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The physiological underpinnings of the necessity of sleep remain uncertain. Recent evidence suggests that sleep increases the convection of cerebrospinal fluid (CSF) and promotes the export of interstitial solutes, thus providing a framework to explain why all vertebrate species require sleep. Cardiovascular, respiratory and vasomotor brain pulsations have each been shown to drive CSF flow along perivascular spaces, yet it is unknown how such pulsations may change during sleep in humans. To investigate these pulsation phenomena in relation to sleep, we simultaneously recorded fast fMRI, magnetic resonance encephalography (MREG), and electroencephalography (EEG) signals in a group of healthy volunteers. We quantified sleep-related changes in the signal frequency distributions by spectral entropy analysis and calculated the strength of the physiological (vasomotor, respiratory, and cardiac) brain pulsations by power sum analysis in 15 subjects (age 26.5 6 4.2 years, 6 females). Finally, we identified spatial similarities between EEG slow oscillation (0.2-2 Hz) power and MREG pulsations. Compared with wakefulness, nonrapid eye movement (NREM) sleep was characterized by reduced spectral entropy and increased brain pulsation intensity. These effects were most pronounced in posterior brain areas for very low-frequency (£ 0.1 Hz) vasomotor pulsations but were also evident brain-wide for respiratory pulsations, and to a lesser extent for cardiac brain pulsations. There was increased EEG slow oscillation power in brain regions spatially overlapping with those showing sleep-related MREG pulsation changes. We suggest that reduced spectral entropy and enhanced pulsation intensity are characteristic of NREM sleep. With our findings of increased power of slow oscillation, the present results support the proposition that sleep promotes fluid transport in human brain. [ABSTRACT FROM AUTHOR]

Throughout the body, lymphatic fluid movement supports critical functions including clearance of excess fluid and metabolic waste. The glymphatic system is the analog of the lymphatic system in the CNS. As such, the glymphatic system plays a key role in regulating directional interstitial fluid movement, waste clearance, and, potentially, brain immunity. The glymphatic system enables bulk movement of CSF from the subarachnoid space along periarterial spaces, where it mixes with interstitial fluid within the parenchyma before ultimately exiting from the parenchyma via perivenous spaces. This review focuses on important questions about the structure of this system, why the brain needs a fluid transport system, and unexplored aspects of brain fluid transport. We provide evidence that astrocytes and blood vessels determine the shape of the perivascular space, ultimately controlling the movement of perivascular fluid. Glymphatic fluid movement has the potential to alter local as well as global transport of signaling molecules and metabolites. We also highlight the evidence for cross talk among the glymphatic system, cardiovascular system, gastrointestinal tract, and lymphatic system. Much remains to be studied, but we propose that the glymphatic/lymphatic system acts as a cornerstone in signaling between the brain and body. [ABSTRACT FROM AUTHOR]

Chronic electroencephalography (EEG) is a widely used tool for monitoring cortical electrical activity in experimental animals. Although chronic implants allow for high-quality, long-term recordings in preclinical studies, the electrodes are foreign objects and might therefore be expected to induce a local inflammatory response. We here analyzed the effects of chronic cranial electrode implantation on glymphatic fluid transport and in provoking structural changes in the meninges and cerebral cortex of male and female mice. Immunohistochemical analysis of brain tissue and dura revealed reactive gliosis in the cortex underlying the electrodes and extensive meningeal lymphangiogenesis in the surrounding dura. Meningeal lymphangiogenesis was also evident in mice prepared with the commonly used chronic cranial window. Glymphatic influx of a CSF tracer was significantly enhanced at 30 d postsurgery in both awake and ketaminexylazine anesthetized mice with electrodes, supporting the concept that glymphatic influx and intracranial lymphatic drainage are interconnected. Altogether, the experimental results provide clear evidence that chronic implantation of EEG electrodes is associated with significant changes in the brain's fluid transport system. Future studies involving EEG recordings and chronic cranial windows must consider the physiological consequences of cranial implants, which include glial scarring, meningeal lymphangiogenesis, and increased glymphatic activity. [ABSTRACT FROM AUTHOR]

The glymphatic system is a brainwide CSF transport system that uses the perivascular space for fast inflow of CSF. Arterial pulsations are a major driver of glymphatic CSF inflow, and hypertension that causes vascular pathologies, such as arterial stiffening and perivascular alterations, may impede the inflow. We used dynamic contrast-enhanced MRI to assess the effect of hypertension on glymphatic transport kinetics in male young and adult spontaneously hypertensive (SHR) rats compared with age-matched normotensive Wistar-Kyoto rats (WKY). We anesthetized the rats with dexmedetomidine/isoflurane and infused paramagnetic contrast (Gd-DOTA) into the cisterna magna during dynamic contrast-enhanced MRI to quantify glymphatic transport kinetics. Structural MRI analysis showed that cerebroventricular volumes are larger and brain volumes significantly smaller in SHR compared with WKY rats, regardless of age. We observed ventricular reflux of Gd-DOTA in SHR rats only, indicating abnormal CSF flow dynamics secondary to innate hydrocephalus. One-tissue compartment analysis revealed impeded glymphatic transport of Gd-DOTA in SHR compared with WKY rats in both age groups, implying that glymphatic transport, including solute clearance from brain parenchyma, is impaired during evolving hypertension in young SHR, an effect that worsens in states of chronic hypertension. The study demonstrates the suppression of glymphatic clearance in SHR rats and thus offers new insight into the coexistence of hypertension and concomitant vascular pathologies in Alzheimer's disease. The study further highlights the importance of considering the distribution of tracers in the CSF compartment in the analysis of the glymphatic system. [ABSTRACT FROM AUTHOR]

Microinfarcts occur commonly in the aging brain as a consequence of diffuse embolic events and are associated with the development of vascular dementia and Alzheimer's disease. However, the manner in which disperse microscopic lesions reduce global cognitive function and increase the risk for Alzheimer's disease is unclear. The glymphatic system, which is a brain-wide perivascular network that supports the recirculation of CSF through the brain parenchyma, facilitates the clearance of interstitial solutes including amyloid β and tau. We investigated whether glymphatic pathway function is impaired in a murine model of multiple microinfarcts induced by intraarterial injection of cholesterol crystals. The analysis showed that multiple microinfarcts markedly impaired global influx of CSF along the glymphatic pathway. Although suppression of global glymphatic function was transient, resolving within 2 weeks of injury, CSF tracers also accumulated within tissue associated with microinfarcts. The effect of diffuse microinfarcts on global glymphatic pathway function was exacerbated in the mice aged 12 months compared with the 2- to 3-month-old mice. These findings indicate that glymphatic function is focally disrupted around microinfarcts and that the aging brain is more vulnerable to this disruption than the young brain. These observations suggest that microlesions may trap proteins and other interstitial solutes within the brain parenchyma, increasing the risk of amyloid plaque formation. [ABSTRACT FROM AUTHOR]

Microglia are involved in synaptic pruning both in development and in the mature CNS. In this study, we investigated whether microglia might further contribute to circuit plasticity by modulating neuronal recruitment from the neurogenic subventricular zone (SVZ) of the adult mouse striatum. We found that microglia residing in the SVZ and adjacent rostral migratory stream (RMS) comprise a morphologically and antigenically distinct phenotype of immune effectors. Whereas exhibiting characteristics of alternatively activated microglia, the SVZ/RMS microglia were clearly distinguished by their low expression of purinoceptors and lack of ATP-elicitable chemotaxis. Furthermore, the in vivo depletion of these microglia hampered the survival and migration of newly generated neuroblasts through the RMS to the olfactory bulb. SVZ and RMS microglia thus appear to comprise a functionally distinct class that is selectively adapted to the support and direction of neuronal integration into the olfactory circuitry. Therefore, this unique microglial subpopulation may serve as a novel target with which to modulate cellular addition from endogenous neural stem and progenitor cells of the adult brain. [ABSTRACT FROM AUTHOR]

The glymphatic pathway expedites clearance of waste, including soluble amyloid β (Aβ) from the brain. Transport through this pathway is controlled by the brain's arousal level because, during sleep or anesthesia, the brain's interstitial space volume expands (compared with wakefulness), resulting in faster waste removal. Humans, as well as animals, exhibit different body postures during sleep, which may also affect waste removal. Therefore, not only the level of consciousness, but also body posture, might affect CSF-interstitial fluid (ISF) exchange efficiency. We used dynamic-contrast-enhanced MRI and kinetic modeling to quantify CSF-ISF exchange rates in anesthetized rodents' brains in supine, prone, or lateral positions. To validate the MRI data and to assess specifically the influence of body posture on clearance of Aβ, we used fluorescence microscopy and radioactive tracers, respectively. The analysis showed that glymphatic transport was most efficient in the lateral position compared with the supine or prone positions. In the prone position, in which the rat's head was in the most upright position (mimicking posture during the awake state), transport was characterized by "retention" of the tracer, slower clearance, and more CSF efflux along larger caliber cervical vessels. The optical imaging and radiotracer studies confirmed that glymphatic transport and Aβ clearance were superior in the lateral and supine positions. We propose that the most popular sleep posture (lateral) has evolved to optimize waste removal during sleep and that posture must be considered in diagnostic imaging procedures developed in the future to assess CSF-ISF transport in humans. [ABSTRACT FROM AUTHOR]

The nonspecific and variable presentation of traumatic brain injury (TBI) has motivated an intense search for blood-based biomarkers that can objectively predict the severity of injury. However, it is not known how cytosolic proteins released from traumatized brain tissue reach the peripheral blood. Here we show in a murine TBI model that CSF movement through the recently characterized glymphatic pathway transports biomarkers to blood via the cervical lymphatics. Clinically relevant manipulation of glymphatic activity, including sleep deprivation and cisternotomy, suppressed or eliminated TBI-induced increases in serum S100, GFAP, and neuron specific enolase. We conclude that routine TBI patient management may limit the clinical utility of blood-based biomarkers because their brain-toblood transport depends on glymphatic activity. [ABSTRACT FROM AUTHOR]

Center for Translational Neuromedicine, University of Rochester Medical School, Rochester, New York 14642 Experimental advances in the study of neuroglia signaling have been greatly accelerated by the generation of transgenic mouse models. In particular, an elegant manipulation that interferes with astrocyte vesicular release of gliotransmitters via overexpression of a dominant-negative domain of vesicular SNARE (dnSNARE) has led to documented astrocytic involvement in processes that were traditionally considered strictly neuronal, including the sleep-wake cycle, LTP, cognition, cortical slow waves, depression, and pain. A key premise leading to these conclusions was that expression of the dnSNARE was specific to astrocytes. Inconsistent with this premise, we report here widespread expression of the dnSNARE transgene in cortical neurons. We further demonstrate that the activity of cortical neurons is reversibly suppressed in dnSNARE mice. These findings highlight the need for independent validation of astrocytic functions identified in dnSNARE mice and thus question critical evidence that astrocytes contribute to neurotransmission through SNAREdependent vesicular release of gliotransmitters. [ABSTRACT FROM AUTHOR]

Traumatic brain injury (TBI) is an established risk factor for the early development of dementia, including Alzheimer's disease, and the post-traumatic brain frequently exhibits neurofibrillary tangles comprised of aggregates of the protein tau. We have recently defined a brain-wide network of paravascular channels, termed the "glymphatic" pathway, along which CSF moves into and through the brain parenchyma, facilitating the clearance of interstitial solutes, including amyloid-β, from the brain. Here we demonstrate in mice that extracellular tau is cleared from the brain along these paravascular pathways. After TBI, glymphatic pathway function was reduced by ˜60%, with this impairment persisting for at least 1 month post injury. Genetic knock-out of the gene encoding the astroglial water channel aquaporin-4, which is importantly involved in paravascular interstitial solute clearance, exacerbated glymphatic pathway dys-function after TBI andpromoted the development of neurofibrillary pathology and neurodegeneration in the post-traumatic brain. These findings suggest that chronic impairment of glymphatic pathway function after TBI may be a key factor that renders the post-traumatic brain vulnerable to tau aggregation and the onset of neurodegeneration. [ABSTRACT FROM AUTHOR]

CSF from the subarachnoid space moves rapidly into the brain along paravascular routes surrounding penetrating cerebral arteries, exchanging with brain interstitial fluid (ISF) and facilitating the clearance of interstitial solutes, such as amyloidβ, in a pathway that we have termed the "glymphatic" system. Prior reports have suggested that paravascular bulk flow of CSF or ISF may be driven by arterial pulsation. However, cerebral arterial pulsation could not be directly assessed. In the present study, we use in vivo two-photon microscopy in mice to visualize vascular wall pulsatility in penetrating intracortical arteries. We observed that unilateral ligation of the internal carotid artery significantly reduced arterial pulsatility by ~50%, while systemic administration of the adrenergic agonist dobutamine increased pulsatility of penetrating arteries by ~60%. When paravascular CSF-ISF exchange was evaluated in real time using in vivo two-photon and ex vivo fluorescence imaging, we observed that internal carotid artery ligation slowed the rate of paravascular CSF-ISF exchange, while dobutamine increased the rate of paravascular CSF-ISF exchange. These findings demonstrate that cerebral arterial pulsatility is a key driver of paravascular CSF influx into and through the brain parenchyma, and suggest that changes in arterial pulsatility may contribute to accumulation and deposition of toxic solutes, including amyloid β, in the aging brain. [ABSTRACT FROM AUTHOR]

Astrocytes in hippocampal slices can dynamically regulate synaptic transmission in a process mediated by increases in intracellular Ca2+. However, it is debated whether astrocytic Ca2+signals result in release of glutamate. We here compared astrocytic Ca2+signaling triggered by agonist exposure versus photolysis side by side. Using transgenic mice in which astrocytes selectively express the MrgA1 receptor, we found that receptor-mediated astrocytic Ca2+ signaling consistently triggered neuronal hyperpolarization and decreased the frequency of miniature excitatory postsynaptic currents (EPSCs). In contrast, photolysis of caged Ca2+ (o-nitrophenyl-EGTA) in astrocytes led to neuronal depolarization and increased the frequency of mEPSCs through a metabotropic glutamate receptor-mediated pathway. Analysis of transgenic mice in which astrocytic vesicular release is suppressed (dominant-negative SNARE mice) and pharmacological manipulations suggested that glutamate is primarily released by opening of anion channels rather than exocytosis. Combined, these studies show that photolysis but not by agonists induced astrocytic Ca2+ signaling triggers glutamate release. [ABSTRACT FROM AUTHOR]

Microinfarcts are a common clinical feature of the aging brain, particularly in patients with cognitive decline or vascular or Alzheimer's dementia. However, the natural history of these lesions remains largely unexplored. Here we describe a mouse (C57BL/6J) model of multiple diffuse microinfarcts induced by unilateral internal carotid artery injection of cholesterol crystals (40 -70 /xm). Microinfarcts were spread throughout the deep cortex, subcortical tissue, and hippocampus and were comprised of a core positive for CD68 (a marker for reactive microglia and macrophages), surrounded by large regions of glial fibrillary acidic protein-positive reactive astrogliosis. Widespread reactive gliosis, including mislocalization of the astrocytic water channel aquaporin 4 persisted long after injury, recovering only after 1 month after stroke. Within the cortex, neuronal cell death progressed gradually over the first month, from ~35% at 3 d to 60% at 28 d after stroke. Delayed demyelination was also observed in lesions, beginning 28 d after stroke. These findings demonstrate that microinfarct development follows a distinct course compared to larger regional infarcts such as those induced by middle cerebral artery occlusion. The long-lasting gliosis, delayed neuronal loss, and demyelination suggest that the therapeutic window for microinfarcts may be much wider (perhaps days to weeks) than for larger strokes. [ABSTRACT FROM AUTHOR]

The article offers information on the causation and treatment of a neurodegenerative disease called Alexander disease. As mentioned, it is caused due to dysfunction of astrocytes by mutations in the glial fibrillary acidic protein (GFAP) gene. The symptoms include frontal leukodystrophy in young patients and hindbrain lesions with atrophy of the medulla oblongata and cervical spinal cord in late onset conditions. It treated by reducing GFAP toxicity with drug Ceftriaxone.

Spinal cord injury (SCI) is often complicated by secondary injury as a result of the innate inflammatory response to tissue trauma and swelling. Previous studies have shown that excessive ATP release from peritraumatic regions contributes to the inflammatory response to SCI by activation of low-affinity P2X7 receptors. Because connexin hemichannels constitute an important route for astrocytic ATP release, we here evaluated the impact on post-traumatic ATP release of deletion of connexins (Cx30/Cx43) in astrocytes. In vivo bioluminescence imaging showed a significant reduction in ATP release after weight-drop injury in mice with deletion of Cx43 compared with Cx43-expressing littermates, both on a Cx30 knockout background. Moreover, astrogliosis and microglia activation were reduced in peritraumatic areas of those mice lacking Cx43; motor recovery was also significantly improved, and the traumatic lesion was smaller. Combined, these observations are consistent with a contribution by astrocytic hemichannels to post-traumatic ATP release that aggravates secondary injury and restrains functional recovery after experimental spinal cord injury. Connexins may thereby constitute a new therapeutic target in spinal cord injury. [ABSTRACT FROM AUTHOR]

Defining the microanatomic differences between the human brain and that of other mammals is key to understanding its unique computational power. Although much effort has been devoted to comparative studies of neurons, astrocytes have received far less attention.Wereport here that protoplasmic astrocytes in human neocortex are 2.6-fold larger in diameter and extend 10-fold more GFAP (glial fibrillary acidic protein)-positive primary processes than their rodent counterparts. In cortical slices prepared from acutely resected surgical tissue, protoplasmic astrocytes propagate Ca2+ waves with a speed of 36 μm/s, approximately fourfold faster than rodent. Human astrocytes also transiently increase cystosolic Ca2+ in response to glutamatergic and purinergic receptor agonists. The human neocortex also harbors several anatomically defined subclasses of astrocytes not represented in rodents. These include a population of astrocytes that reside in layers 5- 6 and extend long fibers characterized by regularly spaced varicosities. Another specialized type of astrocyte, the interlaminar astrocyte, abundantly populates the superficial cortical layers and extends long processes without varicosities to cortical layers 3 and 4. Human fibrous astrocytes resemble their rodent counterpart but are larger in diameter. Thus, human cortical astrocytes are both larger, and structurally both more complex and more diverse, than those of rodents. On this basis, we posit that this astrocytic complexity has permitted the increased functional competence of the adult human brain. [ABSTRACT FROM AUTHOR]

Astrocytes are electrically nonexcitable cells that communicate by means of Ca2+ signaling. Long-distance intercellular Ca2+ waves are initiated by release of ATP and activation of purinergic receptors on nearby cells. Previous studies have implicated connexin 43 (Cx43) in ATP release, but definitive proof that ATP exits through Cx43 hemichannels does not exist. Here, through several alternative approaches, we show that ATP anions can permeate through Cx43 hemichannels. First, openings of Cx43 hemichannels were detected in both cell-attached and inside-out patch recordings in C6 cells expressing Cx43, but not in C6 cells expressing Cx43-eGFP (enhanced green fluorescent protein) or a C-terminus truncation mutant of Cx43. Second, Cx43 hemichannel openings were inhibited by three structurally different gap-junction channel blockers, but not by the P2X7 blocker Brilliant blue G. Third, bioluminescence imaging of ATP combined with single-channel recording in the inside-out patch configuration showed that ATP efflux coincided with channel openings and was absent when the Cx43 hemichannel was closed. Fourth, ion replacement experiments confirmed that Cx43 hemichannels are permeable to ATP. In summary, these observations provide the first direct evidence for efflux of ATP through Cx43 hemichannels. Furthermore, a putative Cx43 hemichannel with characteristics identical to the Cx43 hemichannel in C6 cells was identified in the membrane of hippocampal astrocytes in acutely prepared slices. [ABSTRACT FROM AUTHOR]

Gliosis is a pathological hallmark of posttraumatic epileptic foci, but little is known about these reactive astrocytes beyond their high glial fibrillary acidic protein (GFAP) expression. Using diolistic labeling, we show that cortical astrocytes lost their nonoverlapping domain organization in three mouse models of epilepsy: posttraumatic injury, genetic susceptibility, and systemic kainate exposure. Neighboring astrocytes in epileptic mice showed a 10-fold increase in overlap of processes. Concurrently, spine density was increased on dendrites of excitatory neurons. Suppression of seizures by the common antiepileptic, valproate, reduced the overlap of astrocytic processes. Astrocytic domain organization was also preserved in APP transgenic mice expressing a mutant variant of human amyloid precursor protein despite a marked upregulation of GFAP. Our data suggest that loss of astrocytic domains was not universally associated with gliosis, but restricted to seizure pathologies. Reorganization of astrocytes may, in concert with dendritic sprouting and new synapse formation, form the structural basis for recurrent excitation in the epileptic brain. [ABSTRACT FROM AUTHOR]

Preconditioning is an endogenous mechanism in which a nonlethal exposure increases cellular resistance to subsequent additional severe injury. Here we show that connexin 43 (Cx43) plays a key role in protection afforded by preconditioning. Cx43 null mice were insensitive to hypoxic preconditioning, whereas wild-type littermate mice exhibited a significant reduction in infarct volume after occlusion of the middle cerebral artery. In cultures, Cx43-deficient cells responded to preconditioning only after exogenous expression of Cx43, and protection was attenuated by small interference RNA or by channel blockers. Our observations indicate that preconditioning reduced degradation of Cx43, resulting in a marked increase in the number of plasma membrane Cx43 hemichannels. Consequently, efflux of ATP through hemichannels led to accumulation of its catabolic product adenosine, a potent neuroprotective agent. Thus, adaptive modulation of Cx43 can offset environmental stress by adenosine-mediated elevation of cellular resistance. [ABSTRACT FROM AUTHOR]

Protoplasmic astrocytes are critically important to energy metabolism in the CNS. Our current understanding of the metabolic interactions between neurons and glia is based on studies using cultured cells, from which mainly inferential conclusions have been drawn as to the relative roles of neurons and glia in brain metabolism. In this study, we used functional genomics to establish the relative compartmentalization of neuronal and astrocytic metabolic pathways in the adult brain. To this end, fluorescence-activated cell sorting was used to directly isolate neurons and protoplasmic astrocytes from the cortex of adult mice. Microarray analysis showed that astrocytes and neurons each express transcripts predicting individual self-sufficiency in both glycolysis and oxidative metabolism. Surprisingly, most enzymes in the tricarboxylic acid (TCA) cycle were expressed at higher relative levels in astrocytes than in neurons. Mass spectrometric analysis of the TCA cycle intermediates confirmed that freshly isolated adult astrocytes maintained an active TCA cycle, whereas immuno-electron microscopy revealed that fine astrocytic processes encompassing synapses contained a higher density of mitochondria than surrounding cells. These observations indicate that astrocytes exhibit robust oxidative metabolism in the intact adult brain and suggest a prominent contribution of astrocytic metabolism to functional brain imaging, including BOLD (blood-oxygen level-dependent) functional magnetic resonance imaging signals. [ABSTRACT FROM AUTHOR]

The efficiency of neural circuits is enhanced not only by increasing synaptic strength but also by increasing intrinsic excitability. In contrast to the detailed analysis of long-term potentiation (LTP), less attention has been given to activity-dependent changes in the intrinsic neuronal excitability. By stimulating hippocampal CA1 pyramidal neurons with synaptic inputs correlating with postsynaptic neuronal spikes, we elicited an LTP of intrinsic excitability (LTP-IE) concurring with synaptic LTP. LTP-IE was manifested as a decrease in the action potential threshold that was attributable to a hyperpolarized shift in the activation curve of voltage-gated sodium channels (VGSCs) rather than activity-dependent changes in synaptic inputs or A-type K+ channels. Cell-attached patch recording of VGSC activities indicated such an activity-dependent change in VGSCs. Induction of LTP-IE was blocked by the NMDA receptor antagonist APV, intracellular BAPTA, the CaM kinase inhibitors KN-62 and autocamtide-2-related inhibitory peptide, and the protein synthesis inhibitors emetine and anisomycin. The results suggest that induction of LTP-IE shares a similar signaling pathway with the late phase of synaptic LTP and requires activation of the NMDA glutamate receptor subtype, Ca2+ influx, activity of CaM kinase II, and function of the protein synthesis. This new form of hippocampal neuronal plasticity could be a cellular correlate of learning and memory besides synaptic LTP. [ABSTRACT FROM AUTHOR]

Advances in fluorescent calcium indicating dyes over the past decade have identified calcium signaling as the tool by which astrocytes communicate among themselves and with neighboring neurons. Studies of astrocyte-neuron interactions have shown that calcium signaling is a potent modulator of the strength of both excitatory and inhibitory synapses. The concept that astrocytes possess a mechanism for rapid cell communication has not been incorporated, however, into the supportive functions of astrocytes. Because many of the classical tasks of astrocytes are linked to the blood- brain barrier, we have here examined the expression of proteins required for calcium signaling in their vascular end-foot processes. The gap junction protein, Cx43, was expressed intensively around the vessels interconnecting astrocytic end-foot processes. These gap junctions permitted diffusion of Lucifer yellow, specifically along the path of glial end feet apposed to the vessel wall. The purinergic receptors, P2Y(2) and P2Y(4), were also strongly expressed at the gliovascular interface and colocalized with GFAP around larger vessels in cortex. Multiphoton imaging of freshly prepared brain slices loaded with Fluo-4/AM revealed that ATP mobilized cytosolic calcium in astrocytic end feet, whereas electrical stimulation triggered calcium waves propagating along the vessel wall. Brain endothelial cells and pericytes were physically separated from astrocytes by the basal lamina and responded only weakly to ATP. These observations identify astrocytic end-foot processes plastered at the vessel wall as a center for purinergic signaling. It is speculated that calcium signaling may play a role in astrocytic functions related to the blood-brain barrier, including blood flow regulation, metabolic trafficking, and water homeostasis. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the role of gap junctions in cell death. Composition of gap junctions; Assessment of the effect of nonfunctional connexin mutations on cell resistance; Examination of the role of intercellular coupling in injury resistance.

Germinal matrix (GM) is a richly vascularized collection of neuronal-glial precursor cells in the developing brain, which is selectively vulnerable to hemorrhage in premature infants. It has rapid angiogenesis associated with high levels of vascular endothelial growth factor (VEGF). Because pericytes provide structural stability to blood vessels, we asked whether pericytes were fewer in the GM than in the subjacent white matter and neocortex and, if so, whether angiogenic inhibition could increase the pericyte density in the GM. We found pericyte coverage and density less in the GM vasculature than in the cortex or white matter in human fetuses, premature infants, and premature rabbit pups. Notably, although VEGF suppression significantly enhanced pericyte coverage in the GM, it remained less than in other brain regions. Therefore, to further elucidate the basis of fewer pericytes in the GM vasculature, we examined expression of ligand-receptor systems responsible for pericyte recruitment. Transforming growth factor-β1 (TGF-β1) protein expression was lower, whereas sphingosine-1-phosphate1 (S1P1) and N-cadherin levels were higher in the GM than in the cortex or white matter. Low TGF-β1 may be involved in promoting endothelial proliferation, whereas elevated S1P1 with N-cadherin may assist vascular maturation. Hence, a paucity of pericytes in the GM vasculature may contribute to its propensity to hemorrhage, and a lower expression of TGF-β1 could be a basis of reduced pericyte density in its vasculature. [ABSTRACT FROM AUTHOR]