The brain may be the organ where sexual desire begins, but it takes a spine to finish the job. Neuroscientists Lique Coolen and William Truitt of the University of Cincinnati have pinpointed the neural circuitry that triggers ejaculation—in the lower spinal cord.
Coolen used toxins to disable neurons in the lowest quarter of male rats' spinal cords and then put the rats in cages with females. The toxin-addled males behaved exactly like normal rats, but they never ejaculated.
"The action is controlled in the spine and not the brain; it's essentially a reflex," Coolen says.
But ejaculation is a complicated process all the same. The trigger cells in the spine seem to generate and respond to a unique combination of neurotransmitters, which allows the cells to act as messengers between the brain and the reproductive organs.
Members of Coolen's lab are studying these chemical signals in the hope of harnessing them to treat the ejaculatory dysfunction that, at some point, affects one in three men. "But discussing any clinical applications at this point is probably... premature," Coolen says.