Effect Of Exogenous Sex Hormones Before Sexual Differentiation On Sexual Orientation In Adult Rats

ObjectiveIt has been found that sex hormones before brain sexual differentiation destined to mediate sexual orientation of rats. It is now recognized that androgen is the factor responsible for masculinization of brain, while estrogen influence the level of androgen via the hypothalamic- pituitary- gonad axis.The objective of the present study was to establish a video-computer assisted experimental system of sexual preference and sexual behavior in rats. At the same time, we tried to establish the rat homosexual models induced by exogenous hormones to study the relation between sex hormones before sexual differentiation and adult sexual orientation, therefore set up a basis for further neurobiologic research into homosexuality.Materials and Methods1 Exiperimental SystemThe video-computer assisted sexual preference and sexual behavior experimental system in rats is composed of rat observation box, a soundproofcontainer, video apparatus and a computer.The video image was analyzed using MiceGrayAuto and MiceGrayManu software designed by our research group.2 AnimalsFemale and male Sprague-Dawley rats3 Methods3.1 Testing proceduresPart 1 (female rats given exogenous androgen):Postnatal Sprague-Dawley female rats (1 day old) were randomly distributed into five groups and each group were injected (i.p) the following dose of testosterone propionate (TP): 0 (vehicle, 50ul aseptic oil), 25ug, 125ug, 250ug, 500ug (dissolved in 50ul of aseptic oil) . The female rats were anesthetized with 10% chloral hydrate solution (5ml/kg) and castrated at the age of 70 days. Two weeks after the castration, the animals were submitted for analysis of sexual preference and feminine sexual behavior. One week later, these tests were repeated. After these tests, the same animals were tested for masculine sexual behavior.Part 2 (male rats given exogenous estrogen):Postnatal Sprague-Dawley male rats (1 day old) were randomly distributed into five groups and each group were injected (i.p) the following dose of of estradiol benzoate(EB): 0 (vehicle, 50ul aseptic oil), lug, 10ug, 25ug, 100ug (dissolved in 50ul of aseptic oil). At the age of 90 days, the animals were submitted first for sexual preference and then for masculine sexual behavior. One week later, these tests wererepeated. After the termination of these tests, the males were anesthetized with 10% chloral hydrate solution (5ml/kg) and castrated. Two weeks after the castration, the animals were tested for feminine sexual behavior.3.2 Behavior testingSexual behavior of female rats1) Sexual Preference: Each experimental female animal was placed into the observation box and observed for 15 min, the total time spent near each of the stimulus animals was recorded.2) Feminine Sexual Behavior: Each experimental female animal was observed for 30 min. A lordosis quotient was computed by dividing the number of lordosis of the experimental animal by the total number of mounts of the stimulus male.3) Masculine Sexual Behavior: Each experimental female animal was observed for 15 min, mount frequency and mount latency were recorded.Sexual behavior of male ratsThe analysis of sexual preference and feminine sexual behavior of male rats were the same as the female rats, for masculine sexual behavior, the following measures were recorded: mount frequency; mount latency; intromission frequency; intromission latency; ejaculation latency and postejaculatory interval.4 Data analysisSPSS-10.0 and SAS-6.12 for windows were performed for analysis of data. Statistical analysis methods included Wilcoxon Signed Ranks Test; Kruskal-Wallis H Test; Chi-Square ( x 2) ; Fisher's Exact Test; Anova and Paired-Sample T Test.Results1 The characteristics of the systemThe real-time video-computer assisted experimental system was used in our study to observe the sexual preference and sexual behavior. This system is direct and objective, the images were clear and steady, and the image data were analyzed using MiceGr...