2,500 
m 
u. 
I 
u 
on 
= 
OVX+EB 
OVX-EB+P 
FIGURE 5. Effects of progesterone on the magnitude of the LH surge and 
activation of LHRH neurons. (A) Effect of administration of the 
progesterone antagonist RU 486 on the amplitude of the LH 
surge (shaded bar) and degree of c-Fos expression within LHRH 
neurons (striped bar) at the time of the peak of the LH surge. For 
comparison , the values of the RU 486-treated rats are depicted 
along with untreated proestrus rats. (B) Effect of administration 
of estrogen only or estrogen plus progesterone to ovariectomized 
rats on the magnitude of the LH surge (shaded bar) and degree 
of c-Fos expression (striped bar) in LHRH neurons at the time of 
the peak of the LH surge. 
SOURCE: Lee et al. 1990a 
125 
