Periapical surgery and different root obturation protocols for upper central incisor: A finite elements analysis.

BACKGROUND: The aim of this study was to determine the effect of root canal filling using different obturation materials combined with apicoectomy in upper central incisors under loading with 1 N and 100 N. The effect of incomplete root formation was also investigated. METHODS: Based on a CBCT-scan, a model of an upper central incisor was created. The model was altered to simulate different clinical situations: root canal treatment, apicoectomy at two different lengths and with different obturation protocols, and immature root formation after trauma. In each model the tooth was loaded with 1 and 100 N, and peak Von Mises stress of bone and tooth, elastic strain of the periodontal ligament, as well as rotation and displacement of the tooth were measured. RESULTS: Periapical surgery increases stress in dentin and the surrounding bone. Different obturation materials only produce minor differences in a coronally intact tooth. CONCLUSIONS: Interincisal angle or loading direction strongly affects all measured values and needs to be considered when planning periapical surgery or comparing finite element analysis. Immature roots show the highest stress values in this study, reaching half the yield strength of dentine.

[Long-term Development of Acute Tinnitus]. / Langzeit-Entwicklung von akutem Tinnitus.

BACKGROUND: Aim was to assess correlations between hearing threshold and mental health measures at tinnitus onset and tinnitus severity after 6 months. Short self-report questionnaires were used to permit later use in ENT-practices. METHOD: 28 patients with tinnitus of no longer than 4 weeks filled out questionnaires at inclusion (T1), and at 6 weeks (T2), 3 (T3) and 6 months (T4) after tinnitus onset. An audiogram was recorded at T1. Tinnitus loudness and sound sensitivity were assessed by numeric rating scales, tinnitus-distress was recorded with the short form of the tinnitus questionnaire. Mental health and personality factors were measured by the depressivity, anxiety and somatic severity scales of the Patient Health Questionnaire, and the resilience scale. RESULTS: Tinnitus loudness and distress were stable throughout the investigation period whereas sound sensitivity decreased. Resilience did not represent a predictor for tinnitus severity after 6 months. Depressivity and hearing loss at T1 had an effect on later tinnitus loudness, while depressivity and age at T1 showed an effect on sound sensitivity and tinnitus-related distress at T4. CONCLUSION: Stability of tinnitus severity during the 6 months after onset supports the hypothesis of early manifestation. RESULTS also support the hypothesis that later tinnitus severity is related to psychological distress and hearing impairment at onset. RESULTS suggest to use hearing aids to alleviate tinnitus loudness, and to include tools for the identification of depressive disorders at an early stage to identify patients that might benefit from psychotherapeutic interventions.

[Pars plana vitrectomy for idiopathic macular hole--visual improvement or merely surgical stress?]. / PPV bei idiopathischem Makulaforamen--Visusverbesserung oder nur operative Belastung?

BACKGROUND: The aim of this study was to compare the functional results of surgical treatment of idiopathic macular holes in controlled clinical studies with those of the "real world" in the clinical routine. METHODS: The operated eyes of patients of a rural district (Saalfeld-Rudolstadt, Germany) during 2000-2009 were analysed based on the documentation of the postoperative care of all ophthalmologists in this region. RESULTS: 37 eyes of 37 patients (age 71 years, 45; 80) (median, [min; max]) operated in 7 clinical institutes were analysed. The past medical history until surgery was 4 months (1; 72) and the preoperative visual acuity (VA) 0.2 (0.01; 0.5). The observational period after surgery was 2.3 years (1; 6 years), all eyes were documented over more then 1 year thereafter. At the last control the VA improved ≥ 2 lines in 17 eyes (46%) and decreased ≥ 2 lines in 8 (22%). 13 eyes (35%) obtained a VA ≥ 0.5. A short preoperative period corresponded with a visual improvement (K = 0.40, p = 0.01). A further increase of VA after one year could be observed only due to cataract surgery or Nd:YAG laser capsulotomy. 8 eyes (22%) needed at least one more vitreoretinal surgery. DISCUSSION: Reasons for the disappointing functional results compared with the literature could be long medical history, not differentiated grades of macular holes and developing surgical techniques during the analysis period. Retrospective analyses of the outcome of routine practical work seems to be a necessary complement of controlled clinical studies despite their methodical deficits. New prognostic criteria are needed for a better indication for surgery and an improved counselling of the patient.

Ballistic parameters of cal. 9 mm x 17 mm industrial blank cartridges (cattle cartridges).

INTRODUCTION: Cal. 9 mm x 17 mm industrial blank cartridges deserve special interest in the field of forensic ballistic. This calibre is most often used in Kerner-type livestock stunners, but also in different power tools. The legal framework of these industrial blank cartridges is provided by the C.I.P. and DIN 7260 regulations. The aim of this investigation is to describe and compare two experimental test procedures for measurement of maximum gas pressure and kinetic energy of cal. 9 mm x 17 mm industrial blank cartridges according to standardized C.I.P. and DIN 7260 protocols and to provide these ballistic data. METHODS: Using two different pressure measurement barrels and standardized test projectiles, the maximum gas pressure and the kinetic energy of the test projectiles are investigated. While the pressure take-off point in C.I.P. protocol is at the cartridge mouth, the DIN 7260 protocol is modified using a pressure take-off point in the cartridge chamber. For each test protocol (C.I.P. and DIN), maximum gas pressure, velocity, impulse and energy of the test projectiles are measured. Each ten cartridges from the same ammunition lot of four different energy levels (red, blue, yellow, green) are investigated. RESULTS: While the cartridge energy values are comparable between the two different test protocols, maximum gas pressure measured in the DIN set-up (3907 bar) far surpasses the gas pressure in the C.I.P. protocol (1586 bar). Both test protocols observed higher energy values of the green and yellow cartridges than regulated in DIN 7260. CONCLUSION: Enormous gas pressure values of more than 3900 bar emphasize the power of industrial blank cartridges. Once again, the harmlessness of these blank cartridges and the weapons/tools that are operated with these propellants is refuted.

Dynamic pressure measurement of cartridge operated vole captive bolt devices.

INTRODUCTION: Vole captive bolt devices are powder actuated spring guns that are used as a pest control mean. After having triggered the explosion of the blank cartridge by touching a metal ring around the muzzle, the vole is killed by the massive propulsion of the gas jet. Improper use and recklessness while handling these devices may cause severe injuries with the hand of the operator at particular risk. Currently, there are no experimental investigations on the ballistic background of these devices. METHODS: An experimental test set-up was designed for measurement of the firing pressure and the dynamic force of the gas jet of a vole captive bolt device. Therefore, a vole captive bolt device was prepared with a pressure take-off channel and a piezoelectric transducer for measurement of the firing pressure. For measurement of the dynamic impact force of the gas jet an annular quartz force sensor was installed on a test bench. Each three simultaneous measurements of the cartridges' firing pressure and the dynamic force of the blast wave were taken at various distances between muzzle and load washer. RESULTS: The maximum gas pressure in the explosion chamber was up to 1100 bar. The shot development over time showed a typical gas pressure curve. Flow velocity of the gas jet was up to 2000 m/s. The maximum impact force of the gas jet at the target showed a strong inverse ratio to the muzzle's distance and was up to 11,500 N for the contact shot distance. Energy density of the gas jet for the close contact shot was far beyond the energy density required for skin penetration. CONCLUSION: The unique design features (short tube between cartridge mouth and muzzle and narrow diameter of the muzzle) of these gadgets are responsible for the high firing pressure, velocity and force of the gas jet. These findings explain the trauma mechanics of the extensive tissue damage observed in accidental shots of these devices.

Influences of TP53 expression on cellular radiation response and its relevance to diagnostic biodosimetry for mission environmental monitoring.

TP53 is a transcriptional activator and regulates genomic instability and cellular responses to DNA damage in response to ionising radiation. The molecular mechanism behind p53-mediated responses, such as, apoptosis and genomic instability remains unclear. An in vitro model of biological effects to irradiation was established. In order to elucidate the functional role of TP53 under different stress-reaction pathways and identify possible biological indicators, p53 was stably transfected into HL-60 cells, which provides a p53 minus background. Significantly enhanced radiosensitivity and growth suppression were observed. G(2) accumulation was obtained. Radiation-induced apoptosis of HL-60 cells was significantly inhibited by TP53, indicating that, in the event of DNA damage, TP53 is able to prevent cell death of HL-60 leukaemia cells by sustaining an arrest of the cell cycle at G(2) phase. Further evidence will be presented to identify specific radiation-targeted genes or signals as possible biomarkers for early diagnosis of radiation damage as well as mission environmental monitoring.

Evidence for tinnitus-related plasticity in the auditory and limbic system, demonstrated by arg3.1 and c-fos immunocytochemistry.

Distributions of arg3.1 and c-fos immunoreactive neurons (IRN) in gerbil auditory cortex (AC) and amygdala showed characteristic differences when comparing systemic application of the tinnitus-eliciting drug salicylate with acoustic stimulation or saline injections. In AC, arg3.1 IRN induced by stimulation focused in regions corresponding to the frequency content of the stimulus. Injections of salicylate (350 mg/kg body weight) led to accumulation of arg3.1 IRN in the high frequency domain, while saline injections produced a diffuse distribution. After all treatments, c-fos IRN outnumbered arg3.1 IRN in AC and showed a broad distribution. In subcortical auditory structures arg3.1 IRN were absent in all but one brain. In ventral cochlear nucleus, c-fos IRN were always found after stimulation and often also after saline injections, whereas none were present when injecting salicylate. Similarly, in inferior colliculus, numbers of c-fos IRN were lowest after salicylate injections. In the amygdala, c-fos and arg3.1 IRN were increased substantially after salicylate injections compared to auditory stimulation or saline injections. In particular in its central nucleus, c-fos and arg3.1 IRN were found exclusively after the tinnitus-inducing treatment, suggesting that coactivation of the AC and the amygdala may by an essential feature of tinnitus-related activation.

Expression of c-fos in auditory and non-auditory brain regions of the gerbil after manipulations that induce tinnitus.

Subjective tinnitus is a phantom sound sensation that does not result from acoustic stimulation and is audible to the affected subject only. Tinnitus-like sensations in animals can be evoked by procedures that also cause tinnitus in humans. In gerbils, we investigated brain activation after systemic application of sodium salicylate or exposure to loud noise, both known to be reliable tinnitus-inductors. Brains were screened for neurons containing the c-fos protein. After salicylate injections, auditory cortex was the only auditory area with consistently increased numbers of immunoreactive neurons compared to controls. Exposure to impulse noise led to prolonged c-fos expression in auditory cortex and dorsal cochlear nucleus. After both manipulations c-fos expression was increased in the amygdala, in thalamic midline, and intralaminar areas, in frontal cortex, as well as in hypothalamic and brainstem regions involved in behavioral and physiological defensive reactions. Activation of these non-auditory areas was attributed to acute stress, to aversive-affective components and autonomous reactions associated with the treatments and a resulting tinnitus. The present findings are in accordance with former results that provided evidence for suppressed activation in auditory midbrain but enhanced activation of the auditory cortex after injecting high doses of salicylate. In addition, our present results provide evidence that acute stress coinciding with a disruption of hearing may evoke activation of the auditory cortex. We interpret these results in favor of our model of central tinnitus generation.

Sexual conflict and polyspermy under sperm-limited conditions: in situ evidence from field simulations with the free-spawning marine echinoid Evechinus chloroticus.

For free-spawning organisms that release gametes into the sea, sperm limitation (too few sperm to fertilize all eggs) is a major factor limiting reproductive success. Given such circumstances, the presence of several mechanisms to prevent polyspermy (too many sperm) may seem paradoxical; however, a growing body of data suggests that natural fertilization levels, though variable, can routinely be high. Under such conditions, polyspermy is much more likely. The tension between sperm limitation and polyspermy represents sexual conflict because males, in competing to fertilize as many eggs as possible, can impose lethal costs on eggs if multiple sperm gain entry. Here we present data for a marine invertebrate indicating high levels of polyspermy under sperm-limited conditions. When the sea urchin Evechinus chloroticus was induced to spawn in situ, mean rates of polyspermy were [Formula: see text], and polyspermy was recorded at rates as high as 62.7%. Polyspermy was nearly always present, even when fertilization rates were <50%, confirming predictions that it should be present under sperm-limited conditions. Both sperm limitation and polyspermy imposed substantial reproductive costs, and we conclude that both sexual conflict related to polyspermy and sperm limitation have been simultaneous strong selective forces shaping the evolution of reproductive traits in the sea.

Effect of energy source and xylanase addition on energy metabolism, performance, chemical body composition and total body electrical conductivity (TOBEC) of broilers.

Three diets containing either no supplemented fat (LF), 12% soybean oil (SO) or 12% coconut oil (CO) were fed to broilers to examine energy utilization in two experiments. Heat production and energy retained as fat and protein were measured in the first experiment using a respiration technique in combination with C- and N-balance and controlled (pair-fed) feeding conditions. Growth performance, carcass composition, chemical body composition and total body electrical conductivity (TOBEC) were evaluated in a second experiment under ad libitum feeding conditions (from hatching to day 35). Moreover, each of the three diet types was tested with or without the addition of a xylanase-containing enzyme preparation in the growth experiment. Energy utilization (experiment 1), expressed as the ratio between total retained energy and metabolizable energy intake, amounted to 0.33, 0.36 and 0.39 in LF-, SO- and CO-fed groups, respectively. Applying ad libitum feeding conditions in the second experiment caused a significant reduction in feed intake and weight gain in broilers fed the CO-diet. The feed-to-gain ratio was significantly lower in birds given the fat-supplemented diets. The highest degree of fatness as indicated by the highest percentage of abdominal and visceral fat and by highest total fat content was found in birds fed the CO-diet. The higher the body protein content and the lower the body fat content, the higher the TOBEC value should be. This was confirmed when LF-fed broilers were compared to their CO-fed counterparts. However, fat type seemed to be related to TOBEC values since SO-fed broilers had similar TOBEC values as CO-fed birds, whereas chemical body composition was comparable to LF-fed broilers. Xylanase addition significantly increased weight gain up to 21 days of age and decreased the feed-to-gain ratio slightly, whereas none of the other parameters were influenced by this treatment. An interaction between energy source and enzyme supplementation was not observed. It is concluded that feeding of coconut oil was most effective in terms of energy retention, but failed to induce an adequate performance under ad libitum feeding conditions due to a reduced voluntary feed intake. TOBEC measurements in relation to chemical body composition were rather inconclusive.

A subdominant CD8(+) cytotoxic T lymphocyte (CTL) epitope from the Plasmodium yoelii circumsporozoite protein induces CTLs that eliminate infected hepatocytes from culture.

Previous studies indicated that the Plasmodium yoelii circumsporozoite protein (PyCSP) 57-70 region elicits T cells capable of eliminating infected hepatocytes in vitro. Herein, we report that the PyCSP58-67 sequence contains an H-2(d) binding motif, which binds purified K(d) molecules in vitro with low affinity (3, 267 nM) and encodes an H-2(d)-restricted cytotoxic T lymphocyte (CTL) epitope. Immunization of BALB/c mice with three doses of a multiple antigen peptide (MAP) construct containing four branches of amino acids 57 to 70 linked to a lysine-glycine core [MAP4(PyCSP57-70)] and Lipofectin as the adjuvant induced both T-cell proliferation and a peptide-specific CTL response that was PyCSP59-67 specific, H-2(d) restricted, and CD8(+) T cell dependent. Immunization with either DNA encoding the PyCSP or irradiated sporozoites demonstrated that this CTL epitope is subdominant since it is not recognized in the context of whole CSP immunization. The biological relevance of this CTL response was underlined by the demonstration that it could mediate genetically restricted, CD8(+)- and nitric-oxide-dependent elimination of infected hepatocytes in vitro, as well as partial protection of BALB/c mice against sporozoite challenge. These findings indicate that subdominant epitopes with low major histocompatibility complex affinity can be used to engineer epitope-based vaccines and have implications for the selection of epitopes for subunit-based vaccines.

Pneumonectomy in cystic fibrosis.

A 17-year-old boy and a 12-year-old girl with cystic fibrosis (forced expiratory volume in 1 sec, 36% and 14% of predicted values, respectively) developed severe right-sided lung infections with abscess formations and complete atelectases unresponsive to medical therapy. In both patients, unilateral emergency pneumonectomy resulted in rapid clinical improvement. Despite her severe underlying lung disease, the girl experienced a remarkable increase in quality of life; 2 years after surgery, she died from respiratory failure. The male patient has now survived for 4 years, and lung transplantation still remains a therapeutic option for him. We believe that pneumonectomy is a valuable rescue therapy for patients with cystic fibrosis and intractable unilateral lung infections who are at high risk of dying while waiting for lung transplantation.

Pan DR binding sequence provides T-cell help for induction of protective antibodies against Plasmodium yoelii sporozoites.

Pan-DR epitope (PADRE) peptides have demonstrated the capacity to deliver help for antibody responses in vivo. They were also found, fortuitously, to be able to provide significant helper T-cell activity in vivo. This suggested that linear constructs, containing the PADRE epitope, might be as efficient at generating an immune response as large multivalent antigens. Plasmodium falciparum and P. yoelii PADRE constructs were capable of inducing a high titre IgG antibody response that recognized intact sporozoites. We now report that these antibodies can inhibit sporozoite invasion of hepatocytes in vitro and that mice immunized with the PyCSP-PADRE linear construct were protected when challenged with P. yoelii sporozoites.

The optimization of helper T lymphocyte (HTL) function in vaccine development.

Helper T lymphocyte (HTL) responses play an important role in the induction of both humoral and cellular immune responses. Therefore, HTL epitopes are likely to be a crucial component of prophylactic and immunotherapeutic vaccines. For this reason, Pan DR helper T cell epitopes (PADRE), engineered to bind most common HLA-DR molecules with high affinity and act as powerful immunogens, were developed. Short linear peptide constructs comprising PADRE and Plasmodium-derived B cell epitopes induced antibody responses comparable to more complex multiple antigen peptides (MAP) constructs in mice. These antibody responses were composed mostly of the IgG subclass, reactive against intact sporozoites, inhibitory of schizont formation in liver invasion assays, and protective against sporozoite challenge in vivo. The PADRE HTL epitope has also been shown to augment the potency of vaccines designed to stimulate a cellular immune response. Using a HBV transgenic murine model, it was found that CTL tolerance was broken by PADRE-CTL epitope lipopeptide, but not by a similar construct containing a conventional HTL epitope. There are a number of prophylactic vaccines that are of limited efficacy, require multiple boosts, and/or confer protection to only a fraction of the immunized population. Also, in the case of virally infected or cancerous cells, new immunotherapeutic vaccines that induce strong cellular immune responses are desirable. Therefore, optimization of HTL function by use of synthetic epitopes such as PADRE or pathogen-derived, broadly crossreactive epitopes holds promise for a new generation of highly efficacious vaccines.

Geographic distribution and clinical description of leishmaniasis cases in Peru.

Studies were conducted from 1986 through 1993 to further define the geographic distribution and relative importance of different species of Leishmania as a cause of leishmaniasis in Peru. Patients with a clinical diagnosis of cutaneous and/or mucosal or diffuse cutaneous leishmaniasis were enrolled at the Naval Medical Research Institute Detachment (NAMRID) Laboratory in Lima, the Tropical Disease Clinic at San Marcos University Daniel A. Carrión, the Central Military Hospital, and a Ministry of Health hospital in Cusco, Peru. Clinical features, lesion aspirates, and biopsy tissue were obtained from each patient. All specimens were collected and assayed separately, including multiple specimens from some of the same patients for Leishmania parasites by inoculating aliquots of either aspirates or biopsy tissue suspensions onto Senekji's blood agar medium. Stocks of Leishmania isolates were used to prepare promastigotes to produce extracts for identifying the Leishmania species by the cellulose acetate electrophoresis enzyme technique. A total of 351 isolates of Leishmania were obtained from 350 patients who were infected primarily in the low and high jungle of at least 15 different Departments of Peru. Of the 351 isolates, 79% were identified as L. (V.) braziliensis, 7% as L. (V.) guyanensis, 10% as L. (V.) peruviana, 2% as L. (V.) lainsoni, and 1.7% as L. (L.) amazonensis. The clinical form of disease varied depending on the species of Leishmania, with L. (V.) braziliensis being associated most frequently with cutaneous, mucosal ulcers and mixed cutaneous and mucosal disease, and L. (V) peruviana, L. (V.) guyanensis, L. (V.) lainsoni with cutaneous lesions. Leishmania (L.) amazonensis was isolated from six patients, three with cutaneous lesions, one with mucosal lesions, and two with diffuse cutaneous lesions. Among all of the leishmaniasis cases, males were affected more frequently, and cases occurred among patients less than 10 to more than 51 years of age. These data further defined the geographic distribution and the relative frequency of Leishmania species associated with different clinical forms of leishmaniasis in Peru.

Efficacy of sodium stibogluconate alone and in combination with allopurinol for treatment of mucocutaneous leishmaniasis.

A randomized, open, controlled clinical trial was designed to evaluate the efficacy, tolerance, and safety of sodium stibogluconate plus allopurinol and sodium stibogluconate alone as treatment of patients with mucocutaneous leishmaniasis. In phase 1 of the study, all 22 patients with severe disease had improvement of their lesions, but only two had clinical cure (both of these patients received sodium stibogluconate alone). In phase 2, which included 59 patients with moderate disease, the cure rate among sodium stibogluconate recipients was 75% (21 of 28) compared with 63.6% (14 of 22) among the sodium stibogluconate plus allopurinol recipients. The rates of clinical adverse events were similar among both groups. Thrombocytopenia was more frequent in the sodium stibogluconate plus allopurinol recipients, but the difference was not statistically significant. Eight patients (two sodium stibogluconate recipients and six sodium stibogluconate plus allopurinol recipients) withdrew from the study because of severe thrombocytopenia. In this study, the addition of allopurinol to sodium stibogluconate provided no clinical benefit as treatment of mucocutaneous leishmaniasis.

Induction of protective CTL responses against the Plasmodium yoelii circumsporozoite protein by immunization with peptides.

To determine the optimum combination, concentration, and formulation of synthetic peptides and adjuvants to induce protective CTL responses against the Plasmodium yoelii circumsporozoite protein (PyCSP), BALB/c mice were immunized with linear and multiple antigen peptides (MAP) including PyCSP CTL and Th epitopes in Montanide's ISA51, Lipofectin, and Lipofectamine. An H-2K(d)-restricted PyCSP CTL epitope, SYVPSAEQI (amino acids (aa) 280-288), recognized by protective CTL clones, was included in the following peptides: a 9-aa linear peptide (SYVPSAEQI; PyCSP9), a 20-aa linear peptide (aa 280-299; SYVPSAEQILEFVKQISSL; PyCSP20), a MAP containing four branches of PyCSP20 (MAP(280-299)), and a linear peptide and a MAP(MAP(280-299)p2p30) in which PyCSP20 was colinearly synthesized with two universal Th epitopes from tetanus toxin (p2p30). A MAP containing the PyCSP Th epitope (aa 57-70; KIYNRNIVNRLLGD) was included in some experiments. The highest specific lytic activity against peptide-pulsed target cells was obtained with splenocytes from mice immunized with three doses at 3-wk intervals of MAP(280-299)p2p30 in Lipofectin or Lipofectamine. Forty percent of the mice immunized with MAP(280-299)p2p30 and Lipofectin were protected against sporozoite challenge. Immunization with CTL and Th epitopes co-linearly synthesized in a MAP induced significantly better CTL than did immunization with the same sequence as a linear peptide, or immunization with a mixture of two individual MAPs, one with the CTL epitope and the second with the Th epitope.

The use of and familiarity with neurological eponyms at the close of the 20th century by Dutch neurologists. An inventory.

In order to get an impression on the opinion of the use of neurological eponyms we sent questionnaires on 205 eponyms to 850 members of the Netherlands Association for Neurology. The responses by 256 (30%) were analyzed. A positive correlation was found between age and the knowledge of eponyms. The best known eponyms belong to category II (tests and manoeuvres). Surprisingly, many of the responding colleagues did not prefer descriptive terms to eponyms: 57% of the eponyms were preferred by more than 50% of the respondents.

Salicylate evokes c-fos expression in the brain stem: implications for tinnitus.

Subjective tinnitus, a distracting internal noise is experienced by humans and animals. Mongolian gerbils were treated with salicylate as a tinnitus-evoking agent. After salicylate treatment, c-fos expression in auditory brain stem nuclei was as low as after saline treatment (control). Pronounced differences between groups were found, however, in areas susceptible to stress, with many immunoreactive cells in the locus coeruleus, the midbrain periaqueductal grey and the lateral parabrachial nucleus of salicylate-treated animals. These results suggest that salicylate may evoke tinnitus through a combined effect on auditory and non-auditory brain nuclei. While activity in auditory brain stem nuclei is reduced, stress-susceptible areas are activated. It seems possible that the interaction of these effects at particular locations of the brain causes tinnitus.