PRA. 9. TXA2 analogue, U46619, at 10 nM elicited 3.6 fold leftwards shift of the noradrenaline concentration-responses curves in PRA and increased the maximal contraction by 32 +/- 3%, whereas in the presence of 1 microM SQ30741, 10 nM NPY did not potentiate noradrenaline responses. 10. The present results indicate that NPY may play a role in the regulation of retinal blood flow through both a direct contractile action, independent of the vessel size and a potentiation of the responses induced by noradrenaline in the proximal part of the retinal circulation, both effects being mediated by Y1 receptors. NPY promotes Ca2+ influx through voltage-dependent Ca2+ channels and stimulates the synthesis of contractile prostanoids in PRA and DRA, although only in PRA does the peptide trigger the release of an endothelium-derived contractile factor which facilitates the contraction and also seems to account for the potentiating effect of NPY.

Circadian rhythm of neuropeptide Y-like immunoreactivity in the iris-ciliary body of the rat

Neuropeptide Y (NPY)-like immunoreactivity (LI) in the iris-ciliary body of rats kept under constant darkness (DD) and in 12 h light-12 h dark cycle (LD) was determined by enzyme immunoassay. NPY-LI contents in the iris-ciliary body were found to oscillate in circadian fashion under DD and LD conditions, with a peak at about circadian time 12 (CT 12) and a trough at around CT 0. Unilateral superior cervical ganglionectomy caused a significant decrease in NPY-LI levels in the sympathectomized eye compare to the contralateral intact eye, independent of lighting phase. These results suggest the presence of an endogenous circadian rhythm in NPY-LI content in the rat iris-ciliary body, and the possible involvement of a sympathetic input from the superior cervical ganglion.

Neuropeptide Y suppresses the neurogenic inflammatory response in the rabbit eye; mode of action

Ocular injury in the rabbit causes miosis and breakdown of the blood aqueous barrier (aqueous flare response, AFR), reflecting a sensory nerve-mediated inflammatory response, elicited by the release of tachykinins and calcitonin gene-related peptide (CGRP) from C-fibers. Neuropeptide Y (NPY) occurs in sympathetic fibers in the eye. The study was designed to examine whether NPY and related peptides interfere with the inflammatory response to ocular injury in the rabbit in vivo. The isolated rabbit iris was studied with respect to NPY binding sites and second messenger coupling. The AFR and the miotic response to a standardized injury (infrared irradiation (IR) of the iris) were suppressed dose-dependently by NPY (0.01-1.0 nmol) injected intravitreally 30 min prior the trauma. The treated eye was compared with the contralateral eye, which received 0.9% saline and IR. The Y1 receptor agonist [Pro34]NPY, the Y2 receptor agonist NPY 13-36 and the structurally related peptide YY (1 nmol each) suppressed the AFR in response to IR. Injection of either NPY or the Y1 and Y2 receptor agonists (0.3 nmol each) suppressed the AFR evoked by exogenously applied CGRP (0.15 nmol). Saturation studies with 125I-NPY revealed both high and 'moderate' affinity binding sites in the iris. The Bmax values were 26 and 321 fmol/mg protein, respectively. NPY suppressed the forskolin-stimulated adenylate cyclase activity (IC50 value 19 nM). NPY did not affect basal or noradrenaline-induced accumulation of inositol phosphates in the iris. In conclusion, the rabbit iris seems to be rich in NPY receptors linked to inhibition of adenylate cyclase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue-specific expression of the human neuropeptide Y gene in transgenic mice

Neuropeptide Y (NPY) is the most abundant neuropeptide detected in the mammalian brain, and is found throughout the central and peripheral nervous system. This peptide is a proposed regulator of appetite, blood pressure, and pituitary hormone release. Previous experiments have demonstrated the ability of 5' sequences within the human NPY gene to promote transcription in cultured neuronal cells. To identify sequences in this gene that regulate tissue-specific expression, a NPY/CAT fusion gene, containing approximately 850 bp of NPY sequences, was microinjected into fertilized mouse ova. Five lines of transgenic mice were derived from these ova and several tissues from mice of each line were tested for transgene expression using the CAT assay. One line demonstrated X-chromosome-linked transmission of the transgene while the other lines demonstrated autosomally-linked transmission. Three lines demonstrated transgene expression with significant levels of CAT activity detectable only in tissues which have been shown to express endogenous NPY. One autosomally-linked line did not demonstrate significant levels of transgene activity because the transgene appeared to have undergone structural alteration during genomic integration. No transgene activity was detected in either male of female mice from the X-linked line, suggesting a positional regulation of the transgene locus other than X-inactivation in this line. The present research demonstrated the NPY regulatory sequences included in pCATNPY delta 796 sufficiently directed tissue-appropriate gene expression in transgenic mice.

Characterization of neuropeptide Y-like immunoreactivity in vertebrate retina

We have determined the endogenous levels of neuropeptide Y-like immunoreactivity (NPY-LI) in retinal extracts from pigs, cats, rabbits, chickens, and frogs by radioimmunoassay (RIA). The NPY-LI levels varied among the species. The highest concentration was found in frog retina, where seasonal variations were seen, 861 +/- 31 pmol g(-1) wet weight in the autumn and 334 +/- 26 pmol g(-1) wet weight in the spring. Lower levels were demonstrated in chicken and pig retina, 4.1 +/- 0.4 and 3.6 +/- 0.3 pmol g(-1) wet weight, respectively. The lowest concentration was demonstrated in rabbit retina, 2.0 +/- 0.3 pmol g(-1) wet weight. (All values are expressed as mean +/- S.E.M.). The NPY-LI in pig, rabbit, chicken and frog retina was characterized by high-performance liquid chromatography (HPLC). The main part of the extracted NPY-LI had an elution volume close to that to the porcine NPY. We have also analysed the evoked release of endogenous NPY from frog retina, induced either with light flashes (3 Hz, 300 lx), or with potassium depolarization of the neurons (40 mM). Light flashes and potassium induced an increased release of NPY-LI of 61 and 77%, respectively. NPY-LI in the efflux had the same HPLC retention time as that extracted directly from the retina.

Effects of cervical sympathetic nerve stimulation and neuropeptide Y (NPY) on cranial blood flow in the cat

Effects of cervical sympathetic nerve stimulation (SNS) at 10 Hz and intravenous infusion of neuropeptide Y (NPY), 10 and 100 pmol x kg body wt-1 x min-1 for 5 min, on regional blood flow in the cat were investigated with radioactive microspheres. Sympathetic nerve stimulation caused significant reductions in blood flows in the facial tissues including the eye. Alpha-adrenoceptor blockade with phenoxybenzamine and combined beta- and alpha-adrenoceptor blockade with propranolol and phenoxybenzamine abolished the effects of sympathetic nerve stimulation in most facial tissues except in the tongue, upper eyelid and masseter muscle. In most cranial tissues, neuropeptide Y reduced regional blood flow and increased vascular resistance. No effect of neuropeptide Y on vascular resistance was observed in the choroid. In the present study, evidence for a non-adrenergic component in sympathetic vasoconstriction was found in the tongue, upper eyelid and masseter muscle but not in the majority of feline facial tissues. Neuropeptide Y was a potent vasoconstrictor in many cranial tissues, while in parts of the uvea, the effects of neuropeptide Y were less pronounced.

Neuropeptide Y (NPY): a vasoconstrictor in the eye, brain and other tissues in the rabbit

The effect of neuropeptide Y (NPY) on uveal vascular resistance was studied in rabbits by direct determination of uveal blood flow from a cannulated vortex vein. Regional blood flows, in the eye, the brain and several other tissues, were measured, with radioactive microspheres, during neuropeptide Y-infusion in rabbits with and without alpha-adrenoceptor blockade. Intravenous infusion of increasing doses of neuropeptide Y caused a dose-dependent increase in the total uveal vascular resistance. Maximal effect, a 70% increase, was achieved with 120 pmol kg-1 min-1. In the microsphere experiments, this dose rate was given i.v. over 10 minutes and blood flow determinations were made before and at 2 and 10 minutes after the start of the infusion. After 2 minutes of neuropeptide Y, there were marked blood flow reductions in the spleen, kidneys, adrenal glands, gastro-intestinal tract, choroid plexus and pineal and pituitary gland. The effect in the eye was small at 2 minutes, but at 10 minutes local blood flows in the choroid and the ciliary body were decreased by 50% and the iridal blood flow by 30%. Retinal blood flow was not affected by neuropeptide Y. At 10 minutes there were also significant blood flow reductions in the brain, tongue, masseter muscle and several glandular tissues. The effects of neuropeptide Y on local blood flow in rabbits that had been subjected to alpha-adrenoceptor blockade were very similar to the effects in the animals without alpha-adrenoceptor blockade. The results show that, in the rabbit, neuropeptide Y has marked effects on local blood flows in several tissues, including the eye, and suggest that neuropeptide Y may significantly contribute to the uveal vasoconstriction during sympathetic nerve stimulation.

Neuropeptide Y and somatostatin inhibit stimulated cyclic AMP production in rabbit ciliary processes

The interaction of adrenergic and peptide receptors linked to adenylate cyclase and the inhibition by bioactive peptides of stimulated cyclic AMP production has been investigated in intact, excised rabbit ciliary processes. Cyclic AMP production stimulated by isoproterenol, vasoactive intestinal peptide, or forskolin was inhibited by the biologically active peptides neuropeptide Y, somatostatin, and the synthetic somatostatin analogue SMS 201-995. IC50s determined from dose-response curves of inhibition are consistent with the known abilities of these ligands to modulate cyclic AMP and physiological responses in other tissues. Inhibition by neuropeptide Y or SMS 201-995 was unaffected by the specific alpha 2-adrenergic antagonist yohimbine, which shows that peptide inhibition is not occurring via peptide binding to the inhibitory alpha 2-adrenergic receptor. These results suggest that endogenous peptides may participate in modulation of cyclic AMP production and subsequent physiological events influenced by cyclic AMP levels in rabbit ciliary processes by inhibiting stimulated cyclic AMP synthesis.

Inhibitory effects of neuropeptide Y on sympathetic neurotransmission in the rabbit iris-ciliary body

Neuropeptide Y (NPY, 1-300 nM) mediated a concentration-dependent inhibition of field stimulation-evoked [3H]norepinephrine (NE) overflow from the isolated, superfused rabbit iris-ciliary body. At equimolar concentrations (100 nM), the homologous neuropeptide peptide YY (PYY) mimicked the effects of NPY, whereas pancreatic polypeptide (PP) and the C-terminal fragment of NPY did not modify [3H]NE release. NPY-induced inhibition of [3H]NE release was unaffected by pretreatment of tissues with atropine (100 nM) plus yohimbine (100 nM) and was non-additive with the maximal prejunctional effects of carbamycholine or clonidine, indicating that NPY acts independently of prejunctional muscarinic or alpha 2-adrenergic receptor activity to reduce [3H]NE overflow. It is concluded that NPY is a specific, potent modulator of adrenergic neurosecretion in the rabbit iris-ciliary body. These findings confirm the role of NPY as a co-transmitter at ocular sympathetic neuroeffector junctions, either mimicking or augmenting the actions of endogenously released norepinephrine.

Non-adrenergic sympathetic vasoconstriction in the eye and some other facial tissues in the rabbit

The effects of unilateral sympathetic nerve stimulation (SNS) on regional blood flow in the rabbit were studied with radioactive microspheres. SNS at 10 or 4 Hz caused an approximately 60% reduction in choroidal blood flow, which was partly resistant to alpha-adrenoceptor blockade with phenoxybenzamine. The vasoconstriction evoked by SNS at 2 Hz was completely abolished by alpha-adrenoceptor blockade. A similar response was seen in the iris, ciliary body, masseter muscle and lacrimal gland. In the harderian gland, however, SNS (2 Hz) after alpha-adrenoceptor blockade caused a significant reduction in blood flow. In the salivary glands, combined beta- and alpha-adrenoceptor blockade with propranolol and phenoxybenzamine revealed a slight non-adrenergic vasoconstriction during SNS at 10 Hz; however, the blood flow was significantly increased during SNS at 4 and 2 Hz following alpha-adrenoceptor blockade. These results indicate that there is a frequency-dependent, non-adrenergic component in the sympathetic vasoconstriction of the eye and several facial tissues. In the salivary glands, beta-adrenoceptor-mediated vasodilatation tends to mask a non-adrenergic vasoconstriction.

Peptide immunoreactivity of the ciliary ganglion and its accessory cells in the rat

By means of immunohistochemistry, calcitonin gene-related peptide, Leu-enkephalin and neuropeptide Y localize to rat ciliary and accessory ganglion cells. The proportion of ciliary and accessory neurons immunoreactive to each peptide is provided and compared to previous data for vasoactive intestinal peptide. These findings indicate considerable neurochemical complexity for a parasympathetic ganglion with a small cell population.

Pterygopalatine ganglion cells contain neuropeptide Y

By immunohistochemistry, neuropeptide Y (NPY) localizes to neurons in the rat pterygopalatine ganglion. These cells also are intensely or moderately reactive with acetylcholinesterase histochemistry. In contrast, both tyrosine hydroxylase immunohistochemistry and glyoxylic acid-induced fluorescence for catecholamines stain smaller clustered cells, similar in appearance to small intensely fluorescent (SIF) cells and clearly distinct from the NPY-immunoreactive cells. By reverse phase high-performance liquid chromatography, the NPY-immunoreactive material in the rat pterygopalatine ganglion migrates as a single peak characteristic of the peptide. We conclude that NPY-containing cholinergic cells are present in this classical parasympathetic ganglion. NPY-like immunoreactive neurons similarly occur in the pterygopalatine ganglion of the guinea pig.

Sympathetic innervation of the rat cornea as demonstrated by the retrograde and anterograde transport of horseradish peroxidase-wheat germ agglutinin

The sympathetic innervation of the rat cornea was studied by using the method of intraaxonal transport of horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA). In the first set of experiments, the relative number of superior cervical ganglion neurons that innervate the rat central cornea was estimated by the method of retrograde HRP-WGA transport. Following tracer application to the scarificed central corneal surface, 49-198 labeled neurons were observed in the ophthalmic region of the ipsilateral trigeminal ganglion and zero to four cells in the rostral pole of the ipsilateral superior cervical ganglion. In the second set of experiments, the three-dimensional distribution and termination sites of the corneal sympathetic nerve fibers were investigated by the technique of HRP-WGA anterograde transport from the superior cervical ganglion. HRP-WGA-labeled axons in corneal whole mounts were identified by the presence within their axoplasm of linear arrays of HRP-TMB reaction product, and their distribution was plotted faithfully onto line drawings made with a drawing tube attachment. Large numbers of HRP-labeled fibers were found in all animals within the corneoscleral limbus where the majority were associated with blood vessels. Fewer fibers (zero to 14 per animal) entered the cornea proper. The latter fibers entered the peripheral cornea in the deep to middle layers of the stroma and ascended into progressively more superficial layers as they coursed centrally. The majority of fibers branched infrequently in the peripheral cornea and increased in branching complexity near the central cornea. HRP-labeled axonal varicosities suggestive of terminal and preterminal expansions were located preferentially in the subepithelial layer of the corneal stroma and in the basal epithelium. Approximately 75% of the axonal varicosities were located in the central half of the cornea. The results of the current investigation reveal that the rat cornea is innervated sparsely by sympathetic nerve fibers derived from the superior cervical ganglion. These data provide additional support to current theories that corneal sympathetic nerve fibers may influence select aspects of corneal physiology, including ion transport and hydration, mitogenesis and wound healing, and sensitivity.

Surgical and pharmacological reductions in sympathetic nerve activity increase the neuropeptide Y-immunoreactivity content of the rat iris but not the vas deferens

Decentralization of the superior cervical ganglion (S.C.G.) of the rat elevated the neuropeptide-Y immunoreactivity (NPY-ir) content of the ganglion on day 1 (+43%) but not on day 3 post-surgery. The content of NPY-ir in the iris was increased by decentralization (+40%) 3 days post-surgery, and treatment with clonidine (+43%), and pempidine (+82%). The levels of NPY-ir in the rat vas deferens were not affected by either surgical or pharmacological treatment. These results suggest NPY is released from sympathetic nerves in the iris but not vas deferens during normal sympathetic activity.

Co-existence of neuropeptides in sympathetic, cranial autonomic and sensory neurons innervating the iris of the guinea-pig

We have used double-labelling immunofluorescence to identify the peptide content of autonomic and sensory neurons innervating the iris of albino guinea-pigs. Four major classes of neurons were identified on the basis of their distributions, origins and immunohistochemical characteristics. A dense plexus of noradrenergic axons in the constrictor and dilator muscles of the iris originated from the superior cervical ganglion, and contained immunoreactivity (IR) to both neuropeptide Y (NPY) and dynorphin (DYN). The constrictor and dilator muscles were also supplied with a dense plexus of axons with IR to substance P (SP). These axons probably originated from SP-IR nerve cell bodies located along the ciliary nerves, and are almost certainly the same axons as those producing cholinergic pupilloconstriction. The iris was also innervated by unmyelinated, capsaicin-sensitive axons with IR to both SP and calcitonin gene-related peptide. Most of these axons also contained IR to DYN and some were also IR for cholecystokinin. These axons are almost certainly sensory. Axons containing IR to both NPY and vasoactive intestinal peptide (VIP) were common in the ciliary processes, and also formed a sparse plexus near the ciliary margin of the dilator muscle. Following surgical sympathetic denervation these axons showed IR for dopamine-beta-hydroxylase; they seemed to originate from the sphenopalatine ganglion. These results demonstrate that there are well-defined patterns of coexistence of neuropeptides in the autonomic and sensory neurons supplying the iris of guinea-pigs. To understand the physiological roles of these peptides, it will be necessary to consider the possibility of complex interactions between them.

Melanotropin release inhibiting activity of neuropeptide Y: structure-activity relationships

We have recently shown that the release of alpha-MSH by the intermediate lobe of the frog pituitary is inhibited by neuropeptide Y (NPY). Using the perifusion technique, we have compared in the present study, the alpha-MSH release inhibiting activities of NPY, various NPY short chain analogues and two other members of the pancreatic polypeptide family, peptide YY (PYY) and avian pancreatic polypeptide (APP). The order of biological potency was NPY greater than NPY[2-36] greater than NPY[16-36] greater than NPY[25-36] greater than NPY[1-15]. Among the two pancreatic polypeptides tested, PYY appeared to be almost as potent as NPY while APP was 6 times less active than NPY. Neither NPY[1-15] nor NPY[16-36] could antagonize the inhibitory effect of NPY on alpha-MSH release. The structure-activity relationship study suggests that the bioactive determinant of NPY is located in the C-terminal part of the molecule.