Experimental and genetic evidence for the impact of CD5 and CD6 expression and variation in inflammatory bowel disease.

Crohn's disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBD) resulting from the interaction of multiple environmental, genetic and immunological factors. CD5 and CD6 are paralogs encoding lymphocyte co-receptors involved in fine-tuning intracellular signals delivered upon antigen-specific recognition, microbial pattern recognition and cell adhesion. While CD5 and CD6 expression and variation is known to influence some immune-mediated inflammatory disorders, their role in IBD remains unclear. To this end, Cd5- and Cd6-deficient mice were subjected to dextran sulfate sodium (DSS)-induced colitis, the most widely used experimental animal model of IBD. The two mouse lines showed opposite results regarding body weight loss and disease activity index (DAI) changes following DSS-induced colitis, thus supporting Cd5 and Cd6 expression involvement in the pathophysiology of this experimental IBD model. Furthermore, DNA samples from IBD patients of the ENEIDA registry were used to test association of CD5 (rs2241002 and rs2229177) and CD6 (rs17824933, rs11230563, and rs12360861) single nucleotide polymorphisms with susceptibility and clinical parameters of CD (n=1352) and UC (n=1013). Generalized linear regression analyses showed association of CD5 variation with CD ileal location (rs2241002CC) and requirement of biological therapies (rs2241002C-rs2229177T haplotype), and with poor UC prognosis (rs2241002T-rs2229177T haplotype). Regarding CD6, association was observed with CD ileal location (rs17824933G) and poor prognosis (rs12360861G), and with left-sided or extensive UC, and absence of ankylosing spondylitis in IBD (rs17824933G). The present experimental and genetic evidence support a role for CD5 and CD6 expression and variation in IBD's clinical manifestations and therapeutic requirements, providing insight into its pathophysiology and broadening the relevance of both immunomodulatory receptors in immune-mediated disorders.

Lysophosphatidic Acid-Mediated GPR35 Signaling in CX3CR1+ Macrophages Regulates Intestinal Homeostasis.

Single-nucleotide polymorphisms in the gene encoding G protein-coupled receptor 35 (GPR35) are associated with increased risk of inflammatory bowel disease. However, the mechanisms by which GPR35 modulates intestinal immune homeostasis remain undefined. Here, integrating zebrafish and mouse experimental models, we demonstrate that intestinal Gpr35 expression is microbiota dependent and enhanced upon inflammation. Moreover, murine GPR35+ colonic macrophages are characterized by enhanced production of pro-inflammatory cytokines. We identify lysophosphatidic acid (LPA) as a potential endogenous ligand produced during intestinal inflammation, acting through GPR35 to induce tumor necrosis factor (Tnf) expression in macrophages. Mice lacking Gpr35 in CX3CR1+ macrophages aggravate colitis when exposed to dextran sodium sulfate, which is associated with decreased transcript levels of the corticosterone-generating gene Cyp11b1 and macrophage-derived Tnf. Administration of TNF in these mice restores Cyp11b1 expression and intestinal corticosterone production and ameliorates DSS-induced colitis. Our findings indicate that LPA signals through GPR35 in CX3CR1+ macrophages to maintain TNF-mediated intestinal homeostasis.

The Copper/Zinc Ratio Correlates With Markers of Disease Activity in Patients With Inflammatory Bowel Disease.

BACKGROUND: Zinc (Zn) and copper (Cu) are trace elements that serve as cofactors in catalytic processes with impact on immune responses. In patients with inflammatory bowel disease (IBD), decreased levels of serum Zn and Cu have been observed. Here, we investigated the effect of inflammation on serum concentrations of these trace elements in patients with IBD. METHODS: In this cross-sectional study, 98 patients with Crohn disease (CD) and 56 with ulcerative colitis (UC) were prospectively enrolled. Disease activity parameters, such as C-reactive protein (CRP) and fecal calprotectin (FC) were compared to serum Zn, Cu, and Cu/Zn ratio. RESULTS: Zinc insufficiency was observed in 11.2% of patients with CD and 14.3% with UC, Cu insufficiency in 20.4% with CD and 7.1% with UC. Anemia, hypoalbuminemia, increased FC, and elevated CRP were more frequently present in Zn-insufficient patients with IBD. In contrast, lower serum CRP values and a trend to lower FC were observed in Cu-insufficient patients. In multiple linear regression models adjusted for age, gender, and serum albumin, CRP positively correlated with serum Cu (P < 0.001) and the Cu/Zn ratio in both CD and UC (P < 0.001) but not with serum Zn concentrations. FC levels correlated only with the Cu/Zn ratio in patients with UC (P < 0.038). CONCLUSION: Systemic inflammation inversely affected the serum Zn and Cu concentrations and, consequently, resulted in an increased Cu/Zn ratio.

Loss of the branched-chain amino acid transporter CD98hc alters the development of colonic macrophages in mice.

Comprehensive development is critical for gut macrophages being essential for the intestinal immune system. However, the underlying mechanisms of macrophage development in the colon remain elusive. To investigate the function of branched-chain amino acids in the development of gut macrophages, an inducible knock-out mouse model for the branched-chain amino acid transporter CD98hc in CX3CR1+ macrophages was generated. The relatively selective deletion of CD98hc in macrophage populations leads to attenuated severity of chemically-induced colitis that we assessed by clinical, endoscopic, and histological scoring. Single-cell RNA sequencing of colonic lamina propria macrophages revealed that conditional deletion of CD98hc alters the "monocyte waterfall"-development to MHC II+ macrophages. The change in the macrophage development after deletion of CD98hc is associated with increased apoptotic gene expression. Our results show that CD98hc deletion changes the development of colonic macrophages.

Extracellular ATP and Purinergic P2Y2 Receptor Signaling Promote Liver Tumorigenesis in Mice by Exacerbating DNA Damage.

Release of ATP to the extracellular compartment and subsequent activation of purinergic receptors is a conserved mechanism mediating inflammatory responses and cell fate decisions in various organs including the liver. Previous findings suggest that extracellular ATP may promote liver tumorigenesis, however, the underlying mechanisms are poorly understood. Therefore, our aim was to dissect the functions of extracellular ATP and P2Y2 receptors (P2Y2R) during hepatocarcinogenesis. Liver tumors were induced in wild-type and P2y2r -/- knockout mice by intraperitoneal diethylnitrosamine (DEN) injection. Tumorigenesis was analyzed after 8 to 10 months and molecular analyses were performed at different stages of tumorigenesis in vivo, as well as in primary mouse hepatocytes in vitro. Liver tumor incidence and tumor numbers were strongly reduced in P2y2r -/- mice, whereas tumor size and morphology were comparable to wild-type controls, suggesting that P2Y2R contributes to tumor initiation. Mechanistically, hepatocyte proliferation in DEN-treated P2y2r -/- mice was reduced, which correlated with reduced c-JUN and CCND1 but increased p21 expression. Moreover, DNA damage as determined by hepatocellular expression of γH2A.X and of genes related to genotoxic stress, as well as STAT3 phosphorylation, was reduced in the absence of P2y2r. Administration of genotoxic agents to primary hepatocytes in vitro confirmed that DNA damage was indeed exacerbated by extracellular ATP, subsequent P2Y2R activation, and downstream intracellular calcium-dependent signal transduction. In conclusion, our data reveal that extracellular ATP and subsequent P2Y2R function stimulate DNA damage responses and hepatocyte proliferation, thereby promoting hepatocarcinogenesis. Targeting this pathway may be an attractive approach for chemoprevention of hepatocellular carcinoma. SIGNIFICANCE: Extracellular ATP and subsequent P2Y2 receptor function stimulate DNA damage responses and hepatocyte proliferation, thereby promoting hepatocarcinogenesis in mice. Targeting this pathway may be an attractive approach for chemoprevention of hepatocellular carcinoma. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/4/699/F1.large.jpg.

NLRP6 Deficiency in CD4 T Cells Decreases T Cell Survival Associated with Increased Cell Death.

The nucleotide-binding oligomerization domain (NOD)-like receptors belong to the family of pattern recognition receptors (PRRs). NOD-like receptors play a role in regulation of innate immune response by recognition of both pathogen-associated molecular patterns that are engulfed during phagocytic process and danger-associated molecular patterns that are mainly byproducts of cell stress mediated response. NOD-like family pyrin domain containing 6 (NLRP6) is one of the 14 pyrin domain-containing receptors. NLRP6 is highly expressed by epithelial and goblet cells to regulate epithelial renewal and mucus production in mice and humans, but its function in T cells is rather unknown. Increased caspase-1 activation and cell death were observed in mouse Nlrp6-deficient T cells following adoptive transfer into Rag2-deficient mice, indicating that Nlrp6 deficiency in CD4+ T cells led to decreased survival.

Metabolite-Sensing G Protein-Coupled Receptors Connect the Diet-Microbiota-Metabolites Axis to Inflammatory Bowel Disease.

Increasing evidence has indicated that diet and metabolites, including bacteria- and host-derived metabolites, orchestrate host pathophysiology by regulating metabolism, immune system and inflammation. Indeed, autoimmune diseases such as inflammatory bowel disease (IBD) are associated with the modulation of host response to diets. One crucial mechanism by which the microbiota affects the host is signaling through G protein-coupled receptors (GPCRs) termed metabolite-sensing GPCRs. In the gut, both immune and nonimmune cells express GPCRs and their activation generally provide anti-inflammatory signals through regulation of both the immune system functions and the epithelial integrity. Members of GPCR family serve as a link between microbiota, immune system and intestinal epithelium by which all these components crucially participate to maintain the gut homeostasis. Conversely, impaired GPCR signaling is associated with IBD and other diseases, including hepatic steatosis, diabetes, cardiovascular disease, and asthma. In this review, we first outline the signaling, function, expression and the physiological role of several groups of metabolite-sensing GPCRs. We then discuss recent findings on their role in the regulation of the inflammation, their existing endogenous and synthetic ligands and innovative approaches to therapeutically target inflammatory bowel disease.

Altered purinergic signaling in the tumor associated immunologic microenvironment in metastasized non-small-cell lung cancer.

OBJECTIVES: Purines are well-known as intracellular sources for energy but they also act as extracellular signaling molecules. In the recent years, there has been a growing interest in the therapeutic potential of purinergic signaling for cancer treatment. This is the first study to analyze lung purine levels and purinergic receptors in non-small-cell lung cancer (NSCLC) patients. MATERIALS AND METHODS: In this prospective clinical trial we enrolled 26 patients with NSCLC and 21 patients with chronic obstructive pulmonary disease (COPD) without signs of malignancy. The purine concentrations were analyzed in bronchoalveolar lavage fluid (BALF) using fluorescent/luminescent assays. Expression of purinergic receptors and ectonucleotidases were analyzed using real time quantitative polymerase chain reaction (RT-qPCR). RESULTS: Patients with NSCLC have significantly lower ATP and ADP concentrations in BALF than patients with COPD (p=0.006 and p=0.009). Expression of the ectonucleotidase CD39 is significantly higher in BAL cells from cancer patients compared to COPD (p=0.001) as well as in metastasized tumors compared to non-metastasized tumors (p=0.009). Receptor-analysis revealed a higher expression of P2X4 (p=0.03), P2X7 (p=0.001) and P2Y1 (p=0.003) in BAL cells of tumors with distant metastasis. CONCLUSION: Our data suggests a role for CD39 in lung cancer tumor microenvironment, influencing tumor invasiveness and metastasization. Potentially the increased degradation of ATP and ADP leads to a subversion of their anti-neoplastic effects. Furthermore P2Y1, P2X4 and P2X7 receptors are upregulated in BAL cells in metastatic disease. Our findings might facilitate the identification of new therapeutic targets for cancer immunotherapy.

MicroRNA-155 modulates P2R signaling and Th2 priming of dendritic cells during allergic airway inflammation in mice.

BACKGROUND: Dendritic cells (DCs) are the professional antigen-presenting cells (APCs) in the lung. They are known to be key players in the induction and maintenance of allergic asthma by cross-linking innate and adaptive immune responses. MicroRNAs (miRNAs) are known to influence cell fate and function by translational suppression or induction of messenger RNA (mRNA) degradation. miR-155 has been shown to be a crucial regulator of the immune system. However, its function in the pathogenesis of allergic airway inflammation (AAI) is not completely elucidated yet. METHODS: Wild type (WT) and miR-155-deficient (miR-155(-/-) ) mice were used in ovalbumin (OVA) and house dust mite (HDM) models of AAI. Adoptive transfer of sensitized DCs to the lungs, migration, and T-cell priming assays were used to investigate the functional relevance of miR-155 in DCs. RESULTS: miR-155(-/-) mice showed reduced eosinophilic airway inflammation compared to WT mice in both models of AAI. Furthermore, miR-155(-/-) DCs showed limited Th2 priming capacity and failed to induce airway inflammation in allergen-exposed WT mice. miR-155 deficiency on DCs was also associated with impaired purinergic receptor signaling, as miR-155(-/-) DCs showed reduced chemotaxis and IL-1beta secretion upon stimulation with ATP, probably due to direct targeting of ectonucleoside triphosphate diphosphohydrolases (ENTPD) by miR-155. CONCLUSIONS: miR-155 deficiency alleviates AAI by diminishing Th2 priming capacity and ATP-/P2R-induced activation of DCs in mice, suggesting this miRNA as a potential therapeutic target of AAI.

Attenuated allergic airway inflammation in Cd39 null mice.

BACKGROUND: Extracellular Adenosine-5'-Triphosphate (ATP) is known to accumulate in the lung, following allergen challenge, and contributes via activation of purinergic receptors on dendritic cells (DC), to the development of allergic airway inflammation (AAI). Extracellular ATP levels in the airways are normally tightly regulated by CD39. This ectonucleotidase is highly expressed by DC purified from skin (Langerhans cells) and bone marrow, and has been shown to modulate DC adaptive/haptenic immune responses. In this study, we have evaluated the impact of Cd39 deletion and associated perturbation of purinergic signaling in AAI. METHODS: Standard ovalbumin (OVA)-alum and house dust mite (HDM) bone marrow-derived DC (BMDC)-dependent models of AAI were used to study effects of Cd39. Migration assays, time lapse microscopy, and T-cell priming assays were further used to determine functional relevance of Cd39 expression on BMDC in the setting of immune and Th2-mediated responses in these models. RESULTS: Cd39(-/-) mice exhibited marked increases in BALF ATP levels but paradoxically exhibited limited AAI in both OVA-alum and HDM models. These pathophysiological abnormalities were associated with decreased myeloid DC activation and chemotaxis toward ATP, and were linked to purinergic receptor desensitization responses. Further, Cd39(-/-) DCs exhibited limited capacity to both prime Th2 responses and form stable immune synaptic interactions with OVA-transgenic naïve T cells. CONCLUSIONS: Cd39-deficient DCs exhibit limited capacity to induce Th2 immunity in a DC-driven model of AAI in vivo. Our data demonstrate a role of CD39 and perturbed purinergic signaling in models of AAI.

Purinergic receptor type 6 contributes to airway inflammation and remodeling in experimental allergic airway inflammation.

RATIONALE: Extracellular nucleotides have recently been identified as proinflammatory mediators involved in asthma pathogenesis by signaling via purinergic receptors, but the role of the purinergic receptor type 6 (P2Y6R) has not been previously investigated. OBJECTIVES: To investigate the role of P2Y6R in asthma pathogenesis. METHODS: Acute and chronic OVA model and also HDM model of allergic inflammation in C57Bl/6 mice treated with specific P2Y6R antagonist and P2Y6R(-/-) mice were evaluated for classical features of asthmatic inflammation. In addition, primary epithelial cell culture from human and epithelial cell lines from mouse and human were stimulated with P2Y6R agonist and treated with P2Y6R antagonist and assessed for IL-6, IL-8/CXCL8 and KC levels. Experiments with P2Y6R(-/-) and P2Y6R(+/+) chimera were performed to discriminate the role of P2Y6R activation in structural lung cells and in cells from hematopoietic system. MEASUREMENTS AND MAIN RESULTS: We observed that the intratracheal application of a P2Y6R antagonist (MRS2578) and P2Y6R deficiency inhibited cardinal features of asthma, such as bronchoalveolar lavage eosinophilia, airway remodeling, Th2 cytokine production, and bronchial hyperresponsiveness in the ovalbumin-alum model. MRS2578 was also effective in reducing airway inflammation in a model using house dust mite extracts to induce allergic lung inflammation. Experiments with bone marrow chimeras revealed the importance of the P2Y6R expression on lung structural cells in airway inflammation. In accordance with this finding, we found a strong up-regulation of P2Y6 expression on airway epithelial cells of animals with experimental asthma. Concerning the underlying mechanism, we observed that MRS2578 inhibited the release of IL-6 and IL-8/KC by lung epithelial cells in vivo, whereas intrapulmonary application of the P2Y6R agonist uridine-5'-diphosphate increased the bronchoalveolar levels of IL-6 and KC. In addition, selective activation of P2Y6 receptors induced the release of IL-6 and KC/IL-8 by murine and human lung epithelial cells in vitro. CONCLUSIONS: P2Y6R expression on airway epithelial cells is up-regulated during acute and chronic allergic airway inflammation, and selective blocking of P2Y6R or P2Y6R deficiency on the structural cells reduces cardinal features of experimental asthma. Thus, blocking pulmonary P2Y6R might be a target for the treatment of allergic airway inflammation.

Spreading depression: from serendipity to targeted therapy in migraine prophylaxis.

Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

BDNF and its receptors in human myasthenic thymus: implications for cell fate in thymic pathology.

Here we show that in myasthenic thymus several cell types, including thymic epithelial cells (TEC) and immune cells, were the source and the target of the neurotrophic factor brain-derived growth factor (BDNF). Interestingly, many actively proliferating medullary thymocytes expressed the receptor TrkB in vivo in involuted thymus, while this population was lost in hyperplastic or neoplastic thymuses. Furthermore, in hyperplastic thymuses the robust coordinated expression of BDNF in the germinal centers together with the receptor p75NTR on all proliferating B cells strongly suggests that this factor regulates germinal center reaction. Finally, all TEC dying of apoptosis expressed BDNF receptors, indicating that this neurotrophin is involved in TEC turnover. In thymomas both BDNF production and receptor expression in TEC were strongly hindered. This may represent an attempt of tumour escape from cell death.

Reduction of hippocampal cell death and proteolytic responses in tissue plasminogen activator knockout mice after transient global cerebral ischemia.

Knockout mice deficient in tissue plasminogen activator (tPA) are protected against hippocampal excitotoxicity. But it is unknown whether similar neuroprotection occurs after transient global cerebral ischemia, which is known to selectively affect the hippocampus. In this study, we tested the hypothesis that hippocampal cell death in tPA knockout mice would be reduced after transient global cerebral ischemia, and this neuroprotection would occur concomitantly with amelioration of both intra- and extracellular proteolytic cascades. Wild-type and tPA knockout mice were subjected to 20 min of transient bilateral occlusions of the common carotid arteries. Three days later, Nissl and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling staining demonstrated that hippocampal cell death was significantly reduced in tPA knockout brains compared with wild-type brains. Caspase-3 and the two major brain gelatinases (matrix metalloproteinase (MMP)-9 and MMP-2) were assessed as representative measurements of intra- and extracellular proteolysis. Post-ischemic levels of caspase-3, MMP-9 and MMP-2 were similarly reduced in tPA knockouts compared with wild-type hippocampi. Taken together, these data suggest that endogenous tPA contributes to hippocampal injury after cerebral ischemia, and these pathophysiologic pathways may involve links to aberrant activation of caspases and MMPs.

Neuroanatomic correlates of stroke-related myocardial injury.

BACKGROUND: Myocardial injury can occur after ischemic stroke in the absence of primary cardiac causes. The neuroanatomic basis of stroke-related myocardial injury is not well understood. OBJECTIVE: To identify regions of brain infarction associated with myocardial injury using a method free of the bias of an a priori hypothesis as to any specific location. METHODS: Of 738 consecutive patients with acute ischemic stroke, the authors identified 50 patients in whom serum cardiac troponin T (cTnT) elevation occurred in the absence of any apparent cause within 3 days of symptom onset. Fifty randomly selected, age- and sex-matched patients with ischemic stroke without cTnT elevation served as controls. Diffusion-weighted images with outlines of infarction were co-registered to a template, averaged, and then subtracted to find voxels that differed between the two groups. Voxel-wise p values were determined using a nonparametric permutation test to identify specific regions of infarction that were associated with cTnT elevation. RESULTS: The study groups were well balanced with respect to stroke risk factors, history of coronary artery disease, infarction volume, and frequency of right and left middle cerebral artery territory involvement. Brain regions that were a priori associated with cTnT elevation included the right posterior, superior, and medial insula and the right inferior parietal lobule. Among patients with right middle cerebral artery infarction, the insular cluster was involved in 88% of patients with and 33% without cTnT elevation (odds ratio: 15.00; 95% CI: 2.65 to 84.79). CONCLUSIONS: Infarctions in specific brain regions including the right insula are associated with elevated serum cardiac troponin T level indicative of myocardial injury.

Mouse model of microembolic stroke and reperfusion.

BACKGROUND AND PURPOSE: To test the role of fibrinolysis in stroke, we used a mouse model in which preformed 2.5- to 3-microm-diameter fibrin microemboli are injected into the cerebral circulation. The microemboli lodge in the downstream precapillary vasculature and are susceptible to fibrinolysis. METHODS: We injected various doses of microemboli into the internal carotid artery in mice and characterized their distribution, effects on cerebral blood flow, neurological deficit, infarct area, and spontaneous dissolution. By comparing wild-type and tissue plasminogen activator (tPA) knockout (tPA-/-) mice, we analyzed the role of endogenous tPA in acute thrombotic stroke. RESULTS: Microemboli cause dose-dependent brain injury. Although moderate doses of microemboli are followed by spontaneous reperfusion, they result in reproducible injury. Gene knockout of tPA markedly delays dissolution of cerebral emboli and restoration of blood flow and aggravates ischemic thrombotic infarction in the brain. CONCLUSIONS: We describe a microembolic model of stroke, in which degree of injury can be controlled by the dose of microemboli injected. Unlike vessel occlusion models, this model can be modulated to allow spontaneous fibrinolysis. Application to tPA-/- mice supports a key role of endogenous tPA in restoring cerebral blood flow and limiting infarct size after thrombosis.

Preliminary traction as a single determinant of avascular necrosis in developmental dislocation of the hip.

The role of preliminary traction before closed reduction in the treatment of developmental dysplasia of the hip has been questioned by many authors lately. However, the studies advocating or opposing the use of this treatment modality include several other parameters besides traction. Thus, it is unclear whether the affection is the result of preliminary traction or concurrent variables such as the "human position." This study aimed to put forward the effect of preliminary traction as a single determinant of avascular necrosis. We had two groups of patients who had developmental dislocation of the hip. The first group consisted of 52 patients treated with preliminary traction before closed reduction and the other group comprised 40 patients treated with closed reduction without preliminary traction. Both groups were similar in age, gender, side, level of dislocation, and method and duration of immobilization. Three patients from the first group developed avascular necrosis, which was not statistically significant. Preliminary traction did not affect the rate of avascular necrosis.

Impaired neurotransmitter release and elevated threshold for cortical spreading depression in mice with mutations in the alpha1A subunit of P/Q type calcium channels.

The P/Q type voltage-gated Ca2+ channels are involved in membrane excitability and Ca2+-dependent neurotransmitter release within the CNS. Mutations in the CacnalA gene encoding the alpha1A subunit of the P/Q type Ca2+ channel have recently been reported in tottering mice and a more severely affected allele, leaner. Here we show using in vivo cortical microdialysis that evoked increases of extracellular glutamate levels are markedly attenuated in both mutants upon KCl-induced depolarization compared with wild-type mice. Tottering and leaner mice also show a 10-fold resistance to cortical spreading depression induced by cortical electrical stimulation or KCl application to the pial surface. A slower transcortical propagation speed and failure to sustain regenerative spread of the depolarizing wave were more pronounced in leaner neocortex. Both signaling defects appeared unrelated to the developmental history of repeated cortical spike-wave discharges, since neither were observed in the stargazer mouse, a Ca2+ channel gamma2 subunit mutant with a similar seizure phenotype. These data demonstrate two cortical excitability defects revealed by prolonged depolarization in cerebral networks expressing mutant P/Q type Ca2+ channels, and are the first to identify a gene linked to a spreading depression phenotype.

MRI measurement of the temporal evolution of relative CMRO(2) during rat forepaw stimulation.

This study reports the first measurement of the relative cerebral metabolic rate of oxygen utilization (rCMRO(2)) during functional brain activation with sufficient temporal resolution to address the dynamics of blood oxygen level-dependent (BOLD) MRI signal. During rat forepaw stimulation, rCMRO(2) was determined in somatosensory cortex at 3-sec intervals, using a model of BOLD signal and measurements of the change in BOLD transverse relaxation rate, the resting state BOLD transverse relaxation rate, relative cerebral blood flow (rCBF), and relative cerebral blood volume (rCBV). Average percentage changes from 10 to 30 sec after onset of forepaw stimulation for rCBF, rCBV, rCMRO(2), and BOLD relaxation rate were 62 +/- 16, 17 +/- 2, 19 +/- 17, and -26 +/- 12, respectively. A poststimulus undershoot in BOLD signal was quantitatively attributed to the temporal mismatch between changes in blood flow and volume, and not to the role of oxygen metabolism. Magn Reson Med 42:944-951, 1999.

Evidence of a cerebrovascular postarteriole windkessel with delayed compliance.

A pronounced temporal mismatch was observed between the responses of relative cerebral blood volume (rCBV) measured by magnetic resonance imaging and relative cerebral blood flow measured by laser-Doppler flowmetry in rat somatosensory cortex after electrical forepaw stimulation. The increase of relative cerebral blood flow after stimulus onset and decrease after stimulus cessation were accurately described with a single exponential time constant of 2.4 +/- 0.8 seconds. In contrast, rCBV exhibited two distinct and nearly sequential processes after both onset and cessation of stimulation. A rapid change of rCBV (1.5 +/- 0.8 seconds) occurring immediately after onset and cessation was not statistically different from the time constant for relative cerebral blood flow. However, a slow phase of increase (onset) and decrease (cessation) with an exponential time constant of 14 +/- 13 seconds began approximately 8 seconds after the rapid phase of CBV change. A modified windkessel model was developed to describe the temporal evolution of rCBV as a rapid elastic response of capillaries and veins followed by slow venous relaxation of stress. Venous delayed compliance was suggested as the mechanism for the poststimulus undershoot in blood oxygen-sensitive magnetic resonance imaging signal that has been observed in this animal model and in human data.