Suppression of the lordosis reflex in female rats by chronic central melatonin implants

Pellets with beeswax:melatonin concentrations of 1:0, 5:1, and 2:1 were implanted near the suprachiasmatic nucleus of ovariectomized female rats. In repeated standard measures of the lordosis reflex after estrogen replacement, females with pellets containing either melatonin concentration were consistently less sexually receptive than were females with pure beeswax implants. Suppression of behavioral receptivity by melatonin is consistent with other antireproductive effects of the hormone. Melatonergic action could account for certain pharmacological findings previously attributed to serotonergic action.