DICER1 loss and Alu RNA induce age-related macular degeneration via the NLRP3 inflammasome and MyD88.

Alu RNA accumulation due to DICER1 deficiency in the retinal pigmented epithelium (RPE) is implicated in geographic atrophy (GA), an advanced form of age-related macular degeneration that causes blindness in millions of individuals. The mechanism of Alu RNA-induced cytotoxicity is unknown. Here we show that DICER1 deficit or Alu RNA exposure activates the NLRP3 inflammasome and triggers TLR-independent MyD88 signaling via IL18 in the RPE. Genetic or pharmacological inhibition of inflammasome components (NLRP3, Pycard, Caspase-1), MyD88, or IL18 prevents RPE degeneration induced by DICER1 loss or Alu RNA exposure. These findings, coupled with our observation that human GA RPE contains elevated amounts of NLRP3, PYCARD, and IL18 and evidence of increased Caspase-1 and MyD88 activation, provide a rationale for targeting this pathway in GA. Our findings also reveal a function of the inflammasome outside the immune system and an immunomodulatory action of mobile elements.

Chronic Dicer1 deficiency promotes atrophic and neovascular outer retinal pathologies in mice.

Degeneration of the retinal pigmented epithelium (RPE) and aberrant blood vessel growth in the eye are advanced-stage processes in blinding diseases such as age-related macular degeneration (AMD), which affect hundreds of millions of people worldwide. Loss of the RNase DICER1, an essential factor in micro-RNA biogenesis, is implicated in RPE atrophy. However, the functional implications of DICER1 loss in choroidal and retinal neovascularization are unknown. Here, we report that two independent hypomorphic mouse strains, as well as a separate model of postnatal RPE-specific DICER1 ablation, all presented with spontaneous RPE degeneration and choroidal and retinal neovascularization. DICER1 hypomorphic mice lacking critical inflammasome components or the innate immune adaptor MyD88 developed less severe RPE atrophy and pathological neovascularization. DICER1 abundance was also reduced in retinas of the JR5558 mouse model of spontaneous choroidal neovascularization. Finally, adenoassociated vector-mediated gene delivery of a truncated DICER1 variant (OptiDicer) reduced spontaneous choroidal neovascularization in JR5558 mice. Collectively, these findings significantly expand the repertoire of DICER1 in preserving retinal homeostasis by preventing both RPE degeneration and pathological neovascularization.

DICER1 deficit induces Alu RNA toxicity in age-related macular degeneration.

Geographic atrophy (GA), an untreatable advanced form of age-related macular degeneration, results from retinal pigmented epithelium (RPE) cell degeneration. Here we show that the microRNA (miRNA)-processing enzyme DICER1 is reduced in the RPE of humans with GA, and that conditional ablation of Dicer1, but not seven other miRNA-processing enzymes, induces RPE degeneration in mice. DICER1 knockdown induces accumulation of Alu RNA in human RPE cells and Alu-like B1 and B2 RNAs in mouse RPE. Alu RNA is increased in the RPE of humans with GA, and this pathogenic RNA induces human RPE cytotoxicity and RPE degeneration in mice. Antisense oligonucleotides targeting Alu/B1/B2 RNAs prevent DICER1 depletion-induced RPE degeneration despite global miRNA downregulation. DICER1 degrades Alu RNA, and this digested Alu RNA cannot induce RPE degeneration in mice. These findings reveal a miRNA-independent cell survival function for DICER1 involving retrotransposon transcript degradation, show that Alu RNA can directly cause human pathology, and identify new targets for a major cause of blindness.

The newest member of the VEGF family.

In this issue of Blood, Singh et al establish the existence of a new soluble isoform of vascular endothelial growth factor receptor 3 (sVEGFR-3), which is synthesized and secreted by corneal epithelial cells; they show that sVEGFR-3 modulates lymphangiogenesis by impounding vascular endothelial growth factor (VEGF) C and rendering it unable to activate its cognate receptors, thereby maintaining the natural alymphatic disposition of the cornea.

CCR3 is a target for age-related macular degeneration diagnosis and therapy.

Age-related macular degeneration (AMD), a leading cause of blindness worldwide, is as prevalent as cancer in industrialized nations. Most blindness in AMD results from invasion of the retina by choroidal neovascularisation (CNV). Here we show that the eosinophil/mast cell chemokine receptor CCR3 is specifically expressed in choroidal neovascular endothelial cells in humans with AMD, and that despite the expression of its ligands eotaxin-1, -2 and -3, neither eosinophils nor mast cells are present in human CNV. Genetic or pharmacological targeting of CCR3 or eotaxins inhibited injury-induced CNV in mice. CNV suppression by CCR3 blockade was due to direct inhibition of endothelial cell proliferation, and was uncoupled from inflammation because it occurred in mice lacking eosinophils or mast cells, and was independent of macrophage and neutrophil recruitment. CCR3 blockade was more effective at reducing CNV than vascular endothelial growth factor A (VEGF-A) neutralization, which is in clinical use at present, and, unlike VEGF-A blockade, is not toxic to the mouse retina. In vivo imaging with CCR3-targeting quantum dots located spontaneous CNV invisible to standard fluorescein angiography in mice before retinal invasion. CCR3 targeting might reduce vision loss due to AMD through early detection and therapeutic angioinhibition.

Sequence- and target-independent angiogenesis suppression by siRNA via TLR3.

Clinical trials of small interfering RNA (siRNA) targeting vascular endothelial growth factor-A (VEGFA) or its receptor VEGFR1 (also called FLT1), in patients with blinding choroidal neovascularization (CNV) from age-related macular degeneration, are premised on gene silencing by means of intracellular RNA interference (RNAi). We show instead that CNV inhibition is a siRNA-class effect: 21-nucleotide or longer siRNAs targeting non-mammalian genes, non-expressed genes, non-genomic sequences, pro- and anti-angiogenic genes, and RNAi-incompetent siRNAs all suppressed CNV in mice comparably to siRNAs targeting Vegfa or Vegfr1 without off-target RNAi or interferon-alpha/beta activation. Non-targeted (against non-mammalian genes) and targeted (against Vegfa or Vegfr1) siRNA suppressed CNV via cell-surface toll-like receptor 3 (TLR3), its adaptor TRIF, and induction of interferon-gamma and interleukin-12. Non-targeted siRNA suppressed dermal neovascularization in mice as effectively as Vegfa siRNA. siRNA-induced inhibition of neovascularization required a minimum length of 21 nucleotides, a bridging necessity in a modelled 2:1 TLR3-RNA complex. Choroidal endothelial cells from people expressing the TLR3 coding variant 412FF were refractory to extracellular siRNA-induced cytotoxicity, facilitating individualized pharmacogenetic therapy. Multiple human endothelial cell types expressed surface TLR3, indicating that generic siRNAs might treat angiogenic disorders that affect 8% of the world's population, and that siRNAs might induce unanticipated vascular or immune effects.

Short-interfering RNAs induce retinal degeneration via TLR3 and IRF3.

The discovery of sequence-specific gene silencing by endogenous double-stranded RNAs (dsRNA) has propelled synthetic short-interfering RNAs (siRNAs) to the forefront of targeted pharmaceutical engineering. The first clinical trials utilized 21-nucleotide (nt) siRNAs for the treatment of neovascular age-related macular degeneration (AMD). Surprisingly, these compounds were not formulated for cell permeation, which is required for bona fide RNA interference (RNAi). We showed that these "naked" siRNAs suppress neovascularization in mice not via RNAi but via sequence-independent activation of cell surface Toll-like receptor-3 (TLR3). Here, we demonstrate that noninternalized siRNAs induce retinal degeneration in mice by activating surface TLR3 on retinal pigmented epithelial cells. Cholesterol conjugated siRNAs capable of cell permeation and triggering RNAi also induce the same phenotype. Retinal degeneration was not observed after treatment with siRNAs shorter than 21-nts. Other cytosolic dsRNA sensors are not critical to this response. TLR3 activation triggers caspase-3-mediated apoptotic death of the retinal pigment epithelium (RPE) via nuclear translocation of interferon regulatory factor-3. While this unexpected adverse effect of siRNAs has implications for future clinical trials, these findings also introduce a new preclinical model of geographic atrophy (GA), a late stage of dry AMD that causes blindness in millions worldwide.

Corneal avascularity is due to soluble VEGF receptor-1.

Corneal avascularity-the absence of blood vessels in the cornea-is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders. But the molecular underpinnings of the avascular phenotype have until now remained obscure and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice and Pax6+/- patients with aniridia are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.

Small interfering RNA-induced TLR3 activation inhibits blood and lymphatic vessel growth.

Neovascularization in response to tissue injury consists of the dual invasion of blood (hemangiogenesis) and lymphatic (lymphangiogenesis) vessels. We reported recently that 21-nt or longer small interfering RNAs (siRNAs) can suppress hemangiogenesis in mouse models of choroidal neovascularization and dermal wound healing independently of RNA interference by directly activating Toll-like receptor 3 (TLR3), a double-stranded RNA immune receptor, on the cell surface of blood endothelial cells. Here, we show that a 21-nt nontargeted siRNA suppresses both hemangiogenesis and lymphangiogenesis in mouse models of neovascularization induced by corneal sutures or hindlimb ischemia as efficiently as a 21-nt siRNA targeting vascular endothelial growth factor-A. In contrast, a 7-nt nontargeted siRNA, which is too short to activate TLR3, does not block hemangiogenesis or lymphangiogenesis in these models. Exposure to 21-nt siRNA, which we demonstrate is not internalized unless cell-permeating moieties are used, triggers phosphorylation of cell surface TLR3 on lymphatic endothelial cells and induces apoptosis. These findings introduce TLR3 activation as a method of jointly suppressing blood and lymphatic neovascularization and simultaneously raise new concerns about the undesirable effects of siRNAs on both circulatory systems.

The endogenous soluble VEGF receptor-2 isoform suppresses lymph node metastasis in a mouse immunocompetent mammary cancer model.

BACKGROUND: Cancer metastasis contributes significantly to cancer mortality and is facilitated by lymphangiogenesis and angiogenesis. A new splicing variant, endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2) that we recently identified is an endogenous selective inhibitor of lymphangiogenesis. To evaluate the antimetastatic potential of esVEGFR-2, gene therapy with vector expressing esVEGFR-2 (pesVEGFR-2) or endostatin (pEndo) as a positive control was conducted on murine metastatic mammary cancer. METHODS: Syngeneic inoculated metastatic mammary cancers received direct intratumoral injection of pesVEGFR-2, pEndo or pVec as control, once a week for six weeks. In vivo gene electrotransfer was performed on the tumors after each injection. RESULTS: Deaths from metastasis were much lower in the pesVEGFR-2 and pEndo groups than in those of the pVec. Tumor volume was significantly lower in the pesVEGFR-2 and the pEndo groups throughout the study. Multiplicity of lymph node and lung metastatic nodules was significantly suppressed in the pesVEGFR-2 and pEndo groups. Moreover, the total number of overall metastasis including the other organs was also decreased in these groups. However, pesVEGFR-2 was not able to decrease the number of lungs, ovaries, kidneys and adrenals with metastasis as counted by unilateral or bilateral metastasis. The number of CD34+/Lyve-1⁻ blood microvessels was significantly decreased in the pEndo group, while the number of CD34⁻/Lyve-1+ lymphatic vessels was significantly decreased in the pesVEGFR-2 and pEndo groups. In addition, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed in the pesVEGFR-2 and pEndo groups. Levels of apoptosis were significantly increased in the pEndo group, whereas the rates of cell proliferation were significantly decreased in the pesVEGFR-2 and pEndo groups. CONCLUSIONS: Our data demonstrate that esVEGFR-2 can inhibit mainly lymph node metastasis. The antimetastatic activity of esVEGFR-2 may be of high clinical significance in the treatment of metastatic breast cancer because lymph node involvement is a most important prognostic factor in cancer patients.

Latent Sensitization in a Mouse Model of Ocular Neuropathic Pain.

PURPOSE: Chronic ocular pain is poorly understood and difficult to manage. We developed a murine model of corneal surface injury (CSI)-induced chronic ocular neuropathic pain. The study focuses on changes in corneal nerve morphology and associated short- and long-term pain-like behavior after CSI. METHODS: CSI was induced in mice by local application of an alkali solution (0.75 N NaOH). Corneal nerve architecture, morphology, density, and length were studied. Eye-wiping was evaluated before and after CSI in response to hypertonic saline (2 M NaCl). Naltrexone (NTX) or Naloxone-methiodide (NLX-me), opioid receptor antagonists, were given subcutaneously (s.c., 3 mg/kg) or topically (eye drop, 100 µM), and then an eye-wiping test was performed. RESULTS: CSI caused partial corneal deinnervation followed by gradual reinnervation. Regenerated nerves displayed increased tortuosity, beading, and branching. CSI enhanced hypertonic saline-induced eye-wiping behavior compared to baseline or sham-injury (P < 0.01). This hypersensitivity peaked at 10 days and subsided 14 days after CSI. Administration of NTX, or NLX-me, a selective peripheral opioid antagonist, reinstated eye-wiping behavior in the injury group, but not in the sham groups (P < 0.05). CONCLUSIONS: This study introduces a model of chronic ocular pain and corneal neuropathy following CSI. CSI induces central and peripheral opioid receptor-dependent latent sensitization (LS) that is unmasked by systemic or topical administration of opioid antagonists. TRANSLATIONAL RELEVANCE: This model of chronic ocular pain establishes LS as a new inhibitory mechanism in the oculotrigeminal system and may be used for potential diagnostic and therapeutic interventions for ocular neuropathy.

Are female patients with orofacial pain medically compromised?

BACKGROUND: Chronic pain has been linked to various medical conditions. The authors assessed whether certain medical conditions are more prevalent in female patients with orofacial pain than in age-matched controls. METHODS: The study sample consisted of 87 female adult subjects from a university-based orofacial pain center (OPC) and 87 age-matched female subjects from a university-based undergraduate dental clinic (UDC). Subjects were evaluated between February 2003 and July 2003, and they completed a standardized, 78-question medical history questionnaire as part of routine clinical protocol. Using the subjects' medical histories, the authors compared 11 major medical categories and 77 individual conditions for both groups. For statistical analyses, the authors used nonparametric Kolmogorov-Smirnov Z tests and chi2 tests and calculated odds ratios (ORs). RESULTS: The medical histories of subjects in the OPC group indicated a significantly greater number of medical conditions than did those of the subjects in the UDC group (Z = -4.411, P < .0001). Specifically, subjects in the OPC group reported having significantly more neurological (Z = -5.304, P < .0001), gastrointestinal (Z = -2.897, P = .004), pulmonary (Z = -2.298, P = .022), dermatologic (Z = -2.984, P = .003) and other conditions (Z = -2.885, P = .004) than did subjects in the UDC group. Subjects in the OPC group reported having 12 individual medical conditions significantly more often (P < .05, ORs ranged from 2.5 to 9.7) than did subjects in the UDC group. CONCLUSIONS: Female patients with orofacial pain complaints appear to have more systemic problems than do female patients seeking routine dental care. CLINICAL IMPLICATIONS: The presence of multiple medical conditions can influence orofacial pain management options and treatment outcomes. Patients with more medically complicated orofacial pain may require treatment on a multidisciplinary basis.

Self-report health questionnaire: a necessary and reliable tool in dentistry.

This study was designed to assess whether the number and type of medical conditions elicited by self-report on a questionnaire were equivalent to those obtained through verbal inquiry by blinded trained dentists. The study sample consisted of 100 adult patients who were seeking treatment from the University of Kentucky Orofacial Pain Center. Evaluations occurred between September 2003 and January 2004. Patients completed a standardized medical health questionnaire containing 92 questions. Subsequently, the patients were questioned verbally about their medical history by uniformly trained dentists, using a systems review approach as part of routine clinical protocol. The medical histories obtained by both methods were statistically analyzed using Kappa values, paired and independent sample t-tests. The nature of the questionnaire did not distinguish between past and present conditions, and did not give information regarding onset, severity, duration, and impact of the marked conditions. It was concluded that even though a self-reported health questionnaire is precise and consistent, more detailed information can be obtained by verifying marked medical conditions through a verbal inquiry. Every history and examination should include a combination of both a self-reported medical health questionnaire and a verbal inquiry to aid in diagnosis and treatment.

Photoreceptor avascular privilege is shielded by soluble VEGF receptor-1.

Optimal phototransduction requires separation of the avascular photoreceptor layer from the adjacent vascularized inner retina and choroid. Breakdown of peri-photoreceptor vascular demarcation leads to retinal angiomatous proliferation or choroidal neovascularization, two variants of vascular invasion of the photoreceptor layer in age-related macular degeneration (AMD), the leading cause of irreversible blindness in industrialized nations. Here we show that sFLT-1, an endogenous inhibitor of vascular endothelial growth factor A (VEGF-A), is synthesized by photoreceptors and retinal pigment epithelium (RPE), and is decreased in human AMD. Suppression of sFLT-1 by antibodies, adeno-associated virus-mediated RNA interference, or Cre/lox-mediated gene ablation either in the photoreceptor layer or RPE frees VEGF-A and abolishes photoreceptor avascularity. These findings help explain the vascular zoning of the retina, which is critical for vision, and advance two transgenic murine models of AMD with spontaneous vascular invasion early in life. DOI:http://dx.doi.org/10.7554/eLife.00324.001.

Soluble VEGFR-2: an antilymphangiogenic variant of VEGF receptors.

The vascular endothelial growth factor (VEGF) family of secreted proteins and their receptors are major regulators of blood vessel development (hemangiogenesis) and lymphatic vessel development (lymphangiogenesis). VEGF acts through a complex system of receptor tyrosine kinases, which can be membrane bound or soluble. New data concerning the receptor system are still emerging, thus contributing to the complexity of the system. Very recently a soluble form of VEGFR-2, termed sVEGFR-2, which is a result of alternative splicing, has been discovered. Earlier, it has been shown that a secreted/soluble form of VEGFR-1, termed sVEGFR-1, is produced by alternative splicing and exerts an antihemangiogenic effect by binding VEGF-A. The newly discovered spliced variant of sVEGFR-2 binds the lymphangiogenic growth factor VEGF-C and thus inhibits VEGF-C-induced activation of VEGFR-3, consequently inhibiting lymphatic endothelial cell proliferation. Its inactivation in murine embryos permits hyperplasia of dermal lymphatics and invasion of lymphatics into the cornea. Tumor lymphangiogenesis seems to influence the metastatic behavior of malignant cells. A correlation has been found between the downregulation of sVEGFR-2 and the malignant progression of neuroblastoma, which is characterized by lymphogenic metastases in progressed stages. Data show that lymphangiogenesis is regulated by both activators and inhibitors, and its balance is crucial in health and disease.

Neuroblastoma progression correlates with downregulation of the lymphangiogenesis inhibitor sVEGFR-2.

PURPOSE: Tumor progression correlates with the induction of a dense supply of blood vessels and the formation of peritumoral lymphatics. Hemangiogenesis and lymphangiogenesis are potently regulated by members of the vascular endothelial growth factor (VEGF) family. Previous studies have indicated the upregulation of VEGF-A and -C in progressed neuroblastoma, however, quantification was performed using semiquantitative methods, or patients who had received radiotherapy or chemotherapy were studied. EXPERIMENTAL DESIGN: We have analyzed primary neuroblastoma from 49 patients using real-time reverse transcription-PCR and quantified VEGF-A, -C, and -D and VEGF receptors (VEGFR)-1, 2, 3, as well as the soluble form of VEGFR2 (sVEGFR-2), which has recently been characterized as an endogenous inhibitor of lymphangiogenesis. None of the patients had received radiotherapy or chemotherapy before tumor resection. RESULTS: We did not observe upregulation of VEGF-A, -C, and -D in metastatic neuroblastoma, but found significant downregulation of the lymphangiogenesis inhibitor sVEGFR-2 in metastatic stages III, IV, and IVs. In stage IV neuroblastoma, there were tendencies for the upregulation of VEGF-A and -D and the downregulation of the hemangiogenesis/lymphangiogenesis inhibitors VEGFR-1 and sVEGFR-2 in MYCN-amplified tumors. Similarly, MYCN transfection of the neuroblastoma cell line SH-EP induced the upregulation of VEGF-A and -D and the switching-off of sVEGFR-2. CONCLUSION: We provide evidence for the downregulation of the lymphangiogenesis inhibitor sVEGFR-2 in metastatic neuroblastoma stages, which may promote lymphogenic metastases. Downregulation of hemangiogenesis and lymphangiogenesis inhibitors VEGFR-1 and sVEGFR-2, and upregulation of angiogenic activators VEGF-A and VEGF-D in MYCN-amplified stage IV neuroblastoma supports the crucial effect of this oncogene on neuroblastoma progression.

Alternatively spliced vascular endothelial growth factor receptor-2 is an essential endogenous inhibitor of lymphatic vessel growth.

Disruption of the precise balance of positive and negative molecular regulators of blood and lymphatic vessel growth can lead to myriad diseases. Although dozens of natural inhibitors of hemangiogenesis have been identified, an endogenous selective inhibitor of lymphatic vessel growth has not to our knowledge been previously described. We report the existence of a splice variant of the gene encoding vascular endothelial growth factor receptor-2 (Vegfr-2) that encodes a secreted form of the protein, designated soluble Vegfr-2 (sVegfr-2), that inhibits developmental and reparative lymphangiogenesis by blocking Vegf-c function. Tissue-specific loss of sVegfr-2 in mice induced, at birth, spontaneous lymphatic invasion of the normally alymphatic cornea and hyperplasia of skin lymphatics without affecting blood vasculature. Administration of sVegfr-2 inhibited lymphangiogenesis but not hemangiogenesis induced by corneal suture injury or transplantation, enhanced corneal allograft survival and suppressed lymphangioma cellular proliferation. Naturally occurring sVegfr-2 thus acts as a molecular uncoupler of blood and lymphatic vessels; modulation of sVegfr-2 might have therapeutic effects in treating lymphatic vascular malformations, transplantation rejection and, potentially, tumor lymphangiogenesis and lymphedema (pages 993-994).

Modulation of angiogenesis by a tetrameric tripeptide that antagonizes vascular endothelial growth factor receptor 1.

Vascular endothelial growth factor receptor-1 (VEGFR-1, also known as Flt-1) is involved in complex biological processes often associated to severe pathological conditions like cancer, inflammation, and metastasis formation. Consequently, the search for antagonists of Flt-1 has recently gained a growing interest. Here we report the identification of a tetrameric tripeptide from a combinatorial peptide library built using non-natural amino acids, which binds Flt-1 and inhibits in vitro its interaction with placental growth factor (PlGF) and vascular endothelial growth factor (VEGF) A and B (IC(50) approximately 10 microm). The peptide is stable in serum for 7 days and prevents both Flt-1 phosphorylation and the capillary-like tube formation of human primary endothelial cells stimulated by PlGF or VEGF-A. Conversely, the identified peptide does not interfere in VEGF-induced VEGFR-2 activation. In vivo, this peptide inhibits VEGF-A- and PlGF-induced neoangiogenesis in the chicken embryo chorioallantoic membrane assay. In contrast, in the cornea, where avascularity is maintained by high levels of expression of the soluble form of Flt-1 receptor (sFlt-1) that prevents the VEGF-A activity, the peptide is able to stimulate corneal mouse neovascularization in physiological condition, as reported previously for others neutralizing anti-Flt-1 molecules. This tetrameric tripeptide represents a new, promising compound for therapeutic approaches in pathologies where Flt-1 activation plays a crucial role.

Brain activity during stimulation of the trigeminal nerve with noxious heat.

OBJECTIVE: The aim of this study was to observe areas of brain activation with painful hot stimulation to the trigeminal nerve. STUDY DESIGN: Nine healthy pain-free women (mean age 26.2 +/- 6.9 yrs) with a natural, regular menstrual cycle participated in the study. Whole-brain functional magnetic resonance imaging (fMRI) data were acquired for each participant on day 2 or 3 after the onset of menses using echo-planar imaging at 1.5T with near-isotropic spatial resolution and a temporal resolution of 4 s. RESULTS: Whole-brain fMRI with a Peltier thermode inside the head coil yielded a feasible imaging protocol with little disturbance from the thermode. Painful thermal stimulation of the left trigeminal system activated discrete brain regions within the insula, cingulate gyrus, thalamus, inferior parietal lobe/postcentral gyrus, right middle and inferior frontal gyri, cuneus, precuneus, and precentral gyrus. CONCLUSION: Painful stimulation of the trigeminal nerve resulted in activation of similar brain areas generally known for pain processing of painful peripheral stimulation.

Influence of estrogen on brain activation during stimulation with painful heat.

PURPOSE: Several studies have shown that women express higher pain sensitivity during periods of low estrogen than during periods of high estrogen. The aim of this study was to show whether the difference in pain sensitivity could be visualized as a function of brain activity by means of functional magnetic resonance imaging (fMRI). METHODS: Nine healthy, pain-free women (mean age, 26.2 +/- 6.9 years) with a natural, regular menstrual cycle participated in the study. Whole-brain fMRI data were acquired during a period of high and during a period of low estrogen at 1.5 T using echo-planar imaging with near-isotropic spatial resolution and a temporal resolution of 4 seconds. Heat pain thresholds were obtained before the scans, and pain ratings were obtained before and after each scan. Blood samples were taken after each scan to verify the appropriate level of estrogen. RESULTS: The heat pain thresholds during the low (46.4 degrees +/- 3.5 degrees C) and high (46.4 degrees +/- 3.8 degrees C) estrogen conditions were not significantly different. The pain ratings before (4.6 +/- 2.2 low versus 3.6 +/- 2.1 high) and during the scans (4.4 +/- 2.4 low versus 4.7 +/- 2.3 high) also did not differ between the 2 conditions. Generally, similar patterns of activation were observed for both estrogen conditions. However, significant differences were found in the magnitude of activation of the anterior part of the anterior cingulate (BA 24/32), the cerebellum, and the precuneus. Furthermore, activations in the anterior part of the anterior cingulate, left cerebellum, and precuneus were unique to the low-estrogen phase. These regions have been linked with attention to or anticipation of pain. CONCLUSIONS: The results of this study suggest that the affective component of pain may be enhanced during the low-estrogen phase of the menstrual cycle in healthy women.