Researchers have identified a protein present in all mammalian semen that they believe could directly affect the female brain in order to stimulate ovulation. Known as the nerve growth factor, it's typically found in nerve cells where it regulates nerve maintenance. TG Daily reports:
NGF in the semen acts as a hormonal signal, working through the hypothalamus of the female brain and the pituitary gland. This triggers the release of other hormones that signal the ovaries to release an egg or eggs.

While the protein may function differently from animal to animal, the team found it in every species they checked, from llamas, cattle and koalas to pigs, rabbits, mice, and humans - implying it's pretty important.

Just how it works, though, its role in various species, and its clinical relevance to human infertility are still unclear.

..."The idea that a substance in mammalian semen has a direct effect on the female brain is a new one," says Adams. "This latest finding broadens our understanding of the mechanisms that regulate ovulation and raises some intriguing questions about fertility."
Researchers believe that this NGF discovery may someday be able to help couples or single women struggling with fertility problems.