Sexually dimorphic nucleus 4345497 215544402 2008-05-28T17:52:09Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. '''Sexually dimorphic nucleus''' (SDN), is believed to be related to sexual behaviors by scientists. It is a cluster of cells located in the [[preoptic area]] of [[hypothalamus]] of the brain. The volume of SDN is significantly larger (about twice) in males than in females, caused mainly by greater cell number and larger cell size, in male SDN.<ref name="Roselli"> {{cite journal |author=Roselli C, Larkin k, Resko J, Stellflug J, and Stormshak F |title=Volume of a Sexually Dimorphic Nucleus in the Ovine Medial Preoptic Area/Anterior Hypothalamus Varies with Sexual Partner Preference |journal=Endocrinology |volume=145 |issue=2 |pages=478–483 |year=2004 |pmid=14525915 |doi=10.1210/en.2003-1098}}</ref> SDN and its homologues widely exist in human, mammal and some other animal brains, including the third interstitial nucleus of the anterior hypothalamus (INAH3) in humans, ovine sexually dimorphic nucleus (oSDN) in the medial preoptic area/anterior hypothalamus (MPOA/AH) in sheep, sexually dimorphic nucleus in the preoptic area (SDN-POA) in rats, anterior hypothalamic nucleus (AHdc) in macaques, specific area in medial preoptic nucleus (POM) in quails, etc.. <ref name="Balthazart"> {{cite journal |author=Balthazart J, Ball G |title=Topography in the preoptic region: Differential regulation of appetitive and consummatory male sexual behaviors |journal=Frontiers in Neuroendocrinology |volume=28 |pages=161–178 |year=2007 |pmid=17624413 |doi=10.1016/j.yfrne.2007.05.003}}</ref> <ref name="Vasey"> {{cite journal |author=Vasey P, Pfaus J |title=A sexually dimorphic hypothalamic nucleus in a macaque species with frequent female=female mounting and same-sex sexual partner preference |journal=Behavioural Brain Research |volume=157 |pages=265–272 |year=2005 |pmid=15639177 |doi=10.1016/j.bbr.2004.07.005}}</ref> <!-- Image with unknown copyright status removed: [[Image:SDN.jpg|center|SDN]] --> ==Sexually Dimorphic Nucleus in Medial Preoptic Area== <!-- Image with unknown copyright status removed: [[Image:SDN-POA.jpg|center|SDN in medial preoptic area]] --> ===Formation and organization of SDN in medial preoptic area=== ==== Sex differences in SDN caused by exposure to [[testosterone]] (prenatal)==== The volume of SDN in medial preoptic area is modified by hormones, among which testosterone is proved to be of much importance. The larger volume of male SDN is correlated to the higher concentration of fetal testosterone level in males than in females. Also, there is evidence that testosterone acts during specific prenatal period to organize the development of [[aromatase]]-expressing neurons into the male-typical SDN (testosterone is transformed to [[estrogen]] by aromatase). The effect of testosterone is also reflected by the influence of fetal intrauterine position on the morphology of SDN-POA. Studies demonstrated that male rats which were gestated between two male fetuses (2M) have 2-fold larger SDN-POA volumes than those gestated between two female fetuses (2F). At the same time, the testosterone levels, as well as the 17β-estradiol (product of testosterone) levels, were found to be significantly larger in 2M males than in 2F males on gestation day 21 (testosterone can be transferred from adjacent male fetuses to the target rats). However, evidence fails to show any relationship between SDN volume and female fetal position.<ref> {{cite journal |author=Pei M, Matsuda k, Sakamoto H and Kawata M |title=Intrauterine proximity to male fetuses affects the morphology of the sexually dimorphic nucleus of the preoptic area in the adult rat brain |journal=European Journal of Neuroscience |volume=23 |pages=1234–1240 |year=2006 |pmid=16553785 |doi=10.1111/j.1460-9568.2006.04661.x}}</ref> <ref> {{cite journal |author=Roselli C, Stadelman H, Reeve R, Bishop C, Stormshak F |title=The ovine sexually dimorphic nucleus of the medial preoptic area is organized prenatally by testosterone |journal=Endocrinology |volume=148 |issue=9 |pages=4450–4457 |year=2007 |pmid=17540718 |doi=10.1210/en.2007-0454}}</ref> ====Sex differences in the volume of SDN caused by [[apoptosis]] (postnatal)==== According to some studies, the volume difference of SDN between males and females is related to apoptosis during early development after birth. In rats, central division of the medial preoptic nucleus (MPNc) is an important component of SDN-POA and evidence showed that the number of apoptotic cells within MPNc is greater in females than in males between postnatal day (PD) 7 and PD10. In MPNc, the levels of some proteins, which are related to apoptosis, were shown to be of significant difference between males and females. Such proteins include [[Bcl-2]] and Bax. Bcl-2 is an antiapoptotic protein. The level of Bcl-2 in PD8 male rats is much higher than that in female rats of the same age, hence the number of apoptotic cells of MPNc in PD8 male rats is much lower than PD8 female rats. On the other hand, Bax, a proapoptotic protein, shows lower level in PD8 males than in PD8 females. Also, the number of active caspase-3-ir cells was observed to be greater in females than in males, indicating higher level of apoptosis in female MPNc. Apoptosis also occurs in the anteroventral periventricular nucleus (AVPV), which is also a sexually dimorphic area and is located in the periventricular gray area at the rostral extreme of the [[third ventricle]]. In contrast with SDN-POA, AVPV has larger size in females than in males. It is proved that Bcl-2 level in AVPV is higher whereas Bax level is lower in females than in males, just as being opposite of those in MPNc. As indicated in these two cases, apoptotic cell death plays a critical role in the formation of sexually dimorphic nucleus, and the apoptotic cell number within SDN negatively correlates with the volume of SDN between different sexes. <ref> {{cite journal |author=Tsukahara S, Kakeyama M, Toyofuku Y |title=Sex Differences in the level of Bcl-2 Family Proteins and Caspase-3 Activation in the Sexually Dimorphic Nuclei of the Preoptic Area in Postnatal Rats |journal=Journal of Neurobiology |volume=66 |issue=13 |pages=1411–1419 |year=2006 |pmid=17013925 |doi=10.1002/neu.20276}}</ref> ===Role of SDN in controlling of male sexual behaviors=== Male sexual behaviors can be divided into two phases: the appetitive phase, which contains highly variable sequence of behaviors such as attracting and courting, and the consummatory phase, during which highly stereotyped copulatory behaviors occur. The medial preoptic area of the brain is considered to control the expression of both male [[copulation]] and male appetitive sexual behavior. It is found that large lesions of SDN-POA severely disrupt copulatory behavior in rats. Also, cell-body lesions of SDA pars compacta (a [[homologue|homology]] of SDN-POA) in gerbils produce severe disruptions of male copulatory behavior. Moreover, a study on medial preoptic nucleus (POM) (homologue of medial preoptic nucleus in rats) in quails showed that the activation of male copulatory behavior requires the [[aromatization|aromaticity]] of [[androgen]] (testosterone) into an estrogen (17β-estradiol). Like in SDN-POA, aromatase-expression neurons are a specific marker of the nuclear boundary of POM in squails. The intensity of male copulatory behavior is found to positively correlates with the number of the aromatase-expression neurons in the caudal part of POM.<ref name="Balthazart"> </ref> Appetitive behaviors are also partly controlled by medial preoptic area as aromatase-knockout mice show deficits in sexual motivation. However, appetitive behaviors are disrupted by the lesions in rostral part rather than caudal part of medial preoptic area. Lesions of the rostral part of medial preoptic area also diminish preference for female by male rats. Furthermore, [[in vivo]] dialysis experiments showed that the level of extracellular [[dopamine]] in the mPOA increases as the sexual appetitive sequences progress. mPOA’s involvement in the control of appetitive sexual behaviors is also confirmed by pharmacological manipulations of the dopaminergic system in it. In rats, lesions to mPOA can eliminate the male copulatory behavior but can only diminish appetitive behavior, which suggests that some other parts of the brain, except for mPOA, are also responsible for sexually appetitive behavior.<ref name="Balthazart"> </ref> ===Role of SDN in sexual partner preference=== ====Role of SDN in male partner preference==== Researches on the ovine sexually dimorphic nucleus (oSDN) in sheep demonstrate that the volume of oSDN varies with sexual partner preference in rams (volume of SDN in male-oriented rams is larger than femle-oriented rams). In nature, about 8% of rams prefer male partners instead of female partners (male-oriented rams). In one study conducted by Roselli, et al., 4 femal-oriented rams and 9 male-oriented rams were exposed to 2 estrous ewes and 2 rams, with their sexual behaviors (mounts and [[ejaculation]]s) being recorded. Female-oriented rams displayed significantly more mounts and ejaculations with ewes than with stimulus rams, whereas male-oriented rams showed the opposite. Then series of brain sections, including hypothalamic, [[temporal lobe]] and [[diencephalic|diencephalon]] tissues, were imaged. Also, [[in situ hybridization]] was conducted to examine the level of the expression of cytochrome P450 aromatase in these brain sections. The results showed that the volume of oSDN in male-oriented rams is approximately 2 times greater than that in female-oriented rams. The number of neurons within oSDN is significantly greater in male-oriented rams than in female-oriented rams, so it is with the mean length of the oSDN. But the neuron density is similar in both kinds of rams. In addition, aromatase [[mRNA]] levels are also tested, showing that the level of aromatase mRNA is significantly greater in female-oriented rams than male-oriented rams..<ref name="Roselli"> </ref> Other species have similar relationships between sexual preferences and the volume of SDN. For example, INAH3 in humans (homologue of oSDN) is significantly larger in heterosexual men than in homosexual men. ====Damage of SDN and changes in sexual partner preferences in males==== Bilateral damage to SDN in the medial preoptic area in male [[ferrets]] causes the change of males from male-typical preference to female-typical preference. Male ferrets which were sexually experienced and responded to female body odor, when treated by bilateral lesions to SDN, change to respond to male body odor. It is probable that SDN plays an important role in leading to mating and successful reproduction.<ref> {{cite journal |author=Alekseyenko O, Waters P, Zhou H, Baum M |title=Bilateral damage to the sexually dimorphic medial preoptic area/anterior hypothalamus of male ferrets causes a female-typical preference for and a hypothalamic Fos response to male body odors |journal=Physiology & Behavior |volume=90 |pages=438–449 |year=2007 |pmid=17118411 |doi=10.1016/j.physbeh.2006.10.005}}</ref> ====Role of SDN in female partner preference==== Although SDN is much related to sexual partner preferences in males, it does not show the same relationship to partner preferences in females. Evidence shows that SDN in medial preoptic area is not the prerequisite for the expression of male-typical sexual behaviour and sexual partner preferences in females. One piece of evidence comes from the study on female [[Japanese macaque]], which routinely court, mount (with [[pelvic thrusting|pelvic thrust]]), compete for, and even prefer certain female sexual partners over certain males. The part of the brain examined is the anterior hypothalamic nucleus (AHdc), a homologue of SDN-POA. Comparison of the AHdc nucleus volumes between Japanese macaque and rhesus macaque (a closely related sister species of Japanese macaque) shows that there is no significant difference between the volume of AHdc in more male-typical macaques and that in female-typical macaques.<ref name="Vasey"> </ref> ===Effects of proteins and other molecules on SDN in medial preoptic area=== ====NELL2==== NELL2 is a tissue-specific protein in the nervous system. It contains EGF ([[epidermal growth factor]])-like repeat domain and its gene expression is regulated by estrogen. NELL2 is also known to play a neuroprotective role rat [[hippocampal|hippocampus]] neurons. When NELL2 synthesis is blocked by intracerebroventricular injection of [[antisense]] (AS) NELL2 oligodeoxynucleotide (ODN) into neonatal male rat brains (postnatal day0-day5), the size of SDN-POA is decreased. Since volume of SDN is related to the level of testosterone, it is quite possible that the volume is finally due to the neuroprotective effect of estradiol which is produced from testosterone by aromatase. So the result that NELL2 blockage reduces the size of SDN-POA suggests that it probably has neuroprotective effect on SDN-POA.<ref> {{cite journal |author=Ellis S, Mouihate A, Pittman Q|title=Neuroendocrine programming and sexual differentiation |journal=Frontiers in Neuroendocrinology |volume=27 |pages=95–99 |year=2006}}</ref> ====[[Somatostatin]]==== The sex-specific transcription of somatostatin gene coincides with the establishment of sex differences in SDN-POA. It is observed that somatostatin mRNA appears in the SDN-POA of both males and females. On postnatal day 8 through postnatal day 35, the area of somatostatin mRNA-positive cells was significantly larger in males than in females, with males attain the maximum size of that area on day15 before decrease whereas females show no changes. Eventually the expression of somatostatin mRNA shows no difference between sexes. It is possible that somatostatin is related to the estrogen-dependent organization of SDN-POA.<ref> {{cite journal |author=Chitose O, Yasuhiko K, Sakuma Y |title=Transient transcription of the somatostatin gene at the time of estrogen-dependent organization of the sexually dimorphic nucleus of the rat preoptic area |journal=Endocrinology |volume=148 |issue=3 |pages=1144–1149 |year=2007 |pmid=17138650}}</ref> ====[[Fenitrothion]]==== Fenitrothion is a kind of [[organophosphate]] and it can affect the development of [[reproductive system]] of male rats. Treatment with fenitrothion to male rats causes regression of androgen-dependent organ weights because fenitrothion is a potent competitive [[androgen receptor]] antagonist. Its effect on SDN-POA is different between male rats and female rats. In male rats, prenatal exposure to fenitrothion causes significantly increase of the volume of SDN-POA; whereas, in female rats, prenatal exposure to fenitrothion causes significantly decrease of the volume of SDN-POA. One possible explanation is that fenitrothion can alter the activity of aromatase, which then alters the level of estrogens converted by it from androgens and finally alters the volume of SDN-POA.<ref> {{cite journal |author=Struve M, Turner K, Dorman D |title=Preliminary investigation of changes in the sexually dimorphic nucleus of the rat medial preoptic area following prenatal exposure to fenitrothion |journal=Journal of Applied Toxicology |volume=27 |issue=6 |pages=631–636 |year=2007 |pmid=17582585 |doi=10.1002/jat.1267}}</ref> ====[[Diethylstilbestrol]] (DES)==== Diethylstilbestrol (DES) is a synthetic nonsteroidal estrogen and was widely used for preventing threatened abortion. DES also has effect on development of the reproductive system. Low dose of DES exhibits inhibitory effect on plasma testosterone concentration in male rats while promotes follicular maturation in female rats. Experiments were done to see the effects of DES on SDN-POA volume. It is demonstrated that DES treatment altered the volume of SDN-POA in females by increasing it, resulting in larger volume SDN than controlled females. However, low dose of DES did not change the volume of SDN-POA in male rats.<ref> {{cite journal |author=Yamamoto M, Shirai M, Tamura A, Kobayashi T, Kohara S, Murakami M and Arishima K |title=Effects of maternal exposure to a low dose of diethylstilbestrol on sexual dimorphic nucleus volume and male reproductive system in rat offspring |journal=The Journal of Toxicological Sciences |volume=30 |pages=7–18 |year=2005 |doi=10.2131/jts.30.7}}</ref> ====[[Morphine]]==== Morphine can also alter the activities within the sexually dimorphic brain regions. Prenatal exposure to morphine increases copulatory behavior in male rats while decreases estrous behavior in female rats.<ref> {{cite journal |author=Slamberova R, Vathy I, Hnatczuk O |title=Expression of proopiomelanocortin and proenkephalin mRNA in sexually dimorphic brain regions are altered in adult male and female rats treated prenatally with morphine |journal=Journal of Applied Toxicology |volume=63 |issue=5 |pages=399–408 |year=2004 |pmid=15140157}}</ref> ==Other Sexually Dimorphic Areas in the Brain== Ventromedial nucleus of the hypothalamus (VMN) has long been considered as a sexually dimorphic nucleus. It is an important region for regulating the sexual responses in female rodents. The neurons within VMN have significant estrogen-dependent functional and structural plasticity. The synaptic organization of the VMN is sexually dimorphic. Females have more [[dendritic|dendrite]] [[synapse|chemical synapse]]s within VMN while males have more somatic synapses within that region. In addition, the size of postsynaptic densities of axospinous and axosomatic synapses is sexually dimorphic, with males having larger density than females. Estrogen plays an important role in modulating the sexually dimorphic synaptic connectivity of VMN. Estradiol levels are high on proestrus rats and return to low levels on diestrus rats. The volume of cell bodies within VMN in [[proestrus|estrous cycle]] rats and male rats is larger than [[diestrus|estrous cycle]] rats. Also, proestrus rats have significantly higher synapse density in VMN than diestrus rats. Moreover, [[GABA|Gamma-aminobutyric acid]]plays a role in VMN development such as sexual differentiation.<ref> {{cite journal |author=Susana I, Dulce Madeira M |title=Estrogen Modulates the Sexually Dimorphic Synaptic Connectivity of the Ventromedial Nucleus |journal=The Journal of Comparative Neurology |volume=484 |pages=68–79 |year=2005 |PMID: 15717306}}</ref> <ref> {{cite journal |author=Zhou J, Pfaff D, Chen G |title=Sex Differences in estrogenic regulation of neuronal activity in neonatal cultures of ventromedial nucleus of the hypothalamus |journal=PNAS |volume=102 |issue=41 |pages=14907–14912 |year=2005 |pmid=16204378 |doi=10.1073/pnas.0507440102}}</ref> ==References== {{reflist}} ==External links== {{cite web |title =Journal of Anatomy |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1256598}} {{cite web |title =BrainInfo |url=http://braininfo.rprc.washington.edu/indexabout.html}} [[Category:Limbic system]] [[Category:Neuroendocrinology]] [[Category:Sexuality]]