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(the isoform responsible for estradiol's feedback actions upon GnRH secretion), pro-
gesterone receptor (PR), and androgen receptor (AR) [ 2 , 15 , 69 ]. In the ARC popula-
tion of rats, mice, and sheep, the percentages of co-localization of ER-alpha range
from 70 to 99%, whereas in the RP3V and preoptic region they range from 50 to 99%
[ 9 , 15 , 18 , 33 , 70 ]. The percentage of both ARC and RP3V populations that co-
localize the beta isoform of the estrogen receptor is considerably less, ranging from
11 to 25% in the ARC and 21-31% in the RP3V of rats and mice [ 15 , 23 ]. Other
kisspeptin populations have not been directly examined for steroid receptor co-local-
ization, but given that sex steroids regulate Kiss1 expression in the medial amygdala
in rats and mice [ 14 ], and the presence of ER and AR in this area [ 71 ], it seems likely
that kisspeptin cells in the amygdala are also a direct target for gonadal steroids.
Preliminary evidence suggests that other nuclear steroid receptors are also present in
kisspeptin cells: approximately 50% of KNDy cells in the ovine ARC co-localize
type II glucocorticoid receptors [ 72 ]. Furthermore, there is recent evidence that other
types of receptors for circulating hormones are present in ARC kisspeptin cells:
receptors for prolactin [ 73 ] and insulin [ 74 ] have each been co-localized to a subset
of KNDy neurons. Taken together, these fi ndings point to a potential convergence of
endogenous hormonal cues onto the ARC kisspeptin population, which may place
them in a unique position to respond to multiple signals related to stress, nutrition,
and the environment, as well as reproductive endocrine status.
Distribution of Kiss1r
In contrast to the wealth of information on the neuroanatomical distribution of
kisspeptin cells and fi bers, there is very limited data available on the location of
Kiss1r mRNA and no data on Kiss1r protein. The only data in humans is from early
studies before the role of Kiss1r in reproductive neuroendocrinology was recog-
nized, so they provide almost no information on hypothalamic expression of this
receptor [ 75 , 76 ]. Moreover, most of the studies since then in monkeys and rodents
used RT-PCR of mRNA extracted from large tissue blocks or micro-dissected areas
(Table 3.5 ). Consequently, these reports do not provide any information on the loca-
tion of Kiss1r within these relatively large volumes of tissue. Quantitative compari-
sons between areas using this approach are also problematic because the ratio of
Kiss1r mRNA to a housekeeping gene is partially dependent on the percentage of
Kiss1r -containing cells within the block. Thus, variations in the precision of micro-
dissection contribute signifi cantly to the values reported. There have been a number
of studies using ISH, or related techniques, that can provide cellular resolution, but
most of these have been focused on whether GnRH neurons contain Kiss1r and do
not provide more general neuroanatomical information. Thus, detailed descriptions
in this section rely largely on two studies. One of these used ISH in rats, but pro-
vided only a few low-power images [ 77 ]. The other used transgenic mice in which
IRES-LacZ cassettes had been inserted into the Kiss1r gene so that
-galactosidase
could be identifi ed with Xgal staining as a marker for Kiss1r- containing cells [ 78 ].
Although this provides the only detailed description of Kiss1r expression in the
β
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