Embryonic Development of Kisspeptin Neurones in Rat

Kisspeptins, encoded by the Kiss1 gene, play a key role in the regulation of reproductive function, although very little is known about the ontogenesis of this system. The present study aimed to determine the period of arcuate nucleus (ARC) kisspeptin cell birth and the embryonic stage and neuroanatomical sites of onset of kisspeptin immunoreactivity. Bromodeoxyuridine (BrdU) was administered to female rats at various gestational stages and double immunohistochemistry against kisspeptin and BrdU was performed on brain sections from their offspring. The period of neurogenesis of ARC kisspeptin neurones begun between embryonic day (E) 12.5 and E13.5, reached its peak at E15.5 and was not completely over at E17.5. Kiss1 mRNA was detected in mediobasal hypothalamic punches of embryos aged E14.5, E16.5, E18.5 and E22.5 by real-time reverse transcriptase-polymerase chain reaction. Accordingly, kisspeptin-immunoreactive (-IR) cells were consistently detected in the embryonic ARC from E14.5 and their number increased until E18.5 to reach approximately half the level observed in adults. Between E18.5 and E22.5, the number of kisspeptin-IR cells and hypothalamic Kiss1 expression significantly decreased, regardless of sex, and this decrease persisted until birth. Taken together, these results demonstrate that rat ARC kisspeptin neurones are born locally during an extended embryonic period and are able to synthesise kisspeptins rapidly after their birth, consistent with the hypothesis of a role during embryonic activation of the hypothalamic-hypophyseal-gonadal axis. A sex-independent decrease of kisspeptin-IR cell numbers was observed during the perinatal period, suggestive of important regulations of kisspeptin neurones around birth.