INTERACCIÓN ENTRE EL EXTRACTO DE Hygrophila tyttha Y LA ESCOPOLAMINA EN UNA PRUEBA DE MEMORIA EPISÓDICA EN RATAS / Interaction Between Hygrophila tyttha Extract and Scopolamine in a Episodic Memory Test in Rats

El presente estudio tuvo como objetivo evaluar la interacción entre el extracto etanólico concentrado de la planta Hygrophila tyttha (500 mg/kg, vía oral) y el antagonista colinérgico escopolamina (0,3 mg/kg, intraperitoneal) en un modelo animal de memoria episódica. El extracto de la planta se obtuvo mediante percolación a partir del material vegetal fresco y se administró 30 minutos antes que la escopolamina. Treinta minutos después de ésta los animales se entrenaron en la tarea de reconocimiento del contexto espacial y una hora más tarde se evaluó la exploración del campo y de los objetos en él contenidos. Los resultados mostraron que la administración de escopolamina, asociada o no al extracto de Hygrophila tyttha, deterioró el reconocimiento del contexto espacial, impidió la habituación al campo abierto, pero no afectó la exploración de los objetos. El único efecto de la asociación del extracto con escopolamina fue un aumento significativo de la actividad exploratoria del campo abierto. Estos resultados sugieren que el extracto de Hygrophila tyttha no tuvo interacciones significativas sobre el efecto amnésico de la escopolamina, pero si potenció su actividad estimulante de la actividad exploratoria.

The main objective of this study was to evaluate the interaction between the concentrated ethanolic extract of Hygrophila tyttha (500 mg/kg, per os) and the cholinergic antagonist scopolamine (0.3 mg/kg, intraperitoneal) in an animal model of episodic memory. The extract was obtained by percolation from fresh vegetal material and was administered 30 minutes before scopolamine. Thirty minutes after the scopolamine the subjects were trained in a spatial context recognition task. One hour after the training the exploration of both the open field and the objects. The results showed that scopolamine administration, associated or not to Hygrophila tyttha extract, impaired both spatial context recognition and open field habituation but did not affect object exploration. The only effect of Hygrophila tyttha extract and scopolamine joint administration was a significant increase in open field exploratory behavior. Such results suggest that Hygrophila tyttha extract did not have significant interactions with scopolamine amnesic effect, while it did potentiate the exploratory behavior stimulant effect of scopolamine.

Thigmotactic responses in an open-field

The goal of the present study was to investigate the role of thigmotaxis (the tendency to remain close to vertical surfaces) in rat exploratory behavior in an open-field. Thigmotaxis was investigated in a parametric way, using 24 experimentally adult naive male Wistar rats (210-230 g). Exploratory behavior was studied in an open-field (N = 12) in 5-min sessions and behavior was analyzed in terms of where it occurred: in areas surrounded by two, one, or no walls. Another group of rats (N = 12) was studied in an open-field with blocks placed near two of the corners so as to make these corner areas surrounded by three walls. The floor of the open-fields was divided into 20-cm squares in order to locate the exact place of occurrence of each behavior. The following behaviors were recorded: entries into the squares, rearings, and groomings. In both types of open-field the rats chose to remain longer in the squares surrounded by the largest possible number of walls. In one of the open-fields, the mean time (seconds) spent in squares surrounded by two walls was longer than the time spent in squares surrounded by one or no walls (37.2, 7.7, and 1.8 s, respectively). In the other open-field, the mean time spent in squares surrounded by three walls was longer than the time spent in squares surrounded by two, one or no walls (41.7, 20.4, 7.0, and 2.6 s, respectively). Other measures presented a similar profile. These results indicate that rats are sensitive to the number of walls in an environment and prefer to remain close to them.

Effects of septal cholinergic lesion on rat exploratory behavior in an open-field

The medial septum participates in the modulation of exploratory behavior triggered by novelty. Also, selective lesions of the cholinergic component of the septohippocampal system alter the habituation of rats to an elevated plus-maze without modifying anxiety indices. We investigated the effects of the intraseptal injection of the cholinergic immunotoxin 192 IgG-saporin (SAP) on the behavior of rats in an open-field. Thirty-nine male Wistar rats (weight: 194-230 g) were divided into three groups, non-injected controls and rats injected with either saline (0.5 æl) or SAP (237.5 ng/0.5 æl). Twelve days after surgery, the animals were placed in a square open-field (120 cm) and allowed to freely explore for 5 min. After the test, the rats were killed by decapitation and the septum, hippocampus and frontal cortex were removed and assayed for acetylcholinesterase activity. SAP increased acetylcholinesterase activity in the septum, hippocampus and frontal cortex and decreased the total distance run (9.15 ± 1.51 m) in comparison to controls (13.49 ± 0.91 m). The time spent in the center and at the periphery was not altered by SAP but the distance run was reduced during the first and second minutes (2.43 ± 0.36 and 1.75 ± 0.34 m) compared to controls (4.18 ± 0.26 and 3.14 ± 0.25 m). SAP-treated rats showed decreased but persistent exploration throughout the session. These results suggest that septohippocampal cholinergic mechanisms contribute to at least two critical processes, one related to the motivation to explore new environments and the other to the acquisition and storage of spatial information (i.e., spatial memory)