Innervation of cerebral arteries by nerves containing 5-hydroxytryptamine and noradrenaline

Effects of early high-dose vasopressor administration in patients after aneurysmal subarachnoid hemorrhage: a retrospective single-center study

BACKGROUND

Although the use of vasopressors is recommended after aneurysmal subarachnoid hemorrhage (aSAH) to maintain adequate cerebral perfusion pressure, data on potential adverse effects on delayed cerebral ischemia (DCI) are lacking. The aim of this study was to evaluate the effects of early high-dose vasopressor therapy with norepinephrine alone or additional vasopressin on the subsequent occurrence of DCI, DCI-related infarction and functional outcomes.

METHODS

Retrospective evaluation of aSAH patients admitted between January 2010 and December 2022. Demographic, clinical and outcome data as well as daily norepinephrine equivalent (NEE) scores were collected. Potential risk factors for DCI, DCI-related infarction and functional outcome 3 months after discharge were assessed by logistic regression analyses.

RESULTS

A total of 288 patients were included. 208 patients (72%) received vasopressor therapy during the first 14 postictal days with a mean NEE score of 3.8 µg/kgBW/h. The highest NEE scores were observed in the acute phase after hemorrhage and mainly in poor-grade patients. The mean NEE score during the postictal days 1-4 was significantly higher in patients who developed DCI or DCI-related infarction and who had an unfavorable functional outcome. Multivariable logistic regression analysis identified a high NEE score on postictal days 1-4 as an independent predictor of DCI and unfavorable functional outcome.

CONCLUSIONS

Vasopressor use is common in aSAH patients in the acute phase after hemorrhage. Our results suggest that high NEE scores during the first 4 days after ictus represent an independent prognostic factor and might aggravate the complex cerebral sequelae associated with the disease.

Cerebral sympatholysis: experiments on in vivo cerebrovascular regulation and ex vivo cerebral vasomotor control

Whether cerebral sympathetic-mediated vasomotor control can be modulated by local brain activity remains unknown. This study tested the hypothesis that the application or removal of a cognitive task during a cold pressor test (CPT) would attenuate and restore decreases in cerebrovascular conductance (CVC), respectively. Middle cerebral artery blood velocity (transcranial Doppler) and mean arterial pressure (finger photoplethysmography) were examined in healthy adults (n = 16; 8 females and 8 males) who completed a control CPT, followed by a CPT coupled with a cognitive task administered either 1) 30 s after the onset of the CPT and for the duration of the CPT or 2) at the onset of the CPT and terminated 30 s before the end of the CPT (condition order was counterbalanced). The major finding was that the CPT decreased the index of CVC, and such decreases were abolished when a cognitive task was completed concurrently and restored when the cognitive task was removed. As a secondary experiment, vasomotor interactions between sympathetic transduction pathways (α1-adrenergic and Y1-peptidergic) and compounds implicated in cerebral blood flow control [adenosine, and adenosine triphosphate (ATP)] were explored in isolated porcine cerebral arteries (wire myography). The data reveal α1-receptor agonism potentiated vasorelaxation modestly in response to adenosine, and preexposure to ATP attenuated contractile responses to α1-agonism. Overall, the data suggest a cognitive task attenuates decreases in CVC during sympathoexcitation, possibly related to an interaction between purinergic and α1-adrenergic signaling pathways.NEW & NOTEWORTHY The present study demonstrates that the cerebrovascular conductance index decreases during sympathoexcitation and this response can be positively and negatively modulated by the application or withdrawal of a nonexercise cognitive task. Furthermore, isolated vessel experiments reveal that cerebral α1-adrenergic agonism potentiates adenosine-mediated vasorelaxation and ATP attenuates α1-adrenergic-mediated vasocontraction.

Investigating the relationship between high-dose norepinephrine administration and the incidence of delayed cerebral infarction in patients with aneurysmal subarachnoid hemorrhage: A single-center retrospective evaluation

BACKGROUND

One of the longest-standing treatments to prevent delayed cerebral infarction (DCI) in patients with aneurysmal subarachnoid hemorrhage (aSAH) remains raising the blood pressure to a certain level of mean arterial pressure. This may require high doses of norepinephrine, which has been associated with severe end organ damage. With this study, we aimed to investigate the effects of norepinephrine on the incidence of DCI in a clinical setting.

METHODS

We conducted a retrospective evaluation of patients with aSAH admitted to our institution between November 2018 and March 2021. Potential risk factors for DCI were analyzed and significant predictors were assessed by means of a logistic regression analysis to account for potential confounders.

RESULTS

In this study, 104 patients were included. Hereof, 39 (38%) showed radiologic signs of DCI between day three and 14 post-intervention. These patients had more frequent vasospasms (n = 37 vs. 30, p = 0.022), a higher Hunt & Hess score (3 ± 2 vs. 2 ± 1, p = 0.004), a lower initial Glasgow Coma Scale score (9 ± 5 vs. 12 ± 4, p = 0.003) and received a higher median norepinephrine dose (20,356μg vs. 6,508μg, p < 0.001). A logistic regression analysis revealed that only high-dose norepinephrine administration (OR 2.84, CI 1.56-7.8) and vasospasm (OR 3.07, CI 1.2-7.84) appeared to be significant independent risk factors for DCI.

CONCLUSION

Our results indicate a significant association between higher dose norepinephrine administration and the occurrence of DCI. Future research including greater sample sizes and a prospective setting will be necessary to further investigate the relationship.

Integrative cerebral blood flow regulation in ischemic stroke

Optimizing cerebral perfusion is key to rescuing salvageable ischemic brain tissue. Despite being an important determinant of cerebral perfusion, there are no effective guidelines for blood pressure (BP) management in acute stroke. The control of cerebral blood flow (CBF) involves a myriad of complex pathways which are largely unaccounted for in stroke management. Due to its unique anatomy and physiology, the cerebrovascular circulation is often treated as a stand-alone system rather than an integral component of the cardiovascular system. In order to optimize the strategies for BP management in acute ischemic stroke, a critical reappraisal of the mechanisms involved in CBF control is needed. In this review, we highlight the important role of collateral circulation and re-examine the pathophysiology of CBF control, namely the determinants of cerebral perfusion pressure gradient and resistance, in the context of stroke. Finally, we summarize the state of our knowledge regarding cardiovascular and cerebrovascular interaction and explore some potential avenues for future research in ischemic stroke.

Migraine pharmacology and brain ischemia

Introduction: The aim of this review article was to analyze in details the mechanism of drugs’ effects in the treatment and prevention of a migraine attack, as well as to discuss the hypotheses of migraine pathogenesis.

Migraine attack treatment agents: The main agents for migraine attack treatment have an anti-nociceptive activity.

Agents for migraine preventive treatment: β-blocker propranolol also has anti-serotonin and analgesic activities, and most drugs used for the prophylactic treatment of migraine have a vasodilating activity.

Vascular hypothesis of migraine pathogenesis: Despite numerous studies that have expanded our understanding of migraine pathogenesis, the importance of the vascular component in the pathogenesis of this disease has not questioned yet.

Neurogenic hypotheses of cortical spreading depression: It is necessary to take into account the points of this hypothesis in the context of the pathophysiology of migraine.

Neurochemical serotonin hypotheses of migraine pathogenesis: Serotonin plays an important role in the pathogenesis of migraine.

Trigemino-vascular hypotheses of migraine pathogenesis: The trigemino-vascular hypothesis claims to solve the problem of migraine pain.

Migraine and ischemic brain damage: Migraine is a risk factor for ischemic stroke and cognitive disorders.

Search for the new anti-ischemic anti-migraine preparations: A methodology for the search for new anti-ischemic anti-serotonin drugs for the treatment of migraine is proposed.

Conclusion: Belonging of a drug to one or another pharmacological group does not always correspond to its therapeutic effect on the pathogenetic processes of migraine. Migraine with its variety of forms cannot fit only one of the proposed hypotheses on the pathogenesis of this disease.

Graphical abstract:

Impella RP Versus Pharmacologic Vasoactive Treatment in Profound Cardiogenic Shock due to Right Ventricular Failure

The aim was to translationally compare a pharmacologic strategy versus treatment with the Impella RP in profound RV cardiogenic shock (CS). The pigs were allocated to either vasoactive therapy with norepinephrine (0.10 μg/kg/min) for the first 30 min, supplemented by an infusion of milrinone (0.4 μg/kg/min) for additional 150 min, or treatment with the Impella RP device for 180 min. Total RV workload (Pressure-volume-area × heart rate*10³(mmHg/min)) remained unaffected upon treatment with the Impella RP and increased in the vasoactive group (CS 179[147;228] to norepinephrine 268[247;306](p = 0.002 compared to Impella RP) and norepinephrine + milrinone 366[329;422] (p = 0.002 compared to Impella RP). A trend towards higher venous cerebral oxygen saturation was observed with norepinephrine than Impella RP (Impella RP 51[47;61]% vs norepinephrine 62[57;71]%; p = 0.07), which became significantly higher with the addition of milrinone (Impella RP 45[32;63]% vs norepinephrine + milrinone 73[66;81]%; p = 0.002). The Impella RP unloaded the failing RV. In contrast, vasoactive treatment led to enhanced cerebral venous oxygen saturation.

Tryptophan Metabolism and Gut-Brain Homeostasis

Tryptophan is an essential amino acid critical for protein synthesis in humans that has emerged as a key player in the microbiota-gut-brain axis. It is the only precursor for the neurotransmitter serotonin, which is vital for the processing of emotional regulation, hunger, sleep, and pain, as well as colonic motility and secretory activity in the gut. Tryptophan catabolites from the kynurenine degradation pathway also modulate neural activity and are active in the systemic inflammatory cascade. Additionally, tryptophan and its metabolites support the development of the central and enteric nervous systems. Accordingly, dysregulation of tryptophan metabolites plays a central role in the pathogenesis of many neurologic and psychiatric disorders. Gut microbes influence tryptophan metabolism directly and indirectly, with corresponding changes in behavior and cognition. The gut microbiome has thus garnered much attention as a therapeutic target for both neurologic and psychiatric disorders where tryptophan and its metabolites play a prominent role. In this review, we will touch upon some of these features and their involvement in health and disease.

Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

CBF regulation in hypertension and Alzheimer's disease

PURPOSE

To review the recent developments on the effect of chronic high mean arterial blood pressure (MAP) on cerebral blood flow (CBF) autoregulation and supporting the notion that CBF autoregulation impairment has connection with chronic cerebral diseases. Method: A narrative review of all the relevant papers known to the authors was conducted. Results: Our understanding of the connection between cerebral perfusion impairment and chronic high MAP and cerebral disease is rapidly evolving, from cerebral perfusion impairment being the result of cerebral diseases to being the cause of cerebral diseases. We now better understand the intertwined impact of hypertension and Alzheimer's disease (AD) on cerebrovascular sensory elements and recognize cerebrovascular elements that are more vulnerable to these diseases. Conclusion: We conclude with the suggestion that the sensory elements pathology plays important roles in intertwined mechanisms of chronic high MAP and AD that impact cerebral perfusion.

Sympathetic activity contributes to the fMRI signal

The interpretation of functional magnetic resonance imaging (fMRI) studies of brain activity is often hampered by the presence of brain-wide signal variations that may arise from a variety of neuronal and non-neuronal sources. Recent work suggests a contribution from the sympathetic vascular innervation, which may affect the fMRI signal through its putative and poorly understood role in cerebral blood flow (CBF) regulation. By analyzing fMRI and (electro-) physiological signals concurrently acquired during sleep, we found that widespread fMRI signal changes often co-occur with electroencephalography (EEG) K-complexes, signatures of sub-cortical arousal, and episodic drops in finger skin vascular tone; phenomena that have been associated with intermittent sympathetic activity. These findings support the notion that the extrinsic sympathetic innervation of the cerebral vasculature contributes to CBF regulation and the fMRI signal. Accounting for this mechanism could help separate systemic from local signal contributions and improve interpretation of fMRI studies.

Locus Coeruleus Degeneration Induces Forebrain Vascular Pathology in a Transgenic Rat Model of Alzheimer's Disease

Noradrenergic locus coeruleus (LC) neuron loss is a significant feature of mild cognitive impairment and Alzheimer's disease (AD). The LC is the primary source of norepinephrine in the forebrain, where it modulates attention and memory in vulnerable cognitive regions such as prefrontal cortex (PFC) and hippocampus. Furthermore, LC-mediated norepinephrine signaling is thought to play a role in blood-brain barrier (BBB) maintenance and neurovascular coupling, suggesting that LC degeneration may impact the high comorbidity of cerebrovascular disease and AD. However, the extent to which LC projection system degeneration influences vascular pathology is not fully understood. To address this question in vivo, we stereotactically lesioned LC projection neurons innervating the PFC of six-month-old Tg344-19 AD rats using the noradrenergic immunotoxin, dopamine-β-hydroxylase IgG-saporin (DBH-sap), or an untargeted control IgG-saporin (IgG-sap). DBH-sap-lesioned animals performed significantly worse than IgG-sap animals on the Barnes maze task in measures of both spatial and working memory. DBH-sap-lesioned rats also displayed increased amyloid and inflammation pathology compared to IgG-sap controls. However, we also discovered prominent parenchymal albumin extravasation with DBH-sap lesions indicative of BBB breakdown. Moreover, microvessel wall-to-lumen ratios were increased in the PFC of DBH-sap compared to IgG-sap rats, suggesting that LC deafferentation results in vascular remodeling. Finally, we noted an early emergence of amyloid angiopathy in the DBH-sap-lesioned Tg344-19 AD rats. Taken together, these data indicate that LC projection system degeneration is a nexus lesion that compromises both vascular and neuronal function in cognitive brain areas during the prodromal stages of AD.

Molecular determinants of beta-adrenergic signaling to voltage-gated K+ channels in the cerebral circulation

Voltage-gated K⁺ (K_v ) channels are major determinants of membrane potential in vascular smooth muscle cells (VSMCs) and regulate the diameter of small cerebral arteries and arterioles. However, the intracellular structures that govern the expression and function of vascular K_v channels are poorly understood. Scaffolding proteins including postsynaptic density 95 (PSD95) recently were identified in rat cerebral VSMCs. Primarily characterized in neurons, the PSD95 scaffold has more than 50 known binding partners, and it can mediate macromolecular signaling between cell-surface receptors and ion channels. In cerebral arteries, Shaker-type K_v 1 channels appear to associate with the PSD95 molecular scaffold, and PSD95 is required for the normal expression and vasodilator influence of members of this K⁺ channel gene family. Furthermore, recent findings suggest that the β1-subtype adrenergic receptor is expressed in cerebral VSMCs and forms a functional vasodilator complex with K_v 1 channels on the PSD95 scaffold. Activation of β1-subtype adrenergic receptors in VSMCs enables protein kinase A-dependent phosphorylation and opening of K_v 1 channels in the PSD95 complex; the subsequent K⁺ efflux mediates membrane hyperpolarization and vasodilation of small cerebral arteries. Early evidence from other studies suggests that other families of K_v channels and scaffolding proteins are expressed in VSMCs. Future investigations into these macromolecular complexes that modulate the expression and function of K_v channels may reveal unknown signaling cascades that regulate VSMC excitability and provide novel targets for ion channel-based medications to optimize vascular tone.

Inflow of oxygen and glucose in brain tissue induced by intravenous norepinephrine: relationships with central metabolic and peripheral vascular responses

As an essential part of sympathetic activation that prepares the organism for "fight or flight," peripheral norepinephrine (NE) plays an important role in regulating cardiac activity and the tone of blood vessels, increasing blood flow to the heart and the brain and decreasing blood flow to the organs not as necessary for immediate survival. To assess whether this effect is applicable to the brain, we used high-speed amperometry to measure the changes in nucleus accumbens (NAc) levels of oxygen and glucose induced by intravenous injections of NE in awake freely moving rats. We found that NE at low doses (2-18 μg/kg) induces correlative increases in NAc oxygen and glucose, suggesting local vasodilation and enhanced entry of these substances in brain tissue from the arterial blood. By using temperature recordings from the NAc, temporal muscle, and skin, we show that this central effect is associated with strong skin vasoconstriction and phasic increases in intrabrain heat production, indicative of metabolic neural activation. A tight direct correlation between NE-induced changes in metabolic activity and NAc levels of oxygen and glucose levels suggests that local cerebral vasodilation is triggered via a neurovascular coupling mechanism. Our data suggest that NE, by changing vascular tone and cardiac activity, triggers a visceral sensory signal that rapidly reaches the central nervous system via sensory nerves and induces neural activation. This neural activation leads to a chain of neurovascular events that promote entry of oxygen and glucose in brain tissue, thus preventing any possible metabolic deficit during functional activation. NEW & NOTEWORTHY Using high-speed amperometry and thermorecording in freely moving rats, we demonstrate that intravenous norepinephrine at physiological doses induces rapid correlative increases in nucleus accumbens oxygen and glucose levels coupled with increased intrabrain heat production. Although norepinephrine cannot cross the blood-brain barrier, by changing cardiac activity and vascular tone, it creates a sensory signal that reaches the central nervous system via sensory nerves, induces neural activation, and triggers a chain of neurovascular events that promotes intrabrain entry of oxygen and glucose.

Impaired cerebral autoregulation: measurement and application to stroke

Cerebral autoregulation (CA) is a protective mechanism that maintains cerebral blood flow at a relatively constant level despite fluctuations of cerebral perfusion pressure or arterial blood pressure. It is a universal physiological mechanism that may involve myogenic, neural control as well as metabolic regulations of cerebral vasculature in response to changes in pressure or cerebral blood flow. Traditionally, CA has been represented by a sigmoid curve with a wide plateau between about 50 mm Hg and 170 mm Hg of steady-state changes in mean arterial pressure, defined as static CA. With the advent of transcranial Doppler, measurement of cerebral blood flow in response to transient changes in arterial pressure has been used to assess dynamic CA. However, a gold standard for measuring CA is not currently available. Stroke has been the leading cause of long-term adult disability throughout the world. A better understanding of CA and its response to pathological derangements can help assess the severity of stroke, guide management decisions, assess response to interventions and provide prognostic information. The objective of this review is to provide a comprehensive insight about physiology of autoregulation, measurement methodologies and clinical applications in stroke to help build a consensus for what should be included in an internationally agreed protocol for CA testing and monitoring, and to promote its translation into clinical bedside practice for stroke management.

The role of perivascular innervation and neurally mediated vasoreactivity in the pathophysiology of Alzheimer's disease

Neuronal death is a hallmark of Alzheimer's disease (AD) and considerable work has been done to understand how the loss of interconnectivity between neurons contributes to the associated dementia. Often overlooked however, is how the loss of neuronal innervation of blood vessels, termed perivascular innervation, may also contribute to the pathogenesis of AD. There is now considerable evidence supporting a crucial role for the neurovascular unit (NVU) in mediating the clearance of the β-amyloid (Aβ) peptide, one of the main pathological constituents of AD, from the brain. Moreover, efficient removal appears to be dependent on the communication of cells within the NVU to maintain adequate vascular tone and pulsatility. This review summarizes the composition of the NVU, including the sources of perivascular innervation and how the NVU mediates Aβ clearance from the brain. It also explores evidence supporting the hypothesis that loss of neurally mediated vasoreactivity contributes to Aβ pathology in the AD brain.

Pericytes impair capillary blood flow and motor function after chronic spinal cord injury

Blood vessels in the central nervous system (CNS) are controlled by neuronal activity. For example, widespread vessel constriction (vessel tone) is induced by brainstem neurons that release the monoamines serotonin and noradrenaline, and local vessel dilation is induced by glutamatergic neuron activity. Here we examined how vessel tone adapts to the loss of neuron-derived monoamines after spinal cord injury (SCI) in rats. We find that, months after the imposition of SCI, the spinal cord below the site of injury is in a chronic state of hypoxia owing to paradoxical excess activity of monoamine receptors (5-HT₁) on pericytes, despite the absence of monoamines. This monoamine-receptor activity causes pericytes to locally constrict capillaries, which reduces blood flow to ischemic levels. Receptor activation in the absence of monoamines results from the production of trace amines (such as tryptamine) by pericytes that ectopically express the enzyme aromatic L-amino acid decarboxylase (AADC), which synthesizes trace amines directly from dietary amino acids (such as tryptophan). Inhibition of monoamine receptors or of AADC, or even an increase in inhaled oxygen, produces substantial relief from hypoxia and improves motoneuron and locomotor function after SCI.

Severe Cerebral Vasospasm in Patients with Hyperthyroidism

Cerebral vasospasm associated with hyperthyroidism has not been reported to cause cerebral infarction. The case reported here is therefore the first of cerebral infarction co-existing with severe vasospasm and hyperthyroidism. A 30-year-old woman was transferred to our hospital in a stuporous state with right hemiparesis. At first, she complained of headache and dizziness. However, she had no neurological deficits or radiological abnormalities. She was diagnosed with hyperthyroidism 2 months ago, but she had discontinued the antithyroid medication herself three days ago. Magnetic resonance imaging and angiography showed cerebral infarction with severe vasospasm. Thus, chemical angioplasty using verapamil was performed two times, and antithyroid medication was administered. Follow-up angiography performed at 6 weeks demonstrated complete recovery of the vasospasm. At the 2-year clinical follow-up, she was alert with mild weakness and cortical blindness. Hyperthyroidism may influence cerebral vascular hemodynamics. Therefore, a sudden increase in the thyroid hormone levels in the clinical setting should be avoided to prevent cerebrovascular accidents. When neurological deterioration is noticed without primary cerebral parenchyma lesions, evaluation of thyroid function may be required before the symptoms occur.

The effects of different aerobic exercise intensities on serum serotonin concentrations and their association with Stroop task performance: a randomized controlled trial

PURPOSE

Acute exercise improves selective aspects of cognition such as executive functioning. Animal studies suggest that some effects are based on exercise-induced alterations in serotonin (5-HT) secretion. This study evaluates the impact of different aerobic exercise intensities on 5-HT serum levels as well as on executive functioning considering 5-HT as a potential mediator.

METHODS

121 young adults (23.8 ± 3.6 years) were examined in a randomized controlled trial including three exercise intervention (35 min) groups (low intensity, 45 % of the maximal heart rate (HRmax); moderate intensity, 65 % HRmax; high intensity, 85 % HRmax) and one control group. 5-HT levels and response inhibition (measured by a computerized Stroop test) were assessed pre- and post-intervention.

RESULTS

There was a significant (p = 0.022) difference between groups regarding serum Δ5-HT levels. Post hoc tests indicated significant (p = 0.013) higher 5-HT serum levels for the high-intensity group compared to the control group while other groups did not differ significantly from each other. Serum Δ5-HT levels and exercise intensity were shown to be linearly associated through polynomial contrast analysis (p = 0.003). Furthermore, ANOVA revealed a significant difference for Stroop parameter reading (p = 0.030) and a tendency for reverse Stroop effect (p = 0.061). Correlation analysis showed that augmented 5-HT levels were associated with improved results in response inhibition.

CONCLUSIONS

This study indicates that intensive acute exercise increases serum 5-HT levels compared to a control group. These findings might be relevant for many other related research fields in exercise science, since 5-HT receptors are expressed on many different cell types including endothelia and immune cells.

Partial pharmacologic blockade shows sympathetic connection between blood pressure and cerebral blood flow velocity fluctuations

Cerebral autoregulation (CA) dampens transfer of blood pressure (BP)-fluctuations onto cerebral blood flow velocity (CBFV). Thus, CBFV-oscillations precede BP-oscillations. The phase angle (PA) between sympathetically mediated low-frequency (LF: 0.03-0.15Hz) BP- and CBFV-oscillations is a measure of CA quality. To evaluate whether PA depends on sympathetic modulation, we assessed PA-changes upon sympathetic stimulation with and without pharmacologic sympathetic blockade. In 10 healthy, young men, we monitored mean BP and CBFV before and during 120-second cold pressor stimulation (CPS) of one foot (0°C ice-water). We calculated mean values, standard deviations and sympathetic LF-powers of all signals, and PAs between LF-BP- and LF-CBFV-oscillations. We repeated measurements after ingestion of the adrenoceptor-blocker carvedilol (25mg). We compared parameters before and during CPS, without and after carvedilol (analysis of variance, post-hoc t-tests, significance: p<0.05). Without carvedilol, CPS increased BP, CBFV, BP-LF- and CBFV-LF-powers, and shortened PA. Carvedilol decreased resting BP, CBFV, BP-LF- and CBFV-LF-powers, while PAs remained unchanged. During CPS, BPs, CBFVs, BP-LF- and CBFV-LF-powers were lower, while PAs were longer with than without carvedilol. With carvedilol, CPS no longer shortened resting PA. Sympathetic activation shortens PA. Partial adrenoceptor blockade abolishes this PA-shortening. Thus, PA-measurements provide a subtle marker of sympathetic influences on CA and might refine CA evaluation.

Neurovascular coupling in humans: Physiology, methodological advances and clinical implications

Neurovascular coupling reflects the close temporal and regional linkage between neural activity and cerebral blood flow. Although providing mechanistic insight, our understanding of neurovascular coupling is largely limited to non-physiologicalex vivopreparations and non-human models using sedatives/anesthetics with confounding cerebrovascular implications. Herein, with particular focus on humans, we review the present mechanistic understanding of neurovascular coupling and highlight current approaches to assess these responses and the application in health and disease. Moreover, we present new guidelines for standardizing the assessment of neurovascular coupling in humans. To improve the reliability of measurement and related interpretation, the utility of new automated software for neurovascular coupling is demonstrated, which provides the capacity for coalescing repetitive trials and time intervals into single contours and extracting numerous metrics (e.g., conductance and pulsatility, critical closing pressure, etc.) according to patterns of interest (e.g., peak/minimum response, time of response, etc.). This versatile software also permits the normalization of neurovascular coupling metrics to dynamic changes in arterial blood gases, potentially influencing the hyperemic response. It is hoped that these guidelines, combined with the newly developed and openly available software, will help to propel the understanding of neurovascular coupling in humans and also lead to improved clinical management of this critical physiological function.

Beta1-adrenergic receptor-mediated dilation of rat cerebral artery requires Shaker-type KV1 channels on PSD95 scaffold

Postsynaptic density-95 (PSD95) is a scaffolding protein in cerebral vascular smooth muscle cells (cVSMCs), which binds to Shaker-type K(+) (KV1) channels and facilitates channel opening through phosphorylation by protein kinase A. β1-Adrenergic receptors (β1ARs) also have a binding motif for PSD95. Functional association of β1AR with KV1 channels through PSD95 may represent a novel vasodilator complex in cerebral arteries (CA). We explored whether a β1AR-PSD95-KV1 complex is a determinant of rat CA dilation. RT-PCR and western blots revealed expression of β1AR in CA. Isoproterenol induced a concentration-dependent dilation of isolated, pressurized rat CA that was blocked by the β1AR blocker CGP20712. Cranial window imaging of middle cerebral arterioles in situ showed isoproterenol- and norepinephrine-induced dilation that was blunted by β1AR blockade. Isoproterenol-induced hyperpolarization of cVSMCs in pressurized CA was blocked by CGP20712. Confocal images of cVSMCs immunostained with antibodies against β1AR and PSD95 indicated strong colocalization, and PSD95 co-immunoprecipitated with β1AR in CA lysate. Blockade of KV1 channels, β1AR or disruption of PSD95-KV1 interaction produced similar blunting of isoproterenol-induced dilation in pressurized CA. These findings suggest that PSD95 mediates a vasodilator complex with β1AR and KV1 channels in cVSMCs. This complex may be critical for proper vasodilation in rat CA.

Regulation of myogenic tone and structure of parenchymal arterioles by hypertension and the mineralocorticoid receptor

Proper perfusion is vital for maintenance of neuronal homeostasis and brain function. Changes in the function and structure of cerebral parenchymal arterioles (PAs) could impair blood flow regulation and increase the risk of cerebrovascular diseases, including dementia and stroke. Hypertension alters the structure and function of large cerebral arteries, but its effects on PAs remain unknown. We hypothesized that hypertension increases myogenic tone and induces inward remodeling in PAs; we further proposed that antihypertensive therapy or mineralocorticoid receptor (MR) blockade would reverse the effects of hypertension. PAs from 18-wk-old stroke-prone spontaneously hypertensive rats (SHRSP) were isolated and cannulated in a pressure myograph. At 50-mmHg intraluminal pressure, PAs from SHRSP showed higher myogenic tone (%tone: 39.1 ± 1.9 vs. 28.7 ± 2.5%, P < 0.01) and smaller resting luminal diameter (34.7 ± 1.9 vs. 46.2 ± 2.4 μm, P < 0.01) than those from normotensive Wistar-Kyoto rats, through a mechanism that seems to require Ca(2+) influx through L-type voltage-gated Ca(2+) channels. PAs from SHRSP showed inward remodeling (luminal diameter at 60 mmHg: 55.2 ± 1.4 vs. 75.7 ± 5.1 μm, P < 0.01) and a paradoxical increase in distensibility and compliance. Treatment of SHRSP for 6 wk with antihypertensive therapy reduced PAs' myogenic tone, increased their resting luminal diameter, and prevented inward remodeling. In contrast, treatment of SHRSP for 6 wk with an MR antagonist did not reduce blood pressure or myogenic tone, but prevented inward remodeling. Thus, while hypertensive remodeling of PAs may involve the MR, myogenic tone seems to be independent of MR activity.

Norepinephrine as a potential aggravator of symptomatic cerebral vasospasm: two cases and argument for milrinone therapy

Background. During hypertensive therapy for post-subarachnoid hemorrhage (SAH) symptomatic vasospasm, norepinephrine is commonly used to reach target blood pressures. Concerns over aggravation of vasospasm with norepinephrine exist. Objective. To describe norepinephrine temporally related deterioration in neurological examination of two post-SAH patients in vasospasm. Methods. We retrospectively reviewed two charts of patients with delayed cerebral ischemia (DCI) post-SAH who deteriorated with norepinephrine infusions. Results. We identified two patients with DCI post-SAH who deteriorated during hypertensive therapy with norepinephrine. The first, a 43-year-old male presented to hospital with DCI, failed MABP directed therapy with rapid deterioration in exam with high dose norepinephrine and MABP of 140–150 mm Hg. His exam improved on continuous milrinone and discontinuation of norepinephrine. The second, a 39-year-old female who developed DCI on postbleed day 8 responded to milrinone therapy upfront. During further deterioration and after angioplasty, norepinephrine was utilized to drive MABP to 130–140 mm Hg. Progressive deterioration in examination occurred after angioplasty as norepinephrine doses escalated. After discontinuation of norepinephrine and continuation of milrinone, function dramatically returned but not to baseline. Conclusions. The potential exists for worsening of DCI post-SAH with hypertensive therapy directed by norepinephrine. A potential role exists for vasodilation and inotropic directed therapy with milrinone in the setting of DCI post-SAH.

Extensive projections of myenteric serotonergic neurons suggest they comprise the central processing unit in the colon

BACKGROUND

5-Hydroxytryptamine (5-HT, serotonin) is an important regulator of colonic motility and secretion; yet the role of serotonergic neurons in the colon is controversial.

METHODS

We used immunohistochemical techniques to examine their projections throughout the enteric nervous system and interstitial cells of Cajal (ICC) networks in the murine proximal to mid colon.

KEY RESULTS

Serotonergic neurons, which were mainly calbindin positive, occurred only in myenteric ganglia (1 per 3 ganglia). They were larger than nNOS neurons but similar in size to Dogiel Type II (AH) neurons. 5-HT neurons, appeared to make numerous varicose contacts with each other, most nNOS neurons, Dogiel Type II/AH neurons and glial cells. 5-HT, calbindin and nNOS nerve fibers also formed a thin perimuscular nerve plexus that was associated with ganglia, which contained both nNOS positive and negative neurons, which lay directly upon the submucosal pacemaker ICC network. Neurons in perimuscular ganglia were surrounded by 5-HT varicosities. Submucous ganglia contained nNOS positive and negative neurons, and calbindin positive neurons, which also appeared richly supplied by serotonergic nerve varicosities. Serotonergic nerve fibers ran along submucosal arterioles, but not veins. Varicosities of serotonergic nerve fibers were closely associated with pacemaker ICC networks and with intramuscular ICC (ICC-IM). 5-HT2B receptors were found on a subpopulation of non-5-HT containing myenteric neurons and their varicosities, pacemaker ICC-MY and ICC-IM.

CONCLUSIONS & INFERENCES

Myenteric serotonergic neurons, whose axons exhibit considerable divergence, regulate the entire enteric nervous system and are important in coordinating motility with secretion. They are not just interneurons, as regularly assumed, but possibly also motor neurons to ICC and blood vessels, and some may even be sensory neurons.

Changes in maternal posterior and anterior cerebral artery flow velocity during pregnancy and postpartum--a longitudinal study

BACKGROUND

To evaluate the normal range of blood flow velocity in the maternal anterior (ACA) and posterior cerebral arteries (PCA) along the normal pregnancy and postpartum period.

METHODS

Transcranial Doppler ultrasound was used to measure the systolic, diastolic, and mean blood velocities in the ACA and PCA during normal gestation. The resistance and pulsatility indices were calculated. Data were analyzed using multilevel modeling, incorporating random effects models, to construct mean and percentile curves.

RESULTS

We performed 355 measurements on 59 patients, which showed that systolic and mean velocity in the ACA decreased, whereas diastolic velocity increased in the PCA during normal pregnancy. Resistance and pulsatility indices in both vessels increased to a maximum in the second trimester, decreased during the third trimester, and increased during the postpartum period.

CONCLUSIONS

This study provides normative data for ACA and PCA velocity and indices during pregnancy and postpartum, demonstrating changes in velocity that suggest a shift of cerebral blood flow from the anterior to the posterior cerebral circulation.

Synthesis, transport, and metabolism of serotonin formed from exogenously applied 5-HTP after spinal cord injury in rats

Spinal cord transection leads to elimination of brain stem-derived monoamine fibers that normally synthesize most of the monoamines in the spinal cord, including serotonin (5-hydroxytryptamine, 5-HT) synthesized from tryptophan by enzymes tryptophan hydroxylase (TPH, synthesizing 5-hydroxytryptophan, 5-HTP) and aromatic l-amino acid decarboxylase (AADC, synthesizing 5-HT from 5-HTP). Here we examine whether spinal cord caudal to transection remains able to manufacture and metabolize 5-HT. Immunolabeling for AADC reveals that, while most AADC is confined to brain stem-derived monoamine fibers in spinal cords from normal rats, caudal to transection AADC is primarily found in blood vessel endothelial cells and pericytes as well as a novel group of neurons (NeuN positive and GFAP negative), all of which strongly upregulate AADC with injury. However, immunolabeling for 5-HT reveals that there is no detectable endogenous 5-HT synthesis in any structure in the spinal cord caudal to a chronic transection, including in AADC-containing vessels and neurons, consistent with a lack of TPH. In contrast, when we applied exogenous 5-HTP (in vitro or in vivo), AADC-containing vessels and neurons synthesized 5-HT, which contributed to increased motoneuron activity and muscle spasms (long-lasting reflexes, LLRs), by acting on 5-HT2 receptors (SB206553 sensitive) located on motoneurons (TTX resistant). Blocking monoamine oxidase (MAO) markedly increased the sensitivity of the motoneurons (LLR) to 5-HTP, more than it increased the sensitivity of motoneurons to 5-HT, suggesting that 5-HT synthesized from AADC is largely metabolized in AADC-containing neurons and vessels. In summary, after spinal cord injury AADC is upregulated in vessels, pericytes, and neurons but does not endogenously produce 5-HT, whereas when exogenous 5-HTP is provided AADC does produce functional amounts of 5-HT, some of which is able to escape metabolism by MAO, diffuse out of these AADC-containing cells, and ultimately act on 5-HT receptors on motoneurons.

The effects of hypertension on the cerebral circulation

Maintenance of brain function depends on a constant blood supply. Deficits in cerebral blood flow are linked to cognitive decline, and they have detrimental effects on the outcome of ischemia. Hypertension causes alterations in cerebral artery structure and function that can impair blood flow, particularly during an ischemic insult or during periods of low arterial pressure. This review will focus on the historical discoveries, novel developments, and knowledge gaps in 1) hypertensive cerebral artery remodeling, 2) vascular function with emphasis on myogenic reactivity and endothelium-dependent dilation, and 3) blood-brain barrier function. Hypertensive artery remodeling results in reduction in the lumen diameter and an increase in the wall-to-lumen ratio in most cerebral arteries; this is linked to reduced blood flow postischemia and increased ischemic damage. Many factors that are increased in hypertension stimulate remodeling; these include the renin-angiotensin-aldosterone system and reactive oxygen species levels. Endothelial function, vital for endothelium-mediated dilation and regulation of myogenic reactivity, is impaired in hypertension. This is a consequence of alterations in vasodilator mechanisms involving nitric oxide, epoxyeicosatrienoic acids, and ion channels, including calcium-activated potassium channels and transient receptor potential vanilloid channel 4. Hypertension causes blood-brain barrier breakdown by mechanisms involving inflammation, oxidative stress, and vasoactive circulating molecules. This exposes neurons to cytotoxic molecules, leading to neuronal loss, cognitive decline, and impaired recovery from ischemia. As the population ages and the incidence of hypertension, stroke, and dementia increases, it is imperative that we gain a better understanding of the control of cerebral artery function in health and disease.

Autonomic blockade during sinusoidal baroreflex activation proves sympathetic modulation of cerebral blood flow velocity

BACKGROUND AND PURPOSE

Pharmacological blockade showed sympathetic origin of 0.03 to 0.15 Hz blood pressure (BP) oscillations and parasympathetic origin of 0.15 to 0.5 Hz RR-interval (RRI) oscillations, but has not been used to determine origin of cerebral blood flow velocity (CBFV) oscillations at these frequencies. This study evaluated by pharmacological blockade whether 0.1 Hz CBFV oscillations are related to sympathetic and 0.2 Hz CBFV oscillations to parasympathetic modulation.

METHODS

In 11 volunteers (24.6 ± 2.3 years), we monitored RRIs, BP, and proximal middle cerebral artery CBFV, at rest, during 180 s sympathetic BP activation by 0.1 Hz sinusoidal neck suction (NS), and during 180 s parasympathetic RRI activation by 0.2 Hz NS. We repeated recordings after 25 mg carvedilol, and after 0.04 mg/kg atropine. Autoregressive analysis quantified RRI-, BP-, and CBFV-spectral powers at 0.1 Hz and 0.2 Hz. We compared parameters at rest, during 0.1 Hz, or 0.2 Hz NS, with and without carvedilol or atropine (analysis of variance, post hoc testing; significance, P<0.05).

RESULTS

Carvedilol significantly increased RRIs and lowered BP, CBFV, and 0.1 Hz RRI-, BP-, and CBFV-powers at baseline (P=0.041 for CBFV-powers), and during 0.1 Hz NS-induced sympathetic activation (P<0.05). At baseline and during 0.2 Hz NS-induced parasympathetic activation, atropine lowered RRIs and 0.2 Hz RRI-powers, but did not change BP, CBFV, and 0.2 Hz BP- and CBFV-powers.

CONCLUSIONS

Attenuation of both 0.1 Hz CBFV and BP oscillations after carvedilol indicates a direct relation between 0.1 Hz CBFV oscillations and sympathetic modulation. Absent effects of atropine on BP, CBFV, and 0.2 Hz BP and CBFV oscillations suggest that there is no direct parasympathetic influence on 0.2 Hz BP and CBFV modulation.

Effect of pregnancy on autoregulation of cerebral blood flow in anterior versus posterior cerebrum

Severe preeclampsia and eclampsia are associated with brain edema that forms preferentially in the posterior cerebral cortex possibly because of decreased sympathetic innervation of posterior cerebral arteries and less effective autoregulation during acute hypertension. In the present study, we examined the effect of pregnancy on the effectiveness of cerebral blood flow autoregulation using laser Doppler flowmetry and edema formation by wet:dry weight in acute hypertension induced by phenylephrine infusion in the anterior and posterior cerebrum from nonpregnant (n=8) and late-pregnant (n=6) Sprague-Dawley rats. In addition, we compared the effect of pregnancy on sympathetic innervation by tyrosine hydroxylase staining of posterior and middle cerebral arteries (n=5-6 per group) and endothelial and neuronal NO synthase expression using quantitative PCR (n=3 per group). In nonpregnant animals, there was no difference in autoregulation between the anterior and posterior cerebrum. However, in late-pregnant animals, the threshold of cerebral blood flow autoregulation was shifted to lower pressures in the posterior cerebrum, which was associated with increased neuronal NO synthase expression in the posterior cerebral cortex versus anterior. Compared with the nonpregnant state, pregnancy increased the threshold of autoregulation in both brain regions that was related to decreased expression of endothelial NO synthase. Lastly, acute hypertension during pregnancy caused greater edema formation in both brain cortices that was not attributed to changes in sympathetic innervation. These findings suggest that, although pregnancy shifted the cerebral blood flow autoregulatory curve to higher pressures in both the anterior and posterior cortices, it did not protect from edema during acute hypertension.

Norepinephrine promotes the β1-integrin-mediated adhesion of MDA-MB-231 cells to vascular endothelium by the induction of a GROα release

The migratory activity of tumor cells and their ability to extravasate from the blood stream through the vascular endothelium are important steps within the metastasis cascade. We have shown previously that norepinephrine is a potent inducer of the migration of MDA-MB-468 human breast carcinoma cells and therefore investigated herein, whether the interaction of these cells as well as MDA-MB-231 and MDA-MB-435S human breast carcinoma cells with the vascular endothelium is affected by this neurotransmitter as well. By means of a flow-through assay under physiologic flow conditions, we show that norepinephrine induces an increase of the adhesion of the MDA-MB-231 cells, but not of MDA-MB-468 and MDA-MB-435S cells to human pulmonary microvascular endothelial cells (HMVEC). The adhesion of MDA-MB-231 cells was based on a norepinephrine-mediated release of GROα from HMVECs. GROα caused a β1-integrin-mediated increase of the adhesion of MDA-MB-231 cells. Most interestingly, this effect of norepinephrine, similar to the aforementioned induction of migration in MDA-MB-468 cells, was mediated by β-adrenergic receptors and therefore abrogated by β-blockers. In conclusion, norepinephrine has cell line-specific effects with regard to certain steps of the metastasis cascade, which are conjointly inhibited by clinically established β-blockers. Therefore, these results may deliver a molecular explanation for our recently published retrospective data analysis of patients with breast cancer which shows that β-blockers significantly reduce the development of metastases.

Sex differences in the expression of serotonin-synthesizing enzymes in mouse trigeminal ganglia

Migraine headaches are more prevalent in women and often occur during the early phases of the menstrual cycle, implying a link between migraine and ovarian steroids. Serotonin (5-HT) and its receptors have been proposed to play a key role in the pathophysiology of migraine. The trigeminal ganglion (TG) has been proposed as a site for 5-HT synthesis based on the expression of the rate limiting enzyme in peripheral 5-HT synthesis, tryptophan hydroxylase 1 (TPH1), in female rodent trigeminal ganglia. Tryptophan hydroxylase levels vary over the estrus cycle, however, the expression and potential regulation of other enzymes involved in 5-HT synthesis has not been reported in this tissue. C57/BL6 mice of both sexes expressed TPH1 and aromatic amino acid decarboxylase (AADC), the key enzymes involved in 5-HT synthesis. Levels of both enzymes were significantly higher in juvenile males compared with females. In naturally cycling females TPH1 and AADC expression was highest during proestrus when compared with the other phases of the cycle, and this regulation was mirrored at the mRNA level. In situ hybridization experiments detected TPH1 and AADC mRNA in presumptive neurons in the trigeminal ganglion. Both key enzymes involved in the synthesis of 5-HT are expressed in mouse trigeminal ganglion and are localized to neurons. The levels of these enzymes are dependent on gender and estrus cycle stage, suggesting that ovarian steroids might play a role in the regulation of sensory neuron 5-HT synthesis.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.

The effect of ovariectomy and estrogen on penetrating brain arterioles and blood-brain barrier permeability

OBJECTIVE

We investigated the effect of estrogen replacement on the structure and function of penetrating brain arterioles (PA) and blood-brain barrier (BBB) permeability.

MATERIALS AND METHODS

Female ovariectomized Sprague-Dawley rats were replaced with estradiol (E(2)) and estriol (E(3)) (OVX + E; N=13) and compared to ovariectomized animals without replacement (OVX; N=14) and intact controls (CTL, proestrous; N=13). Passive and active diameters, percent tone, and passive distensibility of pressurized PA were compared. In addition, BBB permeability to Lucifer Yellow, a marker of transcellular transport, was compared in cerebral arteries.

RESULTS

Ovariectomy increased myogenic tone in PA, compared to CTL, that was not ameliorated by estrogen treatment. Percent tone at 75 mmHg for CTL vs. OVX and OVX + E was 44+/-3% vs. 51+/-1% and 54+/-3% (P<0.01 vs. CTL for both). No differences were found in passive diameters or distensibility between the groups. BBB permeability increased 500% in OVX vs. CTL animals; however, estrogen replacement restored barrier properties: flux of Lucifer Yellow for CTL, OVX, and OVX + E was (ng/mL): 3.4+/-1.2, 20.2+/-5.3 (P<0.01 vs. CTL), and 6.15+/-1.2 (n.s.).

CONCLUSIONS

These results suggest that estrogen replacement may not be beneficial for small-vessel disease in the brain, but may limit BBB disruption and edema under conditions that cause it.

Statins decrease dendritic arborization in rat sympathetic neurons by blocking RhoA activation

Clinical and experimental evidence suggest that statins decrease sympathetic activity, but whether peripheral mechanisms involving direct actions on post-ganglionic sympathetic neurons contribute to this effect is not known. Because tonic activity of these neurons is directly correlated with the size of their dendritic arbor, we tested the hypothesis that statins decrease dendritic arborization in sympathetic neurons. Oral administration of atorvastatin (20 mg/kg/day for 7 days) significantly reduced dendritic arborization in vivo in sympathetic ganglia of adult male rats. In cultured sympathetic neurons, statins caused dendrite retraction and reversibly blocked bone morphogenetic protein-induced dendritic growth without altering cell survival or axonal growth. Supplementation with mevalonate or isoprenoids, but not cholesterol, attenuated the inhibitory effects of statins on dendritic growth, whereas specific inhibition of isoprenoid synthesis mimicked these statin effects. Statins blocked RhoA translocation to the membrane, an event that requires isoprenylation, and constitutively active RhoA reversed statin effects on dendrites. These observations that statins decrease dendritic arborization in sympathetic neurons by blocking RhoA activation suggest a novel mechanism by which statins decrease sympathetic activity and protect against cardiovascular and cerebrovascular disease.

Cortical blood flow assessment with frequency-domain laser Doppler microscopy

We report the assessment of cerebral blood flow (CBF) changes with a wide-field laser Doppler imager based on a CCD camera detection scheme, in vivo, in mice. The setup enables the acquisition of data in minimally invasive conditions. In contrast with conventional laser Doppler velocimeters and imagers, the Doppler signature of moving scatterers is measured in the frequency domain, by detuning a heterodyne optical detection. The quadratic mean of the measured frequency shift is used as an indicator of CBF. We observe a significant variability of this indicator in an experiment designed to induce blood flow changes.

Effect of sympathetic and parasympathetic mediators on the release of calcitonin gene-related peptide and prostaglandin E from rat dura mater, in vitro

Although not without controversy, an influence of the autonomic nervous system in headache is a matter for current debate. A possible contact site of autonomic and sensory nerves is the dura mater, where they form a dense network accompanying blood vessels. We investigated interactions between autonomic and nociceptive fibres by measuring release of calcitonin gene-related peptide (CGRP) and prostaglandin E2 (PGE2) from the dura mater, in vitro. The parasympathomimetic agent carbachol did not change basal release of CGRP or PGE2, whereas it diminished release induced by a mixture of inflammatory mediators. Norepinephrine did not change induced release of CGRP or PGE2, nor basal release of CGRP. However, basal release of PGE2 was enhanced by norepinephrine, and this enhancement was reduced by serotonin through 5-HT(1D) receptors. We conclude that sympathetic transmitters may control nociceptor sensitivity via increased basal PGE2 levels, a possible mechanism to facilitate headache generation. Parasympathetic transmitters may reduce enhanced nociceptor activity.

Mechanisms involved in the early increase of serotonin contraction evoked by endotoxin in rat middle cerebral arteries

The present study investigated the mechanisms involved in the increased 5-hydroxytryptamine (5-HT) vasoconstriction observed in rat middle cerebral arteries exposed in vitro to lipopolysaccharide (LPS, 10 microg x ml-1) for 1-5 h. Functional, immunohistochemical and Western blot analysis and superoxide anion measurements by ethidium fluorescence were performed. LPS exposure increased 5-HT (10 microm) vasoconstriction only during the first 4 h. In contrast to control tissue, indomethacin (10 microm), the COX-2 inhibitor NS 398 (10 microm), the TXA2/PGH2 receptor antagonist SQ 29548 (1 microm) and the TXA2 synthase inhibitor furegrelate (1 microm) reduced 5-HT contraction of LPS-treated arteries from hour one. The iNOS inhibitor aminoguanidine (0.1 mm) increased 5-HT contraction from hour three of LPS incubation. The superoxide anion scavenger superoxide dismutase (SOD, 100 U ml-1) and the H2O2 scavenger catalase (1000 U ml-1), as well as the respective inhibitors of NAD(P)H oxidase and xanthine oxidase, apocynin (0.3 mm) and allopurinol (0.3 mm), reduced 5-HT contraction after LPS incubation. LPS induced an increase in superoxide anion levels that was abolished by PEG-SOD. Subthreshold concentrations of the TXA2 analogue U 46619, xanthine/xanthine oxidase and H2O2 potentiated, whereas those of sodium nitroprusside inhibited, the 5-HT contraction. COX-2 expression was increased at 1 and 5 h of LPS incubation, while that of iNOS, Cu/Zn-SOD and Mn-SOD was only increased after 5 h. All the three vascular layers expressed COX-2 and Cu/Zn-SOD. iNOS expression was detected in the endothelium and adventitia after LPS. In conclusion, increased production of TXA2 from COX-2, superoxide anion and H2O2 enhanced vasoconstriction to 5-HT during the first few hours of LPS exposure; iNOS and SOD expression counteracted that increase at 5 h. These changes can contribute to the disturbance of cerebral blood flow in endotoxic shock.

Perivascular innervation of penetrating brain parenchymal arterioles

We investigated the functional heterogeneity of cerebral pial arteries that are extrinsically innervated versus penetrating brain parenchymal arterioles (PA) that are intrinsically innervated by comparing myogenic activity and reactivity to neurotransmitter. Pial middle cerebral arteries (MCA, n = 6) and PA (n = 6) that branched off the MCA and penetrated the brain tissue were isolated from male Wistar rats and studied in vitro under pressurized conditions for reactivity to serotonin (5-hydroxytryptamine, 5-HT), noradrenaline (NA), and indolactam-V (IL-V), a protein kinase C (PKC) agonist. In a separate group of vessels from the same locations (n = 12), perivascular nerve density was determined after staining for protein gene product 9.5 (PGP 9.5). PAs were significantly smaller than MCAs, and possessed greater myogenic tone at all pressures studied. MCAs reacted to both 5-HT and NA with concentration-dependent contraction, however, PA had little to no response to either neurotransmitter. The percent constriction to 5-HT and NA for MCA versus PA at the maximum concentration was: 31 +/- 6% versus 1.0 +/- 1.0% and 13 +/- 5% versus 2.6 +/- 1.8% (P < 0.01). However, both types of vessels contracted with similar reactivity to PKC activation with IL-V (41 +/- 4% versus 37 +/- 7%, ns). Perivascular nerve density correlated with reactivity such that MCAs were densely innervated with varicose fibers within the adventitia; however, PA had very few or no adventitial fibers. The differential response to neurotransmitter suggests that there is significant heterogeneity in the cerebral circulation. It appears that in PA, the dominant vasoconstricting stimulus is intrinsic myogenic tone and that the role of neurotransmitter and intrinsic innervation is beyond that of controlling CBF.

Noradrenergic constriction of cerebral arteries as detected by transcranial Doppler (TCD) in the rabbit

Interpretation of transcranial Doppler (TCD) recordings requires assumptions about flow or diameter of the insonated vessel. This study aimed at assessing if activation of the sympathetic system could affect blood velocity (bv) in basal cerebral arteries. In anaesthetized rabbits, stimulation of cervical sympathetic nerve (cervSN) was used selectively to activate the sympathetic pathway to the head while monitoring bv in all major cerebral arteries. cervSN stimulation at 10 Hz produced: 1. in internal carotid artery (ICA) and ICA-supplied arteries (ICA-s), a consistent bv increase ranging between 20 and 70%, 2. in the basilar artery, a transient decrease by 15-30%. These effects were mimicked, in both territories, by injection of phenylephrine into the ICA. Because cerebral blood flow is known to be reduced by cervSN stimulation, the increase in bv in ICA and ICA-s must be ascribed to constriction of the insonated vessels. These effects should be considered when monitoring bv during sympathetic activation tests or exercise.