Abstract
The present work aimed at studying the influence of the estrous cycle in the forced swim test, an animal model of depression. For this, 44 male and female Wistar rats were divided into five groups according to the hormonal state in the first day of the study: metaestrus (N = 12), diestrus (N = 8), proestrus (N = 7), estrous (N = 6) and males (N = 11). They were housed in groups of five, with water and food ad libitum under a 12/12 h light/dark cycle. Females were screened daily for the estrous cycle. The animals were subjected to two swimming sessions in a glass cylinder with water up to 15 cm at 28±2o C. The data of the first five minutes of a 15-min first session were compared to those of a 5-min second session 24 h later. The results indicate that the latency to the first immobility was substantially reduced in the second session and was longer for females in diestrus and proestrus in the first session. The results also indicate that females in diestrus and proestrus exhibited less immobility than males in the first session; females in diestrus also exhibited less immobility than females in metaestrus. Females in metaestrus and diestrus, as well as males, did not present the decrease in total immobility times in the second session. The present results are analyzed in terms of differential effects of progesterone and estrogen on a learning component and an affective component.
Highlights
Studies on the influences of sex differences on behavior are scarce and, in general, present contradictory and disperse data
Studies on the behavioral effects of the menstrual cycle in humans and estrous cycle in rodents investigate a variety of reproductive (Carter, 1993; McCarthy & Becker, 1993) and non-reproductive behaviors which influence cognitive abilities (Kimura, 1992; Dreher et al, 2006), exploratory and motor activity (Kennet et al, 1986; Curzon, Haaren & Kennett, 1990; Alonso et al, 1991; Blanchard et al, 1993; Morgan, Schulking & Pfaff, 2004), defense reaction and defensive attack (Blanchard et al, 1980; Morgan et al, 2004), as well as learned helplessness (Gouveia Jr., 2001)
Few studies report on the relations between the estrous cycle and behavioral tests like the elevated plus-maze (Gouveia Jr. & Morato, 2002), learned helplessness (Jenkins et al, 2000) and elevated T-maze (Gouveia Jr. et al, 2004)
Summary
Studies on the influences of sex differences on behavior are scarce and, in general, present contradictory and disperse data. The modulation of female behavioral states by sex hormones (in rodents, the estrous cycle) has only recently been properly approached This is an important matter for pharmacology and human medicine, since many drugs have their effects altered by gender and hormonal condition. The forced swim test (FST), known as behavioral despair (Porsolt et al, 1977, 1978), is considered an animal model of depression and is mainly used in the screening of antidepressant drugs (Sánchez & Meier, 1997; Petit-Demouliere, Chenu & Bourin, 2005). There is some evidence demonstrating that both variables are dissociable in terms of what they index; while the total duration of immobility is taken as a score of affective effects, the latency for the first episode of immobility is taken as a score of contextual/emotional learning and memory effects (West, 1990)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
