One-shot contraception, the future of animal population control

A newly developed nonsurgical method to deliver long-term contraception to both male and female animals with a single shot his could be the Holy Grail for animal population control.

The Caltech biologists' technique, so far used only in mice, holds promise as an alternative to spaying and neutering feral animals.

The approach was developed in the lab of Bruce Hay. His team was inspired by work conducted in recent years by David Baltimore and others showing that an adeno-associated virus (AAV)--a small, harmless virus that is unable to replicate on its own, that has been useful in gene-therapy trials--can be used to deliver sequences of DNA to muscle cells, causing them to produce specific antibodies that are known to fight infectious diseases, such as HIV, malaria, and hepatitis C.

Lead author Juan Li and her colleagues thought the same approach could be used to produce infertility. They used an AAV to deliver a gene that directs muscle cells to produce an antibody that neutralizes gonadotropin-releasing hormone (GnRH) in mice.

GnRH is what the researchers refer to as a "master regulator of reproduction" in vertebrates; it stimulates the release of two hormones from the pituitary that promote the formation of eggs, sperm, and sex steroids. Without it, an animal is rendered infertile.

Inhibiting GnRH is an ideal way to inhibit fertility and behaviors caused by sex steroids, such as aggression and territoriality, says Hay, noting that in the study, his team also shows that female mice can be rendered infertile using a different antibody that targets a binding site for sperm on the egg. "This target is ideal when you want to inhibit fertility but want to leave the individual otherwise completely normal in terms of reproductive behaviors and hormonal cycling."

Hay's team has dubbed the new approach "vectored contraception" and says that there are many other proteins that are thought to be important for reproduction that might also be targeted by this technique.

The researchers are particularly excited about the possibility of replacing spay-neuter programs with single injections.

Spaying and neutering of animals to control fertility, unwanted behavior, and population numbers of feral animals is costly and time consuming, and therefore often doesn't happen, says Hay, adding that there is a strong desire in many parts of the world for quick, nonsurgical approaches to inhibiting fertility. They think vectored contraception provides such an approach.

The study appears in Current Biology.