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PubMed1986

Age and sex differences in motor performance of pre-school Nigerian children.

Differences in motor performance according to chronological age and gender of 341 young Nigerian children (ages 3 to 5) were examined. Motor test items designed by Morris et al. (1981) were administered to the subjects. Analysis of variance was used to determine significant differences in the motor performance of the groups. In the whole sample, more age differences than sex differences in performance were noted. Except for the balancing and running performances of the girls, a fairly linear trend of improvement with age was observed in the motor performances of the groups. At each age level the boys consistently performed better than the girls in four of the six motor tests (catching, standing long jump, tennis ball throw and speed run). Generally, the 4- and 5-year-old children performed homogeneously, with a great disparity in performance noted for the 3-year-old children. The results of this study confirm that age and sex differences in motor performance occur at early childhood. Prospective studies should seek to control the extraneous factors which influence motor development and account for the observed differences in motor performance of pre-school children.

Age Factors↗

PubMed2004

Selective sex differences in declarative memory.

Sex invariance of a six-factor, higher order model of declarative memory (two second-order factors: episodic and semantic memory; and four first-order factors: recall, recognition, fluency, and knowledge) was established for 1,796 participants (35-85 years). Metric invariance of first- and second-order factor loadings across sex was demonstrated. At the second-order level, a female advantage was observed for both episodic and semantic memory. At the first-order level, sex differences in episodic memory were apparent for both recall and recognition, whereas the differences in semantic memory were driven by a female superiority in fluency. Additional tests of sex differences in three age groups (35-50, 55-65, and 70-85 years of age) indicated that the female superiority in declarative memory diminished with advancing age. The factor-specific sex differences are discussed in relation to sex differences in hippocampal function.

Adult↗

PubMed1993

When similarity is a liability: effects of sex-based preferential selection on reactions to like-sex and different-sex others.

In 2 laboratory studies, 145 male and female undergraduates were selected for the role of manager either on the basis of merit or preferentially on the basis of their sex. Results of the first study indicated that when female subjects had been selected preferentially as compared with on a merit basis, they reacted more negatively to female (but not to male) applicants for an entry-level position in terms of personnel evaluations and competence ratings and they recommended female applicants for hire less frequently and less enthusiastically. No differences in personnel evaluations were found as a result of preferential selection when subjects were male (Study 1) or when subjects were provided with favorable information about their ability (Study 2). Implications for implementation of affirmative action programs are discussed.

Adolescent↗

PubMed1997

Sex differences in visual recognition memory: support for a sex-related difference in attention in adults and children.

The selectivity hypothesis of Meyers-Levy (1989) proposes that cognitive sex differences reflect underlying differences in information processing between males and females. Males are considered to be more likely to organize information in a self-related manner, whereas females are more likely to adopt a comprehensive approach to information processing. We tested this hypothesis in children (10-15 years) and adults using recognition memory tasks. Tests were devised which employed male-oriented objects, female oriented objects, or random objects. In both the child and adult samples, females performed significantly better than males on tests using random and female-oriented objects. Males performed at the level of females only when tested for recognition of male-oriented objects. These results demonstrate that this sex difference is present prior to puberty and support the concept of sex differences in information processing.

Adolescent↗

PubMed1999

Social interactions unmask sex differences in humoral immunity in voles.

Sex differences in immune function are well established among laboratory rodents, with males typically having lower immunity than females. This sex difference may reflect the suppressive effects of testosterone on immune function. Because polygynous males generally have higher circulating testosterone concentrations than monogamous males, sex differences in immune function are hypothesized to be more pronounced among polygynous as compared to monogamous species. Sex differences in immune function have not been consistently observed among individually housed Microtus in the laboratory; thus, social interactions are hypothesized to be necessary for the expression of sex differences in immune function. We assessed the effect of differential housing conditions on humoral immunity and steroid hormone concentrations in polygynous meadow voles Microtus pennsylvanicus, and monogamous prairie voles M. ochrogaster. We examined humoral immunity by immunizing voles with keyhole limpet haemocyanin (KLH) and measuring antibody production 5, 10, 15 and 30 days postimmunization. Overall, meadow voles mounted higher anti-KLH immunoglobulin (Ig)M and IgG responses than prairie voles, regardless of the housing condition. Sex differences in antibody production were only observed among meadow voles housed in pairs, in which females had higher anti-KLH IgM and IgG responses than males. Sex differences in antibody production were not observed among prairie voles or meadow voles housed individually. Sex and species differences in circulating oestradiol, testosterone, and corticosterone concentrations were not related to differences in humoral immunity. These data suggest that sex differences in immune function are more pronounced among polygynous species than monogamous species, but may be context dependent. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2003

Pharmacogenetic analysis of sex differences in opioid antinociception in rats.

Sex differences in opioid antinociception have been reported in rodents and monkeys, with opioids being more potent in males than females. In the present study, the influence of rat strain on sex differences in opioid antinociception was examined in a warm water tail-withdrawal procedure. Antinociceptive tests were conducted with the high-efficacy micro-opioid morphine, and the less efficacious opioids buprenorphine, butorphanol and nalbuphine. Baseline nociceptive latencies were consistently higher in males than their female counterparts. Sex differences in opioid antinociception were observed in all strains tested, with the opioids being more potent and/or effective in males. The magnitude of the sex differences was related to the relative efficacy of the opioid, with morphine, buprenorphine, butorphanol and nalbuphine being on average 2.2-, 2.6-, 15.9- and 11.9-fold more potent in males. Sex differences also varied markedly across strains, with large differences consistently obtained in the F344 and F344-Sasco strains, moderate differences in the ACI, DA, Lewis, Sprague Dawley, Wistar and Wistar-Kyoto strains, and small differences in the Long Evans-Blue Spruce, Long Evans, Brown Norway and Holtzman strains. When compared across strains, there was no relationship between sex differences in nociceptive sensitivity and opioid sensitivity. These findings provide strong support for the role of genetic factors in determining sex differences in opioid antinociception, and suggest that the use of low-efficacy opioids, coupled with the use of rat strains that display small and large sex differences in opioid antinociception, may provide a sensitive tool to investigate the mechanisms underlying sex differences in opioid antinociception.

Analgesics↗

PubMed1986

Sex differences in [3H]-estradiol binding in brain and pituitary after acute dopaminergic treatment. In vivo studies in the rat.

Responses to estrogen differ between the sexes, yet sex differences in specific binding of estradiol (E2) to its receptor are not observed consistently. Dopaminergic treatment has been shown to increase binding of 3H-E2 in selected brain areas and anterior pituitary in the female rat, and the dopaminergic system is sexually differentiated. In order to determine whether or not dopaminergic stimulation might induce sex differences in 3H-E2 binding, male and female gonadectomized-adrenalectomized rats were pretreated either with bromocriptine, a dopamine agonist, or with diethyldithiocarbamate (DDC), an inhibitor of dopamine beta-hydroxylase. DDC was used in order to increase endogenous release of dopamine. After such acute dopaminergic treatment, specific binding of 3H-E2 in nuclear and extranuclear fractions of 6 brain areas and pituitary in vivo was determined 1 h after intravenous injection of 3H-E2 (1 microgram/kg body weight). Administration of either bromocriptine or DDC increased specific 3H-E2 binding to nuclear and extranuclear fractions of basal hypothalamus and anterior pituitary from female but not from male rats, thus inducing sex differences in binding in these two tissues. Bromocriptine also increased specific binding in the pineal in females. Total binding was increased in a crude membrane fraction (P2) from pituitary of female but not of male rats after administration of DDC, but the percent of extranuclear specific binding found in the P2 fraction was decreased after DDC in both males and females. The findings suggest that dopaminergic stimulation may induce sex differences in 3H-E2 binding by increasing binding in some brain areas and anterior pituitary in females but not in males.

Animals↗

PubMed1990

The vocal motor neurons of Xenopus laevis: development of sex differences in axon number.

Sex differences in the number of muscle fibers in the larynx of clawed frogs (Xenopus laevis) develop after metamorphosis. In order to examine possible contributions of neural innervation to this process, we prepared sections of the laryngeal nerve from tadpole stage 56, when the sexes can first be distinguished, through adulthood, and counted axons on electron micrographs. The adult number of axons is achieved by a sexually differentiated pattern of axonal addition and loss. Axon numbers are high at tadpole stage 56 and equal for males and females; thereafter, males have more axons. Sex differences are most pronounced at tadpole stage 62 because between stages 59 and 62 the number of laryngeal axons in males increases by an average of 119 per nerve. Ultrastructural evidence is congruent with the hypothesis that new axons are added to the laryngeal nerve between tadpole stages 56 and 62. The loss of axons from the laryngeal nerve is greater for females than for males. Between tadpole stages 56 and adulthood, overall axon number decreases by 47% in males and by 64% in females. Signs of axonal degeneration are present in both sexes before metamorphosis but are rare at juvenile or adult stages. The numbers of axons in juvenile frogs do not differ from those in adults and continue to be greater in males than in females. In contrast to the amount of axon addition and loss, the timing of axon loss and the percentage of myelinated axons is the same for males and females throughout development. Thus sex differences in the innervation of laryngeal muscle originate before metamorphosis and could contribute to the marked sex differences in muscle fiber addition that occur thereafter.

Animals↗

PubMed1982

Hemispheric asymmetry and sex differences in a comparative judgement task.

Visual field differences and sex differences in a complex semantic processing task were examined. Two different print size Kana words which represented concrete objects were paired and displayed tachistoscopically to the left or the right visual field. Subjects decided if the relationship of the print size and real life size of the word pairs was appropriate or not by pressing a key. Results revealed that female subjects showed faster reaction times to the right visual field stimulation while males showed a tendency toward a left visual field superiority. Possible hemisphere difference in mechanisms between the sexes were discussed.

Brain Mapping↗

PubMed1985

Emergence and characterization of sex differences in spatial ability: a meta-analysis.

Sex differences in spatial ability are widely acknowledged, yet considerable dispute surrounds the magnitude, nature, and age of first occurrence of these differences. This article focuses on 3 questions about sex differences in spatial ability: What is the magnitude of sex differences in spatial ability? On which aspects of spatial ability are sex differences found? and When, in the life span, are sex differences in spatial ability first detected? Implications for clarifying the linkage between sex differences in spatial ability and other differences between males and females are discussed. We use meta-analysis, a method for synthesizing empirical studies, to investigate these questions. Results of the meta-analysis suggest that sex differences arise on some types of spatial ability but not others, that large sex differences are found only on measures of mental rotation, that smaller sex differences are found on measures of spatial perception, and that, when sex differences are found, they can be detected across the life span.

Adolescent↗

PubMed1984

Sex differences in social adjustment. Effects of sex role socialization and role stress.

This study focuses on the social role functioning component of psychiatric disorders. It assesses sex differences in social adjustment in regard to: work, marriage, parenthood, relations with friends and extended family, and the nuclear family as a whole. Hypotheses predicting sex differences in social adjustment are derived from socialization and role stress frameworks and tested with data from a New Haven community epidemiologic study, utilizing the Social Adjustment Scale-Self Report (SAS-SR). The data show that, consistent with socialization-derived predictions, women manifest greater feelings of inadequacy than men in instrumental work role performance, while men manifest greater emotional inhibition and interpersonal friction. Morever, consistent with role stress frameworks, women express greater conflict and resentment than men in regard to family relationships, but not in regard to friendship relationships. In addition, women's subjective disinterest and impaired functioning in their work role is greater for housewives than for employed women. The implications of these findings for social supports research are discussed.

Aggression↗

PubMed2000

Sex differences in the epidemiology of tuberculosis in San Francisco.

SETTING: Worldwide differences in sex-specific tuberculosis case rates remain fundamentally unexplained. OBJECTIVE: To explore various factors that may explain sex differences in tuberculosis incidence rates for San Francisco from 1991-1996. DESIGN: A retrospective epidemiologic analysis of sex-specific tuberculosis incidence rates in San Francisco from 1991-1996. Stratified analyses were performed on age at diagnosis, racial/ethnic group, human immunodeficiency virus (HIV) status, and place of birth. Molecular fingerprinting with IS6110 data was used to study sex differences in the incidence of disease for recently transmitted and reactivated cases of tuberculosis. RESULTS: In the study period, the male to female incidence rate ratio was 2.1 (95% CI 1.9-2.3). Stratified analyses revealed differences in sex-specific rates after the age of 14 and the highest male:female ratios were seen in the US-born, white, and black populations. High ratios were also observed for cases with clustered fingerprints, similar to those observed for the US-born population. In sub-populations with predominantly reactivated cases of tuberculosis, ratios were also above unity after adolescence, but the effect was less pronounced. CONCLUSION: The ongoing transmission of tuberculosis in the US-born population is one of the factors that explains the difference in sex-specific rates of disease in San Francisco. Observed differences in tuberculosis rates between the sexes may be due to a difference in transmission dynamics rather than diagnosis or reporting biases.

AIDS-Related Opportunistic Infections↗

PubMed1984

The number of pre-shock trials affects sex differences in passive avoidance behavior.

Different groups of male and female Wistar rats were exposed to a standard passive avoidance procedure in which the number of pre-shock trials was experimentally manipulated (1, 3 or 9 trials). Sexually dimorphic passive avoidance behavior was observed after 1 and 3 pre-shock trials. Entrance latencies on the pre-shock trials did not differ for males and females after 1 trial. In the 3 trial condition, latencies differed between the sexes and were also a function of repeated trials for male subjects, as their latencies increased over trials, while those of females did not. When 9 pre-shock trials were presented, the sex difference in entrance latencies was still observed, but latencies increased for both males and females. Although the results of the experiment suggest that sex differences in passive avoidance behavior might be attributable to sex differences in habituation processes to the stimuli associated with exposure to the platform, correlations between the latencies on the final pre-shock trial and behavior on the post-shock trial were not significant. The variables responsible for the occurrence of sexual dimorphism in passive avoidance behavior remain, therefore, largely unknown. The interpretation of this behavioral difference in terms of more general differences between males and females should proceed very cautiously.

Animals↗

PubMed2001

Structural and functional sex differences in the human hypothalamus.

Sex differences in the brain may be the basis not only for sex differences in reproduction, gender identity (the feeling of being male or female), and sexual orientation (heterosexuality vs homosexuality), but also for the sex difference in prevalence of psychiatric and neurological diseases ( Swaab and Hofman, 1995 ). In this brief article we discuss a few examples of structural and functional sex differences in the human brain.

Aging↗

PubMed1985

Sex differences in avian embryo pulmonary surfactant production: evidence for sex chromosome involvement.

Sex differences in fetal pulmonary surfactant production have been shown in mammalian species, with the female at an advantage. A relationship between fetal sexual differentiation and the development of pulmonary surfactant production has been proposed. We hypothesized that if sex chromosomal factors play a role in causing the surfactant sex difference, then a reversal in the sex karyotype would be associated with a reversal in the surfactant sex difference and in some sex-specific responses to hormonal regulators of fetal surfactant production. To test this, we measured the surfactant-related phospholipids phosphatidylcholine and saturated phosphatidylcholine (SPC) in lung homogenates of avian embryos in which the male sex karyotype is homozygous (ZZ) and the female heterozygous (ZW). The following experimental groups were monitored: untreated controls on days 15 through 21 of gestation; embryos injected with 250 micrograms 17 beta-estradiol or of the antiestrogen CI 628; embryos injected with 250 micrograms testosterone or of the antiandrogen Flutamide; and embryos injected with 0.75 micrograms dexamethasone or 100 micrograms 11-deoxycortisol. Untreated controls exhibited significantly higher PC/milligram lung weight and SPC/milligram lung weight ratios in male embryos at gestation days 15 through 19. Hormone treatments also produced sex-specific effects. Dexamethasone significantly accelerated the male lung SPC concentration (35% over control) without affecting that of females. Glucocorticoid inhibition with 11-deoxycortisol significantly reduced the lung SPC concentration of both males and females, each by 19%. Testosterone significantly increased the female lung SPC concentration by 23%, and Flutamide significantly lowered this in the females by 24%. Estrogen reversed the sex difference by producing a relatively small (16%) decrease in the male lung SPC content while significantly increasing that of the females by 32%. CI 628 produced a modest and proportionate reduction of the lung SPC content in both sexes. These data provide evidence for a male advantage in fetal pulmonary surfactant production in the avian system, the reverse to that observed in humans, rabbits, rats, and mice. The known sex-specific responses of the developing surfactant system to glucocorticoids and to androgens are also reversed in the chick embryo as compared to the mammal. This gives additional support to the proposed link between the process of fetal sexual differentiation and the dimorphism in fetal pulmonary surfactant production and suggests that the sex chromosomes play an important regulatory role in the dimorphism of fetal surfactant production.

Animals↗

PubMed1984

Changes in sex differences in sexual behavior: a replication of a study on West German students (1966-1981).

In 1966, at the start of the student movement and the sexual liberalization process, we studied the sexual behavior and attitudes of 3,666 male and female students from 12 West German universities by mailed questionnaires. In 1981 we replicated this study with 1,922 students from 13 universities (10 the same as 1966, 3 founded after 1966). In both studies the students were selected at random. Results of these comparative studies are presented with a view to the changes in sex differences. Sex differences in masturbation behavior have considerably decreased since 1966; masturbation is nonetheless still the form of sexual behavior with the most striking differences between the sexes. The sex differences in coital behavior are now reversed, female students being earlier and more active than males. As regards the tendency to change partners or for sexual relations outside a steady relationship, the differences between men and women have disappeared. In their attitudes to sexuality, female students in 1981 are somewhat more liberal than their male counterparts, whereas hardly any difference could be found in 1966. These changes in sex differences are observed in all subsamples, i.e., in young and old, in strictly religious and nonreligious students, and in students from both upper- and lower-class backgrounds (educational level of parents).

Adult↗

PubMed1991

Sex differences in androgen receptors and aromatase activity in microdissected regions of the rat brain.

Males are generally more responsive than females to the behavioral and neuroendocrine actions of androgens. The present experiments were performed to determine whether these differences may result from sex differences in the number of androgen receptors (AR) in specific brain areas. For this reason, AR binding was compared in both cytosol (ARc) and cell nuclear KCl extracts (ARn) from microdissected brain regions of gonadectomized male and female rats treated with doses of testosterone (T) that produced equivalent physiological circulating androgen levels. In addition, microsomal aromatase activity was measured as a biochemical index of tissue responsiveness to T, since estrogen formation in certain brain areas is regulated by androgen. One week after exogenous T administration, males exhibited significantly higher levels of ARn than females in the bed nucleus of the stria terminalis, periventricular preoptic area, and ventromedial nucleus. Males also had significantly higher aromatase levels in these same areas plus the medial preoptic nucleus and anterior hypothalamus. There were no significant differences in ARn concentrations in eight other nuclei that were examined for significant sex differences in ARc levels observed under these experimental conditions. When ARc levels were compared in untreated gonadectomized male and female rats, males had greater levels of ARc in the bed nucleus of the stria terminalis only, indicating that new receptor synthesis may be responsible for the sex differences observed in T-treated rats. These results suggest that sex differences in neural responsiveness to androgens may be due in part to sex differences in ARn occupation in specific brain regions.

Animals↗

PubMed2003

Two perspectives on the origin of sex differences in the brain.

Most sex differences in brain function are attributed to sex differences in the effects of gonadal secretions. In addition, however, male and female cells differ because of differential effects of sex chromosome genes expressed within the cells themselves. The latter conclusion comes from numerous studies in which sexual phenotype appears to be insensitive to the effects of sex hormones during development or cases in which sex differences develop before the onset of sex-specific patterns of gonadal secretions. Recently, mouse models have become available in which the genetic sex of brain cells is independent of the gonadal type (testes vs. ovaries), which allows a test of the role of sex chromosome genes in brain development. This paper reviews the evidence that genetic sex of brain cells influences their sexual phenotype, and critically discusses the relative advantages of various experimental approaches to study this effect.

Animals↗