Delta and Kappa opioid receptors on mouse sperm cells: expression, localization and involvement on in vitro fertilization.

•Delta and Kappa opioid receptors are present in mouse mature spermatozoa.•The activation of sperm delta opioid receptor before the IVF reduces the number of reached blastocysts from this sperm.•The deleterious effect of Delta opioid agonist in sperm is reverted by Delta opioid antagonist.