The Development of Kisspeptin Circuits in the Mammalian Brain - Kisspeptin Signaling in Reproductive Biology - page 238

Fig. 11.10 Schematic diagram developmental changes in Kiss1 expression in the AVPV/PeN
( a ) and ARC ( b ) of rodents. ( a ) Kiss1 expression in the AVPV/PeN has not been detected on the
day of birth or during other days of the “critical period” of perinatal development ( light blue shad-
ing ). Kiss1 mRNA expression is fi rst detected in the AVPV/PeN on postnatal day 10 (PND 10) in
both males and females. The sex difference emerges by PND 12. Male Kiss1 gene expression in
the AVPV/PeN only slightly increases after that time to adulthood, whereas females have a steady
increase in Kiss1 expression that reaches adulthood levels around the time of puberty. ( b ) 1 Kiss1
is expressed in the ARC before birth. Analysis of combined male and female embryonic rat brains
demonstrates increasing levels of Kiss1 in the ARC throughout prenatal development ( gray shad-
ing ), with a slight drop before birth. Comparative analysis of embryonic Kiss1 mRNA levels
between sexes has not yet been determined. 2 During the neonatal period, Kiss1 expression in the
rodent ARC is sexually dimorphic, with females expressing more Kiss1 than males. This may cor-
relate with differences in the circulating sex steroid milieu, but requires further investigation. 3
Peripubertal Kiss1 levels in the ARC decrease signifi cantly in females to levels similar to males. 4
There may be a slight increase in ARC Kiss1 expression during puberty leading to adulthood lev-
els, though such an increase is controversial at present
second postnatal week of life and is sexually dimorphic, it remains to be answered
how this population becomes sexually differentiated. Recent data suggest that epi-
genetic processes, precipitated by postnatal sex steroid signaling, may induce the
AVPV/PeN Kiss1 sex difference [ 5 ], especially because a role for the major neuronal