Effect of prolactin on the attractiveness of male odors to females in meadow voles: independent and additive effects with testosterone.
This study investigated the roles of testosterone and prolactin in seasonal changes in the attractiveness of odors of male meadow voles to long-photoperiod females. Prolactin was reduced in long-photoperiod males by treatment with bromocryptine (Experiment 1) and increased in short-photoperiod males by replacement with ovine prolactin (Experiment 2). Testosterone was manipulated by castration and testosterone replacement. During long photoperiods, the attractiveness of the odor produced by male meadow voles depends on the circulating titers of both prolactin and testosterone. Males with high titers of both hormones produced scents that were highly attractive to females; those with low titers of both hormones produced unattractive scents. When the concentration of one hormone was high and the other low, long-photoperiod males produced scents of intermediate attractiveness. During short photoperiods, the attractiveness of the male's scents depended strictly on his prolactin titers. Males with high prolactin titers produced attractive scents, and males with low prolactin titers produced unattractive scents, regardless of their prolactin concentrations. Thus, high titers of both testosterone and prolactin are needed to produce attractive scents in males exposed to long photoperiods, whereas high prolactin titers are sufficient in short-photoperiod males.