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

Both coiling and clipping induce the time-dependent release of endogenous neuropeptide Y into serum

Background

The vaso- and psychoactive endogenous Neuropeptide Y (NPY) has repeatedly been shown to be excessively released after subarachnoid hemorrhage and in numerous psychiatric disorders. NPY is stored in sympathetic perivascular nerve fibers around the major cerebral arteries. This prospective study was designed to analyze the impact of microsurgical and endovascular manipulation of the cerebral vasculature versus cranio- and durotomy alone on the serum levels of NPY.

Methods

58 patients (drop-out n = 3; m:f = 26:29; mean age 52.0 ± 14.1 years) were prospectively enrolled. The vascular group underwent repair for unruptured intracranial aneurysms (UIA) of the anterior circulation [endovascular aneurysm occlusion (EV) n = 13; microsurgical clipping (MS) n = 17]; in the non-vascular group, 14 patients received microsurgical resection of a small-sized convexity meningioma (CM), and 11 patients with surgically treated degenerative lumbar spine disease (LD) served as control. Plasma was drawn (1) before treatment (t0), (2) periprocedurally (t1), (3) 6 h postprocedurally (t2), (4) 72 h postprocedurally (t3), and (5) at the 6-week follow-up (FU; t4) to determine the NPY levels via competitive enzyme immunoassay in duplicate serum samples. We statistically evaluated differences between groups by calculating one-way ANOVA and for changes along the time points using repeated measure ANOVA.

Results

Except for time point t0, the serum concentrations of NPY ranged significantly higher in the vascular than in the non-vascular group (p < 0.001), with a slight decrease in both vascular subgroups 6 h postprocedurally, followed by a gradual increase above baseline levels until FU. At t3, the EV subgroup showed significantly higher NPY levels (mean ± standard deviation) than the MS subgroup (0.569 ± 0.198 ng/mL vs. 0.415 ± 0.192 ng/mL, p = 0.0217). The highest NPY concentrations were measured in the EV subgroup at t1, t3, and t4, reaching a climax at FU (0.551 ± 0.304 ng/mL).

Conclusion

Our study reveals a first insight into the short-term dynamics of the serum levels of endogenous NPY in neurosurgical and endovascular procedures, respectively: Direct manipulation within but also next to the major cerebral arteries induces an excessive release of NPY into the serum. Our findings raise the interesting question of the potential capacity of NPY in modulating the psycho-behavioral outcome of neurovascular patients.

Prenatal exposure to alcohol: mechanisms of cerebral vascular damage and lifelong consequences

Alcohol is a well-known teratogen, and prenatal alcohol exposure (PAE) leads to a greater incidence of many cardiovascular-related pathologies. Alcohol negatively impacts vasculogenesis and angiogenesis in the developing fetal brain, resulting in fetal alcohol spectrum disorders (FASD). Ample preclinical evidence indicates that the normal reactivity of cerebral resistance arterioles, which regulate blood flow distribution in response to metabolic demand (neurovascular coupling), is impaired by PAE. This impairment of dilation of cerebral arteries may carry implications for the susceptibility of the brain to cerebral ischemic damage well into adulthood. The focus of this review is to consolidate findings from studies examining the influence of PAE on vascular development, give insights into relevant pathological mechanisms at the vascular level, evaluate the risks of ethanol-driven alterations of cerebrovascular reactivity, and revisit different preventive interventions that may have promise in reversing vascular changes in preclinical FASD models.

Cell type specificity of neurovascular coupling in cerebral cortex

Identification of the cellular players and molecular messengers that communicate neuronal activity to the vasculature driving cerebral hemodynamics is important for (1) the basic understanding of cerebrovascular regulation and (2) interpretation of functional Magnetic Resonance Imaging (fMRI) signals. Using a combination of optogenetic stimulation and 2-photon imaging in mice, we demonstrate that selective activation of cortical excitation and inhibition elicits distinct vascular responses and identify the vasoconstrictive mechanism as Neuropeptide Y (NPY) acting on Y1 receptors. The latter implies that task-related negative Blood Oxygenation Level Dependent (BOLD) fMRI signals in the cerebral cortex under normal physiological conditions may be mainly driven by the NPY-positive inhibitory neurons. Further, the NPY-Y1 pathway may offer a potential therapeutic target in cerebrovascular disease.

Neuropeptide Y in the rostral ventromedial medulla reverses inflammatory and nerve injury hyperalgesia in rats via non-selective excitation of local neurons

Chronic pain reflects not only sensitization of the ascending nociceptive pathways, but also changes in descending modulation. The rostral ventromedial medulla (RVM) is a key structure in a well-studied descending pathway, and contains two classes of modulatory neurons, the ON-cells and the OFF-cells. Disinhibition of OFF-cells depresses nociception; increased ON-cell activity facilitates nociception. Multiple lines of evidence show that sensitization of ON-cells contributes to chronic pain, and reversing or blocking this sensitization is of interest as a treatment of persistent pain. Neuropeptide Y (NPY) acting via the Y1 receptor has been shown to attenuate hypersensitivity in nerve-injured animals without affecting normal nociception when microinjected into the RVM, but the neural basis for this effect was unknown. We hypothesized that behavioral anti-hyperalgesia was due to selective inhibition of ON-cells by NPY at the Y1 receptor. To explore the possibility of Y1 selectivity on ON-cells, we stained for the NPY-Y1 receptor in the RVM, and found it broadly expressed on both serotonergic and non-serotonergic neurons. In subsequent behavioral experiments, NPY microinjected into the RVM in lightly anesthetized animals reversed signs of mechanical hyperalgesia following either nerve injury or chronic hindpaw inflammation. Unexpectedly, rather than decreasing ON-cell activity, NPY increased spontaneous activity of both ON- and OFF-cells without altering noxious-evoked changes in firing. Based on these results, we conclude that the anti-hyperalgesic effects of NPY in the RVM are not explained by selective inhibition of ON-cells, but rather by increased spontaneous activity of OFF-cells. Although ON-cells undoubtedly facilitate nociception and contribute to hypersensitivity, the present results highlight the importance of parallel OFF-cell-mediated descending inhibition in limiting the expression of chronic pain.

Neuropeptide Y - an early biomarker for cerebral vasospasm after aneurysmal subarachnoid hemorrhage

OBJECTIVES

In the human brain, the potent vasoconstrictive neuropeptide Y (NPY) is abundantly expressed. Neuropeptide Y, which is stored in perivascular nerve fibers of the cerebral arteries, regulates the cerebral vascular diameter as well as cerebral blood flow. However, the role of NPY in the pathogenesis of cerebral vasospasm (CV) related to subarachnoid hemorrhage (SAH) is unclear. We prospectively analyzed and compared the release of endogenous NPY in the cerebrospinal fluid (CSF) of 66 patients with SAH to NPY release in a control group. Additionally, we correlated the levels of NPY with CV and consecutive ischemic stroke.

METHODS

Sixty-six consecutive patients (40 women, 26 men; mean age 53·1 years) with aneurysmal SAH were included. In the SAH group, CSF was drawn daily from day 1 to day 10 after the onset of SAH. The CSF of 29 patients undergoing spinal anesthesia for orthopedic surgery served as control samples. The NPY levels were determined in duplicate CSF samples by means of a competitive enzyme immunoassay (EIA). The levels of NPY in CSF were correlated with the development of CV over the 10-day period after the onset of SAH and to the occurrence of consecutive ischemic stroke. To evaluate CSF NPY levels as a predictive biomarker for vasospasm, we calculated the sensitivity and specificity as well as the positive and negative predictive values.

RESULTS

The NPY levels were significantly higher in the SAH group than in the control group (p < 0·001). The treatment modality (clip versus coil) did not influence the level of NPY in CSF (p > 0·05). Patients with CV showed significantly higher NPY levels than patients without CV during the entire observation period. The NPY levels of the non-CV group dissipated over time, whereas the CV group showed continuously increasing values. The NPY levels from day 4 to 10 were significantly higher in patients with CV-related stroke than in non-stroke patients. Using 0·3 ng/ml as a cut-off value, NPY levels on day 3 predicted the occurrence of CV with a sensitivity and specificity of 82% and 72%, respectively. High NPY levels, starting on day 4, significantly correlated with poor Glasgow Outcome Score grading at the follow-up (p < 0·05).

DISCUSSION

Our data indicate that NPY is involved in the pathogenesis of SAH-related CV and ischemia. Neuropeptide Y represents an early and reliable biomarker for the prediction of CV and consecutive stroke due to aneurysmal SAH.

Neuronal nitric oxide synthase expressing neurons: a journey from birth to neuronal circuits

Nitric oxide (NO) is an important signaling molecule crucial for many physiological processes such as synaptic plasticity, vasomotricity, and inflammation. Neuronal nitric oxide synthase (nNOS) is the enzyme responsible for the synthesis of NO by neurons. In the juvenile and mature hippocampus and neocortex nNOS is primarily expressed by subpopulations of GABAergic interneurons. Over the past two decades, many advances have been achieved in the characterization of neocortical and hippocampal nNOS expressing neurons. In this review, we summarize past and present studies that have characterized the electrophysiological, morphological, molecular, and synaptic properties of these neurons. We also discuss recent studies that have shed light on the developmental origins and specification of GABAergic neurons with specific attention to neocortical and hippocampal nNOS expressing GABAergic neurons. Finally, we summarize the roles of NO and nNOS-expressing inhibitory neurons.

Activation of cortical 5-HT(3) receptor-expressing interneurons induces NO mediated vasodilatations and NPY mediated vasoconstrictions

GABAergic interneurons are local integrators of cortical activity that have been reported to be involved in the control of cerebral blood flow (CBF) through their ability to produce vasoactive molecules and their rich innervation of neighboring blood vessels. They form a highly diverse population among which the serotonin 5-hydroxytryptamine 3A receptor (5-HT_3A)-expressing interneurons share a common developmental origin, in addition to the responsiveness to serotonergic ascending pathway. We have recently shown that these neurons regroup two distinct subpopulations within the somatosensory cortex: Neuropeptide Y (NPY)-expressing interneurons, displaying morphological properties similar to those of neurogliaform cells and Vasoactive Intestinal Peptide (VIP)-expressing bipolar/bitufted interneurons. The aim of the present study was to determine the role of these neuronal populations in the control of vascular tone by monitoring blood vessels diameter changes, using infrared videomicroscopy in mouse neocortical slices. Bath applications of 1-(3-Chlorophenyl)biguanide hydrochloride (mCPBG), a 5-HT₃R agonist, induced both constrictions (30%) and dilations (70%) of penetrating arterioles within supragranular layers. All vasoconstrictions were abolished in the presence of the NPY receptor antagonist (BIBP 3226), suggesting that they were elicited by NPY release. Vasodilations persisted in the presence of the VIP receptor antagonist VPAC1 (PG-97-269), whereas they were blocked in the presence of the neuronal Nitric Oxide (NO) Synthase (nNOS) inhibitor, L-NNA. Altogether, these results strongly suggest that activation of neocortical 5-HT_3A-expressing interneurons by serotoninergic input could induces NO mediated vasodilatations and NPY mediated vasoconstrictions.

The possible role of neuropeptide Y after spontaneous subarachnoid hemorrhage

OBJECTIVE

Neuropeptide Y (NPY), a highly potent vasoconstrictive neuropeptide, is widely expressed in the human brain, regulating vessel diameter and cerebral blood flow. Earlier studies focusing on the possible role of NPY in the context of aneurismal subarachnoid hemorrhage (SAH) and vasospasm have produced conflicting results. However, despite extensive research efforts, the pathophysiological mechanisms underlying the SAH-related vasospasm and delayed cerebral ischemia (DCI) have not been clarified. We, therefore, attempted to investigate the role of NPY in SAH-induced vasospasm in a larger, well documented patient population utilizing modern analytical tools. We focused on the release of the potent vasoconstrictor NPY in cerebrospinal fluid (CSF) and blood, and its correlation to vasospasm and stroke in the early clinical stage.

METHODS

Thirty-seven patients with SAH and a control group consisting of 29 patients were included. Eighteen patients developed stroke, 21 patients met the Doppler sonographical criteria for vasospasm. Twenty-nine patients had aneurysms of the anterior circulation and four patients of the posterior circulation. All patients had ventricular drainage inserted and an arterial catheter. Blood and CSF were drawn daily for NPY analysis during a 10-day interval.

RESULTS

The levels of NPY in CSF and plasma were significantly higher after SAH than in the control group (p = 0.001). The vasospasm group showed NPY levels in CSF which continuously ranged above the NPY levels of the non-vasospasm group (p = 0.001). Patients with stroke caused by vasospasm had significantly higher levels of NPY (p = 0.001).

DISCUSSION

NPY is released excessively into blood and CSF following SAH. Patients with cerebral infarction caused by vasospasm had significantly higher levels of NPY. Our results indicate a certain role for NPY in the pathophysiology of vasospasm due to SAH and justify further studies in this area of research.

Classification of NPY-expressing neocortical interneurons

Neuropeptide Y (NPY) is an abundant neuropeptide of the neocortex involved in numerous physiological and pathological processes. Because of the large electrophysiological, molecular, and morphological diversity of NPY-expressing neurons their precise identity remains unclear. To define distinct populations of NPY neurons we characterized, in acute slices of rat barrel cortex, 200 cortical neurons of layers I-IV by means of whole-cell patch-clamp recordings, biocytin labeling, and single-cell reverse transcriptase-PCR designed to probe for the expression of well established molecular markers for cortical neurons. To classify reliably cortical NPY neurons, we used and compared different unsupervised clustering algorithms based on laminar location and electrophysiological and molecular properties. These classification schemes confirmed that NPY neurons are nearly exclusively GABAergic and consistently disclosed three main types of NPY-expressing interneurons. (1) Neurogliaform-like neurons exhibiting a dense axonal arbor, were the most frequent and superficial, and substantially expressed the neuronal isoform of nitric oxide synthase. (2) Martinotti-like cells characterized by an ascending axon ramifying in layer I coexpressed somatostatin and were the most excitable type. (3) Among fast-spiking and parvalbumin-positive basket cells, NPY expression was correlated with pronounced spike latency. By clarifying the diversity of cortical NPY neurons, this study establishes a basis for future investigations aiming at elucidating their physiological roles.

Fetal alcohol exposure alters cerebrovascular reactivity to vasoactive intestinal peptide in adult sheep

Chronic fetal alcohol exposure impairs neural and vascular development. We have previously shown that fetal alcohol exposure is associated with attenuated hypoxic cerebral vasodilation and reduced neuronal vasoactive intestinal peptide (VIP) expression in fetal sheep. In the present study, we tested the hypothesis that fetal alcohol exposure alters vascular development, leading to altered cerebral vascular reactivity to VIP in adulthood. Penetrating intracerebral arterioles were harvested from the brains of adult (10-13 months old) offspring of ewes that had received intravenous infusions of alcohol (1.5 g/kg) or same-volume saline (90 min/day, 5 days/week) during days 30-82 of gestation (full term = 145 days). The isolated arterioles were cannulated with a micropipette system that allowed luminal perfusion and control of luminal pressure and developed spontaneous tone at 40 degrees C and 60 mm Hg luminal pressure. There was no difference in myogenic tone between arterioles exposed prenatally to alcohol (n = 18) and saline controls (n = 17). However, fetal alcohol exposure significantly (p = 0.03) enhanced the dilator responses of adult intracerebral arterioles to VIP [0.1 nM to 1 microM, logEC(50): -8.6 +/- 0.2 (alcohol) vs. -7.4 +/- 0.8 (saline)]. In contrast, there was no difference in dilator responses to H(+) (pH 6.8 buffer), to adenosine (10 nM to 0.1 mM), or to CGS21680 (an adenosine A(2A) receptor agonist, 0.01 nM to 10 microM). Thus, fetal alcohol exposure alters vasomotor sensitivity to VIP in adult intracerebral arterioles - perhaps a compensatory response to alcohol-induced underdevelopment of neurotransmitter pathways involved in cerebral vascular regulation.

Acute, subacute and chronic effects of central neuropeptide Y on energy balance in rats

Central neuropeptide Y (NPY) injection has been reported to cause hyperphagia and in some cases also hypometabolism or hypothermia. Chronic central administration induced a moderate rise of short duration in body weight, without consistent metabolic/thermal changes. In the present studies the acute and subsequent subacute ingestive and metabolic/thermal changes were studied following intracerebroventricular (i.c.v.) injections of NPY in cold-adapted and non-adapted rats, or the corresponding chronic changes following i.c.v. NPY infusion. Besides confirming basic earlier data, we demonstrated novel findings: a temporal relationship for the orexigenic and metabolic/thermal effects, and differences of coordination in acute/subacute/chronic phases or states. The acute phase (30-60 min after injection) was anabolic: coordinated hyperphagia and hypometabolism/hypothermia. NPY evoked a hypothermia by suppressing any (hyper)metabolism in excess of basal metabolic rate, without enhancing heat loss. Thus, acute hypothermia was observed in sub-thermoneutral but not thermoneutral environments. The subsequent subacute catabolic phase exhibited opposite effects: slight increase in metabolic rate, rise in body temperature, reaching a plateau within 3-4 h after injection -- this was maintained for at least 24 h; meanwhile the food intake decreased and the normal daily weight gain stopped. This rebound is only indirectly related to NPY. Chronic (7-day long) i.c.v. NPY infusion induced an anabolic phase for 2-3 days, followed by a catabolic phase and fever, despite continued infusion. In cold-adaptation environment the primary metabolic effect of the infusion induced a moderate hypothermia with lower daytime nadirs and nocturnal peaks of the circadian temperature rhythm, while at near-thermoneutral environments in non-adapted rats the infusion attenuated only the nocturnal temperature rise by suppressing night-time hypermetabolism. Further finding is that in cold-adapted animals, the early feeding effect of NPY-infusion was enhanced, whereas the early hypothermic effect in cold was limited by interference with competing thermoregulatory mechanisms.

Cholinergic modulation of the cortical microvascular bed

Cortical microvessels receive a cholinergic input that originates primarily from basal forebrain neurons which, upon stimulation, induce significant increases in cortical perfusion together with a dilation of intracortical microvessels. Heterogeneous mAChRs have been detected in cortical microvessels with expression of M2 and M5 subtypes in endothelial cells, while M1 and M3, and possibly M5 mAChR subtypes, were expressed in smooth muscle cells. Application of ACh to isolated and pressurized microarterioles, whether at basal tone or pharmacologically preconstricted, elicited only a dilation. This response was dependent on NO production, and was mediated by a mAChR, the pharmacology of which correlated best with the M5 receptor subtype. ACh afferents also project to intracortical neurons that synthesize NO and VIP. These correspond to distinct sub-populations of GABA interneurons which were found to send numerous projections to local microvessels. Preliminary results suggest expression of the VPAC1 receptor in the smooth muscle cells of intracortical arterioles, where it could mediate dilation as it does in cerebral arteries. Together these results indicate that basal forebrain ACh fibers can directly affect the cortical microvascular bed, but further suggest that specific populations of GABA interneurons could serve as a functional relay to adapt perfusion to locally increased neuronal activity. In confirmed cases of Alzheimer's disease, we found a severe ACh denervation of both cortical microvessels and NO neurons, suggesting that two important regulators of cortical perfusion are dysfunctional in this pathology.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Immunohistochemical localization of the VIP1 receptor (VPAC1R) in rat cerebral blood vessels: relation to PACAP and VIP containing nerves

The two structurally related peptides, vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP), are present in cerebral vascular nerve fibers. Biologic actions of VIP are exerted through two receptors, VPAC1 and VPAC2, having similar binding affinity for both VIP and PACAP. In the current study, the authors have developed a specific antibody against the rVPAC1 receptor to examine the localization of rVPAC1 immunoreactivity in cerebral arteries and arterioles of the rat by immunohistochemistry using fluorescence confocal microscopy. Specificity of the antiserum was ensured by immunoblotting and immunocytochemistry of cells transfected with cDNA encoding the different PACAP-VIP receptor subtypes. The rVPAC1 receptor immunoreactivity was localized to the plasmalemma of circularly orientated smooth muscle cells on superficial cerebral arteries and arterioles taken from the basal surface of the brain. By double immunostaining VIP immunoreactive nerve fibers and, to a lesser extent, those containing PACAP were shown to have intimate contact with the receptor protein. Vasoactive intestinal polypeptide and PACAP containing cerebrovascular nerve fibers were found in separate nerve populations with different distribution pattern and density. In brain sections processes of cortical VIP-, but not PACAP-, containing neurons seemed to innervate the rVPAC1 receptor of pial arterioles on the brain surface. The current findings provide the neuroanatomical substrate for a role of VIP and maybe PACAP in the regulation of cerebral blood flow.

Basal forebrain nitric oxide synthase (NOS)-containing neurons project to microvessels and NOS neurons in the rat neocortex: cellular basis for cortical blood flow regulation

Stimulation of basal forebrain neurons results in local increases in cortical cerebral blood flow that are dependent upon cholinergic and nitrergic mechanisms. In the present study, we investigated the possibility that basal forebrain nitric oxide synthase (NOS)-containing neurons project to microvessels and NOS interneurons in the rat cerebral cortex. We performed quisqualic (QUIS) acid lesions of the basal forebrain and evaluated their effects on cortical NOS immunostained nerve terminals, with emphasis on those associated with microvessels and NOS interneurons, both at the light and/or electron microscopic levels. The results show that basal forebrain NOS neurons provide about one third of the overall cortical NOS innervation. Further, the data indicate that basalocortical NOS fibres establish privileged associations with microvessels and NOS neurons, as respective denervations of 60 and 45% were observed following lesion. At the electron microscopic level, most perivascular NOS neuronal elements corresponded to nerve terminals and a majority ( approximately 25%) of these were located in the immediate vicinity of the blood vessels, similar to the perivascular distribution reported previously for classic neurotransmitters/neuromediators. NOS terminals abutting on cortical NOS neurons were primarily nonjunctional. Altogether, these results raise the possibility that not only cholinergic but also nitrergic basal forebrain neurons are involved in the flow response observed following stimulation of the basal forebrain. Further, they suggest interactions between basalocortical and intracortical NOS neurons. We conclude that these interactions are involved in the spatial and temporal regulation of cortical perfusion following basal forebrain activation, and that they may become dysfunctional in pathologies such as Alzheimer's disease which affects both the basal forebrain and the cortical NOS neurons.

Expression of neuropeptide Y receptors mRNA and protein in human brain vessels and cerebromicrovascular cells in culture

Neuropeptide Y (NPY) has been suggested as an important regulator of CBF. However, except for the presence of Y1 receptors in large cerebral arteries, little is known about its possible sites of action on brain vessels. In this study, we sought to identify the NPY receptors present in the human cerebrovascular bed. Specific Y1 receptor binding sites, localized on the smooth muscle of human pial vessels and potently competed by NPY, polypeptide YY (PYY), and the selective Y1 receptor antagonist BIBP 3226, were identified by quantitative radioautography of the Y1 radioligand [125I]-[Leu31, Pro34]-PYY. In contrast, no specific binding of the Y2-([125I]-PYY3-36) and Y4/Y5-(125I-human pancreatic polypeptide [hPP]) radioligands could be detected. By in situ hybridization, expression of Y1 receptor mRNA was restricted to the smooth muscle layer of pial vessels, whereas no specific signals were detected for either Y2, Y4, or Y5 receptors. Similarly, using reverse transcriptase-polymerase chain reaction (RT-PCR), mRNA for Y1 but not Y2, Y4, or Y5 receptors was consistently detected in isolated human pial vessels, intracortical microvessels, and capillaries. In human brain microvascular cells in culture, PCR products for the Y1 receptors were exclusively found in the smooth muscle cells. In cultures of human brain astrocytes, a cell type that associates intimately with brain microvessels, PCR products for Y1, Y2, and Y4 but not Y5 receptors were identified. Finally, NPY significantly inhibited the forskolin-induced cAMP production in smooth muscle but not in endothelial cell cultures. We conclude that smooth muscle Y1 receptors are the primary if not exclusive NPY receptors associated with human brain extraparenchymal and intraparenchymal blood vessels, where they most likely mediate cerebral vasoconstriction.

Dopaminergic regulation of cerebral cortical microcirculation

Functional variations in cerebral cortical activity are accompanied by local changes in blood flow, but the mechanisms underlying this physiological coupling are not well understood. Here we report that dopamine, a neurotransmitter normally associated with neuromodulatory actions, may directly affect local cortical blood flow. Using light and electron-microscopic immunocytochemistry, we show that dopaminergic axons innervate the intraparenchymal microvessels. We also provide evidence in an in vitro slice preparation that dopamine produces vasomotor responses in the cortical vasculature. These anatomical and physiological observations reveal a previously unknown source of regulation of the microvasculature by dopamine. The findings may be relevant to the mechanisms underlying changes in blood flow observed in circulatory and neuropsychiatric disorders.

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.

Vasomotor and permeability effects of bradykinin in the cerebral microcirculation

All components of an intracerebral kallikrein-kinin system have been described. Thus, bradykinin (BK) acting from the parenchymal site as well as from the blood site may influence cerebral microcirculation. BK is a potent dilator of extra- and intraparenchymal cerebral arteries when acting from the perivascular site. The vasomotor effect of BK is mediated by B2 receptors which appear to be located at the abluminal membrane of the endothelial cell. The effect of BK is mediated by NO. prostanoids, free radicals, H2O2 or leukotrienes depending on the animal species and on the location of the artery. Selective opening of the blood-brain barrier for small tracers (Na(+)-fluorescein; MW, 376) has been found in cats during cortical superfusion or intraarterial application of BK. This leakage is mediated by B2 receptors located at the luminal and abluminal membrane of the endothelial cells. Formation of brain edema has been found after ventriculo-cisternal perfusion or interstitial infusion of BK. This can be explained by increase of vascular permeability and cerebral blood flow due to arterial dilation thus enhancing driving forces for the extravasation. An increase of the BK concentration in the interstitial space of the brain up to concentrations which induce extravasation, dilatation and oedema formation has been found under several pathological conditions. Thus, BK may be involved in oedema formation after cold lesion, concussive brain injury, traumatic spinal cord and ischemic brain injury. The mediator role of BK in brain edema is further supported by therapeutic results. Brain swelling due to cold lesion or ischemia could be diminished by treatment with kallikrein-inhibitors. Similarly, dilatation of cerebral arterioles after concussive brain injury was reduced by blockade of B2 receptors. Thus, all criteria favour BK as one mediator of vasogenic oedema.

Vasorelaxant effect of PACAP-27 on canine cerebral arteries and rat intracerebral arterioles

The vasorelaxant effects of pituitary adenylate cyclase activating polypeptide (PACAP)-27 were examined and compared with those of PACAP-38 and vasoactive intestinal polypeptide (VIP) on isolated canine cerebral arteries and rat intracerebral arterioles in vitro. The addition of PACAP-27, PACAP-38 or VIP resulted in similar concentration-dependent relaxations in both canine basilar arteries and rat intracerebral arterioles. There were regional differences in the PACAP-27-induced relaxations measured in canine cerebral arteries. The maximum relaxation induced by PACAP-27 was significantly lower in the basilar arteries (23.0 +/- 5.6%) than in the rostrally located arteries (proximal middle cerebral arteries: 45.4 +/- 5.7%, anterior cerebral arteries: 55.2 +/- 5.8%). The maximum relaxation induced by PACAP-27 in the basilar arteries was significantly enhanced by mechanical removal of the endothelium (16.4 +/- 4.5% vs. 32.7 +/- 5.8%) as well as by pretreatment with indomethacin or aspirin (12.9 +/- 4.1% vs. 48.7 +/- 6.1% and 46.5 +/- 9.2%, respectively). Incubation of canine cerebral arteries with PACAP-27 in vitro resulted in an increased release of prostaglandin F2 alpha in the buffer from 14.5 +/- 2.1 pg/min/1 mg vessel to 31.1 +/- 4.2 pg/min/1 mg vessel, while other cyclooxygenase cascade metabolites such as prostaglandin E2, thromboxane B2 and 6-keto prostaglandin F1 alpha did not change. These data suggest that the PACAP-27-induced relaxation of canine basilar arteries may be associated with prostaglandin F2 alpha or its precursor, prostaglandin H2.

Characterization of neuropeptide Y (NPY) receptors in human cerebral arteries with selective agonists and the new Y1 antagonist BIBP 3226

1. We have characterized pharmacologically the receptor subtype(s) responsible for the neuropeptide Y (NPY)-induced vasoconstriction in human cerebral arteries. NPY, PYY and several of their derivatives with well defined affinities at the known Y1 and Y2 receptor subtypes were used. Moreover, we tested the ability of the new Y1 receptor antagonist, BIBP 3226, to antagonize the NPY-induced cerebral vasoconstriction. 2. NPY, PYY and their agonists with high affinities at the Y1 receptor subtype ([Leu31-Pro34]-NPY and [Leu31-Pro34]-PYY) elicited strong, long lasting and concentration-dependent contractions of human cerebral arteries. Compounds with Y2 affinity such as PYY3-36 or NPY13-36 either elicited a submaximal contraction at high concentrations or failed to induce any significant vasomotor response. Also, the application of NPY or the specific Y1 agonist, [Leu31-Pro34]-NPY, to human cerebral vessels pretreated with the Y1 agonist, NPY13-36, resulted in contractile responses identical to those obtained when these compounds were tested without prior application of NPY13-36. 3. The order of agonist potency at the human cerebrovascular receptor was: [Leu31-Pro34]-NPY = [Leu31-Pro34]-PYY > or = NPY > PYY > PYY3-36 > > > NPY13-36, which corresponded to that reported previously at the neuronal and vascular Y1 receptors. 4. Increasing concentrations (10(-9)-10(-6) M) of the Y1 receptor antagonist, BIBP 3226, to human cerebral vessels caused a parallel and rightward shift in the NPY dose-response curves without any significant change in the maximal contractile response. The calculated pA2 was 8.52 +/- 0.13, a value compatible with the reported affinity at the rodent and human Y1 receptor. 5. We conclude that Y1 receptors exclusively, mediate the NPY-induced contraction in human cerebral arteries and we show that BIBP 3226 is a potent and competitive antagonist of this YI-mediated vasoconstriction.

Cholinergic and vasoactive intestinal polypeptidergic innervation of the cerebral arteries

Acetylcholine and vasoactive intestinal polypeptide are not only two vasoactive agonists that predominantly induce a vasodilatation of the cerebral arteries, but also correspond to neurotransmitters that innervate the various anatomical segments of the cerebral vasculature. The distinct patterns of the cerebrovascular cholinergic and vasoactive intestinal polypeptidergic innervation, their neurochemistry, in vitro and in vivo pharmacology, as well as the putative pathophysiological implications of these neurotransmission systems are critically summarized on the basis of the most recently published literature.

Subtypes of receptors for neuropeptide Y: implications for the targeting of therapeutics

Neuropeptide Y is a 36 amino acid peptide that was originally discovered in extracts of porcine brain. The peptide has a broad distribution in the central or peripheral nervous system. Receptors for this peptide were originally subdivided into postsynaptic Y-1 receptors and presynaptic Y-2 receptors. The Y-1 receptor has recently been cloned and appears to mediate several effects of NPY including vasoconstriction and an anxiolytic effect in animal models of anxiety. The Y-2 receptor inhibits the release of neurotransmitters in the CNS by the inhibition of the mobilization of intracellular calcium. Additional receptors have been proposed including a Y-3 receptor that recognizes NPY but not the related endocrine peptide, PYY. The functional importance of these newer receptors remains to be established. The absence of useful antagonists has made the study of NPY a challenge for investigators in the field. The potential utility of such molecules is discussed.

Localized dynamic changes in cortical blood flow with whisker stimulation corresponds to matched vascular and neuronal architecture of rat barrels

The hypothesis that functional groups of neurons in whisker barrels are linked to a modular organization of cortical vessels was tested. Endovascular casts demonstrated cortical capillary networks resembling the whisker barrel pattern that were fed from the middle cerebral artery. In histological sections, dense capillaries apparently were confined to single barrels and were supplied by one or a few penetrating arterioles. The barrel field in cortical layer IV was localized in relation to surface arteriovenous patterns. Living vessels were imaged through a closed cranial window under anesthesia with a fluorescence microscope and SIT or ICCD cameras. After intracarotid injections of fluorescein isothiocyanatedextrans, saline, or 3 microns latex beads, changes in arteriolar diameter, arteriovenous transit times (AVTTs), and bead velocities were measured. When row C whiskers were stroked at 4-5 Hz for 1 min, blood flow increased in arterioles that supplied contralateral row C barrels as demonstrated by postmortem histology. AVTTs slowed significantly in vessels supplying adjacent cortex. We hypothesize that cerebral vascular units supply individual whisker barrels and are functionally linked to them for precise focal regulation of cerebral blood flow.

Pharmacologic effects in vivo in brain by vector-mediated peptide drug delivery

Pharmacologic effects in brain caused by systemic administration of neuropeptides are prevented by poor transport of the peptide through the brain vascular endothelium, which comprises the blood-brain barrier in vivo. In the present study, successful application of a chimeric peptide approach to enhance drug delivery through the blood-brain barrier for the purpose of achieving a central nervous system pharmacologic effect is described. The chimeric peptide was formed by linkage of a potent vasoactive intestinal peptide (VIP) analogue, which had been monobiotinylated, to a drug transport vector. The vector consisted of a covalent conjugate of avidin and the OX26 monoclonal antibody to the transferrin receptor. Owing to the high concentration of transferrin receptors on brain capillary endothelia, OX26 targets brain and undergoes receptor-mediated transcytosis through the blood-brain barrier. Systemic infusion of low doses (12 micrograms/kg) of the VIP chimeric peptide in rats resulted in an in vivo central nervous system pharmacologic effect: a 65% increase in cerebral blood flow. Biotinylated VIP analogue without the brain transport vector was ineffective.

The Kallmann's syndrome variant (KSV) model of the schizophrenias

The KSV model of the schizophrenias proposes that up to 70% of schizophrenics have a pathogenic allele, or abnormal expression, of the KALIG-1 gene which is located at Xp22.3. This gene encodes a nerve-cell adhesion molecule (N-CAM) like protein, and is deleted in 66% of patients with Kallmann's syndrome, anosmia with secondary hypogonadism. Although superficially distinct, the schizophrenias and Kallmann's syndrome show numerous parallel trait defects which occur with a similar sex distribution. These defects are usually more profound in Kallmann's syndrome. Occasionally, Kallmann's patients exhibit additional defects, such as ichthyosis, which are due to the further deletion or translocation of adjacent genes. Since schizophrenics exhibit virtually all known trait defects in Kallmann's except these, it suggests that the aberrant genes are defective, but not deleted in schizophrenia. It also appears that compensatory mechanisms, involving serine proteases, are active in schizophrenia, which largely preserve fertility, but at the expense of an increased vulnerability to develop a psychosis by an episodic disruption of the blood-CSF barrier. Consequently, schizophrenia is rare in Kallmann's patients, while most schizophrenics are capable of reproduction.

Cerebral vasoconstrictor mediators

Endogenous cerebral vasoconstrictor mediators regulate vascular resistance and blood flow in the brain as a whole and in various regions and participate in the pathogenesis of cerebral circulatory disturbances. Vasoconstrictors are effective in the treatment of diseases associated with cerebral vasodilatation. There are variations in the response of cerebral arteries from primate and subprimate mammals; therefore, information as to similarities and differences in their response is quite important in evaluating the physiological role, involvement in pathogenesis and therapeutic usefulness of the mediators in healthy men and patients. In this review we described characteristics of the action of vasoconstrictors (amines, peptides, prostanoids, and others) on isolated cerebral arteries from mammals, including humans and monkeys.

Modulation of bradykinin-induced plasma extravasation in the rat knee joint by sympathetic co-transmitters

We describe the contribution of various sympathetic post-ganglionic neuron mediators to bradykinin-induced plasma extravasation in the knee joint of the rat. Co-perfusion of the sympathetic post-ganglionic neuron mediators, norepinephrine or neuropeptide Y with bradykinin resulted in diminished plasma extravasation. In contrast, the putative sympathetic post-ganglionic neuron mediators of bradykinin-induced plasma extravasation, namely prostaglandin E2, ATP, the selective adenosine A2-receptor agonist, CGS21680 or the endothelium-derived relaxing factor (as its precursor L-arginine) all greatly enhanced bradykinin-induced plasma extravasation, but produced little or no increase in plasma extravasation administered alone. The data show that sympathetic post-ganglionic neuron-derived mediators may either inhibit or enhance plasma extravasation induced by bradykinin, and we hypothesize that differential release of mediators from the sympathetic post-ganglionic neuron terminal, in response to varying stimuli, regulates local plasma extravasation during inflammation.

Mediators of vascular and parenchymal mechanisms in secondary brain damage

Several putative mediators of vasogenic brain edema will be considered with respect to the following criteria: 1) their effect on blood-brain barrier (BBB) permeability, 2) their vasomotor actions which may increase driving forces for transmural bulk flow, 3) their influence on edema formation, 4) their actual tissue concentration in pathological states, and 5) the therapeutic results after specific treatment. Bradykinin (BK) can induce brain edema by increasing BBB permeability to small solutes and enhancing blood pressure in the microcirculation due to arterial dilatation and venous constriction. Its interstitial concentration is enhanced after experimental trauma. Since kallikrein inhibitors reduce brain swelling all criteria favour BK as a mediator of vasogenic edema. Arachidonic acid (AA) opens BBB also for large tracers but exerts only small vasomotor effects. The edema formation is associated with an increase of the AA concentration in the interstitial space. However, convincing therapeutic results on inhibition of AA are still lacking. In addition to the formation of vasogenic edema AA has been found to induce cytotoxic edema. From experiments dealing with the vasomotor effects Ellis et al. (Am J Physiol 255: H397-H400, 1988) concluded an interaction of BK and AA in brain injury. However, our own results do not favour this hypothesis since we found divergent vasomotor and permeability effects of BK and AA. Histamine (HA) opens BBB unspecifically and dilates cerebral vessels, mechanisms by which edema formation can be explained.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient cerebral vasodilatory effect of neuropeptide Y mediated by nitric oxide

The effects of intracarotidly injected neuropeptide Y (NPY; 0.1 micrograms/kg) on the local cerebral blood volume (CBV) and blood flow (CBF) in the parieto-temporal cortex were examined by the photoelectric method in 17 anesthetized cats. CBV reflects the cumulative crosssectional area of the cerebral microvascular beds. NPY immediately caused transient but significant increases in CBV and CBF, which lasted for less than 5 min. Thereafter, CBV returned to and remained at the control level, although CBF was decreased by 30-40% for 60 min during the monitoring period. The CBV increases after NPY were prevented by a 15-min preinjection of 0.35 mg/kg/min of NG-monomethyl-L-arginine (L-NMMA), which is a competitive blocker of nitric oxide synthesis. The CBV increases after NPY reappeared following a 15-min administration of 0.25 mg/kg/min of L-arginine, which is a precursor of nitric oxide. We conclude that NPY administered in vivo exerts a previously unreported effect of transient vasodilatation on the cerebral microvessels. This action appears to be mediated by nitric oxide, which is a major candidate as an endothelium-derived relaxing factor (EDRF).

Neuropeptide Y in the primate model of subarachnoid hemorrhage

The cause of cerebral vasospasm after subarachnoid hemorrhage (SAH) remains unknown. Recently, an association between the potent vasoconstricting peptide, neuropeptide Y, and delayed cerebral vasospasm after SAH has been postulated. This was based on the findings of increased neuropeptide Y levels in the cerebrospinal fluid (CSF) and plasma after SAH in animals and humans. For this study, the primate model of SAH was used to assess the possible role of neuropeptide Y in delayed vasospasm after SAH. Fifteen cynomolgus monkeys underwent placement of a clot of either whole blood or red blood cells in the subarachnoid space around the middle cerebral artery (MCA). Sequential arteriography for assessment of MCA diameter and sampling of blood and CSF for neuropeptide Y were performed: before SAH (Day 0); 7 days after SAH, when signs of delayed cerebral vasospasm peak in this model and in humans; 12 days after SAH; and 28 days after SAH. Subarachnoid hemorrhage did not evoke changes in CSF or plasma levels of neuropeptide Y. Nine monkeys had arteriographic evidence of vasospasm on Day 7, but no change in neuropeptide Y levels occurred in plasma or CSF. In addition, neuropeptide Y levels did not change, even after resolution of vasospasm on Day 12 or Day 28. Neuropeptide Y levels were substantially higher in CSF than in arterial plasma (p less than 0.003 at each interval). No correlation was found between neuropeptide Y levels in CSF and in plasma. These results do not confirm a relationship between neuropeptide Y levels in the CSF or peripheral plasma and delayed cerebral vasospasm in SAH.

Changes in neuropeptide Y after experimental traumatic brain injury in the rat

We utilized a model of fluid percussion (FP) brain injury in the rat to examine the hypothesis that alterations in brain neuropeptide Y (NPY) concentrations occur following brain injury. Male rats (n = 44) were subjected to FP traumatic brain injury. One group of animals (n = 38) was killed at 1 min, 15 min, 1 h, or 24 h after brain injury, and regional brain homogenates were analyzed for NPY concentrations using radioimmunoassay. A second group of animals (n = 6) was killed for NPY immunocytochemistry. Concentrations of NPY in the injured left parietal cortex were significantly elevated at 15 min post injury (p less than 0.05). No changes were observed in other brain regions. NPY-immunoreactive fibers were seen at 15 min post injury predominantly in the injured cortex and adjacent hippocampus. These temporal changes in NPY immunoreactivity, together with previous observations concerning posttraumatic changes in regional CBF in these same areas, suggest that an increase in region NPY concentrations after brain injury may be involved in part in the pathogenesis of posttraumatic hypoperfusion.

Effects of intracarotid infusion of neuropeptide Y on cerebral blood flow in rats

Neuropeptide Y (NPY) was continuously administered to Wistar rats intracarotidly via the external carotid artery and local cerebral blood flow (LCBF) was measured by a quantitative autoradiography using [14C]iodoantipyrine. A remarkable reduction in LCBF was observed in the NPY infused hemisphere. This depression was irregular and was particularly evident in the hippocampus, selective thalamic nuclei and the cerebral cortex.

The role of bradykinin in the etiology of vasogenic brain edema and perilesional brain dysfunction

The feline infusion model of brain edema was used to evaluate the role of bradykinin in the etiology and pathophysiology of vasogenic brain edema. Bradykinin (3 or 90 ug in 600 microL saline) did not alter normocapnic regional cerebral blood flow (rCBF) nor induce specific changes in either the somatosensory (SEP) or motor (MEP) evoked potentials. The mean increases in ICP (from 4.5 to 16.1 mmHg) and peri-infusion white matter water content (from 69.4 to 79.8 ml/100 g tissue), mean decrease in lumped craniospinal compliance (from 0.040 to 0.014 ml/mmHg) and local histological changes were all similar to those after 600 microL saline infusion. The interstitial bradykinin infusion caused focal blood-brain-barrier (BBB) opening to Evans Blue dye and was chemotaxic for granulocytes. After the infusion there was a global loss of rCBF CO2 reactivity but there was no ischemia at normocapnia. These results show that bradykinin in brain edema fluid, at concentrations greater than those found in neuropathological conditions, can open the BBB of normal cerebral parenchymal capillaries and cause vascular dysregulation. In neuropathological conditions bradykinin may therefore potentiate formation of vasogenic brain edema but does not contribute to perilesional brain dysfunction.

Regulation of the cerebral circulation by endothelium

Endothelium exerts an important influence on cerebral vascular tone through the production and release of a diverse group of vasoactive factors. Relaxing factors produced by endothelium include nitric oxide (or a nitric oxide-containing compound), a hyperpolarizing factor, and prostacyclin. Endothelium-derived contracting factors include cyclooxygenase products of arachidonic acid and endothelins. Several pathophysiological conditions are associated with increased formation of endothelium-derived contracting factors. Such endothelial dysfunction in the cerebral circulation may shift the balance of vascular tone toward constriction and may potentially contribute to the onset or maintainance of cerebral ischemia and stroke.

Prepro-vasoactive intestinal polypeptide-derived peptide sequences in cerebral blood vessels of rats: on the functional anatomy of metabolic autoregulation

This study describes the distribution of peptide sequences derived from the prepro-vasoactive intestinal polypeptide (preproVIP) molecule in perivascular nerves of rat brain arteries and arterioles. The peptides were identified by immunohistochemistry using highly specific antibodies. Five peptide sequences (preproVIP 60-76, peptide histidine isoleucine (PHI), preproVIP 111-122, VIP, and preproVIP 156-170) were identified in the perivascular nerves throughout the arterial cerebral circulation. The density of the immunoreactive fibers was highest in the nerves of the larger extracerebral arteries, declining in smaller branching arteries. All peptide sequences were identified in the nerves of small pial arterioles overlying the cortical convexity, whereas capillaries and veins contained no immunoreactive material. Dendritic processes of neocortical neurons immunoreactive for VIP and PHI could be followed towards the brain surface where the processes penetrated into the pial layer, often close to the pial vasculature. Some of the processes were also observed to enter the Virchow-Robin space, close to the arterioles. It is possible that cortical nerve cells containing VIP and PHI release the peptides in the perivascular space during periods of activity and thereby contribute to local vasodilatation associated with changes of neuronal function.

Peptidergic innervation in the cerebral blood vessels of the guinea pig: an immunohistochemical study

The distribution of peptidergic nerve fibers containing substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in the cerebral arteries and veins of the guinea pig was studied using immunohistochemical techniques. The ultrastructure of these immunoreactive nerve terminals was also compared. The cerebral arteries were innervated by abundant peptidergic nerve fibers with characteristic running patterns, i.e., SP fibers in a meshwork, VIP and NPY fibers in a spiral fashion. Only CGRP fibers showed both meshwork and spiral patterns. In the cerebral veins, the abundant SP fibers innervated the cortical veins, deep cerebral veins, and dural sinuses. However, CGRP, VIP, and NPY fibers in extremely low density were noted merely in the cortical veins. Electron microscopic observations demonstrated that SP-immunoreactive nerve terminals existed apart from the arterial smooth muscle cells, while VIP- and NPY-immunoreactive nerve terminals adjoined them. As for CGRP nerve terminals, some existed close to the arterial smooth muscle cells, and others were found some distance from them. These morphological characteristics observed by light and electron microscopy suggest that SP fibers are not related directly to the vasomotor function, but VIP and NPY fibers are, and that CGRP fibers have a more complicated function. The distribution patterns of the peptidergic nerve fibers are consistent with the suggestion that vasomotor peptidergic fibers may function actively on cerebral arteries and passively on cerebral veins and that SP fibers regarded as sensory fibers may provide information regarding cerebral vascular conditions, innervating every part of both cerebral arteries and veins.

Neuropeptide Y and the cerebral circulation

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