Neuropeptide Y: cerebrovascular innervation and vasomotor effects in the cat

Blockade of neuropeptide Y-induced potentiation of noradrenaline-evoked vasoconstriction by D-myo-inositol-1.2.6-trisphosphate (PP56) in rabbit femoral arteries

Neuropeptide Y (NPY) potentiates noradrenaline (NA)-evoked constriction of circular segments of the rabbit femoral artery. The potentiation occurs exclusively in the lower concentration-range of the agonist NA (10(-8)-3 x 10(-7) M) without any change in maximum contractile effect. NPY per se is without contractile effect in the rabbit femoral artery. The recently developed substance, D-myo-inositol-1.2.6-trisphosphate (PP56), which is an isomer of inositol-1.4.5-trisphosphate, is without effect per se on the rabbit femoral artery, nor does it affect NA-induced contractions. However, it was found to completely antagonize NPY-induced potentiation of the NA concentration-response curve.

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.

Solubilization of the neuropeptide Y receptor from rat brain membranes

The neuropeptide Y (NPY) receptor was solubilized from rat brain membranes with the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS). The binding of 125I-NPY to CHAPS extracts was protein, time, and temperature dependent. Unlabeled NPY and the related peptides peptide YY (PYY) and pancreatic polypeptide inhibited 125I-NPY binding to solubilized receptors with relative potencies similar to those seen with membrane-bound receptors: NPY greater than PYY much greater than pancreatic polypeptide. Scatchard analysis of equilibrium binding data showed the CHAPS extracts to contain a single population of binding sites with a KD of 3.6 +/- 0.4 nM (mean +/- SEM) and a Bmax of 5.0 +/- 0.2 pmol/mg of protein. In addition the 125I-NPY binding to the soluble receptor was not inhibited by guanosine-5'-O-(3-thiotriphosphate), in contrast to the GTP sensitivity displayed by the membrane-bound receptor. Gel filtration chromatography using Sepharose 6B revealed a single peak of binding activity corresponding to a Mr of approximately 67,000, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis after chemical cross-linking revealed a single band at Mr 62,000. After solubilization and gel chromatography a 50- to 100-fold purification of the NPY receptor was obtained.

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.

Cardiovascular, neuropeptide Y, and adrenergic responses in stress are sexually differentiated

Cardiovascular and sympatho-adrenomedullary responsiveness at rest and during stress were studied in weight-matched, sexually mature male and female rats. At rest, although there were no sex differences in cardiovascular parameters, females had two-fold higher plasma levels of norepinephrine (NE) and epinephrine. Resting plasma levels of neuropeptide Y-immunoreactivity (NPY-ir, a putative sympathetic cotransmitter and a vasoconstrictor) were similar in both sexes. Stresses of handling and cold (4 degrees C) water exposure induced greater pressor and tachycardic responses in males than in females. Males but not females exhibited a protracted recovery from the stress-induced pressor responses and a 2-fold increase in plasma NPY-ir suggesting that NPY release is sexually differentiated. Only in males, low basal plasma NE and NPY-ir levels inversely correlated with greater cold-induced pressor responses. Furthermore, in areflexic pithed rats, pressor adrenergic and NPY responses were greater in males than in females suggesting the possibility of "down"-regulation of vascular adrenergic receptors in females (due to elevated circulating catecholamines) and "up"-regulation of NPY and adrenergic receptors in males.

Studies on colocalization of neuropeptide Y, vasoactive intestinal polypeptide, catecholamine-synthesizing enzymes and acetylcholinesterase in the larynx of the rat

In the present immunohistochemical study, the distribution of nerve fibers containing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) in the larynx was examined and compared with that of fibers containing tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH), and with that of acetylcholinesterase (AChE)-positive nerve fibers, in intact and vagotomized rats and in rats subjected to removal of the superior cervical ganglion (SCG). Fibers showing TH/DBH-like immunoreactivity (LI) were only found in the walls of arteries and arterioles, whereas AChE-positive nerve fibers were located close to the acini and ducts of the glands, in blood vessel walls, in the perichondrium and in the lamina propria. NPY-LI and VIP-LI coexisted in local AChE-positive ganglionic cells and in a subpopulation of the AChE-positive fibers, NPY-LI also being present in some periarterial fibers showing TH/DBH-LI. Unilateral removal of the SCG eliminated the TH/DBH-innervation in the upper but not the lower parts of the larynx ipsilaterally, whereas the NPY-innervation of the arteries in the upper parts only partly disappeared and the NPY-innervation of the other structures remained unchanged. The distribution of VIP-innervation was unchanged after vagotomy and removal of the SCG. The results suggest that VIP is present in the postganglionic parasympathetic innervation, whereas NPY is present in both the postganglionic parasympathetic and sympathetic innervation of the rat larynx.

Increased plasma levels of neuropeptide Y-like immunoreactivity and catecholamines in severe hypertension remain after treatment to normotension in man

Circulating levels of neuropeptide Y (NPY)-like immunoreactivity (-LI), adrenaline and noradrenaline (NA) were analysed in 17 patients admitted to the emergency ward due to severe hypertension; blood pressure mean 204/127 mmHg. The levels of NPY-LI and NA were significantly higher (P less than 0.001) in the hypertensives as compared to a normotensive control group. HPLC analysis revealed that the plasma contained besides NPY-LI also several NPY-LI fragments of low hydrophobicity. Following 2 to 3 weeks treatment the blood pressure had decreased to a mean of 150/89 mmHg. However, circulating levels of NPY-LI (P less than 0.001) and NA (P less than 0.01) were still significantly higher than in controls in spite of the marked reduction in blood pressure. Simultaneous measurements of adrenaline did not reveal any significant changes and these values did not differ compared with those in the normotensive subjects. The findings suggest that peripheral markers of the sympathetic system (NPY-LI and NA) in severe hypertension is not directly related to the blood pressure level.

Neuropeptide Y and vasoactive intestinal peptide in experimental subarachnoid hemorrhage: immunocytochemistry, radioimmunoassay and pharmacology

The involvement of noradrenaline (NA), neuropeptide Y, (NPY), 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) has been examined in the late phase of spasm after an experimental subarachnoid hemorrhage (SAH) in a rat model. Immunocytochemistry and radioimmunoassay of blood vessels from the circle of Willis did not show significant differences in NPY- and VIP-like immunoreactivity 2 days post SAH as compared to control vessels. The postjunctional effects of NA, NPY, 5-HT, ACh and VIP were studied two days after SAH using a sensitive in vitro system. NPY induced contractions were significantly (p less than 0.01) weaker (lower Emax) in SAH as compared to control rats while the relaxant responses to ACh and VIP were slightly increased after SAH. These observations reveal that in a rat model of SAH, with an approximately 20% in vivo constriction at two days, dynamic changes occur in cerebral artery reactivity despite any obvious change in sympathetic or parasympathetic perivascular nerve networks.

Perivascular innervation of the cerebral arteries in spontaneously hypertensive rats--an immunohistochemical study

Perivascular innervation in cerebral arteries of spontaneously hypertensive rats and of normotensive Wistar-Kyoto rats was studied. Adrenergic nerve fibers and neuropeptide Y-containing nerve fibers, indicative of vasoconstrictor nerves, were denser in all cerebral arteries of spontaneously hypertensive rats than those of Wistar-Kyoto rats. In contrast, cholinergic nerve fibers and vasoactive intestinal polypeptide, substance P-containing nerve fibers, indicative of vasodilator nerves, remained unchanged in all cerebral arteries of spontaneously hypertensive rats, as compared with findings in the Wistar-Kyoto rats. Thus, not only adrenergic nerve fibers but also neuropeptide Y-containing nerve fibers may play an important role in preventing the disruption of the blood-brain barrier and the development of hypertensive encephalopathy in spontaneously hypertensive rats.

Neuropeptide Y- and vasoactive intestinal polypeptide-containing nerve fibers in the human cerebral arteries: characteristics of distribution

Perivascular innervation in cerebral arteries from 28 human fetuses at twelve to twenty-eight weeks' gestational age was studied histochemically. Neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)- containing nerve fibers were densely distributed along with adrenergic and cholinergic nerve fibers in the major pial arteries at the base of the brain, an area that forms the circle of Willis, and in the lenticulostriate arteries. In contrast, distribution was sparse in the cortical circumflex branches of the middle cerebral artery, as compared with findings in the lenticulostriate artery of the same diameter. Densely distributed perivascular nerve fibers in the lenticulostriate arteries may play an important role in the pathogenesis of intracerebral hemorrhage.

The effect of neuropeptide Y on mucociliary activity in the rabbit maxillary sinus

The effect of neuropeptide Y (NPY) on mucociliary activity in the rabbit maxillary sinus was investigated in vivo by injecting NPY at increasing dosages into the maxillary artery, response being recorded photoelectrically. At dosages of 0.1-5.0 micrograms/kg, NPY reduced mucociliary activity dose-dependently, the maximum decrease being 14.6 +/- 1.8%, at a dosage of 5.0 micrograms/kg. The NPY-induced reduction of the mucociliary activity manifested brief latency, the peak effect occurring within 3 min followed by a slow return to the baseline value 4-9 min after injection. The response of mucociliary activity to NPY remained unaffected by pretreatment with the alpha-adrenergic antagonists yohimbine (alpha 2) at 100.0 micrograms/kg and phentolamine (alpha 1 + alpha 2) at 0.2-1.0 mg/kg, indicating that the effect of NPY is not mediated via alpha-receptors. Pretreatment with the calcium antagonist nifedipine at 100.0 micrograms/kg inhibited the effect of NPY, suggesting that the NPY-induced decrease may be calcium dependent.

Development of AChE-positive, NA-containing and VIP- and NPY-immunoreactive nerves in the major cerebral arteries of the rat

The development of cerebrovascular nerves containing noradrenaline (NA), acetylcholinesterase (AChE), neuropeptide Y (NPY), and vasoactive intestinal polypeptide (VIP) was studied in rats from before birth to adulthood. All these nerves entered the cranial cavity along the cerebral carotid, internal ethmoidal, and vertebral arteries during the early stages of development, but the subsequent growth and distribution of NA-containing and NPY-immunoreactive (IR) nerves differed greatly from that of AChE-positive and VIP-IR nerves. NA-containing and NPY-IR nerves extended rapidly from the cerebral carotid artery and spread over all the major arteries of the internal carotid system by postnatal day 3, as well as descending the posterior ramus of the cerebral carotid to mingle with nerves from the vertebral artery around the mid-basilar artery by day 5. AChE-positive and VIP-IR nerves from the internal ethmoidal artery covered the whole internal carotid system during the first postnatal week, and projected to the upper basilar artery after the second week, while those from the cerebral carotid artery remained limited to the middle cerebral artery throughout development. By day 21, all major arteries of the internal carotid system had dense plexuses of the four nerve types that were similar to those observed in adult rats. The vertebrobasilar system also had a well-organized network of NA-containing and NPY-IR nerves, but only a poor supply of AChE-positive and VIP-IR nerves. Even on day 30, the latter two nerve types were sometimes absent from the middle to caudal basilar artery, owing to a lack of interdigitation by nerves from the internal ethmoidal and vertebral arteries.

PYY-like material and its spatial relationship with NPY, CGRP and 5-HT in the lung of the Syrian golden hamster

We investigated the presence of peptide YY, neuropeptide Y, calcitonin gene-related peptide and serotonin in the hamster lung by radioimmunoassay, high performance liquid chromatography and immunocytochemistry. Lung-tissue concentrations of peptide YY and neuropeptide Y were 1.3 +/- 0.2 and 2.5 +/- 0.2 pmol/g wet weight, respectively. These two closely related pancreatic peptides were demonstrated in separate peaks with high performance liquid chromatography. The peptide YY appeared fragmented as immunoreactive peptide YY eluted primarily late in the gradient but showed additional peaks early in the gradient. Peptide YY-like immunoreactivity (PYY-LI) was predominantly observed in one or more cells of neuroepithelial bodies in all airways peripheral to bronchioles, and in solitary neuroendocrine cells primarily located in the same peripheral areas. Neuropeptide Y-LI was seen in individual, thin nerve fibers around arteries and veins, in the airway lamina propria, and in the airway epithelium; in the latter also immunopositive nerve terminals were located. This pattern did not appear to coincide with that of calcitonin gene-related peptide-LI in epithelial nerve fibers and terminals. Peptide YY-LI, calcitonin gene-related-LI and serotonin-LI were present in cells of one and the same neuroepithelial body. However, peptide YY-LI was never found to be co-localized with calcitonin gene-related-LI or serotonin-LI, but the latter two were co-localized as previously reported.

Centrally truncated neuropeptide Y analog acts as an agonist for Y1 receptors on SK-N-MC cells

The similarity of neuropeptide Y (NPY) to pancreatic polypeptide (PP), whose X-ray crystallographic structure is known, has allowed computer-assisted molecular modelling of NPY and predictions of its three-dimensional structure. Utilizing these techniques, Krstenansky et al. (Proc. Natl. Acad. Sci. U.S.A., 86 (1989) 4377-4381) reported that a centrally truncated analog of porcine NPY, [D-Cys7-Aoc8-17-Cys20]pNPY, which was designed to maintain the tertiary structure of the native molecule, bound to sites on membranes from mouse brain with even higher affinity than native NPY. As brain membranes may represent a heterogeneous mixture of receptor subtypes, we decided to characterize the activity of this analog on a defined cell line. SK-N-MC cells are a human epithelioma cell line with high-affinity receptors of the Y1 subtype which are coupled to inhibition of adenylate cyclase. (D-Cys7-Aoc8-17-Cys20]pNPY bound to receptors on SK-N-MC cells, but in contrast to membranes from mouse brain, with a lower affinity than pNPY. Furthermore, [D-Cys7-Aoc8-17-Cys20]pNPY was able to inhibit isoproterenol-stimulated cAMP production in these cells. Therefore, it appears that the central amino acids deleted from this analog are not involved in NPY binding, and biological activity can be maintained by conservation of the tertiary structure of NPY around the binding surface.

Peptide-containing nerve fibres in guinea-pig coronary arteries: immunohistochemistry, ultrastructure and vasomotility

The peptidergic innervation of guinea-pig coronary arteries was investigated by means of immunohistochemical, ultrastructural and in vitro pharmacological techniques. A network of nerves was demonstrated in all major epicardial arteries by means of an antiserum to the neuronal marker protein gene product 9.5. The majority of nerve fibres possessed neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity, the number and distribution of nerves immunoreactive for NPY being similar to that of nerves containing TH immunoreactivity. Numerous nerve fibres displaying immunoreactivity for substance P, neuropeptide K and calcitonin gene-related peptide (CGRP) were also found. In double-stained preparations substance P immunoreactivity was co-localized with CGRP and with neuropeptide K immunoreactivities in the same varicose nerve fibres. Ultrastructural studies revealed the presence of numerous axon varicosities at the adventitial-medial border. NPY immunoreactivity was localized in large granular vesicles in nerve varicosities which also contained numerous small granular vesicles. Large granular vesicle-containing nerves also displayed immunoreactivity for dopamine-beta-hydroxylase. With an in vitro method, the vasomotor responses to perivascular peptides were characterized in epicardial and intramyocardial arteries. In epicardial arteries neither noradrenaline nor NPY elicited a contractile response. Only in some intramyocardial arteries was an NPY-mediated contraction demonstrated. No potentiating effect of noradrenaline and NPY was observed in either epicardial or intramyocardial arterial segments. In contrast, CGRP, substance P and vasoactive intestinal peptide (VIP) all produced a concentration-dependent relaxation of both epicardial and intramyocardial arteries. These results suggest that peptide-containing nerves associated with guinea-pig coronary arteries may predominantly be involved in mediating vasodilation.

Neuropeptide Y and sympathetic neurotransmission

The coexistence of neuropeptide Y (NPY) with noradrenaline (NA) in perivascular nerves as well as in sympathetic nerves to muscle in the heart, spleen and vas deferens suggests a role for NPY in autonomic transmission. Sympathetic nerve stimulation or reflexogenic activation in experimental animals or man are associated with NPY release as revealed by overflow mainly upon strong activation. This difference between NPY and NA secretion may be related to the partly separate subcellular storage whereby NPY seems to be exclusively present in the large dense-cored vesicles. The NPY secretion is likely to be regulated by the local biophase concentrations of NA acting on prejunctional alpha-2-adrenoceptors since alpha-2 agonists inhibit and antagonists enhance NPY overflow, respectively. Furthermore, after NA has been depleted by reserpine, the nerve stimulation-evoked release of NPY is enhanced leading to a progressive depletion of tissue content of NPY. Exogenous NPY binds to both pre- and postjunctional receptors, inhibits NA and NPY release, enhances NA-evoked vasoconstriction and induces vasoconstriction per se. The prejunctional action of NPY which is especially noticeable in the vas deferens may serve to reduce transmitter secretion upon excessive stimulation. The long-lasting vasoconstriction evoked by sympathetic stimulation in several tissues including skeletal muscle, nasal mucosa and spleen, which remains in animals pretreated with reserpine (to deplete NA) combined with preganglionic denervation (to prevent the concomitant excessive NPY release and depletion), is mimicked by NPY and highly correlated to NPY release. Under these circumstances the NPY content in the local venous effluent reaches levels at which exogenous NPY evokes vasoconstriction.

Neuropeptide Y- and substance P-like immunoreactive nerve fibers in the rat dura mater encephali

Density and pattern of nerve fibers with neuropeptide Y-like immunoreactivity (NPY-LI) and substance P-like immunoreactivity (SP-LI) in the rat dura mater encephali were investigated by light and electron microscopy using whole-mount preparations. NPY-LI fibers are observed throughout the encephalic dura mater. A remarkable net of NPY-LI nerve fibers is located in the walls of the sagittal and transverse sinuses. Beyond that NPY-LI network, distinct NPY-LI nerve fibers or plexus occur in the rostral falx, parietal dura mater of the olfactory bulb, supratentorial dura mater, parietal dura mater of the cerebellum, tentorium cerebelli and the ventral dura mater. Electron microscopic studies reveal that NPY-LI is exclusively located in unmyelinated axons of small and large nerve fiber bundles, with or without a perineural sheath. Immunopositive C-fibers are predominantly associated with the vascular bed. SP-LI nerve fibers have a moderate and more uniform distribution in the encephalic dura mater. A distinct plexus of SP-LI fibers follows the branches of the middle meningeal artery and the adjacent dura mater. SP-LI fibers are most prominent in the parietal dura mater of the cerebellum. Fine beaded SP-LI fibers, arising from larger SP-LI fiber bundles, are observed in close association to the capillary bed. SP-LI axons are all unmyelinated. They are found in larger nerve fiber bundles with a perineural sheath or in Schwann cells lacking any perineural sheath. The function of NPY-LI and SP-LI nerve fibers in the rat dura mater is discussed in relation to their topography, density and termination.

Neuropeptide Y antagonistic properties of D-myo-inositol-1.2.6-trisphosphate in guinea pig basilar arteries

The antagonistic properties on neuropeptide Y (NPY)-induced contraction of the guinea pig basilar artery of D-myo-inositol-1.2.6-triphosphate (PP56) has been examined using a sensitive in vitro system. It was observed that PP56 did not per se cause contraction or relaxation of precontracted vessel segments. However, it was found to be a non-competitive antagonist of NPY-induced contraction. This effect was observed in the concentration range 10(-8)-10(-6) M PP56. A slight potentiation of endothelin I-induced contraction was seen at high concentrations (10(-3) M). In contrast there was no modulation of the contractile effects elicited by bradykinin, noradrenaline, 5-hydroxytryptamine (5-HT) or prostaglandin F2 alpha (PGF2 alpha) apart from a slight reduction in maximum effect at 10(-4) M and 10(-3) M PP56. PP56 was observed to possess antihistaminic and anticholinergic properties in the concentration range 10(-5) M-10(-3) M. The relaxant effects of vasoactive intestinal peptide, calcitonin gene-related peptide, neurokinin A and substance P were only modified to a minor extent by PP56 in concentrations of 10(-4) M and 10(-3) M. In conclusion, PP56 appears to be the first non-peptide which potently and rather selectively antagonizes NPY-induced contractions of the guinea pig basilar artery. In high concentrations, PP56 may modify the responses of other agents tested, including histamine and acetylcholine.

Changes in the levels of neuropeptide Y-LI in the external jugular vein in connection with vasoconstriction following subarachnoid haemorrhage in man. Involvement of sympathetic neuropeptide Y in cerebral vasospasm

NPY is a putative neurotransmitter mainly co-localized with noradrenaline in sympathetic fibers which innervate the cerebral vasculature. The origin of most of the perivascular NPY fibers seems to be in the superior cervical ganglion. To investigate involvement of Neuropeptide Y (NPY) mechanisms in subarachnoid haemorrhage (SAH), twenty patients with SAH were investigated. NPY-LI (-like immunoreactivity) levels in the external jugular vein were assessed using radioimmunoassay in blood samples collected post-operatively (or after SAH in non-surgical patients) on days 1,2,3, 5,7 and 9. These levels were compared with the clinical course and blood flow velocity changes monitored with ultrasonic Doppler equipment from both middle cerebral arteries (MCA) and both internal carotid arteries (ICA). Compared to NPY-LI levels in 14 controls (mean 116 +/- 3 pmol/1), increased levels (up to 253 pmol/l) and a close relationship between velocities and NPY-LI levels were found in a subpopulation of the SAH patients. When comparing the mean haemodynamic index (V MCA/ipsilateral V ICA) and mean NPY-LI levels in each of the 20 patients, a correlation of r = 0.75, p = 0.0001 was found. Increased NPY-LI were found (131 +/- 8 pmol/l) when simultaneous Doppler velocity recordings showed vasoconstriction (Haemodynamic index greater than 5) compared with samples taken when the haemodynamic index was less than 5, p less than 0.05. When MCA velocity exceeded 120 cm/sec. increased levels were found (129 +/- 9 pmol/l) compared with the conditions when MCA velocity was less than 120 cm/sec (113 +/- 5 pmol/l), p = 0.06. The results indicate a possible NPY involvement in cerebral vasoconstriction after SAH.

Neuropeptide Y and the cerebral circulation

The significance of neuropeptide Y (NPY) in the cerebral circulation has been examined in the rat using immunocytochemistry, isolated cerebral artery preparations, and quantitative autoradiographic techniques for determining local CBF and glucose utilisation. In the rat the middle cerebral artery and the lenticulostriate artery from which blood is supplied to the caudate nucleus were found to be invested with numerous perivascular NPY immunoreactive nerve fibres. NPY (3-300 nM) contracted rat middle cerebral artery segments in a concentration-dependent manner. Intracerebral microinjections of NPY (200 pmol) or vehicle (1 microliter) were performed in rats after full recovery from anaesthesia via previously implanted guide cannulae. Following injection of NPY into the striatum, local blood flow was markedly decreased by 36% throughout the ipsilateral caudate nucleus (e.g., from 104 +/- 25 to 67 +/- 15 ml 100 g-1 min-1; mean +/- SD), whereas glucose use in this region was not altered significantly (e.g., 73 +/- 8 and 74 +/- 10 mumol 100 g-1 min-1 with vehicle and NPY, respectively). Intrastriatal NPY did not alter CBF or glucose use in the majority of other brain areas, including all of the 40 contralateral regions examined and almost all regions within the ipsilateral hemisphere. In a small number of highly discrete brain areas remote from the injection site (e.g., amygdala), there were significant reductions in blood flow with minimal changes in glucose use. Since NPY is present around rat cerebral blood vessels, is capable of evoking their contraction, and has the ability to produce reductions in blood flow independently of oxidative metabolism, this neuropeptide may be of major importance in cerebrovascular regulation.

Thalamic origin of neuropeptide Y innervation of the accessory optic nucleus of the pigeon (Columba livia)

Immunohistochemical and tracing techniques were used in combination to reveal the source of a neuropeptide Y-like immunoreactive (NPY-LI) plexus in the nucleus of the basal optic root (nBOR) of the pigeon accessory optic system. Injections of rhodamine-labeled latex microspheres into nBOR produced retrograde labeling of a population of neurons interposed between the principal optic nucleus of the dorsolateral thalamus (equivalent to the mammalian dorsal lateral geniculate nucleus) and the ventral lateral geniculate nucleus. The retrogradely labeled neurons were distributed mainly in the immediate vicinity of the lateral, dorsal, and ventral aspects of the nucleus rotundus. Immunohistochemical methods revealed many NPY-containing somata within the same intergeniculate thalamic area. Double-labeling immunohistochemical and retrograde tracing experiments evidenced that many NPY-LI neurons in the intergeniculate area contained rhodamine microspheres that had been previously injected into the ipsilateral nBOR. The projection of that general thalamic area to the nBOR was then confirmed by means of anterograde transport of Phaseolus vulgaris leucoagglutinin. In these experiments, the intergeniculate region was demonstrated to project to all divisions of the nBOR and to every other retino-recipient structure, including the suprachiasmatic nucleus. Finally, electrolytic lesions of the intergeniculate area produced a dramatic reduction in the number of NPY-LI axons and terminals within the ipsilateral nBOR and also within other retino-recipient structures. These data indicate the existence of a thalamic NPY-LI projection to the pigeon nBOR of the accessory optic system. This chemically specific projection originates from the intergeniculate area, which was shown in this study to project to all other retino-recipient structures. Thus, NPY may have a role in the functional organization of the accessory optic system and also of the avian visual system as a whole.

Characterization of functional neuropeptide Y receptors in a human neuroblastoma cell line

We identified receptors for neuropeptide Y (NPY) on an established human neuroblastoma cell line, SK-N-MC, which are functionally coupled to adenylate cyclase through the inhibitory guanine nucleotide-binding protein of adenylate cyclase, Gi. Intact SK-N-MC cells bound radiolabeled NPY with a KD of 2 nM and contained approximately 83,000 receptors/cell. Unlabeled porcine and human NPY and structurally related porcine peptide YY (PYY) competed with labeled NPY for binding to the receptors. NPY inhibited cyclic AMP accumulation in SK-N-MC cells stimulated by isoproterenol, dopamine, vasoactive intestinal peptide, cholera toxin, and forskolin. NPY inhibited isoproterenol-stimulated cyclic AMP production in a dose-dependent manner, with half-maximal inhibition at 0.5 nM NPY. Porcine and human NPY and porcine PYY gave similar dose-response curves. NPY also inhibited basal and isoproterenol-stimulated adenylate cyclase activity in disrupted cells. Pertussis toxin treatment of the cells completely blocked the ability of NPY to inhibit cyclic AMP production and adenylate cyclase activity. The toxin catalyzed the ADP-ribosylation of a 41-kDa protein in SK-N-MC cells that corresponds to Gi. The receptors on SK-N-MC cells appeared to be specific for NPY, as other neurotransmitter drugs, such as alpha-adrenergic, dopaminergic, muscarinic, and serotonergic antagonists, did not compete for either NPY binding or NPY inhibition of adenylate cyclase. Thus, SK-N-MC cells may be a useful model for investigating NPY receptors and NPY-mediated signal transduction.

Pharmacology of noradrenaline and neuropeptide tyrosine (NPY)-mediated sympathetic cotransmission

Pharmacological and physiological aspects for neuropeptide Y (NPY) and noradrenaline (NA) cotransmission have been studied in the peripheral sympathetic nervous control of blood vessels, heart, spleen and vas deferens. NPY coexists with NA in large dense cored vesicles and is released compared to NA mainly upon high frequency stimulation or strong reflex sympathetic activation. NPY release is inhibited via prejunctional alpha-2 adrenoceptors and adenosine receptors but facilitated by angiotensin II or beta-receptor activation. NPY exerts prejunctional inhibitory actions on both NA and NPY release, enhances the vasoconstrictor effect of NA and evokes potent, long-lasting vasoconstriction. Specific receptor mechanisms for NPY exist at both the pre- and postjunctional levels; a large amidated C-terminal portion of NPY is necessary for receptor binding, inhibition of cyclic AMP formation and vasoconstrictor effects. Denervation results in supersensitivity for both NA and NPY-evoked vasoconstriction. Reserpine pretreatment is associated with depletion of NA as well as NPY; the effect on NPY is entirely dependent on an intact nerve activity. Reserpine treatment combined with preganglionic denervation depletes NA by 99% while NPY levels are maintained intact. The characteristic appearance of the nerve stimulation evoked vasoconstrictor response with a high correlation to NPY outflow after reserpine treatment, suggests that NPY may be involved as a transmitter in a variety of vascular beds. NPY-synthesis in ganglia seems to be regulated by nicotinic receptor activity; secondary stimulation by eg reserpine stimulates and nicotine antagonists decrease NPY-synthesis. Many classical pharmacological agents including guanethidine, clonidine, yohimbine, angiotensin II, nicotine and desipramine influence NPY release. A complex interplay therefore seems to occur at both the pre- and postjunctional levels of transmission for the classical transmitter NA and the coexisting peptide NPY, creating a great diversity of chemical signalling potential.

Three types of neurochemically defined autonomic fibres innervate the carotid baroreceptor and chemoreceptor regions in the guinea-pig

The innervation of the carotid body, carotid sinus, and neighbouring arteries (common carotid artery; external carotid artery; occipital artery; ascending pharyngeal artery) was investigated in guinea-pigs by means of glyoxylic acid-induced catecholamine-fluorescence and immunohistochemistry using a variety of antisera against neuropeptides and tyrosine hydroxylase (TH). Fibres displaying catecholamine-fluorescence, TH- and neuropeptide Y-like immunoreactivity (NPY-LI) were less numerous in the carotid sinus than in all other arterial segments. Vasoactive intestinal polypeptide (VIP)-LI axons were almost lacking in the common carotid, external carotid and occipital arteries, consistently found in the carotid sinus, and more numerous in the ascending pharyngeal artery. Catecholaminergic, TH-, NPY- and VIP-LI fibres were observed deep in the media of the carotid sinus, where the baroreceptor terminals are located. In contrast, they did not enter the media in the adjacent arterial segments. All these fibres disappeared following excision of the superior cervical ganglion, but were unaffected by combined transection of the carotid sinus nerve and resection of the no-dose ganglion, suggesting a sympathetic origin. Double-staining immunofluorescence revealed at least three types of autonomic, presumably sympathetic fibres in the carotid sinus: 1) TH+/NPY+, 2) NPY+/VIP+, and 3) VIP+ fibres. This points to a non-noradrenergic efferent innervation of the carotid sinus in addition to the hitherto known noradrenergic sympathetic fibres. The three populations of autonomic fibres seen in the carotid sinus were also observed in the carotid body, but the paucity of NPY+/VIP+ double-labelled fibres raises doubt as to the functional significance of this particular fibre type in modulating arterial chemoreception. The multiplicity of neurochemically defined autonomic nerves to the carotid baro- and chemoreceptor regions probably reflects functionally separate pathways that are differently regulated and exert different effects.

Stimulation of the superior sagittal sinus in the cat causes release of vasoactive peptides

External jugular vein blood was sampled in the anesthetized cat during electrical stimulation of the superior sagittal sinus (SSS), and the levels of calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), substance P (SP) and neuropeptide Y (NPY) were measured with sensitive radioimmunoassays. CGRP levels rose by 85% and VIP levels by 300% while there was no change in SP or NPY levels in the same samples. These data provide the first evidence that activation of the trigeminovascular system, by selective stimulation of nociceptive craniovascular afferents, causes releases of vasodilator peptides and further implicates this system in the pathophysiology of migraine.

Sympathetic and nonsympathetic neuropeptide Y-containing nerves in the rat myocardium and coronary arteries

We have examined the neuropeptide Y-containing intrinsic nerves of the heart in young (6-week-old) and adult (4-month-old) rats to determine whether they project to the coronary arteries or are capable of doing so if the neuropeptide Y-containing extrinsic nerves are removed. Chronic treatment of neonates with guanethidine was used to permanently destroy the sympathetic nerves. In the young treated animals, 33-54% of the neuropeptide Y remained in the heart despite a 90-99% reduction in norepinephrine; these proportions did not change in the animals that were allowed to develop to adulthood. The level of neuropeptide Y in the right atrium of young animals was unexpectedly high (252 +/- 28.7 pmol/g) compared with adults (75.4 +/- 18.8 pmol/g). The coronary arteries in the control rats received a moderately dense supply of neuropeptide Y-containing nerves; after guanethidine, all neuropeptide Y-containing nerves innervating the large coronary arteries disappeared, but some were still seen in association with small resistance vessels. No compensatory proliferation of the intrinsic neuropeptide Y-containing neurons occurred in the adult sympathectomized animals, and the intrinsic nerves did not reinnervate the large coronary arteries. These results are discussed in relation to the clinical syndrome of coronary artery spasm.

Effects of neuropeptide Y and noradrenaline on uterine artery blood pressure and blood flow velocity in the pregnant guinea-pig

Neuropeptide Y (NPY) coexists with noradrenaline (NA) in many peripheral sympathetic nerves. Since it has been found that patients with preeclampsia have elevated myometrial levels of both NPY and NA, we have examined the effects of NPY and NA on blood pressure and blood flow velocity in the uterine artery of the term pregnant guinea-pig (n = 7). We found that NPY (10-1000 pmol) significantly increased local blood pressure, with increases ranging from 15.4% (P less than 0.05) to 46.4% (P less than 0.001) as compared to control. NA (10-1000 pmol) had similar effects, increasing local blood pressure (5%-57.5% (P less than 0.01]. NPY had no significant effect on uterine blood flow velocity as measured by pulsed Doppler ultrasound, whereas NA (10-1000 pmol) decreased local uterine blood flow velocity (5.9%-30.2% (P less than 0.05]. The effect of NPY on blood pressure was phentolamine-resistant, indicating that it is not alpha-adrenoceptor-mediated. The results indicate that NPY and NA have significant pressor effects in the local uterine circulation during pregnancy in the guinea-pig.

Neuronal pathways in the guinea-pig lumbar sympathetic ganglia as revealed by immunohistochemistry

Tyrosine hydroxylase (TH)- and peptide-immunoreactivity of postganglionic neurons and of nerve fibres in guinea pig lumbar paravertebral sympathetic ganglia 2-4 after transection of the communicating rami and the visceral branches, respectively, were investigated by single- and double-labelling techniques. Six subpopulations of postganglionic neurons were discriminated immunohistochemically: two cell types, which were immunoreactive to only one of the applied antisera - TH, and vasoactive intestinal polypeptide (VIP); and four cell types in which immunoreactivity was colocalized - TH/neuropeptide Y (NPY), NPY/VIP, dynorphin/alpha-neoendorphin and dynorphin (alpha-neoendorphin)/NPY. Small intensely fluorescent (SIF) cells dependent on their location exhibited differential immunobehaviour to NPY-/dynorphin-(alpha-neoendorphin-) and TH-antisera. Immunoreactivity to substance P (SP), calcitonin gene-related peptide (CGRP), met-enkephalin-arg-phe (MEAP) and leu-enkephalin was present in nerve fibres but not in postganglionic neurons with frequent colocalization of SP/CGRP- and MEAP/leu-enkephalin- and, sometimes leu-enkephalin/SP- and dynorphin/SP-immunoreactivity. TH-immunoreactive intraganglionic nerve fibres were numerically more increased after cutting the visceral branches, than after transection of the communicating rami. Vice versa, NPY-, VIP-, dynorphin- and alpha-neoendorphin-immunoreactive nerve fibres were particularly increased in number after cutting the communicating rami. Many but not all of the nerve fibres exhibited colocalization of two of these peptides. SP-, CGRP-, and enkephalin-immunoreactive nerve fibres were not visibly affected by cutting the visceral branches but virtually disappeared after lesioning the communicating rami.

Neuropeptide Y potentiates purinergic as well as adrenergic responses of the rabbit ear artery

The localisation of neuropeptide Y in the rabbit central ear artery and its pharmacological action on this preparation were investigated. Immunohistochemical studies demonstrated the presence of neuropeptide Y-like immunoreactivity in the perivascular nerves supplying the rabbit ear artery. Forty-eight hours after treatment with reserpine (5 mg/kg i.p. 48 h and 3 mg/kg i.p. 24 h prior to the experiment) catecholamine fluorescence in the rabbit central ear artery was abolished and the neuropeptide Y-like immunoreactivity was substantially reduced, suggesting that noradrenaline and neuropeptide Y were colocalised in sympathetic nerves. Contractile responses to exogenous noradrenaline (1 microM) and alpha,beta-methylene ATP (1 microM) were both significantly potentiated following incubation with neuropeptide Y (0.3 microM); the degree of potentiation being similar for both agonists. Electrical field stimulation of the rabbit central ear artery (16 and 64 Hz) produced frequency-dependent contractile responses which were abolished by tetrodotoxin (1 microM) and which were significantly potentiated in the presence of neuropeptide Y (0.3 microM). The responses to stimulation at 16 Hz were enhanced to a greater extent than the responses at 64 Hz. After blocking the noradrenergic component of the neurogenic response with prazosin (1 microM), the residual purinergic component, at both 16 and 64 Hz, was significantly enhanced in the presence of neuropeptide Y. However, following desensitisation of the P2-purinoceptor with alpha,beta-methylene ATP, neuropeptide Y had no significant effect on the residual noradrenergic component.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Long-term chemical sympathectomy leads to an increase of neuropeptide Y immunoreactivity in cerebrovascular nerves and iris of the developing rat

Short-term (surgical) and long-term (chemical) sympathectomy have revealed the presence of a population of neuropeptide Y-like immunoreactive nerve fibres which do not degenerate in parallel with noradrenaline-containing nerves supplying cerebral vessels and the iris of the rat. Two days after bilateral removal of the superior and middle cervical ganglia of 7-week-old rats, noradrenaline-containing nerves could not be detected along any of the arteries of the rat circle of Willis or of the iris, but 18-32% of neuropeptide Y-like immunoreactive nerves remained. Long-term treatment (6 weeks) with guanethidine commencing in developing 1-week-old rats caused degeneration of the sympathetic neurons in cervical ganglia and disappearance of 5-hydroxydopamine-labelled nerves (that showed dense-cored vesicles at the electron microscope level) from rat cerebral vessels, but did not significantly change the density of neuropeptide Y-like immunoreactive axons on the vessels. Furthermore, whilst in control rats neuropeptide Y-like immunoreactivity was localized largely within 5-hydroxydopamine-labelled cerebrovascular nerves, after long-term sympathectomy with guanethidine, neuropeptide Y-like immunoreactivity was seen only in nerves lacking small dense-cored vesicles. A small number of catecholamine-containing nerves appeared along the internal carotid and anterior cerebral arteries after long-term sympathectomy; these may arise from neurons of central origin. These results suggest that as a consequence of long-term sympathectomy with guanethidine, compensatory changes occur, involving an increase in the expression of neuropeptide Y-like immunoreactivity in non-sympathetic axons in cerebrovascular nerves and iris of the rat. In contrast, the neuropeptide Y-like immunoreactive nerves in the dura mater appear to be entirely sympathetic, since none were present after short-term sympathectomy and none appeared after long-term sympathectomy.

An immunohistochemical localization of neuropeptide Y (NPY) in its amidated form in human frontal cortex

The distribution of neuropeptide Y (NPY)-immunoreactive neurons was studied in human frontal cerebral cortex from surgical biopsy specimens by immunohistochemical techniques. NPY-containing neurons were identified in all cortical sublayers except sublayer I. The stained neurons were of the multipolar, bitufted, round or triangular form with dendritic and axonal processes. The immunoreactive neurons were considered to be cortical interneurons, due to their nonpyramidal form, and since their processes could be followed intracortically particularly in direction to superficial cortical layers. The NPY precursor molecule is processed to NPY by a dibasic cleavage, and NPY is further enzymatically amidated before release and receptor activation can be achieved. Antisera raised against Cys-NPY(32-36)amide recognize amidated NPY not cross-reacting with nonamidated NPY. These antisera and immunohistochemistry revealed the presence of a population of NPYamide-immunoreactive cells morphologically indistinguishable from the NPY-immunoreactive cells in the human frontal cortex. By comparing the number of immunoreactive cells in adjacent sections, it appears that the number of NPY-immunoreactive cells was higher than those immunoreactive to NPYamide. Also, the density of NPY fibers was much higher compared with the number stained with NPYamide antiserum. The present immunohistochemical study indicates that NPY in its amidated form is contained in a subpopulation of human cortical NPY-immunoreactive neurons and may participate as an active neurotransmitter/modulator within the human cerebral cortex.

Perivascular innervation of the mesenteric artery in spontaneously hypertensive rats

Perivascular innervation of the mesenteric arteries of 7-week-old and 6-month-old spontaneously hypertensive rats and normotensive Wistar-Kyoto rats was examined. The densities of neuropeptide Y-containing nerve fibers and adrenergic nerve fibers were increased in the distal regions of mesenteric arteries of spontaneously hypertensive rats as compared with findings in Wistar-Kyoto rats. However, the densities of cholinergic nerve fibers, vasoactive intestinal polypeptide-containing, and substance P-containing nerve fibers in the mesenteric arteries of the spontaneously hypertensive rats were unchanged in comparison with findings in the Wistar-Kyoto rats. Thus, not only adrenergic nerve fibers but also neuropeptide Y-containing nerve fibers may play an important role in the development and maintenance of hypertension in spontaneously hypertensive rats.

Increased neuropeptide Y concentrations in cerebrospinal fluid from patients with aneurysmal subarachnoid hemorrhage

We investigated the possible relation between neuropeptides and cerebral vasoconstriction in samples of ventricular or cisternal cerebrospinal fluid from 14 patients with subarachnoid hemorrhage. Neuropeptide Y, calcitonin gene-related peptide, atrial natriuretic peptide, and pituitary polypeptide 7B2 were present in the cerebrospinal fluid of these patients. Concentrations of calcitonin gene-related peptide and 7B2 were not significantly different from those in control subjects, but that of atrial natriuretic peptide was significantly lower. Although the mean concentration of neuropeptide Y was not significantly higher than control, consecutive determinations showed an increase 6-11 days after the onset of subarachnoid hemorrhage. An initially high 7B2 concentration decreased gradually, although half the patients showed a second increase greater than 10 days after the onset. Considering the well-recognized vasoconstrictive effect of neuropeptide Y, it is possible that this increase in its concentration in the cerebrospinal fluid plays a role in the pathogenesis of the cerebral vasospasm that is often seen after subarachnoid hemorrhage.

Comparison of peptidergic mechanisms in different parts of the guinea pig superior mesenteric artery: immunocytochemistry at the light and ultrastructural levels and responses in vitro of large and small arteries

The presence and distribution of peptide-containing nerve fibres and axon terminals have been studied in the proximal part of the superior mesenteric artery (SMA) (i.e. conductance vessel) and in the finer ramifications of the SMA close to the intestine (outer diameter 200 microns, i.e. resistance vessel). Light microscopic immunocytochemistry revealed that the proximal part of the SMA possessed a rich supply of neuropeptide Y (NPY)- and tyrosine hydroxylase (TH)-immunoreactive nerve fibres, forming a loose perivascular network which increased in density distally. The vasoactive intestinal peptide (VIP) immunoreactivity was moderate in the proximal artery and only a few VIP fibres could be identified in the distal portion of the SMA. Calcitonin gene-related peptide (CGRP)-, neurokinin (NK)- and substance P (SP)-immunoreactive fibres had an intermediate density in both arterial regions, but their distribution pattern varied. Electron microscopic immunocytochemistry showed that NPY-immunoreactive nerve terminals were close to the smooth muscle cells of the medial layer in both parts of the SMA, indicative of a vasomotor role. Although the VIP-immunoreactive terminals had a similar localization they were seen less frequently. CGRP-, NK- and SP-immunoreactive axons had an identical distribution in the two vascular regions. Interestingly, they were usually seen more distant from the medial layer, localized in the adventitia. Examination of vasomotor responses to perivascular peptides revealed significant regional differences: NPY produced only weak contractions (13 +/- 3%) of proximal vessel segment of the conductance type, while strong concentration-dependent contractions were seen in distal parts of the SMA (resistance vessel). In neither region was any interaction with noradrenaline demonstrated. Proximal segments of the SMA revealed a stronger and more potent response to VIP and peptide histidine isoleucine than did distal segments, while on the other hand acetylcholine was more potent and elicited stronger effects in distal segments. CGRP, NKA and SP relaxed precontracted arteries by 50-75% and there was no significant difference in responsiveness to these peptides in the two regions of the SMA.

Neuropeptide Y (NPY): a coronary vasoconstrictor and potentiator of catecholamine-induced coronary constriction

The vasoactive effect of neuropeptide Y (NPY) a peptide commonly found in perivascular nerves, including those of the heart, was assessed in the coronary circulation of the isolated perfused dog heart and in superfused segments of isolated canine coronary arteries. The intracoronary administration of 0.7-23.5 nmol NPY to hearts during beta adrenergic blockade produced a dose-dependent increase in coronary vascular resistance ranging from 0.10 to 0.49 mmHg.min-1.ml-1.100 g-1 without changes in myocardial oxygen consumption. The potency of NPY as a coronary vasoconstrictor was about 250 times that of noradrenaline. Pretreating the coronary system of these hearts with NPY caused a marked potentiation of the vasocontractile effect of noradrenaline, displacing its dose-response curve to the left in a non-parallel fashion. The addition of 0.2-3.7 nmol NPY did not induce contraction in superfused helical segments of large coronary arteries but it potentiated the tension developed in response to 0.18 microM adrenaline in a concentration-dependent manner. Pretreatment of these arteries with 3.7 nmol NPY caused a significant leftward displacement of the adrenaline contractile effect. These results show that NPY is a potent coronary vasoconstrictor and a potentiator of the contractile effect of catecholamines and support the hypothesis that NPY may participate in the regulation of coronary vascular resistance.

Distribution, possible origins and fine structure of neuropeptide Y-containing nerve fibers in the rat liver

The distribution, possible origins and fine structure of neuropeptide Y (NPY)-containing nerve fibers in the rat liver were investigated by immunohistochemistry, nerve transection and immunoelectron microscopy. Light-microscopic immunohistochemistry showed NPY fibers forming a complex network in and around the walls (tunica adventitia and tunica media) of hepatic vessels. They were also closely associated with interlobular bile ducts. The NPY fibers in the liver were almost completely eliminated by transection of the greater splanchnic nerves just distal to the celiac ganglion. Transection of the greater splanchnic nerves just proximal to the celiac ganglion resulted in a marked decrease in NPY fibers, but a significant number remained intact. Under electron microscopy. NPY terminals without a covering of glial processes were seen not only in proximity to smooth muscle cells within the tunica media of hepatic vessels but also in the subendothelial areas of the tunica intima. Some NPY axon terminals devoid of glial ensheathment were located close to the basal lamina of interlobular bile ducts. Occasionally, single axon terminals with NPY were found in the vicinity of or in contact with hepatic cells. There was a small number of NPY fibers that had lost their glial sheaths while running toward lymphatic capillaries. These findings suggest that hepatic NPY arises from the celiac ganglion and paravertebral sympathetic ganglia, and that it is involved in more complex physiological processes than the previously described neuropeptides in the liver, which are localized exclusively to hepatic vessel walls.

Changes of calcitonin gene-related peptide-like immunoreactivity in cerebrovascular nerve fibers in the dog after experimentally produced subarachnoid hemorrhage

After producing a model of subarachnoid hemorrhage (SAH) by a single injection of fresh autologous arterial blood into the cisterna magna in the dog, we immunohistochemically examined changes of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) in perivascular nerve fibers in the large pial arteries by using whole mount preparations. CGRP-LI in cerebrovascular nerve fibers was suppressed after SAH. The suppression was first detected on the 3rd day after SAH, and was most marked during the 7th to 14th day after SAH. CGRP-LI, however, recovered to a normal level by the 42nd day after SAH.

Effects of neuropeptide Y on the renal, mesenteric and hindlimb vascular beds of the conscious rabbit

The effects of neuropeptide Y (NPY, 10 micrograms/kg bolus i.v.) on renal, mesenteric and hindlimb blood flow were determined in intact conscious rabbits with chronically implanted Doppler ultrasonic flow transducers. The role of sympathetic neuro-effectors was assessed using inhibition of peripheral alpha-adrenoceptors with phentolamine in each group, and in the renal flow group following chemical sympathectomy with 6-hydroxydopamine. In controls, NPY caused markedly non-uniform peak responses. Renal blood flow fell from 2.16 +/- 0.12 kHz to a minimum of 0.26 +/- 0.07 kHz following NPY administration (P less than 0.05). Mesenteric blood flow was reduced from 2.04 +/- 1.17 to 1.54 +/- 0.11 kHz (P less than 0.05). blood flow increased transiently from 2.33 +/- 0.15 to a peak of 3.33 +/- 0.19 kHz (P less than 0.05). Renal vascular resistance rose by 1189 +/- 309% and mesenteric resistance by 54 +/- 9% (P less than 0.05), while hindlimb resistance fell by 24 +/- 3% (P less than 0.05). Pretreatment with phentolamine accentuated the peak pressor response and the reduction in heart rate induced by NPY administration but had little effect on the local haemodynamic changes in each vascular bed. There was no change in the renal vascular response to NPY following sympathectomy. Indeed, the peak NPY-induced reduction in renal blood flow seen in control animals (87 +/- 4%) was unaffected by either alpha-adrenoceptor inhibition (90 +/- 5%) or by sympathectomy (86 +/- 5%). In conscious rabbits with intact cardiovascular reflexes, pharmacological doses of NPY cause profound renal vasoconstriction with smaller changes in mesenteric and hindlimb flow.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional distribution of neuropeptide Y and its receptor in the porcine central nervous system

The regional distribution of neuropeptide Y (NPY) immunoreactivity and receptor binding was studied in the porcine CNS. The highest amounts of immunoreactive NPY were found in the hypothalamus, septum pellucidum, gyrus cinguli, cortex frontalis, parietalis, and piriformis, corpus amygdaloideum, and bulbus olfactorius (200-1,000 pmol/g wet weight). In the cortex temporalis and occipitalis, striatum, hippocampus, tractus olfactorius, corpus mamillare, thalamus, and globus pallidus, the NPY content was 50-200 pmol/g wet weight, whereas the striatum, colliculi, substantia nigra, cerebellum, pons, medulla oblongata, and medulla spinalis contained less than 50 pmol/g wet weight. The receptor binding of NPY was highest in the hippocampus, corpus fornicis, corpus amygdaloideum, nucleus accumbens, and neurohypophysis, with a range of 1.0-5.87 pmol/mg of protein. Intermediate binding (0.5-1.0 pmol/mg of protein) was found in the septum pellucidum, columna fornicis, corpus mamillare, cortex piriformis, gyrus cinguli, striatum, substantia grisea centralis, substantia nigra, and cerebellum. In the corpus callosum, basal ganglia, corpus pineale, colliculi, corpus geniculatum mediale, nucleus ruber, pons, medulla oblongata, and medulla spinalis, receptor binding of NPY was detectable but less than 0.5 pmol/mg of protein. No binding was observed in the bulbus and tractus olfactorius and adenohypophysis. In conclusion, immunoreactive NPY and its receptors are widespread in the porcine CNS, with predominant location in the limbic system, olfactory system, hypothalamoneurohypophysial tract, corpus striatum, and cerebral cortex.

Neuropeptide tyrosine (NPY)-induced potentiation of the pressor activity of catecholamines in conscious rats

IV bolus administration of 2.5-50 micrograms NPY (0.6-12.5 nmol) to conscious rats produced a dose- and time-dependent increase in systolic and diastolic blood pressure. Following priming with 2.5 micrograms NPY, or larger doses, the subsequent administrations of noradrenaline produced pressor responses that were potentiated both in magnitude and duration. The NPY-induced potentiation of the pressor response to noradrenaline was dose-dependent and extended to the pressor action of adrenaline and angiotensin II but not to the hypotensions produced by bradykinin or isoproterenol. The potentiation was not related to the fact that multiple doses of catecholamines were repeated. Reserpine did not substantially modify the NPY-induced potentiation of the pressor activity of the catecholamines. Chemical sympathectomy following 6-hydroxydopamine caused a marked supersensitivity to the catecholamines and NPY but obliterated the NPY-induced potentiation of the pressor effect of adrenaline. Nifedipine reduced the pressor action of the catecholamines and NPY but did not attenuate the NPY-induced potentiation of the pressor action of catecholamines. It is concluded that the acute pressor effect of NPY and of the potentiation of the catecholamine pressor effects involve different mechanisms.

Inhibition of cholinergic and non-adrenergic, non-cholinergic bronchoconstriction in the guinea pig mediated by neuropeptide Y and alpha 2-adrenoceptors and opiate receptors

The mechanisms underlying the regulatory influence of neuropeptide Y (NPY) and of alpha 2-adrenoceptor and opiate receptor activation on cholinergic and excitatory non-adrenergic, non-cholinergic (e-NANC) neurotransmission were studied in guinea pig hilus bronchi in vitro. NPY inhibited both the cholinergic and e-NANC bronchial contractions evoked by field stimulation. The NPY attenuation of the e-NANC contraction could not be antagonized by the alpha 2-antagonist, idazoxan, or naloxone. UK 14,304 a specific alpha 2-agonist, also reduced the two nervous components of bronchial contraction and this action was inhibited by idazoxan. NPY and UK 14,304 exerted a minor influence on the bronchial smooth muscle tone per se or on contractions evoked by acetylcholine or neurokinin A. This suggested that the inhibitory responses were caused by a prejunctional action reducing the release of transmitter substances from sensory and cholinergic nerve endings. Furthermore NPY (10(-7) M) seemed to be more potent to inhibit both contractile components than noradrenaline (10(-6) M) in the presence of propranolol (3 X 10(-6) M). Morphine was able to reduce the e-NANC response via a naloxone-sensitive mechanism. The capsaicin-evoked bronchoconstriction and the bronchodilator NANC effect evoked by field stimulation were, however, not influenced by UK 14,304. It is concluded that NPY, alpha 2-receptor and opiate receptor activation inhibit the release of sensory transmitters evoked by field stimulation but not by capsaicin.

Pharmacological characterization of neuropeptide Y and noradrenaline mechanisms in sympathetic control of pig spleen

The mechanisms underlying the functional effects of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) and their release evoked by nerve stimulation were studied with the blood-perfused pig spleen in vivo. Infusion of selective agonists and antagonists suggested the presence of alpha 1- and beta 2-adrenoceptors mediating vasoconstriction and vasodilatation, respectively. NPY caused a slight inhibition of stimulation-evoked [3H]NA release and a clearcut non-adrenergic vasoconstriction. Local pretreatment with phentolamine and prazosin as well as with clonidine and UK 14304 reduced the perfusion pressure response to nerve stimulation. Phentolamine, yohimbine and idazoxan enhanced while clonidine and UK 14304 decreased the output of [3H]NA or NA and NPY-LI. The subsequent addition of propranolol to the alpha-adrenoceptor antagonists was followed by reappearance at a considerable portion of the perfusion pressure response while the output of [3H]NA or NA and NPY-LI was slightly reduced. It is concluded that NPY exerts pre- and post-junctional actions in pig spleen that regulate both NA release and vascular tone. alpha 1-Adrenoceptors are mainly involved in vasoconstriction, and prejunctional alpha 2 mechanisms inhibit both NA and NPY release at a low frequency of stimulation. beta 2-Adrenoceptors mediate vasodilatation when NA release is enhanced with a minor effect on mediator secretion.

Evidence for co-transmitter role of neuropeptide Y in the pig spleen

1. The possible involvement of neuropeptide Y (NPY) in relation to noradrenaline (NA) and adenosine triphosphate (ATP) mechanisms in the sympathetic nervous control of the vascular tone and capsule contraction in the blood perfused pig spleen was investigated in vivo. 2. Local injections or infusions of NA, NPY and alpha-, beta-methylene ATP (mATP) caused vasoconstriction (perfusion pressure increase) and capsule contraction (increased venous blood flow). ATP only evoked vasodilatation. NPY was about 50 fold more potent than NA as a vasoconstrictor, and the NPY response was more long-lasting. Reserpine treatment did not change the effects of NPY. 3. Electrical stimulation of the splenic nerves in control animals caused a frequency-dependent, guanethidine-sensitive output of both NPY-like immunoreactivity (-LI) and NA, suggesting co-release. The output of NPY-LI relative to NA was enhanced at high frequency stimulation. Furthermore, alpha-adrenoceptor blockade by phentolamine enhanced both the output of NPY-LI and NA while inhibition of the neuronal uptake of NA with desipramine reduced the low frequency stimulation-evoked overflow of NPY-LI. Preganglionic denervation did not change the output of NPY-LI or NA. 4. Reserpine treatment reduced both the splenic content of NA and NPY-LI. Preganglionic denervation inhibited the reserpine-induced depletion of the NPY content but not of NA in terminal areas. The stimulation-evoked NPY overflow was markedly enhanced, especially at low-frequency stimulation after reserpine, and the plasma levels of NPY-LI in the venous effluent were then in the nmolar range (i.e. where exogenous NPY induced vasoconstriction). The perfusion-pressure increase upon stimulation in reserpine-treated, preganglionically-denervated animals was highly correlated (r = 0.91) to the NPY overflow. The functional 0.5 Hz responses were reduced after reserpine, while at higher frequencies the functional effects were of similar magnitude to controls but longer-lasting. 5. Tyramine induced a release of NA but not of NPY-LI. Furthermore, the increase in perfusion pressure induced by tyramine was absent after reserpine. 6. After tachyphylaxis to the vasoconstrictor effects of mATP, the nerve stimulation-evoked, functional response as well as the NA and NPY-LI overflow were unchanged. After reserpine treatment, both the perfusion-pressure increase and NPY-LI overflow to nerve stimulation were reduced after mATP tachyphylaxis. 7. In conclusion, release of NPY rather than ATP may explain the long-lasting, non-adrenergic, splenic functional responses in reserpinized animals upon sympathetic stimulation. However, NA is most likely the main splenic transmitter when low-frequency stimulation is used under control conditions.

Effect of oral administration of nifedipine on neuropeptide Y- and noradrenaline-induced vasoconstriction in the human forearm

Neuropeptide Y (NPY) has recently been shown be co-released with noradrenaline (NA) from sympathetic nerves and to cause arterial vasoconstriction in experimental animals and man. The effect of a single oral dose (10 mg capsule) of nifedipine on NPY- and NA-induced reductions of forearm blood flow (FBF) was studied in seven healthy volunteers. Intra-arterial infusions of NPY and NA into the brachial artery before nifedipine caused dose-dependent reductions in FBF with threshold doses of 0.2 and 0.03 nmol x min-1, respectively. The response to NPY was slower in onset and more long lasting than that to NA. Forty-five min after administration of nifedipine, FBF and heart rate had increased significantly (by 49% and seven beats x min-1, respectively, P less than 0.001), while no significant change was observed in systemic blood pressure. The NPY-induced decrease in FBF was slightly but significantly attenuated after compared to before nifedipine (19 +/- 6 vs. 28 +/- 5% at 1.0 nmol NPY x min-1; P less than 0.01). The response to NA was, however, not significantly altered by nifedipine. In conclusion, the NPY-induced reduction in FBF in man was only slightly prevented and the NA response not significantly affected by oral nifedipine administration in a clinically used dose. This suggests that this calcium antagonist, in the present dosage, does not, to any major extent, inhibit the vasoconstrictor effect of NPY or NA in man in vivo.

Involvement of perivascular neuropeptide Y nerve fibres in uterine arterial vasoconstriction in conjunction with pregnancy

The perivascular neuropeptide Y (NPY) innervation and its relation to adrenergic nerves of uterine arteries from non-pregnant and pregnant guinea pigs was analyzed immunocytochemically. The NPY content of the uterine artery was, in addition, measured radioimmunologically (RIA). Vasomotor effects of NPY per se and in combination with other vasoconstrictors were examined using a sensitive in vitro method. Pregnancy did not visibly affect density and distribution of NPY-immunoreactive fibres. The NPY fibres contained in addition immunoreactivity to dopamine-beta-hydroxylase (marker for noradrenergic neurons). RIA revealed a slight decrease of NPY content during pregnancy, probably due to the increased smooth muscle volume of uterine arteries. The contractile effect of NPY on uterine arteries was weak, while vasoconstriction induced by various agonists was potentiated by NPY, particularly during pregnancy. It is concluded that perivascular NPY-containing nerve fibres may be involved in the dramatic blood flow alterations that occur in the uterine circulation in connection with pregnancy and partus.

Ultrastructural localization of phenylethanolamine N-methyltransferase-like immunoreactivity in the rat locus coeruleus

Adrenergic afferents from the rostral ventrolateral medulla are known to modulate the activity of noradrenergic neurons of the locus coeruleus (LC). The light and electron microscopic localization of a polyclonal antiserum directed against the adrenaline synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT) was used to determine the identity and targets of the adrenergic afferents to the LC of the rat brain. By light microscopy, varicose processes showing intense PNMT-like immunoreactivity (LI) were seen throughout the neuropil surrounding neuronal perikarya which in adjacent sections were shown to contain immunoreactivity for the noradrenaline synthesizing enzyme, dopamine-beta-hydroxylase. Electron microscopy confirmed that these labeled varicose processes were primarily axon terminals. Terminals containing PNMT-LI constituted 30% (141 out of 464) of all identifiable terminals within the LC. These terminals were 0.5-1.8 micron in diameter and contained many small, clear and from 2 to 10 larger dense-core vesicles. The targets of the terminals with PNMT-LI were principally unlabeled (i.e. non-PNMT-containing) perikarya and dendrites. The synaptic junctions on perikarya were rare and exclusively symmetric; whereas, those on proximal (large) dendrites were somewhat more numerous and included symmetric as well as asymmetric membrane specializations. However, the vast majority (85% from a total of 141) of the terminals with PNMT-LI formed asymmetric synaptic junctions on unlabeled distal (small) dendrites and dendritic spines. In rare instances, the PNMT-immunoreactive terminals also formed synaptic junctions with other similarly labeled terminals. These findings provide the first ultrastructural evidence that adrenergic terminals in the LC (1) are one of the more prevalent synaptic inputs to the principally noradrenergic neurons; (2) have both symmetric and asymmetric synaptic specializations conventionally associated with inhibition and excitation, respectively; and (3) may modulate other adrenergic terminals through presynaptic mechanisms. In addition to the varicose processes, light microscopy revealed diffuse PNMT-LI throughout the LC. The ultrastructural correlate of this labeling was seen as patches of peroxidase product within the cytoplasm of a few perikarya and dendrites and throughout the cytoplasm of astrocytes identified by their discrete bundles of microfilaments. The detection of PNMT-LI in cells that are not known to synthesize adrenaline is surprising and suggests either a functional diversity for PNMT or amino acid sequence homologies with related enzymes which are enriched in the LC.