Cerebral Capillary Endothelium Research Articles

Phenomenological structure of anxiety disorders in persons who have transferred COVID-19

The SARS-CoV-2 virus is neurotropic because its adhesion protein has a high affinity for Angiotensin-Converting Enzyme 2 receptors, which are expressed, among other things, on the endothelium of cerebral capillaries. There are several theories of the pathogenesis of brain damage in COVID-19: direct viral damage, hypoxia/ischemia and systemic inflamma-tion, autoimmune damage. The study was conducted to study the clinical and psychopatho-logical features of anxiety disorders in patients who suffered from COVID-19. During 2020–2022, 94 patients (49 men and 55 women) with an average age of (33.0±5.0) years who suf-fered from COVID-19 and were diagnosed with anxiety disorders were examined. According to the results of the study was found: a characteristic low mood background; feeling anxious; unmotivated anxiety; internal tension with inability to relax; anxious fears; intrusive anxious thoughts that intensify in the evening and at night, which prevents falling asleep; attacks of fear, which are accompanied by suffocation, a feeling of unreality, fear of death; exaggerated wariness; inability to control anxiety; feeling of loss of control over one's life; irritability; decreased ability to concentrate; motor tension; autonomic hyperactivity; sleep disorders. The data obtained in the course of the study formed the basis for the development of a com-prehensive personalized program for the correction of anxiety disorders in patients with COVID-19 with differentiated use of psychopharmacotherapy, psychotherapy and psy-choeducation. It was concluded that patients are characterized by pronounced manifestations of anxiety disorders: prolonged anxiety-depressive reaction, panic disorder, generalized anx-iety disorder; anxiety disorder of an organic nature. Keywords: SARS-CoV-2 virus, neurotropic virus, anxiety, depressive states.

COVID-19: From Psychological Distress to Neuropsychiatric Manifestations

Back to table of contents Previous article Next article Clinical & ResearchFull AccessCOVID-19: From Psychological Distress to Neuropsychiatric ManifestationsFarah Zaidi, M.D.Farah ZaidiSearch for more papers by this author, M.D.Published Online:30 Jul 2020https://doi.org/10.1176/appi.pn.2020.7b10AbstractThe neuropsychiatric picture of COVID-19 is not fully known yet. Better understanding and prospective monitoring of the neuropsychiatric manifestations related to COVID-19 can inform early detection and treatment planning.In the six months since COVID-19 has transformed life across the globe, there has been a marked increase in psychological distress stemming from fear of this viral illness and the stigma associated with it, challenges related to sheltering in place and physical distancing, financial strain, isolation, and exacerbation of mental illness (including increased risk of death by suicide) and new barriers to care. Shelter-in-place rules have also raised alarms about domestic violence and child abuse.A growing literature is helping us to better understand the virus and its impact beyond the respiratory system, neurotropic potential, and possible mechanisms of underlying pathology. The volume of the National Institutes of Health’s LitCovid has increased from 40 publications in late January 2020 to approximately 1,970 publications in early July. LitCovid is a curated literature site of the National Institutes of Health and the National Center for Biotechnology Information that tracks up-to-date scientific information about COVID-19.Though relatively limited, articles and reports are emerging about acute neurological and neuropsychiatric manifestations of COVID-19 and possible neuropsychiatric sequelae. For example, a retrospective chart review of 214 patients in Wuhan, China, found that approximately 36% of patients had neurological manifestations such as cerebrovascular disease, impaired consciousness, and skeletal muscle injury. Other symptoms of drowsiness, edema, stroke, convulsions, and coma are also reported in literature.An article by Troyer et al. in the July issue of Brain, Behavior, and Immunity described the emergence of neuropsychiatric symptoms such as anxiety, depression, trauma, insomnia, psychosis, delirium, and suicidality related to past viral pandemics, appearing long after the acute viral spread was over. The authors argued persuasively that physicians and health systems should monitor patients exposed to COVID-19 for neuropsychiatric sequelae.Another recent systematic review and meta-analysis by Rogers et al. in Lancet Psychiatry reported the prevalence of delirium in the acute stage of COVID-19 infection. The authors encouraged clinicians to monitor for the emergence of depression, anxiety, posttraumatic stress disorder, and other neuropsychiatric disorders post infection.There are also reports of anosmia/hyposmia and ageusia in patients infected with COVID-19. As such, in late March, the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) launched a COVID-19 Anosmia Reporting Tool. The tool is designed to submit data confidentially to AAO-HNS for anosmia and dysgeusia related to COVID-19. Preliminary findings collected from this tool showed that “anosmia was noted in 73% of patients prior to COVID-19 diagnosis and was the initial symptom in 26.6%.” Based on these findings, it appears that anosmia may be a presenting symptom in COVID-19 before other more commonly known symptoms appear.Proposed mechanisms for pathogenesis of neurological and neuropsychiatric manifestations related to COVID-19 include hypoxic brain injury; interaction of the COVID-19 virus spike protein with ACE-2 receptors of the cerebral capillary endothelium, resulting in damage to the endothelial lining and access to brain; cerebral edema; post-infectious autoimmunity; and immunomodulatory treatments.As the global community continues to learn about and adjust to many emerging aspects of COVID-19, its multisystem impact is increasingly known. Awareness about neuropsychiatric manifestations related to COVID-19 could prepare the psychiatric community in managing at-risk populations. ■LitCovid can be accessed here.Farah Zaidi, M.D., is an inpatient and psychiatric emergency services psychiatrist in a community hospital in San Mateo County. She is on the teaching faculty for the psychiatry residency training program at San Mateo Behavioral Health and Recovery Services. She is also vice president of the Northern California Psychiatric Society and co-chair of its Professional Education Committee. ISSUES NewArchived

Penetration of the blood-brain barrier by peripheral neuropeptides: new approaches to enhancing transport and endogenous expression.

The blood-brain barrier (BBB) is a structural and functional barrier between the interstitial fluid of the brain and the blood; the barrier maintains the precisely controlled biochemical environment that is necessary for neural function. This constellation of endothelial cells, macrophages, pericytes, and astrocytes forms the neurovascular unit which is the structural and functional unit of the blood-brain barrier. Peptides enter and exit the CNS by transport systems expressed by the capillary endothelial cells of the neurovascular unit. Limiting the transport of peptides and proteins into the brain are efflux transporters like P-gp are transmembrane proteins present on the luminal side of the cerebral capillary endothelium and their function is to promote transit and excretion of drugs from the brain to the blood. Nanocarrier systems have been developed to exploit transport systems for enhanced BBB transport. Recent approaches for enhancing endogenous peptide expression are discussed.

Estrogen protects the blood–brain barrier from inflammation-induced disruption and increased lymphocyte trafficking

Sex differences have been widely reported in neuroinflammatory disorders, focusing on the contributory role of estrogen. The microvascular endothelium of the brain is a critical component of the blood–brain barrier (BBB) and it is recognized as a major interface for communication between the periphery and the brain. As such, the cerebral capillary endothelium represents an important target for the peripheral estrogen neuroprotective functions, leading us to hypothesize that estrogen can limit BBB breakdown following the onset of peripheral inflammation.Comparison of male and female murine responses to peripheral LPS challenge revealed a short-term inflammation-induced deficit in BBB integrity in males that was not apparent in young females, but was notable in older, reproductively senescent females. Importantly, ovariectomy and hence estrogen loss recapitulated an aged phenotype in young females, which was reversible upon estradiol replacement. Using a well-established model of human cerebrovascular endothelial cells we investigated the effects of estradiol upon key barrier features, namely paracellular permeability, transendothelial electrical resistance, tight junction integrity and lymphocyte transmigration under basal and inflammatory conditions, modeled by treatment with TNFα and IFNγ. In all cases estradiol prevented inflammation-induced defects in barrier function, action mediated in large part through up-regulation of the central coordinator of tight junction integrity, annexin A1. The key role of this protein was then further confirmed in studies of human or murine annexin A1 genetic ablation models.Together, our data provide novel mechanisms for the protective effects of estrogen, and enhance our understanding of the beneficial role it plays in neurovascular/neuroimmune disease.

Novel pathological features and potential therapeutic approaches for CADASIL: insights obtained from a mouse model of CADASIL.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common condition of hereditary stroke and vascular dementia. CADASIL is caused by Notch3 mutation, leading to progressive degeneration of vascular smooth muscle cells (vSMCs) of the small arteries in the brain. However, the pathogenesis of CADASIL remains largely unknown, and treatment that can stop or delay the progression of CADASIL is not yet available. Using both wild type mice and transgenic mice carrying the human mutant Notch3 gene (CADASIL mice), we have recently characterized the pathological features of CADASIL and determined the therapeutic efficacy of two hematopoietic growth factors, stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) in CADASIL. Our findings have revealed novel pathological changes in the endothelium of cerebral capillaries and in the neural stem cells (NSCs). We have also observed the impairment of cognitive function in CADASIL mice. Moreover, SCF+G-CSF treatment improves cognitive function, inhibits Notch3 mutation-induced vSMC degeneration, cerebral blood bed reduction, cerebral capillary damage, and NSC loss, and increases neurogenesis and angiogenesis. Here we compile an overview of our recently published studies, which provide new insights into understanding the pathogenesis of CADASIL and developing therapeutic strategies for this devastating neurological disease.

Novel model of brain metastasis formation: the influence of polychlorinated biphenyls on blood‐brain barrier integrity and brain metastasis

Anatomically situated at the level of the cerebral capillary endothelium, the blood‐brain barrier (BBB) is a highly dynamic interface comprised of a network of tight junction (TJ) proteins that seal adjacent cells of apposing endothelium. Perturbations in BBB integrity have been associated with numerous CNS disease states, including brain metastasis. Polychlorinated biphenyls (PCBs) comprise a ubiquitous class of toxic substances associated with carcinogenic and tumor promoting effects. Previously, our laboratory has demonstrated that exposure to PCBs are effective in activating endothelial cells and inducing prometastatic properties, however less is known regarding the influence of PCBs in brain cancer metastasis in vivo. In the current study we demonstrate accumulation of PCB 153, PCB 126, and PCB 118 in brain tissue as early as 48 hours post‐systemic exposure (49 mg/kg). This accumulation corresponds with changes in BBB molecular properties. Additionally, we employ our external carotid artery injection (ECI) brain metastasis model, in which luciferase‐tagged tumor cells are introduced directly to the cerebravasculature, coupled with bioluminescence imagining techniques to investigate the role of PCBs in brain metastasis. These studies are critical in understanding the neurotoxic influence of PCBs in brain metastasis. Supported by NIEHS (P42ES07380)

Cerebral edema and its treatment

Cerebral edema is a life-threatening condition that develops as a result of an inflammatory reaction. Most frequently, this is the consequence of cerebral trauma, massive cerebral infarction, hemorrhages, abscess, tumor, allergy, sepsis, hypoxia, and other toxic or metabolic factors. At present, the following types of cerebral edema are differentiated: the vasogenic cerebral edema resulting from an increased permeability of the endothelium of cerebral capillaries to albumin and other plasma proteins; the cytotoxic cerebral edema resulting from the exhaustion of the energy potential of cell membranes without damage to the barrier; the hydrostatic cerebral edema resulting from disturbance of the autoregulation of cerebral blood circulation; the osmotic cerebral edema resulting from dilution of blood; and the interstitial cerebral edema resulting from acute hydrocephaly. Some authors also differentiate ischemic cerebral edema. At present, when various traumas and traumatic cerebral injuries are frequent causes of death in young people, treatment strategy for cerebral edema is of utmost importance. Monitoring of the patient's condition in the intensive care unit is a necessity. It is important to ensure proper positioning of the patient--the head should be tilted at 30 degrees in order to optimize the cerebral perfusion pressure and control of the increase in intracranial pressure. Hyperventilation should be applied. Controlled hypothermia decreases the rate of metabolism in the brain. Slightly positive fluid balance should be maintained using crystalloid or colloid (hypertonic-hyperoncotic) solutions, at the same time maintaining cerebral perfusion pressure exceeding 70 mmHg. The treatment includes administration of antihypertensive medications, nonsteroidal antiinflammatory drugs, and barbiturates. Steroids decrease the permeability of capillaries and the hemato-encephalic barrier, promoting the movement of Na(+)/K(+) ions and water through the main endothelial membrane, and therefore they are used in the treatment of vasogenic cerebral edema as well as edema caused by a cerebral tumor. Glutamate and N-methyl-D-aspartate receptor antagonists improve cerebral microcirculation and metabolism. Trometamol corrects cerebral acidosis. Extended cerebral edema is treated surgically via a bilateral decompressive craniotomy, sometimes including craniotomy of lateral and posterior fossae. The treatment of cerebral edema is complex, and positive results may be expected only if the diagnosis and the provision of assistance are timely.

A Review of Nanocarrier-Based CNS Delivery Systems

Drug delivery to the central nervous system (CNS) is one of the most challenging fields of research and development for pharmaceutical and biotechnology products. A number of hydrophilic therapeutic agents, such as antibiotics, anticancer agents, or newly developed neuropeptides do not cross the blood brain barrier (BBB) after systemic administration. The BBB is formed by the tight junctions at the brain capillary endothelial cells, which strictly control drug transfer from blood to brain. Drug modification, osmotic opening of cerebral capillary endothelium, and alternative routes for administration (e.g., intracerebral delivery) have been successfully used to enhance drug transport to the CNS. The use of nanocarriers, such as liposomes and solid polymeric or lipid nanoparticles may be advantageous over the current strategies. These nanocarriers can not only mask the BBB limiting characteristics of the therapeutic drug molecule, but may also protect the drug from chemical/enzymatic degradation, and additionally provide the opportunity for sustained release characteristics. Reduction of toxicity to peripheral organs can also be achieved with these nanocarriers. This review article discusses the various barriers for drug delivery to the CNS and reviews the current state of nanocarriers for enhancing drug transport into the CNS.

Epoxyeicosatetrinoic acids released by astrocytes: function in cerebral angiogenesis

Epoxyeicosatetrinoic acids (EETs) are bioactive metabolites of arachidonic acid (AA). Our laboratory has cloned and sequenced a P450 cDNA from astrocytes which epoxygenate arachidonic acid leading to formation of EETs. The actions of these products include activation of K + channels and hyperpolarization of cerebral vascular smooth muscle and induction of mitogenic mechanisms in capillary endothelium resulting in tube formation. This communication focuses on the discussing of angiogenic properties of EETs on cerebral capillary endothelium.

Ion Regulation in the Brain: Implications for Pathophysiology

Ions in the brain are regulated independently from plasma levels by active transport across choroid plexus epithelium and cerebral capillary endothelium, assisted by astrocytes. In “resting” brain tissue, extracellular potassium ([K+]o) is lower and [H+]o is higher (i.e., pHo is lower) than elsewhere in the body. This difference probably helps to maintain the stability of cerebral function because both high [K+]o and low [H+]o enhance neuron excitability. Decrease in osmolarity enhances synaptic transmission and neuronal excitability whereas increased osmolarity has the opposite effect. Iso-osmotic low Na+ concentration also enhances voltage-dependent Ca2+ currents and synaptic transmission. Hypertonicity is the main cause of diabetic coma. In normally functioning brain tissue, the fluctuations in ion levels are limited, but intense neuronal excitation causes [K+]o to rise and [Na+]o, [Ca2+]o to fall. When excessive excitation, defective inhibition, energy failure, mechanical trauma, or blood-brain barrier defects drive ion levels beyond normal limits, positive feedback can develop as abnormal ion distributions influence neuron function, which in turn aggravates ion maldistribution. Computer simulation confirmed that elevation of [K+]o can lead to such a vicious circle and ignite seizures, spreading depression (SD), or hypoxic SD-like depolarization (anoxic depolarization).

Regulation of Blood—Brain Barrier Permeability

The blood-brain barrier minimizes the entry of molecules into brain tissue. This restriction arises by the presence of tight junctions (zonulae occludens) between adjacent endothelial cells and a relative paucity of pinocytotic vesicles within endothelium of cerebral arterioles, capillaries, and venules. Many types of stimuli can alter the permeability characteristics of the blood-brain barrier. Acute increases in arterial blood pressure beyond the autoregulatory capacity of cerebral blood vessels, application of hyperosmolar solutions, application of various inflammatory mediators known to be elevated during brain injury, and/or activation of blood-borne elements such as leukocytes can produce changes in permeability of the blood-brain barrier. The second messenger systems that account for increases in permeability of the blood-brain barrier during pathophysiologic conditions, however, remain poorly defined. This review will summarize studies that have examined factors that influence disruption of the blood-brain barrier, and will discuss the contribution of various cellular second messenger pathways in disruption of the blood-brain barrier during pathophysiologic conditions.

Cerebral cell adhesion molecule: a novel leukocyte adhesion determinant on blood-brain barrier capillary endothelium.

The tight junctions of the cerebral capillary endothelium form the highly restrictive blood-brain barrier. Migration of leukocytes across this unique barrier may involve ligation of elements in addition to those of the fenestrated capillaries of the peripheral vascular system. An antibody raised against a bacterial adhesive protein and shown to have cross-reactivity with brain capillaries and to block leukocyte migration into the brain was used to identify and clone a novel determinant on brain microvessels. This cDNA was sequenced, and the expressed protein supported leukocyte adhesion in a CD18-dependent fashion. The high level of brain microvessel expression of this adhesion molecule, termed the cerebral cell adhesion molecule, implicates it in leukocyte transmigration across the blood-brain barrier.

The normal and pathological physiology of brain water.

The physicochemical properties of water enable it to act as a solvent for electrolytes, and to influence the molecular configuration and hence the function--enzymatic in particular--of polypeptide chains in biological systems. The association of water with electrolytes determines the osmotic regulation of cell volume and allows the establishment of the transmembrane ion concentration gradients that underlie nerve excitation and impulse conduction. Fluid in the central nervous system is distributed in the intracellular and extracellular spaces (ICS, ECS) of the brain parenchyma, the cerebrospinal fluid, and the vascular compartment--the brain capillaries and small arteries and veins. Regulated exchange of fluid between these various compartments occurs at the blood-brain barrier (BBB), and at the ventricular ependyma and choroid plexus, and, on the brain surface, at the pia mater. The normal BBB is relatively permeable to water, but considerably less so to ions, including the principal electrolytes Brain fluid regulation takes place within the context of systemic fluid volume control, which depends on the mutual interaction of osmo-, volume-, and pressure-receptors in the hypothalamus, heart and kidney, hormones such as vasopressin, renin-angiotensin, aldosterone, atriopeptins, and digitalis-like immunoreactive substance, and their respective sites of action. Evidence for specific transport capabilities of the cerebral capillary endothelium, for example high Na+K(+)-ATPase activity and the presence at the abluminal surface of a Na(+)--H+ antiporter, suggests that cerebral microvessels play a more active part in brain volume regulation and ion homoeostasis than do capillaries in other vascular beds. The normal brain ECS amounts to 12-19% of brain volume, and is markedly reduced in anoxia, ischaemia, metabolic poisoning, spreading depression, and conventional procedures for histological fixation. The asymmetrical distributions of Na+ K+ and Ca2+ between ICS and ECS underlie the roles of these cations in nerve excitation and conduction, and in signal transduction. The relatively large volume of the CSF, and extensive diffusional exchange of many substances between brain ECS and CSF, augment the ion-homeostasing capacity of the ECS. The choroid plexus, in addition to secreting CSF principally by biochemical mechanisms (there is an additional small component from the extracellular fluid), actively transports some substances from the blood (e.g. nucleotides and ascorbic acid), and actively removes others from the CSF. In contrast with CSF secretion, CSF reabsorption is principally a biomechanical process, passively dependent on the CSF-dural sinus pressure gradient. Pathological increases in intracranial water content imply development of an intracranial mass lesion. The additional water may be distributed diffusely within the brain parenchyma as brain oedema, as a cyst, or as increase in ventricular volume due to hydrocephalus. Brain oedema is classified on the basis of pathophysiology into four categories, vasogenic, cytotoxic, osmotic and hydrostatic. The clinical conditions in which brain oedema presents the greatest problems are tumour, ischaemia, and head injury. Peritumoural oedema is predominantly vasogenic and related to BBB dysfunction. Ischaemic oedema is initially cytotoxic, with a shift of Na+ and CI- ions from ECS to ICS, followed by osmotically obliged water, this shift can be detected by diffusion-weighted MRI. Later in the evolution of an ischaemic lesion the oedema becomes vasogenic, with disruption of the BBB. Recent imaging studies in patients with head injury suggest that the development of traumatic brain oedema may follow a biphasic time course similar to that of ischaemic oedema. Hydrocephalus is associated in the great majority of cases with an obstruction to the circulation or drainage of CSF, or, occasionally, with overproduction of CSF by a choroid plexus papilloma. In either case, the consequence is a ris

Entry of pathogens into the central nervous system

The blood-brain barrier (BBB) is formed by the tight junctions of the cerebral capillary endothelium and the choroid plexus epithelium. The molecular anatomy of the tight junction resembles that of a polarized, transporting epithelium, suggesting some model cell culture systems can provide insight into traffic into the central nervous system. Pathogens target both the endothelium, causing encephalitis, and the choroid plexus, leading to meningitis. Routes of entry are diverse including paracellular and transcellular penetration. In addition, circulating microbial products can induce loss of BBB function. Understanding the heterogeneous molecular interactions between pathogens and the BBB may provide avenues to interrupt the devastating neurological sequelae that accompany central nervous system infections.

Endothelin 1 stimulates Na+,K(+)-ATPase and Na(+)-K(+)-Cl- cotransport through ETA receptors and protein kinase C-dependent pathway in cerebral capillary endothelium.

The effect of endothelins (ET-1 and ET-3) on 86Rb+ uptake as a measure of K+ uptake was investigated in cultured rat brain capillary endothelium. ET-1 or ET-3 dose-dependently enhanced K+ uptake (EC50 = 0.60 +/- 0.15 and 21.5 +/- 4.1 nM, respectively), which was inhibited by the selective ETA receptor antagonist BQ 123 (cyclo-D-Trp-D-Asp-Pro-D-Val-Leu). Neither the selective ETB agonists IRL 1620 [N-succinyl-(Glu9,-Ala11,15)-ET-1] and sarafotoxin S6c, nor the ETB receptor antagonist IRL 1038 [(Cys11,Cys15)-ET-1] had any effect on K+ uptake. Ouabain (inhibitor of Na+,K(+)-ATPase) and bumetanide (inhibitor of Na(+)-K(+)-Cl- cotransport) reduced (up to 40% and up to 70%, respectively) the ET-1-stimulated K+ uptake. Complete inhibition was seen with both agents. Phorbol 12-myristate 13-acetate (PMA), activator of protein kinase C (PKC), stimulated Na+,K(+)-ATPase and Na(+)-K(+)-Cl- cotransport. ET-1- but not PMA-stimulated K+ uptake was inhibited by 5-(N-ethyl-N-isopropyl)amiloride (inhibitor of Na+/H+ exchange system), suggesting a linkage of Na+/H+ exchange with ET-1-stimulated Na+,K(+)-ATPase and Na(+)-K(+)-Cl- cotransport activity that is not mediated by PKC.

Cerebrovascular Angiotensin II Receptors in Spontaneously Hypertensive Rats

The objective of this study was to characterize angiotensin II (AII) receptors in cerebral capillary endothelium and to examine whether the first step in AII responsiveness, namely AII receptor binding, is aberrant in cerebral microvessels obtained from adult spontaneously hypertensive rats (SHR). The binding of [3H]angiotensin II to isolated cerebrocortical microvessels from Sprague-Dawley, Wistar-Kyoto, and SHR rats was used to characterize AII receptors on these vessels. Kinetic experiments yielded an equilibrium-derived Kd (dissociation rate constant/association rate constant) very close to that obtained from Scatchard analysis of saturation binding data. The data indicated that the two normotensive control strains exhibited comparable AII receptor affinity and binding capacity. In contrast, experiments with microvessels from adult SHR indicated a significantly higher Bmax for AII receptors relative to controls. Although experiments assessing functional endothelial alterations in the SHR to AII remain to be performed, the increase in AII receptor number suggests that an abnormality in vascular AII responsiveness may play an important role in this model of hypertension.

Uptake of leucine and alanine by cultured cerebral capillary endothelial cells

Pure cultures of rat cerebral capillary endothelium have been used to study the A- and L-systems of amino acid transport. Leucine is taken up by a non-concentrative mechanism that can be saturated, and competivively inhibited by phenylalanine. Uptake is rapid, with equilibiration apparent 3–min (al experiments performed at 37 °C). The K M for transport was 83 μM ± 26(mean ±S.E.M.., n = 3 which is in good agreement with recent vi vivo report using unanesthtissed rats. Alanine was transported by a saturable, concentrative mechanism. Dependence on Na + -ions was demonstrated by lack of specific uptake in Na + -ffree buffer and reduced uptake after preincubation in ouabain — Na +, K + -ATPase inhibitor. The K M was 325 μM ±88 (mean ± S.E.M., n = 3). The finding ac an active A-system transporter in vitro suggests that the cells may have lost the polarity they demonstrate in vivo. The relevance of these findings to transport of nutrients nd drugs across the blood-brain barrier is discussed.

Tubular invaginations in cerebral endothelium and their relation to smooth-surfaced cisternae in hagfish (Myxine glutinosa)

The organization of vesicular profiles in the endothelium of cerebral capillaries of the hagfish, Myxine glutinosa, has been reinvestigated. Judged from random thin sections the endothelial cells contain numerous vesicles and tubules, in contrast to brain endothelia of most other vertebrates. However, three-dimensional reconstructions based on ultrathin serial sections (thickness ∼18 nm) showed that the profiles represent a system of irregular tubular invaginations of the cell membrane, comparable to the vesicular invaginations demonstrated in extracerebral capillary endothelia of frogs and rats. In addition, smooth-surfaced cisternae were present in close relation to the invaginations. The function of endothelial invaginations is unknown. They do not transport macromolecules, because the blood-brain barrier is practically impermeable to proteins. However, since the system of the invaginations and smooth-surfaced cisternae is structurally similar to the system of caveolae and sarcoplasmic reticulum in smooth muscle cells, a common function seems likely. It is proposed that endothelial invaginations and smooth-surfaced cisternae are involved in regulation of cytosolic Ca++-concentration.

Intracarotid infusions of protamine sulfate disrupt the blood-brain barrier of rabbits

This study examined the effect of intracarotid infusions of protamine sulfate on the blood-brain barrier of the rabbit. Evans blue, which binds tightly to serum albumin, served as the marker for blood-brain barrier disruption. Brains from 12 of 14 rabbits receiving 30–50 mg of protamine sulfate in an intracarotid infusion over 3 min demonstrated intense Evans blue-albumin staining in the distribution of the infused internal carotid artery. In contrast, brains from 5 animals receiving 0.9% saline and from 5 animals receiving 50 mg of protamine sulfate by the intravenous route showed no evidence of blood-brain barrier disruption. Premixing protamine sulfate with heparin prior to intracarotid administration greatly reduced or abolished Evans blue staining of the brain as did delayed administration of the marker dye. Thus, the interaction of the positively charged protamine molecule with the vascular endothelium of cerebral capillaries transiently alters the permeability of the blood-brain barrier in the rabbit.

Morphologic alterations of the blood-brain barrier with experimental meningitis in the rat. Temporal sequence and role of encapsulation.

The cerebral capillary endothelium is unique and functions as an effective blood-brain barrier (BBB) owing to its intercellular tight junctions and rare pinocytotic vesicles. To assess how bacterial meningitis alters the BBB, rats were inoculated intracisternally with three encapsulated meningeal pathogens (Escherichia coli K1+, Streptococcus pneumoniae type III, Haemophilus influenzae type b) and an unencapsulated mutant strain (H. influenzae Rd). After defined infection durations, the morphologic alterations of the cerebral capillary endothelium were quantitatively assessed by transmission electron microscopy. Results revealed a significant increase in pinocytotic vesicle formation (P less than 0.001) early after meningitis induction (4 h) that was sustained with longer infection durations (10 h, 18 h) for all encapsulated strains tested. In addition, there was a progressive increase in completely separated intercellular junctions with increasing infection duration, (P less than 0.05). 4 h after induction of meningitis with H. influenzae Rd, cerebrospinal fluid (CSF) bacterial concentrations, cerebral capillary morphologic changes, and functional BBB permeability to circulating 125I-albumin were similar to those observed with H. influenzae type b. However, prolonging the H. influenzae Rd infection to 18 h allowed for CSF clearance of the organism, thereby precluding the significant increase in separated junctions or progression of functional BBB permeability seen with the encapsulated H. influenzae type b. These data suggest a uniform morphologic explanation for altered BBB permeability in meningitis with a reproducible temporal sequence. Encapsulation does not appear essential for BBB injury, but may facilitate its progression by allowing the organism to evade host clearance.