Finally, sexual impotence (i.e., the inability of adult male rats to engage in copulation with an ovariectomized estrogen + progesterone-primed receptive female rat) has also been linked in male rats with a low oxytocin mRNA content and increased opioid peptide enkephalin and dynorphin mRNA content in the PVN [119] as well as low levels of NO synthase in the PVN [118], which is in line with a facilitatory effect of oxytocin and NO and an inhibitory effect of opioid peptides at the PVN level in the control of sexual behavior, respectively. Here, OXT is linked to erectile dysfunction.