Activity-dependent glial swelling is impaired in aquaporin-4 knockout mice

Interferon-γ controls aquaporin 4-specific Th17 and B cells in neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a CNS autoimmune inflammatory disease mediated by T helper 17 (Th17) and antibody responses to the water channel protein, aquaporin 4 (AQP4), and associated with astrocytopathy, demyelination and axonal loss. Knowledge about disease pathogenesis is limited and the search for new therapies impeded by the absence of a reliable animal model. In our work, we determined that NMOSD is characterized by decreased IFN-γ receptor signalling and that IFN-γ depletion in AQP4201-220-immunized C57BL/6 mice results in severe clinical disease resembling human NMOSD. Pathologically, the disease causes autoimmune astrocytic and CNS injury secondary to cellular and humoral inflammation. Immunologically, the absence of IFN-γ allows for increased expression of IL-6 in B cells and activation of Th17 cells, and generation of a robust autoimmune inflammatory response. Consistent with NMOSD, the experimental disease is exacerbated by administration of IFN-β, whereas repletion of IFN-γ, as well as therapeutic targeting of IL-17A, IL-6R and B cells, ameliorates it. We also demonstrate that immune tolerization with AQP4201-220-coupled poly(lactic-co-glycolic acid) nanoparticles could both prevent and effectively treat the disease. Our findings enhance the understanding of NMOSD pathogenesis and provide a platform for the development of immune tolerance-based therapies, avoiding the limitations of the current immunosuppressive therapies.

Aquaporin-4 Deficiency is Associated with Cognitive Impairment and Alterations in astrocyte-neuron Lactate Shuttle

Cognitive impairment refers to notable declines in cognitive abilities including memory, language, and emotional stability leading to the inability to accomplish essential activities of daily living. Astrocytes play an important role in cognitive function, and homeostasis of the astrocyte-neuron lactate shuttle (ANLS) system is essential for maintaining cognitive functions. Aquaporin-4 (AQP-4) is a water channel expressed in astrocytes and has been shown to be associated with various brain disorders, but the direct relationship between learning, memory, and AQP-4 is unclear. We examined the relationship between AQP-4 and cognitive functions related to learning and memory. Mice with genetic deletion of AQP-4 showed significant behavioral and emotional changes including hyperactivity and instability, and impaired cognitive functions such as spatial learning and memory retention. 18 F-FDG PET imaging showed significant metabolic changes in the brains of AQP-4 knockout mice such as reductions in glucose absorption. Such metabolic changes in the brain seemed to be the direct results of changes in the expression of metabolite transporters, as the mRNA levels of multiple glucose and lactate transporters in astrocytes and neurons were significantly decreased in the cortex and hippocampus of AQP-4 knockout mice. Indeed, AQP-4 knockout mice showed significantly higher accumulation of both glucose and lactate in their brains compared with wild-type mice. Our results show that the deficiency of AQP-4 can cause problems in the metabolic function of astrocytes and lead to cognitive impairment, and that the deficiency of AQP4 in astrocyte endfeet can cause abnormalities in the ANLS system.

Intradermal AQP4 peptide immunization induces clinical features of neuromyelitis optica spectrum disorder in mice

We challenged to create a mouse model of neuromyelitis optica spectrum disorder (NMOSD) induced by AQP4 peptide immunization. Intradermal immunization with AQP4 p201-220 peptide induced paralysis in C57BL/6J mice, but not in AQP4 KO mice. AQP4 peptide-immunized mice showed pathological features similar to NMOSD. Administration of anti-IL-6 receptor antibody (MR16-1) inhibited the induction of clinical signs and prevented the loss of GFAP/AQP4 and deposition of complement factors in AQP4 peptide-immunized mice. This novel experimental model may contribute to further understanding the pathogenesis of NMOSD, elucidating the mechanism of action of therapeutic agents, and developing new therapeutic approaches.

The effect of aquaporin-4 mis-localization on Aβ deposition in mice

The reduced clearance of amyloid-β (Aβ) is thought to contribute to the development of the pathology associated with Alzheimer's disease (AD), which is characterized by the deposition of Aβ plaques. Previous studies have shown that Aβ is cleared via the glymphatic system, a brain-wide network of perivascular pathways that supports the exchange between cerebrospinal fluid and interstitial fluid within the brain. Such exchange is dependent upon the water channel aquaporin-4 (AQP4), localized at astrocytic endfeet. While prior studies have shown that both the loss and mislocalization of AQP4 slow Aβ clearance and promote Aβ plaque formation, the relative impact of the loss or mislocalization of AQP4 on Aβ deposition has never been directly compared. In this study, we evaluated how the deposition of Aβ plaques within the 5XFAD mouse line is impacted by either Aqp4 gene deletion or the loss of AQP4 localization in the α-syntrophin (Snta1) knockout mouse. We observed that both the absence (Aqp4 KO) and mislocalization (Snta1 KO) of AQP4 significantly increases the parenchymal Aβ plaque and microvascular Aβ deposition across the brain, when compared with 5XFAD littermate controls. Further, the mislocalization of AQP4 had a more pronounced impact on Aβ plaque deposition than did global Aqp4 gene deletion, perhaps pointing to a key role that mislocalization of perivascular AQP4 plays in AD pathogenesis.

Low Temperature Delays the Effects of Ischemia in Bergmann Glia and in Cerebellar Tissue Swelling

Cerebral ischemia results in oxygen and glucose deprivation that most commonly occurs after a reduction or interruption in the blood supply to the brain. The consequences of cerebral ischemia are complex and involve the loss of metabolic ATP, excessive K⁺ and glutamate accumulation in the extracellular space, electrolyte imbalance, and brain edema formation. So far, several treatments have been proposed to alleviate ischemic damage, yet few are effective. Here, we focused on the neuroprotective role of lowering the temperature in ischemia mimicked by an episode of oxygen and glucose deprivation (OGD) in mouse cerebellar slices. Our results suggest that lowering the temperature of the extracellular 'milieu' delays both the increases in [K⁺]_e and tissue swelling, two dreaded consequences of cerebellar ischemia. Moreover, radial glial cells (Bergmann glia) display morphological changes and membrane depolarizations that are markedly impeded by lowering the temperature. Overall, in this model of cerebellar ischemia, hypothermia reduces the deleterious homeostatic changes regulated by Bergmann glia.

Honey, I shrunk the extracellular space: Measurements and mechanisms of astrocyte swelling

Astrocyte volume fluctuation is a physiological phenomenon tied closely to the activation of neural circuits. Identification of underlying mechanisms has been challenging due in part to use of a wide range of experimental approaches that vary between research groups. Here, we first review the many methods that have been used to measure astrocyte volume changes directly or indirectly. While the field has recently shifted towards volume analysis using fluorescence microscopy to record cell volume changes directly, established metrics corresponding to extracellular space dynamics have also yielded valuable insights. We then turn to analysis of mechanisms of astrocyte swelling derived from many studies, with a focus on volume changes tied to increases in extracellular potassium concentration ([K+ ]o ). The diverse methods that have been utilized to generate the external [K+ ]o environment highlight multiple scenarios of astrocyte swelling mediated by different mechanisms. Classical potassium buffering theories are tempered by many recent studies that point to different swelling pathways optimized at particular [K+ ]o and that depend on local/transient versus more sustained increases in [K+ ]o .

Glia as a key factor in cell volume regulation processes of the central nervous system

Brain edema is a pathological condition with potentially fatal consequences, related to cerebral injuries such as ischemia, chronic renal failure, uremia, and diabetes, among others. Under these pathological states, the cell volume control processes are fully compromised, because brain cells are unable to regulate the movement of water, mainly regulated by osmotic gradients. The processes involved in cell volume regulation are homeostatic mechanisms that depend on the mobilization of osmolytes (ions, organic molecules, and polyols) in the necessary direction to counteract changes in osmolyte concentration in response to water movement. The expression and coordinated function of proteins related to the cell volume regulation process, such as water channels, ion channels, and other cotransport systems in the glial cells, and considering the glial cell proportion compared to neuronal cells, leads to consider the astroglial network the main regulatory unit for water homeostasis in the central nervous system (CNS). In the last decade, several studies highlighted the pivotal role of glia in the cell volume regulation process and water homeostasis in the brain, including the retina; any malfunction of this astroglial network generates a lack of the ability to regulate the osmotic changes and water movements and consequently exacerbates the pathological condition.

The evaluation of lymph node cell proliferation response by liposomes loaded with major histocompatibility complex class II binding aquaporin 4 antigen peptide

Autoimmune responses to aquaporin 4 (AQP4) cause neuromyelitis optica (NMO); thus, specific immunotolerance to this self-antigen could represent a new NMO treatment. We generated the liposome-encapsulated AQP4 peptide 201-220 (p201-220) to induce immunotolerance. Liposomes were generated using phosphatidylserine and the polyglycidol species PG8MG. The in vivo tissue distribution of the liposomes was tested using an ex vivo imaging system. To confirm the antigen presentation capacity of PG8MG liposomes, dendritic cells were treated with PG8MG liposome-encapsulated AQP4 p201-220 (AQP4-PG8MG liposomes). Immunotolerance induction by AQP4-PG8MG liposomes was evaluated using the ex vivo cell proliferation of lymph node cells isolated from AQP4 p201-220-immunized AQP4-deficient mice. Fluorescent dye-labeled PG8MG liposomes were distributed to the lymph nodes. AQP4 p201-220 was presented on dendritic cells. AQP4-PG8MG liposomes were tended to suppress immune responses to AQP4 p201-220. Thus, the encapsulation of AQP4 peptides in PG8MG liposomes represents a new strategy for suppressing autoimmune responses to AQP4.

Retinal Aquaporin-4 and Regulation of Water Inflow Into the Vitreous Body

Purpose

Details of the posterior eye water dynamics are unclear. Aquaporin-4 (AQP4), a water channel, plays an important role in water dynamics in the central nervous system and is also present in the ocular tissue. The purpose of this study was to reveal the role of AQP4 in the water dynamics of the posterior eye using in vivo JJ vicinal coupling proton exchange (JJVCPE) magnetic resonance imaging (MRI) of AQP4 knockout (KO) mice and their wild-type littermates (controls).

Methods

JJVCPE MRI of the eye was performed on five AQP4 KO mice and seven control mice. We assessed the normalized signal intensities of a region of interest (ROI) set in the vitreous body after H₂¹⁷O administration. The results of the two groups were compared using a two-tailed Mann-Whitney U test.

Results

A statistical analysis revealed that the normalized ROI signal intensities at the steady state were significantly lower (P = 0.010, <0.05) in the AQP4 KO mice (mean ± SD, 84.5% ± 2.7%) than the controls (mean ± SD, 88.8% ± 1.9%).

Conclusions

The present study using JJVCPE MRI of the eye demonstrated that retinal AQP4 has a potential role in the regulation of water inflow into the vitreous body. Absence of AQP4 in the KO mice probably induces lower water outflow from the vitreous body. Our results could help clarify the pathogenesis of various ocular diseases.

The Mechanism of Downregulated Interstitial Fluid Drainage Following Neuronal Excitation

The drainage of brain interstitial fluid (ISF) has been observed to slow down following neuronal excitation, although the mechanism underlying this phenomenon is yet to be elucidated. In searching for the changes in the brain extracellular space (ECS) induced by electrical pain stimuli in the rat thalamus, significantly decreased effective diffusion coefficient (DECS) and volume fraction (α) of the brain ECS were shown, accompanied by the slowdown of ISF drainage. The morphological basis for structural changes in the brain ECS was local spatial deformation of astrocyte foot processes following neuronal excitation. We further studied aquaporin-4 gene (APQ4) knockout rats in which the changes of the brain ECS structure were reversed and found that the slowed DECS and ISF drainage persisted, confirming that the down-regulation of ISF drainage following neuronal excitation was mainly attributable to the release of neurotransmitters rather than to structural changes of the brain ECS. Meanwhile, the dynamic changes in the DECS were synchronized with the release and elimination processes of neurotransmitters following neuronal excitation. In conclusion, the downregulation of ISF drainage following neuronal excitation was found to be caused by the restricted diffusion in the brain ECS, and DECS mapping may be used to track the neuronal activity in the deep brain.

The molecular mechanism of synaptic activity-induced astrocytic volume transient

KEY POINTS

Neuronal activity causes astrocytic volume change via K⁺ uptake through TREK-1 containing two-pore domain potassium channels. The volume transient is terminated by Cl^- efflux through the Ca²⁺ -activated anion channel BEST1. The source of the Ca²⁺ required to open BEST1 appears to be the stretch-activated TRPA1 channel. Intense neuronal activity is synaptically coupled with a physical change in astrocytes via volume transients.

ABSTRACT

The brain volume changes dynamically and transiently upon intense neuronal activity through a tight regulation of ion concentrations and water movement across the plasma membrane of astrocytes. We have recently demonstrated that an intense neuronal activity and subsequent astrocytic AQP4-dependent volume transient are critical for synaptic plasticity and memory. We have also pharmacologically demonstrated a functional coupling between synaptic activity and the astrocytic volume transient. However, the precise molecular mechanisms of how intense neuronal activity and the astrocytic volume transient are coupled remain unclear. Here we utilized an intrinsic optical signal imaging technique combined with fluorescence imaging using ion sensitive dyes and molecular probes and electrophysiology to investigate the detailed molecular mechanisms in genetically modified mice. We report that a brief synaptic activity induced by a train stimulation (20 Hz, 1 s) causes a prolonged astrocytic volume transient (80 s) via K⁺ uptake through TREK-1 containing two-pore domain potassium (K2P) channels, but not Kir4.1 or NKCC1. This volume change is terminated by Cl^- efflux through the Ca²⁺ -activated anion channel BEST1, but not the volume-regulated anion channel TTYH. The source of the Ca²⁺ required to open BEST1 appears to be the stretch-activated TRPA1 channel in astrocytes, but not IP₃ R2. In summary, our study identifies several important astrocytic ion channels (AQP4, TREK-1, BEST1, TRPA1) as the key molecules leading to the neuronal activity-dependent volume transient in astrocytes. Our findings reveal new molecular and cellular mechanisms for the synaptic coupling of intense neuronal activity with a physical change in astrocytes via volume transients.

Molecular mechanisms of K+ clearance and extracellular space shrinkage-Glia cells as the stars

Neuronal signaling in the central nervous system (CNS) associates with release of K⁺ into the extracellular space resulting in transient increases in [K⁺ ]_o . This elevated K⁺ is swiftly removed, in part, via uptake by neighboring glia cells. This process occurs in parallel to the [K⁺ ]_o elevation and glia cells thus act as K⁺ sinks during the neuronal activity, while releasing it at the termination of the pulse. The molecular transport mechanisms governing this glial K⁺ absorption remain a point of debate. Passive distribution of K⁺ via Kir4.1-mediated spatial buffering of K⁺ has become a favorite within the glial field, although evidence for a quantitatively significant contribution from this ion channel to K⁺ clearance from the extracellular space is sparse. The Na⁺ /K⁺ -ATPase, but not the Na⁺ /K⁺ /Cl^- cotransporter, NKCC1, shapes the activity-evoked K⁺ transient. The different isoform combinations of the Na⁺ /K⁺ -ATPase expressed in glia cells and neurons display different kinetic characteristics and are thereby distinctly geared toward their temporal and quantitative contribution to K⁺ clearance. The glia cell swelling occurring with the K⁺ transient was long assumed to be directly associated with K⁺ uptake and/or AQP4, although accumulating evidence suggests that they are not. Rather, activation of bicarbonate- and lactate transporters appear to lead to glial cell swelling via the activity-evoked alkaline transient, K⁺ -mediated glial depolarization, and metabolic demand. This review covers evidence, or lack thereof, accumulated over the last half century on the molecular mechanisms supporting activity-evoked K⁺ and extracellular space dynamics.

Skull diploë is rich in aquaporin-4

Aquaporin-4 (AQP4) is a water conducting membrane integral protein channel which is widely expressed in the astrocyte system of the brain. During the development of the AQP4 positron emission tomography (PET) imaging agent [¹¹C]TGN-020 (N-(1,3,4-thiadiazol-2-yl)pyridine-3-[¹¹C]-carboxamide), significant radioligand uptake was observed in the skull, where there was no known distribution of any aquaporin family proteins. Herein we confirmed via a newly developed method for bone-tissue immunohistology, a hitherto unrecognized distribution of AQP4, and not AQP1, in the skull. Other bony structures, by contrast, showed virtually no uptake of [¹¹C]TGN-020, and likewise, do not express either AQP4 or AQP1. Immunohistological analysis demonstrated that the AQP4 expression in the skull is restricted to the diploë. Consequently, we suspect AQP4 plays a pivotal role in the formation and maintenance of yellow marrow and the diploë. However, elucidating the exact nature of that role will require further studies.

Astrocyte-Selective Volume Increase in Elevated Extracellular Potassium Conditions Is Mediated by the Na+/K+ ATPase and Occurs Independently of Aquaporin 4

Astrocytes and neurons have been shown to swell across a variety of different conditions, including increases in extracellular potassium concentration (^[K+]o). The mechanisms involved in the coupling of K+ influx to water movement into cells leading to cell swelling are not well understood and remain controversial. Here, we set out to determine the effects of ^[K+]o on rapid volume responses of hippocampal CA1 pyramidal neurons and stratum radiatum astrocytes using real-time confocal volume imaging. First, we found that elevating [K+]o within a physiological range (to 6.5 mM and 10.5 mM from a baseline of 2.5 mM), and even up to pathological levels (26 mM), produced dose-dependent increases in astrocyte volume, with absolutely no effect on neuronal volume. In the absence of compensating for addition of KCl by removal of an equal amount of NaCl, neurons actually shrank in ^[K+]o, while astrocytes continued to exhibit rapid volume increases. Astrocyte swelling in ^[K+]o was not dependent on neuronal firing, aquaporin 4, the inwardly rectifying potassium channel Kir 4.1, the sodium bicarbonate cotransporter NBCe1, , or the electroneutral cotransporter, sodium-potassium-chloride cotransporter type 1 (NKCC1), but was significantly attenuated in 1 mM barium chloride (BaCl2) and by the Na+/K+ ATPase inhibitor ouabain. Effects of 1 mM BaCl2 and ouabain applied together were not additive and, together with reports that BaCl2 can inhibit the NKA at high concentrations, suggests a prominent role for the astrocyte NKA in rapid astrocyte volume increases occurring in ^[K+]o. These findings carry important implications for understanding mechanisms of cellular edema, regulation of the brain extracellular space, and brain tissue excitability.

Pharmacological Dissection of Intrinsic Optical Signal Reveals a Functional Coupling between Synaptic Activity and Astrocytic Volume Transient

The neuronal activity-dependent change in the manner in which light is absorbed or scattered in brain tissue is called the intrinsic optical signal (IOS), and provides label-free, minimally invasive, and high spatial (~100 µm) resolution imaging for visualizing neuronal activity patterns. IOS imaging in isolated brain slices measured at an infrared wavelength (>700 nm) has recently been attributed to the changes in light scattering and transmittance due to aquaporin-4 (AQP4)-dependent astrocytic swelling. The complexity of functional interactions between neurons and astrocytes, however, has prevented the elucidation of the series of molecular mechanisms leading to the generation of IOS. Here, we pharmacologically dissected the IOS in the acutely prepared brain slices of the stratum radiatum of the hippocampus, induced by 1 s/20 Hz electrical stimulation of Schaffer-collateral pathway with simultaneous measurement of the activity of the neuronal population by field potential recordings. We found that 55% of IOSs peak upon stimulation and originate from postsynaptic AMPA and NMDA receptors. The remaining originated from presynaptic action potentials and vesicle fusion. Mechanistically, the elevated extracellular glutamate and K⁺ during synaptic transmission were taken up by astrocytes via a glutamate transporter and quinine-sensitive K2P channel, followed by an influx of water via AQP-4. We also found that the decay of IOS is mediated by the DCPIB- and NPPB-sensitive anion channels in astrocytes. Altogether, our results demonstrate that the functional coupling between synaptic activity and astrocytic transient volume change during excitatory synaptic transmission is the major source of IOS.

The Effect of Aquaporin-4 Knockout on Interstitial Fluid Flow and the Structure of the Extracellular Space in the Deep Brain

It has been reported that aquaporin-4 (AQP4) deficiency impairs transportation between the cerebrospinal fluid and interstitial fluid (ISF) as well as the clearance of interstitial solutes in the superficial brain. However, the effect of AQP4 on ISF flow in the deep brain remains unclear. This study compared the brain ISF flow in the caudate nucleus and thalamus of normal rats (NO) and AQP4 knockout rats (KO) using tracer-based magnetic resonance imaging. The rate of brain ISF flow slowed to different degrees in the two regions of KO rats’ brains. Compared with NO rats, the half-life of ISF in the thalamus of KO rats was significantly prolonged, with a corresponding decrease in the clearance coefficient. The tortuosity of the brain extracellular space (ECS) was unchanged in the thalamus of KO rats. In the caudate nucleus of KO rats, the volume fraction of the ECS and the diffusion coefficient were increased, with significantly decreased tortuosity; no significant changes in brain ISF flow were demonstrated. Combined with a change in the expression of glial fibrillary acidic protein and AQP4 in two brain regions, we found that the effect of AQP4 knockout on ISF flow and ECS structure in these two regions differed. This difference may be related to the distribution of astrocytes and the extent of AQP4 decline. This study provides evidence for the involvement of AQP4 in ISF transportation in the deep brain and provides a basis for the establishment of a pharmacokinetic model of the brain’s interstitial pathway.

Fluid Dynamics Inside the Brain Barrier: Current Concept of Interstitial Flow, Glymphatic Flow, and Cerebrospinal Fluid Circulation in the Brain

The discovery of the water specific channel, aquaporin, and abundant expression of its isoform, aquaporin-4 (AQP-4), on astrocyte endfeet brought about significant advancements in the understanding of brain fluid dynamics. The brain is protected by barriers preventing free access of systemic fluid. The same barrier system, however, also isolates brain interstitial fluid from the hydro-dynamic effect of the systemic circulation. The systolic force of the heart, an essential factor for proper systemic interstitial fluid circulation, cannot be propagated to the interstitial fluid compartment of the brain. Without a proper alternative mechanism, brain interstitial fluid would stay stagnant. Water influx into the peri-capillary Virchow-Robin space (VRS) through the astrocyte AQP-4 system compensates for this hydrodynamic shortage essential for interstitial flow, introducing the condition virtually identical to systemic circulation, which by virtue of its fenestrated capillaries creates appropriate interstitial fluid motion. Interstitial flow in peri-arterial VRS constitutes an essential part of the clearance system for β-amyloid, whereas interstitial flow in peri-venous VRS creates bulk interstitial fluid flow, which, together with the choroid plexus, creates the necessary ventricular cerebrospinal fluid (CSF) volume for proper CSF circulation.

Aquaporin-4 Functionality and Virchow-Robin Space Water Dynamics: Physiological Model for Neurovascular Coupling and Glymphatic Flow

The unique properties of brain capillary endothelium, critical in maintaining the blood-brain barrier (BBB) and restricting water permeability across the BBB, have important consequences on fluid hydrodynamics inside the BBB hereto inadequately recognized. Recent studies indicate that the mechanisms underlying brain water dynamics are distinct from systemic tissue water dynamics. Hydrostatic pressure created by the systolic force of the heart, essential for interstitial circulation and lymphatic flow in systemic circulation, is effectively impeded from propagating into the interstitial fluid inside the BBB by the tightly sealed endothelium of brain capillaries. Instead, fluid dynamics inside the BBB is realized by aquaporin-4 (AQP-4), the water channel that connects astrocyte cytoplasm and extracellular (interstitial) fluid. Brain interstitial fluid dynamics, and therefore AQP-4, are now recognized as essential for two unique functions, namely, neurovascular coupling and glymphatic flow, the brain equivalent of systemic lymphatics.

Turning down the volume: Astrocyte volume change in the generation and termination of epileptic seizures

Approximately 1% of the global population suffers from epilepsy, a class of disorders characterized by recurrent and unpredictable seizures. Of these cases roughly one-third are refractory to current antiepileptic drugs, which typically target neuronal excitability directly. The events leading to seizure generation and epileptogenesis remain largely unknown, hindering development of new treatments. Some recent experimental models of epilepsy have provided compelling evidence that glial cells, especially astrocytes, could be central to seizure development. One of the proposed mechanisms for astrocyte involvement in seizures is astrocyte swelling, which may promote pathological neuronal firing and synchrony through reduction of the extracellular space and elevated glutamate concentrations. In this review, we discuss the common conditions under which astrocytes swell, the resultant effects on neural excitability, and how seizure development may ultimately be influenced by these effects.

The Molecular Mechanisms of Neural Flow Coupling: A New Concept

The phenomenon known as neural flow coupling (NFC) occurs at the capillary level where there are no known pressure controlling structures. Recent developments in advanced magnetic resonance imaging technologies have made possible in vivo direct investigations of water physiology that have shed new insight on the water dynamics of the cortical pericapillary space and their complex functionality in relation to NFC. Neural activities initiate a chain of events that ultimately affect NFC. First, neural activities generate extracellular acidification. Extracellular acidosis in turn produces inhibition of aquaporin-4 (AQP-4) located at the end feet of pericapillary astrocytes, the water channel which regulates water influx into the pericapillary space and, hence, interstitial flow. Reduction of pericapillary water pressure results in a negative balance between pericapillary and intraluminal capillary pressure, allowing for capillary caliber expansion. Proton permeability through the tight junctions of the blood brain barrier is significantly high owing to the Grotthuss proton "tunneling" mechanism and, therefore, carbonic anhydrase (CA) type IV (CA-IV) anchored to the luminal surface of brain capillaries functions as scavenger of extracellular protons. CA-IV inhibition by acetazolamide or carbon dioxide results in the accumulation of extracellular protons, causing AQP-4 inhibition and a secondary increase in rCBF.

The speed of swelling kinetics modulates cell volume regulation and calcium signaling in astrocytes: A different point of view on the role of aquaporins

Regulatory volume decrease (RVD) is a process by which cells restore their original volume in response to swelling. In this study, we have focused on the role played by two different Aquaporins (AQPs), Aquaporin-4 (AQP4), and Aquaporin-1 (AQP1), in triggering RVD and in mediating calcium signaling in astrocytes under hypotonic stimulus. Using biophysical techniques to measure water flux through the plasma membrane of wild-type (WT) and AQP4 knockout (KO) astrocytes and of an astrocyte cell line (DI TNC1) transfected with AQP4 or AQP1, we here show that AQP-mediated fast swelling kinetics play a key role in triggering and accelerating RVD. Using calcium imaging, we show that AQP-mediated fast swelling kinetics also significantly increases the amplitude of calcium transients inhibited by Gadolinium and Ruthenium Red, two inhibitors of the transient receptor potential vanilloid 4 (TRPV4) channels, and prevented by removing extracellular calcium. Finally, inhibition of TRPV4 or removal of extracellular calcium does not affect RVD. All together our study provides evidence that (1) AQP influenced swelling kinetics is the main trigger for RVD and in mediating calcium signaling after hypotonic stimulus together with TRPV4, and (2) calcium influx from the extracellular space and/or TRPV4 are not essential for RVD to occur in astrocytes.

Reduced CSF Water Influx in Alzheimer's Disease Supporting the β-Amyloid Clearance Hypothesis

OBJECTIVE

To investigate whether water influx into cerebrospinal fluid (CSF) space is reduced in Alzheimer's patients as previously shown in the transgenic mouse model for Alzheimer's disease.

METHODS

Ten normal young volunteers (young control, 21-30 years old), ten normal senior volunteers (senior control, 60-78 years old, MMSE ≥ 29), and ten Alzheimer's disease (AD) patients (study group, 59-84 years old, MMSE: 13-19) participated in this study. All AD patients were diagnosed by neurologists specializing in dementia based on DSM-IV criteria. CSF dynamics were analyzed using positron emission tomography (PET) following an intravenous injection of 1,000 MBq [15O]H2O synthesized on-line.

RESULTS

Water influx into CSF space in AD patients, expressed as influx ratio, (0.755 ± 0.089) was significantly reduced compared to young controls (1.357 ± 0.185; p < 0.001) and also compared to normal senior controls (0.981 ± 0.253, p < 0.05). Influx ratio in normal senior controls was significantly reduced compared to young controls (p < 0.01).

CONCLUSION

Water influx into the CSF is significantly reduced in AD patients. β-amyloid clearance has been shown to be dependent on interstitial flow and CSF production. The current study indicates that reduction in water influx into the CSF may disturb the clearance rate of β-amyloid, and therefore be linked to the pathogenesis of AD.

TRIAL REGISTRATION

UMIN Clinical Trials Registry UMIN000011939.

Virchow-Robin space and aquaporin-4: new insights on an old friend

Recent studies have strongly indicated that the classic circulation model of cerebrospinal fluid (CSF) is no longer valid. The production of CSF is not only dependent on the choroid plexus but also on water flux in the peri-capillary (Virchow Robin) space. Historically, CSF flow through the Virchow Robin space is known as interstitial flow, the physiological significance of which is now fully understood. This article briefly reviews the modern concept of CSF physiology and the Virchow-Robin space, in particular its functionalities critical for central nervous system neural activities. Water influx into the Virchow Robin space and, hence, interstitial flow is regulated by aquaporin-4 (AQP-4) localized in the endfeet of astrocytes, connecting the intracellular cytosolic fluid space of astrocytes and the Virchow Robin space. Interstitial flow has a functionality equivalent to systemic lymphatics, on which clearance of β-amyloid is strongly dependent. Autoregulation of brain blood flow serves to maintain a constant inner capillary fluid pressure, allowing fluid pressure of the Virchow Robin space to regulate regional cerebral blood flow (rCBF) based on AQP-4 gating. Excess heat produced by neural activities is effectively removed from the area of activation by increased rCBF by closing AQP-4 channels. This neural flow coupling (NFC) is likely mediated by heat generated proton channels.

Water influx into cerebrospinal fluid is primarily controlled by aquaporin-4, not by aquaporin-1: 17O JJVCPE MRI study in knockout mice

Recent studies on cerebrospinal fluid (CSF) homeostasis emphasize the importance of water flux through the pericapillary (Virchow-Robin) space for both CSF production and reabsorption (Oreskovic and Klarica hypothesis), and challenge the classic CSF circulation theory, which proposes that CSF is primarily produced by the choroid plexus and reabsorbed by the arachnoid villi. Active suppression of aquaporin-1 (AQP-1) expression within brain capillaries and preservation of AQP-1 within the choroid plexus together with pericapillary water regulation by AQP-4 provide a unique opportunity for testing this recent hypothesis. We investigated water flux into three representative regions of the brain, namely, the cortex, basal ganglia, and third ventricle using a newly developed water molecular MRI technique based on JJ vicinal coupling between O and adjacent protons and water molecule proton exchanges (JJVCPE imaging) in AQP-1 and AQP-4 knockout mice in vivo. The results clearly indicate that water influx into the CSF is regulated by AQP-4, and not by AQP-1, strongly supporting the Oreskovic and Klarica hypothesis.

7T T₂*-weighted magnetic resonance imaging reveals cortical phase differences between early- and late-onset Alzheimer's disease

The aim of this study is to explore regional iron-related differences in the cerebral cortex, indicative of Alzheimer's disease pathology, between early- and late-onset Alzheimer's disease (EOAD, LOAD, respectively) patients using 7T magnetic resonance phase images. High-resolution T2(∗)-weighted scans were acquired in 12 EOAD patients and 17 LOAD patients with mild to moderate disease and 27 healthy elderly control subjects. Lobar peak-to-peak phase shifts and regional mean phase contrasts were computed. An increased peak-to-peak phase shift was found for all lobar regions in EOAD patients compared with LOAD patients (p < 0.05). Regional mean phase contrast in EOAD patients was higher than in LOAD patients in the superior medial and middle frontal gyrus, anterior and middle cingulate gyrus, postcentral gyrus, superior and inferior parietal gyrus, and precuneus (p ≤ 0.042). These data suggest that EOAD patients have an increased iron accumulation, possibly related to an increased amyloid deposition, in specific cortical regions as compared with LOAD patients.

Mechanisms of astrocyte-mediated cerebral edema

Cerebral edema formation stems from disruption of blood brain barrier (BBB) integrity and occurs after injury to the CNS. Due to the restrictive skull, relatively small increases in brain volume can translate into impaired tissue perfusion and brain herniation. In excess, cerebral edema can be gravely harmful. Astrocytes are key participants in cerebral edema by virtue of their relationship with the cerebral vasculature, their unique compliment of solute and water transport proteins, and their general role in brain volume homeostasis. Following the discovery of aquaporins, passive conduits of water flow, aquaporin 4 (AQP4) was identified as the predominant astrocyte water channel. Normally, AQP4 is highly enriched at perivascular endfeet, the outermost layer of the BBB, whereas after injury, AQP4 expression disseminates to the entire astrocytic plasmalemma, a phenomenon termed dysregulation. Arguably, the most important role of AQP4 is to rapidly neutralize osmotic gradients generated by ionic transporters. In pathological conditions, AQP4 is believed to be intimately involved in the formation and clearance of cerebral edema. In this review, we discuss aquaporin function and localization in the BBB during health and injury, and we examine post-injury ionic events that modulate AQP4-dependent edema formation.

Physical principles for scalable neural recording

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical, magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. Based on this analysis, all existing approaches require orders of magnitude improvement in key parameters. Electrical recording is limited by the low multiplexing capacity of electrodes and their lack of intrinsic spatial resolution, optical methods are constrained by the scattering of visible light in brain tissue, magnetic resonance is hindered by the diffusion and relaxation timescales of water protons, and the implementation of molecular recording is complicated by the stochastic kinetics of enzymes. Understanding the physical limits of brain activity mapping may provide insight into opportunities for novel solutions. For example, unconventional methods for delivering electrodes may enable unprecedented numbers of recording sites, embedded optical devices could allow optical detectors to be placed within a few scattering lengths of the measured neurons, and new classes of molecularly engineered sensors might obviate cumbersome hardware architectures. We also study the physics of powering and communicating with microscale devices embedded in brain tissue and find that, while radio-frequency electromagnetic data transmission suffers from a severe power-bandwidth tradeoff, communication via infrared light or ultrasound may allow high data rates due to the possibility of spatial multiplexing. The use of embedded local recording and wireless data transmission would only be viable, however, given major improvements to the power efficiency of microelectronic devices.

Inhibition of aquaporin-4 significantly increases regional cerebral blood flow

The effects of the aquaporin-4 (AQP-4) inhibitor TGN-020 on regional cerebral blood flow (rCBF) was examined in wild-type (WT) and AQP-4 knockout (KO) mice in vivo. Although baseline absolute rCBF of WT and KO mice were equivalent (158.9 ± 17.7 and 155.5 ± 10.4 ml/100 g/min, respectively), TGN-020 produced a significant increase in rCBF compared with saline-treated WT mice (control), reaching a plateau 20 min after administration (118.45 ± 8.13%, P<0.01). TGN-020 showed no effect on KO mice, supporting the concept that the observed increase in rCBF in WT mice was AQP-4 dependent. Administration of acetazolamide (positive control) produced an even greater increase in rCBF in WT compared with TGN-020 and a similar response in KO mice as well, reaching a sustained plateau 5 min after administration (138.50 ± 9.75 and 138.52 ± 9.76%, respectively, P<0.01 compared with baseline or saline-treated control mice). The study demonstrated that AQP-4 plays a role in regulation of rCBF.

Aquaporin-4 water channels and synaptic plasticity in the hippocampus

Aquaporin-4 (AQP4) is the major water channel expressed in the central nervous system (CNS) and is primarily expressed in glial cells. Many studies have shown that AQP4 regulates the response of the CNS to insults or injury, but far less is known about the potential for AQP4 to influence synaptic plasticity or behavior. Recent studies have examined long-term potentiation (LTP), long-term depression (LTD), and behavior in AQP4 knockout (KO) and wild-type mice to gain more insight into its potential role. The results showed a selective effect of AQP4 deletion on LTP of the Schaffer collateral pathway in hippocampus using an LTP induction protocol that simulates pyramidal cell firing during theta oscillations (theta-burst stimulation; TBS). However, LTP produced by a different induction protocol was unaffected. There was also a defect in LTD after low frequency stimulation (LFS) in AQP4 KO mice. Interestingly, some slices from AQP4 KO mice exhibited LTD after TBS instead of LTP, or LTP following LFS instead of LTD. These data suggest that AQP4 and astrocytes influence the polarity of long-term synaptic plasticity (potentiation or depression). These potentially powerful roles expand the influence of AQP4 and astrocytes beyond the original suggestions related to regulation of extracellular potassium and water balance. Remarkably, AQP4 KO mice did not show deficits in basal transmission, suggesting specificity for long-term synaptic plasticity. The mechanism appears to be related to neurotrophins and specifically brain-derived neurotrophic factor (BDNF) because pharmacological blockade of neurotrophin trk receptors or scavenging ligands such as BDNF restored plasticity. The in vitro studies predicted effects in vivo of AQP4 deletion because AQP4 KO mice performed worse using a task that requires memory for the location of objects (object placement). However, performance on other hippocampal-dependent tasks was spared. The results suggest an unanticipated and selective role of AQP4 in synaptic plasticity and spatial memory, and underscore the growing appreciation of the role of glial cells in functions typically attributed to neurons. Implications for epilepsy are discussed because of the previous evidence that AQP4 influences seizures, and the role of synaptic plasticity in epileptogenesis.

Significance of horizontal propagation of synchronized activities in human epileptic neocortex investigated by optical imaging and immunohistological study

To characterize the physiological condition of human epileptic neocortex, we employed flavoprotein fluorescence imaging (FFI), an optical imaging method which detects intrinsic signals accompanying neural activation, and immunohistologically studied human cortical specimens. The experimented materials were cortical tissues surrounding various intracerebral lesions obtained from 5 patients with epilepsy (epileptic patients: EPs) and 5 without epilepsy (non-epileptic patients: NEPs). These tissues were immersed in oxygenated artificial cerebrospinal fluid immediately after removal in the operating room. Signal changes of FFI in the cortical layers subjected to electrical stimulation were observed under bicuculline methiodide perfusion. Immunohistological staining for parvalbumin (PV), calbindin, and calretinin were performed on the same specimens to evaluate expressions of calcium-binding protein positive cells. The FFI study showed the characteristic cortical propagation pattern of elicited activities horizontally along the cortical layers in EPs but not in NEPs. The propagated area with more than 0.5% signal changes was significantly larger in EPs than in NEPs (p=0.008). Only the expression of PV positive neurons was significantly lower in EPs than in NEPs (p=0.006). The propagated area on FFI and the decrease in PV positive neurons correlated significantly (R=-0.78, p=0.04). The present study visualized the unique horizontal propagation of signal changes on FFI and demonstrated a correlation of this propagation with immunohistological decreases in PV positive neurons in human epileptic cortex. Further investigations may elucidate the mechanism of hyper-excitability and hyper-synchronization in epileptic cortical tissue itself.

Aquaporin-4 positron emission tomography imaging of the human brain: first report

BACKGROUND AND PURPOSE

Aquaporin 4 (AQP-4) is the most abundant aquaporin isoform in the brain. Alterations in its expression and distribution have been correlated with the progression of several clinical disorders; however, the specific roles of AQP-4 in those disorders are not well understood. Visualizing AQP-4 in vivo is expected to provide fresh insights into its roles in disease pathology, as well as aiding the clinical assessment of those disorders.

METHODS

We developed a 11C-labeled analogue of the AQP-4 ligand TGN-020 (2-nicotinamido-1,3,4-thiadiazole) suitable for in vivo positron emission tomography (PET) imaging.

RESULTS

In the present study, we report the first PET images of AQP-4 in the human brain. The results unequivocally demonstrated a specific distribution pattern for AQP-4 within the brain, namely, the subpial and perivascular endfeet of astrocytes. The choroid plexus, where both AQP-4 and AQP-1 are expressed, also showed substantial uptake of the ligand.

CONCLUSIONS

Based on these initial results, we believe [11C]TGN-020 PET will be valuable in determining the role of AQP-4 in disease progression, and for the clinical assessment of water homeostasis under various settings.

Aquaporin-4 regulates extracellular space volume dynamics during high-frequency synaptic stimulation: a gene deletion study in mouse hippocampus

Little is known about the physiological roles of aquaporin-4 (AQP4) in the central nervous system. AQP4 water channels are concentrated in endfeet membranes of astrocytes but also localize to the fine astrocytic processes that abut central synapses. Based on its pattern of expression, we predicted that AQP4 could be involved in controlling water fluxes and changes in extracellular space (ECS) volume that are associated with activation of excitatory pathways. Here, we show that deletion of Aqp4 accentuated the shrinkage of the ECS that occurred in the mouse hippocampal CA1 region during activation of Schaffer collateral/commissural fibers. This effect was found in the stratum radiatum (where perisynaptic astrocytic processes abound) but not in the pyramidal cell layer (where astrocytic processes constitute but a minor volume fraction). For both genotypes the ECS shrinkage was most pronounced in the pyramidal cell layer. Our data attribute a physiological role to AQP4 and indicate that this water channel regulates extracellular volume dynamics in the mammalian brain.

Creation of trophectoderm, the first epithelium, in mouse preimplantation development

Trophectoderm (TE) is the first cell type that emerges during development and plays pivotal roles in the viviparous mode of reproduction in placental mammals. TE adopts typical epithelium morphology to surround a fluid-filled cavity, whose expansion is critical for hatching and efficient interaction with the uterine endometrium for implantation. TE also differentiates into trophoblast cells to construct the placenta. This chapter is an overview of the cellular and molecular mechanisms that control the critical aspects of TE formation, namely, the formation of the blastocyst cavity, the expression of key transcription factors, and the roles of cell polarity in the specification of the TE lineage. Current gaps in our knowledge and challenging issues are also discussed that should be addressed in future investigations in order to further advance our understanding of the mechanisms of TE formation.

Aquaporin-4 promotes memory consolidation in Morris water maze

Aquaporin-4 (AQP4), the most abundant aquaporin in the brain, is polarized at the glial end-feet facing peri-synaptic areas. AQP4 has been hypothesized to modulate water and potassium fluxes associated with neuronal activity in pathophysiological states. However, the role of AQP4 in astroglial signaling under physiological conditions is unclear. Herein, AQP4 knockout mice and wild-type littermates were tested in the Morris water maze (MWM), which allows for investigating the role of AQP4 in long-term learning and memory. Compared with wild-type mice, AQP4 knockout mice appeared actually to find the platform more easy, but to forget more quickly, in the MWM, indicating that AQP4 knockout mice exhibited impaired memory consolidation in MWM. Moreover, the deficits of memory consolidations were associated with defects in theta-burst stimulation-induced long-term potentiation both in vivo and in vitro. Furthermore, AQP4 knockout mice were accompanied by a decrease in the incorporation of adult-generated granule cells into spatial memory networks. Taken together, our findings indicate that AQP4 plays a modulatory role in memory consolidation. Targeting glial AQP4 may be a new therapeutic strategy for neurodegenerative disorders and related memory impairment.

Development of a Novel Ligand, [C]TGN-020, for Aquaporin 4 Positron Emission Tomography Imaging

Aquaporin 4 (AQP4), the most abundant isozyme of the water specific membrane transporter aquaporin family, has now been implicated to play a significant role in the pathogenesis of various disease processes of the nervous system from epilepsy to Alzheimer’s disease. Considering its clinical relevance, it is highly desirable to develop a noninvasive method for the quantitative analysis of AQP distribution in humans under clinical settings. Currently, the method of choice for such diagnostic examinations continues to be positron emission tomography (PET). Here, we report the successful development of a PET ligand for AQP4 imaging based on TGN-020, a potent AQP4 inhibitor developed previously in our laboratory. Utilizing [¹¹C]-TGN-020, PET images were successfully generated in wild type and AQP4 null mice, providing a basis for future evaluation regarding its suitability for clinical studies.

Expansion of corticomedullary junction high-susceptibility region (CMJ-HSR) with aging: a clue in the pathogenesis of Alzheimer's disease?

BACKGROUND

Susceptibility-weighted imaging (SWI) microscopy on a 7.0T system demonstrated the corticomedullary junction (CMJ) to be a high-susceptibility region (HSR) in young normal subjects, suggesting that functional alteration of cortical microcirculation could be assessed with this imaging method.

METHODS

Focused microscopic studies were performed on the parietal association cortex in 74 normal volunteers (ages 20-79 years; 35 female, 39 male) using a SWI algorithm on a system constructed based on General Electric Signa LX (Waukesha, WI, USA), equipped with a 900-mm clear bore superconducting magnet operating at 7.0T.

RESULTS

There was a clear-cut reduction in the thickness of the normal-appearing cortex (cortex, R2 = .5290, P < .001) and expansion of CMJ-HSR (R(2) = .6919, P < .001). The sum of cortex thickness and CMJ-HSR thickness was essentially constant, suggesting that the observed expansion of CMR-HSR with aging likely occurred within the cortical mantle.

CONCLUSION

CMJ-HSR expands significantly as a function of aging. Since CMJ-HSR represents a functionally distinct area with relatively slow venous flow, the observed expansion is believed to reflect alteration in cerebral microcirculation with increased age, providing another clue for pathogenesis of Alzheimer's disease.

Impairment of select forms of spatial memory and neurotrophin-dependent synaptic plasticity by deletion of glial aquaporin-4

Aquaporin-4 (AQP4) is the major water channel in the CNS and is primarily expressed in astrocytes. Little is known about the potential for AQP4 to influence synaptic plasticity, although many studies have shown that it regulates the response of the CNS to injury. Therefore, we evaluated long-term potentiation (LTP) and long-term depression (LTD) in AQP4 knock-out (KO) and wild-type mice. KO mice exhibited a selective defect in LTP and LTD without a change in basal transmission or short-term plasticity. Interestingly, the impairment in LTP in KO mice was specific for the type of LTP that depends on the neurotrophin BDNF, which is induced by stimulation at theta rhythm [theta-burst stimulation (TBS)-LTP], but there was no impairment in a form of LTP that is BDNF independent, induced by high-frequency stimulation. LTD was also impaired in KO mice, which was rescued by a scavenger of BDNF or blockade of Trk receptors. TrkB receptors, which mediate effects of BDNF on TBS-LTP, were not altered in KO mice, but p75NTR, the receptor that binds all neurotrophins and has been implicated in some types of LTD, was decreased. The KO mice also exhibited a cognitive defect, which suggests a new role for AQP4 and astrocytes in normal cognitive function. This defect was evident using a test for location-specific object memory but not Morris water maze or contextual fear conditioning. The results suggest that AQP4 channels in astrocytes play an unanticipated role in neurotrophin-dependent plasticity and influence behavior.

Aquaporins in sensory and pain transmission

Recent data suggest a possible involvement of Aquaporins (AQPs) in pain transmission. AQPs are small membrane channel proteins involved in osmoregulation and, to date, AQP1, AQP2, AQP3, AQP4, AQP5, AQP8 and AQP9 have been found in the nervous system. Nevertheless only AQP1, AQP2 and AQP4 seem to be involved in nociception.

In this review, direct and indirect evidences of the role of AQPs in pain processing will be reported.

Spatiotemporal dynamics of epileptiform propagations: imaging of human brain slices

Seizure activities often originate from a localized region of the cerebral cortex and spread across large areas of the brain. The properties of these spreading abnormal discharges may account for clinical phenotypes in epilepsy patients, although the manner of their propagation and the underlying mechanisms are not well understood. In the present study we performed flavoprotein fluorescence imaging of cortical brain slices surgically resected from patients with partial epilepsy caused by various symptomatic lesions. Elicited neural activities in the epileptogenic tissue spread horizontally over the cortex momentarily, but those in control tissue taken from patients with brain tumors who had no history of epilepsy demonstrated only localized responses. Characteristically, the epileptiform propagation comprised early and late phases. When the stimulus intensity was changed gradually, the early phase showed an all-or-none behavior, whereas the late phase showed a gradual increase in the response. Moreover, the two phases were propagated through different cortical layers, suggesting that they are derived from distinct neural circuits. Morphological investigation revealed the presence of hypertrophic neurons and loss of dendritic spines, which might participate in the aberrant activities observed by flavoprotein fluorescence imaging. These findings indicate that synchronized activities of the early phase may play a key role in spreading abnormal discharges in human cortical epilepsies.

Neuroscience of water molecules: a salute to professor Linus Carl Pauling

More than 35 years ago double Nobel laureate Linus Carl Pauling published a powerful model of the molecular mechanism of general anesthesia, generally referred to as the hydrate-microcrystal (aqueous-phase) theory. This hypothesis, based on the molecular behavior of water molecules, did not receive serious attention during Pauling's life time, when scientific tools for examining complex systems such as the brain were still in their infancy. The situation has since drastically changed, and, now, in the twenty first century, many scientific tools are available for examining different types of complex systems. The discovery of aquaporin-4, a subtype of water channel abundantly expressed in glial systems, further highlighted the concept that the dynamics of water molecules in the cerebral cortex play an important role in important physiological brain functions including consciousness and information processing.