Exploratory behavior and novelty seeking in female Wistar

Exploratory behavior and novelty seeking in female Wistar rats: A correlational study with free- and forced- choice tests J. E. Callejas-Aguilera 1, M. C. Arquillos 1, M. J. Gómez 1, A. Cañete 2, A. Fernández-Teruel 2 y C. Torres 1 Departamento de Psicología, Universidad de Jaén (España) 2 Unidad de Psicología Médica. Departamento de Psiquiatría y Medicina Legal. Universidad Autónoma de Barcelona (España) BACKGROUND AND MAIN GOAL Temperament constitutes a relatively stable and enduring system of the affective or emotional behavior that has been extensively studied through the use of animal models of anxiety/fearfulness, aggression, sociability, impulsivity and novelty-seeking, among others (Eysenck & Eysenck, 1987; Lansade, Bouissou & Erhard, 2008). Differences in exploratory behavior induced by novelty exposure have been widely observed in rodents, and seem to be controlled by genetic influences, as several psychogenetic selection studies suggest (e. g. Blanchard, Mendelsohn & Stamp, 2009). Although several animal tests of novelty-seeking are currently available (e. g. hole-board, open-field, place preference, etc. ), these tests are not exempt of interpretative problems with respect to the behavioral trait they actually evaluate (Bardo, Donohew & Harrington, 1996; Cuenya, Kamenetzky, & Mustaca, 2009). The main aim of the present study was to study whether the novelty seeking behavioral tendency constitutes a temperamental trait that remains stable regardless the free vs. forced nature of the novel situation animals are exposed to, discussing the results within the context of validity of the tests used in this experiment as novelty-seeking animal models. METHOD Subjects Thirty female Wistar rats (with a mean weight of 248 g at the beginning of the experiment) were used. They were individually housed and maintained with food and tap water available ad lib, under conditions of controlled temperature (22º C) and a 12 -h light–dark cycle. Animals were tested between 9: 30 and 13: 00 a. m. and the tests order was counterbalanced. Apparatus and procedures Emergence test Y-Maze Hole-board The rats were placed in the illuminated compartment facing the wall opposite the door. The latencies to enter and then emerge from the dark compartment were recorded. The number of visits and the total and mean times spent in the illuminated compartment after the first entry into the dark box were also recorded. Emergence was taken to be when the animals placed all four paws in the illuminated compartment. The rats were observed for 10 min. An experiment consisted of two trials separated by a 2 min interval. In the first trial, one arm of the Y-maze was closed with a guillotine door. Rats were placed in an arm, their head pointing away from the center of the maze, and they were allowed to visit the two arms for 5 min. During the second trial, animals had free access to the three arms, and were allowed to explore the maze for 5 min. Time spent and visits to each arm on trial 2 (computed by minute) were registered. Ambulation (number of squares crossed), rearing, number of head dips and time spent head dipping were measured for 5 min (computed by minute). Statistical analyses Pearson correlational coeficients where calculated in order to identify linear relationships among the registered scores. Those scores showing significant correlations were submitted to ANOVAS analyses in order to evaluate whether these exploratory behaviors tend to decline over time. P value was set to p<0. 05. RESULTS Y-Maze 1 Y-Maze 2 Y-Maze 3 Y-Maze 4 Y-Maze 5 HB 4 , 015 , 174 , 073 , 171 , 292 HB 3 , 491(* , 352 *) , 468(* , 632(* *) *) , 555(* , 350 *) , 364(* , 552(* ) *) , 435(* , 575(* ) *) DISCUSSION HB 4 , 487(**) , 532(**) , 486(**) , 482(**) * p<. 05 **p<. 01 , 458(*) , 449(*) -, 180 , 943(** 1 ) -, 395(*) 5 Familiar arm 1 Familiar arm 2 3. - In the hole-board it was observed that the number of head-dippings significantly declined during the last minute with respect to previous minutes. Novel arm 5 4 Mean Head-Dipping HB 1 Emergen HB 5 ce , 508(** -, 125 ) , 545(** -, 223 ) , 503(** -, 137 ) , 487(** -, 177 ) 2. - Animals significantly visited more frequently the novel arm during the second trial of the Y-Maze test as compared to the number of entries to the familiar arms (significant arm x minute interaction; minutes 1, 2 and 5). Mean entries to the arms 1. - Significant Pearson correlational values were obtained between the number of head-dippings (Holeboard) and novel arm entries frequency (Y-Maze), and between the former and the emergency latency scores (Emergency test). 3 2 1 0 1 2 3 Time (min) 4 5 4 3 2 1 0 1 2 3 4 5 Time (min) The results obtained in this study indicated that those animals that showed more novelty seeking-related behaviors in the hole-board preferred to visit the novel arm of the Y-Maze, and also showed a shorter emergency latency when exposed to a light-dark test. Present data seem to reveal the utility of these animal tests for studying novelty induced exploratory responses and suggest that these behavioral tendency constitutes a temperamental trait that remains stable regardless the free vs. forced-choice nature of the employed test. REFERENCES ● Bardo, M. T. , Donohew, R. L. , & Harrington, N. G. (1996). Behavioural Brain Research, 77, 23 -43. ● Blanchard, M. 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Supported by the Research Group “Comparative Psychology: Learning, Attention and Memory“ (HUM-642) and by “Fundació La Marató TV 3” (092630/31)