Neuropeptide Y: cerebrovascular innervation and vasomotor effects in the cat

Neuropeptide Y-like immunoreactivity in neurons of the solitary tract nuclei: vesicular localization and synaptic input from GABAergic terminals

The ultrastructural localization of neuropeptide Y-like immunoreactivity (NPY-LI) was examined in the medial nuclei of the solitary tracts (mNTS) of adult rat brain. Peroxidase-antiperoxidase (PAP) reaction product was localized extensively to the central lumen of large (100-150 nm), dense-core vesicles. The labeled vesicles were seen in axon terminals of untreated, control animals and in perikarya and dendrites of rats receiving intraventricular injections of colchicine 24 h prior to sacrifice. The labeled terminals were of two types. The first type contained numerous small, clear vesicles that were rimmed with peroxidase product and 1-6 large, dense-core vesicles that were labeled throughout their central lumen. The second type contained a more homogeneous population of labeled large, dense-core vesicles. Axon terminals showing NPY-LI formed either asymmetric synapses with unlabeled dendrites or were without recognized junctions. Within labeled terminals, as well as within perikarya and dendrites, the majority of the dense-core vesicles were located near non-synaptic portions of the plasmalemma that were heavily ensheathed with glial processes. Only a few unlabeled terminals penetrated the glial investments to form synaptic contacts on soma or dendrites containing NPY-LI. These synaptic contacts were of both symmetric and asymmetric types. Combined immunoperoxidase labeling for glutamic acid decarboxylase and immunogold labeling for NPY further established that at least some of the terminals forming symmetric junctions on the NPY-immunoreactive dendrites were GABAergic. These results provide ultrastructural evidence that in the mNTS, NPY-LI is localized principally to large dense-vesicles within neurons whose output is partially regulated by GABA. The preferential distribution of the labeled vesicles along non-synaptic, glial-invested portions of the plasmalemma suggests that neuronal NPY may modulate the activity of nearby astrocytes. Additionally, the localization of NPY-LI in terminals containing a mixed population of synaptic vesicles and forming asymmetric axodendritic junctions suggests that NPY and/or coexisting transmitter may also exert certain known hypotensive effects by excitation of local intrinsic or projection neurons in this brain region.

Effects of neuropeptide Y, calcitonin gene-related peptide, substance P, and capsaicin on cerebral arteries in man and animals

The smooth-muscle tone of pial, middle, and anterior cerebral arteries from humans, cats, and pigs, respectively, was studied in vitro with respect to the effects of capsaicin and various peptides which are present in local perivascular nerves. Neuropeptide Y (NPY) caused concentration-dependent, potent contractions of the cerebral vessels both in the presence and in the absence of endothelium. In contrast to the response to noradrenaline (NA) and K+, the NPY effect was not altered by changes in the extracellular Ca++ concentration. The relaxant action of the calcium antagonist nifedipine on NPY-evoked contraction of cerebral arteries was not inhibited by a Ca++-deficient medium or by a high-Ca++ medium. Calcitonin gene-related peptide (CGRP), substance P (SP), and capsaicin caused relaxation of precontracted cerebral arteries with an intact endothelium. Calcitonin gene-related peptide was the most potent dilatory agent, and removal of the endothelium did not change the CGRP response. In contrast, the ability of SP to cause relaxation was abolished after removal of the endothelium. Capsaicin, which activates sensory nerves, induced long-lasting relaxation in both the presence and absence of endothelium. In conclusion, in contrast to earlier reported data, the contractile effect of NPY seems to be largely independent of extracellular Ca++, while NA- and K+-induced contractions are dependent on extracellular Ca++. The present results suggest that the relaxant effect of nifedipine on cerebral blood vessels may involve actions other than inhibition of Ca++ influx. The relaxant effect of capsaicin is likely to be induced by release of CGRP rather than SP. The potent effects of these peptides on human pial arteries suggest that neuropeptides may be involved in the control of cerebral blood flow in man.

High levels of NPY in rabbit cerebrospinal fluid and immunohistochemical analysis of possible sources

We have analyzed rabbit cerebrospinal fluid for neuropeptide Y (NPY)-like immunoreactivity, using high performance liquid chromatography (HPLC) and radioimmunoassay (RIA) and examined the anatomical relationship of NPY-containing fibers to the cerebral vasculature and the third cerebral ventricle. Cerebrospinal fluid (CSF) obtained from the cisterna magna of rabbits was injected into a C18 column and subjected to HPLC. The fractions were collected, dried and reconstituted in buffer for NPY radioimmunoassay. A single peak of NPY immunoreactivity was obtained which corresponded in retention time to synthetic porcine NPY. Analysis of CSF samples produced displacement curves parallel to the standard curve. Immunohistochemistry revealed numerous NPY-labeled fibers which penetrated the ependymal lining of the third cerebral ventricle and directly bordered the ventricular lumen. Other fibers were observed in the pia which lines the ventral aspect of the hypothalamus. The basilar artery, its branches and other cerebral vessels were surrounded by NPY-labeled fibers. The results show that: (1) approximately 1 ng/ml of NPY immunoreactivity which corresponds chromatographically to synthetic porcine NPY is present in rabbit CSF; (2) NPY-containing fibers surround the basilar artery and other cerebral vessels; (3) NPY may be released into the CSF from axons in the pia and from axons which penetrate the ependymal lining of the third ventricle. These observations form the basis for our analysis of the vasoconstrictor effects of NPY and its role in cerebrovasospasm after experimental subarachnoid hemorrhage.

Neuropeptide Y and vasoactive intestinal peptide coexist in rat thyroid nerve fibers emanating from the thyroid ganglion

Neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP) occur in nerve fibers around blood vessels and between follicles in the thyroid gland of the mouse and rat. VIP-immunoreactive fibers are numerous, while NPY-immunoreactive fibers are fewer. Most of the latter fibers contain noradrenaline (NA) as well as NPY, while a subpopulation was found to contain VIP instead of NA. We have determined the origins of rat thyroid nerve fibers containing NPY, VIP or NPY/VIP by investigating 3 conceivable sources, i.e. the superior cervical ganglion, the nodose ganglion and the thyroid ganglion. Chemical sympathectomy or removal of the superior cervical ganglion did not affect the frequency of VIP-immunoreactive fibers but eliminated most of the NPY-immunoreactive fibers as well as all NA-containing nerve fibers (recognized by antibodies to dopamine-beta-hydroxylase). The NPY-immunoreactive fibers that remained after sympathectomy occurred around blood vessels and between follicles and contained VIP. Cervical vagotomy (removal of the nodose ganglion including the adjacent vagus) did not overtly affect the frequency of NPY/VIP-, VIP-, or NPY/NA-containing fibers in the thyroid. In contrast, extirpation of the thyroid ganglion, which is situated immediately outside the thyroid capsule, greatly reduced the number of VIP- and NPY/VIP-containing fibers in the rat thyroid. On the whole, the results of radioimmunoassay of NPY and VIP agreed well with the immunocytochemical findings. High performance liquid chromatography confirmed the identity of NPY and VIP. The present findings suggest the existence in the rat thyroid of one NPY-containing nerve fiber population that harbours NA and emanates from the superior cervical ganglion; one NPY-containing fiber population that is non-adrenergic, harbours VIP and originates in the thyroid ganglion; and a second VIP-containing fiber population that is devoid of NPY and appears to derive from the thyroid ganglion.

Potentiation by neuropeptide Y of vasoconstriction in rat resistance arteries

1. The effects of neuropeptide Y (NPY) on resistance arteries were investigated on 3rd generation mesenteric arterioles of the rat. 2. Contractions were elicited by noradrenaline (NA), 5-hydroxytryptamine (5-HT), prostaglandin F2 alpha (PGF2 alpha), depolarization (KCl substituted for NaCl) and by the calcium agonist Bay K 8644, in the absence and in the presence of NPY (100 nM), a concentration which by itself did not induce vasoconstriction. 3. NPY produced a leftward shift of the concentration-response curves to the agonists and to KCl, without any alteration of maximal contractions. 4. NPY also potentiated contractions elicited by addition of CaCl2 to KCl-depolarized vessels, but its effect on calcium-induced contractions decreased with increasing KCl concentrations (from 20 to 100 mM). 5. Calcium-induced contractions were inhibited by the calcium channel blocker nitrendipine, both in the presence and absence of NPY (100 nM). NPY increased slightly (but significantly) the sensitivity to nitrendipine (the apparent KB increased from 2.9 x 10(-10) M to 1.6 x 10(-10) M). 6. The KCl concentration necessary for the maximal effect of Bay K 8644 was decreased in the presence of NPY, and the sensitivity to the calcium channel agonist was increased. 7. Elevating the KCl concentration in the bath from 5 to 20 mM (which gives the same displacement to the left of the KCl concentration-effect curve seen in the presence of NPY) induced a parallel leftward shift of NA and 5-HT concentration-response curves. This shift was identical to the one induced by NPY on 5-HT-evoked contractions, but it was significantly smaller (P less than 0.001) than the shift of the NA concentration-response curve observed in the presence of NPY. In the latter case, NPY enhanced more markedly the contractions induced by low NA concentrations (between 10(-9) and 3 x 10(-8 M) than those induced by high concentrations (up to 3 x 10(-7) M), thus giving a shallow concentration-response curve. 8. The results strongly suggest that NPY partially depolarizes the arterioles and induces an increase in calcium entry through voltage-dependent channels, thus enhancing contractions elicited by agonists or by KCl-depolarization. In addition, they support the view that another mechanism also plays a part in the potentiation by NPY of the effects of low concentrations of NA.

An increase in the expression of neuropeptidergic vasodilator, but not vasoconstrictor, cerebrovascular nerves in aging rats

Perivascular nerve fibres containing noradrenaline (NA), serotonin (5-HT), substance P (SP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) were localized in whole-mount stretch preparations of the arteries of the rat circle of Willis using fluorescence and immunohistochemical techniques. Changes in the pattern and density of these perivascular nerves were studied from birth to 27 months of age. All perivascular nerve types reached a peak density of innervation at 1 month of age. This was followed by a general fall in the density of fluorescent nerve fibres. However, with aging, there was a decrease in the expression of vasoconstrictor neurotransmitters (NA and 5-HT) in cerebrovascular nerves, whereas the expression of vasodilator neurotransmitter (VIP and CGRP) in perivascular nerve fibres supplying the rat cerebral arteries was strikingly increased in old age. The density of NPY- and SP-containing nerve fibres was not significantly altered in old age. These changes are discussed in relation to the increased incidence of cerebrovascular disorders in the elderly.

Neuropeptide Y-containing neurons in the rat striatum: ultrastructure and cellular relations with tyrosine hydroxylase- containing terminals and with astrocytes

The ultrastructural localization of neuropeptide Y (NPY) was comparatively examined in the dorsal (caudate-putamen) and ventral (nucleus accumbens) striatum using the peroxidase-antiperoxidase (PAP) method. In both striatal regions, NPY-like immunoreactivity (IR) was detected in perikarya, dendrites and axons. The labeled perikarya were 15-25 microns in a diameter and contained large, deeply and multiply indented nuclei and prominent Nissl bodies. The labeled dendrites contained a few large (80-150 nm) dense-core vesicles, lacked detectable spines and received few afferents. These morphological characteristics of NPY-IR neurons in both areas are in close accord with previous descriptions for the medium aspiny intrinsic neurons. Axon terminals with terminals with NPY-like IR contain primarily small clear round vesicles, as seen in single or serial sections. These terminals formed junctions that lacked recognizable pre- or post- synaptic densities, but showed parallel spacing between apposed plasmalemmas at presumed synaptic clefts. Targets of the axon terminals with NPY-like IR included unlabeled somata, unlabeled proximal dendrites and labeled and unlabeled distal dendrites. The NPY-IR neurons in the caudate-putamen differed from those in the nucleus accumbens in that (1) there were no recognized appositions between labeled dendrites and labeled terminals, and (2) fewer terminals contained large dense-core vesicles. These findings are consistent with the concept that in the nucleus accumbens, the excitability of the NPY-IR neurons may be more directly modulated by NPY or another transmitter co-existing in the terminals. Catecholamines are known to co-exist with NPY in certain rostrally projecting brainstem nuclei. Therefore, in the two striatal regions, we additionally sought to determine (1) whether the NPY-IR neurons might be modulated by catecholaminergic afferents and (2) whether NPY might co-exist with catecholamines in terminals. Goat antiserum against NPY and rabbit antiserum against tyrosine hydroxylase (TH), the catecholamine-synthesizing enzyme, were simultaneously localized in single sections by PAP and immunoautoradiographic methods, respectively. Quantitative analysis in dually labeled sections from both striatal areas revealed few, if any, direct synaptic contacts between TH-labeled terminals and dendrites containing NPY-like IR. However, there was convergence of separate NPY- and TH-IR terminals on unlabeled dendrites. A few terminals in the nucleus accumbens, but not in the dorsal striatum, showed immunoreactivity methods, to TH and also contained dense-core vesicles with NPY-like IR.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y and vasoactive intestinal polypeptide in cerebral arteries of the rat: relationships between innervation pattern and mechanical response

Possible relationships between the density of peptide innervation and the contractile response of rat cerebral arteries to exogenously applied neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) were examined. The effects of NPY on membrane potential and reactivity of cerebral arteries to exogenous norepinephrine also were studied. In normally innervated arteries there was no apparent correlation between degree of innervation and response to NPY. Marked, prolonged tachyphylaxis to NPY and VIP was observed following brief exposure to these peptides. Surgical removal of the superior cervical ganglia or the sphenopalatine ganglia greatly reduced and, in some cases, eliminated NPY- or VIP-immunoreactive perivascular nerves from cerebral arteries. However, responses of denervated middle cerebral arteries to exogenous NPY or VIP were not different from responses of innervated arteries. Doses of NPY that induced maximal contraction caused no change in membrane potential of the middle cerebral artery. NPY also did not alter the response of cerebral arteries to exogenous norepinephrine. Finally, electrical stimulation of normal or denervated arteries caused only minor constrictor or dilator responses. These results do not support a substantial role for peptidergic perivascular nerves in regulation of pial arterial contractility in the rat.

Cardiovascular significance of neuropeptide Y in the caudal ventrolateral medulla of the rat

The cardiovascular effects of intracisternal and intraparenchymal injection of neuropeptide Y (NPY) into the caudal ventrolateral medulla (CVLM) were investigated in anaesthetized normotensive rats. Intracisternal administration of 1.25 nmol NPY gave rise to a significant fall in blood pressure and heart rate, maximal 1 h postinjection. More localized microinjections of NPY into the CVLM similarly produced dose-dependent falls in blood pressure and heart rate. The bradycardia was significantly reduced or abolished by cardiac vagal blockade induced by: (1) pretreatment with the peripheral muscarinic antagonist methylatropine; or (2) ipsilateral vagotomy. These procedures also gave rise to a small reduction in the hypotensive response to NPY but the remaining component of the response was still significantly different from control, saline responses which were without significant haemodynamic effects. The results of this study provide further evidence for a central role for NPY in cardiovascular control. In the CVLM NPY responses appear to involve at least two different mechanisms: the fall in heart rate results from activation of cardiac vagal neurons in the nucleus ambiguus. The hypotensive response is more complex. The fall in blood pressure may be due in part to an activation of A1 noradrenergic neurons resulting in reduced sympathetic outflow but a small component of the response is a result of the profound slowing of the heart.

Distribution of subgroups of neuropeptide Y-immunoreactive and noradrenergic nerves in the female rat uterine cervix

Nerves in the uterine cervix of the rat were examined with regard to co-existence of markers for noradrenaline and neuropeptide Y, and differential tissue innervation by nerves containing different combinations of these markers. Immunohistochemical labeling of single and adjacent serial cryostat sections, and double labeling was employed. Some animals were treated with the noradrenergic neurotoxin, 6-hydroxydopamine. In control animals neuropeptide Y-immunoreactive fibers were numerous in the myometrium and around arteries; noradrenergic fibers were few in the myometrium and moderate in number around arteries. Myometrial neuropeptide Y-immunoreactive fibers were not decreased, but apparently increased, in 6-hydroxy-dopamine-treated rats; in contrast, perivascular neuropeptide Y-immunoreactive fibers were markedly reduced, but not totally absent. Noradrenergic fibers were absent in the myometrium and around arteries following 6-hydroxydopamine treatment. Labeling of adjacent sections and double labeling revealed coincident labeling of markers for neuropeptide Y and noradrenaline in perivascular, but not myometrial, nerves. We concluded that most myometrial neuropeptide Y-immunoreactive nerves did not contain noradrenaline since they were not sensitive to 6-hydroxydopamine and did not stain doubly; however, perivascular neuropeptide Y-immunoreactive fibers which degenerated after 6-hydroxydopamine treatment and did label doubly must co-store noradrenaline. Some neuropeptide Y-immunoreactive perivascular fibers may contain neuropeptide Y but not noradrenaline. Thus, it appears there is a differential innervation of tissues in the cervix by neuropeptide Y/noradrenergic nerves; this could reflect a differential regulation of tissues innervated by these nerves.

Age-related bidirectional changes in neuropeptide Y peptides in rat adrenal glands, brain, and blood

Age-related changes in neuropeptide Y (NPY) regulation were studied in rat adrenal glands, brains, and blood by radioimmunoassay and biochemical characterization using reversed phase HPLC and gel filtration chromatography. NPY immunoreactivity (pmol/g tissue +/- SEM) in rat adrenal glands increased from 7 +/- 1 (6 weeks old) to 1,500 +/- 580 (69 weeks old). Biochemical characterization by HPLC showed that this increase was due to those of NPY and methionine sulfoxide NPY. In contrast, in rat brain, NPY content decreased in an age-dependent manner specifically in striatum, hippocampus, medulla oblongata, and spinal cord and the sulfoxide form was not detected. In rat blood, the circulating level of NPY was high (3-5 pmol/ml plasma +/- SEM) but did not change significantly with age or by adrenal demedullation. Only a small increase of the sulfoxide form of NPY was observed in aged rat plasma. The age-dependent changes in regulation and modification of NPY in adrenal glands and in specific brain areas may have physiological relevance in the regulation of catecholamine release from adrenal glands and some brain functions during aging.

Sympathetic vascular control of the pig nasal mucosa (2): Reserpine-resistant, non-adrenergic nervous responses in relation to neuropeptide Y and ATP

The possible occurrence of non-adrenergic mechanisms in the sympathetic vascular control of the nasal mucosa was studied in vivo using reserpine-treated pigs (1 mg kg-1, i.v., 24 h earlier) in combination with pharmacological blockade of alpha-adrenoceptors by local phenoxybenzamine (1 mg kg-1, i.a.) infusion. The nasal mucosal depletion (99%) of the content of noradrenaline (NA) in reserpinized animals was not influenced by preganglionic denervation while the depletion (44%) of neuropeptide Y (NPY) was prevented. Upon stimulation with single shocks, 25% of the arterial blood flow reduction and 47% of the nasal mucosal volume reduction (reflecting contraction of venous sinusoids) were still present after reserpine as compared with controls. In reserpinized animals, the vascular responses were slow developing and long-lasting, and about 60% remained at 0.59 Hz and more than 80% at 6.9 Hz. The vascular effects after reserpine were, however, subjected to fatigue, which may explain why phenoxybenzamine treatment still reduced the functional effects in the absence of NA. Local intra-arterial injections of NA, NPY and the metabolically stable adenosine-5'-triphosphate analogue alpha, beta-methylene ATP (mATP) caused reduction in both arterial blood flow and nasal mucosal volume. The C-terminal fragment of NPY (NPY 13-36) also induced nasal vasoconstriction although with a fivefold lower potency than NPY 1-36. Adenosine-5'-triphosphate caused a biphasic vascular effect with vasodilatatory actions at low doses and a short-lasting vasoconstriction followed by vasodilatation at very high doses (100-fold higher than the threshold response to mATP). In contrast to the response to NA, the long-lasting vascular effects of NPY and mATP were resistant to phenoxybenzamine treatment. In conclusion, although NA is likely to mediate most of the sympathetic vascular responses to low-frequency stimulation in the pig nasal mucosa, a large resistance and capacitance vessel component upon high-frequency stimulation seems to be non-adrenergic and mimicked by NPY rather than ATP.

Cerebral arterial innervation by nerve fibers containing calcitonin gene-related peptide (CGRP): I. Distribution and origin of CGRP perivascular innervation in the rat

The origin, density and distribution of calcitonin gene-related peptide (CGRP) immunoreactivity in cerebral perivascular nerves and the trigeminal ganglion of rats were examined in this study. CGRP immunoreactive axons were abundant on the walls of the rostral circulation of the major cerebral arteries in the circle of Willis. The fibers form a grid- or meshwork of longitudinal and circumferential axons studded with numerous varicose swellings. The density of CGRP fibers was particularly high at the bifurcation of major arteries. A few CGRP fibers cross the midline to innervate arteries on the contralateral side of the arterial tree. The arteries of the caudal circulation were sparsely innervated by CGRP fibers. In the trigeminal ganglion, about 30% of the ganglion cells had CGRP immunoreactivity. The cell size of most (75%) of CGRP neurons was less than 30 micron in diameter. There was no significant difference in staining density between small and large CGRP neurons. Unilateral transection of the maxillary and mandibular divisions of the trigeminal nerve caused a substantial decrease of CGRP immunoreactivity in the ipsilateral dorsal two-thirds of the trigeminal nucleus and cervical spinal cord but did not noticeably change the diameter of the vascular lumen or the densities of CGRP fibers in the walls of the cerebral arteries. In contrast, unilateral transection that included the ophthalmic division eliminated CGRP fibers on the ipsilateral cerebral arteries and eliminated CGRP immunoreactivity throughout the trigeminal nucleus in the brainstem and rostral cervical cord. In addition, these lesions caused a significant reduction in the diameter of the denervated arteries. The present study demonstrates that CGRP, a putative neurotransmitter/neuromodulator, is especially abundant in the rostral cerebral circulation and is derived from the ipsilateral ophthalmic division of the trigeminal nerve. In addition, the loss of CGRP perivascular nerves is associated with a reduction of the arterial lumen. This suggests that CGRP is a strong candidate as a nerve-derived trophic factor at trigeminal terminals and provides additional evidence that CGRP is a component in the trigeminovascular system influencing vascular diameter.

Neuropeptide Y (NPY), an endogenous presynaptic modulator of adrenergic neurotransmission in the rat vas deferens: structural and functional studies

The role of neuropeptide tyrosine (NPY) on adrenergic neurotransmission was assessed in the rat vas deferens transmurally stimulated with square pulses of 0.15 or 15 Hz. Nanomoles of NPY inhibited the electrically-induced contractions on the prostatic half but not on the epididymal end of the ductus. NPY was at least 200-fold more potent than norepinephrine or adenosine to produce an equivalent inhibition. Complete amino acid sequence of NPY is required for full agonist activity; deletion of tyrosine at the amino terminus, i.e., NPY fragment 2-36 was 3-fold less potent than the native peptide. NPY fragment 5-36, 11-36 or 25-36 were proportionally less potent than NPY. Avian pancreatic polypeptide was inactive. The presynaptic nature of the NPY activity was established measuring the outflow of 3H-norepinephrine from the adrenergic varicosities of the vas deferens electrically stimulated. In this assay, NPY was more potent than NPY 2-36 or NPY fragment 5-36. No inhibitory action of NPY was detected in K+ depolarized tissues. The inhibitory effect of NPY on the rat vas deferens neurotransmission was not significantly modified by yohimbine, theophylline or naloxone, indicating that the effect of NPY is not due to the activation of alpha 2-adrenoceptors, adenosine receptors or opiate receptors respectively. Picrotoxin or apamin did not modify the inhibitory potency of NPY; verapamil or methoxyverapamil significantly reduced its potency. The inhibitory action of NPY is best explained through the activation of presynaptic NPY receptors that regulate norepinephrine release via a negative feedback mechanism. Structure activity studies give support to the notion of NPY receptors.

Vasomotor responses of rat intracerebral arterioles to vasoactive intestinal peptide, substance P, neuropeptide Y, and bradykinin

The effect of vasoactive peptides on vascular smooth muscle in the cerebral microcirculation was examined using an isolated intracerebral arteriole preparation. Extraluminally applied vasoactive intestinal peptide (VIP) dilated the spontaneous tone of intracerebral arterioles to 118.9 +/- 3.1% of control diameter at pH 7.30, with an EC50 of 7.27 X 10(-8) M. Similar degrees of dilation to VIP were seen in vessels preconstricted by changing bath solution to pH 7.60. Substance P had no effect on vessel diameter at pH 7.30. However, in vessels precontracted by pH 7.60, significant dose-dependent dilation was observed with an EC50 of 2.55 x 10(-10) M. Neuropeptide Y constricted intracerebral arterioles to 81.22 +/- 2.7% of control diameter, with an EC50 of 6.23 x 10(-10) M. Bradykinin dilated intracerebral arterioles at pH 7.30 and pH 7.60 to 130 +/- 3.0% of control diameter. VIP and bradykinin are potent vasodilators of intracerebral arterioles. Neuropeptide Y is a vasoconstrictor. The effect of substance P appeared to be either pH-dependent or dependent on some degree of precontraction by another agonist, but no effect on vessel diameter was seen at pH 7.30.

Co-existence of immunoreactivity to neuropeptide Y and vasoactive intestinal peptide in non-noradrenergic axons innervating guinea pig cerebral arteries after sympathectomy

We have used double-labelling immunofluorescence to examine the coexistence of immunoreactivity (IR) to neuropeptide Y (NPY), tyrosine hydroxylase (TH) and vasoactive intestinal peptide (VIP) in autonomic neurons innervating guinea pig cerebral arteries. In the rostral circle of Willis of control animals. NPY-IR was detected in 86% of axons with TH-IR (noradrenergic) and 18% of VIP-IR (non-noradrenergic) axons. No axons contained both VIP-IR and TH-IR. Ten to 12 days after bilateral removal of the superior cervical ganglia all TH-IR axons had disappeared. The density of VIP-IR axons was unchanged but now 70% of VIP-IR axons contained NPY-IR. These results show that NPY is not exclusively associated with noradrenergic axons in the cerebral vasculature. Furthermore, NPY levels in non-noradrenergic axons increased following sympathetic denervation.

Increased density of perivascular nerves to the major cerebral vessels of the spontaneously hypertensive rat: differential changes in noradrenaline and neuropeptide Y during development

Fluorescence and immunohistochemical techniques were used to study the pattern and density of perivascular nerves containing noradrenaline (NA) and neuropeptide Y (NPY) supplying the major cerebral arteries of 4-, 6-, 8- and 12-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar (WIS) controls. Levels of NA and NPY in the superior cervical ganglia were measured. The density of nerves containing NA and NPY was greater in the hypertensive animals at all ages studied. However, the developmental changes in the density of innervation showed similar trends in both SHR and WIS groups. With few exceptions, there was a significant increase in the density of nerves containing NA from 4 to 6 weeks and from 8 to 12 weeks of age. This was in contrast to a low expression, and in some vessels a significant decrease in the number of NPY-containing nerves from 4 to 6 weeks. The density of nerve fibres containing NPY increased significantly in almost all vessels between 6 and 8 weeks of age and then stabilized. Thus there is a differential time course for the appearance of NA and NPY during development. Furthermore, the hyperinnervation of cerebral vessels in SHR by nerves containing NA and NPY precedes the onset of hypertension and associated medial hypertrophy. High-performance liquid chromatography and enzyme-linked immunosorbant assays show that the NA and NPY contents of the superior cervical ganglion do not reflect the changes in innervation pattern seen in the terminal fibres in the cerebral arteries. This tends to support the view that a local neurovascular mechanism is involved in the maintenance of hypertension. The possibility that increase in NPY as well as NA in cerebral perivascular nerves of hypertensive animals is involved in the protection of the blood-brain barrier against oedema and cerebral haemorrhage is raised.

Effects of neuropeptide Y on canine cerebral circulation

The effects of neuropeptide Y (NPY) on the vascular tone of isolated cerebral arteries and vertebral blood flow (VBF) were studied in dogs. NPY elicited a dose-dependent contraction of arteries derived from the brain with ED50 values of 2 nM for the middle cerebral and basilar arteries. Arteries from the neck did not respond to NPY. Intra-arterial administration of NPY as a bolus reduced the VBF dose dependently, with no significant alteration of mean arterial blood pressure and heart rate. The decrease in VBF developed slowly and had a long duration, which was consistent with the observations made in vitro. NPY suppressed the contractile effect of noradrenaline (NA) on isolated cerebral arteries and pretreatment with NPY suppressed the effect of NA on VBF, indicating that NPY contributes to the inhibitory modulation of postsynaptic adrenergic mechanisms. These findings suggest that NPY could have a role in the regulation of cerebral circulation.

Neuropeptide Y in the rat nucleus accumbens: ultrastructural localization in aspiny neurons receiving synaptic input from GABAergic terminals

The ultrastructure, afferent input, and sites of termination of neurons containing neuropeptide Y-like immunoreactivity (NPY-LI) were examined in the adult rat nucleus accumbens by using the peroxidase-antiperoxidase (PAP) method. The NPY-LI was seen in sparsely distributed, spindle-shaped perikarya having cross-sectional diameters of 15-20 microns. These perikarya exhibited highly invaginated nuclear membranes and thin rims of cytoplasm containing Golgi lamellae, dense-core vesicles, and other organelles. A few large, principally aspiny, dendrites also showed NPY-LI. The dendrites received synaptic input from unlabeled terminals forming both symmetric and asymmetric junctions. Immunolabeling for NPY was evident in other processes that were not clearly differentiated as dendrites or axons. These were seen primarily near glial processes and the basal laminae of blood vessels. A few myelinated and many unmyelinated axons and axon terminals also were labeled for NPY. These terminals contained numerous, small (40-60 nm), clear and one or more large (80-100 nm) dense core vesicles. Forty-seven percent (27 out of 57) of the terminals containing NPY-LI formed symmetric junctions with unlabeled dendrites or dendritic spines. The remainder lacked recognizable densities within single planes of section. The neurons exhibiting NPY-LI in the nucleus accumbens were characterized further with respect to their afferent input from terminals labeled for the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD). Immunogold labeling of a rabbit antiserum against NPY and PAP labeling for a sheep antiserum to GAD were sequentially applied to the same sections. The GAD-labeled terminals formed symmetric junctions primarily with the more numerous unlabeled dendrites. However, a few synaptic junctions also were detected between the GAD-labeled terminals and dendrites showing immunogold labeling for NPY. We conclude (1) that in the rat nucleus accumbens, NPY-LI is found principally in neurons of the aspiny type and (2) that the output from these presumably intrinsic neurons to other neighboring neurons or blood vessels is at least partially modulated by GABA.

Neuropeptide Y- and alpha-adrenergic receptors in pig spleen: localization, binding characteristics, cyclic AMP effects and functional responses in control and denervated animals

The localization of neuropeptide Y binding sites in the pig spleen, as revealed by [125I]Bolton-Hunter-labelled porcine neuropeptide Y and alpha 1-adrenergic receptor binding sites, as revealed by [125I](2-beta/4-hydroxy-phenyl/-ethylaminomethyl)-tetralone as radioligand, was compared with the distribution of neuropeptide Y and noradrenaline nerves, the latter revealed by tyrosine hydroxylase and dopamine-beta-hydroxylase, using immunohistochemistry. A large degree of codistribution was obtained between [125I]neuropeptide Y and alpha 1-binding sites in the capsule, trabeculae, blood vessels and the red pulp of the spleen. Neuropeptide Y and tyrosine hydroxylase as well as dopamine-beta-hydroxylase-positive nerves were identical in the spleen and had a similar gross distribution pattern as the [125I]neuropeptide Y and alpha 1 binding sites. In functional studies using the isolated blood-perfused spleen from pentobarbital-anaesthetized pigs, neuropeptide Y, noradrenaline and the alpha 1-selective agonist phenylephrine contracted the capsule and induced vasoconstriction in the spleen in vivo. However, the selective alpha 2-adrenoceptor agonists clonidine and azepexole had no effects on blood flow or perfusion pressure, suggesting that postjunctional alpha-receptors were of the alpha 1 type. Neuropeptide Y inhibited the forskolin-evoked, cyclic adenosine monophosphate formation in vitro. The [125I]neuropeptide Y binding, with an equilibrium-dissociation constant of 503 +/- 73 pM and a maximal number of specific binding sites of 23 +/- 3 fmol/mg protein, the neuropeptide Y-induced perfusion-pressure increase in vivo and the inhibition of forskolin-evoked cyclic adenosine monophosphate formation in vitro were dependent on the amidation of the C-terminal portion of the peptide molecule. Furthermore, the effects of neuropeptide Y were not changed by alpha- and beta-adrenoceptor blockade using prazosin and propranolol. Two weeks after postganglionic denervation the neuropeptide Y and the noradrenaline contents of the pig spleen were reduced by 97% and 99%, respectively. These changes were associated with a selective supersensitivity for the noradrenaline-induced perfusion-pressure increase in vivo compared with the effect of neuropeptide Y. However, a similar potentiation of the noradrenaline effect was induced by the monoamine-uptake blocker desipramine in the absence of denervation, and there was no change in the functional response to phenylephrine after denervation.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y receptor in pig spleen: binding characteristics, reduction of cyclic AMP formation and calcium antagonist inhibition of vasoconstriction

Specific, high-affinity binding sites for 125I-porcine neuropeptide Y (NPY) were demonstrated in membranes from the pig spleen. The equilibrium dissociation constant (KD) of the receptor 125I-NPY complex was 532 +/- 87 pM and the maximal number of specific binding sites (Bmax) 23 +/- 3 fmol/mg protein. The Scatchard plot for 125I-NPY binding under equilibrium conditions showed a best-fit to a straight line, whereas the dissociation appeared biphasic. 125I-NPY binding was unaffected by adrenoceptor antagonists and was inhibited by the guanosine triphosphate (GTP) analogue guanylylimidodiphosphate, suggesting regulation by a GTP binding protein. A series of NPY analogues showed a good correlation between binding, inhibition of forskolin-induced cyclic adenosine monophosphate (cAMP) formation and vasoconstrictor activity in vivo. A large carboxyl terminal portion of NPY and the carboxyl terminal amide were essential for binding, inhibition of cAMP formation and vasoconstrictor effects. The NPY fragment 13-36, which has been reported to act only on prejunctional NPY receptors, showed only a 10-fold lower potency than NPY-(1-36) both in binding to splenic membranes and vasoconstrictor activity in vivo. Phenylephrine increased phosphatidyl inositol turnover whereas NPY-(1-36) or -(13-36) did not induce formation of inositol phosphates. The calcium antagonists felodipine and nifedipine attenuated the splenic vasoconstrictor response to NPY in vivo but not the NPY-evoked inhibition of cAMP accumulation or the specific binding of 125I-NPY.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative distribution of neuropeptide Y immunoreactivity and receptor autoradiography in rat forebrain

The distributions of neuropeptide Y (NPY) and NPY receptors in rat brain have been compared. High densities of NPY-like fibers and terminals are present in the hypothalamus and the endopiriform nucleus with corresponding low densities of NPY receptor binding sites. Conversely, low densities of fibers and terminals are observed in the thalamus, stria terminalis and hippocampus with corresponding high densities of binding sites. Various hypotheses are discussed to explain those apparent mismatches including the existence of other classes of receptors and possible paracrine actions of NPY-like peptides in the brain.

Possible involvement of neuropeptide Y in sympathetic vascular control of canine skeletal muscle

Sympathetic nerve stimulation (2 min, 2 and 10 Hz) increased perfusion pressure in the blood perfused canine gracilis muscle in situ after pretreatment with atropine, desipramine and beta-adrenoceptor antagonists. This vasoconstriction was accompanied by clear-cut increases in the overflow of endogenous noradrenaline (NA) at both frequencies and, at 10 Hz but not at 2 Hz, also of neuropeptide Y-like immunoreactivity (NPY-LI). The irreversible alpha-adrenoceptor antagonist phenoxybenzamine enhanced the nerve stimulation induced overflows of NA and NPY-LI five- to eightfold and threefold, respectively. The fractional overflows of NA and NPY-LI per nerve impulse were similar in response to the high-frequency stimulation, indicating equimolar release in relation to the tissue contents of the respective neurotransmitter. The maximal vasoconstrictor response elicited by 10 Hz was reduced by about 50% following a dose of phenoxybenzamine which abolished the effect of exogenous NA and the remaining response was more long-lasting. Local i.a. infusion of NPY evoked long-lasting vasoconstriction in the presence of phenoxybenzamine, while the stable adenosine 5(1)-triphosphate (ATP) analogue alpha-beta-methylene ATP was without vascular effects. Locally infused NPY reduced the nerve stimulation evoked NA overflow by 31% (P less than 0.01) at 1 microM in arterial plasma, suggesting prejunctional inhibition of NA release. In conclusion, NPY-LI is released from the canine gracilis muscle upon sympathetic nerve stimulation at high frequencies. There is nerve stimulation evoked vasoconstriction, which is resistant to alpha-adrenoceptor blockade. This may in part be mediated by NPY released together with NA from the sympathetic vascular nerves.

Neuropeptide Y: presence in perivascular noradrenergic neurons and vasoconstrictor effects on skeletal muscle blood vessels in experimental animals and man

The presence of neuropeptide Y (NPY)-like immunoreactivity (-LI) in sympathetic perivascular nerves and the functional effects of NPY and noradrenaline (NA) on vascular tone were studied in skeletal muscle of various species. A dense network of NPY-LI was found around arteries and arterioles but not venules in the gluteus maximus muscle of man, gracilis muscle of dog, tenuissimus muscle of rabbit and quadriceps muscle of cat, rat, guinea pig and pig. The distribution of NPY-immunoreactive (-IR) nerves was closely correlated to the presence of tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH)-positive fibers, two markers for noradrenergic neurons. Double-staining experiments revealed that NPY- and TH-IR as well as NPY- and DBH-IR nerve fibers around arteries and arterioles were identical. The veins and venules, however, lacked or had a very sparse innervation of NPY-, TH- and DBH-positive fibers. The NPY- and TH-IR nerves in quadriceps muscle of the guinea pig were absent after treatment with 6-hydroxydopamine. Lumbosacral sympathetic ganglia from the same species contained many NPY-positive cells which were also TH- and DBH-IR. NPY-LI was also detected by radioimmunoassay in extracts of skeletal muscle from guinea pig, rabbit, dog, pig and man as well as of lumbosacral sympathetic ganglia. The content of NPY-LI in skeletal muscle was relatively low (0.1-0.4 pmol/g), whereas lumbosacral sympathetic ganglia had a much higher content (48-88 pmol/g). NPY (10(-7) M) contracted arterioles in the tenuissimus muscle of the rabbit to a similar extent (by 65%) as NA (10(-6) M), as studied by intravital microscopy in vivo. NPY had no effect on the corresponding venules while NA caused a slight contraction of these vessels. In vitro studies of small human skeletal muscle arteries and veins revealed that NPY was more potent than NA in contracting the arteries, and the highest concentration of NPY (5 x 10(-7) M) caused a contraction of a similar magnitude as NA 10(-5) M. NA contracted veins from human skeletal muscle, while NPY had only small effects. It is suggested that NPY, together with NA, could be of importance for sympathetic control of skeletal muscle blood flow.

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NPY cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.

Differential effects of clonidine and reserpine treatment on neuropeptide Y content in some sympathetically innervated tissues of the guinea-pig

The effects of treatment with reserpine and/or the selective alpha 2-adrenoreceptor agonists clonidine and oxymetazoline on tissue levels of neuropeptide Y (NPY)-like immunoreactivity (-LI) and noradrenaline (NA) were studied in the guinea-pig. Clonidine treatment was associated with an increase in the levels of NPY-LI in the right atrium in a time- and dose-dependent manner. A significant (45%) elevation of the right atrial content of NPY-LI was present 2 h after administration of clonidine (50 micrograms kg-1 s.c.). After 24 h of repeated clonidine treatment the atrial levels of NPY-LI had increased by 95%. Following chronic clonidine treatment for two weeks, however, the right atrial NPY levels were similar to those in control animals. The corresponding cell-body content of NPY-LI in the stellate ganglion, remained unaffected by clonidine treatment. The levels of NPY-LI were also increased in the gastrocnemius muscle, spleen and adrenal gland after clonidine treatment while no changes were detected in the vas deferens or hypothalamus. The reserpine-induced reduction of NPY-LI in the right atrium, spleen, gastrocnemius muscle and adrenal gland was markedly inhibited by concomitant clonidine treatment while no effect was observed on NA depletion. The adrenoreceptor antagonists phentolamine, prazosin and yohimbine all inhibited the increase in cardiac content of NPY-LI seen after clonidine treatment. No elevation of tissue content of NPY-LI was observed after oxymetazoline (50 micrograms kg-1 s.c.) which, however, reversed the reserpine-induced depletion of NPY-LI. The reserpine-induced increase in content of NPY-LI in the stellate ganglion was also inhibited by clonidine and oxymetazoline.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y and non-adrenergic sympathetic vascular control of the cat nasal mucosa

Neuropeptide Y (NPY) coexists with noradrenaline (NA) in a population of perivascular nerves in the cat nasal mucosa. In the present study, NPY was found to exert non-adrenergic nasal vasoconstrictor actions. Postganglionic sympathetic nerve stimulation induced a release of NPY-like immunoreactivity (LI) concomitant with vasoconstriction in the nasal mucosa. About 60 and 70% of the vasoconstrictor responses upon sympathetic stimulation at 2 and 10 Hz, respectively, remained after pretreatment with phenoxybenzamine and propranolol which abolished the effects of exogenous NA. Preganglionic denervation one week prior to the experiments did not change the vasoconstrictor response to sympathetic nerve stimulation or the NA or NPY contents of the nasal mucosa. The levels of NPY-LI in the superior cervical ganglion were however reduced. After reserpine treatment, which depleted the nasal NA content by almost 90% and the NPY content by 50%, a vasoconstrictor response to nerve stimulation was still present. After reserpine treatment combined with preganglionic denervation, nerve stimulation simultaneously induced an increased output of NPY-LI and a marked long-lasting vasoconstriction which was not influenced by phenoxybenzamine and propranolol. The reserpine-induced depletion of NA was not influenced by preganglionic denervation while the reduction in the nasal content of NPY-LI was prevented. In conclusion, NPY could be a non-adrenergic mediator of sympathetic vascular effects in cat nasal mucosa.

Chemical sympathectomy reveals pre- and postsynaptic effects of neuropeptide Y (NPY) in the cardiovascular system

Intravenous injection of neuropeptide Y (NPY) caused short-lasting dose-dependent pressor responses in anesthetized rats. NPY was equipotent with noradrenaline in producing proportional pressor effects. Chemical sympathectomy, following the administration of 100 mg/kg 6-hydroxydopamine (6-OHDA), significantly potentiated the systemic pressor effects elicited by NPY or noradrenaline. Pretreatment with 2 nmol NPY enhanced the noradrenaline-induced pressor response in control rats. NPY did not change the basal tension of isolated rat aortic strips but significantly potentiated the contractile activity induced by 16 nM noradrenaline. This effect of NPY was not observed in aortic strips from rats pretreated with 6-OHDA. The presence of pre- and postsynaptic sites of action for NPY in the cardiovascular system of the rat is discussed.

Neuropeptide Y and noradrenaline mechanisms in relation to reserpine induced impairment of sympathetic neurotransmission in the cat spleen

The mechanisms underlying the reserpine-induced impairment of the functional responses to sympathetic nerve stimulation and output of noradrenaline (NA) and neuropeptide Y (NPY)-like immunoreactivity (-LI) were studied using the isolated blood-perfused cat spleen. Splenic nerve stimulation (10 Hz for 2 min) during control conditions caused perfusion-pressure increase, volume reduction and an increased output of NA and NPY-LI. After administration of phenoxybenzamine, the nerve stimulation-induced perfusion-pressure increase was almost abolished, the volume reduction inhibited and the output of NPY-LI enhanced. After subsequent addition of propranolol, a clear-cut increase in perfusion pressure upon nerve stimulation reappeared. Local infusion of NPY caused a potent, long-lasting, adrenoceptor-resistant increase in perfusion pressure and a relatively smaller volume reduction of the spleen. Twenty-four hours after reserpine pretreatment (1 mg kg-1 i.v.), which depleted the splenic content of NA greater than 95% and NPY-LI by about 50%, the functional responses upon nerve stimulation were markedly reduced. Preganglionic denervation or pretreatment with the ganglionic-blocking agent chlorisondamine did not influence the NA depletion after reserpine treatment. A considerable, adrenoceptor antagonist-resistant, long-lasting functional response as well as a markedly enhanced output of NPY-LI then occurred upon nerve stimulation. In conclusion, reserpine treatment combined with interruption of preganglionic impulse flow reveals non-adrenergic, nerve stimulation evoked splenic functional responses which could be mediated by release of a cotransmitter peptide like NPY.

Perivascular innervation of the cerebral circulation: involvement in the pathophysiology of subarachnoid hemorrhage

The authors describe the perivascular innervation of cerebral circulation. The different nerve fiber systems can be classified as follows: 1. Sympathetic (noradrenaline, neuropeptide Y), 2. Parasympathetic (acetylcholine, vasoactive intestinal peptide/peptide histidine isoleucine (methionine), 3. Sensory (tachykinins, calcitonin gene-related peptide). Each of these systems is outlined by their basic anatomical and physiological facts. Then, the etiology of cerebral vasospasm after subarachnoid hemorrhage is discussed in relation to the cerebrovascular innervation.

Concentrations of putative neurovascular transmitters in major cerebral arteries and small pial vessels of various species

The levels of noradrenaline, neuropeptide Y, 5-hydroxytryptamine, and substance P were measured and compared between the large arteries of the circle of Willis and the small cerebral vessels of the pia mater in the rat, rabbit, cat, and monkey. In all species, noradrenaline and neuropeptide Y concentrations were greater in the larger arteries than in small pial vessels. Noradrenaline concentrations were dramatically reduced following cervical sympathectomy, with the extent of diminution differing greatly in the various species; the effects of cervical ganglionectomy on neuropeptide Y concentrations were less pronounced. 5-Hydroxytryptamine concentrations in rats, cats, and rabbits were significantly greater in the small pial vessels, although measurable concentrations existed in the circle of Willis. In cats and monkeys, substance P was found in major arteries, but was not detectable at the level of the small pial vessels. The differences in the regional distribution of the various neurotransmitter candidates in the cerebrovascular bed may reflect their physiological significance.

Peptides in the mammalian cardiovascular system

Ample immunocytochemical evidence is now available demonstrating that several peptides are present in the mammalian cardiovascular system where they are localised to nerve fibres and myocardial cells. The neuropeptides (neuropeptide Y, calcitonin gene-related peptide, tachykinins and vasoactive intestinal polypeptide) are localised to large secretory vesicles in subpopulations of afferent or efferent nerves supplying the heart and vasculature of several mammals, including man. Although they often exert potent pharmacological effects on the tissues in which they occur their physiological significance has still to be established. They may act directly via specific receptors and/or indirectly by influencing the release and action of other cardiovascular transmitters. In marked contrast, atrial natriuretic peptide is produced by cardiac myocytes and considered to act as a circulating hormone.

Somatostatin 28 and neuropeptide Y innervation in the septal area and related cortical and subcortical structures of the human brain. Distribution, relationships and evidence for differential coexistence

Somatostatin 28- and neuropeptide Y-containing innervations were mapped in the human medial forebrain (eight control brains) with immunohistochemistry, using the sensitive avidin-biotin-peroxidase method. Peptidergic perikarya and fibers had an extensive distribution: they were densest in the ventral striatum (nucleus accumbens, olfactory tubercle and bed nucleus of the stria terminalis) and infralimbic cortex, of intermediate density in the medial septal area and of lowest density in the dorsal and caudal lateral septal nucleus. Somatostatin-like immunoreactive perikarya and fibers were generally more numerous than the neuropeptide Y-like immunoreactive ones, but more faintly labeled. Their pattern of distribution was strikingly similar in some of the limbic structures studied but clearly distinct in others. Excellent overlap of neuropeptide Y and somatostatin-like immunoreactivity was detected in: (1) the medial septal area, where innervation occasionally formed perivascular clusters; (2) the nucleus accumbens and olfactory tubercle, characterized by dense patchy innervation; and (3) the laterodorsal septal nucleus, scarcely innervated. In the latter structures, most peptidergic neurons were double-labeled. On the other hand, both peptidergic innervations clearly differed in the lateroventral septal nucleus and the bed nucleus of the stria terminalis which contained distinct clusters of somatostatin-like immunoreactive neurons devoid of neuropeptide Y-like immunoreactivity. Also, the perineuronal and peridendritic axonal plexuses ('woolly fibers') present in these structures were only labeled with somatostatin. In the infralimbic cortex, the relation between the peptides varied according to the cortical laminae. Coexistence of somatostatin and neuropeptide Y frequently occurred in layer VI and in the subcortical white matter, whereas layer V and particularly layers II and III contained a contingent of neurons labeled only with somatostatin. Dense horizontal terminal networks in layers I and VI however were similar for both peptides. These findings support the existence of two different types of somatostatin-like immunoreactive perikarya as regards colocalization with neuropeptide Y. Their particular topographical segregation within the cortical and subcortical structures analysed suggest that they could have different connections and functional properties.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of adrenergic, opioid and pancreatic polypeptidergic compounds on feeding and other behaviors in neonatal leghorn chicks

The present study examined the effects of intracerebral (IC) administration of pancreatic polypeptide (PP), neuropeptide Y (NPY), norepinephrine (NE), dynorphin and naloxone on food intake in 2-day-old Leghorn chicks. Of the compounds studied, only PP (20 micrograms) and naloxone (10 and 20 micrograms) elevated food intake significantly as compared to saline injections. NPY, a potent orexigenic agent in mammals, did not elevate consumption significantly in a dose-related fashion. This latter finding was attributed to the occurrence of tonic-clonic convulsions following NPY administration. However, for those chicks which did not exhibit behavioral convulsions, food intake appeared to be elevated by 1, 5 and 10 micrograms of NPY. Similarly, NE did not elevate food intake but instead induced sedation and narcolepsy, a behavioral response which could be distinguished from the convulsions observed after NPY. In a separate group of chicks, the effect of NPY on cortical activity was examined. Bipolar electrodes were used to record EEG activity before and after IC injections of saline, NPY or NE. The behavioral convulsions induced by NPY corresponded with an increase in high amplitude sharp-wave activity, which persisted for up to 30 min post-injection. Collectively, these results suggest that the neurochemical substrates for feeding in 2-day-old Leghorn chicks are distinct from those underlying food intake in adult mammals.

Peptide-containing nerve fibers in human cerebral arteries: immunocytochemistry, radioimmunoassay, and in vitro pharmacology

Nerve fibers containing neuropeptide Y, vasoactive intestinal peptide (VIP), substance P (SP), and calcitonin gene-related peptide (CGRP) were seen in the adventitia or at the adventitia-media border of human cerebral arteries obtained during neurosurgical procedures. Radioimmunoassay of human cerebral arteries, removed at autopsy, revealed that the levels of the four peptides did not differ among the major cerebral arteries. There was, however, a gradual decline in peptide concentrations with increasing age of the patients, as measured in the proximal part of the middle cerebral artery. Pharmacological experiments on fresh segments of cerebral (pial) arteries in vitro revealed that neuropeptide Y caused vasoconstriction per se but did not potentiate the contractile response of noradrenaline. VIP, peptide histidine methionine-27 (PHM-27), SP, neurokinin A (NKA), and human CGRP potently relaxed vessels precontracted by prostaglandin F2 alpha, the relative potency being human CGRP greater than SP greater than VIP greater than NKA greater than PHM-27. The amount of relaxation varied between 55% (SP) and 96% (human CGRP) of the prostaglandin F2 alpha-induced contraction. The peptide effects were not antagonized by propranolol, atropine, or cimetidine, suggesting an action that does not involve adrenergic, cholinergic, or histaminergic receptors.

Changes of neuropeptide immunoreactivity in cerebrovascular nerve fibers after experimentally produced SAH. Immunohistochemical study in the dog

The immunoreactivity of vasoactive intestinal polypeptide (VIP)-, substance P (SP)-, and neuropeptide Y (NPY)-containing nerve fibers in the basilar artery (BA) and proximal portion of the middle cerebral artery (M1) was immunohistochemically examined in the dog after experimentally produced subarachnoid hemorrhage (SAH). The SAH was produced by a single injection of fresh autologous arterial blood (1 ml/kg body weight) into the cisterna magna. The density (the averaged number of nerve fibers in a unit area) of VIP-, SP-, and NPY-immunoreactive perivascular nerve fibers in the M1 segment and the BA was markedly decreased (5% to 40% of the normal value) immediately after the injection. The density of VIP- and SP-immunoreactive perivascular fibers increased 2 or 3 weeks after SAH and became normal by the 63rd day after injection. On the other hand, no substantial recovery was observed in the density of NPY-immunoreactive perivascular fibers by 63 days after injection.

Actions of calcium antagonists on pre- and postjunctional effects of neuropeptide Y on human peripheral blood vessels in vitro

The mechanisms underlying the contractile effects of neuropeptide Y (NPY) in relation to those of noradrenaline (NA) on small human blood vessels were studied in vitro. NPY caused contractions of mesenteric veins, renal and skeletal muscle arteries but not of mesenteric arteries. NPY was about 5- to 10-fold more potent than NA. The maximal contractile responses to NPY (5 X 10(-7) M) were 38 +/- 4, 37 +/- 8 and 95 +/- 16% of the response evoked by NA 10(-5) M in the mesenteric vein, renal and skeletal muscle arteries respectively. The NPY effects were resistant to adrenoceptor antagonists. The calcium antagonist nifedipine reduced the effect of NA but not the contractile response to NPY on mesenteric veins. Nifedipine and felodipine reduced the contractile response to both NA and NPY on renal and skeletal muscle arteries. In contrast to the contractile effects of K+, the responses to NPY and NA were largely uninfluenced by changes in extracellular Ca2+ concentrations. Nifedipine still inhibited the NPY contractions in a Ca2+-free medium while high extracellular Ca2+ (7.5 mM) partly reduced the nifedipine effect. NPY reduced the nerve stimulation-evoked [3H]NA overflow from the mesenteric veins via a nifedipine resistant mechanism. The stable analogue alpha, beta-methylene adenosine triphosphate (mATP) was more potent than ATP and had nifedipine-sensitive contractile effects similar to those of NA on the human blood vessels without influencing the nerve-evoked [3H]NA efflux. In conclusion, NPY exerts a potent nifedipine-sensitive vasoconstrictor activity, especially on human skeletal muscle arteries in vitro, although the influx of extracellular calcium may not be a crucial mechanism. The NPY-induced contractions of mesenteric veins and the inhibition of nerve-evoked [3H]NA efflux seem to be mediated via nifedipine resistant messenger systems.

The actions of the peptides, neuropeptide Y and peptide YY, on the vascular and capsular smooth muscle of the isolated, blood-perfused spleen of the dog

The two peptides, neuropeptide Y (NPY) and peptide YY (PYY) were compared for potency on the vascular and extravascular smooth muscle of the isolated, blood-perfused spleen of the dog. The only vascular response to both NPY and PYY was vasoconstriction; the maximum effect was to arrest splenic arterial blood flow completely. On a molar basis both NPY and PYY were significantly more potent (P less than 0.01) as splenic arterial vasoconstrictors than the transmitter noradrenaline (NA). PYY was approximately 7 times more potent as a vasoconstrictor than NPY. In contrast to their potency on the vascular smooth muscle, NPY and PYY were significantly (P less than 0.01) less potent than NA in causing contraction of the splenic capsule. The two peptides were equipotent in eliciting this contraction.

Action and location of neuropeptide tyrosine (Y) on hippocampal neurons of the rat in slice preparations

The action of bath applied NPY (1-1,000 nM) was investigated on hippocampal slices of the rat with extra- and intracellular recording. Neuropeptide Y (NPY) at 10-1,000 nM caused a concentration-dependent, long-lasting reduction of excitatory postsynaptic potentials (EPSPs) in the hippocampal subfield CA1 and the area dentata, and an even stronger reduction of population spikes. Paired pulse experiments with low intensity, stimulation-evoked PSPs showed a marked increase in facilitation in the presence of NPY, indicating a presynaptic action. Spontaneous burst firing of CA1 pyramidal cells in low calcium, high magnesium medium was reduced, indicating a partially postsynaptic inhibitory action of NPY on their dendrites. Intracellular recording from CA1 somata during NPY administration revealed a reduction of the amplitudes of excitatory-inhibitory postsynaptic potential (EPSP-IPSP) sequences in the absence of changes in membrane potential and conductance. Accommodation of firing during long depolarizing pulses and afterhyperpolarizations were unchanged. The innervation pattern of NPY immunoreactive fibers in the same regions was studied in slices adjacent to the ones used for electrophysiology by using antisera against NPY and light and electron microscopy. There is a dense innervation of CA1 by NPY-immunoreactive axons and terminals, particularly in the stratum moleculare. NPY-immunoreactive neurons are present in the stratum oriens and pyramidale. The NPY labeled axons of the stratum moleculare participate in numerous synaptic contacts with the smaller dendritic elements in this layer, many of which belong to pyramidal neurons. These observations provide evidence for a dendritic NPY-immunoreactive innervation of CA1 neurons, which is in keeping with the electrophysiological effects of NPY on pyramidal neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitation of carotid body chemoreceptors by neuropeptide-Y

Neuropeptide-Y (NPY) is a peptide co-localised with noradrenaline in many sympathetic nerves. Recently, it has been found in postganglionic sympathetic nerves running to blood vessels in the carotid body. When NPY is administered to cats by infusion into the arterial blood close to the carotid bodies, breathing is stimulated. This effect is abolished when the carotid sinus nerves are cut. Similar intra-carotid infusions of NPY can be demonstrated to increase the frequency of firing of chemoreceptor afferent nerves. However, NPY introduced into the blood vessels of the carotid body immediately prior to halting its blood flow does not modify the development of chemoreceptor discharge in response to developing asphyxia. The findings are consistent with NPY causing excitation of chemoreceptors by causing local vasoconstriction and stagnant asphyxia.

Nerve fibers containing neuropeptide Y in the cerebrovascular bed: immunocytochemistry, radioimmunoassay, and vasomotor effects

Perivascular nerve fibers containing neuropeptide Y (NPY)-like immunoreactivity were identified around cerebral blood vessels of human, cat, guinea pig, rat, and mouse. The major cerebral arteries were invested by dense plexuses; veins, small arteries, and arterioles were accompanied by few fibers. Removal of the superior cervical ganglion resulted in a reduction of NPY-like material in pial vessels and dura mater. Pretreatment with 6-hydroxydopamine or reserpine reduced the number of visible NPY fibers and the concentration of NPY in rat cerebral vessels. Sequential immunostaining with antibodies toward dopamine-beta-hydroxylase (DBH) (an enzyme involved in the synthesis of noradrenaline) and NPY revealed an identical localization of DBH and NPY in nerve cell bodies in the superior cervical ganglion and in perivascular fibers of pial blood vessels, suggesting their coexistence. Administration of NPY in vitro resulted in concentration-dependent contractions that were not modified by a sympathectomy. The contractions induced by noradrenaline, 5-hydroxytryptamine, and prostaglandin F2 alpha and the dilator responses to calcitonin gene-related peptide were not modified by NPY in rat cerebral arteries. However, the constrictor response to NPY was reduced by 70% in the presence of the calcium entry blocker nifedipine, and abolished following incubation in a calcium-free buffer. These data suggest an interaction of NPY at a postsynaptic site, which for induction of contraction may open calcium channels in the sarcolemma of cerebral arteries.

Elevations of neuropeptide Y-like immunoreactivity and catecholamines in plasma on increased intracranial pressure in the pig

Graded increases of intracranial pressure (ICP) in anaesthetized pigs induced elevations of plasma levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and catecholamines, simultaneously with hypertension and tachycardia. Plasma adrenaline (ADR) increased at a lower ICP-level than did the plasma levels of noradrenaline (NA) and NPY-LI. At the maximal ICP elevation, 22.9 kPa (172 mmHg), plasma NPY-LI was increased about 10-fold, from 48 +/- 8 pmol/l in the basal state, while NA and ADR concentrations increased more than 100-fold. At this maximal ICP-level the plasma levels of NPY-LI were correlated to the concentrations of both NA (r = 0.87, P less than 0.01) and ADR (r = 0.92, P less than 0.001). Plasma NPY-LI continued to increase to about 1000 pmol/l, 10 min after the maximal elevation of ICP was discontinued, while the catecholamines then had declined considerably. A slight cardiac release of NPY-LI was observed at the maximal elevation of ICP. The half-life of NPY-LI in plasma was about 6 min upon systemic infusion. At plasma levels similar to those obtained upon maximal ICP elevation, exogenous NPY caused slight vasoconstriction in the spleen and skeletal muscle, but had no effects on coronary blood flow or systemic blood pressure. This suggests that NPY mainly exerts local actions after release from nerve endings, while levels of circulating NPY in plasma must be very high to influence blood flow in some organs. It is concluded that elevation of ICP results in hypertension and tachycardia related to elevated plasma levels of NPY-LI and catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)

Presynaptic action of neuropeptide Y in area CA1 of the rat hippocampal slice

1. Neuropeptide tyrosine (neuropeptide Y, NPY), a recently isolated endogenous brain peptide, reduces the extracellular population spike evoked by stimulation of stratum radiatum in area CA1 of the in vitro rat hippocampal slice, without reducing the antidromically evoked population spike. To test the hypothesis that NPY acts presynaptically, intracellular recordings were made of pyramidal neurones of area CA1 in vitro. 2. Bath application of 10(-6) M-NPY causes a long-lasting (1-1.5 h), reversible reduction of the orthodromically evoked excitatory post-synaptic potential (e.p.s.p.) recorded intracellularly from CA1 pyramidal neurones. This effect on the e.p.s.p. was dependent upon the concentration of NPY. 3. The resting membrane potential, slope input resistance, and action potential threshold, amplitude and duration of the CA1 pyramidal neurones were not affected by NPY. 4. The responses of CA1 pyramidal neurones to ionophoretic pulses of glutamate, applied to the dendrites during synaptic blockade, was also unaffected by NPY. 5. The evidence supports the hypothesis that NPY acts presynaptically in the CA1 region of hippocampus to reduce excitatory input to the pyramidal neurones.

Mapping of neuropeptide Y-like immunoreactivity in the feline hypothalamus and hypophysis

The distribution of neuropeptide Y (NPY) in the cat hypothalamus and hypophysis was studied with the indirect immunofluorescence technique of Coons and co-workers (Coons, Leduc, and Connolly: J. Exp. Med. 102:49-60, 1955), which provided a detailed map of NPY-like immunoreactive neurons. The immunolabelling was detected in cell bodies, fibers, and terminallike structures widely distributed throughout the whole hypothalamus. A large population of medium-sized NPY-like immunoreactive cell bodies was localized in the area of arcuate nucleus. The number of immunoreactive cell bodies visualized was dramatically increased after intracerebroventricular injections of colchicine. Numerous immunolabelled cell bodies were also visible in the median eminence and scattered in the lateral hypothalamic area. Dense plexuses of NPY-immunoreactive fibers were observed in the arcuate nucleus, internal layer of median eminence, periventricular zone, and paraventricular nucleus. Other regions of hypothalamus displaying numerous NPY-like immunoreactive fibers included dorsal and ventrolateral hypothalamic areas. In contrast, certain hypothalamic areas were almost devoid of NPY-like immunoreactive fibers-namely, the mammillary bodies and suprachiasmatic nucleus. Finally, in neurohypophysis, bright immunofluorescent fibers were observed along the pituitary stalk and penetrating the neural lobe. These results suggest the widespread distribution of the NPY-containing neuronal systems in the cat hypothalamus and hypophysis.

Neuropeptide Y normalizes renin secretion in adrenalectomized rats without changing blood pressure

In the periphery, neuropeptide Y is present in plasma, in the adrenal medulla as well as in sympathetic nerve endings and in the juxtaglomerular apparatus. The aim of the present study was to assess the effect of this peptide on renin secretion. Normotensive rats were adrenalectomized or sham-operated and made hypertensive with methylprednisolone acetate (20 mg/kg s.c. once weekly). Deoxycorticosterone pivalate (10 mg/kg s.c. once weekly) was also given to prevent mineralocorticoid deficiency. Two weeks after initial surgery, 12 adrenalectomized and 8 sham-operated conscious rats were infused for 30 min with neuropeptide Y (0.1 micrograms/min) whereas 8 other adrenalectomized and 9 sham-operated conscious rats received under similar conditions the vehicle of neuropeptide Y (10 microliter/min). Neither before nor during the infusions was there a significant difference in blood pressure and heart rate between the 4 groups of animals. Plasma renin activity, measured at the end of the infusion, was 30.5 ng/ml/hr in the adrenalectomized group receiving vehicle and 6.3 ng/ml/hr in that infused with neuropeptide Y (p less than 0.001). This latter value did not differ from that found in sham-operated rats. These results suggest that neuropeptide Y may play an important role in regulating renin secretion.