Response to exogenous kisspeptin varies according to sex and reproductive condition in Siberian hamsters (Phodopus sungorus)

Most animals experience marked changes in reproductive status across development that are regulated by changes in the hypothalamo–pituitary–gonadal (HPG) axis. The upstream mechanisms regulating this axis remain less well understood. The neuropeptide kisspeptin serves as a positive regulator of reproduction; the precise actions of kisspeptin on the HPG axis in animals of differing developmental and seasonal reproductive states, however, remain unresolved. Further, sex differences in response to kisspeptin have not been fully explored. In Experiment 1, we investigated whether sensitivity to a broad range of kisspeptin doses differed in adult male and female Siberian hamsters held on reproductively inhibitory or stimulatory photoperiods. In Experiment 2, we asked whether the response to kisspeptin differed across stages of reproductive development. Males and females displayed elevated luteinizing hormone (LH) in response to kisspeptin; however, the sexes differed in this response, with males showing greater LH responses to kisspeptin than females. Hamsters responded to kisspeptin across all stages of reproductive development, although the magnitude of this response differed between animals of differental ages and between the sexes. Males showed significant increases in LH at an earlier developmental age than females; females also showed blunted LH responses during early adulthood whereas males remained relatively constant in their response to kisspeptin. These findings suggest that reproductively active and inactive hamsters are responsive to kisspeptin, but that the sexes differ in their responsiveness. Collectively, these data provide further insight into the basic actions of kisspeptin in the regulation of reproduction and provide a potential mechanism for the regulation of differential reproductive responses between the sexes.

Research highlights
► Reproductively responsive and non-responsive hamsters demonstrate comparable luteinizing hormone (LH) responses to injections of exogenous kisspeptin.
► The magnitude of the LH response differed depending on the age of the animals.
► Sex differences were observed in response to kisspeptin that varied depending on reproductive condition of the animals.
► These findings suggest a modest sex difference in the sensitivity to kisspeptin that is dependent on the reproductive state of the animals.