💘 The hidden role of the spinal cord in sexuality

We used to think that the brain managed all stages of the sexual act, except for the final ejaculatory reflex, which is organized in the spinal cord. New discoveries in mice, published in Nature Communications, demonstrate the opposite: spinal circuits are not a simple passive relay; on the contrary, they actively shape sexual arousal, mating, and finally, ejaculation.

The spinal cord is more than just an ejaculation switch

The spinal cord does not merely trigger ejaculation: it also shapes male sexual behavior, reveals a study published in the journal Nature Communications.

Traditionally, it was thought that the brain controlled arousal, courtship, and mating, while the spinal cord was limited to triggering ejaculation reflexively. A group of scientists has instead demonstrated in mice that spinal cord circuits also participate in arousal, mating, and the rhythm of sexual intercourse.


"The spinal cord is not simply a passive relay executing orders from the brain," explains Susana Lima, principal investigator at the Neuroethology Laboratory of the Champalimaud Foundation in Portugal. "It integrates sensory signals, responds to arousal, and adjusts its response based on the animal's internal state."

A key circuit around the bulbospongiosus muscle

The team focused on the bulbospongiosus muscle (BSM), which is essential for sperm expulsion. During ejaculation, this muscle contracts in a well-defined pattern.

Using genetically modified mice in which certain spinal cord neurons (those producing the molecule "galanin" and called Gal⁺ neurons) glow under fluorescent light, the scientists showed that these Gal⁺ neurons are directly connected to the motor neurons that control the BSM. Electrophysiological recordings, using the patch-clamp technique, confirmed that activation of Gal⁺ neurons stimulates these motor neurons via a connection using the glutamate neuroreceptor.

By stimulating these Gal⁺ neurons with light (optogenetics) or electrical current, the scientists induced contractions of the BSM muscle in these mice, but without guaranteeing complete ejaculation, unlike what is observed in rats. Furthermore, repeated stimulations led to progressively weaker responses, suggesting the existence of a refractory phase following muscle activation.

A revised view of sexual control

These Gal⁺ neurons also receive sensory signals from the genitals. The scientists showed in "spinalized" male mice—meaning those whose brains are disconnected from the spinal cord—that simple stimulation of the penis activates both Gal⁺ neurons and BSM motor neurons. This demonstrates that genital signals reach this spinal circuit without brain intervention. Moreover, more pronounced effects were observed when brain signals were absent (in spinalized mice), implying that the brain normally exerts inhibitory control over this spinal circuit until the conditions for ejaculation are met.

When the scientists selectively deactivated the Gal⁺ neurons, the behavior of the male mice changed: delayed ejaculation, more frequent missed matings, and disrupted intercourse rhythm. The contribution of this circuit therefore appears to go beyond the simple mechanics of ejaculation to play an active role in the entire sexual behavior.

These results thus challenge the idea that ejaculation is simply a reflex executed after a green light from the brain. On the contrary, the progression of the sexual act appears to be shaped by a continuous dialogue between sensory signals, internal state (including whether ejaculation has previously occurred or not), and spinal circuits. At the heart of this process, Gal⁺ neurons appear as true integrators, capable of "deciding" when to activate the motor pattern based on received signals and the animal's physiological state.