Electrical stimulation of the superior sagittal sinus suppresses A-type K+ currents and increases P/Q- and T-type Ca2+ currents in rat trigeminal ganglion neurons.

BACKGROUND: Migraine is a debilitating neurological disorder involving abnormal trigeminovascular activation and sensitization. However, the underlying cellular and molecular mechanisms remain unclear. METHODS: A rat model of conscious migraine was established through the electrical stimulation (ES) of the dural mater surrounding the superior sagittal sinus. Using patch clamp recording, immunofluorescent labelling, enzyme-linked immunosorbent assays and western blot analysis, we studied the effects of ES on sensory neuronal excitability and elucidated the underlying mechanisms mediated by voltage-gated ion channels. RESULTS: The calcitonin gene-related peptide (CGRP) level in the jugular vein blood and the number of CGRP-positive neurons in the trigeminal ganglia (TGs) were significantly increased in rats with ES-induced migraine. The application of ES increased actional potential firing in both small-sized IB4-negative (IB4-) and IB4+ TG neurons. No significant changes in voltage-gated Na+ currents were observed in the ES-treated groups. ES robustly suppressed the transient outward K+ current (IA) in both types of TG neurons, while the delayed rectifier K+ current remained unchanged. Immunoblot analysis revealed that the protein expression of Kv4.3 was significantly decreased in the ES-treated groups, while Kv1.4 remained unaffected. Interestingly, ES increased the P/Q-type and T-type Ca2+ currents in small-sized IB4- TG neurons, while there were no significant changes in the IB4+ subpopulation of neurons. CONCLUSION: These results suggest that ES decreases the IA in small-sized TG neurons and increases P/Q- and T-type Ca2+ currents in the IB4- subpopulation of TG neurons, which might contribute to neuronal hyperexcitability in a rat model of ES-induced migraine.

Quantitative susceptibility mapping in the human fetus to measure blood oxygenation in the superior sagittal sinus.

OBJECTIVES: To present the feasibility of performing quantitative susceptibility mapping (QSM) in the human fetus to evaluate the oxygenation (SvO2) of cerebral venous blood in vivo. METHODS: Susceptibility weighted imaging (SWI) data were acquired from healthy pregnant subjects (n = 21, median = 31.3 weeks, interquartile range = 8.8 weeks). The susceptibility maps were generated from the SWI-phase images using a modified QSM processing pipeline, optimised for fetal applications. The processing pipeline is as follows: (1) mild high-pass filtering followed by quadratic fitting of the phase images to eliminate background phase variations; (2) manual creation of a fetal brain mask that includes the superior sagittal sinus (SSS); (3) inverse filtering of the resultant masked phase images using a truncated k-space approach with geometric constraint. Further, the magnetic susceptibility, ∆χv and corresponding putative SvO2 of the SSS were quantified from the generated susceptibility maps. Systematic error in the measured SvO2 due to the modified pipeline was also studied through simulations. RESULTS: Simulations showed that the systematic error in SvO2 when using a mask that includes a minimum of 5 voxels around the SSS and five slices remains < 3% for different orientations of the vessel relative to the main magnetic field. The average ∆χv in the SSS quantified across all gestations was 0.42 ± 0.03 ppm. Based on ∆χv, the average putative SvO2 in the SSS across all fetuses was 67% ± 7%, which is in good agreement with published studies. CONCLUSIONS: This in vivo study demonstrates the feasibility of using QSM in the human fetal brain to estimate ∆χv and SvO2. KEY POINTS: • A modified quantitative susceptibility mapping (QSM) processing pipeline is tested and presented for the human fetus. • QSM is feasible in the human fetus for measuring magnetic susceptibility and oxygenation of venous blood in vivo. • Blood magnetic susceptibility values from MR susceptometry and QSM agree with each other in the human fetus.

Early BBB breakdown and subacute inflammasome activation and pyroptosis as a result of cerebral venous thrombosis.

Cerebral venous thrombosis (CVT) is a rare form of cerebral stroke that causes a variety of symptoms, ranging from mild headache to severe morbidity or death in the more severe forms. The use of anti-coagulant or thrombolytic agents is the classical treatment for CVT. However, the development of new therapies for the treatment of the condition has not been the focus. In this study, we aimed to analyze the pathophysiology of CVT and to identify the pathways associated with its pathology. Moreover, mechanisms that are potential drug targets were identified. Our data showed the intense activation of immune cells, particularly the microglia, along with the increase in macrophage activity and NLRP3 inflammasome activation that is indicated by NLRP3, IL-1ß, and IL-18 gene and caspase-1 upregulation and cleavage as well as pyroptotic cell death. Leukocytes were observed in the brain parenchyma, indicating a role in CVT-induced inflammation. In addition, astrocytes were activated, and they induced glial scar leading to parenchymal contraction during the subacute stage and tissue loss. MMP9 was responsible primarily for the BBB breakdown after CVT and it is mainly produced by pericytes. MMP9 activation was observed before inflammatory changes, indicating that BBB breakdown is the initial driver of the pathology of CVT. These results show an inflammation driven pathophysiology of CVT that follows MMP9-mediated BBB breakdown, and identified several targets that can be targeted by pharmaceutical agents to improve the neuroinflammation that follows CVT, such as MMP9, NLRP3, and IL-1ß. Some of these pharmaceutical agents are already in clinical practice or under clinical trials indicating a good potential for translating this work into patient care.

Extracranial outflow of particles solved in cerebrospinal fluid: Fluorescein injection study.

Cerebrospinal fluid is thought to be mainly absorbed into arachnoid granules in the subarachnoid space and drained into the sagittal sinus. However, some observations such as late outbreak of arachnoid granules in fetus brain and recent cerebrospinal fluid movements study by magnetic resonance images, conflict with this hypothesis. In this study, we investigated the movement of cerebrospinal fluid in fetuses. Several kinds of fluorescent probes with different molecular weights were injected into the lateral ventricle or subarachnoid space in mouse fetuses at a gestational age of 13 days. The movements of the probes were monitored by live imaging under fluorescent microscope. Following intraventricular injection, the probes dispersed into the 3rd ventricle and aqueduct immediately, but did not move into the 4th ventricle and spinal canal. After injection of low and high molecular weight conjugated probes, both probes dispersed into the brain but only the low molecular weight probe dispersed into the whole body. Following intra-subarachnoid injection, both probes diffused into the spinal canal gradually. Neither probe dispersed into the brain and body. The probe injected into the lateral ventricle moved into the spinal central canal by the fetus head compression, and returned into the aqueduct by its release. We conclude this study as follows: (i) The movement of metabolites in cerebrospinal fluid in the ventricles will be restricted by molecular weight; (ii) Cerebrospinal fluid in the ventricle and in the subarachnoid space move differently; and (iii) Cerebrospinal fluid may not appear to circulate. In the event of high intracranial pressure, the fluid may move into the spinal canal.

Lymphatic vasculature in human dural superior sagittal sinus: Implications for neurodegenerative proteinopathies.

Recent reports have characterized functional lymphatic vessels, which drain both fluid and immune cells from the CSF to the deep cervical lymph nodes, lining the dural sinuses in mice. If conserved in the human brain these vessels could have profound implications for neuroinflammatory and neurodegenerative diseases. We provide evidence of the presence of lymphatic vessels in human dura obtained at autopsy, at the level of the superior sagittal sinus, in 4 individuals. Immunohistochemistry for the lymphatic vessel endothelial cell marker podoplanin revealed the widespread presence of multiple structures with a distinct lumen distributed throughout the superior sagittal sinus. These vessels provide a putative infrastructure for drainage of macromolecules from the brain parenchyma and represent an exciting avenue of exploration for involvement in the pathogenesis of neurodegenerative proteinopathies including Parkinson's disease.

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

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

Age-related changes in pial arterial structure and blood flow in mice.

Age-related cerebral blood flow decreases are thought to deteriorate cognition and cause senescence, although the related mechanism is unclear. To investigate the relationships between aging and changes in cerebral blood flow and vasculature, we obtained fluorescence images of young (2-month-old) and old (12-month-old) mice using indocyanine green (ICG). First, we found that the blood flow in old mice's brains is lower than that in young mice and that old mice had more curved pial arteries and fewer pial artery junctions than young mice. Second, using Western blotting, we determined that the ratio of collagen to elastin (related to cerebral vascular wall distensibility) increased with age. Finally, we found that the peak ICG intensity and blood flow index decreased, whereas the mean transit time increased, with age in the middle cerebral artery and superior sagittal sinus. Age-related changes in pial arterial structure and composition, concurrent with the observed changes in the blood flow parameters, suggest that age-related changes in the cerebral vasculature structure and distensibility may induce altered brain blood flow.

Differential trigeminovascular nociceptive responses in the thalamus in the familial hemiplegic migraine 1 knock-in mouse: a Fos protein study.

Familial hemiplegic migraine type 1 (FHM-1) is a monogenic subtype of migraine with aura caused by missense mutations in the CACNA1A gene, which encodes the pore-forming α1 subunit of voltage-gated neuronal CaV2.1 (P/Q-type) calcium channels. Transgenic knock-in mice expressing the CACNA1A R192Q mutation that causes FHM-1 in patients show a greater susceptibility to cortical spreading depression, the likely underlying mechanism of typical human migraine aura. The aim of this study was to compare neuronal activation within the trigeminal pain pathways in response to nociceptive trigeminovascular stimulation in wild-type and R192Q knock-in mice. After sham surgery or electrical stimulation of the superior sagittal sinus for 2h, or stimulation preceded by treatment with naratriptan, mice underwent intracardiac perfusion, and the brain, including the brainstem, was removed. Fos expression was measured in the trigeminocervical complex (TCC) and the lateral (ventroposteromedial, ventrolateral), medial (parafascicular, centromedian) and posterior thalamic nuclei. In the TCC of wild-type animals, the number of Fos-positive cells increased significantly following dural stimulation compared to the sham control group (P<0.001) and decreased after naratriptan treatment (P<0.05). In R192Q knock-in mice, there was no significant difference between the stimulated and sham (P=0.10) or naratriptan pre-treated groups (P=0.15). The number of Fos-positive cells in the R192Q stimulated group was significantly lower compared to the wild-type stimulated mice (P<0.05). In the thalamus, R192Q mice tended to be more sensitive to stimulation compared to the sham control in the medial and posterior nuclei, and between the two strains of stimulated animals there was a significant difference in the centromedian (P<0.005), and posterior nuclei (P<0.05). The present study suggests that the FHM-1 mutation affects more rostral brain structures in this experimental paradigm, which offers a novel perspective on possible differential effects of mutations causing migraine in terms of phenotype-genotype correlations.

Noninvasive monitoring of cerebral blood oxygenation in ovine superior sagittal sinus with novel multi-wavelength optoacoustic system.

Noninvasive monitoring of cerebral blood oxygenation with an optoacoustic technique offers advantages over current invasive and noninvasive methods. We report the results of in vivo studies in the sheep superior sagittal sinus (SSS), a large central cerebral vein. We changed blood oxygenation by increasing and decreasing the inspired fraction of oxygen (FiO(2)). Optoacoustic measurements from the SSS were performed at wavelengths of 700, 800, and 1064 nm using an optical parametric oscillator as a source of pulsed near-infrared light. Actual oxygenation of SSS blood was measured with a CO-Oximeter in blood samples drawn from the SSS through a small craniotomy. The amplitude of the optoacoustic signal induced in the SSS blood at lambda = 1064 nm closely followed the changes in blood oxygenation, at lambda = 800 nm was almost constant, and at lambda = 700 nm was changing in the opposite direction, all in accordance with the absorption spectra of oxy- and deoxyhemoglobin. The optoacoustically predicted oxygenation correlated well with actual blood oxygenation in sheep SSS (R(2) = 0.965 to 0.990). The accuracy was excellent, with a mean difference of 4.8% to 9.3% and a standard deviation of 2.8% to 4.2%. To the best of our knowledge, this paper reports for the first time accurate measurements of cerebral venous blood oxygenation validated against the "gold standard" CO-Oximetry method.

[Effect of GABA-positive drugs on the background and superior sagittalis sinus-electrostimulated activity of neurons in the nucleus trigeminalis caudalis of rats].

There is extensive clinical evidence for the high efficacy of GABA-ergic drugs in prophylactic and abortive treatment of migraine and cluster headache, while the mechanisms of anticephalgic drugs action are not clear, in particular, because of insufficient number of investigations on experimental headache models. In this study, the influence of baclofen (i.v.) in doses 2.5, 5, 10, and 15 mg/kg and valproate (i.v.) in doses 25, 50, 100, and 200 mg/kg on the background activity of the trigeminal nucleus caudalis neurons and that evoked by electrical stimulation of the superior sagittalis sinus was investigated in series of acute experiments on rats. It is established, that baclofen and valproate reduce both the background and evoked activity of trigeminal complex neurons in dose-dependent manner, thus determining the role of GABA-A and GABA-B receptors in realization of this effect. These results provide experimental basis for explanation of the clinical efficacy of the GABA-positive drugs in vascular headaches.

Comparison of three physiologically-based pharmacokinetic models for the prediction of contrast agent distribution measured by dynamic MR imaging.

PURPOSE: To compare the performance of three physiologically-based pharmacokinetic (PBPK) models for predicting gadolinium contrast agent concentration-time curves (Gd-CTCs) obtained in superior sagittal sinus (SSS), cerebral cortex, and psoas muscle. MATERIALS AND METHODS: Three published whole-body PBPK models were modified to predict Gd-CTCs in normal-appearing tissue. The models differed in the number of organs modeled and total number of compartments, and were designated as the "well-mixed," "delay," and "dispersion" models. The suitability of the three models to predict Gd-CTC was studied using data from dynamic contrast-enhanced MR perfusion imaging obtained at 1.5T from 10 patients with glioblastoma multiforme and at 3.0T from five patients with liver metastases. RESULTS: The dispersion model produced better fits than the delay model in the SSS (P < 0.0001) and cerebral cortex (P < 0.0001), and better fits than the well-mixed model in psoas muscle (P < 0.005). No model produced better fits than the dispersion model at any of the three locations. CONCLUSION: In this evaluation, the dispersion model was most robust for prediction of Gd-CTCs derived from dynamic contrast-enhanced (DCE)-MRI. This represents a preliminary step in the development of a PBPK model useful for predicting Gd-CTCs at a time resolution appropriate for dynamic MRI applications.

A hypothesis of cerebral venous system regulation based on a study of the junction between the cortical bridging veins and the superior sagittal sinus. Laboratory investigation.

OBJECT: The cerebral venous regulation involved in various physiological and pathological processes has received little attention. Here the authors describe the anatomy of the junction between the cortical vein and the superior sagittal sinus (SSS) and propose a new theory of cerebral venous regulation. METHODS: Ten adult human cadaveric heads (20 sides), including five specimens into which stained latex had been injected, were used for anatomical study. Formalin-fixed cadaver heads were dissected to demonstrate the cortical veins along the SSS. The characteristics of the cortical bridging veins and their openings into the SSS were established by anatomical, histological, immunohistochemical, and ultrastructural study of the junction. RESULTS: After their subarachnoid course, the cortical bridging veins penetrated the SSS at different points in the dura mater depending on their rostrocaudal position. The venous endothelium stretched beyond the sinus endothelium. The orientation of the collagen fibers changed at the level of the venous openings, with the luminal diameter becoming narrow and oval-shaped. The major finding was the organization of the smooth-muscle cells at the end of each cortical vein. At this site and particularly in the frontoparietal region, the vessel resembled a myoendothelial "sphincter." The authors hypothesize that this organization is involved in cerebral venous system regulation. CONCLUSIONS: The point of convergence between the cortical veins and the SSS is a key area. The authors also hypothesize that the myoendothelial junction acts as a smooth sphincter and that it plays a role in cerebral venous hemodynamics and pathological conditions.