Neuropeptide Y: cerebrovascular innervation and vasomotor effects in the cat

Neuropeptide Y modulates the electrical activity of subfornical organ neurons

The subfornical organ (SFO) is a sensory circumventricular organ, lacking a blood-brain barrier. It is well-recognized as a key center for detection and integration of osmotic, ionic and hormonal signals for maintenance of hydromineral balance and cardiovascular regulation. Recently, the SFO has also been recognized as a center for the detection and integration of circulating satiety signals for regulation of energy balance. Neuropeptide Y (NPY) is a multifunctional neuropeptide, with effects on energy balance, cardiovascular tone and other aspects of homeostasis. Interestingly, despite the overlap of function between SFO and NPY, and observations that SFO expresses several subtypes of Y receptors, NPY regulation of SFO neurons has never been investigated. In this study, we examined the effects of NPY on dissociated rat SFO neurons using patch clamp electrophysiology. We observed that 300 nM NPY caused depolarization of 16 % of SFO neurons tested, and hyperpolarization of 26 %, while the remaining neurons were insensitive to NPY (n = 31). These effects were dose-dependent with an apparent EC50 of 3.9 nM for depolarizing neurons and 3.5 nM for hyperpolarizing neurons. Activation of Y5 receptors alone led to predominately hyperpolarizing effects, while activation of Y1 or Y2 receptors alone led to mixed responses. Voltage-clamp experiments demonstrated that NPY caused increases in voltage-gated K+ current amplitude as well as hyperpolarizing shifts in persistent Na+ current, mediating the hyperpolarizing and depolarizing effects, respectively. These findings indicate that NPY elicits direct electrophysiological effects on SFO neurons, suggesting that NPY acts via the SFO to regulate energy homeostatic function.

Increasing Catecholamine Secretion Through NPY in Pheochromocytomas With False-Negative 123 I-MIBG Scintigraphy

INTRODUCTION

123 I-MIBG has been well established as a functional imaging tool, and 131 I-MIBG therapy is being considered for catecholamine-secreting tumors. Tumors with the characteristics of a noradrenergic biochemical phenotype, small, malignant, metastatic, extra-adrenal, bilateral, and hereditary, especially SDHx -related tumors, are reported to correlate with reduced MIBG uptake. However, the potential molecular mechanisms influencing MIBG uptake have been poorly studied.

PATIENTS AND METHODS

To identify critical genes that may enhance MIBG accumulation in pheochromocytomas (PCCs), we performed RNA-seq analyses for 16 operated patients with PCCs (6 MIBG-negative and 10 MIBG-positive) combined with RT-qPCR for 27 PCCs (5 MIBG-negative and 22 MIBG-positive) and examined primary cultures of the surgical tissues.

RESULTS

In the present study, 6 adrenal nodules of 66 nodules surgically removed from 63 patients with PCCs (9%) were MIBG negative. MIBG, a guanethidine analog of norepinephrine, can enter chromaffin cells through active uptake via the cellular membrane, be deposited in chromaffin granules, and be released via Ca 2+ -triggered exocytosis from adrenal chromaffin cells. When we compared expression of several catecholamine biosynthesis and secretion-associated genes between MIBG-negative and MIBG-positive tumors using transcriptome analyses, we found that neuropeptide Y, which is contained in chromaffin granules, was significantly increased in MIBG-negative tumors. NPY stimulated norepinephrine secretion dose-dependently in primary cell culture derived from MIBG-positive PCC. In our study, MIBG-negative PCCs were all norepinephrine-hypersecreting tumors.

CONCLUSIONS

These data indicate that NPY upregulation in PCCs may stimulate chromaffin granule catecholamine secretion, which is associated with false-negative 123 I-MIBG scintigraphy.

The 5-HT1F receptor as the target of ditans in migraine - from bench to bedside

Migraine is a leading cause of disability in more than one billion people worldwide, yet it remains universally underappreciated, even by individuals with the condition. Among other shortcomings, current treatments (often repurposed agents) have limited efficacy and potential adverse effects, leading to low treatment adherence. After the introduction of agents that target the calcitonin gene-related peptide pathway, another new drug class, the ditans - a group of selective serotonin 5-HT_1F receptor agonists - has just reached the international market. Here, we review preclinical studies from the late 1990s and more recent clinical research that contributed to the development of the ditans and led to their approval for acute migraine treatment by the US Food and Drug Administration and the European Medicines Agency.

Migraine headache pathophysiology

In both episodic and chronic migraine, headache is the most disabling symptom that requires medical care. The migraine headache is the most well-studied symptom of migraine pathophysiology. The trigeminal system and the central processing of sensory information transmitted by the trigeminal system are of considerable importance in the pathophysiology of migraine headache. Glutamate is the main neurotransmitter that drives activation of the ascending trigeminal and trigeminothalamic pathways. The neuropeptide, calcitonin gene-related peptide (CGRP) that is released by the trigeminal system, plays a crucial role in the neurobiology of headache. Peripheral and central sensitizations associated with trigeminal sensory processing are neurobiologic states that contribute to both the development of headache during a migraine attack and the maintenance of chronic migraine.

CGRP and migraine; from bench to bedside

Migraine treatment has reached a new era with the development of drugs that target the trigeminal neuropeptide calcitonin gene-related peptide (CGRP) or its receptor. The CGRP related therapies offer considerable improvements over existing drugs as they are the first to be designed to act on the trigeminal pain system, more specific and with few adverse events. Small molecule CGRP receptor antagonists, such as rimegepant and ubrogepant, are effective for the acute treatment of migraine headache. In contrast, monoclonal antibodies against CGRP or the CGRP receptor are beneficial for the prophylactic treatments in chronic migraine. Here I will provide a historical overview of the long path that led to their successful development. In addition, I will discuss aspects on the biology of CGRP signalling, the role of CGRP in migraine headache, the efficacy of CGRP targeted treatment, and synthesize what currently is known about the role of CGRP in the trigeminovascular system.

CGRP and Migraine: The Role of Blocking Calcitonin Gene-Related Peptide Ligand and Receptor in the Management of Migraine

Migraine is a highly prevalent, complex neurological disorder. The burden of disease and the direct/indirect annual costs are enormous. Thus far, treatment options have been inadequate and mostly based on trial and error, leaving a significant unmet need for effective therapies. While the underlying pathophysiology of migraine is incompletely understood, blocking the calcitonin gene-related peptide (CGRP) using monoclonal antibodies targeting CGRP or its receptor and small molecule CGRP receptor antagonists (gepants) have emerged as a promising therapeutic opportunity for the management of migraine. In this review, we discuss new concepts in the pathophysiology of migraine and the role of CGRP, the current guidelines for treating migraine preventively, the medications that are being used, and their limitations. We then discuss small molecule CGRP receptor antagonists, monoclonal antibodies to CGRP ligand and receptor, as well as the detailed results of Phase II and III trials involving these novel treatments. We conclude with a discussion of the implications of blocking CGRP and its receptor.

Effect of Nimodipine on Histological Alterations in Basilar Artery Following the Bilateral Common Carotid Artery Ligation (Preliminary Study)

Background: The blood supply to tissues is reduced as a result of arterial occlusions. Angiogenesis, collateral circulation and reverse flow mechanisms go into operation to restore a continued adequate supply of blood. Ca++ channels undertake the major part of this function. As a result of the increasing tension on the arterial walls, vascular autonomy is affected, and ischemia and even necrosis are observed. Method: Adult 100 male hybrid rabbits were used in this study. The bilateral carotid arteries were ligated at the carotid bifurcation. The rabbits were divided into 2 main groups: treatment and control, and then both groups were further divided into 5 subgroups consisting of 10 rabbits each. The rabbits were sacrificed between the first day and the end of 8 weeks for histopathological examination of the basilar artery in two groups. Results: In control groups, after 24 hours of the occlusion partial swelling and minor endothelial damage were observed in histopathological sections of the basilar artery. Luminal flattening started to decrease, and expanding of the diameter continued. The increase in the diameters of the basilar artery was higher in animals treated by nimodipine, and that difference was statistically significant (P=0,000). Conclusion: This study revealed that the intimal and medial alterations arising from the increased blood flow rate in the basilar artery might be lessened and even partially prevented by the use of nimodipine.

Neuropeptide Y-mediated sex- and afferent-specific neurotransmissions contribute to sexual dimorphism of baroreflex afferent function

Background

Molecular and cellular mechanisms of neuropeptide-Y (NPY)-mediated gender-difference in blood pressure (BP) regulation are largely unknown.

Methods

Baroreceptor sensitivity (BRS) was evaluated by measuring the response of BP to phenylephrine/nitroprusside. Serum NPY concentration was determined using ELISA. The mRNA and protein expression of NPY receptors were assessed in tissue and single-cell by RT-PCR, immunoblot, and immunohistochemistry. NPY was injected into the nodose while arterial pressure was monitored. Electrophysiological recordings were performed on nodose neurons from rats by patch-clamp technique.

Results

The BRS was higher in female than male and ovariectomized rats, while serum NPY concentration was similar among groups. The sex-difference was detected in Y₁R, not Y₂R protein expression, however, both were upregulated upon ovariectomy and canceled by estrogen replacement. Immunostaining confirmed Y₁R and Y₂R expression in myelinated and unmyelinated afferents. Single-cell PCR demonstrated that Y₁R expression/distribution was identical between A- and C-types, whereas, expressed level of Y₂R was ∼15 and ∼7 folds higher in Ah- and C-types than A-types despite similar distribution. Activation of Y₁R in nodose elevated BP, while activation of Y₂R did the opposite. Activation of Y₁R did not alter action potential duration (APD) of A-types, but activation of Y₂R- and Y₁R/Y₂R in Ah- and C-types frequency-dependently prolonged APD. N-type I_Ca was reduced in A-, Ah- and C-types when either Y₁R, Y₂R, or both were activated. The sex-difference in Y₁R expression was also observed in NTS.

Conclusions

Sex- and afferent-specific expression of Neuropeptide-Y receptors in baroreflex afferent pathway may contribute to sexual-dimorphic neurocontrol of BP regulation.

Cardiovascular responses to intranasal neuropeptide Y in single prolonged stress rodent model of post-traumatic stress disorder

Delivery of neuropeptide Y (NPY) to the brain by intranasal administration shows promise as non-invasive means for preventing or treating PTSD symptoms. Here, radiotelemetry and echocardiography were used to determine effects of intranasal NPY on cardiovascular functions in absence and presence of stress. Male adult Sprague Dawley rats were implanted with radiotelemetric probes, and subjected to single prolonged stress (SPS), followed by intranasal vehicle (V) or NPY (150μg) under conditions shown to prevent development of many of the behavioral neuroendocrine and biochemical impairments. In both groups, mean arterial pressure (MAP) rose rapidly peaking at about 125mmHg, remaining near maximal levels for 1h. SPS also elicited robust rise in heart rate (HR) which was mitigated by intranasal NPY, and significantly lower than V-treated rats 12-50min after exposure to SPS stressors. In the first hr. after SPS, locomotor activity was elevated but only in the V-treated group. By 3h, MAP returned to pre-stress levels in both groups with no further change when monitored for 6days. HR remained elevated during the 6h remaining light phase after SPS. Subsequently HR was at pre-SPS levels during the remaining days. However dark phase HR was low following SPS, gradually recovered over 6days and was associated with reduced activity. When administered in the absence of further stress, intranasal NPY or V elicited similar much smaller, short-lived rises in MAP and HR. Echocardiography revealed no change in HR, stroke volume (SV) or cardiac output (Q) with intranasal NPY in the absence of stress. SPS led to reduced SV and Q but was not affected by NPY. Overall the results demonstrate no major cardiovascular effects of intranasal NPY and indicate possible benefit from transient amelioration of HR response in line with its translational potential to combat PTSD and comorbid impairments.

First study on the peptidergic innervation of the brain superior sagittal sinus in humans

The superior sagittal sinus (SSS) of the mammalian brain is a pain-sensitive intracranial vessel thought to play a role in the pathogenesis of migraine headaches. Here, we aimed to investigate the presence and the potential co-localization of some neurotransmitters in the human SSS. Immunohistochemical and double-labeling immunofluorescence analyses were applied to paraformaldehyde-fixed, paraffin-embedded, coronal sections of the SSS. Protein extraction and Western blotting technique were performed on the same material to confirm the morphological data. Our results showed nerve fibers clustered mainly in large bundles tracking parallel to the longitudinal axis of the sinus, close in proximity to the vascular endothelium. Smaller fascicles of fibers encircled the vascular lumen in a spiral fashion, extending through the subendothelial connective tissue. Isolated nerve fibers were observed around the openings of bridging veins in the sinus or around small vessels extending into the perisinusal dura. The neurotransmitters calcitonin gene related peptide (CGRP), substance P (SP), neuronal nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), tyrosine hydroxylase (TH), and neuropeptide Y (NPY) were found in parietal nerve structures, distributed all along the length of the SSS. Overall, CGRP- and TH-containing nerve fibers were the most abundant. Neurotransmitters co-localized in the same fibers in the following pairs: CGRP/SP, CGRP/NOS, CGRP/VIP, and TH/NPY. Western blotting analysis confirmed the presence of such neurosubstances in the SSS wall. Overall our data provide the first evidence of the presence and co-localization of critical neurotransmitters in the SSS of the human brain, thus contributing to a better understanding of the sinus functional role.

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

Neuropeptide Y in the noradrenergic neurons induces the development of cardiometabolic diseases in a transgenic mouse model

Neuropeptide Y (NPY) is a neuropeptide widely expressed in the brain and a peptide transmitter of sympathetic nervous system (SNS) co-released with noradrenaline (NA) in prolonged stress. Association of a gain-of-function polymorphism in the human NPY gene with dyslipideamia, diabetes and vascular diseases suggests that increased NPY plays a role in the pathogenesis of the metabolic syndrome in humans. In the hypothalamus, NPY plays an established role in the regulation of body energy homeostasis. However, the effects of NPY elsewhere in the brain and in the SNS are less explored. In order to understand the role of NPY co-expressed with NA in the sympathetic nerves and brain noradrenergic neurons, a novel mouse model overexpressing NPY in noradrenergic neurons was generated. The mouse displays metabolic defects such as increased adiposity, hepatosteatosis, and impaired glucose tolerance as well as stress-related hypertension and increased susceptibility to vascular wall hypertrophy. The mouse phenotype closely reflects the findings of the several association studies with human NPY gene polymorphisms, and fits with the previous work on the effects of stress-induced NPY release on metabolism and vasculature. Thus, in addition of promoting feeding and obesity in the hypothalamus, NPY expressed in the noradrenergic neurons in the brain and in the SNS induces the development of cardiometabolic diseases.

Review of the neuroanatomic landscape implicated in glucose sensing and regulation of nutrient signaling: immunophenotypic localization of diabetes gene Tcf7l2 in the developing murine brain

Genetic variants in the transcription factor 7-like 2(Tcf7l2) gene have been found to confer a significant risk of type 2 diabetes and attenuated insulin secretion. Based on its genomic wide association Tcf7l2 is considered the single most important predictor of diabetes to date. Previous studies of Tcf7l2 mRNA localization in the adult brain suggest a putative role of Tcf7l2 in the CNS regulation of energy homeostasis. The present study further characterizes the immunophenotypic distribution of peptide expression in the brains of Tcf7l2 progeny during developmental time periods between E12.5 and P1. Tcf7l2(-/-) is lethal beyond P1. Results show that while negligible TCF7L2 expression is found in the developing brains of Tcf7l2(-/-)mice, TCF7L2 protein is relatively widespread and robustly expressed in the brain by E18.5 and exhibits specific expression within neuronal populations and regions of the brain in Tcf7l2(+/-) and Tcf7l2(+/+) progeny. Strong immunophenotypic labeling was found in the diencephalic structure of the thalamus that suggests a role of Tcf7l2 in the development and maintenance of thalamic activity. Strongly expressed TCF7L2 was localized in select hypothalamic and preoptic nuclei indicative of Tcf7l2 function within neurons controlling energy balance. Definitive neuronal staining for TCF7L2 within nuclei of the brain stem and circumventricular organs extends TCF7L2 localization within autonomic neurons and its potential integration with autonomic function. In addition robust TCF7L2 expression was found in the tectal and tegmental structures of the superior and inferior colliculi as well as transient expression in neuroepithelium of the cerebral and hippocampal cortices of E16 and E18.5. Patterns of TCF7L2 peptide localization when compared to the adult protein synthetic chemical/anatomical landscape of glucose sensing exhibit a good correlational fit between its expression and regions, nuclei, and pathways regulating energy homeostasis via integration and response to peripheral endocrine, metabolic and neuronal signaling. TCF was also found co-localized with peptides that regulate energy homeostasis including AgRP, POMC and NPY. TCF7l2, some variants of which have been shown to impair GLP-1-induced insulin secretion, was also found co-localize with GLP-1 in adult TCF wild type progeny. Impaired Tcf7l2-mediated neural regulation may contribute to the risk and/or underlying pathophysiology of type 2 diabetes that has found high expression in genomic studies of Tcf7l2 variants.

Tracing neural connections to pain pathways with relevance to primary headaches

Background: Symptoms associated with primary headaches are linked to cranial vascular activity and to the central nervous system (CNS).

Review: The central projections of sensory nerves from three cranial vessels are described in order to further understand pain mechanisms involved in primary headaches. Tracers that label small and large calibre primary afferent fibres revealed similar distributions for the central terminations of sensory nerves in the superficial temporal artery, superior sagittal sinus and middle meningeal artery. The sensory nerve fibres from the vessels pass through both the trigeminal and rostral cervical spinal nerves and terminate in the ventrolateral part of the C1-C3 dorsal horns and the caudal and interpolar divisions of the spinal trigeminal nucleus. The C-fibre terminations were located mainly in the superficial layers (Rexed laminae I and II), and the Aδ-fibres terminated in the deep layers (laminae III and IV). The rostral projections from the ventrolateral C1-C2 dorsal horn revealed terminations in the medial and lateral parabrachial nuclei, the cuneiform nucleus, the periaqueductal gray, the deep mesencephalic nucleus, the thalamic posterior nuclear group and its triangular part, and the thalamic ventral posteromedial nucleus. The terminations in the pons and midbrain were predominately bilateral, whereas those in the thalamus were confined to the contralateral side.

Conclusions: The observations, done in rats with the understanding that similar trigeminovascular organization exists in man, reveal vascular projections into the brainstem and some aspects of the central regions putatively involved in the central processing of noxious craniovascular signals.

Expression of trophic peptides and their receptors in chromaffin cells and pheochromocytoma

Pheochromocytomas are catecholamine-producing tumors arising from chromaffin cells of the adrenal medulla or extra-adrenal location. Along with catecholamines, tumoral cells produce and secrete elevated quantities of trophic peptides which are normally released in a regulated manner by the normal adrenal medulla. Among these peptides, the amounts of pituitary adenylate cyclase-activating polypeptide (PACAP), adrenomedullin (AM), and neuropeptide Y (NPY) are particularly high. These peptides can exert endocrine, paracrine or autocrine effects in numerous cell types. In particular, they have been shown to be involved in cell proliferation and survival, catecholamine production and secretion, and angiogenesis. Some of these processes are exacerbated in pheochromocytomas, raising the possibility of the involvement of trophic peptides. Here, we review the expression levels of NPY, PACAP, and AM and theirs receptors in chromaffin cells and pheochromocytomas, and address their possible implication in the adrenal medulla tumorigenesis and malignant development of pheochromocytomas.

Microvascular system of the lumbar dorsal root ganglia in rats. Part II: neurogenic control of intraganglionic blood flow

OBJECT

The dorsal root ganglion (DRG) should not be overlooked when considering the mechanism of low-back pain and sciatica, so it is important to understand the morphological features of the vascular system supplying the DRG. However, the neurogenic control of intraganglionic blood flow has received little attention in the past. The authors used an immunohistochemical technique to investigate the presence and distribution of autonomic and sensory nerves in blood vessels of the DRG.

METHODS

Ten Wistar rats were used. To investigate the mechanism of vasomotion on the lumbar DRG, the authors used immunohistochemical methods. Sections were incubated overnight with antisera to tyrosine hydroxylase (TH), aromatic L-amino-acid decarboxylase (AADC), 5-hydroxytryptamine, substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP), somatostatin (SOM), neuropeptide Y (NPY), leucine-enkephalin, and cholineacetyl transferase (Ch-E). The avidin-biotin complex method was used as the immunohistochemical procedure, and the sections were observed under a light microscope.

RESULTS

In the immunohistochemical study, TH-, AADC-, SP-, CGRP-, VIP-, SOM-, NPY-, and Ch-E-positive fibers were seen within the walls of blood vessels in the DRG. This study revealed the existence of a comprehensive perivascular adrenergic, cholinergic, and peptidergic innervation of intraganglionic blood vessels, with a possible role in neurogenic regulation (autoregulation) of intraganglionic circulation.

CONCLUSIONS

The presence of perivascular nerve plexuses around intraganglionic microvessels suggests that autonomic nerves play an important role in intraganglionic circulation.

Vasomotion of intraradicular microvessels in rat

STUDY DESIGN

This study is to investigate the changes of vasomotion of intraradicular microvessels in vivo.

OBJECTIVE

We have observed microvascular corrosion casts of the lumbar nerve root by scanning electron microscopy and used an immunohistochemical technique to investigate the presence and distribution of autonomic and sensory nerve in blood vessels of the nerve root.

SUMMARY OF BACKGROUND DATA

It is generally considered that the genesis of radiculopathy associated with the degenerative conditions of the spine may result from both mechanical compression and circulatory disturbance. However, the neurogenic control of intraradicular blood flow has received little attention in the past.

METHODS

For three-dimensional observation of intraradicular vessels, we used scanning electron microscopic examination of microvascular corrosion casts in ten Wister rats. To investigate the mechanism of vasomotion of the nerve root, we used immunohistochemical methods. The sections were incubated overnight with antisera to tyrosine hydroxylase, choline acetyl transferase, substance P, calcitonin-gene-related peptide, vasoactive intestinal peptide, somatostatin, neuropeptide Y, leucine-enkephalin, cholecystokinin octapeptide, brain-nitric oxide synthase, and endothelium-nitric oxide synthase. Abidin-biotin complex method was used as the immunohistochemical procedure and the sections were observed under the light microscope.

RESULTS

The general view of whole vascular casts of the lumbar spinal cord and nerve roots showed a high density of vessels. Bifurcation or anastomoses of capillaries approximately took place at right angles in a T-shaped pattern and capillaries showed a lot of ring-like compressions. This ring-like compression on the cast may represent a vascular sphincter in the microvessels. This study also reveals the existence of perivascular adrenergic, cholinergic, peptidergic, and nitroxydergic innervation with a possible role in neurogenic regulation of nerve root circulation.

CONCLUSION

Perivascular nerve plexuses around intraradicular microvessels suggest that the autonomic nerves play an important role in intraradicular circulation.

Cortical cooling induces conditioned consumption reduction in male rats

Previous studies have shown that male rats acquire a conditioned reduction in consumption of a sucrose solution when consumption of that taste solution is followed by cooling the caudate putamen. Because the shaft of the cold probe was not insulated, this cooling also included the cortex and meninges overlying the caudate putamen. When cooling the meninges was eliminated as a factor, the conditioned consumption reduction was weaker but it was not abolished. This suggests that meninges cooling contribute to the conditioned consumption reduction induced when all three structures are cooled, but it is not sufficient. Five experiments were designed to determine whether cooling the cortex also contributes. In the first experiment, the temperature of the cortex and meninges overlying the caudate putamen was measured during cooling. In the following three experiments the ability of male rats to acquire a conditioned consumption reduction was determined after pairing a sucrose solution with cooling the cortex and meninges overlying the caudate putamen, cooling the cortex with and without cooling the dura meninges membrane, and cooling the cortex with and without cooling the entire meninges. When the cortex was cooled without cooling the caudate putamen, dura, or entire meninges, a conditioned consumption reduction was acquired. The last experiment demonstrated that contingent pairing of sucrose and cortical cooling was required to obtain consumption reduction. These results clearly indicate that cortical cooling contributes to the acquisition of conditioned consumption reduction induced when the caudate putamen and overlying cortex and meninges are cooled. Two hypotheses are suggested to account for the ability of neural cooling to act as an unconditioned stimulus in the conditioned consumption reduction paradigm: (1) neuronal inactivation produces physiological changes that can serve as unconditioned stimuli and (2) cooling itself produces physiological changes that can serve as unconditioned stimuli.

Modulator role of neuropeptide Y in human vascular sympathetic neuroeffector junctions

Reverse transcription polymerase chain reaction (RT-PCR) studies identified the mRNA coding for the Y1 and Y2 receptors in human mammary artery/vein and saphenous vein biopsies. Y1 receptors are expressed in vascular smooth muscles and potentiate the contractile action of sympathetic co-transmitters, adenosine triphosphate (ATP) and noradrenaline (NA); BIBP 3226, a competitive Y1 receptor antagonist, blocked the neuropeptide Y (NPY)-induced modulation. The Y2 receptor is expressed in sympathetic nerves terminals and modulates the pool of sympathetic co-transmitters released at the neuroeffector junction. NPY plays a dual role as a modulator of sympathetic co-transmission; it facilitates vascular smooth muscle reactivity and modulates the presynaptic release of ATP and NA. Sympathetic reflexes regulate human vascular resistance, where NPY plays a modulator role of paramount importance following increased sympathetic discharges, such as stress and vascular disease.

Long-term inhibition of angiotensin prevents reduction of periarterial innervation of calcitonin gene-related peptide (CGRP)-containing nerves in spontaneously hypertensive rats

The aim of this study was to investigate age-related changes in the density of calcitonin gene-related peptide (CGRP)-containing nerve fibers in spontaneously hypertensive rats (SHR) and the effects of long-term inhibition of the renin-angiotensin system on these changes. The density of immunocytochemically stained nerve fibers in the mesenteric artery was quantified by computer-assisted image processing. An age-related decrease in the density of CGRP-like immunoreactive (LI)-containing nerve fivers but not neuropeptide Y (NPY)-LI-containing sympathetic nerve fibers was found in the mesenteric artery of SHR but not Wistar Kyoto rats (WKY). The density of NPY-LI-containing sympathetic nerve fibers was significantly greater in SHR than in WKY. SHR were treated for 7 weeks with angiotensin converting enzyme inhibitor (0.005% temocapril), angiotensin II type-1 (AT1) receptor antagonist (0.025% losartan) or vasodilator (0.01% hydralazine) in their drinking water. Each drug treatment significantly lowered the systolic blood pressure measured by tail-cuff method. Long-term treatment of SHR with temocapril and losartan significantly increased the density of CGRP-LI-containing nerve fibers in mesenteric arteries. However, the density after hydralazine treatment was similar to the level in non-treated SHR. The density of NPY-LI-containing nerve fibers was not increased by any of the drug treatments. These results suggest that long-term inhibition of the renin-angiotensin system in SHR prevents remodeling of CGRPergic nerve fibers and prevents the reduction of CGRPergic nerve function.

Neurobiology in primary headaches

Primary headaches such as migraine and cluster headache are neurovascular disorders. Migraine is a painful, incapacitating disease that affects a large portion of the adult population with a substantial economic burden on society. The disorder is characterised by recurrent unilateral headaches, usually accompanied by nausea, vomiting, photophobia and/or phonophobia. A number of hypothesis have emerged to explain the specific causes of migraine. Current theories suggest that the initiation of a migraine attack involves a primary central nervous system (CNS) event. It has been suggested that a mutation in a calcium gene channel renders the individual more sensitive to environmental factors, resulting in a wave of cortical spreading depression when the attack is initiated. Genetically, migraine is a complex familial disorder in which the severity and the susceptibility of individuals are most likely governed by several genes that vary between families. Genom wide scans have been performed in migraine with susceptibility regions on several chromosomes some are associated with altered calcium channel function. With positron emission tomography (PET), a migraine active region has been pointed out in the brainstem. In cluster headache, PET studies have implicated a specific active locus in the posterior hypothalamus. Both migraine and cluster headache involve activation of the trigeminovascular system. In support, there is a clear association between the head pain and the release of the neuropeptide calcitonin gene-related peptide (CGRP) from the trigeminovascular system. In cluster headache there is, in addition, release of the parasympathetic neuropeptide vasoactive intestinal peptide (VIP) that is coupled to facial vasomotor symptoms. Triptan administration, activating the 5-HT(1B/1D) receptors, causes the headache to subside and the levels of neuropeptides to normalise, in part through presynaptic inhibition of the cranial sensory nerves. These data suggest a central role for sensory and parasympathetic mechanisms in the pathophysiology of primary headaches. The positive clinical trial with a CGRP receptor antagonist offers a new promising way of treatment.

Neuropeptide Y (NPY) and C-flanking peptide of NPY in the pineal gland of normal and ganglionectomized sheep

The present immunohistochemical study describes the presence and distribution of nerve fibers containing neuropeptide Y (NPY), and C-Flanking Peptide Of NPY (CPON) in the pineal gland of the sheep. Nerve fibers were detected by using a series of antisera directed against NPY or against CPON. Many positive immunoreactive nerve fibers were identified in the pial capsule of the pineal, in connective septae and in the parenchyma between pinealocytes. The intraparenchymal fibers were particularly evident and created an extensive network throughout the gland. Nerve fibers immunoreactive for all the peptides were also observed in the posterior commissure and in the stria medullaris thalami. No NPY- or CPON-positive neurons were found in the pineal gland. In order to study the site of origin of NPY- and CPON-immunoreactive nerve fibers, the superior cervical ganglia were bilaterally removed in a series of animals. Sympathetic denervation was checked by using an antiserum against tyrosine hydroxylase (TH). Nearly all TH-immunoreactive elements disappeared in the pineal glands of animals sacrificed 15 days after surgery. Also the density of NPY- and CPON-immunoreactive nerve fibers decreased in the animals after the ganglionectomy. However, a number of nerve fibers still remained in the gland. These data indicate that some NPY- and CPON-immunoreactive nerve fibers of the sheep pineal gland derive from an extrasympathetic origin. The very dense innervation of the sheep pineal gland with nerve fibers containing NPY and CPON strongly indicates a functional role for this family of peptides in the pineal gland of this species.

Immunohistochemical distribution of neuropeptide Y in the mesencephalon and rhombencephalon of carp, Cyprinus carpio L. (Cyprinidae: Teleostei)

The localization of neuropeptide Y (NPY)-immunoreactive elements was investigated in the mesencephalon and rhombencephalon of carp, Cyprinus carpio, by using antisera raised against porcine NPY and the immunoperoxidase technique. Concurrently, to identify the distribution of NPY-immunoreactivity, we developed an atlas of the studied areas based on Nissl-stained sections. The NPY-immunoreactive (NPY-ir) elements were located in many zones of the mesencephalon and rhombencephalon. In the mesencephalon, positive fibers were the most abundant elements while neurons were scarce. The rhombencephalon rostral part was characterized by a low to moderate fiber density, distributed in the ventro-medial and ventro-lateral region. Differently the caudal part of the rhombencephalon exhibited several NPY-ir elements. In particular, a high density of immunoreactivity was located in the gustatory area at the level of the nucleus (n.) originis nervi glossopharyngei, in the n. nervi vagi, and in the vagal lobe. The latter can be considered a valid neuroanatomical model for the study of gustatory signal processing in vertebrates. Our results regarding the primary gustatory centers give neuroanatomical support to the view that NPY may act as a neurotransmitter and/or a neuromodulator in a wide neural network for feeding behavior control.

Neuropeptide Y, ubiquitous and elusive

This paper reviews aspects of NPY research that were emerging in 1985, shortly after the isolation and characterization of the peptide. NPY had become known for its widespread distribution especially in the central and peripheral nervous systems, but also in the gastro-intestinal and respiratory tracts and in fibers innervating smooth muscle around blood vessels. Consistent with its distribution, it was determined that NPY is a potent vasoconstrictor, affects neuroendocrine systems and is involved in appetite regulation--areas of research still relevant today. Through advances in technology knowledge about NPY's role in these and newly discovered physiological functions has deepened considerably. Successful cloning of a series of NPY receptors has opened up new and complex research vistas. Lately, the creation of mice genetically modified for NPY as well as for several receptor subtypes has brought many puzzling observations--followed by questions yet to be answered.

Expression of neuropeptide Y is increased in murine endometrial epithelium during the peri-implantation period under regulation by sex steroids

Oligopeptide hormones are involved in cell–cell interaction during embryonal implantation and neuropeptide Y (NPY) is expressed in the human placenta and decidual cells in the third trimester of pregnancy. However, there is no report regarding the intrauterine localisation and the functions of NPY during the peri-implantation period. In the present study, the spatiotemporal changes in NPY expression in the murine uterus during the peri-implantation period were investigated using reverse transcription–polymerase chain reaction (RT-PCR), quantitative RT-PCR and immunohistochemical techniques, as were the effects of sex steroids on NPY mRNA expression in primary cultured murine uterine epithelial cells. Neuropeptide Y mRNA was increased in the pregnant murine uterus, as well as in the pseudopregnant murine uterus, during the peri-implantation period. Immunohistochemical analysis revealed increases in NPY expression in luminal and glandular epithelial cells and decidualised stromal cells. Neuropeptide Y mRNA expression was strongly induced in cultured epithelial cells in response to sex steroids. The data suggest that NPY is involved in cell–cell interactions during embryonic implantation.

Carotid labyrinth of amphibians

The amphibian carotid labyrinth is a characteristic maze-like vascular expansion at the bifurcation of the common carotid artery into the internal and external carotid arteries. The carotid labyrinths of anurans are spherical and those of urodeles are oblong. In the intervascular stroma of both anuran and urodelan carotid labyrinths, the glomus cells (type I cells, chief cells) are distributed singly or in clusters between connective tissue cells and smooth muscle cells. In fluorescence histochemistry, the glomus cells emit intense fluorescence for biogenic monoamines. In fine structure, the glomus cells are characterized by a number of dense-cored vesicles in their cytoplasm. The glomus cells have long, thin cytoplasmic processes, some of which are closely associated with smooth muscle cells, endothelial cells, and pericytes. Afferent, efferent, and reciprocal synapses are found on the glomus cells. The morphogenesis of the carotid labyrinth starts in the larvae at the point where the carotid arch descends to the internal gills. Through the early stages of larval development, the slightly expanded region of the external carotid artery becomes closely connected with the carotid arch. By the end of the foot stage, the expanded region becomes globular, and at the final stage of metamorphosis the carotid labyrinth is close to its adult form. In fine structure, the glomus cells appear as early as the initial stage of larval development. At the middle stages of development, the number of dense-cored vesicles increases remarkably. Distinct afferent synapses are found in juveniles, although efferent synapses can be seen during metamorphosis. The carotid labyrinth is innervated by nerve fibers containing several kinds of regulatory neuropeptides. Double-immunolabeling in combination with a multiple dye filter system demonstrates the coexistence of two different neuropeptides. The amphibian carotid labyrinth has been electrophysiologically confirmed to have arterial chemo- and baroreceptor functions analogous to those of the mammalian carotid body and carotid sinus. The ultrastructural characteristics of the glomus cells during and after metamorphosis suggest that the glomus cells contribute to the chemoreception after metamorphosis. The three-dimensional fine structure of vascular corrosion casts suggests that the amphibian carotid labyrinth has the appropriate architecture for controlling vascular tone and the findings throughout metamorphosis reveal that the vascular regulatory function begins at an early stage of metamorphosis. In addition, immunohistochemical studies suggest that the vascular regulation in the carotid labyrinth is under peptidergic innervation. Thus, the multiple functions of the carotid labyrinth underline the importance of this relatively small organ for maintenance of homeostasis and appropriate blood supply to the cephalic region.

The meninges contribute to the conditioned taste avoidance induced by neural cooling in male rats

After consumption of a novel sucrose solution, temporary cooling of neural areas that mediate conditioned taste avoidance can itself induce conditioned avoidance to the sucrose. It has been suggested that this effect is either a result of inactivation of neurons in these areas or of cooling the meninges. In a series of studies, we demonstrated that cooling the outer layer of the meninges, the dura mater, does not contribute to the conditioned taste avoidance induced by cooling any of these areas. The present experiments were designed to determine whether the inner layers of the meninges are involved. If they are involved, then one would expect that cooling locations in the brain that do not mediate conditioned taste avoidance, such as the caudate putamen (CP), would induce conditioned taste avoidance as long as the meninges were cooled as well. One also would expect that cooling neural tissue without cooling the meninges would reduce the strength of the conditioned taste avoidance. Experiment 1 established that the temperature of the neural tissue and meninges around the cold probes implanted in the CP were cooled to temperatures that have been shown to block synaptic transmission. Experiment 2 demonstrated that cooling the caudate putamen and overlying cortex and meninges induced conditioned taste avoidance. In experiment 3, a circle of meninges was cut away so that the caudate putamen and overlying cortex could be cooled without cooling the meninges. The strength of the conditioned taste avoidance was substantially reduced, but it was not entirely eliminated. These data support the hypothesis that cooling the meninges contributes to the conditioned taste avoidance induced by neural cooling. They also allow the possibility that neural inactivation produces physiological changes that can induce conditioned taste avoidance.

The role of the dura in conditioned taste avoidance induced by cooling the area postrema of male rats

Experiments were designed to assess the contribution of the dura mater to the formation of conditioned taste avoidance induced by cooling the area postrema. The results of the first experiment verified that the temperature of the dura showed a temperature gradient at various distances from the tip of the cold probe. In the second and third experiments, a circle of dura was cut away so that different amounts of the area postrema could be cooled without cooling the overlying dura. Cooling the dura plus the area postrema did not produce a stronger avoidance than just cooling the area postrema. In the fourth experiment, the cerebellar cortex was cooled with and without cooling the dura. Cooling the cerebellar cortex produced conditioned taste avoidance, and cooling the dura plus the cerebellar cortex did not produce a stronger avoidance. Taken together, these results suggest that cooling the dura mater does not contribute to the conditioned taste avoidance induced by cooling the area postrema. The results of the fifth experiment showed that cooling the area postrema produced a stronger conditioned taste avoidance than cooling the cerebellar cortex. It is suggested that the avoidance induced by cooling both of these structures is the result of physiological changes occurring when neurons in these structures are inactivated and when the subdural meninges are cooled. Furthermore, these changes are more severe when the area postrema is cooled.

Neuronal messengers in the human cerebral circulation

In recent years our knowledge of the nervous control of the cerebral circulation has increased. The use of denervations and retrograde tracing in combination with immunohistochemical techniques has demonstrated that cerebral vessels are supplied with sympathetic, parasympathetic, and sensory nerve fibers and possibly central pathways containing a multiplicity of new transmitter substances in addition to the classical transmitters. The majority of these transmitters are neuropeptides. More recently it has been suggested that a gaseous transmitter, nitric oxide (NO) also could participate in the neuronal regulation of cerebral blood flow. Although little is known about the physiological actions and inter-relationships among all these putative neurotransmitters, their presence within cerebrovascular nerve fibers will make it necessary to revise our view on the mechanisms of cerebrovascular neurotransmission.

Neuropeptide Y-mediated constriction and dilation in rat middle cerebral arteries

Neuropeptide Y (NPY) is an important vasoconstrictor in the cerebral circulation. Its constrictor response is because of activation of NPY receptors on the vascular smooth muscle (VSM). Little is known regarding the effects of NPY on the endothelium. In the current study, the authors tested the hypothesis that NPY can either constrict or dilate rat middle cerebral arteries (MCAs). Constriction is elicited by stimulating receptors on the VSM; dilation is elicited by stimulating receptors on the endothelium. Middle cerebral arteries were isolated, cannulated with micropipettes, pressurized to 85 mm Hg, and luminally perfused. The extraluminal application of NPY (mixed agonist), [Leu31, Pro34]-NPY (Y1 agonist), or NPY-[13-36] (Y2 agonist) produced concentration-dependent constrictions. BIBP 3226 (Y1 selective antagonist) significantly attenuated the NPY- and [Leu31, Pro34]-NPY-induced constrictions. The luminal application of NPY, [Leu31, Pro34]-NPY, and NPY-[13-36] produced concentration-dependent dilations of MCAs. The maximum dilation produced by the NPY receptor agonists was approximately 40% of the dilation elicited by the luminal administration of 10(-5) mol/L ATP. Dilations elicited by luminal NPY, [Leu31, Pro34]-NPY, or NPY-[13-36] were abolished by inhibition of nitric oxide synthase with 10(-5) mol/L Nomega-nitro-L-arginine methyl ester (L-NAME) or removal of the endothelium. Dilations produced by luminal NPY or luminal [Leu31, Pro34]-NPY were not affected by BIBP 3226. Stimulation of NPY receptors on vascular smooth muscle constricted MCAs. Stimulation of an NPY receptor other than the Y1 subtype on endothelium dilated the MCAs by releasing nitric oxide.

Functional effects of neuropeptide Y receptors on blood flow and nitric oxide levels in the human nose

The aim of this study was to examine dose-dependent effects of intranasal application of neuropeptide Y (NPY) on nasal mucosal blood flow, blood content, and intranasal nitric oxide (NO) concentration. Blood flow was measured by laser Doppler flowmetry (LDF) and blood content by rhinomanometry. Mucosal biopsies were taken for investigation of Y1 and Y2 receptor mRNA expression, using the reverse transcriptase-polymerase chain reaction (RT-PCR). Intranasal application of NPY evoked a dose-dependent reduction of nasal mucosal blood flow. Maximal vasoconstriction, seen at 12 nmol, was -37.5 +/- 6.2%, p < 0.05 (n = 9). The vasoconstrictive effect developed within 2 to 4 min and lasted > 17 min. NPY evoked a dose-dependent reduction of nasal airway resistance (NAR) on the ipsilateral side. Maximal decrease was -24.0 +/- 10.0% at 12 nmol, p < 0.05 (n = 9). There was a decrease in nasal NO production on the ipsilateral side after application of NPY 12 nmol (-7.4 +/- 1.2%, p < 0.05, n = 8). RT-PCR products corresponding to Y1 receptor but not Y2 receptor mRNA were obtained from biopsies of the nasal mucosa. In conclusion, NPY is a potent vasoconstrictor in the human nose reducing mucosal blood flow, as well as the blood content. The effect is probably mediated via Y1 receptors. NPY receptor agonists may prove beneficial in the treatment of the congested nose in allergic or vasomotor rhinitis.

The human superior cervical ganglion: neuropeptides and peptide receptors

Noradrenaline (NA)- and neuropeptide Y (NPY)-containing cell bodies were found to occur in high numbers (>75% of all cells were positive) in the human superior cervical ganglion and distributed homogeneously throughout the ganglion and showed colocalisation. A few cell bodies were VIP-immunoreactive (-ir) (less than 5%) but none of them showed NOS-, CGRP- or SP-ir. Receptor mRNA expression was studied with RT-PCR. Total RNA from the superior cervical ganglion was successfully extracted. By using appropriate sense and antisense oligonucleotides designed from the published human sequences, we could show the presence of mRNA for the human NPY Y1, NPY Y2 and VPAC1 receptors but not CGRP1 receptor mRNA.

C-peptide potentiates the vasoconstrictor effect of neuropeptide Y in insulin-dependent diabetic patients

Recent findings suggest that proinsulin C-peptide improves renal and nerve function as well as microcirculation in patients with insulin-dependent diabetes possibly by stimulating Na-K+-ATPase activity. Furthermore, in vitro studies on proximal rat renal tubule cells show that the effect of C-peptide on Na+, K+-ATPase activity is potentiated in the presence of the vasoconstrictor peptide neuropeptide Y. The aim of the present study was to examine whether the effects of neuropeptide Y on resting forearm blood flow in insulin-dependent patients is altered in the presence of C-peptide. Forearm blood flow was measured by a plethysmographic method in eight insulin-dependent patients and six healthy control subjects. Neuropeptide Y (20, 200 and 2000 pmol min(-1)) was infused into the brachial artery before and during an i.v. infusion of C-peptide (5 pmol kg(-1) min(-1)). Basal blood flow was 36.7 +/- 2.2 mL min(-1) L(-1) tissue. It decreased in a dose dependent manner by 11 +/- 2, 18 +/- 3 and 25 +/- 3%, respectively, during infusion of neuropeptide Y. Administration of C-peptide increased basal blood flow by 25 +/- 6%, to 46.3 +/- 3.5 mL min(-1) L(-1) tissue (P < 0.01) and forearm glucose uptake by 76 +/- 34% (P < 0.05). Infusion of the three doses of neuropeptide Y during administration of C-peptide decreased forearm blood flow by 14 +/- 4, 22 +/- 3 and 42 +/- 4%. There was a significant difference (43%, P < 0.001) between the reduction in blood flow evoked by the high dose (2000 pmol min(-1)) of neuropeptide Y before and during C-peptide infusion. Similar differences were also obtained when data were calculated as changes in vascular resistance. C-peptide did not affect resting forearm blood flow or the response to neuropeptide Y in healthy controls. In conclusion, the present data demonstrate that C-peptide increases resting forearm blood flow and augments the vasoconstrictor effects of neuropeptide Y in insulin-dependent patients.

Hypoxic adaptation of the peptidergic innervation in the rat carotid body

The abundance of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)-, and neuropeptide Y (NPY)-immunoreactive nerve fibers in the carotid body was compared between normoxic and chronically hypoxic rats (10% O2 and 3.0-4.0% CO2 for 3 months). The immunoreactive fibers appeared as thin processes with many varicosities, and were distributed mainly around the vasculatures. In the normoxic control carotid body, NPY fibers were more numerous than VIP, CGRP, and SP fibers. In the chronically hypoxic rats, the carotid body was enlarged several fold, and the mean absolute number of VIP and NPY fibers was 3.88 and 2.22 times higher than in the normoxic carotid body, respectively, although that of SP and CGRP fibers was not changed. When expressed as density per unit area of the parenchyma, the density of SP and CGRP fibers in the chronically hypoxic carotid body decreased significantly to under 50%, the density of VIP fibers increased significantly 1.80 times, and the density of NPY fibers were unchanged. Immunoreactivity for four neuropeptides was not found in the glomus cells of normoxic or chronically hypoxic carotid bodies. These results suggest that altered peptidergic innervation of the chronically hypoxic carotid body is one feature of hypoxic adaptation. Because these neuropeptides are vasoactive in nature, altered carotid body circulation may contribute to modulation of the chemosensory mechanisms by chronic hypoxia.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

Immunohistochemical localisation of regulatory neuropeptides in human circumvallate papillae

The occurrence and distribution of neuropeptide-containing nerve fibres in the human circumvallate papillae were examined by the peroxidase-antiperoxidase immunolocalisation method using surgical specimens that had not been subjected to radiotherapy, and the abundance of neuropeptide-containing fibres was expressed as the percentage of total nerve fibres demonstrated by protein gene product (PGP) 9.5 immunoreactivity for a quantitative representation of these peptidergic fibres. Substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive (IR) nerve fibres were densely distributed in the connective tissue core of the circumvallate papillae, and some SP and CGRP-IR fibres were associated with the taste buds. A moderate number of vasoactive intestinal polypeptide (VIP)-IR fibres and a few galanin (GAL)-IR fibres were also seen in the connective tissue core and subepithelial layer. There were, however, no VIP-IR or GAL-IR fibres associated with the taste buds. Neuropeptide Y (NPY)-IR fibres were few and were associated with the blood vessels. Within the epithelium of the circumvallate papillae, no peptidergic fibres were found, although a number of PGP 9.5-IR fibres were detected. The abundance of SP, CGRP, VIP, and GAL-IR fibres expressed as the percentage of total PGP 9.5 IR fibres was 25.35+/-3.45%, 22.18+/-3.26%, 10.23+/-1.18%, and 4.12+/-1.05%, respectively. The percentage of NPY-IR fibres was below 3%. In a deeper layer of the papillae, a few VIP, GAL, and NPY-IR ganglion cells were found, and VIP immunoreactivity was detected in a few cells of the taste buds. There was no somatostatin, leucine enkephalin, or methionine enkephalin immunoreactivity in the circumvallate papillae. These results suggest that the dense SP and CGRP-IR fibres within the connective tissue core of the human circumvallate papillae may be involved in the deep sensation of the tongue.

Neuropeptide Y: some viewpoints on a multifaceted peptide in the normal and diseased nervous system

Using immunohistochemical and in situ hybridization methodologies the localization of neuropeptide tyrosine (NPY) and two of its receptors, the Y1- and the Y2-receptor (R), has been analysed in various tissues in normal animals and animals subjected to different experimental procedures as well as animals with a genetic and an acquired disease. (1) Dorsal root ganglion (DRG) neurons are discussed with special focus on the effect of peripheral nerve injury. In normal DRG neurons NPY cannot be detected, whereas Y1-R mRNA and Y1-R-like immunoreactivity (LI) are strongly expressed. The Y1-Rs decorate the membrane of the cell soma and are not transported peripherally into the axonal branches. Y2-R mRNA levels are low. After axotomy there is a marked increase in NPY, a decrease in Y1-Rs and an increase in Y2-Rs. The Y2-R is transported centrifugally. These findings suggest that NPY-ergic mechanisms participate in the adaptive changes of sensory neurons in response to injury. (2) Using specific antibodies the cellular and subcellular localization of the Y1-R protein have been analysed in cerebral blood vessels. The results demonstrate high concentrations of receptors in smooth muscle cells around pial arterioles with lower numbers in large vessels on the basal surface of the brain. In many regions the receptors 'disappear' after the arterioles have entered the brain tissue. At the ultrastructural level the receptors are found both on the endothelial and peripheral side of the muscle cells as well as laterally, where muscle cells oppose each other. The receptor protein is often associated with small vesicles. No NPY-positive nerve fibers were found around the Y1-R-rich arterioles, but they were only seen around the arteries with low Y1-R levels. The Y1-R-rich arterioles were, however, seen close to numerous NPY-positive fibers originating from central interneurons. These findings raise the possibility that centrally originating NPY can influence cerebral blood flow, possibly by stimulating NPY-Rs on the peripheral side of the muscle cells. However, also blood borne NPY, released under special conditions, such as stress from sympathetic nerves and the adrenal medulla and transported with blood, may stimulate receptors on the endothelial side of the smooth muscle cells. (3) In the arcuate nucleus Y1- and Y2-Rs are found, whereby the Y1-Rs are located in its ventro-medial portion and co-localized with POMC peptides, and the Y2-R in its ventromedial part, partly co-localized with NPY. NPY nerve endings makes synaptic contact with the POMC/Y1-R-positive neurons. In a mouse model for genetic anorexia very high levels of NPY were observed in arcuate neurons as compared to control mice. However, NPY mRNA levels were not different between the two groups. Taken together these findings are in good agreement with the view that NPY in the arcuate nucleus plays an important role in regulating feeding behaviour. (4) After intracerebral prion inoculation in mice an upregulation of NPY mRNA levels was observed in CA3 pyramidal neurons, and this effect was seen at a time point just before the first behavioural symptoms were manifested. At approximately the same time there was a dramatic decrease in Y2-R binding in strata oriens and radiatum of the CA1 region of the hippocampus, whereas in other regions no changes or much smaller changes were observed. Also, there was only a very slight decrease in Y2-R mRNA levels in CA3 neurons. It thus appears as if the prion disease prevents ligand binding to the Y2-R, perhaps by influencing traffic of receptor proteins, possibly at the level of cell membrane-associated caveolae, which have been implicated in the conversion of normal protein to scrapie protein. It is possible that these changes in NPY-ergic mechanisms may underlie some of the central symptoms associated with the prion disease. (ABSTRACT TRUNCATED)

Global cerebral blood flow decreases during pain

Positron emission tomography studies have identified a common set of brain regions activated by pain. No studies, however, have quantitatively examined pain-induced CBF changes. To better characterize CBF during pain, 14 subjects received positron emission tomography scans during rest, during capsaicin-evoked pain (250 micrograms, intradermal injection), and during innocuous vibration. Using the H215O intravenous bolus method with arterial blood sampling, global CBF changes were assessed quantitatively. Painful stimulation produced a 22.8% decrease in global CBF from resting levels (P < 0.0005). This decrease was not accounted for by arterial PCO2 or heart rate changes. Although the exact mechanism remains to be determined, this pain-induced global decrease represents a previously unidentified response of CBF.

Increased neuropeptide Y pressor activity in Goldblatt hypertensive rats: in vivo studies with BIBP 3226

Nanomoles of neuropeptide Y (NPY) and noradrenaline (NA), administered i.v. to pentobarbital-anesthetized rats, caused nearly equipotent dose-dependent pressor responses in normotensive rats. However, in renovascular Goldblatt hypertensive rats, the dose-response curves for both NPY and NA were significantly displaced to the left, approximately threefold. Intravenous administration of BIBP 3226 (30-180 microg/kg) did not consistently lower blood pressure, per se, but did evoke competitive antagonism of the NPY pressor response in both rat populations. The magnitude of the NPY antagonism evoked by BIBP 3226 was comparable in normotensive and hypertensive rats. The absence of NA antagonism demonstrates the selectivity of the BIBP 3226 blockade.

Direct evidence for the role of neuropeptide Y in sympathetic nerve stimulation-induced vasoconstriction

Neuropeptide Y (NPY) is a vasoconstrictor peptide and a cotransmitter with norepinephrine (NE) in sympathetic nerve terminals and is thought to be involved in sympathetic nerve stimulation (SNS)-induced vasoconstriction. Using BIBP-3226, a Y1 receptor selective antagonist, we examined this hypothesis in the isolated and perfused mesenteric vascular bed. SNS produced a frequency-dependent increase in perfusion pressure and concomitant overflow of NPY immunoreactivity in the perfusate. [Leu31,Pro34]NPY potentiated NE-induced and ATP-induced vasoconstriction, indicating the presence and biological action of Y1 receptors in this vascular bed. The potentiation effect of [Leu31,Pro34]NPY of the increase in perfusion pressure by NE, ATP, or SNS was prevented by BIBP-3226. In addition, SNS-induced vasoconstriction at both high and low frequencies was significantly attenuated by BIBP-3226 at a concentration that completely blocked the [Leu31,Pro34]NPY-induced potentiation of the NE- or ATP-induced vasoconstrictor effect. These results suggest that approximately 30% of vasoconstriction produced by SNS depends on NPY in the mesenteric vascular bed.

Localization of neuropeptide Y Y1 receptors in cerebral blood vessels

The localization of neuropeptide Y (NPY) Y1 receptor (R) -like immunoreactivity (LI) has been studied in cerebral arteries and arterioles of the rat by immunohistochemistry using fluorescence, confocal, and electron microscopy. High levels of Y1-R-LI were observed in smooth muscle cells (SMCs) in the small arterioles of the pial arterial network, especially on the basal surface of the brain, and low levels in the major basal cerebral arteries. The levels of Y1-R-LI varied strongly between adjacent SMCs. Y1-R-LI was associated with small endocytosis vesicles, mainly on the outer surface of the SMCs, but also on their endothelial side and often laterally at the interface between two SMCs. NPY-immunoreactive (Ir) nerve fibers could not be detected in association with the Y1-R-rich small arterioles but only around arteries with low Y1-R levels. A dense network of central NPY-Ir nerve fibers in the superficial layers of the brain was lying close to the strongly Y1-R-Ir small arterioles. The results indicate that NPY has a profound effect on small arterioles of the brain acting on Y1-Rs, both on the peripheral and luminal side of the SMCs. However, the source of the endogenous ligand, NPY, remains unclear. NPY released from central neurons may play a role, in addition to blood-borne NPY.