Sex is a complex process, not just physically but neurologically. Scientists have long known that the brain’s reward system, particularly the neurotransmitter dopamine, plays a role in pleasure and motivation.
However, new research published in Neuron reveals that dopamine doesn’t act alone—its intricate interplay with another neurotransmitter, acetylcholine, controls the precise progression of sexual behavior in male mice. These findings could one day help develop treatments for sexual dysfunctions such as premature ejaculation, which affects an estimated 20% to 30% of sexually active men.
“Sexual behavior is a complex sequence of events,” senior author Qinghua Liu of the National Institute of Biological Sciences in Beijing said in a recent statement. “The study revealed the dynamics of how different chemicals work together in the brain to regulate the transitions through different stages of male sexual behavior.”
Sex is a Window into the Brain’s Pleasure Center
Previous studies have focused on how sex is initiated, but little was known about what happens in the brain during the full sequence of sex, from mounting to penetration (intromission) to ejaculation. To investigate, the research team turned to the nucleus accumbens, a brain region central to the reward system and known for its dopamine response.
Using advanced imaging techniques, the scientists injected fluorescent sensors into the nucleus accumbens of male mice. These sensors could detect and light up when neurotransmitters like dopamine and acetylcholine were released, allowing researchers to track brain activity in real time during sexual encounters.
Their observations revealed a carefully timed interplay between the two chemicals. Acetylcholine began releasing rhythmically just before the mice started mounting. About six seconds later, dopamine levels also started rising. During intromission, the levels of both neurotransmitters fluctuated in sync with the mouse’s thrusting movements.
Perhaps the most striking finding was how dopamine levels shifted as mice approached ejaculation. The researchers observed that dopamine release slowed down significantly just before ejaculation and then rapidly spiked during the transition from intromission to climax.
“We are able to look at these events at a very fine time resolution to understand how neurotransmitters interact with each other,” added first author Ai Miyasaka, a postdoctoral fellow at the University of Tsukuba in Japan.
Dopamine Plays a Role in Different Parts of Sex
The researchers also explored the role of dopamine by analyzing its interaction with specific nerve receptors. The brain contains two major dopamine receptors, known as D1R and D2R, which help regulate the effects of dopamine. During intromission, nerve cells expressing these receptors were less active than usual.
When the scientists artificially activated D1R neurons, the mice suddenly reverted to the mounting stage instead of progressing to ejaculation. On the other hand, when they activated D2R neurons, the mice stopped engaging in sexual activity altogether.
“We uncovered the precise dopamine signaling mechanism that helps ensure that sexual behavior follows the correct sequence,” Liu said.
Implications for Human Sexual Health
While humans and mice differ in sexual behaviors, the brain regions and neurotransmitter systems involved in sex are remarkably similar across species. Understanding the precise neurological mechanisms in mice could provide insight into human sexual health as well.
In particular, these findings may help scientists develop better treatments for premature ejaculation, a condition that can significantly impact quality of life and relationships. By identifying how dopamine and acetylcholine regulate the transition between different stages of sex, researchers now have a more detailed blueprint of the brain’s role in ejaculation.
“Now we have a precise understanding of how dopamine works during sex and ejaculation,” noted Miyasaka. “I believe our study has opened the door to the development of clinical treatments.”
Kenna Hughes-Castleberry is the Science Communicator at JILA (a world-leading physics research institute) and a science writer at The Debrief. Follow and connect with her on BlueSky or contact her via email at kenna@thedebrief.org