All you gay people who thought you had free will.
Nope, you are bitches to destiny, physics, and the amount of testosterone that was produced when you were a fetus.
Read em and weap boys...
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 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 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 quails. 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.[3]
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 vivodialysis 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.
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 male sheep (rams). Homosexual rams (roughly 8% of the population) have been found to have oSDNs that are about half the size of those in heterosexual rams.[2] In one study conducted by Roselli, et al., 4 heterosexual rams and 9 homosexual rams were exposed to 2 estrous ewes and 2 rams, with their sexual behaviors (mounts andejaculations) being recorded. Heterosexual rams displayed significantly more mounts and ejaculations with ewes than with stimulus rams, whereas homosexual rams showed the opposite. 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. The results showed that the volume of oSDN in heterosexual rams is approximately 2 times greater than that in homosexual rams. The number of neurons within oSDN is significantly greater in homosexual rams than in heterosexual 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 heterosexual rams than in homosexual rams.[2]
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.[8]