Individual differences among grapheme-color synesthetes: brain-behavior correlations

Grapheme-color synesthetes experience specific colors associated with specific number or letter characters. To determine the neural locus of this condition, we compared behavioral and fMRI responses in six grapheme-color synesthetes to control subjects. In our behavioral experiments, we found that a subject's synesthetic experience can aid in texture segregation (experiment 1) and reduce the effects of crowding (experiment 2). For synesthetes, graphemes produced larger fMRI responses in color-selective area human V4 than for control subjects (experiment 3). Importantly, we found a correlation within subjects between the behavioral and fMRI results; subjects with better performance on the behavioral experiments showed larger fMRI responses in early retinotopic visual areas (V1, V2, V3, and hV4). These results suggest that grapheme-color synesthesia is the result of cross-activation between grapheme-selective and color-selective brain areas. The correlation between the behavioral and fMRI results suggests that grapheme-color synesthetes may constitute a heterogeneous group.     

Neurocognitive mechanisms of synesthesia

Synesthesia is a condition in which stimulation of one sensory modality causes unusual experiences in a second, unstimulated modality. Although long treated as a curiosity, recent research with a combination of phenomenological, behavioral, and neuroimaging methods has begun to identify the cognitive and neural basis of synesthesia. Here, we review this literature with an emphasis on grapheme-color synesthesia, in which viewing letters and numbers induces the perception of colors. We discuss both the substantial progress that has been made in the past fifteen years and some open questions. In particular, we focus on debates in the field relating to the neural basis of synesthesia, including the relationship between synesthesia and attention and the role of meaning in synesthetic colors. We propose that some, but probably not all, of these differences can be accounted for by differences in the synesthetes studied and discuss some methodological implications of these individual differences.     

Oxidized LDL induces mitochondrially associated reactive oxygen/nitrogen species formation in endothelial cells

Exposure of cells to complex mixtures of oxidized lipids such as those found in oxidized low-density lipoprotein (oxLDL) induce reactive oxygen and nitrogen species (ROS/RNS) formation. The source of the ROS/RNS within cells is unknown; it is thought they may be involved in redox cell signaling. Although this possibility was initially overlooked, it is becoming clear that mitochondria, which are a source of superoxide and hydrogen peroxide, may play a critical role in the response of cells on exposure to oxidized lipids. In this study, we tested the possibility that mitochondria are a potential source of oxLDL-dependent formation of ROS/RNS in endothelial cells. Using confocal microscopy, we demonstrated that a significant proportion of oxLDL-dependent dichlorodihydrofluorescein (DCF) fluorescence is colocalized to mitochondria. In support of this concept, rho0 endothelial cells showed a substantial decrease in ROS/RNS formation stimulated by oxLDL. In contrast, mostly nonmitochondrial DCF fluorescence was detected in cells exposed to an extracellular source of hydrogen peroxide. The exposure of cells to a nitric oxide synthase inhibitor and urate resulted in a decrease in oxLDL-induced DCF fluorescence that was restored by addition of nitric oxide donors to the medium. Taken together, these results suggest that oxLDL-dependent DCF fluorescence is mitochondrially associated and may be due to the formation of peroxynitrite.     

Differential regulation of endoplasmic reticulum structure through VAP-Nir protein interaction

The endoplasmic reticulum (ER) exhibits a characteristic tubular structure that is dynamically rearranged in response to specific physiological demands. However, the mechanisms by which the ER maintains its characteristic structure are largely unknown. Here we show that the integral ER-membrane protein VAP-B causes a striking rearrangement of the ER through interaction with the Nir2 and Nir3 proteins. We provide evidence that Nir (Nir1, Nir2, and Nir3)-VAP-B interactions are mediated through the conserved FFAT (two phenylalanines (FF) in acidic tract) motif present in Nir proteins. However, each interaction affects the structural integrity of the ER differently. Whereas the Nir2-VAP-B interaction induces the formation of stacked ER membrane arrays, the Nir3-VAP-B interaction leads to a gross remodeling of the ER and the bundling of thick microtubules along the altered ER membranes. In contrast, the Nir1-VAP-B interaction has no apparent effect on ER structure. We also show that the Nir2-VAP-B interaction attenuates protein export from the ER. These results demonstrate new mechanisms for the regulation of ER structure, all of which are mediated through interaction with an identical integral ER-membrane protein.     

Isolation and molecular characterization of Toxoplasma gondii from chickens from Sri Lanka

The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 100 free-range chickens (Gallus domesticus) from Sri Lanka was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT). Antibodies were found in 39 chickens with titers of 1:5 in 8, 1:10 in 8, 1:20 in 4, 1:40 in 5, 1:80 in 5, 1:160 in 5, 1:320 in 2, 1:640 or more in 2. Hearts and brains of 36 chickens with MAT titers of 1:5 or more were bioassayed in mice. Tissues of 3 chickens with doubtful titers of 1:5 were pooled and fed to a cat; the cat shed T. gondii oocysts in its feces. Tissues from 61 chickens with titers of less than 1:5 were pooled and fed to 2 T. gondii-free cats; the cats did not shed oocysts. Toxoplasma gondii was isolated from 11 of 36 seropositive chickens by bioassay in mice. All 12 T. gondii isolates were avirulent for mice. Genotyping of 12 isolates using the SAG2 locus indicated that 6 were type III, and 6 were type II. This is the first report of genetic characterization of T. gondii from any host in Sri Lanka.     

A comparison of several serologic tests to detect antibodies to Toxoplasma gondii in naturally exposed bottlenose dolphins (Tursiops truncatus)

Toxoplasma gondii infection in marine mammals is intriguing and indicative of contamination of the ocean environment and coastal waters with oocysts. In a previous study, 138 of 141 (97.8%) bottlenose dolphins (Tursiops truncatus) from the coasts of Florida and California had antibodies to T. gondii by the modified agglutination test (MAT). Although the MAT has been found to be highly sensitive and specific for T. gondii antibodies from several species of terrestrial animals, it has not yet been validated for T. gondii infections in marine mammals. Furthermore, T. gondii has yet not been isolated from dolphins. In the present study, sera from 146 (60 from the 2004 samples and 86 from the 2003 samples) T. truncatus from the coastal areas of South Carolina and Florida were tested for antibodies to T. gondii. Sera from 2004 were tested by the MAT, the indirect fluorescent antibody test (IFAT), the Sabin-Feldman dye test (DT), an indirect hemagglutination test (IHAT), an enzyme-linked immunosorbent assay (ELISA), and Western blot. All 60 dolphins were seropositive, with MAT titers of 1:20 in 3, 1:40 in 19, 1:80 in 29, 1:160 in 2, 1:1,280 in 3, 1:2,560 in 2, and 1:5,120 or higher in 2, and these results were confirmed in another laboratory. The DT titers of these dolphins were <1:10 in 53, 1:800 in 3, 1:1,600 in 2, and 1:3,200 in 2. The IHAT titers were <1:64 in 52, 1:128 in 1, 1:512 in 2, and 1:2,048 in 5. The IFAT titers were <1:20 in 3, 1:20 in 11, 1:40 in 36, 1:80 in 2, 1:160 in 1, and 1:320 or higher in 7. All 7 DT-positive dolphins had high MAT titers, but 2 were negative by the IHAT. Western blot results closely followed MAT results; ELISA results matched MAT results, which were 1:40 or higher. In sera from the 2003 samples, MAT antibodies were found in 86 of 86 dolphins with titers of 1:25 in 29, 1:50 in 23, 1:100 in 27, 1:200 in 3, 1:1,600 in 1, and 1:3,200 in 3; these sera were not tested by other means. Overall, MAT antibodies were found in all 146 dolphin sera tested. Because marine mammals are considered sentinel animals indicative of contamination of the coastal and marine waters by T. gondii oocysts, serologically positive infections need to be validated by the detection of T. gondii organisms in the tissues of seropositive animals.     

Interaction of Kazal-type inhibitor domains with serine proteinases: biochemical and structural studies

The interaction of domains of the Kazal-type inhibitor protein dipetalin with the serine proteinases thrombin and trypsin is studied. The functional studies of the recombinantly expressed domains (Dip-I+II, Dip-I and Dip-II) allow the dissection of the thrombin inhibitory properties and the identification of Dip-I as a key contributor to thrombin/dipetalin complex stability and its inhibitory potency. Furthermore, Dip-I, but not Dip-II, forms a complex with trypsin resulting in an inhibition of the trypsin activity directed towards protein substrates. The high resolution NMR structure of the Dip-I domain is determined using multi-dimensional heteronuclear NMR spectroscopy. Dip-I exhibits the canonical Kazal-type fold with a central alpha-helix and a short two-stranded antiparallel beta-sheet. Molecular regions essential for inhibitor complex formation with thrombin and trypsin are identified. A comparison with molecular complexes of other Kazal-type thrombin and trypsin inhibitors by molecular modeling shows that the N-terminal segment of Dip-I fulfills the structural prerequisites for inhibitory interactions with either proteinase and explains the capacity of this single Kazal-type domain to interact with different proteinases.     

Odontoblast cells immortalized by telomerase produce mineralized dentin-like tissue both in vitro and in vivo

The formation of dentin provides one well accepted paradigm for studying mineralized tissue formation. For the assembly of dentin, several cellular signaling pathways cooperate to provide neural crest-derived mesenchymal cells with positional information. Further, "cross-talk" between signaling pathways from the mesenchymal derived odontoblast cells and the epithelially derived ameloblasts during development is responsible for the formation of functional odontoblasts. These intercellular signals are tightly regulated, both temporally and spatially. When isolated from the developing tooth germ, odontoblasts quickly lose their potential to maintain the odontoblast-specific phenotype. Therefore, generation of an odontoblast cell line would be a valuable reproducible tool for studying the modulatory effects involved in odontoblast differentiation as well as the molecular events involved in mineralized dentin formation. In this study an immortalized odontoblast cell line, which has the required biochemical machinery to produce mineralized tissue in vitro, has been generated. These cells were implanted into animal models to determine their in vivo effects on dentin formation. After implantation, we observed a multistep, programmed cascade of gene expression in the exogenous odontoblasts as the dentin formed de novo. Some of the genes expressed include the dentin matrix proteins 1, 2, and 3, which are extracellular matrix molecules responsible for the ultimate formation of mineralized dentin. The biological response was also examined by histology and radiography and confirmed for mineral deposition by von Kossa staining. Thus, a transformed odontoblast cell line was created with high proliferative capacity that might ultimately be used for the regeneration and repair of dentin in vivo.