Melatonin treatment affects the attractiveness of the anogenital area scent in meadow voles (Microtus pennsylvanicus).

Seasonal differences exist in the attractiveness of scents in meadow voles, Microtus pennsylvanicus. To determine whether photoperiodically induced changes in the attractiveness of a sex-specific scent is governed by melatonin, we implanted long-photoperiod male and female scent donors with a Silastic implant containing a 10-mm active length of melatonin, a 20-mm active length of melatonin, or no melatonin. The first experiment shows that 8 weeks of melatonin treatment is sufficient to induce long-photoperiod voles to produce scents that are no longer attractive to the opposite sex. The second experiment shows that a similar time course of melatonin treatment was sufficient to induce long-photoperiod females treated with melatonin to produce scents that are attractive to short-photoperiod females. Melatonin implants lowered the gonadal hormone titers and reduced the weight of the gonads of treated long-photoperiod voles to titers and weights that are characteristic of short-photoperiod voles. In both experiments, the behavioral and physiological effects were independent of whether scent donors received 10- or 20-mm implants of melatonin. Together, the results of the two experiments reveal that melatonin mediates the photoperiodically induced changes in gonadal hormone titers that control the seasonal differences in the sexual attractiveness of the anogenital area scent produced by meadow voles.