Oxygen imaging of hypoxic pockets in the mouse cerebral cortex

Consciousness is lost within seconds upon cessation of cerebral blood flow. The brain cannot store oxygen, and interruption of oxidative phosphorylation is fatal within minutes. Yet only rudimentary knowledge exists regarding cortical partial oxygen tension (Po2) dynamics under physiological conditions. Here we introduce Green enhanced Nano-lantern (GeNL), a genetically encoded bioluminescent oxygen indicator for Po2 imaging. In awake behaving mice, we uncover the existence of spontaneous, spatially defined "hypoxic pockets" and demonstrate their linkage to the abrogation of local capillary flow. Exercise reduced the burden of hypoxic pockets by 52% compared with rest. The study provides insight into cortical oxygen dynamics in awake behaving animals and concurrently establishes a tool to delineate the importance of oxygen tension in physiological processes and neurological diseases.

Overuse of EEG and ECG in children with breath-holding spells and its implication for the management of the spells

AIM

Breath-holding spells (BHS) are common in children, but evidence-based clinical guidelines are lacking. We investigated a large population-based cohort of BHS patients, to propose a refined description of typical BHS and guidelines for its management.

METHODS

In a cross-sectional retrospective study, patients diagnosed with BHS in Southern Sweden 2004-2018 were recruited. Disease characteristics and diagnostic data were collected from patient medical records.

RESULTS

In total, 519 patients, mean age at diagnosis 19.8 ± 13.8 months with equal gender distribution, were included. In 48.3%, BHS had already been diagnosed after one spell. During spells, 78.0% of patients were unresponsive. For 71.5%, atonic, tonic, tonic-clonic or myoclonic seizures were reported, and 78.0% of patients had a spell lasting less than 1 min. Electroencephalography was conducted in 30.4% and Electrocardiography in 45.1%. Six children (3.8%) had a pathological electroencephalogram, four of which had concomitant epilepsy and only 0.9% of children had electrocardiogram findings suggesting pathology, none showing long QT syndrome.

CONCLUSION

Children with BHS were frequently subjected to unnecessary diagnostic interventions. We characterise a typical presentation of BHS and propose a management-algorithm, which is expected to reduce unnecessary usage of electroencephalography and electrocardiography.

Potentiating glymphatic drainage minimizes post-traumatic cerebral oedema

Cerebral oedema is associated with morbidity and mortality after traumatic brain injury (TBI)1. Noradrenaline levels are increased after TBI2-4, and the amplitude of the increase in noradrenaline predicts both the extent of injury5 and the likelihood of mortality6. Glymphatic impairment is both a feature of and a contributor to brain injury7,8, but its relationship with the injury-associated surge in noradrenaline is unclear. Here we report that acute post-traumatic oedema results from a suppression of glymphatic and lymphatic fluid flow that occurs in response to excessive systemic release of noradrenaline. This post-TBI adrenergic storm was associated with reduced contractility of cervical lymphatic vessels, consistent with diminished return of glymphatic and lymphatic fluid to the systemic circulation. Accordingly, pan-adrenergic receptor inhibition normalized central venous pressure and partly restored glymphatic and cervical lymphatic flow in a mouse model of TBI, and these actions led to substantially reduced brain oedema and improved functional outcomes. Furthermore, post-traumatic inhibition of adrenergic signalling boosted lymphatic export of cellular debris from the traumatic lesion, substantially reducing secondary inflammation and accumulation of phosphorylated tau. These observations suggest that targeting the noradrenergic control of central glymphatic flow may offer a therapeutic approach for treating acute TBI.

Age- and glaucoma-induced changes to the ocular glymphatic system

The ocular glymphatic system supports bidirectional fluid transport along the optic nerve, thereby removes metabolic wastes including amyloid-β. To better understand this biological process, we examined the distributions of intravitreally and intracisternally infused tracers in full-length optic nerves from different age groups of mice. Aging was linked to globally impaired ocular glymphatic fluid transport, similar to what has seen previously in the brain. Aging also reduced the pupillary responsiveness to light stimulation and abolished light-induced facilitation in anterograde ocular glymphatic flow. In contrast to normal aging, in the DBA/2 J model of glaucoma, we found a pathological increase of glymphatic fluid transport to the anterior optic nerve that was associated with dilation of the perivascular spaces. Thus, aging and glaucoma have fundamentally different effects on ocular glymphatic fluid transport. Manipulation of glymphatic fluid transport might therefore present a new target for the treatment of glaucoma.

A SPECT-based method for dynamic imaging of the glymphatic system in rats

The glymphatic system is a brain-wide waste drainage system that promotes cerebrospinal fluid circulation through the brain to remove waste metabolites. Currently, the most common methods for assessing glymphatic function are ex vivo fluorescence microscopy of brain slices, macroscopic cortical imaging, and MRI. While all these methods have been crucial for expanding our understanding of the glymphatic system, new techniques are required to overcome their specific drawbacks. Here, we evaluate SPECT/CT imaging as a tool to assess glymphatic function in different anesthesia-induced brain states using two radiolabeled tracers, [111In]-DTPA and [99mTc]-NanoScan. Using SPECT, we confirmed the existence of brain state-dependent differences in glymphatic flow and we show brain state-dependent differences of CSF flow kinetics and CSF egress to the lymph nodes. We compare SPECT and MRI for imaging glymphatic flow and find that the two imaging modalities show the same overall pattern of CSF flow, but that SPECT was specific across a greater range of tracer concentrations than MRI. Overall, we find that SPECT imaging is a promising tool for imaging the glymphatic system, and that qualities such as high sensitivity and the variety of available tracers make SPECT imaging a good alternative for glymphatic research.

Glymphatic influx and clearance are accelerated by neurovascular coupling

Functional hyperemia, also known as neurovascular coupling, is a phenomenon that occurs when neural activity increases local cerebral blood flow. Because all biological activity produces metabolic waste, we here sought to investigate the relationship between functional hyperemia and waste clearance via the glymphatic system. The analysis showed that whisker stimulation increased both glymphatic influx and clearance in the mouse somatosensory cortex with a 1.6-fold increase in periarterial cerebrospinal fluid (CSF) influx velocity in the activated hemisphere. Particle tracking velocimetry revealed a direct coupling between arterial dilation/constriction and periarterial CSF flow velocity. Optogenetic manipulation of vascular smooth muscle cells enhanced glymphatic influx in the absence of neural activation. We propose that impedance pumping allows arterial pulsatility to drive CSF in the same direction as blood flow, and we present a simulation that supports this idea. Thus, functional hyperemia boosts not only the supply of metabolites but also the removal of metabolic waste.

Astrocytic chloride is brain state dependent and modulates inhibitory neurotransmission in mice

Information transfer within neuronal circuits depends on the balance and recurrent activity of excitatory and inhibitory neurotransmission. Chloride (Cl^-) is the major central nervous system (CNS) anion mediating inhibitory neurotransmission. Astrocytes are key homoeostatic glial cells populating the CNS, although the role of these cells in regulating excitatory-inhibitory balance remains unexplored. Here we show that astrocytes act as a dynamic Cl^- reservoir regulating Cl^- homoeostasis in the CNS. We found that intracellular chloride concentration ([Cl^-]_i) in astrocytes is high and stable during sleep. In awake mice astrocytic [Cl^-]_i is lower and exhibits large fluctuation in response to both sensory input and motor activity. Optogenetic manipulation of astrocytic [Cl^-]_i directly modulates neuronal activity during locomotion or whisker stimulation. Astrocytes thus serve as a dynamic source of extracellular Cl^- available for GABAergic transmission in awake mice, which represents a mechanism for modulation of the inhibitory tone during sustained neuronal activity.

Glymphatic-assisted perivascular brain delivery of intrathecal small gold nanoparticles

Nanoparticles are ultrafine particulate matter having considerable potential for treatment of central nervous system (CNS) disorders. Despite their tiny size, the blood-brain barrier (BBB) restricts their access to the CNS. Their direct cerebrospinal fluid (CSF) administration bypasses the BBB endothelium, but still fails to give adequate brain uptake. We present a novel approach for efficient CNS delivery of ¹¹¹In-radiolabelled gold nanoparticles (AuNPs; 10-15 nm) via intra-cisterna magna administration, with tracking by SPECT imaging. To accelerate CSF brain influx, we administered AuNPs intracisternally in conjunction with systemic hypertonic saline, which dramatically increased the parenchymal AuNP uptake, especially in deep brain regions. AuNPs entered the CNS along periarterial spaces as visualized by MRI of gadolinium-labelled AuNPs and were cleared from brain within 24 h and excreted through the kidneys. Thus, the glymphatic-assisted perivascular network augment by systemic hypertonic saline is a pathway for highly efficient brain-wide distribution of small AuNPs.

SPECT/CT imaging reveals CNS-wide modulation of glymphatic cerebrospinal fluid flow by systemic hypertonic saline

Intrathecal administration enables central nervous system delivery of drugs that do not bypass the blood-brain barrier. Systemic administration of hypertonic saline (HTS) enhances delivery of intrathecal therapeutics into the neuropil, but its effect on solute clearance from the brain remains unknown. Here, we developed a dynamic in vivo single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging platform to study the effects of HTS on whole-body distribution of the radiolabeled tracer ^99mTc-diethylenetriaminepentaacetic acid (DTPA) administered through intracisternal, intrastriatal, or intravenous route in anesthetized rats. Co-administration of systemic HTS increased intracranial exposure to intracisternal ^99mTc-DTPA by ∼80% during imaging. In contrast, HTS had minimal effects on brain clearance of intrastriatal ^99mTc-DTPA. In sum, SPECT/CT imaging presents a valuable approach to study glymphatic drug delivery. Using this methodology, we show that systemic HTS increases intracranial availability of cerebrospinal fluid-administered tracer, but has marginal effects on brain clearance, thus substantiating a simple, yet effective strategy for enhancing intrathecal drug delivery to the brain.

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We established a SPECT/CT platform for imaging glymphatic drug delivery in vivo

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Hypertonic saline (HTS) elevates intracranial availability of CSF-infused ^99mTc-DTPA

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HTS triples the availability of ^99mTc-DTPA in several deep brain regions

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HTS has negligible effects on clearance of intrastriatally infused DTPA

An ocular glymphatic clearance system removes β-amyloid from the rodent eye

Despite high metabolic activity, the retina and optic nerve head lack traditional lymphatic drainage. We here identified an ocular glymphatic clearance route for fluid and wastes via the proximal optic nerve in rodents. β-amyloid (Aβ) was cleared from the retina and vitreous via a pathway dependent on glial water channel aquaporin-4 (AQP4) and driven by the ocular-cranial pressure difference. After traversing the lamina barrier, intra-axonal Aβ was cleared via the perivenous space and subsequently drained to lymphatic vessels. Light-induced pupil constriction enhanced efflux, whereas atropine or raising intracranial pressure blocked efflux. In two distinct murine models of glaucoma, Aβ leaked from the eye via defects in the lamina barrier instead of directional axonal efflux. The results suggest that, in rodents, the removal of fluid and metabolites from the intraocular space occurs through a glymphatic pathway that might be impaired in glaucoma.

A three-dimensional, population-based average of the C57BL/6 mouse brain from DAPI-stained coronal slices

Fluorescence imaging of immunolabeled brain slices is a key tool in neuroscience that enable mapping of proteins or DNA/RNA at resolutions not possible with non-invasive techniques, including magnetic resonance or nuclear imaging. The signal in specific regions is usually quantified after manually drawing regions of interest, risking operator-bias. Automated segmentation methods avoid this risk but require multi-sample average atlases with similar image contrast as the images to be analyzed. We here present the first population-based average atlas of the C57BL/6 mouse brain constructed from brain sections labeled with the fluorescence nuclear stain DAPI. The data set constitutes a rich three-dimensional representation of the average mouse brain in the DAPI staining modality reconstructed from coronal slices and includes an automatic segmentation/spatial normalization pipeline for novel coronal slices. It constitutes the final population-based average template, individual reconstructed brain volumes, and native coronal slices. The comprehensive data set and accompanying spatial normalization/segmentation software are provided. We encourage the community to utilize it to improve and validate methods for automated brain slice analysis.

PDGF-B Is Required for Development of the Glymphatic System

The glymphatic system is a highly polarized cerebrospinal fluid (CSF) transport system that facilitates the clearance of neurotoxic molecules through a brain-wide network of perivascular pathways. Herein we have mapped the development of the glymphatic system in mice. Perivascular CSF transport first emerges in hippocampus in newborn mice, and a mature glymphatic system is established in the cortex at 2 weeks of age. Formation of astrocytic endfeet and polarized expression of aquaporin 4 (AQP4) consistently coincided with the appearance of perivascular CSF transport. Deficiency of platelet-derived growth factor B (PDGF-B) function in the PDGF retention motif knockout mouse line Pdgfbret/ret suppressed the development of the glymphatic system, whose functions remained suppressed in adulthood compared with wild-type mice. These experiments map the natural development of the glymphatic system in mice and define a critical role of PDGF-B in the development of perivascular CSF transport.

Increased glymphatic influx is correlated with high EEG delta power and low heart rate in mice under anesthesia

The glymphatic system is responsible for brain-wide delivery of nutrients and clearance of waste via influx of cerebrospinal fluid (CSF) alongside perivascular spaces and through the brain. Glymphatic system activity increases during sleep or ketamine/xylazine (K/X) anesthesia, yet the mechanism(s) facilitating CSF influx are poorly understood. Here, we correlated influx of a CSF tracer into the brain with electroencephalogram (EEG) power, heart rate, blood pressure, and respiratory rate in wild-type mice under six different anesthesia regimens. We found that glymphatic CSF tracer influx was highest under K/X followed by isoflurane (ISO) supplemented with dexmedetomidine and pentobarbital. Mice anesthetized with α-chloralose, Avertin, or ISO exhibited low CSF tracer influx. This is the first study to show that glymphatic influx correlates positively with cortical delta power in EEG recordings and negatively with beta power and heart rate.

THE YIELD OF RABIES VIRUS IN THE CHICK EMBRYO

Rabies virus was inoculated intracerebrally in 8 day old chick embryos and the virus activity of pools of embryos titered after incubation at 35-36 degrees C. for different lengths of time. The virus reached a titer of 10(-5.5) to 10(-6.5) in 5 to to 6 days and remained at a rather constant level until the 9th day of the infection. The report by Kligler and Bernkopf that rabies virus will invade the very young embryo after inoculation on the chorioallantoic membrane was confirmed.

MAMMALIAN RED CELLS AS A SOURCE OF "SMALL PARTICLES"

1. Small particles essentially similar to those previously isolated from other tissues have been isolated from mammalian red blood cells (horse blood). 2. About one-third of the dry weight of the particles is lipids. 3. The particles produce hemolysins against the homologous erythrocytes when inoculated into a foreign species. 4. The fact that the particles can be isolated from mammalian red cells which do not contain visible granules is taken to indicate that some at least of the particles isolated from whole organs represent disintegrated "stroma."

THE INFLUENCE OF AGE OF HOST AND TEMPERATURE OF INCUBATION ON INFECTION OF THE CHICK EMBRYO WITH VESICULAR STOMATITIS VIRUS

Chick embryos after 7 days of incubation were found to be much more susceptible to infection with vesicular stomatitis virus than were 10 day embryos. They had a 100 per cent mortality and were very suitable for titrations of the virus. The rate of increase of virus in 7 and 10 day embryos was studied. Two different temperatures of incubation were employed, 35–36°C. and 39–40°C., and the growth curves for the virus under the different conditions are presented. 10 day embryos were highly resistant and at 39–40°C. more than half of them survived. At the lower temperature of incubation, 35–36°C., all 10 day embryos died, but they survived much longer than did 7 day embryos. In the 7 day embryos death occurred after about 12 hours at 39–40°C. and after about 16 hours at 35–36°C., or earlier at the higher temperature. In embryos of both ages the virus titer reached at the higher temperature was only about 1 per cent of that reached at 35–36°C., even in those that died.

Total hip arthroplasty in high congenital dislocation. 21 hips with a minimum five-year follow-up

Total arthroplasty was performed on 21 congenitally dislocated hips in 18 women. In all cases the femoral head was dislocated cranially at least one-fifth of the height of the pelvis. The components were both cemented, the acetabulum being replaced to its original position. The acetabular roof was reconstructed by bone graft in 13 hips, and trochanteric osteotomy was done in 18 hips. The patients were assessed at a median follow-up time of 7.5 years when their median age was 54 years. Nine patients had been revised or required revision. At follow-up the average functional score (according to Charnley) was 6 for pain, 4 for walking ability and 5 for range of motion. The Harris hip score was 82. The patients' subjective evaluation of their satisfaction with the late results on a visual analogue scale was 93, range 23 to 100. The high loosening rate in such patients demands regular follow-up and preparedness for revision surgery.

Trapezium replacement arthroplasty

Thirty-one patients (34 joints) with pain due to carpometacarpal joint derangement were reviewed 1/2 to 12 years after a trapezium replacement arthroplasty using a Swanson silicone prosthesis. At review, 25 hands were free from pain, and nine had some pain on exertion. Mobility and strength were generally well restored. The radiographic examination revealed 12 prosthesis-fractures, three dislocations, and five cases of incongruity. However, all patients were satisfied with the results of the operation.

Vaccination Against Paratuberculosis (Johne's Disease)

A total of 289 lambs, on farms where Paratuberculosis (Johne's disease) of sheep was prevalent, were vaccinated over a period of 3 years with one or two injections of heat killed Mycobacterium paratuberculosis suspended in mineral oil. This type of vaccine was known previously to elicit a powerful and protracted immunological response. A total of 266 lambs on the same farms were left unvaccinated as controls.

During the experimental period 16 of the unvaccinated animals, but none of the vaccinated sheep, succumbed to Paratuberculosis.

The experiment was terminated 3½ years after it was started, and the intestines of the remaining sheep were carefully searched for lesions of Paratuberculosis. Such lesions were found in 4 of the vaccinated animals but in 21 of the unvaccinated controls.

Both these differences are statistically highly significant, and it may be concluded that under the conditions of the present experiment the vaccine has provoked a satisfactory resistance to subsequent infection.

This vaccine does not contain living bacilli, and has proven to be safe for field use also in other respects.

A Specific Antigen Recovered from Tissue Infected with M. Paratuberculosis (Johne's Bacillus)

Intestinal mucosa of sheep infected with M. paratuberculosis (Johne's bacillus) contains two substances that seem to be specific for this disease. One of these substances—the antigen—has been previously described (1, 2, 3, 4). It fixes complement in suitable mixtures with a specific antiserum. The second substance in the infected mucosa—the inhibitor—impedes the fixation of complement by the antigen.

The inhibitor is soluble at all hydrogen-ion concentrations between pH 3 and pH 9. This fact may be used to separate it from the antigen which is insoluble between pH 3 and pH 5. The inhibitor is not precipitated by 3 per cent trichloroacetic acid, and it is insoluble in ether. It will withstand boiling, but does not dialyze through a cellophane membrane.

The inhibiting substance was found to be present in all of the 13 infected intestines which were tested, while 13 normal intestines which were also tested as controls were not found to contain any of the inhibiting principle.

The inhibitor is thus a product of the specific morbid process. It seems reasonable to assume that its function in the tissue is somehow directed against the antigen as it is in vitro, where it inhibits one of the functions of the antigen.

To our knowledge no soluble, specific “antiinfectious” substances have previously been known to arise in the organism as a result of infection except the “antibodies” which are globulins or inseparably associated with globulins. The results reported in this paper, however, do seem to indicate that the organism may also form antiinfectious substances of other kinds, and these may also play a role in the pathogenesis of infectious diseases.

A Specific Antigen Recovered from Tissue Infected with M. Paratuberculosis (Johne's Bacillus)

The specific paratuberculosis antigen found in the intestinal mucosae of sheep with Johne's disease was further investigated.

The antigen is quite resistant to low pH, but it is insoluble between approximately pH 3 and pH 5. Preliminary extraction of dried and ground mucosa at pH 4 to 4.5 will render subsequently prepared antigenic extracts more active, this is believed to be due to the removal of an inhibiting substance in the acid extract.

No matter whether this preliminary extraction has been employed or not, it is best to carry out the antigenic extraction itself at about pH 9 and at 100 C, for one hour.

As has previously been shown, a thorough mechanical grinding of the dried tissue is the most effective means of demasking the antigen in the mucosa. It was found that grinding in a ball-mill is much more effective than grinding by hand in a mortar. Also, that there is an optimum length of time that the tissue should be ground, since longer grinding again reduces the activity.

A Specific Antigen Recovered from Tissue Infected with M. Paratuberculosis (Johne's Bacillus)

The specific antigen found in intestines of sheep infected with paratuberculosis (Johne's disease) was investigated.

The antigen was precipitated by 50 per cent saturation with ammonium sulfate, and by 2 per cent trichloroacetic acid. It does not diffuse through a dialyzing membrane. Extracts have been obtained containing the antigen, that give a negative Molisch test for carbohydrate but they give a positive Biuret test.

The antigen is insoluble in ether and thermostable.

It is therefore concluded that the antigen is either a protein or closely associated with a protein.

In 31 out of 33 cases tested the antigen was found to be masked in the infected mucosa. Practical methods of demasking the antigen are described although the nature of the masking is not understood.

A Specific Antigen Recovered from Tissue Infected with M. Paratuberculosis (Johne's Bacillus)

A specific antigen has been found in the mucous membrane of the intestine of sheep infected with paratuberculosis (Johne's disease). This antigen fixes complement in the presence of sera from natural cases of the disease.

The antigen in the mucosa is masked so that saline extracts of the fresh mucous membrane are not active in the complement fixation test. However, after drying and extraction with ether infected intestines yielded active specific antigens in 14 out of 17 experiments.

Complement-fixing antibodies were found to be present in the blood of a high percentage of natural cases of the disease and appear early in the infection. Nonspecific reactions seem to be rare.

Studies on Influenzal Infections in the Chick-Embryo

Infections in the chick-embryo with two recently isolated human strains of influenzal virus and two strains of swine-virus have been studied with relation to the influence of the temperature of incubation and the age of the host. The findings indicate that the temperature is of considerable importance and that 35–36 C is more suitable than 39–40 C for titrational purposes, as titrations carried out at 39–40 C gave very low and irregular 50-percent-infectivity endpoints. The explanation seems to be that a larger dose of virus was needed to infect at the higher temperature, and further that in many infected eggs the concentration of virus was not high enough to give positive red-cell agglutination. Both these factors contributed to the low endpoints obtained in the titrations at 39–40 C. This would probably be less conspicuous with strains having a higher agglutinin/infectivity ratio. Whether some intermediate temperature might be more suitable than 35–36 C has not been tested. Incubation at 37 C as used by Hirst for purposes of titration and isolation is obviously satisfactory. How 37 C compares with 35–36 C as to susceptibility of the embryo and amount of virus produced would have to be clarified by direct comparison.

The strains tested killed the embryos regularly at the lower temperature and infections and deaths were prevented by immune sera. The swine-strains also killed at 39–40 C but a few survivors were found with the human strains at that temperature. The report (24) that H. influenzæ suis is necessary in addition to the swine-virus if high mortality is to result from the infection is probably to be explained by differences in the strains of virus used.

The 7- and 12-day embryos apparently did not differ markedly in their resistance although the 7-day eggs were probably slightly more susceptible.

The route of inoculation (on the chorioallantoic membrane or into the amnion) and the amount of virus used did not greatly affect the rate of increase of virus in the fluids with strains TW 772 and V 15 strain 2. Strain TW 771, on the other hand, seemed to depend more on the route of inoculation and the size of the inoculum, the concentration rising quicker after a large inoculum.

Finally, the effect of Na-sulfadiazine on the infection was tested. It was found that 20 mg of Na-sulfadiazine per embryo did not reduce the number of positive infections in critical virus-dilutions; or in other words, titrations in eggs containing this amount of the drug did not show a lower infectivity-endpoint than did titrations in normal control eggs. Should it be desired to use an antibacterial agent with inocula that are not completely free of bacteria, Na-sulfadiazine would seem to be suitable as far as the virus is concerned.