The hidden role of the spinal cord in sexuality

Copyright : Constanze Lenschow & Ana Rita Mendes

We used to think that the brain controlled all stages of sexual activity, except for the final ejaculatory reflex, which is controlled by the spinal cord. New discoveries in mice, published in Nature Communications, show that spinal circuits are not simply passive relays; on the contrary, they actively shape sexual arousal, mating, and finally ejaculation.

The spinal cord is not just a simple ejaculation switch.

The spinal cord does not just trigger ejaculation: it also shapes male sexual behavior, according to 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 as a reflex. A group of scientists from INCIA in collaboration with the Champalimaud Institute (Portugal) has demonstrated, however, that in mice, the 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 Champalimaud Foundation’s Neuroethology Laboratory. “It integrates sensory signals, reacts to excitement, and adjusts its response according to 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 that produce the molecule “galanin” and are called Gal+ neurons) glow under fluorescent light, the scientists showed that these Gal+ neurons are directly connected to the motoneurons that control the BSM. Electrophysiological recordings, using the patch-clamp technique, confirmed that activation of Gal+ neurons stimulates these motoneurons through a connection using glutamate as neurotransmitter.

A revised view of sexual control.

These Gal⁺ neurons also receive sensory signals from the genitals. Researchers have shown in spinal male mice, i.e., whose brains are disconnected from the spinal cord, that simple stimulation of the penis activates both Gal⁺ neurons and BSM motoneurons. This demonstrates that genital signals reach this spinal circuit without the intervention of the brain. In addition, more pronounced effects were observed when brain signals were absent (in spinal mice), implying that the brain normally exerts inhibitory control over this spinal circuit until the conditions for ejaculation are met.

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

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

Activity of galanin neurons in the spinal cord in relation to the phase of sexual activity in male mice. The activation of these specific neurons gradually increases throughout the cycle until it triggers ejaculation.

Reference

Constanze Lenschow, Ana Rita P. Mendes, Liliana Ferreira, Bertrand Lacoste, Hugo Marques, Nicolas Gutierrez-Castellanos, Camille Quilgars, Sandrine S. Bertrand & Susana Q. Lima
A galanin-positive population of lumbar spinal cord neurons modulates sexual arousal and copulatory behavior in male mice.
Nat Commun 16, 8282 (2025). https://doi.org/10.1038/s41467-025-63877-2

Contact

Constanze Lenschow
constanze.lenschow@u-bordeaux.fr
INCIA