LH surge in GNR23 mice. A, Profile of LH surge in OVX mice of all three genotypes treated with estrogen and progesterone. Note that the LH surge in hemizygous (+/-) mice (* p<0.05) is markedly flattened in profile whereas evaluation of LH levels at the time of peak LH secretion (18:00h) reveals an absence of the LH surge in homozygous (-/-) GNR23 females. Bar at bottom indicates light schedule. B, Pituitary response to exogenous GnRH. Mean (+SEM) LH levels before (pre-) and 10 min after (post-) 200ng/kg GnRH s.c. to wild-type (black bars) and homozygous GNR23 (open bars) female mice. * p<0.05. C, Dual-label immunocytochemistry showing a GnRH neuron expressing c-Fos (black nuclear staining) in the rostral preoptic area (rPOA) of a hmz GNR23 mouse. D, Mean (+SEM) number of medial septal (MS) and rPOA GnRH neurons/coronal section expressing c-Fos at 18:00h in the three genotypes. E, Mean (+SEM) percentage of rPOA GnRH neurons expressing c-Fos at 18:00h. Scale bar in C represents 50μm.