Circadian Regulation of Kisspeptin in Female Reproductive Functioning - Kisspeptin Signaling in Reproductive Biology - page 384

Fig. 18.4 Ipsilateral SCN projections gate the daily activation of GnRH cells and the AVPV Kiss1
expression rhythms in OVX + E 2 rats. ( Left ) Schematic coronal section showing the lesion location
at two rostrocaudal levels from an animal that received a successful unilateral SCN lesion ( shaded ).
MPO, SCN, and optic chiasm (OX) are indicated. ( Right ) Kiss1 expression is signifi cantly lower
on the ipsilateral than on the contralateral side of the lesion in animals with successful unilateral
SCN lesions but not in animals in which the unilateral lesion missed the SCN. Bars, mean ± SEM.
Asterisk , statistically different ( n =5 successful lesions, paired Student t test, P = 0.016; n = 7
missed lesions, paired Student t test, P =0.33). From Horvath TL, Cela V, van der Beek EM.
Gender-specific apposition between vasoactive intestinal peptide-containing axons and
gonadotrophin-releasing hormone-producing neurons in the rat. Brain Res. 1998;795(1-2):277-281,
with permission from Elsevier Limited. And from Smarr BL, Morris E, de la Iglesia HO. The
Dorsomedial Suprachiasmatic Nucleus Times Circadian Expression of Kiss1 and the Luteinizing
Hormone Surge. Endocrinology. 2012. Epub 2012/03/29, with permission from The Endocrine
Society
suggesting that the SCN communicates ipsilaterally to AVPV kisspeptin cells and
that this stimulation is necessary for activation of the GnRH system. By using a
lighting regimen previously established by this group to desynchronize rhythms in
the dorsomedial and ventrolateral SCN [ 109 ], the authors show that the dorsomedial
SCN oscillates independently of the LD cycle and that both AVPV Kiss1 expression
and the LH surge are coupled to oscillations in this SCN subregion (Fig. 18.5 ) [ 53 ].
Together with previous data supporting a role for AVPergic circadian control of
AVPV kisspeptin neurons [ 54 - 56 , 110 ], these data provide strong evidence for an
important role of this indirect SCN-kisspeptin circuit in initiating the GnRH/LH
surge to stimulate ovulation.
Previous fi ndings indicate that that administration of AVP can only induce the
preovulatory LH surge within a narrow time window [ 111 ], suggesting a gated
mechanism of control at SCN target loci. The gating of SCN information fl ow may
be controlled within kisspeptin cells in the AVPV, at the level of GnRH neurons, or
a combination of both mechanisms. To select among these possibilities, we exam-
ined whether (1) kisspeptin cells within the AVPV respond in a time-dependent