Innervation of cerebral blood vessels: morphology, plasticity, age-related, and Alzheimer's disease-related neurodegeneration

Cervical Ganglion Sympathectomy to Treat Cerebral Vasospasm in Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) is still a significant cause of death and disability after aneurysmal subarachnoid hemorrhage. Cerebral vasospasm represents one of the most reported mechanisms associated with DCI. The management of DCI-related vasospasm remains a significant challenge for clinicians; induced hypertension, intraarterial vasodilators, and/or intracranial vessel angioplasty-particularly in refractory or recurrent cases-are the most used therapies. Because an essential role in the pathophysiology of cerebral vasospasm has been attributed to the adrenergic sympathetic nerves, a "sympatholytic" intervention, consisting of a temporary interruption of the sympathetic pathways using local anesthetics, has been advocated to minimize the vascular narrowing and reverse the consequences of cerebral vasospasm on tissue perfusion. In this review, we have analyzed the existing literature on the block of the cervical ganglions, particularly the stellate ganglion, in managing refractory cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage. These findings could help clinicians to understand the potential role of such intervention and to develop future interventional trials in this setting.

Age-Related Variation in Sympathetic Nerve Distribution in the Human Spleen

Introduction: The cholinergic anti-inflammatory pathway (CAIP) has been proposed as an efferent neural pathway dampening the systemic inflammatory response via the spleen. The CAIP activates the splenic neural plexus and a subsequent series of intrasplenic events, which at least require a close association between sympathetic nerves and T cells. Knowledge on this pathway has mostly been derived from rodent studies and only scarce information is available on the innervation of the human spleen. This study aimed to investigate the sympathetic innervation of different structures of the human spleen, the topographical association of nerves with T cells and age-related variations in nerve distribution.

Materials and Methods: Spleen samples were retrieved from a diagnostic archive and were allocated to three age groups; neonates, 10–25 and 25–70 years of age. Sympathetic nerves and T cells were identified by immunohistochemistry for tyrosine hydroxylase (TH) and the membrane marker CD3, respectively. The overall presence of sympathetic nerves and T cells was semi-automatically quantified and expressed as total area percentage. A predefined scoring system was used to analyze the distribution of nerves within different splenic structures.

Results: Sympathetic nerves were observed in all spleens and their number appeared to slightly increase from birth to adulthood and to decrease afterward. Irrespective to age, more than halve of the periarteriolar lymphatic sheaths (PALSs) contained sympathetic nerves in close association with T cells. Furthermore, discrete sympathetic nerves were observed in the capsule, trabeculae and red pulp and comparable to the total amount of sympathetic nerves, showed a tendency to decrease with age. No correlation was found between the number of T cells and sympathetic nerves.

Conclusion: The presence of discrete sympathetic nerves in the splenic parenchyma, capsule and trabecular of human spleens could suggest a role in functions other than vasoregulation. In the PALS, sympathetic nerves were observed to be in proximity to T cells and is suggestive for the existence of the CAIP in humans. Since sympathetic nerve distribution shows interspecies and age-related variation, and our general understanding of the relative and spatial contribution of splenic innervation in immune regulation is incomplete, it remains difficult to estimate the anti-inflammatory potential of targeting splenic nerves in patients.

Regulation of Blood Flow in the Cerebral Posterior Circulation by Parasympathetic Nerve Fibers: Physiological Background and Possible Clinical Implications in Patients With Vertebrobasilar Stroke

Posterior circulation involves the vertebrobasilar arteries, which supply oxygen and glucose to vital human brainstem structures and other areas. This complex circulatory- perfusion system is not homogenous throughout the day; rather, its hemodynamic changes rely on physiological demands, ensuring brainstem perfusion. This dynamic autoregulatory pattern maintains cerebral perfusion during blood pressure changes. Accumulative evidence suggests that activity within the autonomic nervous system is involved in the regulation of cerebral blood flow. Neither the sympathetic nor parasympathetic nervous systems work independently. Functional studies have shown a tight and complicated cross talk between these systems. In pathological processes where sympathetic stimulation is present, systemic vasoconstriction is followed, representing the most important CNS parasympathetic trigger that will promote local vasodilation. Stroke is a clear example of this process. The posterior circulation is affected in 30% of strokes, causing high morbidity and mortality outcomes. Currently, the management of ischemic stroke is focused on thrombolytic treatment and endovascular thrombectomy within an overall tight 4.5 to 6 h ischemic time window. Therefore, the autonomic nervous system could represent a potential therapeutic target to modulate reperfusion after cerebral ischemia through vasodilation, which could potentially decrease infarct size and increase the thrombolytic therapeutic ischemic window. In addition, shifting the autonomic nervous system balance toward its parasympathetic branch has shown to enhance neurogenesis and decrease local inflammation. Regretfully, the vast majority of animal models and human research on neuromodulation during brain ischemia have been focused on anterior circulation with disappointing results. In addition, the source of parasympathetic inputs in the vertebrobasilar system in humans is poorly understood, substantiating a gap and controversy in this area. Here, we reviewed current available literature regarding the parasympathetic vascular function and challenges of its stimulation in the vertebrobasilar system.

Gross and Micro-Anatomical Study of the Cavernous Segment of the Abducens Nerve and Its Relationships to Internal Carotid Plexus: Application to Skull Base Surgery

The present study aims to provide detailed observations on the cavernous segment of the abducens nerve (AN), emphasizing anatomical variations and the relationships between the nerve and the internal carotid plexus. A total of 60 sides underwent gross-anatomical study. Five specimens of the AN were stained using Sihler’s method. An additional five specimens were subjected to histological examination. Four types of AN course were observed: a single nerve along its entire course, duplication of the nerve, division into separate rootlets at the point of contact with the cavernous part of the internal carotid artery (ICA), and early-branching before entering the orbit. Due to the relationships between the ICA and internal carotid plexus, the cavernous segment of the AN can be subdivided into a carotid portion located at the point of contact with the posterior vertical segment of the cavernous ICA and a prefissural portion. The carotid portion of the cavernous AN segment is a place of angulation, where the nerve always directly adheres to the ICA. The prefissural portion of the AN, in turn, is the primary site of fiber exchange between the internal carotid plexus and either the AN or the lateral wall of the cavernous sinus.

Effect of bilateral carotid occlusion on cerebral hemodynamics and perivascular innervation: An experimental rat model

We aimed to investigate the effect of chronic cerebral hypoperfusion on cerebral hemodynamics and perivascular nerve density in a rat model. Bilateral common carotid artery (CCA) ligation (n = 24) or sham‐operation (n = 24) was performed with a 1‐week interval. A subgroup (ligated n = 6; sham‐operated n = 3) underwent magnetic resonance imaging (MRI) before the procedures and 2 and 4 weeks after the second procedure. After termination, carotids were harvested for assessment of complete ligation and nerve density in cerebral arteries that were stained for the general neural marker PGP 9.5 and sympathetic marker TH by computerized image analysis. Five rats were excluded because of incomplete ligation. MRI‐based tortuosity of the posterior communicating artery (Pcom), first part of the posterior cerebral artery (P1) and basilar artery was observed in the ligated group, as well as an increased volume (p = 0.05) and relative signal intensity in the basilar artery (p = 0.04; sham‐group unchanged). Immunohistochemical analysis revealed that compared to sham‐operated rats, ligated rats had increased diameters of all intracircular segments and the extracircular part of the internal carotid artery (p < 0.05). Ligated rats showed a higher general nerve density compared to controls in P1 (10%, IQR:8.7–10.5 vs. 6.6%, IQR:5.5–7.4, p = 0.003) and Pcom segments (6.4%, IQR:5.8–6.5 vs. 3.2%, IQR:2.4–4.3, p = 0.003) and higher sympathetic nerve density in Pcom segments (3.7%, IQR:2.8–4.8 vs. 1.7%, IQR:1.3–2.2, p = 0.02). Bilateral CCA occlusion resulted in redistribution of blood flow to posteriorly located cerebral arteries with remarkable changes in morphology and perivascular nerve density, suggesting a functional role for perivascular nerves in cerebral autoregulation.

Enhanced contractility of intraparenchymal arterioles after global cerebral ischaemia in rat - new insights into the development of delayed cerebral hypoperfusion

AIM

Delayed cerebral hypoperfusion is a secondary complication found in the days after transient global cerebral ischaemia that worsens the ischaemic damage inflicted by the initial transient episode of global cerebral ischaemia. A recent study demonstrated increased cerebral vasoconstriction in the large arteries on the brain surface (pial arteries) after global cerebral ischaemia. However, smaller arterioles inside the brain (parenchymal arterioles) are equally important in the regulation of cerebral blood flow and yet their pathophysiology after global cerebral ischaemia is largely unknown. Therefore, we investigated whether increased contractility occurs in the intraparenchymal arterioles.

METHODS

Global cerebral ischaemia was induced in male Wistar rats by bilateral common carotid occlusion for 15 min combined with hypovolaemia. Regional cerebral blood flow was determined by quantitative autoradiography. Intraparenchymal arterioles were isolated and pressurized, and concentration-response curves to endothelin-1 with and without the endothelin B receptor-selective antagonist BQ788 was generated. Endothelin B receptor expression was investigated by quantitative flow cytometry and immunohistochemistry.

RESULTS

We observed increased endothelin-1-mediated contractility of parenchymal arterioles correlating with reduced cerebral blood flow of the cortex, hippocampus and caudate nucleus 48 h after global cerebral ischaemia. The increased endothelin-1-mediated contractility was abolished by BQ788, and the vascular smooth muscle cell-specific expression of endothelin B receptors was significantly increased after global cerebral ischaemia.

CONCLUSION

Increased endothelin-1-mediated contractility and expression of endothelin B receptors in the intraparenchymal vasculature contributes to the development of delayed cerebral hypoperfusion after global cerebral ischaemia in combination with vascular changes of the pial vasculature.

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.

Parasympathetic innervation of vertebrobasilar arteries: is this a potential clinical target?

This review aims to summarise the contemporary evidence for the presence and function of the parasympathetic innervation of the cerebral circulation with emphasis on the vertebral and basilar arteries (the posterior cerebral circulation). We consider whether the parasympathetic innervation of blood vessels could be used as a means to increase cerebral blood flow. This may have clinical implications for pathologies associated with cerebral hypoperfusion such as stroke, dementia and hypertension. Relative to the anterior cerebral circulation little is known of the origins and neurochemical phenotypes of the parasympathetic innervation of the vertebrobasilar arteries. These vessels normally provide blood flow to the brainstem and cerebellum but can, via the Circle of Willis upon stenosis of the internal carotid arteries, supply blood to the anterior cerebral circulation too. We review the multiple types of parasympathetic fibres and their distinct transmitter mechanisms and how these vary with age, disease and species. We highlight the importance of parasympathetic fibres for mediating the vasodilatory response to sympathetic activation. Current trials are investigating the possibility of electrically stimulating the postganglionic parasympathetic ganglia to improve cerebal blood flow to reduce the penumbra following stroke. We conclude that although there are substantial gaps in our understanding of the origins of parasympathetic innervation of the vertebrobasilar arteries, activation of this system under some conditions might bring therapeutic benefits.

Autonomic function and brain volume

OBJECTIVE

The aim of this study is to review the evidence on the role of the autonomic nervous system as a determinant of brain volume. Brain volume measures have gained increasing attention given its biological importance, particularly as a measurement of neurodegeneration.

METHODS

Using an integrative approach, we reviewed publications addressing the anatomical and physiological characteristics of brain autonomic innervation focusing on evidence from diverse clinical populations with respect to brain volume.

RESULTS

Multiple mechanisms contribute to changes in brain volume. Autonomic influence on cerebral blood volume is of significant interest.

CONCLUSION

We suggest a role for the autonomic innervation of brain vessels in fluctuations of cerebral blood volume. Further investigation in several clinical populations including multiple sclerosis is warranted to understand the specific role of parenchyma versus blood vessels changes on final brain volume.

Beyond neurovascular coupling, role of astrocytes in the regulation of vascular tone

The brain possesses two intricate mechanisms that fulfill its continuous metabolic needs: cerebral autoregulation, which ensures constant cerebral blood flow over a wide range of arterial pressures and functional hyperemia, which ensures rapid delivery of oxygen and glucose to active neurons. Over the past decade, a number of important studies have identified astrocytes as key intermediaries in neurovascular coupling (NVC), the mechanism by which active neurons signal blood vessels to change their diameter. Activity-dependent increases in astrocytic Ca(2+) activity are thought to contribute to the release of vasoactive substances that facilitate arteriole vasodilation. A number of vasoactive signals have been identified and their role on vessel caliber assessed both in vitro and in vivo. In this review, we discuss mechanisms implicating astrocytes in NVC-mediated vascular responses, limitations encountered as a result of the challenges in maintaining all the constituents of the neurovascular unit intact and deliberate current controversial findings disputing a main role for astrocytes in NVC. Finally, we briefly discuss the potential role of pericytes and microglia in NVC-mediated processes.

Molecular Mechanisms for Exercise Training-Induced Changes in Vascular Structure and Function: Skeletal Muscle, Cardiac Muscle, and the Brain

Compared with resting conditions, during incremental exercise, cardiac output in humans is elevated from ~5 to 25 L min(-1). In conjunction with this increase, the proportion of cardiac output directed toward skeletal muscle increases from ~20% to 85%, while blood flow to cardiac muscle increases 500% and blood flow to specific brain structures increases nearly 200%. Based on existing evidence, researchers believe that blood flow in these tissues is matched to the increases in metabolic rate during exercise. This phenomenon, the matching of blood flow to metabolic requirement, is often referred to as functional hyperemia. This chapter summarizes mechanical and metabolic factors that regulate functional hyperemia as well as other exercise-induced signals, which are also potent stimuli for chronic adaptations in vascular biology. Repeated exposure to exercise-induced increases in shear stress and the induction of angiogenic factors alter vascular cell gene expression and mediate changes in vascular volume and blood flow control. The magnitude and regulation of this coordinated response appear to be tissue specific and coupled to other factors such as hypertrophy and hyperplasia. The cumulative effects of these adaptations contribute to increased exercise capacity, reduced relative challenge of a given submaximal exercise bout and ameliorated vascular outcomes in patient populations with pathological conditions. In the subsequent discussion, this chapter explores exercise as a regulator of vascular biology and summarizes the molecular mechanisms responsible for exercise training-induced changes in vascular structure and function in skeletal and cardiac muscle as well as the brain.

[Neck pain and headache as the only manifestation of cervical artery dissection]

OBJECTIVE

To analyze clinical and neuroimaging data in patients with neck pain and headache as the only manifestation of the internal carotid artery (ICA) dissection (ICAD) and vertebral artery (VA) dissection (VAD).

MATERIAL AND METHODS

One hundred and sixty-one patients (mean age - 37.4±4,99 years, 84 women, 52%) with cervical artery dissection (CAD) verified by magnetic resonance imaging (MRI) were enrolled. Neck pain and headache were the only CAD manifestation in 33 patients (mean age 37,3±7,4 yars, 28 women, 85%).

RESULTS

The localization of the dissections in these patients was the following: one VA (15 patients), two VA (9), one ICA (7), two ICA (1), one ICA + two VA (1). The whole number of dissected arteries was 45: extracranial localization - 38, extra-intracranial - 6, intracranial - 1. Dissection led to stenosis of the arterial lumen in 41 arteries, to occlusion - in 2 and to dual lumen in 2 arteries. Small aneurism was found in 4 arteries. Combination of headache and the neck pain was observed in 26 out of 33 patients (79%), the only headache in 4 patients, the only neck pain in 3 patients. Along with this, 9 out of 24 VAD patients had the shoulder and/or arm pain. Headache in VAD patients was located more often in the occipital region (18 out of 24) that had never been observed in ICAD patients (p=0.0009). Fronto-temporal pain was observed more often in ICAD patients (5 out of 8 patients) than in VAD (2 out of 24 patients) (p=0.003). Neck pain in all VAD patients in comparison with 3 out ofI8 [CAD patients had posterior localization (p=0,007). Anterolateral neck pain was observed in 4 out ofI8 ICAD patients and in no patients with VAD (p=0.0009). The pain appearance was abrupt in all ICAD patients and most of the VAD patients. In 8 VAD patients the pain has been increasing during several hours. The pain intensity was severe in 19 patients, moderate in 12 and mild in 2. The characteristics of the pain were as following: constrictive/dull (26 patients), throbbing (1 patient) or combined (6 patients). Pain was increasing in a stepwise manner during the first days in 14 out of 24 VAD patients and in no one of ICAD patients (p=0.008). The mean pain duration period was 31 8 ± 15,7 days. Pain relief drugs were ineffective or had a short effect in 97% of patient.

CONCLUSION

Isolated pain is more characteristic for women with VAD. Usually pain is presented as a combination of headache and neck pain. Pain localization, mode of appearance and the course are different in VAD and ICAD. The rarity of occlusion among patients with <<pain-only>> manifestation let to suggest that the intramural hematoma in this group of patients spreads to the adventitia that can reflect media weakness. Arterial wall changes underlying its weakness seem to be sex-hormone dependent taking into consideration the high predominace of women in cad manifested by isolated pain.

Role of the sympathetic autonomic nervous system in hypoxic remodeling of the fetal cerebral vasculature

Fetal hypoxia triggers compensatory angiogenesis and remodeling through mechanisms not fully elucidated. In response to hypoxia, hypoxia-inducible factor drives expression of cytokines that exert multiple effects on cerebral structures. Among these, the artery wall is composed of a heterogeneous cell mix and exhibits distinct patterns of cellular differentiation and reactivity. Governing these patterns are the vascular endothelium, smooth muscle (SM), adventitia, sympathetic perivascular nerves (SPN), and the parenchyma. Although an extensive literature details effects of nonneuronal factors on cerebral arteries, the trophic role of perivascular nerves remains unclear. Hypoxia increases sympathetic innervation with subsequent release of norepinephrine (NE), neuropeptide-Y (NPY), and adenosine triphosphate, which exert motor and trophic effects on cerebral arteries and influence dynamic transitions among SM phenotypes. Our data also suggest that the cerebrovasculature reacts very differently to hypoxia in fetuses and adults, and we hypothesize that these differences arise from age-related differences in arterial SM phenotype reactivity and proximity to trophic factors, particularly of neural origin. We provide an integration of recent literature focused on mechanisms by which SPN mediate hypoxic remodeling. Our recent findings suggest that trophic effects of SPN on cerebral arteries accelerate functional maturation through shifts in SM phenotype in an age-dependent manner.

Pericytes: brain-immune interface modulators

The premise that the central nervous system is immune-privileged arose from the fact that direct contact between immune and nervous cells is hindered by the blood-brain barrier. However, the blood-brain barrier also comprises the interface between the immune and nervous systems by secreting chemo-attractant molecules and by modulating immune cell entry into the brain. The majority of published studies on the blood-brain barrier focus on endothelial cells (ECs), which are a critical component, but not the only one; other cellular components include astroglia, microglia, and pericytes. Pericytes are poorly studied in comparison with astrocytes or ECs; they are mesenchymal cells that can modify their ultrastructure and gene expression in response to changes in the central nervous system microenvironment. Pericytes have a unique synergistic relationship with brain ECs in the regulation of capillary permeability through secretion of cytokines, chemokines, nitric oxide, matrix metalloproteinases, and by means of capillary contraction. Those pericyte manifestations are related to changes in blood-brain barrier permeability by an increase in endocytosis-mediated transport and by tight junction disruption. In addition, recent reports demonstrate that pericytes control the migration of leukocytes in response to inflammatory mediators by up-regulating the expression of adhesion molecules and releasing chemo-attractants; however, under physiological conditions they appear to be immune-suppressors. Better understanding of the immune properties of pericytes and their participation in the effects of brain infections, neurodegenerative diseases, and sleep loss will be achieved by analyzing pericyte ultrastructure, capillary coverage, and protein expression. That knowledge may provide a mechanism by which pericytes participate in the maintenance of the proper function of the brain-immune interface.

Brain ischemia in patients with intracranial hemorrhage: pathophysiological reasoning for aggressive diagnostic management

Patients with intracranial hemorrhage have to be managed aggressively to avoid or minimize secondary brain damage due to ischemia, which contributes to high morbidity and mortality. The risk of brain ischemia, however, is not the same in every patient. The risk of complications associated with an aggressive prophylactic therapy in patients with a low risk of brain ischemia can outweigh the benefits of therapy. Accurate and timely identification of patients at highest risk is a diagnostic challenge. Despite the availability of many diagnostic tools, stroke is common in this population, mostly because the pathogenesis of stroke is frequently multifactorial whereas diagnosticians tend to focus on one or two risk factors. The pathophysiological mechanisms of brain ischemia in patients with intracranial hemorrhage are not yet fully elucidated and there are several important areas of ongoing research. Therefore, this review describes physiological and pathophysiological aspects associated with the development of brain ischemia such as the mechanism of oxygen and carbon dioxide effects on the cerebrovascular system, neurovascular coupling and respiratory and cardiovascular factors influencing cerebral hemodynamics. Consequently, we review investigations of cerebral blood flow disturbances relevant to various hemodynamic states associated with high intracranial pressure, cerebral embolism, and cerebral vasospasm along with current treatment options.

Astrocyte regulation of cerebral vascular tone

Cerebral blood flow is controlled by two crucial processes, cerebral autoregulation (CA) and neurovascular coupling (NVC) or functional hyperemia. Whereas CA ensures constant blood flow over a wide range of systemic pressures, NVC ensures rapid spatial and temporal increases in cerebral blood flow in response to neuronal activation. The focus of this review is to discuss the cellular mechanisms by which astrocytes contribute to the regulation of vascular tone in terms of their participation in NVC and, to a lesser extent, CA. We discuss evidence for the various signaling modalities by which astrocytic activation leads to vasodilation and vasoconstriction of parenchymal arterioles. Moreover, we provide a rationale for the contribution of astrocytes to pressure-induced increases in vascular tone via the vasoconstrictor 20-HETE (a downstream metabolite of arachidonic acid). Along these lines, we highlight the importance of the transient receptor potential channel of the vanilloid family (TRPV4) as a key molecular determinant in the regulation of vascular tone in cerebral arterioles. Finally, we discuss current advances in the technical tools available to study NVC mechanisms in the brain as it relates to the participation of astrocytes.

The senescence hypothesis of disease progression in Alzheimer disease: an integrated matrix of disease pathways for FAD and SAD

Alzheimer disease (AD) is a progressive, neurodegenerative disease characterised in life by cognitive decline and behavioural symptoms and post-mortem by the neuropathological hallmarks including the microtubule-associated protein tau-reactive tangles and neuritic plaques and amyloid-beta-protein-reactive senile plaques. Greater than 95 % of AD cases are sporadic (SAD) with a late onset and <5 % of AD cases are familial (FAD) with an early onset. FAD is associated with various genetic mutations in the amyloid precursor protein (APP) and the presenilins (PS)1 and PS2. As yet, no disease pathway has been fully accepted and there are no treatments that prevent, stop or reverse the cognitive decline associated with AD. Here, we review and integrate available environmental and genetic evidence associated with all forms of AD. We present the senescence hypothesis of AD progression, suggesting that factors associated with AD can be seen as partial stressors within the matrix of signalling pathways that underlie cell survival and function. Senescence pathways are triggered when stressors exceed the cells ability to compensate for them. The APP proteolytic system has many interactions with pathways involved in programmed senescence and APP proteolysis can both respond to and be driven by senescence-associated signalling. Disease pathways associated with sporadic disease may be different to those involving familial genetic mutations. The interpretation we provide strongly points to senescence as an additional underlying causal process in dementia progression in both SAD and FAD via multiple disease pathways.

The adaptation of the cerebral circulation to pregnancy: mechanisms and consequences

The adaptation of the cerebral circulation to pregnancy is unique from other vascular beds. Most notably, the growth and vasodilatory response to high levels of circulating growth factors and cytokines that promote substantial hemodynamic changes in other vascular beds is limited in the cerebral circulation. This is accomplished through several mechanisms, including downregulation of key receptors and transcription factors, and production of circulating factors that counteract the vasodilatory effects of vascular endothelial growth factor (VEGF) and placental growth factor. Pregnancy both prevents and reverses hypertensive inward remodeling of cerebral arteries, possibly through downregulation of the angiotensin type 1 receptor. The blood-brain barrier (BBB) importantly adapts to pregnancy by preventing the passage of seizure provoking serum into the brain and limiting the permeability effects of VEGF that is more highly expressed in cerebral vasculature during pregnancy. While the adaptation of the cerebral circulation to pregnancy provides for relatively normal cerebral blood flow and BBB properties in the face of substantial cardiovascular changes and high levels of circulating factors, under pathologic conditions, these adaptations appear to promote greater brain injury, including edema formation during acute hypertension, and greater sensitivity to bacterial endotoxin.

Impact of COPD exacerbation on cerebral blood flow

We aimed to investigate the impact of chronic obstructive pulmonary disease (COPD) exacerbation on cerebral blood flow (CBF). In 21 COPD patients - in both exacerbation and stable phases -Doppler ultrasonographies of internal carotid artery (ICA) and vertebral artery (VA) were performed. There were significant differences in total, anterior and posterior CBF, ICA and VA flow volumes in exacerbated COPD compared to stable COPD. Total CBF was correlated with cross-sectional areas of left and right ICA, whereas independent predictor of total CBF was cross-sectional area of right ICA. Increased CBF might indicate cerebral autoregulation-mediated vasodilatation to overcome COPD exacerbation induced hypoxia.

Neurochemical Characterization of Pterygopalatine Ganglion Branches in Humans

Background

Pterygopalatine ganglion (PPG) branches, seem to be involved in the pathophysiology of facial pain. The functions of these branches, including a recently discovered orbital branch, are not completely known but could be of clinical significance. This study was designed to characterize PPG branches through immunohistochemical stain and study their anatomy, specifically the orbital branches.

Methods

In a cadaver study of four specimens, the pterygopalatine fossa (PPF) was dissected out of its bony surroundings as a tissue block. Subsequently, cryostat sectioning of these blocks was performed. In one specimen the PPF was microscopically dissected. Recently discovered neural structures were identified, dissected out of the tissue block, and cryosectioned. All cryostat sectionings were immunohistochemically stained for protein gene product (PGP) 9.5, nitric oxide synthase (NOS), and tyrosine hydroxylase (TH).

Results

A recently discovered neural connection between the PPG and the ophthalmic nerve could be confirmed and classified as an orbital PPG branch. The connection stained throughout for PGP 9.5 and partially stained for NOS. In other orbital branches, both NOS and TH+ nerve fibers were found. The PPG contained NOS+ cells. TH labeling was also found in nerve fibers running through the PPG and the vidian nerve.

Conclusion

The recently discovered orbital PPG branch is of a mixed parasympathetic and sensory nature. In the other orbital branches, sympathetic fibers were shown as well. This knowledge may add to understanding the symptomatology and therapies of headache syndromes such as nerve block.

The influence of pregnancy and gender on perivascular innervation of rat posterior cerebral arteries

The authors investigated the influence of pregnancy and gender on the density of trigeminal and sympathetic perivascular nerves in posterior cerebral arteries (PCA) and the reactivity to norepinephrine and calcitonin gene-related peptide (CGRP). PCAs were isolated from nonpregnant, late-pregnant, postpartum, and male rats, mounted and pressurized on an arteriograph chamber to obtain concentration-response curves to norepinephrine and CGRP. Arteries were immunostained for CGRP-, tyrosine hydroxylase-, and protein gene product 9.5 (PGP 9.5)-containing perivascular nerves, and nerve density was determined morphologically. Pregnancy had a trophic effect on trigeminal perivascular innervation (P < .01 vs male); however, this was not accompanied by a change in reactivity to CGRP. Sympathetic and PGP 9.5 nerve densities were not altered by pregnancy or gender, and there were no differences in reactivity to norepinephrine. Together, these results suggest that the increase in trigeminal innervation during pregnancy is more related to nociception than in controlling resting cerebral blood flow.

Neurovascular coupling in the mammalian brain

Normal brain function requires proper supply of oxygen and glucose in a timely and local manner. This is achieved through an orchestrated intercellular communication between neurones, astrocytes and microvessels that results in a rapid and restricted increase in cerebral blood flow, a process known as neurovascular coupling. Astrocytic end-feet make close contacts with neuronal synapses and blood vessels and, given their ability to release vasoactive signals following neuronal activation, have been recognized as key intermediaries in the neurovascular response. Both dilating and constricting signals appear to be released from astrocytes upon increases in intracellular Ca(2+) concentration, and both dilatation and constriction of brain vessels have been observed in previous studies. In this article, we discuss the various astrocyte-derived vasodilating and vasoconstricting signals, their interactions and effects on astrocytes and vascular smooth muscle cells, and suggest the importance of the intrinsic properties of the latter cell type on the overall neurovascular response. We present a working model in which the rise in astrocytic Ca(2+) following neuronal activation leads not only to the rapid activation of calcium-activated K(+) channels in astrocytic end-feet, but also to their modulation by metabolites of the arachidonic acid pathway, which in general have been proposed to act on vascular smooth muscle cells rather than on astrocytes. We propose that this latter mechanism may in turn modulate K(+) signalling from astrocytes to smooth muscle cells, influencing the overall effects of the vasodilating and vasoconstricting signals released during neuronal activation.

Pregnancy prevents hypertensive remodeling and decreases myogenic reactivity in posterior cerebral arteries from Dahl salt-sensitive rats: a role in eclampsia?

Previous studies have demonstrated that pregnancy prevents protective hypertension-induced remodeling of cerebral arteries using nitric oxide synthase (NOS) inhibition to raise mean arterial pressure (MAP). In the present study, we investigated whether this effect of pregnancy was specific to NOS inhibition by using the Dahl salt-sensitive (SS) rat as a model of hypertension. Nonpregnant ( n = 16) and late-pregnant ( n = 17) Dahl SS rats were fed either a high-salt diet (8% NaCl) to raise blood pressure or a low-salt diet (<0.7% NaCl). Third-order posterior cerebral arteries were isolated and pressurized in an arteriograph chamber to measure active responses to pressure and passive remodeling. Several vessels from each group were stained for protein gene product 9.5 to determine perivascular nerve density. Blood pressure was elevated in both groups on high salt. The elevated MAP was associated with significantly smaller active and passive diameters ( P < 0.05) and inward remodeling in the nonpregnant hypertensive group only. Whereas no structural changes were observed in the late-pregnant hypertensive animals, both late-pregnant groups had diminished myogenic reactivity ( P < 0.05). Nerve density in both the late-pregnant groups was significantly greater when compared with the nonpregnant groups, suggesting that pregnancy has a trophic influence on perivascular innervation of the posterior cerebral artery. However, hypertension lowered the nerve density in both nonpregnant and late-pregnant animals. It therefore appears that pregnancy has an overall effect to prevent hypertension-induced remodeling regardless of the mode of hypertension. This effect may predispose the brain to autoregulatory breakthrough, hyperperfusion, and eclampsia when MAP is elevated.

Perivascular nerve damage in the cerebral circulation following traumatic brain injury

Traumatic brain injury (TBI) causes cerebral vascular dysfunction. Most have assumed that it was the result of endothelial and/or smooth muscle alteration. No consideration, however, has been given to the possibility that the forces of injury may also damage the perivascular nerve network, thereby contributing to the observed abnormalities. To test this premise, we subjected rats to impact acceleration. At 6 h, 24 h and 7 days post-TBI, cerebral basal arteries were removed and processed with antibody targeting protein gene product 9.5 (PGP-9.5), with parallel assessments of 5-hydroxytryptamine (5-HT) accumulation in the perivascular nerves. Additionally, Fluoro-Jade was also used as a marker of axonal degeneration. The perivascular nerve network revealed no abnormality in sham animals. However, by 6 h post injury, Fluoro-Jade reactivity appeared in the perivascular regions, with the number of fibers increasing with time. By 24 h post injury, a significant reduction in the perivascular 5-HT accumulation occurred, together with a reduction in PGP-9.5 fiber staining. At 7 days, a recovery of the PGP-9.5 immunoreactivity occurred, however, it did not reach a control-like distribution. These studies suggest that neurogenic damage occurs following TBI and may be a contributor to some of the associated vascular abnormalities.

Separate development of nitric oxide synthase- and vasoactive intestinal polypeptide-immunoreactive nerves arising from the vertebral artery in the rat

Development of nitric oxide synthase (NOS)-and vasoactive intestinal polypeptide (VIP)-immunoreactive (-IR) nerves supplying the basilar and vertebral arteries (BA and VA) was investigated in White Wistar rats, using double immunohistochemistry. NOS-IR and VIP-IR nerves via the anterior circulation (AC), which mostly expressed NO(+)/VIP(+), extended to the BA during the second postnatal week, and usually reached as far as the rostral two third of the BA on PND 20. NOS-IR nerves were completely lack in the cBA and the VA on PND10, and often absent from these arterial regions even at PND 20. Nevertheless, a small number of VIP(+)/NOS(-) nerves were localized in the walls from the caudal BA (cBA) to the VA on PND 5. On PND 20, they frequently met with the descending NOS-IR and VIP-IR nerves via the AC around the lower portion of the middle BA. Fiber bundles containing NOS(+)/VIP(+) axons were first visualized on the caudal VA at PND 30 and observed frequently at PND 80, with a distinct increase in number of NOS-IR and VIP-IR nerves supplying the cBA and the VA. Thus, NOS-IR nerves coming from the VA develop through its own characteristic sequence that lags markedly behind the time of appearance for VIP-IR nerves from the same vascular route and for NOS-IR and VIP-IR nerves via the AC.

Development of nitric oxide synthase-immunoreactive nerves in the cerebral arteries of the rat

Development of cerebrovascular nitrergic nerves was investigated in the rat, using immunohistochemistry for nitric oxide synthase (NOS) and quantitative analysis. Cerebral perivascular NOS nerves usually appeared on the walls of both the intracranial part of the internal carotid artery (ICA) and the internal ethmoidal arteries (IEA) at birth. NOS nerves via the IEA grew more rapidly than those via the ICA. They extended over all the major arteries located more rostral than the middle part of the basilar arteries during the third postnatal week, while those from the ICA remained limited to the caudal segment of the anterior circulation and to the rostral segment of the posterior circulation throughout development. The appearance of NOS nerves on the vertebrate artery (VA) was not demonstrated before the third postnatal week, being apparently far late in development as compared to that of the same nerve type on the ICA and IEA.

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.

Microvascular plasticity in aging

Understanding the bases of aging-related cognitive decline remains a central challenge in neurobiology. Quantitative studies reveal little change in the number of neurons or synapses in most of the brain but their ongoing replacement is reduced, resulting in a significant loss of neuronal plasticity with senescence. Aging also may alter neuronal function and plasticity in ways that are not evident from anatomical studies of neurons and their connections. Since the nervous system is dependent upon a consistent blood supply, any aging-related changes in the microvasculature could affect neuronal function. Several studies suggest that, as the nervous system ages, there is a rarefaction of the microvasculature in some regions of the brain, as well as changes in the structure of the remaining vessels. These changes contribute to a decline in cerebral blood flow (CBF) that reduces metabolic support for neural signaling, particularly when levels of neuronal activity are high. In addition to direct effects on the microvasculature, aging reduces microvascular plasticity and the ability of the vessels to respond appropriately to changes in metabolic demand. This loss of microvascular plasticity has significance beyond metabolic support for neuronal signaling, since neurogenesis in the adult brain is regulated coordinately with capillary growth.

Zinc sulphate-induced anosmia decreases the nerve fibre density in the anterior cerebral artery of the rat

Detailed quantitative studies have demonstrated a topographical heterogeneity of nerve fibre densities in the cerebral arteries at the base of the brain as well as local changes in ageing and Alzheimer's patients. In this study, we test the hypothesis that local patterns of innervation are influenced by changes in flow fluctuations. This was investigated by inducing chronic anosmia and monitoring the nerve fibre density in the basal cerebral arteries in the adult rat. The olfactory epithelium was examined after staining with hematoxylin and eosin and showed a marked reduction of thickness in the anosmic group compared to the control group. The olfactory bulb was histochemically stained for succinate dehydrogenase (SDH) activity and showed a reduced staining in the anosmic group compared to the controls. Whole mount preparations of the basal cerebral arteries were immunostained for the general neural marker protein gene product (PGP) 9.5. The nerve fibre densities of the vessel walls were quantified by image analysis and expressed as area percentage and intercept density. This analysis showed a significant reduction in area percentage for the first part of the anterior cerebral artery, as well as for the second part of the anterior cerebral artery, and a significant reduction in intercept density for the second part of the anterior cerebral artery in the anosmic group. We conclude that peripherally induced anosmia decreases nerve fibre density in the anterior cerebral artery that may be due to a decreased metabolic activity in the rhinencephalon and, as a consequence, a reduction of flow fluctuations in the blood vessels supplying this area occurs.