A silicon carbide array for electrocorticography and peripheral nerve recording.

OBJECTIVE: Current neural probes have a limited device lifetime of a few years. Their common failure mode is the degradation of insulating films and/or the delamination of the conductor-insulator interfaces. We sought to develop a technology that does not suffer from such limitations and would be suitable for chronic applications with very long device lifetimes. APPROACH: We developed a fabrication method that integrates polycrystalline conductive silicon carbide with insulating silicon carbide. The technology employs amorphous silicon carbide as the insulator and conductive silicon carbide at the recording sites, resulting in a seamless transition between doped and amorphous regions of the same material, eliminating heterogeneous interfaces prone to delamination. Silicon carbide has outstanding chemical stability, is biocompatible, is an excellent molecular barrier and is compatible with standard microfabrication processes. MAIN RESULTS: We have fabricated silicon carbide electrode arrays using our novel fabrication method. We conducted in vivo experiments in which electrocorticography recordings from the primary visual cortex of a rat were obtained and were of similar quality to those of polymer based electrocorticography arrays. The silicon carbide electrode arrays were also used as a cuff electrode wrapped around the sciatic nerve of a rat to record the nerve response to electrical stimulation. Finally, we demonstrated the outstanding long term stability of our insulating silicon carbide films through accelerated aging tests. SIGNIFICANCE: Clinical translation in neural engineering has been slowed in part due to the poor long term performance of current probes. Silicon carbide devices are a promising technology that may accelerate this transition by enabling truly chronic applications.

Rational design of nitrofuran derivatives: Synthesis and valuation as inhibitors of Trypanosoma cruzi trypanothione reductase.

The rational design and synthesis of a series of 5-nitro-2-furoic acid analogues are presented. The trypanocidal activity against epimastigote forms of Trypanosoma cruzi and the toxic effects on human HeLa cells were tested. Between all synthetic compounds, three of thirteen had an IC50 value in the range of Nfx, but compound 13 exhibited an improved effect with an IC50 of 1.0 ± 0.1 µM and a selective index of 70 in its toxicity against HeLa cells. We analyzed the activity of compounds 8, 12 and 13 to interfere in the central redox metabolic pathway in trypanosomatids, which is dependent of reduced trypanothione as the major pivotal thiol. The three compounds behaved as better inhibitors of trypanothione reductase than Nfx (Ki values of 118 µM, 61 µM and 68 µM for 8, 12 and 13, respectively, compared with 245 µM for Nfx), all following an uncompetitive enzyme inhibition pattern. Docking analysis predicted a binding of inhibitors to the enzyme-substrate complex with binding energy calculated in-silico that supports such molecular interaction.

Outbreak of Notozothecium bethae (Monogenea: Dactylogyridae) in Myleus schomburgkii (Actinopterygii: Characiformes) cultured in the Peruvian Amazon.

The presence of Notozothecium bethae was investigated in 76 black band myleus (Myleus schomburgkii [Actinopterygii: Charasiformes]) born and kept in captivity in two semi-intensive breeding cages in the northern region of Peru. Among the 76 cultivated specimens of M. schomburgkii examined in the present study, 100 % had monogenean on the gill and the parasites were identified as Notozothecium bethae. During the survey no bacteria was isolated, and no protozoan or other metazoan parasites were found. The prevalence of N. bethae remained constant throughout the present study. Mean intensity of N. bethae in the months of April and May was exceptionally high in both facilities. The massive infection of N. bethae on the gills of M. schomburgkii was associated with mortality. This is the first report of N. bethae in M. schomburgkii born in captivity and cultured in the Amazon region. The mortality due the presence of this parasite emphasise the need for disease control strategies of cultured M. schomburgkii.

The reliability and accuracy of two methods for proximal caries detection and depth on directly visible proximal surfaces: an in vitro study.

This study aimed to determine the reliability and accuracy of the ICDAS and radiographs in detecting and estimating the depth of proximal lesions on extracted teeth. The lesions were visible to the naked eye. Three trained examiners scored a total of 132 sound/carious proximal surfaces from 106 primary teeth and 160 sound/carious proximal surfaces from 140 permanent teeth. The selected surfaces were first scored visually, using the 7 classes in the ICDAS. They were then assessed on radiographs using a 5-point classification system. Reexaminations were conducted with both scoring systems. Teeth were then sectioned and the selected surfaces histologically classified using a stereomicroscope (×5). Intrareproducibility values (weighted kappa statistics) for the ICDAS for both primary and permanent teeth were >0.9, and for the radiographs between 0.6 and 0.8. Interreproducibility values for the ICDAS were >0.85, for the radiographs >0.6. For both primary and permanent teeth, the accuracy of each examiner (Spearman's correlation coefficient) for the ICDAS was ≥0.85, and for the radiographs ≥0.45. Corresponding data were achieved when using pooled data from the 3 examiners for both the ICDAS and the radiographs. The associations between the 2 detection methods were measured to be moderate. In particular, the ICDAS was accurate in predicting lesion depth (histologically) confined to the enamel/outer third of the dentine versus deeper lesions. This study shows that when proximal lesions are open for inspection, the ICDAS is a more reliable and accurate method than the radiograph for detecting and estimating the depth of the lesion in both primary and permanent teeth.

Effects of ayahuasca on binocular rivalry with dichoptic stimulus alternation.

RATIONALE: During binocular rivalry, two incompatible images are presented to each eye and these monocular stimuli compete for perceptual dominance, with one pattern temporarily suppressed from awareness. One variant of stimulus presentation in binocular rivalry experiments is dichoptic stimulus alternation (DSA), when stimuli are applied to the eyes in rapid reversals. There is preliminary report that in contrast with healthy controls, schizophrenic patients can maintain binocular rivalry even at very high DSA rates. OBJECTIVE: The study was undertaken to investigate whether binocular rivalry survives high rates of DSA induced by the South American hallucinogenic beverage ayahuasca. METHODS: Ten individuals who were participating in ayahuasca ceremonials were requested to volunteer for binocular rivalry tests (DSA=0, 3.75, 7.5, 15 and 30 Hz) without and after drinking the brew. RESULTS: Ingestion of ayahuasca increased mean dominance periods both in standard binocular rivalry conditions (no DSA) and tests with DSA. At higher DSA rates (15 and 30 Hz) the total length of dominance periods was longer on the brew. CONCLUSION: It is discussed that ayahuasca-induced survival of binocular rivalry at high DSA rates may be related to slow visual processing and increased mean dominance periods may result from hallucinogen-induced alteration of gamma oscillations in the visual pathways.

The concept of plants as teachers among four mestizo shamans of Iquitos, northeastern Peru.

In the city of Iquitos and its vicinity there is even today a rich tradition of folk medicine. Practitioners, some of whom qualify as shamans, make an important contribution to the psychosomatic health of the inhabitants of this area. Among them there are those called vegetalistas or plant specialists and who use a series of plants called doctores or plant teachers. It is their belief that if they fulfill certain conditions of isolation and follow a prescribed diet, these plants are able to "teach" them how to diagnose and cure illnesses, how to perform other shamanic tasks, usually through magic melodies or icaros, and how to use medicinal plants. Four shamans were questioned about the nature and identity of these magic plants, what are the dietary prescriptions to be followed, how the transmission of shamanic power takes place, the nature of their helping spirits, and the function of the magic melodies or icaros given to them by the plant teachers.

The healing practices of a Peruvian shaman.

The use of psychotropic plants among the mestizo population of the northwestern Amazon has already been the subject of some research. However, the field is far from fully investigated. Practitioners locally known by the name of "vegetalistas" or simply "maestros" have preserved considerable knowledge of plant lore, and still today contribute substantially to the health care of both rural and urban population. The present paper is based on field work with one particular such practitioner, Don Emilio Andrade Gómez, a 65-year-old shaman who lives in the vicinity of Iquitos (3 degrees 50S 73 degrees 15W), northeastern Peru. Some of the basic ideas of his cosmovision are presented. Special attention is given to the concept of "doctor" or "plant teacher", applied to certain plants which are supposed to "teach medicine", if the appropriate conditions of isolation and diet are observed. Some of these plants are added to the hallucinogenic beverage known in the region by the Quéchua name ayahuasca, made from the stem of Banisteriopsis species, and one or several additives. During the period of isolation the spirits of these plants teach the initiate certain melodies or "icaros" that he will later use when practising his shamanistic activities. During field work in 1981 and 1982 the author collected various specimens of "plant teachers", part of which have now been identified, and are also presented.