Sex Differences In Anatomy Research Articles

The factorial structure of self-reported androgen-promoted physiological traits

Androgens make major contributions to average sex differences in anatomy, physiology, and behavior. Despite having established their crucial role in sexual differentiation, much remains to be learned about how androgens coordinate their influences. The present study was undertaken to shed light on androgenic effects on the body using self-reported survey data. We analyzed the ratings provided by over 11,000 college students on the magnitude of eleven traits that previous research has shown to be influenced by testosterone or other androgens. Predictably, the average values for all eleven traits were significantly greater in males than in females. Nevertheless, when data were analyzed separately according to sex of the respondents, some of the traits failed to positively correlate with one another, suggesting that not all an-drogen-influenced traits differentiate in a simple fashion. Factor analysis of these eleven traits by sex reinforced this view by identifying four factors. In men, the primary factor loaded most heavily on: masculine body build, masculine mannerisms, overall physical strength, upper body strength, and lower body strength. The primary factor for women was limited to: upper body strength, lower body strength, and overall physical strength. In both sexes, the primary factor was interpreted as reflecting the influence of perinatal and post-pubertal testosterone exposure. The other three factors may reflect the effects of other androgens (e.g., androstenediol), or the influence of female hormones such as estradiol. Findings were discussed in terms of future use of self-reported physiological measures for assessing androgenic effects on the human body.

Fainting, emancipation and the ‘weak and sensitive’ sex

Fainting, emancipation and the ‘weak and sensitive’ sex

Reduced neuron density, enlarged minicolumn spacing and altered ageing effects in fusiform cortex in schizophrenia

Background Structural and functional MRI studies report reduced volume and activation of the fusiform gyrus in schizophrenia. The fusiform cortex is involved in object naming and face recognition. Neuron cell size, shape and density, glial cell density and minicolumn spacing in layers III and V of the fusiform cortex were assessed following systematic random sampling from 13 controls and 11 schizophrenic patients. Pyramidal cell density was reduced in schizophrenia. Non-pyramidal cell density was reduced in layer III of the left hemisphere in schizophrenia, mostly in females. Non-pyramidal cells were larger in schizophrenia. Glial cell density was unaltered. Fusiform minicolumn spacing was asymmetrically wider in the right hemisphere of normal control subjects. Minicolumns were less dense in schizophrenia, particularly in the left hemisphere of females and the right hemisphere of males. Reduced neuron density in the fusiform cortex in schizophrenia contributes to evidence of functional–anatomical abnormalities from neuroimaging and neuropathology studies. Anatomical sex differences in schizophrenia may relate to anatomical and cognitive sex differences associated with fusiform cortex in the normal population. Wider minicolumn spacing is consistent with reduced cell density and is linked to altered ageing in schizophrenia.

Spondylolysis in a pre‐contact San Francisco Bay population: behavioural and anatomical sex differences

AbstractSpondylolysis refers to a separation of the spinal body from the arch. Researchers have documented that these fractures occur due to stresses related to activities involving the lower limb and back. Spondylolysis in sacral and lumbar vertebrae of 146 (66 males, 66 females, 14 indeterminates) California Amerinds were examined to determine whether sex differences were present. Sacral anatomy (i.e. sacralisation and lumbarisation, sacral base angles, and superior facet morphology) was analysed in relation to spondylolysis and sex, to explore whether sex differences could be better explained through activity patterns or anatomical variation. Spondylolysis afflicted 24 individuals (16.4%). Males had more than twice the rate of spondylolysis than did females (26% and 11%, respectively). Activity patterns, such as thrusting and throwing shafted obsidian points, could explain the sex differences. Males were most frequently buried with obsidian point artefacts, whereas females were buried with mortar and pestles. For sacral anatomy, only males had lumbarisation, and all other anatomical variation had no significant sex differences. Lumbarisation related to spondylolysis in males. In this study, sacral anatomical variation could not fully account for sex differences in spondylolysis; activity patterns provided a better explanation. Nonetheless, anatomical variation may predispose males to spondylolysis, or spondylolysis may affect sacral anatomy. Copyright © 2008 John Wiley & Sons, Ltd.

Zebra finch sexual differentiation: the aromatization hypothesis revisited.

Zebra finches have emerged as an outstanding model system for the investigation of the mechanisms regulating brain and behavior. Their song system has proven especially useful, as the function of discrete anatomical regions have been identified, and striking parallels exist between the morphology of these regions and the level of their function in males and females. That is, the structures are substantially more developed in males, who sing, compared to females, who do not. These parallels extend from higher (telencephalic) centers to the brainstem motor nucleus that innervates the muscles of the vocal organ. Other dimorphic aspects of reproduction in the zebra finch, such as copulatory behaviors and sexual partner preference, however, are not associated with known sex differences in anatomy. In many species, sex differences in neural and peripheral structures and behavior are regulated by secretions from the gonads, which of course are sexually dimorphic themselves. In birds, sex differences at all of these levels (gonad, brain, and behavior) can be mediated by steroid hormones. However, it is not entirely clear that gonadal secretions normally participate at all of the levels. This paper reviews the evidence relating to the role of gonadal steroids in the sexual differentiation of reproductive behaviors and the central and peripheral structures known to regulate them in zebra finches, with a focus on estradiol, which has been most extensively studied in the masculinization of song system morphology and function.

Effects of endocrine‐active chemicals on the development of sex characteristics of Daphnia magna

AbstractStandard reproductive assays with daphnids involve parthenogenetically reproducing females and exclude the assessment of effects on sexual reproduction. The goals of this study were to characterize sexual differentiation of male and female daphnids (Daphnia magna) and to evaluate whether exposure to putative endocrine‐disrupting chemicals may perturb the development of sex characteristics. Anatomical sex differences that developed during maturation in males included elongated first antennae and morphologic alterations in the head capsule and carapace edge. Reproductive maturation in females was associated with the development of a brood chamber and abdominal process. Alterations in the growth rates of the first antennae of males and the abdominal process of females were used to evaluate the effects of chemical exposure on the development of these sex characteristics during maturation. Exposure of female daphnids to the nonsteroidal vertebrate estrogen diethylstilbesterol and the insect juvenile hormone analog methoprene at concentrations as low as 3.0 and 0.080 μM, respectively, stimulated development of the abdominal process. Exposure of males to the steroidal vertebrate androgen androstenedione (≥6.0 μM) stimulated development of the first antennae. These results demonstrate that the development of secondary sex characteristics in daphnids can be altered by chemical exposure.

Effects of novelty and pain on behavior and hippocampal extracellular ACh levels in male and female rats

In vivo microdialysis was used to assess the effects of novelty and pain on hippocampal ACh release in male and female rats. Experiments were carried out during the dark phase and consisted of 2 days of tests: on Day 1, after Baseline 1, animals were exposed to a new cage (Novelty) to which, 30 min later, a plastic cylinder (Object) was introduced. On Day 2, after Baseline 2, the Formalin test (50 μl of formalin 10%, s.c. injected in the dorsal hindpaw) was carried out in the animal's home cage. All behaviors were recorded. The extracellular levels of ACh in the dorsal hippocampus were estimated, in 10-min samples, by assay of ACh in the dialysates by HPLC. On Day 1 the raw values of ACh were higher in females than in males, but no sex difference was present when the percentage of change was considered. In both sexes the Novelty and Object tests induced an increase in ACh levels with respect to Baseline. Higher levels of exploration were present in females than males during the first 10 min of Novelty. On Day 2, ACh release increased in both sexes during the Formalin test. No sex difference in either ACh raw values or the percentages of change were found. Females showed higher levels of licking and lower levels of activity than males. The present study shows that novelty and pain induce similar hippocampal cholinergic activation in male and female rats but different behaviors. The results are discussed in light of the several anatomical and functional sex differences present in the hippocampus.

Dogmas and unsolved problems in brain sex differentiation

Throughout the animal kingdom, nervous systems differ between sexes. Sexual dimorphisms in neuroanatomical, physiological, and neurochemical parameters are reflected by sex-specific forms of behavior, in particular with regard to reproduction, and sex differences in neuroendocrine regulation. The present volume of Biomedical Reviews is mainly concerned with sex differences in the mammalian and human brain. However, it should at least be mentioned that the most convincing correlations between neuroanatomical and behavioral data have been provided by studies of the sexual differentiation of song control systems in bird species, in which the males sing and the females do not. In mammals, research used to locus on the hypothalamus commonly seen as the center for control of reproductive behavior and integration of hormonal and neural responses of the organism. We have therefore asked A. Matsumoto and Y. Arai to review the evidence for the hypothesis that sexually dimorphic functions of the hypothalamus are indeed based on a sex-specific neural circuitry. Notwithstanding the central role of the hypothalamus, it is important to note that more and more, often subtle, anatomical and/or functional sex differences have been and continue to be detected in other areas of the central nervous system. Of particular interest are sex differences in neural systems than are known. Biomedical Reviews 1997; 7: 1-3.

Sexual dimorphism of the anterior commissure and massa intermedia of the human brain

Neuroanatomical sex differences were observed in the midsagittal area of both the anterior commissure and the massa intermedia on analysis of postmortem tissue from 100 age-matched male and female individuals. The anterior commissure, a fiber tract whose axons in primates primarily connect the two temporal lobes, was an average of 12%, or 1.17 mm2 larger in females than in males. The massa intermedia, a structure that crosses the third ventricle between the two thalami, was present in 78% of the females and 68% of the males. Among subjects with a massa intermedia, the structure was an average of 53.3% or 17.5 mm2 larger in females than in males. Inclusive of subjects with and without a massa intermedia, this structure was a mean of 76% or 16.93 mm2 greater in females than in males. These sex differences were present despite the fact that the brains of males were larger than those of females. Since a majority of subjects were adults, it is unknown when sexual differentiation occurred. Anatomical sex differences in structures that connect the two cerebral hemispheres may, in part, underlie functional sex differences in cognitive function and cerebral lateralization.

Sex differences in the corpus callosum of the living human being

The sexual dimorphism of the corpus callosum has remained controversial since the original report by de Lacoste-Utamsing and Holloway in 1982, for several reasons: (1) measurements have been performed in a variety of ways in different laboratories, in part because published reports frequently do not describe the methodology in detail; (2) despite known age-related changes during both childhood and adulthood, no investigators have explicitly age-matched subjects; and (3) the size and shape of corpora callosa vary considerably among individuals, requiring large sample sizes to demonstrate significant sex differences. Therefore, we have examined magnetic resonance images for 24 age-matched children and 122 age-matched adults for possible sex differences in the corpus callosum. While we observed a dramatic sex difference in the shape of the corpus callosum, there was no conclusive evidence of sexual dimorphism in the area of the corpus callosum or its subdivisions. Utilizing several criteria, there were significant sex differences in shape: subjective evaluation indicated that the posterior region of the corpus callosum, the splenium, was more bulbous shaped in females as a group and in women, and more tubular-shaped in males as a group and in men; mathematical evaluation confirmed this observation in that the maximum width of the splenium was significantly greater in women than in men, and that the percentage by which the average width of the splenium was greater than that of the adjacent corpus callosum was significantly greater in females than in males. However, sex differences in bulbosity did not reach significance in children (aged 2-16 yr). In contrast, among the area measurements of the corpus callosum and 22 subdivisions, only 1 exhibited a significant sex difference, which would be expected by chance. The area of the corpora callosa increased significantly with age in children and decreased significantly with age in adults. In adults, the midsagittal surface area of the cerebral cortex decreased significantly with age in women but not in men. These anatomical sex differences could, in part, underlie gender-related differences in behavior and neuropsychological function.

Spatial configurations: Erikson reexamined

In a 1951 study, Erik Erikson reported differences in preadolescents' play constructions. He claimed that his findings reflected differences between males and females in their experience and perception of space. The present study replicated but also expanded the original design. In order to control for possible sex bias of materials, a constructed scene using only blocks was added to Erikson's original design. The results failed to replicate Erikson's findings. In fact, in the construction of scenes from blocks, more females than males built erected structures; this was true across all ages. These findings are in direct contrast to Erikson's results, and they lead to the conclusion that the materials provided, not innate anatomical sex differences, account for the resulting spatial configurations.

73 NAMING MALE AND FEMALE GENITALIA

To document the clinical impression that young girls in the U.S. are given little or confusing information about their external genitalia, families were interviewed and preschool books and toys evaluated. 30 highly educated mothers were asked by their pediatrician about the terms for genitalia they used with their 25 female and 31 male children between 1 and 18 years of age. Mothers used words for male external genitalia with 100% of their boys, and words for testicles in addition to penis were reported for 39%. Only 8% of the girls were given a specific label(s) for their external genitalia; vagina was the sole sex organ term for 88%. Women reported with regret that they had learned words for their own external genitalia only in adolescence or adulthood. Yet they had not provided their girls with a different experience.Of the recent books on sex and reproduction for children grade 1 or below available in local libraries and bookstores, the few which dealt explicitly with anatomical sex differences were similarly misleading. Of these 11 books, only 1 used a term for female external genitalia, but all labeled the male. “Anatomically correct” dolls showed male genitalia, penis and scrotum. So-called female dolls had no genitalia. Neither parents, books nor toys help the young girl identify and understand her major sex organs. This avoidance or omission may reflect a persisting intrapsychic and societal discomfort with the external female genitalia and may interfere with the little girl's pride and pleasure in those genital parts most interesting and important during toilet training and the preschool years.