Chapter 31: Circumventricular organ capillaries

Glucose Transport and Utilization in the Hippocampus: From Neurophysiology to Diabetes-Related Development of Dementia

The association of diabetes with cognitive dysfunction has at least 60 years of history, which started with the observation that children with type 1 diabetes mellitus (T1D), who had recurrent episodes of hypoglycemia and consequently low glucose supply to the brain, showed a deficit of cognitive capacity. Later, the growing incidence of type 2 diabetes mellitus (T2D) and dementia in aged populations revealed their high association, in which a reduced neuronal glucose supply has also been considered as a key mechanism, despite hyperglycemia. Here, we discuss the role of glucose in neuronal functioning/preservation, and how peripheral blood glucose accesses the neuronal intracellular compartment, including the exquisite glucose flux across the blood-brain barrier (BBB) and the complex network of glucose transporters, in dementia-related areas such as the hippocampus. In addition, insulin resistance-induced abnormalities in the hippocampus of obese/T2D patients, such as inflammatory stress, oxidative stress, and mitochondrial stress, increased generation of advanced glycated end products and BBB dysfunction, as well as their association with dementia/Alzheimer's disease, are addressed. Finally, we discuss how these abnormalities are accompained by the reduction in the expression and translocation of the high capacity insulin-sensitive glucose transporter GLUT4 in hippocampal neurons, which leads to neurocytoglycopenia and eventually to cognitive dysfunction. This knowledge should further encourage investigations into the beneficial effects of promising therapeutic approaches which could improve central insulin sensitivity and GLUT4 expression, to fight diabetes-related cognitive dysfunctions.

Neuropeptides in Cancer: Friend and Foe?

Neuropeptides are small regulatory molecules found throughout the body, most notably in the nervous, cardiovascular, and gastrointestinal systems. They serve as neurotransmitters or hormones in the regulation of diverse physiological processes. Cancer cells escape normal growth control mechanisms by altering their expression of growth factors, receptors, or intracellular signals, and neuropeptides have recently been recognized as mitogens in cancer growth and development. Many neuropeptides and their receptors exist in multiple subtypes, coupling with different downstream signaling pathways and playing distinct roles in cancer progression. The consideration of neuropeptide/receptor systems as anticancer targets is already leading to new biological and diagnostic knowledge that has the potential to enhance the understanding and treatment of cancer. In this review, recent discoveries regarding neuropeptides in a wide range of cancers, emphasizing their mechanisms of action, signaling cascades, regulation, and therapeutic potential, are discussed. Current technologies used to manipulate and analyze neuropeptides/receptors are described. Applications of neuropeptide analogs and their receptor inhibitors in translational studies and radio-oncology are rapidly increasing, and the possibility for their integration into therapeutic trials and clinical treatment appears promising.

TRPV1-Mediated Sensing of Sodium and Osmotic Pressure in POMC Neurons in the Arcuate Nucleus of the Hypothalamus

The central melanocortin system conducted by anorexigenic pro-opiomelanocortin (POMC) neurons and orexigenic agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus (ARC) not only regulates feeding behavior but also blood pressure. Excessive salt intake raises the Na+ concentration ([Na+]) in the cerebrospinal fluid (CSF) and worsens hypertension. The blood–brain barrier is immature in the ARC. Therefore, both AgRP and POMC neurons in the ARC have easy access to the electrolytes in the blood and can sense changes in their concentrations. However, the sensitivity of AgRP and POMC neurons to Na+ remains unclear. This study aimed to explore how the changes in the extracellular Na+ concentration ([Na+]) influence these neurons by measuring the cytosolic Ca2+ concentration ([Ca2+]i) in the single neurons isolated from the ARC that were subsequently immunocytochemically identified as AgRP or POMC neurons. Both AgRP and POMC neurons responded to increases in both [Na+] and osmolarity in C57BL/6 mice. In contrast, in transient receptor potential vanilloid 1 (TRPV1) knockout (KO) mice, POMC neurons failed to respond to increases in both [Na+] and osmolarity, while they responded to high glucose and angiotensin II levels with increases in [Ca2+]i. Moreover, in KO mice fed a high-salt diet, the expression of POMC was lower than that in wild-type mice. These results demonstrate that changes in [Na+] and osmolarity are sensed by the ARC POMC neurons via the TRPV1-dependent mechanism.

Autonomic control of energy balance and glucose homeostasis

Neurons in the central nervous system (CNS) communicate with peripheral organs largely via the autonomic nervous system (ANS). Through such communications, the sympathetic and parasympathetic efferent divisions of the ANS may affect thermogenesis and blood glucose levels. In contrast, peripheral organs send feedback to the CNS via hormones and autonomic afferent nerves. These humoral and neural feedbacks, as well as neural commands from higher brain centers directly or indirectly shape the metabolic function of autonomic neurons. Notably, recent developments in mouse genetics have enabled more detailed studies of ANS neurons and circuits, which have helped elucidate autonomic control of metabolism. Here, we will summarize the functional organization of the ANS and discuss recent updates on the roles of neural and humoral factors in the regulation of energy balance and glucose homeostasis by the ANS.

Cutting-edge techniques should be harnessed to unravel how metabolism is modulated by a key part of the body’s nervous system. The autonomic nervous system (ANS) regulates many involuntary physiological processes, such as heart rate, breathing, and blood pressure. Scientists now believe that the ANS is involved in regulating metabolism, but its precise roles are unclear. Jong-Woo Sohn and Uisu Hyun at the Korea Advanced Institute of Science and Technology, Daejeon, Korea, reviewed understanding of how the ANS regulates energy balance, appetite, and glucose homeostasis. Recently-developed mouse models have provided insights into how ANS neurons translate neuronal and hormonal signals into commands during feeding, sending instructions to the liver, and mediating blood glucose levels. Several hormones have been identified that may act on a specific part of the ANS to influence appetite and metabolism.

Neuroinflammation, Sleep, and Circadian Rhythms

Molecules involved in innate immunity affect sleep and circadian oscillators and vice versa. Sleep-inducing inflammatory molecules are activated by increased waking activity and pathogens. Pathologies that alter inflammatory molecules, such as traumatic brain injury, cancer, cardiovascular disease, and stroke often are associated with disturbed sleep and electroencephalogram power spectra. Moreover, sleep disorders, such as insomnia and sleep disordered breathing, are associated with increased dysregulation of inflammatory processes. Inflammatory molecules in both the central nervous system and periphery can alter sleep. Inflammation can also modulate cerebral vascular hemodynamics which is associated with alterations in electroencephalogram power spectra. However, further research is needed to determine the interactions of sleep regulatory inflammatory molecules and circadian clocks. The purpose of this review is to: 1) describe the role of the inflammatory cytokines interleukin-1 beta and tumor necrosis factor-alpha and nucleotide-binding domain and leucine-rich repeat protein-3 inflammasomes in sleep regulation, 2) to discuss the relationship between the vagus nerve in translating inflammatory signals between the periphery and central nervous system to alter sleep, and 3) to present information about the relationship between cerebral vascular hemodynamics and the electroencephalogram during sleep.

A genetic map of the mouse dorsal vagal complex and its role in obesity

The brainstem dorsal vagal complex (DVC) is known to regulate energy balance and is the target of appetite-suppressing hormones, such as glucagon-like peptide 1 (GLP-1). Here we provide a comprehensive genetic map of the DVC and identify neuronal populations that control feeding. Combining bulk and single-nucleus gene expression and chromatin profiling of DVC cells, we reveal 25 neuronal populations with unique transcriptional and chromatin accessibility landscapes and peptide receptor expression profiles. GLP-1 receptor (GLP-1R) agonist administration induces gene expression alterations specific to two distinct sets of Glp1r neurons-one population in the area postrema and one in the nucleus of the solitary tract that also expresses calcitonin receptor (Calcr). Transcripts and regions of accessible chromatin near obesity-associated genetic variants are enriched in the area postrema and the nucleus of the solitary tract neurons that express Glp1r and/or Calcr, and activating several of these neuronal populations decreases feeding in rodents. Thus, DVC neuronal populations associated with obesity predisposition suppress feeding and may represent therapeutic targets for obesity.

Neurology and the COVID-19 Pandemic: Gathering Data for an Informed Response

PURPOSE OF REVIEW

The current coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is one of the greatest medical crises faced by our current generation of health care providers. Although much remains to be learned about the pathophysiology of SARS-CoV-2, there is both historical precedent from other coronaviruses and a growing number of case reports and series that point to neurologic consequences of COVID-19.

RECENT FINDINGS

Olfactory/taste disturbances and increased risk of strokes and encephalopathies have emerged as potential consequences of COVID-19 infection. Evidence regarding whether these sequelae result indirectly from systemic infection or directly from neuroinvasion by SARS-CoV-2 is emerging.

SUMMARY

This review summarizes the current understanding of SARS-CoV-2 placed in context with our knowledge of other human coronaviruses. Evidence and data regarding neurologic sequelae of COVID-19 and the neuroinvasive potential of human coronaviruses are provided along with a summary of patient registries of interest to the Neurology community.

Mechanisms of GABA-mediated inhibition of the angiotensin II-induced cytosolic Ca2+ increase in rat subfornical organ neurons

Neurons in the subfornical organ (SFO) sense both neurotransmitters and circulating humoral factors such as angiotensin II (AII) and atrial natriuretic peptide (ANP), and regulate multiple physiological functions including drinking behavior. We recently reported that AII at nanomolar concentrations induced a persistent [Ca²⁺]_i increase in acutely dissociated SFO neurons and that this effect of AII was reversibly inhibited by GABA. In the present study, we studied the inhibitory mechanism of GABA using Ca²⁺ imaging and patch-clamp electrophysiology. The AII-induced persistent [Ca²⁺]_i increase was inhibited by GABA in more than 90% of AII-responsive neurons and by other two SFO inhibitory ligands, ANP and galanin, in about 60 and 30% of neurons respectively. The inhibition by GABA was mimicked by the GABA_A and GABA_B receptor agonists muscimol and baclofen. The involvement of both GABA receptor subtypes was confirmed by reversal of the GABA-mediated inhibition only when the GABA_A and GABA_B receptors antagonists bicuculline methiodide and CGP55845 were both present. The GABA_B agonist baclofen rapidly and reversibly inhibited voltage-gated Ca²⁺ channel (VGCC) currents recorded in response to depolarizing pulses in voltage-clamp electrophysiology using Ba²⁺ as a charge carrier (I_Ba). Baclofen inhibition of I_Ba was antagonized by CGP55845, confirming GABA_B receptor involvement; was reduced by N-ethylmaleimide, suggesting downstream Gi-mediated actions; and was partially removed by a large prepulse, indicating voltage-dependency. The magnitude of I_Ba inhibition by baclofen was reduced by the application of selective blockers for N-, P/Q-, and L-type VGCCs (ω-conotoxin GVIA, ω-agatoxin IVA, and nifedipine respectively). Overall, our study indicates that GABA inhibition of the AII-induced [Ca²⁺]_i increase is mediated by both GABA_A and GABA_B receptors, and that GABA_B receptors associated with Gi proteins suppress Ca²⁺ entry through VGCCs in SFO neurons.

Polycomb represses a gene network controlling puberty via modulation of histone demethylase Kdm6b expression

Female puberty is subject to Polycomb Group (PcG)-dependent transcriptional repression. Kiss1, a puberty-activating gene, is a key target of this silencing mechanism. Using a gain-of-function approach and a systems biology strategy we now show that EED, an essential PcG component, acts in the arcuate nucleus of the hypothalamus to alter the functional organization of a gene network involved in the stimulatory control of puberty. A central node of this network is Kdm6b, which encodes an enzyme that erases the PcG-dependent histone modification H3K27me3. Kiss1 is a first neighbor in the network; genes encoding glutamatergic receptors and potassium channels are second neighbors. By repressing Kdm6b expression, EED increases H3K27me3 abundance at these gene promoters, reducing gene expression throughout a gene network controlling puberty activation. These results indicate that Kdm6b repression is a basic mechanism used by PcG to modulate the biological output of puberty-activating gene networks.

The blood-brain barrier in health and disease: Important unanswered questions

The blood vessels vascularizing the central nervous system exhibit a series of distinct properties that tightly control the movement of ions, molecules, and cells between the blood and the parenchyma. This "blood-brain barrier" is initiated during angiogenesis via signals from the surrounding neural environment, and its integrity remains vital for homeostasis and neural protection throughout life. Blood-brain barrier dysfunction contributes to pathology in a range of neurological conditions including multiple sclerosis, stroke, and epilepsy, and has also been implicated in neurodegenerative diseases such as Alzheimer's disease. This review will discuss current knowledge and key unanswered questions regarding the blood-brain barrier in health and disease.

Ischemic Stroke Induced Area Postrema Syndrome With Intractable Nausea, Vomiting, and Hiccups

The area postrema (AP) is a small, circumventricular organ located in the dorsal medulla and is characterized by an anastomosed capillary network with no blood-brain barrier. It contains the chemoreceptor trigger zone for vomiting, which is activated by noxious stimuli in the blood. Lesions to the AP produce a clinical syndrome referred to as area postrema syndrome (APS), which is characterized by intractable nausea, vomiting, and hiccups. APS manifests frequently as neuromyelitis optica spectrum disorders (NMOSD), where antibodies attack aquaporin-4 receptors, which are found in abundance in the AP. Its vascular supply is delivered by the anterior spinal artery or, at times, by small vessel branches of the vertebral artery itself.

Ischemic stroke is the fifth leading cause of death in the United States; however, APS due to ischemic stroke has rarely been described. We present a case of a 62-year-old male with ischemic stroke in the cerebellum and brainstem, which produced intractable APS due to extension within his AP. He was treated with metoclopramide 10 mg four times daily and ondansetron 8 mg every eight hours, which relieved his symptoms. Recognizing that the patient’s intractable nausea and vomiting was attributable to AP involvement was valuable in limiting further extraneous workup and focusing on our medical management. Ischemic stroke should be considered in the differential for APS. Given the size of the AP, thin-cut high-resolution diffusion-weighted MRI is warranted in patients with clinical APS. Recognizing that intractable nausea and vomiting may be attributable to stroke is valuable in mitigating extraneous and ineffective medical management. The patient case we describe in our report further outlines these findings.

Obesity induced by Borna disease virus in rats: key roles of hypothalamic fast-acting neurotransmitters and inflammatory infiltrates

Human obesity epidemic is increasing worldwide with major adverse consequences on health. Among other possible causes, the hypothesis of an infectious contribution is worth it to be considered. Here, we report on an animal model of virus-induced obesity which might help to better understand underlying processes in human obesity. Eighty Wistar rats, between 30 and 60 days of age, were intracerebrally inoculated with Borna disease virus (BDV-1), a neurotropic negative-strand RNA virus infecting an unusually broad host spectrum including humans. Half of the rats developed fatal encephalitis, while the other half, after 3-4 months, continuously gained weight. At tripled weights, rats were sacrificed by trans-cardial fixative perfusion. Neuropathology revealed prevailing inflammatory infiltrates in the median eminence (ME), progressive degeneration of neurons of the paraventricular nucleus, the entorhinal cortex and the amygdala, and a strikingly high-grade involution of the hippocampus with hydrocephalus. Immune histology revealed that major BDV-1 antigens were preferentially present at glutamatergic receptor sites, while GABAergic areas remained free from BDV-1. Virus-induced suppression of the glutamatergic system caused GABAergic predominance. In the hypothalamus, this shifted the energy balance to the anabolic appetite-stimulating side governed by GABA, allowing for excessive fat accumulation in obese rats. Furthermore, inflammatory infiltrates in the ME and ventro-medial arcuate nucleus hindered free access of appetite-suppressing hormones leptin and insulin. The hormone transport system in hypothalamic areas outside the ME became blocked by excessively produced leptin, leading to leptin resistance. The resulting hyperleptinemic milieu combined with suppressed glutamatergic mechanisms was a characteristic feature of the found metabolic pathology. In conclusion, the study provided clear evidence that BDV-1 induced obesity in the rat model is the result of interdependent structural and functional metabolic changes. They can be explained by an immunologically induced hypothalamic microcirculation-defect, combined with a disturbance of neurotransmitter regulatory systems. The proposed mechanism may also have implications for human health. BDV-1 infection has been frequently found in depressive patients. Independently, comorbidity between depression and obesity has been reported, either. Future studies should address the exciting question of whether BDV-1 infection could be a link, whatsoever, between these two conditions.

Three-plane description of astroglial populations of OVLT subdivisions in rat: Tanycyte connections to distant parts of third ventricle

This study demonstrates glial and gliovascular markers of organon vasculosum laminae terminalis (OVLT) in three planes. The distribution of glial markers displayed similarities to the subfornical organ. There was an inner part with vimentin- and nestin-immunopositive glia whereas GFAP and the water-channel aquaporin 4 were found at the periphery. This separation indicates different functions of the two regions. The presence of nestin may indicate stem cell-capabilities whereas aquaporin 4 has been reported to promote the osmoreceptor function. Glutamine synthetase immunoreactivity was sparse like in the area postrema and subfornical organ. The laminin and β-dystroglycan immunolabelings altered along the vessels such as in the subfornical organ indicating altering gliovascular relations. The different subdivisions of OVLT received glial processes of different origins. The posterior periventricular zone contained short vimentin-immunopositive processes from the ependyma of the adjacent surface of the third ventricle. The lateral periventricular zone received forceps-like process systems from the anterolateral part of the third ventricle. Most interestingly, the "dorsal cap" received a mixed group of long GFAP- and vimentin-immunopositive processes from a distant part of the third ventricle. The processes may have two functions: a guidance for newly produced cells like radial glia in immature brain and/or a connection between distant parts of the third ventricle and OVLT.

Pathomechanisms of Blood-Brain Barrier Disruption in ALS

The blood-brain barrier (BBB) and the blood-spinal cord barrier (BSCB) are responsible for controlling the microenvironment within neural tissues in humans. These barriers are fundamental to all neurological processes as they provide the extreme nutritional demands of neural tissue, remove wastes, and maintain immune privileged status. Being a semipermeable membrane, both the BBB and BSCB allow the diffusion of certain molecules, whilst restricting others. In amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases, these barriers become hyperpermeable, allowing a wider variety of molecules to pass through leading to more severe and more rapidly progressing disease. The intention of this review is to discuss evidence that BBB hyperpermeability is potentially a disease driving feature in ALS and other neurodegenerative diseases. The various biochemical, physiological, and genomic factors that can influence BBB permeability in ALS and other neurodegenerative diseases are also discussed, in addition to novel therapeutic strategies centred upon the BBB.

Persistent cytosolic Ca2+ increase induced by angiotensin II at nanomolar concentrations in acutely dissociated subfornical organ (SFO) neurons of rats

It is known that angiotensin II (AII) is sensed by subfornical organ (SFO) to induce drinking behaviors and autonomic changes. AII at picomolar concentrations have been shown to induce Ca²⁺ oscillations and increase in the amplitude and frequency of spontaneous Ca²⁺ oscillations in SFO neurons. The present study was conducted to examine effects of nanomolar concentrations of AII using the Fura-2 Ca²⁺-imaging technique in acutely dissociated SFO neurons. AII at nanomolar concentrations induced an initial [Ca²⁺]_i peak followed by a persistent [Ca²⁺]_i increase lasting for longer than 1 hour. By contrast, [Ca²⁺]_i responses to 50 mM K⁺, maximally effective concentrations of glutamate, carbachol, and vasopressin, and AII given at picomolar concentrations returned to the basal level within 20 min. The AII-induced [Ca²⁺]_i increase was blocked by the AT1 antagonist losartan. However, losartan had no effect when added during the persistent phase. The persistent phase was suppressed by extracellular Ca2+ removal, significantly inhibited by blockers of L and P/Q type Ca²⁺ channels , but unaffected by inhibition of Ca²⁺ store Ca²⁺ ATPase. The persistent phase was reversibly suppressed by GABA and inhibited by CaMK and PKC inhibitors. These results suggest that the persistent [Ca²⁺]_i increase evoked by nanomolar concentrations of AII is initiated by AT1 receptor activation and maintained by Ca²⁺ entry mechanisms in part through L and P/Q type Ca²⁺ channels, and that CaMK and PKC are involved in this process. The persistent [Ca²⁺]_i increase induced by AII at high pathophysiological levels may have a significant role in altering SFO neuronal functions.

Beta-catenin signaling regulates barrier-specific gene expression in circumventricular organ and ocular vasculatures

The brain, spinal cord, and retina are supplied by capillaries that do not permit free diffusion of molecules between serum and parenchyma, a property that defines the blood-brain and blood-retina barriers. Exceptions to this pattern are found in circumventricular organs (CVOs), small midline brain structures that are supplied by high permeability capillaries. In the eye and brain, high permeability capillaries are also present in the choriocapillaris, which supplies the retinal pigment epithelium and photoreceptors, and the ciliary body and choroid plexus, the sources of aqueous humor and cerebrospinal fluid, respectively. We show here that (1) endothelial cells in these high permeability vascular systems have very low beta-catenin signaling compared to barrier-competent endothelial cells, and (2) elevating beta-catenin signaling leads to a partial conversion of permeable endothelial cells to a barrier-type state. In one CVO, the area postrema, high permeability is maintained, in part, by local production of Wnt inhibitory factor-1.

The Differences in Postprandial Serum Concentrations of Peptides That Regulate Satiety/Hunger and Metabolism after Various Meal Intake, in Men with Normal vs. Excessive BMI

The energy balance regulation may differ in lean and obese people. The purposes of our study were to evaluate the hormonal response to meals with varying macronutrient content, and the differences depending on body weight.

METHODS

The crossover study included 46 men, 21⁻58 years old, normal-weight and overweight/obese. Every subject participated in two meal-challenge-tests with high-carbohydrate (HC), and normo-carbohydrate (NC) or high-fat (HF) meals. Fasting and postprandial blood was collected for a further 240 min, to determine adiponectin, leptin and total ghrelin concentrations.

RESULTS

In normal-weight individuals after HC-meal we observed at 60min higher adiponectin concentrations (12,554 ± 1531 vs. 8691 ± 1070 ng/mL, p = 0.01) and significantly (p < 0.05) lower total ghrelin concentrations during the first 120 min, than after HF-meal intake. Fasting and postprandial leptin levels were significantly (p < 0.05) higher in overweigh/obese men. Leptin concentrations in normal-weight men were higher (2.72 ± 0.8 vs. 1.56 ± 0.4 ng/mL, p = 0.01) 180 min after HC-meal than after NC-meal intake.

CONCLUSIONS

Our results suggest that in normal-body weight men we can expect more beneficial leptin, adiponectin, and total ghrelin response after HC-meal intake, whereas, in overweight/obese men, the HC-meal intake may exacerbate the feeling of hunger, and satiety may be induced more by meals with lower carbohydrate content.

AT1 receptors in the subfornical organ modulate arterial pressure and the baroreflex in two-kidney, one-clip hypertensive rats

The subfornical organ (SFO), a forebrain circumventricular organ that lies outside the blood-brain barrier, has been implicated in arterial pressure and baroreflex responses to angiotensin II (ANG II). We tested whether pharmacological inhibition or selective silencing of SFO ANG II type 1 receptors (AT₁R) of two-kidney, one-clip rats with elevated plasma ANG II decreases resting arterial pressure and renal sympathetic nerve activity (RSNA) and/or modulates arterial baroreflex responses of heart rate (HR) and RSNA. Male Sprague-Dawley rats underwent renal artery clipping [2-kidney, 1-clip (2K,1C)] or sham clipping (sham). After 6 wk, conscious rats instrumented with vascular catheters, renal nerve electrodes, and a cannula directed to the SFO were studied. In another set of experiments, rats were instrumented with hemodynamic and nerve radio transmitters and injected with scrambled RNA or silencing RNA targeted against AT₁R. Mean arterial pressure (MAP) was significantly higher in 2K,1C rats. Acute SFO injection with the AT₁R inhibitor losartan did not change MAP in sham or 2K,1C rats. Baroreflex curves of HR and RSNA were shifted rightward in 2K,1C rats. Losartan exerted no effect. SFO AT₁R knockdown did not influence MAP in sham rats but decreased MAP in 2K,1C rats, despite no change in plasma ANG II or resting RSNA. AT₁R knockdown prevented the reduction in maximum gain and slope of baroreflex responses of HR and RSNA; the reduced RSNA response to baroreceptor unloading was partially restored in 2K,1C rats. These findings show that AT₁R activation within the SFO contributes to hypertension and baroreflex dysfunction in 2K,1C rats and highlight the temporal requirement for reversal of these effects.

Neuroimmune Communication in Health and Disease

The immune and nervous systems are tightly integrated, with each system capable of influencing the other to respond to infectious or inflammatory perturbations of homeostasis. Recent studies demonstrating the ability of neural stimulation to significantly reduce the severity of immunopathology and consequently reduce mortality have led to a resurgence in the field of neuroimmunology. Highlighting the tight integration of the nervous and immune systems, afferent neurons can be activated by a diverse range of substances from bacterial-derived products to cytokines released by host cells. While activation of vagal afferents by these substances dominates the literature, additional sensory neurons are responsive as well. It is becoming increasingly clear that although the cholinergic anti-inflammatory pathway has become the predominant model, a multitude of functional circuits exist through which neuronal messengers can influence immunological outcomes. These include pathways whereby efferent signaling occurs independent of the vagus nerve through sympathetic neurons. To receive input from the nervous system, immune cells including B and T cells, macrophages, and professional antigen presenting cells express specific neurotransmitter receptors that affect immune cell function. Specialized immune cell populations not only express neurotransmitter receptors, but express the enzymatic machinery required to produce neurotransmitters, such as acetylcholine, allowing them to act as signaling intermediaries. Although elegant experiments have begun to decipher some of these interactions, integration of these molecules, cells, and anatomy into defined neuroimmune circuits in health and disease is in its infancy. This review describes these circuits and highlights continued challenges and opportunities for the field.

Methodology and effects of repeated intranasal delivery of DNSP-11 in awake Rhesus macaques

BACKGROUND

To determine if the intranasal delivery of neuroactive compounds is a viable, long-term treatment strategy for progressive, chronic neurodegenerative disorders, such as Parkinson's disease (PD), intranasal methodologies in preclinical models comparable to humans are needed.

NEW METHOD

We developed a methodology to evaluate the repeated intranasal delivery of neuroactive compounds on the non-human primate (NHP) brain, without the need for sedation. We evaluated the effects of the neuroactive peptide, DNSP-11 following repeated intranasal delivery and dose-escalation over the course of 10-weeks in Rhesus macaques. This approach allowed us to examine striatal target engagement, safety and tolerability, and brain distribution following a single ¹²⁵I-labeled DNSP-11 dose.

RESULTS

Our initial data support that repeated intranasal delivery and dose-escalation of DNSP-11 resulted in bilateral, striatal target engagement based on neurochemical changes in dopamine (DA) metabolites-without observable, adverse behavioral effects or weight loss in NHPs. Furthermore, a ¹²⁵I-labeled DNSP-11 study illustrates diffuse rostral to caudal distribution in the brain including the striatum-our target region of interest.

COMPARISON WITH EXISTING METHODS

The results of this study are compared to our experiments in normal and 6-OHDA lesioned rats, where DNSP-11 was repeatedly delivered intranasally using a micropipette with animals under light sedation.

CONCLUSIONS

The results from this proof-of-concept study support the utility of our repeated intranasal dosing methodology in awake Rhesus macaques, to evaluate the effects of neuroactive compounds on the NHP brain. Additionally, results indicate that DNSP-11 can be safely and effectively delivered intranasally in MPTP-treated NHPs, while engaging the DA system.

Low-Fat Diet With Caloric Restriction Reduces White Matter Microglia Activation During Aging

Rodent models of both aging and obesity are characterized by inflammation in specific brain regions, notably the corpus callosum, fornix, and hypothalamus. Microglia, the resident macrophages of the central nervous system, are important for brain development, neural support, and homeostasis. However, the effects of diet and lifestyle on microglia during aging are only partly understood. Here, we report alterations in microglia phenotype and functions in different brain regions of mice on a high-fat diet (HFD) or low-fat diet (LFD) during aging and in response to voluntary running wheel exercise. We compared the expression levels of genes involved in immune response, phagocytosis, and metabolism in the hypothalamus of 6-month-old HFD and LFD mice. We also compared the immune response of microglia from HFD or LFD mice to peripheral inflammation induced by intraperitoneal injection of lipopolysaccharide (LPS). Finally, we investigated the effect of diet, physical exercise, and caloric restriction (40% reduction compared to ad libitum intake) on microglia in 24-month-old HFD and LFD mice. Changes in diet caused morphological changes in microglia, but did not change the microglia response to LPS-induced systemic inflammation. Expression of phagocytic markers (i.e., Mac-2/Lgals3, Dectin-1/Clec7a, and CD16/CD32) in the white matter microglia of 24-month-old brain was markedly decreased in calorically restricted LFD mice. In conclusion, LFD resulted in reduced activation of microglia, which might be an underlying mechanism for the protective role of caloric restriction during aging-associated decline.

In vitro models and systems for evaluating the dynamics of drug delivery to the healthy and diseased brain

The blood-brain barrier (BBB) plays a crucial role in maintaining brain homeostasis and transport of drugs to the brain. The conventional animal and Transwell BBB models along with emerging microfluidic-based BBB-on-chip systems have provided fundamental functionalities of the BBB and facilitated the testing of drug delivery to the brain tissue. However, developing biomimetic and predictive BBB models capable of reasonably mimicking essential characteristics of the BBB functions is still a challenge. In addition, detailed analysis of the dynamics of drug delivery to the healthy or diseased brain requires not only biomimetic BBB tissue models but also new systems capable of monitoring the BBB microenvironment and dynamics of barrier function and delivery mechanisms. This review provides a comprehensive overview of recent advances in microengineering of BBB models with different functional complexity and mimicking capability of healthy and diseased states. It also discusses new technologies that can make the next generation of biomimetic human BBBs containing integrated biosensors for real-time monitoring the tissue microenvironment and barrier function and correlating it with the dynamics of drug delivery. Such integrated system addresses important brain drug delivery questions related to the treatment of brain diseases. We further discuss how the combination of in vitro BBB systems, computational models and nanotechnology supports for characterization of the dynamics of drug delivery to the brain.

An expert opinion on PANDAS/PANS: highlights and controversies

OBJECTIVES

'Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections' (PANDAS) identified a unique subgroup of patients with abrupt onset of obsessive compulsive disorder (OCD) symptoms clinically related to Streptococcus infection and accompanied by neuropsychological and motor symptoms. After almost 20 years, PANDAS has not been accepted as distinct disorder and new criteria for paediatric acute-onset neuropsychiatric syndrome (PANS) have been replaced it, highlighting the fact that several agents rather than only Streptococcus might be involved.

METHODS

Extensive review of the PANDAS/PANS literature was performed on PubMed.

RESULTS

Although antibiotics have been reported to be effective for acute and prophylactic phases in several uncontrolled studies and non-steroidal anti-inflammatory drugs (NSAID) are used during exacerbations, clinical multicenter trials are still missing. Selective serotonin reuptake inhibitors (SSRIs) and cognitive behavioural therapy (CBT) are still the first line of recommendation for acute onset OCD spectrum. Immunological therapies should be restricted to a few cases.

CONCLUSIONS

While PANDAS has found no confirmation as a distinct syndrome, and it is not presented in DSM-5, patients with acute onset OCD spectrum, neurocognitive and motor symptoms should be evaluated for inflammatory, infective, immunological and metabolic abnormalities with a comprehensive diagnostic algorithm.

Evidence for intraventricular secretion of angiotensinogen and angiotensin by the subfornical organ using transgenic mice

Direct intracerebroventricular injection of angiotensin II (ANG II) causes increases in blood pressure and salt and water intake, presumably mimicking an effect mediated by an endogenous mechanism. The subfornical organ (SFO) is a potential source of cerebrospinal fluid (CSF), ANG I, and ANG II, and thus we hypothesized that the SFO has a secretory function. Endogenous levels of angiotensinogen (AGT) and renin are very low in the brain. We therefore examined the immunohistochemical localization of angiotensin peptides and AGT in the SFO, and AGT in the CSF in two transgenic models that overexpress either human AGT (A⁺ mice), or both human AGT (hAGT) and human renin (SRA mice) in the brain. Measurements were made at baseline and following volumetric depletion of CSF. Ultrastructural analysis with immunoelectron microscopy revealed that superficially located ANG I/ANG II and AGT immunoreactive cells in the SFO were vacuolated and opened directly into the ventricle. Withdrawal of CSF produced an increase in AGT in the CSF that was accompanied by a large decline in AGT immunoreactivity within SFO cells. Our data provide support for the hypothesis that the SFO is a secretory organ that releases AGT and possibly ANG I/ANG II into the ventricle at least under conditions when genes that control the renin-angiotensin system are overexpressed in mice.

Subfornical organ neurons integrate cardiovascular and metabolic signals

The subfornical organ (SFO) is a critical circumventricular organ involved in the control of cardiovascular and metabolic homeostasis. Despite the plethora of circulating signals continuously sensed by the SFO, studies investigating how these signals are integrated are lacking. In this study, we use patch-clamp techniques to investigate how the traditionally classified "cardiovascular" hormone ANG II, "metabolic" hormone CCK and "metabolic" signal glucose interact and are integrated in the SFO. Sequential bath application of CCK (10 nM) and ANG (10 nM) onto dissociated SFO neurons revealed that 63% of responsive SFO neurons depolarized to both CCK and ANG; 25% depolarized to ANG only; and 12% hyperpolarized to CCK only. We next investigated the effects of glucose by incubating and recording neurons in either hypoglycemic, normoglycemic, or hyperglycemic conditions and comparing the proportions of responses to ANG (n = 55) or CCK (n = 83) application in each condition. A hyperglycemic environment was associated with a larger proportion of depolarizing responses to ANG (χ², P < 0.05), and a smaller proportion of depolarizing responses along with a larger proportion of hyperpolarizing responses to CCK (χ², P < 0.01). Our data demonstrate that SFO neurons excited by CCK are also excited by ANG and that glucose environment affects the responsiveness of neurons to both of these hormones, highlighting the ability of SFO neurons to integrate multiple metabolic and cardiovascular signals. These findings have important implications for this structure's role in the control of various autonomic functions during hyperglycemia.

Physiological roles for the subfornical organ: a dynamic transcriptome shaped by autonomic state

The subfornical organ (SFO) is a circumventricular organ recognized for its ability to sense and integrate hydromineral and hormonal circulating fluid balance signals, information which is transmitted to central autonomic nuclei to which SFO neurons project. While the role of SFO was once synonymous with physiological responses to osmotic, volumetric and cardiovascular challenge, recent data suggest that SFO neurons also sense and integrate information from circulating signals of metabolic status. Using microarrays, we have confirmed the expression of receptors already described in the SFO, and identified many novel transcripts expressed in this circumventricular organ including receptors for many of the critical circulating energy balance signals such as adiponectin, apelin, endocannabinoids, leptin, insulin and peptide YY. This transcriptome analysis also identified SFO transcripts, the expressions of which are significantly changed by either 72 h dehydration, or 48 h starvation, compared to fed and euhydrated controls. Expression and potential roles for many of these targets are yet to be confirmed and elucidated. Subsequent validation of data for adiponectin and leptin receptors confirmed that receptors for both are expressed in the SFO, that discrete populations of neurons in this tissue are functionally responsive to these adipokines, and that such responsiveness is regulated by physiological state. Thus, transcriptomic analysis offers great promise for understanding the integrative complexity of these physiological systems, especially with development of technologies allowing description of the entire transcriptome of single, carefully phenotyped, SFO neurons. These data will ultimately elucidate mechanisms through which these uniquely positioned neurons respond to and integrate complex circulating signals.

Leptin levels are reduced by intravenous ghrelin administration and correlated with cue-induced alcohol craving

Increasing evidence supports the role of appetite-regulating pathways, including ghrelin and leptin, in alcoholism. This study tested the hypothesis that intravenous exogenous ghrelin administration acutely decreases endogenous serum leptin levels, and that changes in leptin levels negatively correlate with alcohol craving. This was a double-blind, placebo-controlled human laboratory study. Non-treatment-seeking, alcohol-dependent, heavy drinkers (n=45) were randomized to receive intravenous ghrelin or placebo, followed by a cue-reactivity procedure, during which participants were exposed to neutral (juice) and alcohol trial cues. There was a main effect for intravenous ghrelin administration, compared with placebo, in reducing serum leptin levels (P<0.01). Post hoc analysis showed significant differences in serum leptin levels at the alcohol trial (P<0.05) that persisted at the end of the experiment (P<0.05). By contrast, there were no significant differences in serum leptin levels at the juice trial (P=not significant (NS)). The change of serum leptin level at the alcohol trial correlated with the increase in alcohol urge (P<0.05), whereas urge to drink juice was not correlated with the leptin change at the juice trial (P=NS). These findings provide preliminary evidence of ghrelin-leptin cross-talk in alcoholic individuals and suggest that their relationship may have a role in alcohol craving.

GABA and glycine receptors in the nucleus ambiguus mediate tachycardia elicited by chemical stimulation of the hypothalamic arcuate nucleus

We have previously reported that stimulation of the hypothalamic arcuate nucleus (ARCN) by microinjections of N-methyl-d-aspartic acid (NMDA) elicits tachycardia, which is partially mediated via inhibition of vagal inputs to the heart. The neuronal pools and neurotransmitters in them mediating tachycardia elicited from the ARCN have not been identified. We tested the hypothesis that the tachycardia elicited from the ARCN may be mediated by inhibitory neurotransmitters in the nucleus ambiguus (nAmb). Experiments were done in urethane-anesthetized, artificially ventilated, male Wistar rats. In separate groups of rats, unilateral and bilateral microinjections of muscimol (1 mM), gabazine (0.01 mM), and strychnine (0.5 mM) into the nAmb significantly attenuated tachycardia elicited by unilateral microinjections of NMDA (10 mM) into the ARCN. Histological examination of the brains showed that the microinjections sites were within the targeted nuclei. Retrograde anatomic tracing from the nAmb revealed direct bilateral projections from the ARCN and hypothalamic paraventricular nucleus to the nAmb. The results of the present study suggest that tachycardia elicited by stimulation of the ARCN by microinjections of NMDA is mediated via GABAA and glycine receptors located in the nAmb.

Rapid linkage of innate immunological signals to adaptive immunity by the brain-fat axis

Innate immunity signals induced by pathogen/damage-associated molecular patterns are essential for adaptive immune responses, but it is unclear if the brain plays a role in this process. Here we show that while tumor necrosis factor (TNF) quickly increased in the brain of mice following bacterial infection, intra-brain TNF delivery mimicked bacterial infection to rapidly increase peripheral lymphocytes, especially in the spleen and fat. Multiple mouse models revealed that hypothalamic responses to TNF were accountable for this increase of peripheral lymphocytes in response to bacterial infection. Finally, hypothalamic induction of lipolysis was found to mediate the brain's action in promoting this increase in peripheral adaptive immune response. Thus, the brain-fat axis is important for rapidly linking innate immunity to adaptive immunity.

[Role of tanycytes within the blood-hypothalamus interface]

Information exchanges between the brain and the periphery are key stages in the regulation of various physiological functions. The mediobasal hypothalamus, which ensures a large part of these functions, must be permanently informed about the physiological state of the body to guarantee the maintaining of homeostasis. For that purpose, it possesses a peculiar blood-brain interface due to the presence of specialized glial cells called tanycytes. This review describes the organization of the blood-hypothalamus interface and characterizes the peculiar place of tanycytes within it, as well as their striking capacity to remodel their own interface in order to ensure the regulation of various physiological functions.

In vivo effects of bumetanide at brain concentrations incompatible with NKCC1 inhibition on newborn DGC structure and spontaneous EEG seizures following hypoxia-induced neonatal seizures

Neonatal seizures caused by perinatal asphyxia and hypoxic-ischemic encephalopathy can be refractory to conventional anticonvulsants. This may be due to the depolarizing effects of gamma-aminobutyric acid (GABA) achieved by the activity of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). The aim of this study is to evaluate the long-term effects of bumetanide, a NKCC1 inhibitor, on hippocampal neurogenesis and seizure susceptibility in hypoxia-induced neonatal seizure model. Wistar rats were subjected to hypoxia-induced neonatal seizures at postnatal day 10 (P10). Following acute seizures, the rats were treated with intraperitoneal injection (i.p.) of bumetanide at a dose of 0.5mg/kg for 3 weeks. In later adulthood, hypoxia-induced seizures increased the number of newborn dentate gyrus cells (DGCs), promoted mossy fiber sprouting (MFS) and reduced the apical dendritic complexity of newborn DGCs 1 month after the insults. In addition, these seizures resulted in long-lasting consequences, such as spontaneous electroencephalography (EEG) seizures, though spatial learning impairments were not seen. Bumetanide treatments significantly enhanced cell proliferation and dendritic development of newborn DGCs after neonatal seizures, accompanied by the decreased seizure activity. However, systemic administration of bumetanide resulted in much lower brain concentrations, and was incompatible with NKCC1 inhibition in blood-brain barrier (BBB)-protected brain tissue. Our results suggested that bumetanide might have long-term effects in suppressing seizure activity, and altering the neurogenesis after neonatal seizures. These effects of bumetanide may be mediated by the targets outside the BBB-protected central nerve system (CNS) or CNS-located target(s) other than NKCC1.

Liraglutide as a potentially useful agent for regulating appetite in diabetic patients with hypothalamic hyperphagia and obesity

Hypothalamic hyperphagia and obesity are characterized by a lack of satiety and an abnormally high appetite that is difficult to control. We herein report the cases of two patients with hypothalamic hyperphagia and obesity with MRI-detectable hypothalamic lesions. These patients suffered from diabetes mellitus associated with an abnormal eating behavior and weight gain. Liraglutide was successfully used to treat their diabetes mellitus and suppress their abnormal appetites. Glucagon-like peptide-1 analogues, including liraglutide, are promising treatment options in patients with hypothalamic hyperphagia and obesity, as these agents enhance the hypothalamic input of the satiety signal, which is lacking in such patients.

Gut hormones and obesity: physiology and therapies

Over the past 30 years, it has been established that hormones produced by the gut, pancreas, and adipose tissue are key players in the control of body weight. These hormones act through a complex neuroendocrine system, including the hypothalamus, to regulate metabolism and energy homeostasis. In obesity, this homeostatic balance is disrupted, either through alterations in the levels of these hormones or through resistance to their actions. Alterations in gut hormone secretion following gastric bypass surgery are likely to underlie the dramatic and persistent loss of weight following this procedure, as well as the observed amelioration in type 2 diabetes mellitus. Medications based on the gut hormone GLP-1 are currently in clinical use to treat type 2 diabetes mellitus and have been shown to produce weight loss. Further therapies for obesity based on other gut hormones are currently in development.

Brain-gut-adipose-tissue communication pathways at a glance

One of the ‘side effects’ of our modern lifestyle is a range of metabolic diseases: the incidence of obesity, type 2 diabetes and associated cardiovascular diseases has grown to pandemic proportions. This increase, which shows no sign of reversing course, has occurred despite education and new treatment options, and is largely due to a lack of knowledge about the precise pathology and etiology of metabolic disorders. Accumulating evidence suggests that the communication pathways linking the brain, gut and adipose tissue might be promising intervention points for metabolic disorders. To maintain energy homeostasis, the brain must tightly monitor the peripheral energy state. This monitoring is also extremely important for the brain’s survival, because the brain does not store energy but depends solely on a continuous supply of nutrients from the general circulation. Two major groups of metabolic inputs inform the brain about the peripheral energy state: short-term signals produced by the gut system and long-term signals produced by adipose tissue. After central integration of these inputs, the brain generates neuronal and hormonal outputs to balance energy intake with expenditure.

Miscommunication between the gut, brain and adipose tissue, or the degradation of input signals once inside the brain, lead to the brain misunderstanding the peripheral energy state. Under certain circumstances, the brain responds to this miscommunication by increasing energy intake and production, eventually causing metabolic disorders. This poster article overviews current knowledge about communication pathways between the brain, gut and adipose tissue, and discusses potential research directions that might lead to a better understanding of the mechanisms underlying metabolic disorders.

Role of the hypothalamic arcuate nucleus in cardiovascular regulation

Recently the hypothalamic arcuate nucleus (Arc) has been implicated in cardiovascular regulation. Both pressor and depressor responses can be elicited by the chemical stimulation of the Arc. The direction of cardiovascular responses (increase or decrease) elicited from the Arc depends on the baseline blood pressure. The pressor responses are mediated via increase in sympathetic nerve activity and involve activation of the spinal ionotropic glutamate receptors. Arc-stimulation elicits tachycardic responses which are mediated via inhibition of vagal input and excitation of sympathetic input to the heart. The pathways within the brain mediating the pressor and tachycardic responses elicited from the Arc have not been delineated. The depressor responses to the Arc-stimulation are mediated via the hypothalamic paraventricular nucleus (PVN). Gamma aminobutyric acid type A receptors, neuropeptide Y1 receptors, and opiate receptors in the PVN mediate the depressor responses elicited from the Arc. Some circulating hormones (e.g., leptin and insulin) may reach the Arc via the leaky blood-brain barrier and elicit their cardiovascular effects. Although the Arc is involved in mediating the cardiovascular responses to intravenously injected angiotensin II and angiotensin-(1-12), these effects may not be due to leakage of these peptides across the blood-brain barrier in the Arc; instead, circulating angiotensins may act on neurons in the SFO and mediate cardiovascular actions via the projections of SFO neurons to the Arc. Cardiovascular responses elicited by acupuncture have been reported to be mediated by direct and indirect projections of the Arc to the RVLM.

Increased vascular permeability in the circumventricular organs of adult rat brain due to stimulation by extremely low frequency magnetic fields

It has been demonstrated that the exposure of biological systems to magnetic fields (MFs) can produce several beneficial effects: tissue recovery in chronic wounds, re-establishment of blood circulation after tissue ischemia or in necrotic tissues, improvement after epileptic episodes, angiogenesis, etc. In the current study, the effects of extremely low frequency (ELF) MF on the capillaries of some circumventricular organs (CVOs) are demonstrated; a vasodilator effect is reported as well as an increase in their permeability to non-liposoluble substances. For this study, 96 Wistar male rats (250 g body mass) were used and divided into three groups of 32 rats each: a control group (no treatment); a sham ELF-MF group; and an experimental group subjected to ELF-MF (120 Hz harmonic waves and 0.66 mT, root mean square) by the use of Helmholtz coils. All animals were administered colloidal carbon (CC) intravenously to study, through optical and transmission electron microscopy, the capillary permeability in CVOs and the blood-brain barrier (BBB) in brain areas. An increase in capillary permeability to CC was detected in the ELF-MF-exposed group as well as a significant increase in vascular area (capillary vasodilation); none of these effects were observed in individuals of the control and sham ELF-MF groups. It is important to investigate the mechanisms involved in the phenomena reported here in order to explain the effects of ELF-MF on brain vasculature.

Different vascular permeability between the sensory and secretory circumventricular organs of adult mouse brain

The blood-brain barrier (BBB) prevents free access of circulating molecules to the brain and maintains a specialized brain environment to protect the brain from blood-derived bioactive and toxic molecules; however, the circumventricular organs (CVOs) have fenestrated vasculature. The fenestrated vasculature in the sensory CVOs, including the organum vasculosum of lamina terminalis (OVLT), subfornical organ (SFO) and area postrema (AP), allows neurons and astrocytes to sense a variety of plasma molecules and convey their information into other brain regions and the vasculature in the secretory CVOs, including median eminence (ME) and neurohypophysis (NH), permits neuronal terminals to secrete many peptides into the blood stream. The present study showed that vascular permeability of low-molecular-mass tracers such as fluorescein isothiocyanate (FITC) and Evans Blue was higher in the secretory CVOs and kidney as compared with that in the sensory CVOs. On the other hand, vascular permeability of high-molecular-mass tracers such as FITC-labeled bovine serum albumin and Dextran 70,000 was lower in the CVOs as compared with that in the kidney. Prominent vascular permeability of low- and high-molecular-mass tracers was also observed in the arcuate nucleus. These data demonstrate that vascular permeability for low-molecular-mass molecules is higher in the secretory CVOs as compared with that in the sensory CVOs, possibly for large secretion of peptides to the blood stream. Moreover, vascular permeability for high-molecular-mass tracers in the CVOs is smaller than that of the kidney, indicating that the CVOs are not totally without a BBB.

Neuroendocrine control of metabolism

Metabolism is controlled through homeostatic system consisting of central centers, gut hormones, hormones from adipose tissue and the other hormonal axes. This cooperation is based on cross-talk between central and peripheral signals. Among them the hypothalamus plays a crucial role, with interconnected nuclei forming neuronal circuits. Other regions in the brain, such as the brain stem, the endocannabinoid system, the vagal afferents, are also involved in energy balance. The second component is peripheral source of signals--the gastrointestinal tract hormones. Additionally, adipokines from adipose tissue, thyrotropic, gonadotropic and somatotropic axes play a role in energy homeostasis. Knowledge about all components of this neuroendocrine circuit will be helpful in developing novel therapeutic approaches against the metabolic syndrome and its components.

High-fat-diet exposure induces IgG accumulation in hypothalamic microglia

The mediobasal hypothalamic arcuate nucleus (ARC), with its relatively ‘leaky’ blood-brain barrier that allows more circulating molecules to enter the brain, has emerged as a key sensor of blood-borne signals. In both the ARC and white adipose tissue (WAT), consumption of a high-fat diet (HFD) rapidly induces infiltration of microglia (ARC) or macrophages (WAT). Animals with HFD-induced obesity (DIO) and insulin resistance additionally accumulate B cells in WAT, increasing the local production of pathogenic antibodies. We therefore investigated whether DIO mice or genetically obese ob/ob mice have increased IgG in the ARC, analogous to the recent observations in WAT. Following 16 weeks of exposure to a HFD, wild-type (WT) mice had significantly increased IgG-immunoreactivity (ir) signaling that was specific to the ARC and was exclusively concentrated in microglia. By contrast, IgG-ir of age-matched obese ob/ob mice fed standard chow had ARC IgG levels comparable with those in chow-fed WT control mice. However, following 2 weeks of HFD exposure, ob/ob mice also had a significant increase of IgG-ir in the ARC. In summary, our findings reveal a novel pathophysiological phenomenon, specific for the hypothalamic ARC, that is induced by exposure to a HFD and can be enhanced, but not caused, by genetic obesity.

The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread

Bordering the ventricular cerebrospinal fluid (CSF) are epithelial cells of choroid plexus (CP), ependyma and circumventricular organs (CVOs) that contain homeostatic transporters for mediating secretion/reabsorption. The distributional pathway ("nexus") of CP-CSF-ependyma-brain furnishes peptides, hormones, and micronutrients to periventricular regions. In disease/toxicity, this nexus becomes a conduit for infectious and xenobiotic agents. The sleeping sickness trypanosome (a protozoan) disrupts CP and downstream CSF-brain. Piperamide is anti-trypanosomic but distorts CP epithelial ultrastructure by engendering hydropic vacuoles; this reflects phospholipidosis and altered lysosomal metabolism. CP swelling by vacuolation may occlude CSF flow. Toxic drug tools delineate injuries to choroidal compartments: cyclophosphamide (vasculature), methylcellulose (interstitium), and piperazine (epithelium). Structurally perturbed CP allows solutes to penetrate the ventricles. There, CSF-borne pathogens and xenobiotics may permeate the ependyma to harm neurogenic stem cell niches. Amoscanate, an anti-helmintic, potently injures rodent ependyma. Ependymal/brain regions near CP are vulnerable to CSF-borne toxicants; this proximity factor links regional barrier breakdown to nearby periventricular pathology. Diverse diseases (e.g., African sleeping sickness, multiple sclerosis) take early root in choroidal, circumventricular, or perivascular loci. Toxicokinetics informs on pathogen, anti-parasitic agent, and auto-antibody distribution along the CSF nexus. CVOs are susceptible to plasma-borne toxicants/pathogens. Countering the physico-chemical and pathogenic insults to the homeostasis-mediating ventricle-bordering cells sustains brain health and fluid balance.

The arcuate nucleus as a circumventricular organ in the mouse

The present study searched for morphological correlates of the permeability of the ventromedial arcuate nucleus of the mouse to blood-borne proteins. First, we determined that highly permeable microvessels are detected in the ventromedial arcuate nucleus using a rat monoclonal antibody to a mouse-specific endothelial phenotype (clone MECA32) recently recognized as a marker of endothelial fenestral diaphragms and previously shown to label circumventricular organs. Second, in the mild conditions of tissue fixation mandatory for use of MECA32, we observed that after a rapid vascular flush with saline, endogenous immunoglobulins are especially retained in circumventricular organs and ventromedial arcuate nucleus. The ventromedial arcuate nucleus thus shares features in common with classical circumventricular organs.

Circulating signals as critical regulators of autonomic state--central roles for the subfornical organ

To maintain homeostasis autonomic control centers in the hypothalamus and medulla must respond appropriately to both external and internal stimuli. Although protected behind the blood-brain barrier, neurons in these autonomic control centers are known to be influenced by changing levels of important signaling molecules in the systemic circulation (e.g., osmolarity, glucose concentrations, and regulatory peptides). The subfornical organ belongs to a group of specialized central nervous system structures, the circumventricular organs, which are characterized by the lack of the normal blood-brain barrier, such that circulating lipophobic substances may act on neurons within this region and via well-documented efferent neural projections to hypothalamic autonomic control centers, influence autonomic function. This review focuses on the role of the subfornical organ in sensing peripheral signals and transmitting this information to autonomic control centers in the hypothalamus.

Aquaporin-1 in blood vessels of rat circumventricular organs

Although the water channel protein aquaporin-1 (AQP1) is widely observed outside the rat brain in continuous, but not fenestrated, vascular endothelia, it has not previously been observed in any endothelia within the normal rat brain and only to a limited extent in the human brain. In this immunohistochemical study of rat brain, AQP1 has also been found in microvessel endothelia, probably of the fenestrated type, in all circumventricular organs (except the subcommissural organ and the vascular organ of the lamina terminalis): in the median eminence, pineal, subfornical organ, area postrema and choroid plexus. The majority of microvessels in the median eminence, pineal and choroid plexus, known to be exclusively fenestrated, are shown to be AQP1-immunoreactive. In the subfornical organ and area postrema in which many, but not all, microvessels are fenestrated, not all microvessels are AQP1-immunoreactive. In the AQP1-immunoreactive microvessels, the AQP1 probably facilitates water movement between blood and interstitium as one component of the normal fluxes that occur in these specialised sensory and secretory areas. AQP1-immunoreactive endothelia have also been seen in a small population of blood vessels in the cerebral parenchyma outside the circumventricular organs, similar to other observations in human brain. The proposed development of AQP1 modulators to treat various brain pathologies in which AQP1 plays a deleterious role will necessitate further work to determine the effect of such modulators on the normal function of the circumventricular organs.

The role of gut hormones and the hypothalamus in appetite regulation

The World Health Organisation has estimated that by 2015 approximately 2.3 billion adults will be overweight and more than 700 million obese. Obesity is associated with an increased risk of diabetes, cardiovascular events, stroke and cancer. The hypothalamus is a crucial region for integrating signals from central and peripheral pathways and plays a major role in appetite regulation. In addition, there are reciprocal connections with the brainstem and higher cortical centres. In the arcuate nucleus of the hypothalamus, there are two major neuronal populations which stimulate or inhibit food intake and influence energy homeostasis. Within the brainstem, the dorsal vagal complex plays a role in the interpretation and relaying of peripheral signals. Gut hormones act peripherally to modulate digestion and absorption of nutrients. However, they also act as neurotransmitters within the central nervous system to control food intake. Peptide YY, pancreatic polypeptide, glucagon-like peptide-1 and oxyntomodulin suppress appetite, whilst ghrelin increases appetite through afferent vagal fibres to the caudal brainstem or directly to the hypothalamus. A better understanding of the role of these gut hormones may offer the opportunity to develop successful treatments for obesity. Here we review the current understanding of the role of gut hormones and the hypothalamus on food intake and body weight control.