EFFECTS OF ATIPAMEZOLE, A NOVEL ALPHA-2-ADRENOCEPTOR ANTAGONIST, IN OPEN-FIELD, PLUS-MAZE, 2 COMPARTMENT EXPLORATORY, AND FORCED SWIMMING TESTS IN THE RAT

The behavioral effects of atipamezole (0.5-4.5 mg/kg), a new and highly selective alpha-2-adrenoceptor antagonist, were studied in four behavioral models: open-field, elevated plus-maze, two compartment exploratory test and forced swimming test. Atipamezole (1.5 and 4.5 mg/kg) produced a dose-dependent suppression of locomotor activity in the open field test. In the two compartment exploratory test, the same doses of atipamezole decreased locomotor activity in a 5 min test but not in a 10 min test. The numbers of transitions between the compartments were not significantly affected by atipamezole. Doses of 0.5-4.5 mg/kg did not significantly change the time spent in the open arms or the total number of arm entries in the plus-maze, and doses of 1.5 and 4.5 mg/kg decreased defecation marginally. Vocalization during the forced swimming test was increased by atipamezole (1.5 mg/kg) but the duration of immobility was not increased over the dose range (0.5-1.5 mg/kg) of atipamezole used. Our results suggest that, in the rat, atipamezole decreases motor activity in the early phase of the exploration of new surroundings. In the doses used, atipamezole may suppress defecation and increase vocalization in rats.