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Fig. 11.7 Kiss1 gene expression in the murine ARC on PND 1. ( a ) Representative photomicro-
graphs for Kiss1 expression in newborn females (F) and males (M) that were 0-4 h old. ( b ) The
mean number of Kiss1 neurons in the ARC, as well as the relative level of Kiss1 mRNA/cell, for
PND 1 male and female mice that were 0-4 h old. Newborn males had signifi cantly fewer ARC
Kiss1 cells and lower mRNA per cell than newborn females ( P < 0.05). 3V third ventricle; GPC
grains per cell. Modifi ed from Poling MC, Kauffman AS 2012 Sexually dimorphic testosterone
secretion in prenatal and neonatal mice is independent of kisspeptin-kiss1r and GnRH signaling.
Endocrinology 153:782-793. With permission from The Endocrine Society
age of PND 4 [ 64 ]. Poling and Kauffman provided greater temporal resolution of
expression in PND 1 mice: they found notable Kiss1 expression in both sexes at
both 0-4 h and 16-20 h after birth (Fig. 11.7 ), without a signifi cant change in Kiss1
levels between these time-points [ 98 ]. Parenthetically, NKB, which is co-expressed
in ARC Kiss1 neurons in adulthood, was also readily expressed in the ARC of both
sexes on PND 1 [ 98 ]. One rat study noted an increase in Kiss1 expression in the
ARC between PND 1 and 3 in both sexes [ 47 ], with an additional increase at PND
8 in females only. Another study noted similar but non-signifi cant trends in both
males and females [ 64 ].
The role of Kiss1 in the ARC during early neonatal life is unknown. Because
kisspeptin signaling regulates the pubertal and adult reproductive axis, it is possible
that kisspeptin plays a similar role earlier in neonatal development. However, since
the reproductive axis is typically quiescent at this time, it is not clear what functional
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