Efecto de las descripciones y el reforzamiento sobre la generación de reglas / Effect of descriptions and reinforcement on rule-generation

Se evaluó el efecto de las descripciones verbales y diferentes densidades de consecuencias sobre la adquisición y transferencia de una respuesta de igualación de primer orden, así como en la formulación de reglas. Participaron veinte estudiantes asignados a cuatro grupos que se diferenciaron por la presentación de textos incompletos al final de cada sesión y las densidades de las consecuencias. Las reglas solicitadas al final de cada sesión se analizaron elaborando categorías a partir de estudios previos. Se observaron efectos en la adquisición de la respuesta en entrenamiento y transferencia. Se discute que la ejecución efectiva no siempre conlleva la emergencia de reglas precisas, por otro lado se reveló efecto instruccional de los textos sobre la formulación de reglas precisas, así como la densidad de las consecuencias.

The effect of verbal descriptions and different amounts of consequences onthe acquisition and transfer of a first order matching-to-sample response, as well as rule-formulation, was assessed. Twenty undergraduate students were assigned to four groups, which differentiated regarding the inclusion ofincomplete texts and feedback at the end of each session. The rules, wrotedown at the end of each session, were analyzed using categories derived from previous studies. The effects were observed at the response acquisitionduring the trainings and tests. It is discussed that an effective performancedoes not always lead to precise verbal descriptions and the instructionaleffect of the incomplete texts upon the formulation of effective rules.

In vitro and in vivo assays of 3, 5-disubstituted-tetrahydro-2H-1,3,5-thiadiazin-2-thione derivatives against Trypanosoma cruzi

Cytotoxicity assays of 24 new 3,5-disubstituted-tetrahydro-2H-1,3,5-thiadiazin-2-thione derivatives were performed. The 17 compounds with higher anti-epimastigote activity and lower cytotoxicity were, thereafter, screened against amastigote of Trypanosoma cruzi. Out of these 17 derivatives S-2d was selected to be assayed in vivo, because of its remarkable trypanocidal properties. To determine toxicity against J774 macrophages, a method based on quantification of cell damage, after 24 h, was used. Cell respiration, an indicator of cell viability, was assessed by the reduction of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] to formazan. Anti-amastigote activity was estimated after 48 h by microscopic counts of May Grünwald-Giemsa-stained monolayers. Nifurtimox and benznidazole were used as reference drugs. For the in vivo experiences, mice were infected with 10(4) blood trypomastigotes and then treated during 15 days with S-2d or nifurtimox by oral route. All of the compounds were highly toxic at 100 µg/ml for macrophages and a few of them maintained this cytotoxicity even at 10 µg/ml. Of the derivatives assayed against amastigotes 3k and S-2d showed an interesting activity, that was held even at 1µg/ml. It is demonstrated that the high anti-epimastigote activity previously reported is mainly due to the non-specific toxicity of these compounds. In vivo assays assessed a reduction of parasitemia after administration of S-2d to infected mice