Sexual Dimorphism Characteristics Research Articles

Sexual Dimorphism in Commercially Important Fish Species in India: A Review

Sexual dimorphism in fishes is an important biological aspect, which helps distinguish males and females based on various primary and secondary sexual characteristics. Based on sexual dimorphic characteristics fishes can be categorized as monomorphic, temporary dimorphic and permanent dimorphic. These characters can be either persistent or non-persistent types in fishes. Sexual dimorphism also can be determined using biometric characteristics as well. In fish, males typically display more conspicuous sexual characteristics compared to females, including the development of vibrant colouration, nuptial tubercles, or the formation of accessory organs. Sexual dimorphism is a significant trait helpful in categorizing and classifying fish species more accurately. It also has significant implications for commercial fisheries, which can aid in catch from the wild. This also can contribute to understanding the intricacies of aquatic ecosystems but also underscores the practical applications of studying sexual dimorphism in the context of sustainable fisheries management.

A new genus and a new species of wasp-mimicking Harpactorini (Hemiptera, Heteroptera, Reduviidae, Harpactorinae), with an updated key to the Neotropical genera.

Quasigraptocleptesmaracristinaegen. nov., sp. nov. (Hemiptera, Heteroptera, Reduviidae, Harpactorinae, Harpactorini) is described based on male and female specimens from Brazil. Photographs and comments about the syntypes of Myocorisnigriceps Burmeister, 1835, Myocorisnugax Stål, 1872, Myocoristipuliformis Burmeister, 1838 and Xystonyttusichneumoneus (Fabricius, 1803) are presented. The intra-specific variability and sexual dimorphic characteristics among specimens of Q.maracristinaesp. nov. are recorded. General characteristics of Hiranetis Spinola, 1837, Graptocleptes Stål, 1866, Quasigraptocleptesgen. nov. and Parahiranetis Gil-Santana, 2015, which seem to be closer genera, are compared, including those of the male genitalia of some species. A key to the species of Myocoris Burmeister, 1835, and an updated key to Neotropical wasp-mimicking Harpactorini genera are provided.

Growth Patterns and Growth-Axis Gene Expressions in Sexual Dimorphism of Silurus asotus Linnaeus, 1758

Aquaculture has tremendous economic significance in distinguishing males and females in the juvenile Silurus asotus (Linnaeus, 1758) to obtain a female population with tremendous growth potential. To investigate the potential biological markers between young males and females S. asotus, we analyzed the characteristics of sexual dimorphism by measuring the 14 length traits and 9 weight indicators in an artificial insemination population at 3, 5, and 7 months. In addition, quantitative real-time PCR (qRT-PCR) was performed to determine the sexually dimorphic expression of the growth hormone-1 gene (GH-1), growth hormone receptor gene (GHR), and insulin-like growth factor gene (IGF-1) in the hypothalamus, pituitary, gonad, and liver, at 3, 5, and 7 months. The results showed that in morphology, except for eye diameter and the distance between the pelvic and anal fins in 3-month fish, all other morphological indicators were significantly ( P < 0.05 ) or very significantly ( P < 0.01 ) different between juvenile males and females. The visceral weight, eviscerated weight, and intestine weight in females were significantly ( P < 0.05 ) or very significantly ( P < 0.01 ) higher than in males at 5 and 7 months. Joint static allometric analyses on 14 length indicators relative to weight showed different sex growth patterns in 3-month, 5-month, and 7-month fish. In gene expression patterns, GH-1, IGF-1, and GHR were highly expressed in the pituitary, with higher levels in females ( P < 0.05 or P < 0.01 ). In contrast, the three genes were all more highly expressed in the testis than in the ovary ( P < 0.01 ), indicating their essential roles in testis development. Our results demonstrate that S. asotus has female-biased sexual dimorphism. The length traits related to head shapes could be the potential phenotype marker to distinguish females and males in 7-month juveniles.

Morphologic variations in the craniofacial structures in Japanese adults and their relationship with sex differences

The morphology of the human face varies broadly, with genetic and environmental factors determining these variations. Examining variations in the 3-dimensional (3D) craniomandibular morphology and identifying related factors (eg, sex differences) are important in orthodontic clinics. This study observed shape variations in the 3D facial morphology of Japanese adults showing skeletal Class 1 malocclusion and examined the association of sexual dimorphism with shape variations. Sixty cone-beam computed tomography images of Japanese adults (30 males and 30 females) with skeletal Class I malocclusion were employed. In each cone-beam computed tomography image, wire mesh fitting was conducted as previously described. A principal component (PC) analysis after Procrustes registration and the PC clustering method was conducted to observe the shape variations. A PC regression analysis was conducted to determine the sexual morphologic characteristics. Nine PCs depicting 62% of the morphology were determined. Four typical phenotypes were found, mainly related to mandibular protrusion (PC1) and the vertical divergence of the face (PC2). PCs related to sex determination were PC3 (robustness of the mandibular angle in males), PC5 (greater size and shape of the coronoid and mastoid processes in males), and PC7 (greater maxillary width in males), accounting for 16% of total variations. The major shape variations in skeletal Class 1 subjects were related to nonsexual dimorphic characteristics (ie, mandibular protrusion and facial divergence). Sexual dimorphic characteristics were evaluated in detail and accounted for 16% of total morphologic variations.

A study on morphometric and sexual dimorphism characteristics of giant huntsman spider in Kandi, sangareddy region of Telangana state, India

A study on morphometric and sexual dimorphism characteristics of giant huntsman spider in Kandi, sangareddy region of Telangana state, India

Cranial morphology of the orectolobiform shark, Chiloscyllium punctatum Müller & Henle, 1838

Elasmobranchs, comprising sharks, skates, and rays, have a long evolutionary history extending back into the Palaeozoic. They are characterized by various unique traits including a predominantly cartilaginous skeleton, superficial prismatic phosphatic layer, and permanent tooth replacement. Moreover, they exhibit a more or less marked sexual dimorphism. Especially the morphology of the chondrocranium and the elements of the whole cranial region of extant and extinct chondrichthyans can provide valuable information about corresponding functions, e.g. the feeding apparatus might reflect the diet of the animals. However, studies on sexual dimorphisms are lacking in orectolobiform sharks, therefore, little is known about possible sexual dimorphic characters in the cranial region in this group. For this reason, we present in this study a comprehensive morphological description of the cranial region of the brownbanded bamboo shark Chiloscyllium punctatum Müller & Henle, 1838, with a special focus on its sexual dimorphic characters. Our results reveal clear morphological differences in both sexes of the examined C. punctatum specimens, particularly in the chondrocranium and the mandibular arch. The female specimen shows a comparatively more robust and compact morphology of the chondrocranium. This pattern is also evident in the mandibular arch, especially in the palatoquadrate. The present study is the first to describe the morphology of an orectolobiform shark species in detail using both manual dissection and micro-CT data. The resulting data furthermore provide a starting point for pending studies and are intended to be a first step in a series of comparative studies on the morphology of the cranial region of orectolobiform sharks, including the determination of possible sexual dimorphic characteristics.

Gender determination analysis using anthropometrical dimensions of 2D:4D, foot index and mandibular canine index.

Introduction:Sex determination is a challenge for forensic experts during mass disasters. Teeth are an excellent source in both living and nonliving population, where bodies are mutilated beyond recognition. Mandibular canines can be employed for gender determination in such situations. Similarly, second-to-fourth digit ratio (2D:4D) and foot index (FI) are sexually dimorphic and differ in males and females. Mandibular canine index (MCI), 2D:4D and FI are considered quick, easy and reproducible methods for determining the sex of an individual.Aim:This study aimed to determine the combined role of MCI, 2D:4D and FI in denoting gender identity and establish their correlation.Materials and Methods:The present study comprised of 100 dental students (50 males and 50 females) of our institution, aged 19–25 years, with specific inclusion and exclusion criteria. The measurements were done using a Vernier caliper, a divider and a ruler, and MCI, 2D:4D and FI were calculated using their specific formulae. The calculated values of FI, MCI and 2D:4D were subjected to statistical analysis.Results:There was a statistically significant difference observed between left MCI (P < 0.05), right and left 2D:4D and FI (P < 0.05). The results revealed that 2D:4D was less, whereas MCI and FI were higher in males than in females. The observed MCI was compared with standard MCI, and left MCI revealed higher sexual dimorphic characteristics (15.2%). Although the overall correlation between 2D:4D, FI and MCI was insignificant, the measurements were comparable.Conclusion:This study indicated that the anthropometric dimensions of 2D:4D, FI and MCI can be used for sex determination independently with accurate results.

Beauty Is in the Eye of the Beholder: The Appraisal of Facial Attractiveness and Its Relation to Conscious Awareness.

Previous research suggests that facial attractiveness relies on features such as symmetry, averageness and above-average sexual dimorphic characteristics. Due to the evolutionary and sociobiological value of these characteristics, it has been suggested that attractiveness can be processed in the absence of conscious awareness. This raises the possibility that attractiveness can also be appraised without conscious awareness. In this study, we addressed this hypothesis. We presented neutral and emotional faces that were rated high, medium and low for attractiveness during a pilot experimental stage. We presented these faces for 33.33 ms with backwards masking to a black and white pattern for 116.67 ms and measured face-detection and emotion-discrimination performance, and attractiveness ratings. We found that high-attractiveness faces were detected and discriminated more accurately and rated higher for attractiveness compared with other appearance types. A Bayesian analysis of signal detection performance indicated that faces were not processed significantly at-chance. Further assessment revealed that correct detection (hits) of a presented face was a necessary condition for reporting higher ratings for high-attractiveness faces. These findings suggest that the appraisal of attractiveness requires conscious awareness.

PERTUMBUHAN, UMUR, DAN DIMORFISME SEKSUAL IKAN PELANGI ARFAK, Melanotaenia arfakensis Allen, 1990 DI SISTEM SUNGAI PRAFI, MANOKWARI, PAPUA BARAT

ABSTRACTArfak rainbow fish, Melanotaenia arfakensis is an endemic fish on several river systems in the northeastern part of the Vogelkop peninsula. This study aims to describe the growth, age at first maturity, and sexual dimorphism of this endemic fish on the Nimbai Stream and the Aimasi Stream, the Prafi River system. The fish were caught using handnet, then were measured their standard length and individual weight. Data were analyzed to estimated growth patterns, von Bertalanffy's growth rate, age at first maturity and sexual dimorphism characteristics. The results showed that male growth patterns varied, with a tendency of the increase in body length faster than that of body weight (negative allometric patterns) with b values ranging from 2.886 to 3.132. On the other hand, the female individuals had positive allometric patterns (b values ranged from 3.062 to 3.378). The growth rate (K) of male body length was faster (0.165-0.174) than that of female individuals (0.159-0.163). Male individuals reached the first maturity condition earlier (at age of 1.83-2.18 years) than female individuals (at age of 2.49-2.64 years). Sexual characteristics between the sexes are related to body height starting to appear when fish are of a standard length of larger than 18.22 mm or when male fish begin to approach the time of the first sexual maturity. Understanding of growth, age, and the characteristics of the sexual dimorphism of endemic fish has an important meaning in monitoring population conditions and for conservation efforts in their natural habitat.

Abstract 104: Aortic Dilation and Elasticity in Thoracic Aortic Aneurysm in a Marfan Model is Sexually Dimorphic

Objective: Meta-analysis of data derived from Marfan patients in the Genetically-Triggered Thoracic Aortic Aneurysms and Cardiovascular Conditions (GenTAC) consortium revealed that thoracic aortic aneurysms occur more frequently in men than in women. To determine the characteristics of sexual dimorphism in experimental thoracic aortic aneurysms of a Marfan model, we determined ascending aortic and aortic root morphology in male and female fibrillin-1 haploinsufficent (FBN1 C1041G/+) mice using ultrasonography. Method and Results: Aortas from 4 to 6 week old male and female FBN1 C1041G/+ mice and their wild type littermates were assessed by high frequency ultrasonography. Mice were anesthetized and maintained at a heart rate of 450-550 beats per minute. Ultrasound images were captured using a Vevo 3100 instrument with a 40 MHz tranducer. The maximal luminal diameter of ascending aortic between the sinotubular junction and the innominate artery, and the aortic root diameter at the sinus of valsalva, were measured in mid-systole and end-diastole by two independent observers who were blinded to mice identity. FBN1 C1041G/+ mice demonstrated greater ascending aortic dilation in male mice compared to female mice, whereas no difference in aortic root diameter were detected between male and female wild type littermates. In addition, modest ascending aortic dilation was detected before aortic root dilation in FBN1 C1041G/+ mice. Ascending aortas from FBN1 C1041G/+ mice also demonstrated loss of elasticity as evidenced by reduced expansion in systole. Interestingly, this difference was detected much earlier than expected. Conclusion: The fibrillin-1 haploinsufficent model of Marfan syndrome associated thoracic aortic aneurysm demonstrate sexual dimorphism in ascending aortic dilation. Loss of elasticity in the ascending aorta is also an early manifestation in this thoracic aortic aneurysm model.

Profiling extracellular vesicle release by the filarial nematode Brugia malayi reveals sex-specific differences in cargo and a sensitivity to ivermectin.

The filarial nematode Brugia malayi is an etiological agent of Lymphatic Filariasis. The capability of B. malayi and other parasitic nematodes to modulate host biology is recognized but the mechanisms by which such manipulation occurs are obscure. An emerging paradigm is the release of parasite-derived extracellular vesicles (EV) containing bioactive proteins and small RNA species that allow secretion of parasite effector molecules and their potential trafficking to host tissues. We have previously described EV release from the infectious L3 stage B. malayi and here we profile vesicle release across all intra-mammalian life cycle stages (microfilariae, L3, L4, adult male and female worms). Nanoparticle Tracking Analysis was used to quantify and size EVs revealing discrete vesicle populations and indicating a secretory process that is conserved across the life cycle. Brugia EVs are internalized by murine macrophages with no preference for life stage suggesting a uniform mechanism for effector molecule trafficking. Further, the use of chemical uptake inhibitors suggests all life stage EVs are internalized by phagocytosis. Proteomic profiling of adult male and female EVs using nano-scale LC-MS/MS described quantitative and qualitative differences in the adult EV proteome, helping define the biogenesis of Brugia EVs and revealing sexual dimorphic characteristics in immunomodulatory cargo. Finally, ivermectin was found to rapidly inhibit EV release by all Brugia life stages. Further this drug effect was also observed in the related filarial nematode, the canine heartworm Dirofilaria immitis but not in an ivermectin-unresponsive field isolate of that parasite, highlighting a potential mechanism of action for this drug and suggesting new screening platforms for anti-filarial drug development.

The ultimate legs of Chilopoda (Myriapoda): a review on their morphological disparity and functional variability.

The arthropodium is the key innovation of arthropods. Its various modifications are the outcome of multiple evolutionary transformations, and the foundation of nearly endless functional possibilities. In contrast to hexapods, crustaceans, and even chelicerates, the spectrum of evolutionary transformations of myriapod arthropodia is insufficiently documented and rarely scrutinized. Among Myriapoda, Chilopoda (centipedes) are characterized by their venomous forcipules—evolutionarily transformed walking legs of the first trunk segment. In addition, the posterior end of the centipedes’ body, in particular the ultimate legs, exhibits a remarkable morphological heterogeneity. Not participating in locomotion, they hold a vast functional diversity. In many centipede species, elongation and annulation in combination with an augmentation of sensory structures indicates a functional shift towards a sensory appendage. In other species, thickening, widening and reinforcement with a multitude of cuticular protuberances and glandular systems suggests a role in both attack and defense. Moreover, sexual dimorphic characteristics indicate that centipede ultimate legs play a pivotal role in intraspecific communication, mate finding and courtship behavior. We address ambiguous identifications and designations of podomeres in order to point out controversial aspects of homology and homonymy. We provide a broad summary of descriptions, illustrations, ideas and observations published in past 160 years, and propose that studying centipede ultimate legs is not only essential in itself for filling gaps of knowledge in descriptive morphology, but also provides an opportunity to explore diverse pathways of leg transformations within Myriapoda.

Симметричность лица и выраженность полового диморфизма в его пропорциях у исанзу, традиционных земледельцев восточной Африки

&lt;p&gt;In modern scientific literature on sexual selection, a significant place is occupied by scientific works that examine the relationship between indicators of fluctuating asymmetry of the face, the expression of sexual dimorphism and individual attractiveness and reproductive success. The present study is devoted to analysis of the data of the ethno-psychological research of representatives of Isanzu tribe - one of the traditional agricultural societies of East Africa (Tanzania). An assessment of the degree of symmetry of the faces of men and women of Isanzu tribe, as well as the expression of characteristics of sexual dimorphism in face proportions was the purpose of this study. On the basis of the evaluation of photographic images of 159 men and 56 women of Isanzu tribe we analyzed and compared the following indexes: indexes of fluctuating asymmetry and sexual dimorphism of the face, finger index, the ratio of waist to hips, the ratio of shoulders to hips, and finally indicators of the age in which expression of fluctuating asymmetry reaches its maximum level. The results of the analysis indicate that faces of men and women of Isanzu tribe do not differ in the level of fluctuating asymmetry, male faces are characterized by pronounced masculine traits; as for the calculation of indexes, we did not detect any age differences based on fluctuating asymmetry index, whereas masculine index tends to increase linearly with increasing age&lt;/p&gt;

Sexual dimorphism in an under-ice spawning fish: the burbot (Lota lota)

Sexual dimorphic characteristics arise in response to differing selective pressures on the sexes and can be used to attract mates or signal reproductive readiness. How sexual dimorphism is expressed where visual cues may be of limited use is an underexplored aspect of reproductive ecology. The burbot (Lota lota (L., 1758)) is a common boreal fish that is not overtly sexually dimorphic. It spawns mid-winter in a light-limited under-ice environment. We examined a variety of morphological and reproductive characteristics in burbot from a northern lake over one full year to assess both seasonal and sex-based variation. Spawning occurred under ice in early February. Seasonal variation was more pronounced in females for many of the traits examined. Growth, fin lengths, swim bladder mass, and liver lipid concentration did not differ between the sexes. Male burbot had significantly higher body condition, larger gas glands, and smaller livers. Males also had significantly larger gonads than females, unusual for boreal fishes. The high gonadal investment of male burbot suggests that sperm competition may be intense in this species. This study demonstrates that sexual dimorphism can be subtle and is present in a seemingly monomorphic species—the burbot.

The Left Hand Second to Fourth Digit Ratio (2D:4D) Does Not Discriminate World-Class Female Gymnasts from Age Matched Sedentary Girls

IntroductionThe second to fourth-digit-ratio (2D:4D), a putative marker of prenatal androgen action and a sexually dimorphic trait, has been suggested to be related with sports performance, although results are not univocal. If this relation exists, it is most likely to be detected by comparing extreme groups on the continuum of sports performance.MethodsIn this study the 2D:4D ratio of world-class elite female artistic gymnasts (n = 129), competing at the 1987 Rotterdam World-Championships was compared to the 2D:4D ratio of sedentary age-matched sedentary girls (n = 129), alongside with other anthropometric characteristics including other sexually dimorphic traits such as an androgyny index (Bayer & Bayley) and Heath-Carter somatotype components (endomorphy, mesomorphy, ectomorphy) using AN(C)OVA. 2D:4D was measured on X-rays of the left hand.ResultsLeft hand 2D:4D digit ratio in world class elite female gymnasts (0.921±0.020) did not differ significantly from 2D:4D in age-matched sedentary girls (0.924±0.018), either with or without inclusion of potentially confounding covariates such as skeletal age, height, weight, somatotype components or androgyny index. Height (161.9±6.4 cm vs 155.4±6.6 cm p<0.01), weight (53.9±7.6 kg vs 46.2 6.3 kg p<0.01), BMI (20.51±2.41 kg/m2 vs 19.05±1.56 kg/m2), skeletal age (15.2±1.1 y vs 14.5±1.2 y p>0.01), somatotype components (4.0/3.0/2.9 vs 1.7/3.7/3.2 for endomorphy (p<0.01), mesomorphy (p<0.01) and ectomorphy (p<0.05) respectively) all differed significantly between sedentary girls and elite gymnasts. As expressed by the androgyny index, gymnasts have, on average, broader shoulders relative to their hips, compared to the reference sample. Correlations between the 2D:4D ratio and chronological age, skeletal age, and the anthropometric characteristics are low and not significant.ConclusionAlthough other anthropometric characteristics of sexual dimorphism were significantly different between the two samples, the present study cannot discriminate sedentary girls from world-class female gymnasts by means of the left hand 2D:4D ratio.

Morphometric variation of the skull during postnatal development in the Lowland European bisonBison bonasus bonasus

We studied the variation of linear measurements and skull capacity in Lowland European bisonBison bonasus bonasus (Linnaeus, 1758) during postnatal development, and the dependencies of the parameters in relation to sex, age, and body mass of the animals. Material consisted of 599 bison skulls (310 males and 289 females), within the age range of 1 month to 21 years (males) and to 27 years (females). In the group of calves to 1 year old, no sex connected differences in skull measurements were observed, whereas the skull capacity in older calves was significantly larger (0.01>p>0.001) in males than in females. From the third year of life, most skull measurements display characteristics of sexual dimorphism. Skull development in both sexes is most intensive during the first three years of life, and slows from the age of 5. In older individuals of both sexes (≥ 6 years), orbital breadth continues growing and, in females, breadth of splanchnocranium continues increasing. Growth in a bison’s skull capacity is most intensive up to the third year of life and slows from the age of 5. During postnatal development, a bison skull grows proportionally except the neurocranium, which grows slightly slower in comparison with basal length and its development finishes earlier than that of splanchnocranium. In ontogenesis, a bison skull grows much slower compared to body mass. In relation to body mass, skull capacity and the height of neurocranium grow most slowly while orbital breadth grows most intensively. The results obtained were compared with data on skull sizes of bison born in 1930–1950 and bred in captivity and with skulls of the American bisonBison bison. Inbreeding is probably responsible for some types of phenotypic abnormalities in the skull which appear in modern European bison.

Gender-specific behavioral and immunological alterations in an animal model of autism induced by prenatal exposure to valproic acid

Autism is a severe behavioral disorder characterized by pervasive impairments in social interactions, deficits in verbal and non-verbal communication, and stereotyped behaviors, with a four times higher incidence in boys than in girls. The core symptoms are frequently accompanied by a spectrum of neurobehavioral and immunological derangements, including: aberrant sensitivity to sensory stimulation, anxiety, and decreased cellular immune capacity. Recently, a new potential rodent model of autism induced by prenatal exposure to valproic acid (VPA rats) has been proposed. In order to determine if gender has an influence on alterations observed in VPA rats, male and female rats have been evaluated in a battery of behavioral, immunological, and endocrinological tests. A plethora of aberrations has been found in male VPA rats: lower sensitivity to pain, increased repetitive/stereotypic-like activity, higher anxiety, decreased level of social interaction, increased basal level of corticosterone, decreased weight of the thymus, decreased splenocytes proliferative response to concanavaline A, lower IFN-gamma/IL-10 ratio, and increased production of NO by peritoneal macrophages. Female VPA rats exhibited only increased repetitive/stereotypic-like activity and decreased IFN-gamma/IL-10 ratio. Sexual dimorphism characteristics for measured parameters have been observed in both groups of animals, except social interaction in VPA rats. Our results confirm existence of similarities between the observed pattern of aberrations in VPA rats and features of disturbed behavior and immune function in autistic patients, and suggest that they are gender-specific, which is intriguing in light of disproportion in boys to girls ratio in autism.

Description of the male ofUpogebia miyakeifrom Ryukyu Islands, Japan (Decapoda: Thalassinidea: Upogebiidae)

The small upogebiid shrimp,Upogebia miyakei, was originally described from a female collected from Ishigaki-jima Island, Ryukyu Islands, southern Japan. However, no male specimen has been reported since the discovery of the holotype. During surveys at Iriomote-jima Island and its type locality, both females and males ofU. miyakeiwere collected from the intertidal zone. Based on this material a full description of the male is given, and comparison with the female reveals the sexual dimorphic characteristics. The palm of the first pereiopod of male specimens is about 1.5 times wider than that of females. In male specimens, one or two spines are present on the dorsal margin of the palm of the first pereiopod, while three to six sharp spines are found on female specimens. This species is compared here withUpogebia lincolnifrom Java, Indonesia.

Statistical Shape Analysis of Differences in the Shape of the Corpus Callosum Between Genders

Sexual dimorphic characteristics, which play an important role in human evolution studies and biological research, can be studied morphologically and metrically. Geometric morphometrics allows a better assessment of morphological characteristics. Statistical shape analysis has a long history in neuroanatomical and other research. The aim of this study was to identify shape differences of the corpus callosum between genders. Landmark coordinate data were collected from two-dimensional magnetic resonance imaging scans of 93 homogeneously aged patients, 45 men and 48 women. These data were analyzed using Euclidean distance matrix analysis and thin plate spline analysis. The general shape variability of the corpus callosum of men was greater than that of women (men, 0.134; women, 0.097). We found no significant difference between sexes in the general shape of the corpus callosum, but we did find significant differences in the distances between some landmarks. Deformation of the corpus callosum between men to women was mainly detected in the posterior of the corpus callosum. These results serve as a reference for future studies on shape alterations of the corpus callosum associated with certain conditions.

Sex-/Ovarian Steroid-Dependent Release of Endomorphin 2 from Spinal Cord

Mu-opioid receptor (MOR) agonists have been shown to be more potent analgesics in male than female rodents. Regulation of spinal MOR-coupled antinociception by 17beta-estradiol (estrogen, E2) and progesterone (P) is also sexually dimorphic; pregnancy levels of E2/P activate MOR-coupled analgesic pathways in male but not female rats. We hypothesized that the sexual dimorphic characteristics of MOR-coupled antinociception reflects sexual dimorphism in the regulation of the release from spinal cord of the endogenous MOR agonist, endomorphin 2 (EM2). Parameters of spinal EM2 release manifesting sexual dimorphism include its 1) magnitude: in vitro basal and K+-evoked release of EM2 from spinal tissue of male rats is approximately 50% greater than that observed from spinal cord of females; 2) modulation by ovarian sex steroids: E2/P treatment significantly enhanced K+-evoked EM2 release from spinal tissue of males, but not females; and 3) enhancement by opioid receptor blockade: naloxone enhanced stimulated EM2 release from spinal tissue of both males and females, but it augmented basal release from spinal tissue of only males. Enhancement of EM2 release by naloxone reflects negative coupling of MOR to EM2 release and hence its modulation by negative feedback since only activation of MOR, not kappa-or delta-opioid receptors, was able to inhibit evoked EM2 release. These data reveal that the EM2-MOR spinal analgesic system is more robust and "higher gain" in male versus female rodents. These findings could provide a mechanistic rubric for understanding the male female dichotomy in prevalence and intensity of chronic pain syndromes.