Multiparity favors same-sex partner preference in male rats.

Same-sex partner preference is present in many mammals, including rodents. Several possible causal factors have been proposed for the establishment of this preference. The Fraternal Birth Order effect refers to the observation that older brothers increase the probability of homosexuality in men, but no experiment has analyzed this possibility. In this study, partner preference (tested in a three compartments box) and female and male sexual behavior (studied in a cylindrical arena) were evaluated in young male rats (3 months) born to multiparous mothers that had 4-6 previous gestations and around 12 months of age. Control groups were young male rats born to primiparous young (4 months) or aged (12 months) mothers. In the partner preference test, the males born to multiparous dams spent less time interacting with the receptive female and more time interacting with the sexually active male, and a 39% exhibited same-sex partner preference. This high percentage seems related to multiparity of their mothers and not to maternal age, because the males born to primiparous aged females (12 months) showed a similar low proportion of same-sex partner preference than the males born to young (4 months) primiparous females (4%). In the sexual behavior tests, no male born of a multiparous dam and with same-sex preference ejaculated and 54% displayed proceptivity and lordosis. Present results suggest that the fraternal birth order effect may occur also in rats.

Distribution of estrogen receptors alpha and beta in the brain of male rats with same-sex preference.

Two distinct estrogen receptors (ERs) exist, ERα and ERß. Both receptors participate in sexual differentiation of the rat brain and likely participate in the regulation of adult sexual orientation (i.e. partner preference). This last idea was investigated herein by examining males treated with the aromatase inhibitor, letrozole, administered prenatally (0.56 µg/kg G10-22). This treatment usually provokes same-sex preference in 1-2 males per litter. Vehicle-treated males (with female preference) and females in spontaneous proestrus (with male preference) were included as controls. ERα and ERß expression was analyzed by immunohistochemistry in brain areas known to control masculine sexual behavior and partner preference, like the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and ventromedial hypothalamic nucleus (VMH), as well as other brain regions suspected to participate in these processes. In addition, serum levels of estradiol were determined in all male groups. Letrozole-treated male rats that preferred sexually experienced males (LPM) showed over-expressed ERα in the hippocampal cornu Ammonis (CA 1, 3, 4) and dentate gyrus. The LPM group showed up-regulated ERß expression in the CA2 and reticular thalamic nucleus. The levels of estradiol did not differ between the groups. Higher expression of ERs in these males was different than their expression in females, with male sex-preference. This suggests that males with same-sex preference showed a unique brain, this sui generis steroid receptor expression probably participates in the biological underpinnings of sexual preference.

Male rats with same sex preference show high experimental anxiety and lack of anxiogenic-like effect of fluoxetine in the plus maze test.

Homosexual men show a 2-4 higher risk to suffer anxiety in comparison with heterosexuals. It is unknown if biological factors collaborate to increase such incidence. Fluoxetine produces differential brain activation in homosexuals as compared with heterosexuals, suggesting that it may produce a divergent behavioral effect dependant on sex-preference. The first aim was to evaluate experimental anxiety in male rats that show same-sex preference in the elevated plus maze (EPM). The second goal explored the putative differential effect of fluoxetine (10mg/kg) in male rats with female and same-sex preference in the EPM. To induce same-sex preference males were prenatally treated with letrozole (0.56µg/kg, 10-20 gestation days), while controls were males prenatally treated with letrozole that retain female-preference or which mothers received oil. In both groups we found animals with male preference, but the proportion was higher in males that prenatally received letrozole (10 vs. 27%). Males with same-sex preference spent less time and showed lower number of entries to the open arms of the EPM than males that prefer females, regardless of the prenatal treatment. In males with female preference, fluoxetine reduced the time spent and number of entries to the open arms that was absent in males with same-sex preference. These data suggest that biological factors contribute to the high levels of anxiety in subjects with same-sex preference and that fluoxetine in men may produce a divergent action depending on sexual orientation.

Desired family size and son preference among Hispanic women of low socioeconomic status.

Among 432 Hispanic women aged 18-50 interviewed at a Los Angeles obstetrics and gynecology clinic, respondents reported wanting an average of 2.8 sons but only 0.1 daughters. Being older than 30, having no more than an eighth grade education, being separated, divorced or widowed, being Spanish-speaking or having been born outside the United States, and having a large family of origin were all positively associated with a desire for a greater number of sons. A multivariate analysis indicated that women who preferred to speak Spanish were 10.9 times as likely as those who preferred English to desire a greater number of sons, and those with more children were 2.5 times as likely as those with fewer children to have a strong desire for sons. Family planning programs for Hispanics may be more effective if they acknowledge this important motive for childbearing.

PIP: This study examined desired family size and son preference among low income Hispanic women in Los Angeles, California. The data were obtained from a sample of 432 Hispanic women, recruited from a waiting room of an obstetrics and gynecology clinic in a large public hospital, during 1995-96. Findings indicate a strong son preference, particularly among less acculturated women. A convenience sample of women reported that sons were highly valued in Hispanic families. Some reported sons were less expensive to raise. 55% of the sample group were born in Mexico, and 9% in the US. 55% grew up in cities. 75% reported having 2 or more brothers, and about 75% reported having 2 or more sisters. 63% were pregnant at the time of the interview. 36% who were not pregnant and were sexually active reported use of contraception. 50% used the condom, and 29% used the pill. 69% had children, and 24% had 3 or more children. Women desired, on the average, 2.8 sons and only 0.1 daughters. Older women and less educated women desired a higher number of sons and fewer daughters. Women who were separated, divorced, or widowed desired more sons (3.3) than women who never married (2.6). Women who preferred to speak Spanish (2.9) desired significantly more sons than women who preferred English (1.3). Women born outside the US desired more sons than American-born women. Women with 5 or more siblings desired fewer daughters than women from smaller families. Women with 2 or more children desired more sons (3.4) than women with fewer than 2 children. The multivariate model reveals that desired number of sons was significantly predicted by Spanish language preference and number of children. Women with a preference for Spanish were 10 times, and women with the most children were 2.5 times, more likely to desire a large number of sons.

China: ultrasound abuse in sex selection.

PIP: In China, the combination of the one child policy, a longstanding preference for sons, and the ability to detect the sex of a fetus through ultrasound has led to the excess abortion of female fetuses and a skewed sex ration which is as high as 120 boys for every 100 girls in some regions. By 1990, more than 100,000 ultrasound scanners were in use in China where more than 1.7 million female babies are "missing" each year. While doctors are officially banned from telling parents the gender of a fetus, they usually pass on this information when bribed.^ieng

[Trends and differentials in fertility in Latin America: evidence from the WFS]. / Tendencias y diferenciales de la fecundidad en America Latina: un analisis con los datos de la encuesta mundial de fecundidad .

PIP: This study presents a comprehensive comparative analysis of the data gathered in the World Fertility Survey (WFS) for the 13 participating countries of the Latin American and Caribbean region. The article begins by examining recent and cumulative fertility, and making an effort to include data other than that of the WFS for purposes of error estimation. The presentation takes the form of short descriptions of recent fertility trends in each country, e.g. Costa Rica experienced a marked decline in the past 20-25 years, although the trend slowed during the mid-1970s, possibly because of some legal problems associated with contraceptive distribution, among other factors. Several other factors are then analyzed, which bear upon the explanation of trends and differentials in fertility. Sections on infecundity and childlessness, infant and child mortality, and sex preferences for offspring are included to make available a wider range of WFS comparative results. Examples of data included in tables are, in Paraguay, of couples desiring boys only, 43% are actually using contraceptives, while 59% of couples desiring girls only are actually using contraceptives. In Haiti, Peru, and the Dominican Republic, where the infant mortality is highest, almost 34% of deaths were of children aged 1-4, while in Panama, Trinidad and Tobago and Jamaica, where mortality has diminished most, only 22% of the deaths are in this group. Socioeconomic determinants of cumulative fertility are probed using a log-linear model. 3 proximate determinants of fertility: age at 1st union; contraceptive use; and lactational infecundity are examined and their contributions to fertility differentials assessed. Finally, the role of socioeconomic factors in determining these intermediate variables is analyzed.^ieng

Sex differences in attitudes towards newborn infants among women of Mexican origin.

PIP: This paper analyzes a data set on women of Mexican origin delivering in Los Angeles hospitals, in order to examine whether Mexican women's attitudes toward their 1st-born infants are influenced by the sex of the child, either alone or in combination with other factors, such as the difficulty of labor and delivery or the woman's social support system. The authors' hypothesize that the mother's attitude toward the 1st child will be determined primarily by factors other than the child's sex, since there is evidence to suggest equal sex preference among women in Latin culture. They predict that the most negative attitudes would be expressed in the case of an unplanned pregnancy, of a child being born into an unstable family or with physical abnormalities. The women described in this paper are all from the Mestizo, or Hispanicized peoples from Mexico. The analyses are based on interviews with a sample of 518 low risk women. Data on the medical course of their labor and delivery was also collected from their medical charts. The operationalization and measurement of each predictive variable are explained. Sex differences in women's evaluations of their children were examined with Chi-Square analyses. As expected, almost no differences on any attitude measure were found. In general the mothers were very pleased with their infants, whether male or female, although there is a suggestion that if they were disappointed, they were more likely to be displeased with a female infant than with a male. Regression analyses, more sensitive for picking up sex differences than the simple Chi-Square, were performed to determine which of the predictive variables were most related to the mother's attitude. Results show that sex was not a predictive variable. Contrary to what was predicted, whether or not the baby was planned, appeared to be relatively unimportant in the mother's attitude toward her child. A 2nd surprising finding was that the woman's experience of birth was unrelated to her evaluation of her child. The social support system had a significant impact on the mother's evaluation of her child. For both boys and girls, social support from the baby's father was associated with a positive attitude toward infants. Women were significantly more negative toward their infants if they had a poor relationship with the baby's father. Finally, the more acculturated women expressed less positive attitudes toward their newborns; this relationship was slightly stronger for girls than boys.^ieng

Breastfeeding: patterns, correlates, and fertility effects.

PIP: Paper based on data generated by the World Fertility Survey in 8 countries: Bangladesh, Indonesia, Sri Lanka, Jordan, Peru, Guyana, Colombia, and Panama. The authors address the following issues, among others: the prevalence and duration of breastfeeding; variations in the duration of breastfeeding among different subgroups, classified by age, parity, woman's education, etc,; the key determinants of breastfeeding; and the effect of breastfeeding on fertility. The large majority of women in all the countries breastfed their last 2 children, the number who did not ranging from 2 to 18%. Duration ranged from 9 months (Panama) to 29 months (Bangladesh). Key determinants were women's education, place of residence, husband's occupation, and survival status of the child--consistent for all 8 countries. Women with more education and those living in urban areas breastfeed for shorter periods. Sex of child, age and parity of mother, and mother's work experience showed no independent effect on duration of breastfeeding. Although breastfeeding is not used for family limitation, the possibility that it is used to prolong birth intervals cannot be ruled out. Average length of last closed birth interval increased with prolonged breastfeeding in all 8 countries. 1 month of breastfeeding adds an average of 0.4 months to the birth interval, although there was considerable variation among the countries. To what extent these variations may be due to differences in reporting errors or to other factors could not be determined.^ieng

Boys or girls? Parents' preferences and sex control.

PIP: Recent evidence from the U.S. and from other selected countries is examined on parent sex preferences for their children and how strongly these are held. This involves the significance of these preferences, the social and economic conditions that foster different types of preferences, and how different individuals and societies deal with them. The traditional preference for boys appears to remain nearly universal, which runs contrary to the ideal of "every child a wanted child," and also presents an obstacle to desired declines in fertility in developing countries where sons are still perceived as needed for economic and emotional security. This tendency has been turned around in Japan, Singapore, Hong Kong, and the U.S., where small families are now the ideal. 3 basic approaches to the scientific selection of sex-specific sperm for preselection, the timing of sexual intercourse, the separation of male- and female-bearing sperm followed by artificial insemination, and selective abortion after fetal sex determination indicate that an effective and practical method of sex control is still further off than predicted.^ieng