It has long been known that following spinal cord injury that prevents sensation from reaching the brain, humans and other animals remain able to achieve erection and ejaculation upon stimulation. Thus scientists had known for years that there must be a group of cells in the spinal center that control ejaculation. But the exact location of this spinal ejaculation generator has been a mystery. Dr. Coolen’s research targeted the lumbar spinothalamic neurons in the lower back because these neurons appear active only after ejaculation and not during sexual arousal or mounting. She and her team used highly selective toxin to destroy these thalamic neurons in adult male rats. The rats appeared not to notice; they continued their sexual interest and behavior, including penetration of the female. Normally a male rat can have eight to ten ejaculations over a two hour period — with five minute breaks in between — before they lose interest in a receptive female. But in the rats with numb spinothalamic neurons no longer had the ejaculations, confirming that these were the ejaculation control cells the researchers had been hunting.

Further work showed the thalamic neurons in the spine issue chemical signals to the mesolimbic and mesocortical systems located in the brain, areas previously known to be involved in the regulation of motivation and reward. Thus the researchers have been able to show that the spinal cord and the brain release and exchange various neurochemicals during different stages of sexual behavior. This new knowledge may be used to develop new treatments for the third of men who experience ejaculatory problems and other sexual dysfunction sometime in their lives as well as assist para- and quadra-plegic men who wish to have families.

And what about women? Dr. Coolen also is developing research plans to determine if the same cells that cause ejaculation in men exist in the lumbar spines of women and if so, what they do.