Effects of melatonin administration on oxidative stress and daily locomotor activity patterns in goldfish

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Melatonin has a number of physiological functions in addition to light-dark transduction.In recent years, many in vivo and in vitro studies in rodents have revealedan important antioxidant activity of melatonin, both directly and indirectly. Nevertheless,the potential effects of melatonin as an antioxidant in fish remain unknown.The aim of this research was to evaluate the capacity of melatonin injections (3mg/kg) to attenuate oxidative damage after submitting goldfish to oxidative stresscaused directly by hydrogen peroxide (H2O2) baths and indirectly by hypoxia andsubsequent reoxygenation, as well as the locomotor activity. The results revealed thatmelatonin decreased lipid damage in muscle after hypoxia/reoxygenation (1.22 vs2.27 nmoles lipid peroxides/g tissue), but not in liver. Mortality caused by oxidativestress was not attenuated by melatonin. Surprisingly, melatonin caused an increase ofmortality (50 vs 95%) when administered before hypoxia. Locomotor activity wasalso affected by melatonin but not by the administration of the vehicle, suggesting asedative effect of melatonin in goldfish. In conclusion, melatonin administration provokedslight effects on lipid peroxidation and mortality resulting from oxidativestress, with reduction of locomotor activity in relation to the vehicle

Effect of telencephalic ablation on appetitive instrumental learning in the goldfish (Carassius auratus) / Efectos de la ablación telencefálica sobre el aprendizaje apetitivo instrumental en la carpa dorada (Carassius auratus)

Goldfish received either bilateral ablation of the telencephalon or a sham operation, followed by instrumental training under widely-spaced conditions (one trial per day). Animals were trained to swim in a runway for either continuous reinforcement or 50% partial reinforcement. Thirty-two daily acquisition sessions were followed by 32 daily extinction sessions during which food was withheld. Telencephalic lesions disrupted early acquisition performance, but lesioned animals achieved an asymptotic performance similar to that of sham controls. Extinction was facilitated by the lesions, independently of the schedule of reinforcement used during acquisition. The results are interpreted in relation to comparative research on spaced-trial appetitive instrumental learning in vertebrates (AU)

En este experimento se emplearon carpas doradas (Carassius auratus) con ablación bilateral del telencéfalo o con operación de control en un procedimiento de entrenamiento instrumental con distribución de ensayos ampliamente espaciados (un ensayo por día). Los animales fueron entrenados a nadar en un corredor bajo condiciones de reforzamiento continuo o reforzamiento parcial al 50 por ciento. Se realizaron 32 sesiones diarias de adquisición seguidas de 32 sesiones diarias de extinción en las que la comida fue suprimida. La lesión telencefálica afectó a la adquisición durante los primeros ensayos aunque, al final, los animales lesionados alcanzaron una ejecución asintótica similar a la de los animales controles. La extinción se vio facilitada por las lesiones, independientemente del programa de reforzamiento usado durante la adquisición. Los resultados se interpretan en relación a los estudios comparativos de aprendizaje instrumental apetitivo con ensayos espaciados realizados en otros vertebrados (AU)