Hemodynamics regulate spatiotemporal artery muscularization in the developing circle of Willis.

Vascular smooth muscle cells (VSMCs) envelop vertebrate brain arteries and play a crucial role in regulating cerebral blood flow and neurovascular coupling. The dedifferentiation of VSMCs is implicated in cerebrovascular disease and neurodegeneration. Despite its importance, the process of VSMC differentiation on brain arteries during development remains inadequately characterized. Understanding this process could aid in reprogramming and regenerating dedifferentiated VSMCs in cerebrovascular diseases. In this study, we investigated VSMC differentiation on zebrafish circle of Willis (CoW), comprising major arteries that supply blood to the vertebrate brain. We observed that arterial specification of CoW endothelial cells (ECs) occurs after their migration from cranial venous plexus to form CoW arteries. Subsequently, acta2+ VSMCs differentiate from pdgfrb+ mural cell progenitors after they were recruited to CoW arteries. The progression of VSMC differentiation exhibits a spatiotemporal pattern, advancing from anterior to posterior CoW arteries. Analysis of blood flow suggests that earlier VSMC differentiation in anterior CoW arteries correlates with higher red blood cell velocity and wall shear stress. Furthermore, pulsatile flow induces differentiation of human brain PDGFRB+ mural cells into VSMCs, and blood flow is required for VSMC differentiation on zebrafish CoW arteries. Consistently, flow-responsive transcription factor klf2a is activated in ECs of CoW arteries prior to VSMC differentiation, and klf2a knockdown delays VSMC differentiation on anterior CoW arteries. In summary, our findings highlight blood flow activation of endothelial klf2a as a mechanism regulating initial VSMC differentiation on vertebrate brain arteries.

Different effects of prenatal MAM vs. perinatal THC exposure on regional cerebral blood perfusion detected by Arterial Spin Labelling MRI in rats.

Clinical studies consistently report structural impairments (i.e.: ventricular enlargement, decreased volume of anterior cingulate cortex or hippocampus) and functional abnormalities including changes in regional cerebral blood flow in individuals suffering from schizophrenia, which can be evaluated by magnetic resonance imaging (MRI) techniques. The aim of this study was to assess cerebral blood perfusion in several schizophrenia-related brain regions using Arterial Spin Labelling MRI (ASL MRI, 9.4 T Bruker BioSpec 94/30USR scanner) in rats. In this study, prenatal exposure to methylazoxymethanol acetate (MAM, 22 mg/kg) at gestational day (GD) 17 and the perinatal treatment with Δ-9-tetrahydrocannabinol (THC, 5 mg/kg) from GD15 to postnatal day 9 elicited behavioral deficits consistent with schizophrenia-like phenotype, which is in agreement with the neurodevelopmental hypothesis of schizophrenia. In MAM exposed rats a significant enlargement of lateral ventricles and perfusion changes (i.e.: increased blood perfusion in the circle of Willis and sensorimotor cortex and decreased perfusion in hippocampus) were detected. On the other hand, the THC perinatally exposed rats did not show differences in the cerebral blood perfusion in any region of interest. These results suggest that although both pre/perinatal insults showed some of the schizophrenia-like deficits, these are not strictly related to distinct hemodynamic features.

Variations of the Circle of Willis at the End of the Human Embryonic Period.

Variations of the circle of Willis (CW) influence blood supply to the brain and adjacent structures in adults. We examined the formation of the CW in 20 human embryo samples at the end of the embryonic period using 3-D reconstructions of serial histological sections. The CW was closed in all samples, and did not form in a single plane, but was composed of multiple stair-like planes. The artery acutely curved at the caudal part of the CW, namely, at the inlet of the basilar artery and bifurcation of the P1 segment of the posterior cerebral artery (PCA), reflecting flexure of the mesencephalon and diencephalon at this stage. Variations were observed in 17 of 20 samples-only anterior parts (anterior communicating artery [Acom] and anterior cerebral artery [ACA]) in 10 samples, only posterior parts (posterior communicating artery [Pcom]) in one sample, and both anterior and posterior parts in six samples. Variations included the Acom formed as partially duplicated in three samples, duplicated in four, plexiform in three, and no channel as a result of a single azygos ACA in one. The ACA formed as duplicated in two, median ACA in two, and right hypoplasia in one. The Pcom formed in hypoplasia of either side in six samples. Variations observed in this study are similar to those observed in fetuses, neonates, and adults. The P1 segment of PCA was very large in all samples. The present observations indicate that variations in the CW are present from the initiation of CW formation. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Formation of the circle of Willis during human embryonic development.

The circle of Willis (CW) is a circulatory anastomosis that supplies blood to the brain and adjacent structures. We examined the timing of formation of CW in 20 Japanese human embryo samples by using 3-dimensional reconstruction of serial histological sections. The CW was closed in 1 (n = 6), 2 (n = 8), 2 (n = 3) and 2 (n = 3) samples at Carnegie stages 20, 21, 22, and 23, respectively. The CW was unclosed in 13 samples (unclosed at ACOM alone, 6 samples; ACOM and bilateral P1, 4; left PCOM and right P1, 1; right PCOM and right P1, 1; ACOM and left PCOM, 1). It was difficult to predict whether the circle would close during further development, as such variations frequently exist in adults.

Regulation of pre-natal circle of Willis assembly by vascular smooth muscle Notch signaling.

The circle of Willis (cW) is a major arterial collateral structure interconnecting hemispheric circulation within the brain, and in humans, anatomical variation of the cW is linked to stroke risk. Our prior studies on adult mice deficient in vascular smooth muscle cell (vSMC) Notch signaling revealed altered cerebroarterial maturation and patterning, including an anatomically incompetent cW similar to human variants. However, a developmental dependency on Notch signaling for cW formation in this model remained uncharacterized. Through temporospatial embryonic analyses, we now demonstrate that cW assembly is a pre-natal process highly sensitive to vSMC Notch signals, whose absence results in delayed nascent vascular plexus formation and under-development of the cW including the key anterior communicating artery (AComA) interconnecting anterior forebrain circulation. Mutant embryos additionally feature reduced vSMC coverage, non-uniform calibers and asymmetric branching at bifurcations of the major proximal cerebral arteries. At the cellular level, a notable reduction in vascular endothelial cell proliferation exists in the region of AComA assembly despite the presence of Vegfa. Furthermore, Notch signaling-deficient vSMCs in developing cerebral vessels feature reduced Pdgfrß and Jagged1 levels and impaired proliferation. These collective findings in the embryonic brain support studies in adult animals demonstrating a reliance on intact vSMC Notch signaling for optimal neovascular responses to angiogenic stimuli. Importantly, the new data provide unique insights into the native formation of the cW and underscore a pioneering developmental role for vSMC Notch signaling in regulating temporospatial assembly of the clinically relevant cW.

Effects of magnesium sulfate on preterm fetal cerebral blood flow using Doppler analysis: a randomized controlled trial.

OBJECTIVE: To estimate the effects of maternal administration of magnesium sulfate on the fetal middle cerebral artery using Doppler. METHODS: This is a single-center ancillary study done in conjunction with a randomized, double-masked, placebo- controlled trial in 20 centers. Women at imminent risk of preterm delivery (n=2,241) were allocated randomly to receive magnesium sulfate or placebo. Doppler measurements of the fetal middle cerebral artery were obtained before blinded study-drug administration and subsequently at 1-, 2-, 3-, and 4-hour intervals. Parameters studied included time-average velocity, peak systolic velocity, vessel diameter, heart rate, and calculated blood volume flow. A random-effects model with repeated-measures design was used for analysis. RESULTS: A total of 38 fetuses were studied: 18 received magnesium sulfate and 20 received placebo. Peak systolic velocity was significantly related to gestational age (P<.001). There were no differences between the study groups for middle cerebral artery peak systolic velocity, average velocity, vessel diameter, or calculated volume flow. However, fetal heart rate significantly decreased after treatment with magnesium sulfate. CONCLUSION: Magnesium sulfate had no significant effects on fetal cerebral blood flow analyzed using Doppler. The only parameter in the fetal cerebral circulation significantly modified by magnesium sulfate was the heart rate. The significance of this heart-rate change, vis-à-vis the neuroprotective effects of magnesium sulfate, is unknown. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, www.clinicaltrials.gov, NCT00014989. LEVEL OF EVIDENCE: I.

Evaluation of fetal cerebrovascular circulation and brain development: the role of ultrasound and Doppler.

The human fetal brain is protected from pressure changes by autoregulation of the cerebral circulation. However, antenatal intrauterine cerebrovascular events are found to play an important role in the pathogenesis of perinatal brain damage. Changes in placental vascular resistance, cardiac contractibility, vessel compliance, and blood viscosity alter the normal dynamics of fetal cerebral circulation. The introduction of various sonographic techniques and the collection of data from the arterial and venous cerebral circulation provide a powerful tool for the evaluation of physiological and pathological hemodynamic events. Anatomic and physiological considerations of cerebral vasculature in healthy and disease states are relevant in studying brain development and variations in fetal brain blood perfusion. The major role of ultrasound and Doppler modalities in the evaluation of fetal cerebrovascular circulation is enabled by implementation of these considerations. Changes in flow characteristics in fetal cerebral vasculature can be used for clinical decision making in situations of fetal compromise, such as growth restriction and anemia.

Human fetal medial striate artery or artery of Heubner.

OBJECT: The authors describe some of the features of the medial striate branch or recurrent artery of Heubner (RAH). This structure has indisputable functional, neurological, and neurosurgical significance, and originates from the A(1) and/or A(2) segments of the anterior cerebral artery. METHODS: Microdissection of 94 human fetal specimens was performed. The RAH was observed in 97.3% (single in 71.6%, double in 25.1%, and triple in 3.3%) of the cases. Its origin was from A(2) in 42.3% of specimens, from the A(1)-A(2) junction in 25.7%, and from A(1) in 20%. RESULTS: Five types and 14 subtypes of the RAH were identified, determined based on vessel origin and number. In its course, the RAH gave 1-12 branches, and the terminal part most frequently penetrated into the brain through the anterior perforated substance at the level of the sphenoid segment of the middle cerebral artery. The specimens with a single RAH fenestration, abnormal double RAH anastomosis, and unusual RAH origin and relationship to the surrounding vessels represented new data. CONCLUSIONS: The authors' observations of common anatomical variations in the number and origin of the RAH, as well as its abnormalities, may assist neuroradiologists in the interpretation of diagnostic test results and neurosurgeons in performing procedures in the anterior cerebral circulation.

The cerebral arterial circle (circulus arteriosus cerebri): an anatomical study in fetus and infant samples.

BACKGROUND: Many studies have investigated the variations in the anatomy of each segment of the cerebral arterial circle while a few have addressed the variations of the cerebral arterial circle as a whole. METHODS: Thirty brains of recently deceased Iranian infants and fetuses were dissected. The dissection process was filmed and digitized so as to be readily available for further studies. The variations of the circle as a whole and segmental variations were evaluated. RESULTS: Variants with uni- and bilateral hypoplasia of posterior communicating arteries (PcoAs) were the most common in our study, similar to previous works. No aplasia of the precommunicating part of the anterior cerebral artery (A1), the precommunicating part of the posterior cerebral artery (P1) and anterior communicating artery was seen. Hypoplasia of the right and left PcoA was observed in 8 and 5 cases, respectively. Aplasia of the right PcoA was found in 16.6% and of the left PcoA in 3.3%. CONCLUSION: In this study, we confirmed the previously described finding that the symmetrical, circular configuration of the circulus arteriosus cerebri is present in only about 42.1%. The main differences between the fetal and adult disposition are the diameter of the PcoA and the circular part of the posterior cerebral artery. According to previous studies, the fetal brain older than 4 months has anatomical characteristics very similar to the adult's circle; our finding was mostly similar to adult samples as most samples were from infants, not fetuses.

Normal subtypes of the posterior part of the cerebral arterial circle in human fetuses.

BACKGROUND: Although centuries of the human CAC research are behind us, still there is a stimulus for the authors to describe something new or to add to the "archive" of already known facts about its angioarchitecture. METHODS: With normal configurations of the posterior part of the CAC in early prenatal status, 172 brains of human fetuses from the 13th to the 24th week were used in the purpose of investigation. Brain arteries were injected and microdissected using a surgical microscope. RESULTS: According to diameter values of vascular components in the posterior part of the CAC, 6 basic types and the corresponding number of their subtypes are formed. Incidences of bilateral transitory (18.6%), fetal (9.3%), and adult (33.1%) types, as well bilateral asymmetric types (fetal-transitory in 5.8%, adult-transitory in 14.5%, and adult-fetal in 18.6% of cases), proved that dominant configuration of posterior part had not been present in the period from the fourth to the sixth gestational month. CONCLUSION: The finding of normal subtypes of the posterior part of the CAC, as well as the absence of some subtypes, is a challenge for future studies of the posterior arterial pattern within vascular abnormalities or diseases.

A new phenotypical variant of intrauterine growth restriction?

OBJECTIVES: A link between intrauterine growth restriction and major adult-onset diseases has been reported. In this study we observed a series of hitherto-unrecognized clinical features in a population of children with intrauterine growth restriction. PATIENTS AND METHODS: A total of 77 Italian children (aged 9.45 +/- 2.08 years) with antenatally diagnosed intrauterine growth restriction and small-for-gestational-age birth, along with their parents, were examined. The children with intrauterine growth restriction and were small for gestational age were subdivided into 2 groups ("variant" versus control subjects) according to evidence of auricle morphology deviation from normal. The following variables were determined: (1) external ear auricle geometry; (2) function of the posterior communicating arteries of the circle of Willis, as assessed by transcranial Doppler ultrasonography; (3) articular mobility, as assessed by Beighton's 9-point scale; (4) skin softness; and (5) distortion product-evoked otoacoustic emissions. RESULTS: Intrauterine growth restriction-variant children (n = 27) showed a significant female predominance, a lower proportion of maternal pregnancy-induced hypertension/preeclampsia, and a higher head circumference as compared with intrauterine growth restriction control subjects. Mothers of small-for-gestational-age-variant children showed significantly different auricular geometry parameters as compared with the intrauterine growth restriction controls mothers. An excess of bilaterally nonfunctioning posterior communicating arteries was observed both in the children with the intrauterine growth restriction-variant phenotype and their mothers as compared with the control groups. Significantly increased proportions of joint hypermobility and skin softness were observed in the intrauterine growth restriction-variant children as compared with controls subjects. Children with the intrauterine growth restriction-variant phenotype and their mothers showed bilateral distortion product-evoked otoacoustic emissions notches versus none in the control subjects, with an associated reduction of the area under the curve in both the intrauterine growth restriction-variant children and their mothers. No significant differences between the variant and control groups regarding the fathers were observed. CONCLUSIONS: We propose that the observed phenotypical constellation may represent an unrecognized variant of intrauterine growth restriction.

Embryology of the internal carotid artery dural crossing: apropos of a continuous series of 48 specimens.

The aim of this study was to describe the embryologic and foetal development of the anterior paraclinoid region and more precisely the relationship of the internal carotid artery to the dura mater. This has been done by examining a collection of histological sections, representing a continuous series of 48 embryologic and foetal specimens, covering the period of the first 6 months of intra-uterine life. Neurological and vascular elements develop during the embryologic period; the internal carotid artery is recognizable in the various sections of its course and acquires a histological adult parietal constitution. The foetal period corresponds to the development of the meningeal structures. The superior, medial and lateral walls appear on the fifteenth week of amenorrhoea and do not change after that. The internal carotid artery enters subarachnoid space accompanied by a sleeve of mesenchymatous cells, which fixes it to the anterior clinoid process. The constitution of this sleeve, arising from the superior wall of the lateral sellar compartment, remained independent of the principle vascular part, which allows the formation of a plan of cleavage. The foetal relations of the dura mater and the internal carotid artery were seen to be different from those of adult subjects described in the literature, suggesting an existence of period of maturation postnatally.

3D reconstruction of the cardiovascular and central nervous system of a human embryo Carnegie-stage 15--case report.

A human embryo at Carnegie stage 15 was serially sectioned and 3D computer aided reconstructions were made to demonstrate the cardiovascular system and cranial structures and to study developmental variations at this stage. The development of the heart and pharyngeal arteries was according to the existing literature. Differences were found in the development of the arterial circle of Willis and the central nervous system. The cranial venous system seemed to show great variability. Whereas the telencephalon was not developed according to the stage, the development of the hypophysis had occurred prior to stage 15. From the results we conclude that there are remarkable individual differences in embryological differentiation of structures which have to be taken into account during staging of human embryos.

The tenth vascular component in a rare form of the cerebral arterial circle of fetuses.

The ancient knowledge of the cerebral arterial circle (CAC) angioarchitecture could be supplemented by either a new or a forgotten old fact about it. Therefore, 7 cases of a rare form of the CAC of fetuses were described, where the so-called intermediate communicating artery, as an excess vessel into the posterior part, represented either its new vascular component or the developmental segment of this part. The paper aims at revealing the fetal history and morphological features of this 'underdeveloped' posterior part of the CAC during the 2nd and 3rd gestational trimesters, which could be of anatomical and clinical meaning in similar prenatal and/or postnatal cases.

Comparative morphological variations and abnormalities of circles of Willis: a minireview including two personal cases.

Two rare cases of the circle of Willis are presented. One of them represents a fetal circle of Willis (crown-rump length, or CRL, 17 cm), the other one is adult circle from a male cadaver 65 years of age. Arterial variations and abnormalities of the represented circles of Willis are described. Interpretation of the appearance of variations and abnormalities is based on the acceptable embryological, anatomical, and clinical reports. Summarizing these opinions, we have supplemented them with a hypothesis that arterial variations and abnormalities could preserve their relationships because of constant interaction between primitive arterial remnants and cerebral arteries in postnatal life, unless some pathological lesions appear.

Anatomy of the circle of Willis in three cases of human fetal synophthalmic holoprosencephaly.

In three human fetuses with synophthalmic holoprosencephaly (8, 14, 23 weeks post conceptionem) the circle of Willis was studied using serial histological sections and computer aided three dimensional reconstruction methods. This structure was abnormal in all cases. In two cases the anterior communicating arteries were absent. In all cases the anterior cerebral arteries could not be found. One case showed an incomplete circle with no posterior communicating artery. The results indicate that the malformation of the circle of Willis reflects the malformation of the brain.

Formation of the ocular arteries in the chick embryo: observations of corrosion casts by scanning electron microscopy.

An investigation was carried out on the formation of the blood vessels that supply the optic cup or eyeball in developing chick embryos ranging in age from Hamburger-Hamilton stage 17 (st17) to st44. Corrosion casts of the vasculature were made by injecting resin and examined by scanning electron microscopy. The optic cup was supplied by branches of the cranial ramus of the circle of Willis (CCW) from st17 to st19. By st23, a branch of the CCW and that of the internal carotid artery became anlagen of two ophthalmic arteries, namely, the cerebral ophthalmic artery (COA) and the internal carotid ophthalmic artery (ICOA) respectively. They were continued by primordia of the long posterior ciliary arteries, which connected with each other to form a ring around the pupil. Between st19 and st26, another branch of the CCW was found, by contrast, to supply the primitive pecten. The distal part of the nasal long posterior ciliary artery began to atrophy at st28, so the temporal long posterior ciliary artery only began to supply the ring artery around the pupil by st30. At the same time, the artery supplying the pecten became anastomosed with the ICOA behind the eyeball to form the definitive pectinate artery. By st30, the ophthalmic branch of the stapedial artery had also formed and connected with the distal part of the ICOA behind the eyeball, as well as with the distal part of the COA by st34. The supraorbital branch of the stapedial artery, which had replaced the CCW to anastomose with the ethmoidal artery by st30, was found to be connected to the COA at st36. The main vascular system supplying the eyeball was complete at st36, and its structure at st40 and st44 was fundamentally similar to that at st36.

A comparative study of the circle of Willis in fetal and adult life. The configuration of the posterior bifurcation of the posterior communicating artery.

The configuration of the posterior bifurcation of the posterior communicating artery is commonly described as the 'adult configuration' if the diameter of the precommunicating part of the posterior cerebral artery (P1) is larger than the diameter of the posterior communicating artery itself (PCA). In these cases the blood supply to the occipital lobes is mainly from the vertebro-basilar system. Only in a minority of cases is the fetal or embryonic configuration found. Here the diameter of the PCA is larger than the diameter of the P1 and the blood supply to the occipital lobes is mainly from the internal carotid artery via the posterior communicating artery. In order to track the origin of these different configurations, 53 complete circles of Willis (106 sides) in brains of fetuses and infants aged from 12 weeks to 60 weeks after conception were examined with the aid of an operating microscope, and measurements were made of the diameters of the PCA, P1 and P2. It is concluded that the variations of this part of the circle of Willis are the result of developmental modifications. This is confirmed by a statistical analysis that shows a relation between the stage of development of the brain and the occurrence of the different configurations. The frequencies of the adult and fetal configurations gradually increase at the expense of the transitional configurations. This configuration is found early in development and is characterised by the equality of the diameters of the PCA and P1. These findings contradict the views, found in the literature, that the variations either exist early in development as a consequence of genetic factors or arise after birth as a consequence of mechanical genetic factors.