Effect of botulinum-A toxin injection into bulbospongiosus muscle on ejaculation latency in male rats

Premature ejaculation (PE) is the most common male sexual dysfunction. A variety of pharmacotherapeutic strategies have been employed to treat men suffering with lifelong PE. However, there are currently no pharmaceuticals approved by the U.S. Food and Drug Administration specifically designed for PE treatment.

Given that the bulbospongiosus muscle is involved in the ejaculatory reflex in both humans and rodents and that local administration of botulinum-A can abolish muscle contractions, the current study examined the effect of injection of botulinum-A toxin into the bulbospongiosus muscle on the ejaculatory latency of male rats.

After screening for normal sexual activity with sexually receptive female rats, 33 sexually experienced male Long-Evans rats (Harlan Laboratories, Indianapolis, IN, USA) underwent an additional four pretreatment sexual exposures over the course of the following week, during which all components of sexual behavior were video recorded by trained observers. On the day after their fourth experience, rats were anesthetized and received a single injection of either 0.5 unit (n = 11) or 1 unit (n = 11) of botulinum-A toxin or saline vehicle (n = 11). Botulinum-A toxin was dissolved in 0.1 mL of saline vehicle and injected bilaterally into the bulbospongiosus muscle by the percutaneous route. Beginning 2 days after treatment, sexual behaviors were reexamined over the course of the following week on four separate occasions.

The latency to achieve ejaculation, and the frequencies and latencies of mounts and intromissions were video recorded by trained observers in a blinded fashion.

Relative to pretreatment measurements, bilateral injection of saline vehicle into the bulbospongiosus muscle did not affect ejaculation latencies. However, rats treated with either 0.5 or 1 unit of botulinum-A toxin exhibited significantly longer latencies to achieve ejaculation relative to pretreatment performance. Of note, botulinum-A toxin did not affect the ability to achieve mounts, intromissions, or ejaculation.

These results demonstrate that botulinum-A toxin injection into the bulbospongiosus muscle is a safe and effective treatment that extends ejaculatory latency in rats without affecting the ability to engage in sexual activity or achieve ejaculation. Further studies are required to evaluate this therapeutic concept in PE patients.