[1] Thus far, for all species of mammals investigated, the SDN has been repeatedly found to be considerably larger in males than in females.
In males, a substantial decrease in the cell number of the human SDN was observed between the age of 50–60 years.
The effect of testosterone is also shown by the influence of fetal intrauterine position on the morphology of SDN-POA.
[6][7] According to some studies, the volume difference of SDN between males and females is related to apoptosis during early development after birth.
In MPNc, the levels of some proteins, which are related to apoptosis, were shown to be of significant difference between males and females.
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.
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 of SDN-POA) in gerbils produce severe disruptions of male copulatory behavior.
The intensity of male copulatory behavior is found to positively correlate with the number of the aromatase-expression neurons in the caudal part of POM.
[4] Appetitive behaviors are also partly controlled by medial preoptic area as aromatase-knockout mice show deficits in sexual motivation.
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.
Then series of brain sections, including hypothalamic, temporal lobe and 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.
This research linked an established sexually dimorphic area of the brain to hetero- and homosexual behavior in men.
In sum, some contemporaries cast serious doubt over LeVay's hypothesis that homosexual males have a "female hypothalamus" and that the key mechanism of differentiating the "male brain from originally female brain" is the epigenetic influence of testosterone during prenatal development.
It contains EGF (epidermal growth factor)-like repeat domain and its gene expression is regulated by estrogen.
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.
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.
Estrogen plays an important role in modulating the sexually dimorphic synaptic connectivity of VMN.
[22][23] The anteroventral periventricular nucleus (AVPV) is a cluster of cells located in the preoptic area of the hypothalamus that is typically larger in females than in males.