Efecto de la falta de predicción sobre el status social de ratas / Effect of unpredictability about the social status of rats

Se analizó el efecto que la estimulación aversiva predecible e impredecible provoca sobre el rango social en ratas. Se formaron parejas de ratas Sprague Dawley macho adultas y se procedió a evaluar y caracterizar el rango jerárquico de cada miembro del par. Para ello, se registró la prioridad y desplazamientos de los animales para acceder a una fuente limitada de agua. Una vez verificado el rango de cada individuo, se procedió a someter a los animales dominantes de cada pareja a una sesión de 100 shocks eléctricos no escapables, en donde mitad de los animales lo recibieron a intervalos constantes y la otra a intervalos variables. Posteriormente, se volvió a analizar la jerarquía. Los resultados mostraron que la aplicación de descargas a intervalos variables (descargas no predecibles) provocaron una caída del status de los dominantes, mientras que la misma cantidad de descargas presentadas a intervalos fijos no produjo cambios en la jerarquía de los dominantes.

Prazosin and stress effect on tumoral growth of 7.12-Dimethylbenz[A]anthracene-induced rat mammary tumors

Repeated isolation stress and prazosin effect were evaluated in 7,12-dimetylbenz [A] anthracene (DMBA) mammary tumors. Tumor volume was significantly lower in stressed than in control animals from 10 to 52 days considering day 1 the moment when tumors became palpable and treament began. Control Prazosin (0.5 mg/Kg) rats showed diminished tumor volume after 40 days. Stress Prazosin curve was similar to stress alone. The proportion of progressing tumors in control was significantly higher than in stressed groups, regardless of Prazosin administration. Body weight gain was similar in every group throughout the experiment. Behavioral studies were performed when stress effect was no longer evident. Grooming and the number of fecal boli were similar in all groups, as well as prolactin serum levels, suggesting that habituation took place. No significant differences were observed between groups for estrogen receptors. However, a greater concentration of progesterone receptors was found in Stressed rats, compared to all other groups. We conclude that the decrease of tumor volume provoked by stress could not be reversed by the alpha 1-adrenergic antagonist prazosin. Then, it appears that the main effect of stress is not mediated by the alpha 1-adrenergic receptors. Higher progesterone receptors in stressed rats could explain the differences observed.