Uroguanylin induces electroencephalographic spikes in rats.

Uroguanylin (UGN) is an endogenous peptide that acts on membrane-bound guanylate cyclase receptors of intestinal and renal cells increasing cGMP production and regulating electrolyte and water epithelial transport. Recent research works demonstrate the expression of this peptide and its receptor in the central nervous system. The current work was undertaken in order to evaluate modifications of electroencephalographic spectra (EEG) in anesthetized Wistar rats, submitted to intracisternal infusion of uroguanylin (0.0125 nmoles/min or 0.04 nmoles/min). The current observations demonstrate that 0.0125 nmoles/min and 0.04 nmoles/min intracisternal infusion of UGN significantly enhances amplitude and frequency of sharp waves and evoked spikes (p = 0.03). No statistical significance was observed on absolute alpha and theta spectra amplitude. The present data suggest that UGN acts on bioelectrogenesis of cortical cells by inducing hypersynchronic firing of neurons. This effect is blocked by nedocromil, suggesting that UGN acts by increasing the activity of chloride channels.

Catechin attenuates behavioral neurotoxicity induced by 6-OHDA in rats.

This study was designed to investigate the beneficial effect of catechin in a model of Parkinson's disease. Unilateral, intrastriatal 6-hydroxydopamine (6-OHDA)-lesioned rats were pretreated with catechin (10 and 30 mg/kg) by intraperitoneal (i.p.) injection 2h before surgery and for 14 days afterwards. After treatments, apomorphine-induced rotations, locomotor activity, working memory and early and late aversive memories were evaluated. The mesencephalon was used to determine the levels of monoamines and measurement of glutathione (GSH). Immunohistochemical staining was also used to evaluate the expression of tyrosine hydroxylase (TH) in mesencephalic and striatal tissues. Catechin administration attenuated the increase in rotational behavior and the decrease in locomotor activity observed in lesioned rats. Although catechin did not rescue the impairment of late aversive memory, it protected the animals against 6-OHDA-induced working memory deficits. Furthermore, catechin treatment restored GSH levels, and significantly increased dopamine and DOPAC content, and TH-immunoreactivity in 6-OHDA-lesioned rats. Catechin protected 6-OHDA-lesioned rats due to its antioxidant action, indicating that it could be useful as an adjunctive therapy for the treatment of Parkinson's disease.

[The concept of space in epidemiological research]. / A concepção de espaço na investigação epidemiológica.

Epidemiology's conceptual and methodological shortcomings have placed constraints on the study of health phenomena related to human communities, thus posing a challenge to the field. This paper presents some basic principles resulting from the observation of the field of geography in defining its object - space - and the application of this object to medicine and epidemiology. Such principles state the pertinence of a conceptual and methodological strategy focusing on an approach to geographic space as expressing the population's living conditions. Application of this concept to epidemiological studies is still limited, although such proposals have already been developed in other areas of knowledge. Ecological studies, whose unit of analysis is the group, and the ecological model, based on the idea of an inter-relationship of factors, if improved, could become a promising alternative in this direction. The authors emphasize that researchers should have wholeness as their scientific reference in order to guarantee the non-separation of the complex interactive processes determining health phenomena in the population.

Evaluation of three commercial enzyme-linked immunosorbent assays for diagnosis of Chagas' disease.

Chagas' disease is a common cause of morbidity in Latin American countries. In Brazil, naturally occurring transmission of its etiologic agent, Trypanosoma cruzi, has been almost completely abolished through effective control programs aimed at the triatomid insect vector. Thus, transfusion of blood from infected donors has become the major route for contracting Chagas' disease due to the socioeconomically motivated migration of residents from areas where the disease is endemic to the larger urban centers. Therefore, the employment of screening tests is mandatory for all blood banks throughout the country. We compared the diagnostic performances of three commercially available screening assays used in routine testing in Brazilian blood banks: the Abbott Chagas antibody enzyme immunoassay (Abbott Laboratórios do Brasil, São Paulo), the BIOELISACRUZI kit (Biolab-Mérieux, Rio de Janeiro, Brazil), and the BIOZIMA Chagas kit (Polychaco S.A.I.C., Buenos Aires, Argentina). The evaluation was performed with sera obtained from chagasic patients and healthy residents of four different areas in Brazil where Chagas' disease is either endemic or emergent and where clinical manifestations of the disease and circulating parasite strains vary. The results obtained with each kit were compared to matched in-house enzyme-linked immunosorbent assay and immunofluorescence assay data obtained for each sample. Depending on the area under investigation, the three commercial kits produced specificity values between 93.3 and 100.0%, sensitivity values between 97.7 and 100%, and accuracies ranging from 93.6 to 100.0%.

Lipid extraction attenuates the calcific degeneration of bovine pericardium used in cardiac valve bioprostheses.

Bovine pericardial bioprostheses frequently fail due to dystrophic calcification. Since (a) recent studies indicate that membrane-associated complexed acidic phospholipids play an important role in the process of both physiologic and pathologic calcification, and (b) cytoplasmic organelles and plasma membrane of interstitial cells seem to serve as initial sites of calcific degeneration of bioprosthetic bovine pericardial tissue, this investigation was undertaken to evaluate whether, and if so, to what extent, the mineralization of valve tissue could be attenuated by previous lipid extraction. Pretreatment of glutaraldehyde-preserved bovine pericardium with acidified sulphuric ether (pH 3.0-4.0) attenuated calcification significantly: 28 days after subcutaneous implantation in young rats the degree of mineral deposition was approximately equal to typical 7 days implants in this model. The mechanism of this beneficial effect is suggested to be due to partial extraction of tissue phospholipids, as demonstrated by electron microscopy, thus reducing the number of available sites for deposition of hydroxyapatite crystals. In addition, and importantly, the present results indicate that any attempt to reduce cardiac valve bioprosthesis mineralization will have to take into account the role of lipids and, particularly, the membranous phospholipids in the calcification mechanism.

Calcific degeneration of pericardial valvular xenografts implanted subcutaneously in rats.

Tissue valve dystrophic calcification, resulting in hemodynamic regurgitation and/or stenosis, is the most serious complication when bioprosthetic heart valves are concerned. The objective of this investigation was to define morphologically the sequential development of calcific deposits in pericardial tissue cusps of unimplanted cardiac bioprostheses implanted subcutaneously in rats. Small samples of pericardium were implanted subcutaneously in the dorsal area of young rats weighing 60-80 g. The animals were selected randomly and sacrificed at days 1, 2, 7, 14 and 28 after implantation. The specimens were retrieved and studied morphologically. Calcific deposits were seen grossly as small punctate white masses from day 7 after implantation, progressively becoming more extensive. The light and electron microscopic studies showed that: calcific deposits occurred as early as 24 hours after implantation, the calcific degenerative process was progressive with time, and the mineralization was diffuse, although irregular in degree. The ultrastructural findings revealed that cytoplasmic organelles (mitochondria in particular) and plasma membrane of connective tissue cells appear to serve as initial sites of the process of calcification, which then progresses in the interfibrillar spaces, adjacent to collagen fibrils and elastic fibers.