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Related Experiment Video

Updated: Jun 23, 2026

Assessment of Sexual Behavior of Male Mice

Assessment of Sexual Behavior of Male Mice

Published on: March 5, 2020

Endomorphin-1, effects on male sexual behavior.

Leticia Parra-Gámez¹, A Alejandro García-Hidalgo, A Salazar-Juárez

¹Facultad de Medicina, Universidad Nacional Autónoma de México, Ciudad Universitaria, CP 04510, México. gamezlp@gmail.com

Physiology & Behavior

|May 8, 2009

Summary

Endomorphin-1 (EM-1), an opioid peptide, significantly alters male rat sexual behavior by increasing ejaculation latency and reducing ejaculations. These effects were blocked by naloxone, confirming the role of mu-opioid receptors.

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Assessment of Sexual Behavior of Male Mice

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Published on: March 5, 2020

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Area of Science:

Neuroscience
Behavioral Endocrinology
Pharmacology

Background:

Endogenous opioid peptides modulate various physiological processes.
Endomorphin-1 (EM-1) is a selective agonist for the mu-opioid receptor.
Opioid involvement in sexual behavior is suggested but requires further elucidation.

Purpose of the Study:

To investigate the effects of endomorphin-1 (EM-1) on male rat copulatory behavior.
To determine the role of mu-opioid receptors in mediating these effects.

Main Methods:

Intracerebroventricular injections of varying doses of EM-1 in Wistar rats.
Measurement of sexual behavior parameters including ejaculation latency and interintromission interval.
Assessment of EM-1 effects following pretreatment with the opioid antagonist naloxone.

Main Results:

EM-1 administration dose-dependently increased ejaculation latency and interintromission interval.
EM-1 reduced the number of ejaculations observed during the testing period.
Naloxone pretreatment completely blocked the effects of EM-1 on sexual behavior.

Conclusions:

Activation of mu-opioid receptors by EM-1 significantly modifies male sexual behavior parameters.
These findings confirm the release and function of endogenous opioids during sexual activity.
Opioid systems, particularly via mu-receptors, play a crucial role in regulating ejaculation.